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Metyos , a Paris-based deeptech medical company, is developing a smart biowearable designed to transform how potassium levels are monitored in patients at risk of dyskalemia — a clinical term describing abnormal potassium levels in the blood. Dyskalemia encompasses both hyperkalemia (elevated serum potassium) and hypokalemia (reduced serum potassium), two clinically significant electrolyte disturbances frequently observed in patients with renal and cardiovascular conditions. Accurate potassium monitoring remains critical in at-risk populations. However, potassium monitoring in clinical practice remains largely dependent on periodic laboratory blood tests. Metyos set out to change that. Their solution is a painless, reusable skin patch that continuously tracks potassium levels and sends real-time data directly to a smartphone and healthcare professionals. By enabling continuous monitoring, the device allows patients to make informed daily decisions while providing doctors with richer, longitudinal data for improved care. At a Glance Challenge Develop a manufacturable microneedle-based polymer component for a smart medical biowearable capable of continuous potassium monitoring. Solution Micromolds supported the project with a Design for Manufacturability (DFM) evaluation and precision micro injection molding feasibility trials to validate replication of highly miniaturized microneedle geometries. Outcome Demonstrated that micro injection molding can reliably replicate the required microneedle structures, providing increased confidence in scalability for future development phases. From Concept to Manufacturable Component At the heart of the Metyos device is a polymer microneedle structure engineered to interact with the skin in a minimally invasive manner. These structures must meet strict dimensional and functional requirements while remaining comfortable and safe for continuous wear. However, microneedle geometries present significant manufacturing challenges. High-aspect-ratio micro features (as close as 5:1), delicate tip geometries, and extreme sensitivity to material flow make replication particularly demanding. The needles have 0.130mm diameter through holes, meaning mold shut-offs happening at extreme precision. To evaluate production feasibility, Metyos partnered with Micromolds to explore how micro injection molding of microneedle arrays could support the design and enable scalable manufacturing. “We were happy to collaborate with the Micromolds team. Without their support and willingness to push the boundaries of what is feasible in the world of injection molding, we could not have launched our ambitious project. Innovation stems from collaboration between like-minded companies, and Micromolds proved to be a strong and highly capable partner in our challenge.” Olga Chashchina, PhD, Co-Founder and CTO at Metyos Engineering the Tooling Strategy To evaluate production feasibility, Micromolds conducted a comprehensive Design for Manufacturability (DFM) assessment focused on micro-scale process behaviour and structural integrity. The review addressed: Polymer flow dynamics within micro-scale cavities Transition zones between needle base and tip Feature density and spacing within the array Demolding forces acting on fragile high-aspect-ratio structures Complex venting solutions to overcome air traps at the needle tips Based on this analysis, a precision steel injection mold incorporating a glass insert was developed to support micro-feature replication under controlled molding conditions. Glass insert installed in the mold for microneedle molding Silica insert was machined with selective laser etching technology. This technology was creatively chosen to enable innovative venting solutions which is not possible with traditional manufacturing methods. The venting channel was made of just a few micrometers at the very tip of the needle which allowed us to mold as sharp as possible needle tips. Air venting channel at the needle tip to enable sharp micro needle molding The core side of the mold was machined with precision micro milling technology. The most challenging part was not to crash the glass at the shutoff intersections of steel and glass which required us a lot of iterative testing and CNC facing 1 by 1 micron to achieve precision we need. Quite a few glass inserts were smashed and sacrificed for this stage. Steel mold side of microneedles © 2023 Micromolds A range of materials were selected, as the needles must be rigid and tough and high flow is needed for high aspect micro features, also biocompatibility is a must. Validating Microneedle Array Replication with Micro Injection Molding Initial molding trials focused on validating: Accurate replication of high-aspect-ratio microneedle features Tip sharpness and structural consistency Stable cavity filling behavior Controlled and repeatable demolding Through iterative refinement of process parameters and tooling configuration, consistent replication of the microneedle array was achieved. The validation phase confirmed that the geometry could be reliably molded using a steel tool with integrated glass insert and medical-grade polymer, establishing confidence in manufacturability and future scale-up potential. Supporting the Future of Continuous Health Monitoring The manufacturability evaluation confirmed that precision micro injection molding can replicate the microneedle geometries required for continuous potassium monitoring applications. By validating manufacturability early in the development cycle, Metyos gained increased confidence in scalability and a clearer pathway toward future production. As connected health technologies continue to advance, solutions like the Metyos smart biowearable highlight how innovative device concepts can move from laboratory development toward real-world impact — when supported by the right manufacturing expertise.

As micro injection molding continues to take a fair share of the manufacturing market, it becomes clear that micro mold manufacturing is a critical step to guarantee high-precision and high-quality results. The higher the precision and the quality of the micro mold manufacturing, the higher precision and quality you can get from micro injection molding. This guide covers all the details regarding the micro mold manufacturing process, how they are machined to the tightest tolerance possible for higher precision, what are the types of micro machining that can be applied, and the technologies behind the micro machining process. Table of contents What is micro machining? How are micro molds machined? Types of micro machining methods Non-mechanical methods Mechanical methods How to select the best alternative for micro mold manufacturing What is micro machining? Micro machining can be defined as the manufacturing process used to create 3D parts at a micro scale level. In other words, it means machining with tools with diameters that are smaller than 400 µm and can be as small as 1/3 the diameter of a human hair. Although it has existed since the late 1990s, the most recent developments in micro machining technology and tooling materials have made it possible to see machines with sufficient spindle speed and strong long-lasting cutting tools that can meet the repeatability and strength to run at high speeds as required for micro mold manufacturing. How micro molds are machined? When machining molds for micro injection molding , it is important to pay attention to three essential aspects: Part size Feature size Dimensional tolerances Another important aspect to keep in mind to obtain the best results when machining micro molds is that there is a direct relationship between the material of the mold, the cutting tools and the machining process itself, so making sure they are in synchrony is vital. Of course, there are several different micro machining processes, so it is necessary to select the most suitable option. Types of micro machining methods The types of micro machining methods for micro mold manufacturing can be classified into two categories: non-mechanical methods, and mechanical methods. Non-mechanical methods for micro mold manufacturing Non-mechanical methods for micro mold manufacturing include chemical processes such as wet and dry etching are more frequently used to produce molds for very specialized applications, especially within the optical and biology fields. However, the geometries that can be achieved with these processes are limited. On the other hand, among the non-mechanical methods for micro mold manufacturing, there is one that is worth highlighting: Micro EDM. Micro EDM for micro mold manufacturing EDM stands for Electrical Discharge Machining, so micro EDM is the process that applies traditional electrical discharge machining but at the micro scale level. Micro EDM is a great alternative for micro mold manufacturing because it allows the possibility of achieving both concave and convex microstructures, including the most complex 3D microstructures with high aspect ratio that may be required by several micro injection molding applications. Micro EDM consists in taking advantage of the erosive action of an electrical discharge between a conductive tool (electrode) and the workpiece to achieve material removal. This is normally done in one of two forms: The electrode is made to the desired shape of the cavity that is required. This electrode is then fed vertically over the workpiece, thus eroding the reverse shape into it. Using a very thin wire electrode with a diameter within the micro scale, the desired shape is eroded as the electrode follows the path that has been programmed into the special CNC machine. When using micro EDM for micro mold manufacturing, there are three factors that need to be taken into account in order to achieve the best performance. These factors are: Melting point of the materials Thermal conductivity of the materials Electrical conductivity of the materials According to an experimental study on impulse discharge machinability performed in 2018 by Quanpeng He, Jin Xie, Ruibin Guo, Peixin Ma and Yanjun Lu, “A low melting point and electrical conductivity result in a good micro-machined shape with a low relative wear rate. High electrical conductivity and a low melting point produce low surface roughness, high micro-removal rate, and high discharge energy efficiency. Low thermal conductivity leads to a high aspect ratio and low micro-removal rate”. Micro EDM technology for micro mold manufacturing Micro EDM technology has been widely developed, and the options for micro mold manufacturing include highly capable micro EDM machining centers that feature: Twin axis processing. Combining processes such as Micro EDM Drilling, Micro EDM Sinking, Wire EDM Electrode grinding, and 3D Micro EDM Milling. Tools integration. 8-axis control. Possibility to change between electrodes with different diameters Mechanical methods for micro mold manufacturing While micro EDM is definitely a very cost-effective process that can achieve micro mold manufacturing with high quality and precision, there are some micro injection molding applications that require molds with even more geometric freedom and lower surface roughness. And here is where the mechanical methods for micro mold manufacturing excel. The main idea of using mechanical methods for micro mold manufacturing is taking advantage of the most modern tooling developments for micro machining which use diamond to achieve surfaces with precision to the micro scale level without the need for post processing. Of course, this type of high precision machining can only be possible thanks to the current CNC technologies, which allow experience manufactures to produce microfeatures as precise that can be measured to values below the 5µm. An important achievement of these technologies is the high speed the spindle can reach, which allows to avoid chip build up and heat concentration in micro machining applications. Among the most common CNC high precision processes applied for micro mold manufacturing there are micro turning, micro milling, and micro grinding. And these three are usually performed in combination to achieve the desired results. Micro machining technology for micro mold manufacturing The most common micro machining technology used in the present for micro mold manufacturing is high-speed micro milling. In micro milling processes, normally a diamond tool rotates on a spindle and moves along the surface of the fixed workpiece. During milling operations, the tool rotates along the axis perpendicular to the workpiece. At least three numerically controlled axes are used in this process. Common factors that affect the efficiency and the quality of high-speed micro milling for micro mold manufacturing include: The corner radius of the milling tool. Optimization of the tool path. Tool wear. Angle of the cutter axis. This should always have an inclination to avoid a cutting point with a speed value of 0. Of course, there are other technologies that can be used such as single-point diamond turning, fly cutting, and vibration assisted cutting technologies. However, they are mostly used for highly specialized applications such as optics. How to select the best alternative for micro mold manufacturing For a micro injection molding manufacturer to select the best alternative among the available processes for micro mold manufacturing, it is necessary to consider the specific requirements of the part that will be molded and possible constraints, costs, the number of times the mold will be used (durability or life span), and geometrical complexity. For example, when it comes to costs, a higher removal rate increases production rate and a higher degree of automation reduces labor costs. So, the production rate of the manufacturing process and the degree of automation it requires will be critical factors to analyze. Regarding the mold durability, it usually depends on the material and how it resists high-temperature and high-pressure cycles. For example, aluminum molds may last up to 200 cycles while being made two times faster and cheaper than steel molds. When it comes to geometrical complexity, the higher the complexity the lower the micro milling machinability, so other methods like micro EDM may be required. There are some studies that have provided good information such as tables for complexity index, and a set of rules to select between micro milling machining and micro EDM. However, it is important to remember that they are not completely infallible. Based on all these factors, making the best selection usually requires a certain degree of expertise. Many times, the best solution is to combine both micro milling with micro EDM to obtain the micro mold manufacturing result needed for the micro injection molding application, but this should only be used when the increased cost and extra processing time is justified. Conclusion As a conclusion, the best course of action when deciding between high-speed micro machining and micro EDM to obtain the most suitable mold for the micro injection molding application in hand is to leave it in the hands of an expert.

Injection molding refers to the manufacturing process of injecting the molten material into the mold to produce parts of various shapes and sizes. At the same time, injection molding materials may incorporate but are not limited to metals, elastomers, ceramics, and most usually thermoplastic and thermosetting polymers. However, the topic will swirl around plastic injection molding in this article, specifically covering the context of plastic injection molding undercuts, along with some standard vocabulary typically associated with molding plastic parts with undercuts. Vocabulary Core : A protrusion that forms a plastic part's inner surface or counterpart – the male side of the part. Cavity : A void that forms a plastic part's outer surface – the female side of the part. Parting Line: The parting plane where two halves of the injection mold meet. Slider (Side Action): It is a side action that converts the vertical movement of the mold opening/closing into the horizontal direction. Shutoff: Shutoffs use drafted walls sealing against drafted walls to eliminate the requirement of post-molding machining or removing functional geometry. Bump-off: The slight undercut in part design that can be securely eliminated from a straight-pull mold without side actions. Lifer: It is used to form the internal undercuts of an injection-molded plastic part. It also works for the ejection function. Draft: The draft is a taper applied to the part faces while developing parts. Fusible Core: Fusible cores are helpful when demoldable cores are difficult to use to mold internal cavities and undercut when injection molding the part. Ejector: The ejector system in plastic injection molding is used to forcefully push and eject the final solid parts or samples out of the mold. What Is Undercut In Injection Molding? Undercuts can be characterized as any protrusions or recessed zones of a part parallel to a plastic injection mold's parting line, prohibiting the ejection of the part from the mold. There exist several major types of undercuts, and these are: 1. External undercut 2. Hole 3. Internal undercut 4. Radial undercut 5. Threaded undercut External undercuts are located on the outside of the part, while interior undercuts remain on the inside of the part. Threaded undercuts occurs when threaded part is molded and usually it requires unscrew it to eject out. Holes and radial undercuts originate when some through holes are needed and must be placed in parallel to the parting line of the mold. In any case, undercuts can be molded, but they need a side pull or side action, being an additional part of the mold that moves independently from the two halves. Furthermore, these undercuts can upsurge the cost of the molded part because of an additional 15-30% cost of the mold itself, increased cycle time, and the complexity of the injection molding machine. Purpose of Undercuts in Plastic Injection Molding The following are some of the general purposes to use undercuts in plastic injection molding: Creating interlocking or snap & latch features and acquiring side holes or openings and ports for button and wiring features. Gaining control of vertical threads and barb fittings utilized in medical devices and providing threaded and customized inserts that are not in the drawn line. Coring out thick and impenetrable sections not secured by the core and cavity alone. Consequently, it helps reduce the chances of sink and warp. How to Optimize Part for Injection Molding (Avoiding Undercuts)? Redesign and upgrade the part to avoid undercuts whenever possible since they add to the mold's complexity, maintenance, and overall cost. Minor part design modifications may help prevent undercuts in the mold; it is simply a matter of choosing the proper workaround for the given part. Here are some ways to optimize the part to avoid undercuts in injection molding: Hole to Slot. Through holes or slots can be added through simple modifications in the sidewall of the mold, instead of a side-action mechanism. Creating a hole or slot in the mold is feasible to help eject the part without hooking; otherwise, the part might stick in the mold. It considers the metal in the mold to move across the part's hole and appropriately develop the underside of the undercut. Stripping. Similarly, stripping undercuts can benefit when the feature is sufficiently flexible to deform over the mold during the ejection process. When using stripping undercuts, ensure they are away from stiffening features (ribs and corners) and have a lead angle of 30-45 degrees. Stripping undercuts are discouraged in parts produced using fiber-reinforced plastics. On the other hand, more flexible plastics are acceptable. Moving a Parting Line. The most straightforward way of managing an undercut is to move the mold's parting line to overlap it with the part feature and modify the draft angles accordingly. In addition, this arrangement is appropriate for various designs with undercuts on an outside surface. The limitation of the parting line placement depends on the material flow, geometry, and other characteristics of the part. Shutoffs – Telescoping Shutoffs. Telescoping shutoffs, otherwise called sliding shutoffs, refer to another common injection molding technique and are frequently used to develop clip- and hook-style mechanisms. These are typically utilized for locking together the molded product's two halves and, much of the time can help eliminate the need for undercuts. Essentially, the telescope gets machined into the mold's one half and stretches out into the contrary side during mold operation while shutting off specific features. How To Deal With Undercuts After Part Is Fully Optimized? Even if the part is fully optimized, there may come situations when undercuts are unavoidable. In that situation, here are three of the ways how to deal with injection molding undercuts: Hand-Loaded Inserts A hand-loaded machined insert is embedded into the mold to avoid molten plastic from streaming into these areas. When the cycle is complete, the part gets ejected with inserts, where an operator is needed to take them out with the part for further utilization. Nevertheless, this manual intervention extends cycle time somewhat, in contrast with side actions that may run automatically. Bump-offs If there exists a mild undercut, one can make an independent insert bolted into the mold. During ejection, the plastic momentarily extends over the insert but then resumes its required form. The bumpoff should be smooth with appropriate radial dimensions – the shape should not be too radical – and the material should be sufficiently flexible that it may slip past the bump with no tearing. Side-Actions, Sliding Side-Actions and Cores (Angled Pin Slide) A perpendicular side-action is suitable for round and hollow parts, and the mold gets split horizontally along the part's long axis. Once the molding cycle starts, the mold halves close together. The side-action slides on an angled pin through hydraulic actuators at the same speed to be correctly positioned simultaneously. Then again, when the molding cycle ends, and the mold opens, the side action slides on the angled pin at a similar speed until the side action is adequately withdrawn to allow the undercut to disengage from the part when ejected. Collapsible Cores Collapsible cores produce plastic parts with internal undercuts as an alternate method. These cores get segmented with flexible elements collapsing inward during the initial ejection while releasing the internal undercut. Once collapsed, the part is easily pushed out of the core in the second phase of ejection. Similar to unscrewing molds, collapsible cores can produce threaded closures and fittings. However, dissimilar to unscrewing molds, the collapsible core molds can also create parts with internal features, including O-ring grooves, dimples, and holes in the sidewall of a piece. Ultimately, it eliminates the requirement of external side action. Collapsible cores can be availed as pre-manufactured "blanks" in multiple sizes. Larger standard cores have diameters from 25mm to 90mm while offering a collapse of 1.20–3.75mm per side, which refers to the permissible depth of undercut feature. Smaller cores with diameters of 13–24 mm can also be availed with collapse distances of 1.32–1.50mm per side. These smaller "mini-cores" can only be used when the thread or undercut is interrupted – not continuous through 360°. Lost or Fusible Core Molding Several processes may allow the production of highly complex parts. E.g., parts with large internal undercuts, which cannot be released with the help of traditional injection molding technologies, can be produced using the fusible/lost core molding procedure. Typically, the fusible core molding process makes various parts, including valves, tennis rackets, pumps, and automotive air intake manifolds. Although the process becomes capital intensive, it has the ability to produce complex parts in one go. Eventually, it eliminates the cost and quality issues of secondary operations. The fusible core molding process starts when a die-cast or gravity-cast metal-core is loaded into the injection mold. The rest of the process goes the usual way, meaning that the tool closes, and the plastic part gets molded onto the cast core. When the mold opens, the core and part are ejected together. A replicated core gets loaded into the tool for the following cycle. After molding, the core, which is usually a metal alloy with a low melting point, is melted from the plastic part. Melting can be carried out using several methods. But the hot liquid inductive heating method is chosen since the core can be dissolved quickly, and the oxidation potential of the metal is minimized. The metal core melting can be achieved using various methods, in particular: Circulation of hot fluid through the core (for hollow cores). Immersion of the part and the core in a bath of hot fluid (swimming pool method). Inductive heating (will probably cause oxidation of the metal). Inductive heating in a hot liquid. Once the core gets melted, an inspection process of the parts is accomplished using metal detectors to ensure complete fusion. Afterward, the metal alloy is recast to produce temporary cores for subsequent molding cycles.

Understanding the injection molding cycle time of a part in production is crucial for several reasons. It allows manufacturers to determine their production rate, which influences the quantity of the parts produced and thus efficiency of the machine. Understanding a part’s cycle time and its stages may also help manufacturers to determine changes they can make that may reduce the time taken to produce a part. This article breaks down the stages of the injection molding cycle time, explains how to calculate total cycle time, and offers some tips that may help to reduce the injection molding cycle time. What Is a Cycle Time in Injection Molding? The cycle time for injection molding is the total amount of time taken to complete the key stages of the injection molding process. The average length of this process varies depending on how long it takes to go through each stage of the cycle. For example, a manufacturer’s total injection molding cycle time may go beyond two minutes if it has a large part or some manual work is needed (e. g. placing the inserts when overmolding is used). Suchana A. Jahan, et al, examined average cycle times in their paper “ Thermo-mechanical design optimization of conformal cooling channels using design of experiments approach .” They found that injection times tend to be approximately two seconds, with average cooling times varying between 12.76 and 17.2 seconds. The Stages of the Injection Molding Cycle Time The injection molding cycle time is divided into four stages, each of which is fairly short. Stage No. 1 – Clamping Molds typically come in two halves, which need to be closed material is injected into them. This is accomplished using a clamping unit. The closed mold is then attached to an injection molding machine, with the clamping unit keeping the two halves of the mold connected throughout the molding process. Stage No. 2 – Injection Also referred to as fill time, injection is the process of filling the mold with plastic material. This usually involves using a hopper to feed plastic pellets into the mold. During injection, the barrel of the injector unit is heated and under pressure, which melts the pellets into a more pliable liquid plastic. The volume of material injected into a mold is called a shot. In most cases, the injection time ends when the mold is between 95% and 99% full. The exact amount depends on the nature of the mold. Stage No. 3 – Cooling Once the material makes contact with the mold interiors, it begins cooling. The plastic hardens during this process. Cooling can lead to shrinkage. Hence, it’s vital to inject the mold with the correct volume of material. The mold can’t be opened until the cooling process completes. Several factors affect how long this cooling stage takes. The packing time determines how long it takes to fill the mold with material. As the mold is filled, the pressure inside increases to the point where the flow of material slows down. As the material cools, the pressure decreases, and space becomes available to pack more material if needed. These pressure changes can also lead to discharge, which needs to be accounted for. As the cooling process continues, sealing occurs at the gate of the cavity. This prevents excessive material coming in. Upon reaching the sealing point, the remaining pressure inside the mold continues decreasing as sealed cooling occurs. Stage No. 4 – Ejection The mold is unclamped and opened using an ejection system, which also pushes the completed product out of the mold safely with the help of ejectors. Since the plastic has shrunk and stuck to the mold, the system applies enough force between the product and the mold to detach (demold) it. After that, the produced part can be processed further - to remove sprues or paint. After ejecting, the mold is clamped again and the process repeats for the next product. How to Calculate Injection Molding Cycle Time? Manufacturers can calculate the injection molding cycle time using the following formula: Molding Time (sec) = t1 + t2 + t3 + t4 The “t” numbers are as follows: T1 = Injection time + dwelling time T2 = Cooling time T3 = Time required to remove the molded product T4 = Time needed for opening and closing the mold Cooling time is the main factor affecting the injection molding cycle time. This can vary depending on the cooling capacity of the mold’s cavity. Cooling time is also affected by the type of material used and the product's wall thickness. Determining cooling time is crucial to ensure products are manufactured safely and to the appropriate quality. Configurable mechanical components supplier MiSUMi references “ Molds for Injection Molding " by Keizo Mitani when providing this experimental formula that can estimate cooling time: T = s2 ∙ ln[8 ∙ (θr - θm) / (θe - θm) /π2] / (π2∙α) The following are what each of the parts of this formula refer to: T – Cooling time related to average temperature of the wall thickness measured in seconds s – Wall thickness of the molded product measured in millimeters α – The heat diffusion rate of the plastic at the surface temperature of the cavity (in mm2/s) Use λ/(c∙ρ) to work out the value for α. λ – Coefficient of the plastic’s thermal conductivity c – Specific heat of the plastic ρ – The plastic’s density θr – The molten plastic’s temperature in degrees Celsius θe – The temperature needed for removing the molded product in degrees Celsius θm – The surface temperature of the cavity in degrees Celsius Keep in mind that measuring cooling time is typically done using software with varying formulas until a working solution is reached. How to Reduce the Cycle Time in Production? Reducing the injection molding cycle time allows manufacturers to make more parts in a shorter period. This creates a more efficient production process. The following tips help to reduce the cycle time. Tip No. 1 – Reduce Opening, Closing, and Ejection Times These factors are determined by the machinery used to control the mold. Investing in more efficient clamping and ejection mechanisms results in faster speeds. Tip No. 2 – Optimize the Cooling Process Creating a more robust cooling channel design may allow manufacturers to reduce the time spent on the cooling process. Muhammed Khan, et al, considered this in their research paper “ Cycle Time Reduction in Injection Molding Process by Selection of Robust Cooling Channel Design .” It was found that combining additive and conformal cooling lines provides a faster and more uniform process compared to conventional cooling lines. In particular, additive cooling lines are 11.29% faster than conventional lines. They also result in 8.477% shrinkage when compared to conventional cooling’s 11.39%. Tip No. 3 – Reducing Holding Times Beyond making the cooling process more efficient, manufacturers may simply be able to reduce the amount of time the part spends in holding. The key here is to balance any time reduction with quality. If shaving seconds off the holding time leads to a reduction of part quality, avoid doing it. Tip No. 4 – Alter the Part Design The wall thickness of a part directly affects how long it takes to cool. If a manufacturer can reduce wall thickness, cooling times can decrease. Again, one eye must stay on the part’s quality if when reducing wall thickness. The temperature controller used must also be able to extract heat energy from the cooling fluid quickly enough to make this idea viable. Tip No. 5 – Change the Runner System Cold runners , which are typically used in two and three-plate molds, are slower than hot and insulated runners. The latter two runners aren’t affected by cooling times either, whereas large cold runners sometimes require more cooling time than the part itself. By switching to hot or insulated runners, manufacturers can lower their injection molding cycle time. Understand the Process Several factors affect the total injection molding cycle time, with cooling being the most important. By using the above tips, manufacturers may be able to reduce the time taken to produce parts. The resulting seconds saved per part can allow them to produce many more parts per day, assuming they can implement the above measures without affecting quality.

The mold is one of the most important parts of injection molding. A mold is made up of two halves that have a hollow space between them into which a melted material is injected. This hollow space is shaped by both the core and the cavity when the mold is closed. Many people confuse the cavity with the core. In injection molding , the cavity is the female portion of the mold that forms a product’s external shape. The core is the male part that is responsible for forming the product’s internal shape. This article explores cavities of injection molding in more detail, with a specific focus on multi-cavity injection molding. Single Cavity, Multiple Cavity, and Family Cavity Injection Molding There are three main types of cavity injection molding a manufacturer may leverage: No. 1 – Single Cavity Molds The simplest and most cost-effective option, single cavity molds produce one molded part per production cycle. These molds are easier to produce than multi-cavity molds, which reduces lead times and allows the manufacturer to start production faster. However, they’re not appropriate for parts in high demand as the tool reaches its production limit quickly. Single cavity injection molding may be a good choice for low-volume production runs. This type of injection molding is often called 1 x 1 to reference the fact that there is one cavity inside the mold producing one part per cycle. No. 2 – Multiple Cavity Molds As the name implies, multiple cavity injection molding uses a mold that produces several parts per production cycle. In addition to reducing the cost per part, this speeds up the production process. Creating the mold itself is more expensive. But for high-volume production runs, that expense is quickly accounted for with the faster and more cost-effective production times. Multiple molds are often denoted as multiplication sums, such as 1 x 2, In this case, the mold produces two identical parts per production cycle. This can extend to 1 x 4, 1 x 8, and so on based on the manufacturer’s needs. No. 3 – Family Molds Expanding on the concept of 1 x 1 molds, there are family molds too. Though these tools are more expensive to produce, they can create multiple different molded parts with a single injection mold. Though 1 +1 is the most common, it’s possible to create 1 + 1 + n + ... molds, which would create 'n' different parts per cycle. Examples include: 1 + 1 – The mold produces two different parts per cycle. 2 + 2 –The mold produces 2 different parts with 2 cavities each (4 parts in total). There is also a more modern form of injection molding that involves injection of two different materials into a mold that produces two parts, but this requires valves inside the runners to control polymer flow. Family molds offer challenges when the parts are of different sizes. The manufacturer needs to balance filling each cavity evenly. Large imbalances lead to product quality issues because of not equal pressure distribution. Arrangement of the Cavities After understanding that there are different types of cavity injection molding, a manufacturer needs to determine how to arrange the cavities in the mold. This includes figuring out how many cavities the mold should have. Several factors influence these decisions. Centric Clamping When a mold is closed, it needs to be clamped together to prevent leakage and ensure equal pressure is exerted to each side of the mold. This can be a challenge with larger molds. If a manufacturer clamps the mold at the top and bottom, the center of the mold may not have the appropriate pressure applied to it to produce consistent parts (without flash). Centric clamping must be used in these cases. This type of clamping ensures pressure is placed on the center of the mold. Centric clamping is fairly simple to accomplish with a single-cavity mold. However, multiple and family molds require forethought in clamping mechanisms due to each having several cavities. Easy Tool or Multiple Tool Easy tool is another term for single cavity injection molding. Often, a manufacturer will use a large tool wherein the mold cavity is slightly off-center. This gives the tool larger dimensions but allows for the injection of melt via a side gate. Some manufacturers place the gate directly on the part, allowing a more direct injection that leads to smaller tool sizes. With multiple and family tools, the manufacturer has to consider sprue distance. This distance must be the same for each part or the mold cavities fill unevenly. The article explores different sprue types later. Cavity Pressure According to a Clemson University paper that examined the concept of cavity pressure as a quality indicator in injection molding, cavity pressure is a reliable indicator for part quality and process monitoring. The research found that creating a cavity pressure curve illustrates the molding cycle’s progression, even in the case of micro-injection molding: As demonstrated in the graph, the peak cavity pressure line matches the part weight line. It increases as the weight increases, and decreases accordingly. As such, a manufacturer can track pressure increases and decreases in line with part weight. If pressure decreases substantially for a heavier part, this suggests an issue in the mold that could lead to quality problems. It also found no significant difference in the curves created by different types of materials, leading to cavity pressure being a suitable indicator of product quality. Cavity Surface Finish All injection molded parts have a surface finish applied by the tools used to create them. The type of surface finish applied affects the time and effort required to create a part. The finish must be produced, with each step of refinement adding time to this production effort. Sandblasting and EDM are two common methods for ensuring a stable cavity surface finish. EDM is a subtractive method that uses electrical discharges to create features on a mold. Sandblasting involves forcing solid particles across the part’s surface using compressed air. This serves to clean and smoothen the surface. Examples of Gates and Sprues A sprue is a channel through which molten material flows during the injection molding process. Sprues guide the material from the hopper to the desired location inside the mold. In multiple cavity injection molding, the distance of the sprue is crucial to the production of quality parts. Variances in sprue distances lead to uneven cavity fills that compromise part quality. There are several types of sprue a manufacturer may use in injection molding. Film Section Used for large-area parts, film section sprues and gating involve filling the molded part using a rectangular cross-section. This prevents internal tension and warping, though the sprue has to be mechanically separated from the part after demolding. Tunnel Cut The molded part is filled using a cylindrical and conical cross-section. This is also known as a side injection. Tunnel cuts allow automatic separation of the mold and sprue during demolding, though it also leads to pressure loss and material shearing. Banana Cut Banana cut sprues are curved to enable access to more difficult injection points. It requires the use of easily deformable melt materials, though it does allow automatic ejection of the sprue during demolding. Screen Gating Used specifically for ring-shaped parts, this sprue prevents weld and flow lines from appearing on the part. It evenly distributes the melt as it flows through, allowing the production of high-quality parts. But this sprue must be manually removed during the rework process, leaving marks behind in the process. Cone or Bar Cone and bar sprues offer very little resistance to the melt, which flows straight down into the cavity. This makes it ideal for filling difficult cavities. However, the mold has to be removed manually, again creating visible sprue marks. Ring Ring sprues are ideal for long tubular parts. They solve the problem of the pressure of inflowing melt leading to bends by providing support to the mold on all sides. Understanding Cavity Injection Molding Noting that there are several types of cavity injection molding allows a manufacturer to determine which types of molds serve their products best. For low-volume runs of a single product, a single mold, or easy tool is preferable. In high-volume runs, it’s often best to use a family or multiple mold to produce multiple parts per injection cycle.

The injection molding process is often used when a manufacturer needs to create technical components in large quantities. This isn’t to say it can’t be used for smaller production runs. Injection molding can also be economical for small runs of up to 1,000 parts due to the material savings it offers and newly emerged rapid tooling possibility. This article details the benefits of the injection molding process, the general process and main types of injection molding, and some of the process’s limitations. What Is the Advantage of the Injection Molding Process There are several reasons a manufacturer may use the injection molding process ahead of other part manufacturing processes. Injection molding large Item Quantities With its extremely fast cycle times, which can be as low as 10 seconds, injection molding is ideal for high-volume production runs of 100,000 or more products. This is particularly the case if the manufacturer uses multi-cavity molds, which enable the creation of multiple products per cycle. Cost-Effectiveness Though creating a mold requires a large upfront investment, this investment is repaid by the low cost per part injection molding offers. Even in smaller runs, manufacturers have the option of using aluminum or 3D printing to keep their mold costs down. Precision Injection molding involves injecting molten plastic under high pressure. This pressure forces the molten material against the mold for the creation of intricate shapes and detailed parts. Repeatability The injection molding process enables manufacturers to produce the same part over and over again. When followed correctly, the process ensures no variance between items. Low Waste Manufacturers have full control over the amount of material poured into a mold. This typically means very little waste because the manufacturer only uses the amount of material needed to fill their mold. Large Material Choice There’s a large range of plastics a manufacturer can use for injection molding, which again offers them control over their production process. Injection molding also allows for the use of recycled, bio-degradable, and bio-compatible materials, with the latter being especially important in the food and medical industries. For example, manufacturers can use injection molding to create implants for surgeries. Finally, 2K molding allows a manufacturer to use two materials in a single mold, allowing for the creation of multi-colored and multi-component parts. The Injection Molding Process There are several types of injection molding process, which this article explores in more detail later. However, as a general process, injection molding typically includes the following steps. Step No. 1 – An Idea Before a manufacturer can create a mold, they first need to come up with a product idea. The versatility of injection molding means this idea can be extremely intricate. Step No. 2 – Create a 3D Model Conceptualizing a product before investing in a mold is crucial. Many manufacturers use computer-aided design software to create a 3D model of their idea. In addition to allowing them to view their idea, these 3D models also allow them to check for any issues that may arise when using a mold. Step No. 3 – Mold Design Assuming the 3D model is viable, mold design comes next. The mold is designed around the 3D model to ensure it can create perfect replicas of the product in question. A key issue here is the concept of design for manufacturing (DFM). This is the process of designing a product in a way that maximizes manufacturing efficiency based on the equipment that will be used. It involves the selection of the right tools, materials, and technologies, in addition to using modern design principles. DFM ensures that the designed part can be created using the chosen tools. It’s also a time-consuming process as designers must often find a balance between the designed part and what’s feasible with the tooling. Step No. 4 – Mold Machining With the mold design solidified, it’s created using a relevant material. Such materials include steel, aluminum, and thermoplastics, among others. The material choice depends on the production run. High-volume runs tend to use sturdier materials, such as steel. Step No. 5 – Injection Molding Machine Once created, the mold is set up in a molding machine. The three main types are hydraulic, electric, and hybrid machines. Hydraulic machines offer exceptional clamp force and durability, though that comes at the cost of high energy consumption and imprecise molding. Electric machines are more accurate and energy efficient, but they cost more and require regular maintenance. Hybrid machines combine many of the best aspects of hydraulic and electric, though they also combine maintenance procedures and are more difficult to source parts for. Step No. 6 – Injection and Cooling Methods With the machine chosen, the manufacturer then selects injection and cooling methods. Examples of injection methods include screw and piston. With screw injection, the raw material is poured into a chamber for plasticizing before moving to another chamber that’s used to inject the material into the mold. Piston injection involves using a plunger to push the plasticized material into the mold. For cooling, the manufacturer may use water, which cools the machine and prevents bacterial growth. They may also use oil that involves the use of an oil cooler that keeps cold oil pumping around the machine. Variothermal cooling involves using cyclically changing temperature controls that are ideal for long, thin, and micro-components . Step No. 7 – Plasticizing by Heat Raw material granules are heated to the point where they’re liquefied. The mold is closed and made ready for injection. Step No. 8 – Injection The liquified plastic is injected into the mold based on the machine’s pre-determined settings. Step No. 9 – Repress As the molten material settles in the mold and begins to cool, it also starts to shrink. The repress step compensates for this by adding more molten material to fill any gaps left by shrinkage. Step No. 10 – Cooling The mold is cooled using water or oil coolant. Some manufacturers also experiment with variothermal technology. The coolant typically cycles through the machine and installed mold and cools the injected plastic to make it stable. Step No. 11 – Demolding/ejection The mold is opened and the plastic part is removed. The manufacturer may also have to manually remove the sprue used in the mold, depending on the type of sprue and gate they’ve used. The Three Main Injection Molding Processes: There are many types of injection molding processes, with each having benefits and drawbacks. The three most common are: 1. Thermoplastic Injection Molding Thermoplastic is inserted into the machine as granules and melted down for injection. This melted material accumulates in front of the injection tool ready for insertion. Monitoring is crucial to this injection molding process as several changes can occur during its application. 2. Thermoset Injection Molding Thermosets are often used for parts with thick walls of up to 50mm, such as vehicle headlights. However, recent advances allow this injection molding process to create parts as thin as 1mm . Thermoset molding cures via exposure to heat. 3. Elastomer Injection Molding This is another heat-based process, meaning the molding tool must maintain a higher temperature than the raw material poured into it. Vulcanization times are higher with this form of injection molding. This form of injection molding offers a good alternative to rubber and silicon processing. The Limitations of the Injection Molding Process The injection molding process has several drawbacks to consider before a manufacturer uses it. Though injection molding saves money in terms of material costs and production efficiency, initial set-up costs are high. Injection molding is also not suitable for very large parts, often due to the clamping mechanisms being unable to hold large molds together effectively enough. There’s also a possibility of visual defects, such as weld lines, ejector marks, and defects caused by gates, in some types of injection molding. What Is Made Using the Injection Molding Process? The injection molding process is used to create a wide variety of products. These include general household products, such as toothbrushes, disposable cutlery, drinking straws, and laundry baskets. Injection molding’s precision also enables the creation of medical components, such as disposable syringes, heart valves, tubes, and even artificial joints. The process can also be used to make electrical switches, toys, car and computer parts, and food packaging. The Injection Molding Process – Versatile Product Creation This article has examined the general injection molding process. However, the exact process varies depending on several factors, including the type of injection molding chosen and the manufacturer’s requirements. It’s this versatility, combined with lowered product creation costs and the process’s repeatability, that has made injection molding one of the world’s foremost product manufacturing techniques.

No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Weld lines, which are also referred to as knit lines, are among the most common of these blemishes. This article looks at the issues presented by a weld line in injection molding and the techniques manufacturers can use to avoid them. Why You Need to Avoid Weld Lines Weld lines lead to two significant issues with an injection molded product. The first is that they deform the part’s surface by leaving unsightly lines that the consumer may not want to see. Second, weld lines compromise a product’s structural integrity. The result is a more fragile piece that has a higher likelihood of breaking. What Can Cause a Weld Line in Injection Molding There is no singular cause of a weld line in injection molding. Instead, several issues can lead to the formation of knit lines that manufacturers should aim to manage. Obstructions in the Melt Flow Knit lines typically form around holes and obstructions in the melt flow. If the flow can’t properly access part of the mold, it enters in an inconsistent way that leads to weak areas. Low Melt Temperatures Temperature inconsistencies in key areas of the mold can lead to issues with material flow. In addition to the temperature of the mold itself, variations in the injection molding machine or its runners can also lead to knit lines. In the paper, Study of the Effects of Injection Molding Parameter on Weld Line Formation , Azieatul Azrin Dzulkipli and M.Azuddin concluded that decreases in melt temperature also raise the possibility of weld lines forming. Material Composition The same paper highlights that the material used for the melt also affects both the possibility of weld lines forming and the nature of those lines. For example, a composite material made using polypropylene, fiber, and glass that has a high filler weight will usually have shorter knit lines, though these lines have a wider angle. Pressure Inconsistent application of pressure can lead to flow fronts failing to be pushed close enough together to allow the melt to merge properly. The result is often a broad melt line. Pressure issues tend to occur if the user creates incorrect settings or if the injection molding machinery is faulty. Mold Design Several mold design issues can lead to the formation of a weld line in injection molding. Examples include improperly placed gates, which affect the material flow, and incorrect wall thickness. This demonstrates the importance of design testing and prototyping to ensure a mold fulfills its purpose correctly. Impurities If the material injected into the mold contains impurities, the melt can’t form properly. Weld lines tend to form around these impurities, leading to compromised structural integrity. Impurities can also lead to inconsistent flow, resulting in one part of a flow being faster than another. Excess Mold Release Mold release affects speed. If there is too much mold release, a manufacturer must find a way to create a higher pressure inside the mold. Otherwise, the melt isn’t pushed through the machine at the required speed to prevent knit lines from forming. Techniques to Prevent Weld Line in Injection Molding Just as several issues can cause a weld line in injection molding, there are also several solutions a manufacturer may use. Manufacturers may need to conduct tests with each solution to determine which solves the specific problem that leads to the weld lines in products. Increase Mold Temperature Increasing the temperature in the feed cylinder may solve the issue if the material entering the mold isn’t fully melted. Higher temperatures also lead to more efficient material drying, again preventing knit lines. Change the Product Wall Thickness Wall thickness affects the time taken to fill a mold. Adjusting wall thickness can slow down or speed up the melt at various points in the process, allowing the manufacturer to create a more consistent flow. Move a Gate Melt is injected into a cavity using an opening that’s called a gate. Many molds have several gates that determine how melt is inserted and how it fills the cavity. Adjusting the position of these gates can help manufacturers to limit weld lines by ensuring consistent flow throughout the mold. Reduce Runner System Dimensions Small runner systems conduct heat faster. By reducing the size of the runners, manufacturers can increase the temperature of the molten material at the front of each flow. This reduces the possibility of knit lines by keeping the flow heated for longer. Adjust to a Single Flow Design Having multiple gates can cause weld lines due to inconsistencies in flow speed and direction. By using a single flow source, the manufacturer avoids the issue of multiple flows coming together. Faster Injection Speeds Premature cooldown is a major issue in plastic injection molding. This cooldown often occurs if the melt flows into the mold too slowly. The melt inside the mold starts to cool even as the hotter melt is layering on top of it. Increasing flow speeds can prevent premature cooling. However, it can also lead to weld line’s simply moving to another location on the part if the flow isn’t managed properly. Use Plastic With Lower Viscosity In the research paper A Review Article on Measurement of Viscosity , M. Maheshwar discusses the importance of viscosity in material selection. He points out that viscosity affects a melt’s internal resistance, with higher viscosity leading to more friction. This friction is a form of resistance that can slow down the speed at which melted materials flow through a mold, resulting in knit lines if unmanaged. Use Vibration-Assisted Injection Molding (VAIM) With VAIM, a manufacturer introduces a vibrational movement to the injection screw used during the injection portion of the molding process. In the paper Vibration Assisted Injection Molding for PLA with Enhanced Mechanical Properties and Reduced Cycle Time , researchers from Lehigh University tested how VAIM affects the physical characteristics of polylactic acid (PLA) melt. They discovered that using VAIM reduces injection cycle times by up to 25%. As discussed earlier, shorter cycle times reduce the possibility of melt cooling, leading to fewer knit lines. Conclusion Though weld lines are a prominent challenge in injection molding, several solutions exist that can prevent or reduce the chances of their formation. The key challenge manufacturers face lies in identifying the cause behind the knit lines they observe so they can implement appropriate solutions.

Most of the injection molding tools contain air inside the cavity when tightly closed. When plastic is injected the air needs to squeeze and go out somewhere. Mold venting enables air to pack and free up space for the plastic. The Problem With Poor Mold Venting Failure to vent a mold properly increases mold temperatures and increases the melt’s pressure. The combination of these issues can extremely heat the oxygen in the mold, causing an array of visual defects and part integrity issues, including: Burnt spots Weak and visible weld lines Poor surface finish Poor mechanical properties Incomplete filling, especially in thin sections Irregular dimensions Local corrosion of the mold cavity surface The Mold Venting Methods Mold venting methods are split into standard and non-standard processes for cavity venting. Regardless of the specific method used, the result should always be that gasses leave the mold, thus increasing the quality of the end product. 1. Standard Processes The following are venting methods that are often built into the molds or machinery manufacturers use. 1.1 Parting lines Which are formed by the points where the two halves of a mold meet. This meeting point naturally leaks gases and can be opened for venting. 1.2 Vent pins Which are ejector pins that usually have between six and eight grooves along their bodies. They’re often used during the ejection phase to release gas and air. 1.3 Ejector pins Which apply the force required to eject a part from the mold. Some manufacturers used them to vent deep features in a mold, thus preventing gas traps. 1.4 Tool clearances Which can be used for mold venting, including that of the parting surface, ejector parts, or the core pulling parts. In all cases, manufacturers must be vigilant to ensure blockages don’t occur in the clearance used. 1.5 Injection mold sliders Which switch the vertical movement of a mold opening to a horizontal motion. They typically consist of a slider body, forming surface, wedge, wear plate, and guide pin. They can prevent the displacement caused by pressure building in the injection molding process. 1.6 Mold Inserts Some manufacturers use core inserts to prevent air traps. These inserts are usually placed where melt streams converge to decrease pressure and gas build-up. 2. Non-Standard Processes Beyond the standard methods, manufacturers can use several other techniques for mold venting. 2.1 Using Porous Sintered Materials Porous materials, such as breathable steel, allow gases to flow through them freely. Unfortunately, these materials often have low strength, though their loose texture can help with mold venting. 2.2 Vacuum Technology Vacuuming devices, such as pumps, solve the air trap problem because the cavity is empty prior injection. However, they add cost to the mold and require well-matched parting surfaces to implement. 2.3 Overflow Systems In an ideal world, a manufacturer can design a mold with gas channels, allowing the mold geometry to expel air. When this isn’t possible, they can use overflow wells to direct air into specific areas of the part or increase gas penetration. The idea is that overflow wells provide a path of least resistance away from the main part that the air should follow. 2.4 Venting Valves Venting valves come in external and internal varieties. External valves are usually connected to the mold via a cold runner or channel to allow gases to escape. Internal valves are built into the mold cavity to create a venting channel for gases. 2.5 Exhaust From Vent Groove Molds for medium and large parts require the removal of more gas. Manufacturers place vent grooves on the concave mold, usually at the end of the melt flow. They ensure smooth exhaust while helping prevent overflow. 2.6 Active Air Venting In their paper Active Air Venting of Mold Cavity to Improve Performance of Injection Molded Direct Joining , Kimura F., et al, proposed the use of a micro or nano-structured metal plate that is joined to an injection mold. The plate was made using a porous metal. They evaluated an active system based on this concept on several injection molded specimens. They found that the surface micro or nanostructure used can help with venting, depending on the composition of the structure. 2.7 Air Vents These may be placed on the cavity, near the cavity, or at the furthest end of the melt flow. Venting isn’t limited to the mold. Vents can also be placed on the gate, sprue, and runners used in the process. Though they’re all in different locations, these vents help expel gases as the melt moves from the feed to the mold. 2.8 Mandatory Exhaust This involves placing a vent pint into the mold at the place where gas collects. Though effective, the method leaves a mark on the finished product. Factors to Consider in Designed Mold Venting A wide range of factors affects how manufacturers design mold venting systems. All of the following must be considered before a manufacturer selects the technique they’ll use. Injection Molding Temperature and Pressure Manufacturers have the ability to change mold temperatures and pressures prior to filling. The flow rate depends on these temperature and pressure settings. Temperature, pressure, and the material’s rheological properties also affect viscosity. More viscous materials flow slower than less viscous ones, which affects cooling speeds. Viscous materials also often require deeper venting solutions, as discussed below. Number of Vents There are differing schools of thought on the number of vents needed. Some recommended placing one vent for every inch of the mold, with others stating that at least 30% of the mold’s perimeter should be vented. Wall Thickness and Vent Depth Wall thickness affects the depth of a manufacturer’s venting. As wall thickness increases, the vent depth should do the same. If shear reduces material viscosity, the manufacturer must use a vent depth at the lower end of the range. This often occurs near the gate or at the bottom of a thin rib. Depth should increase if the material’s viscosity increases due to sheer, such as in the thicker areas of the part. The following is a list of vent depth ranges for various materials: ABS: .001-.0015 ACETAL: .0005-.001 ACRYLIC: .0015-.002 CELLULOSE ACETATE: .001-.0015 ETHYLENE VINYL ACETATE: .001-.0015 IONOMER: .0005-.001 LCP: .0005-.0007 NYLON: .0003-.0005 Vent Land Length Long vent land lengths require more pressure to exhaust gases through them. The shorter the land length, the faster gas expulsion becomes. Mold Vent Width Vents are typically 0.25 inches for small parts and 0.5 inches for large parts. These are standard widths. However, nothing stops a manufacturer from using smaller or larger vent widths. Mold Vent Surface Finish Polishing a vent with diamond paste on a felt bob prevents the vent from leaving a milled finish on a surface. Alternatively, manufacturers perform stoning and grinding operations that match the direction of airflow to prevent the vent’s surface finish from being applied to the part. Mold Vent Relief This is the machined area that connects to the vent. The area feeds into a channel, which may connect with other channels. Ideally, the primary relief channel’s width should match that of the vent it’s connected to, thus improving efficiency. Mold Vent Shape Shape impacts the pressure applied within the vent. Think of vents as constrictions. With this thinking, manufacturers can use the coefficient of discharge to compare theoretical discharge to actual discharge. Vent Clogging The gases produced during injection molding aren’t pure. They contain chemical substances that deposit inside the vents, eventually leading to clogging. In the paper Development of the vent clogging monitoring methods for injection molding , Bongju Kim, et.al, proposed using cavity-gas-pressure (CGP) sensors inside vents to detect deposit buildups. These sensors detect changes in internal vent pressure, which can indicate deposits that need to be cleared. Avoiding and Minimizing Bad Mold Venting Defects In addition to accounting for the factors that affect venting decisions, manufacturers can also take steps to minimize defects. Processing and flow analysis both help in this regard. Processing - Injection Molding Processors have to analyze the end product for defects and make adjustments based on what they see. For example, a processor may slow the melt injection velocity if burning is present because doing so creates more time for gases to escape. However, this isn’t a catch-all solution. Processors must examine everything from barrel temperatures to material viscosity to determine which approach works best. Flow Analysis Flow analysis exists to help manufacturers determine weld line locations, dead zones, and how the mold will fill. The process can also help identify venting issues. DuPont recommends spraying the mold with kerosene or hydrocarbon-based spray prior to injection. These sprays leave black spots on the part in areas where the air is trapped. Conclusion Mold venting is a crucial part of the injection molding process. If manufacturers fail to take venting into account, they’ll likely produce deformed parts that have visual and structural defects. Understanding the factors that influence how a mold should be vented, coupled with the standard and non-standard techniques used for venting, can prevent these issues.

Even minor errors can cause physical defects in a part during the injection molding process. These defects may damage the part’s structural integrity or make it less physically appealing, with both problems likely leading to the part being unsaleable. Injection molding sink marks are an example of such a defect. This article examines what these marks are and how manufacturers can prevent them. What Are Injection Molding Sink Marks? Injection molding sink marks are small depressions or craters that tend to develop in the thicker areas of an injection molded part. They typically occur due to shrinkage, which affects the inner portions of the product. These marks have several potential causes, meaning solving them is rarely a simple task. Possible Causes of Injection Molding Sink Marks The causes of injection molding sink marks can be broken down into five main categories: Poor Part Design Optimization Issues with Machines or Processes Materials Operator Issues Mold Design Problems Poor Part Design Optimization In an ideal world, parts would be designed with uniform wall thickness. When this isn’t the case, the designer must account for varying wall thickness. Failure to do so by building walls that are too thick in the part can lead to the development of sink marks. The melt can’t flow as consistently into these areas as it can to other areas of the part, leading to visual defects. Issues With Machines or Processes Several issues with the machines used or the injection molding process implemented can cause sink marks: Sink marks may occur if the second stage of the process, often called the pack and hold time, is too short. Though pressure may be correct in this scenario, the short time means the part’s gate doesn’t get sealed. Without the seal, the melt may exit the part, leading to the creation of sink marks. Cooling of the melt must be sufficient to prevent sink marks. If the barrel temperature is too high, the melt enters the mold at a higher temperature, leading to cooling inconsistencies in thicker areas of the part. If a part takes too long to cool, the possibility of sink marks increases. Adjusting the part’s wall thickness can aid in faster cooling. So too can proper regulation of cooling by ensuring runners, nozzles, and barrels are maintained at sufficient temperatures. If the injection speed is too fast, manufacturers may find they end up with inadequate pressure levels. Increasing packing pressure can solve this issue, as can slowing down the melt flow. Materials An incorrect flow rate is usually to blame if the materials used in the melt result in the creation of injection molding sink marks. This is particularly the case if the marks appear far away from the gate. The problem here is that an incorrect flow rate hinders pressure transmission. Solving the problem usually requires the manufacturer to expand the gate, thus eliminating bottlenecking issues that hinder flow. Operator Issues The operator may be the cause of sink marks if they allow inconsistencies in the process cycle. Such inconsistencies can include failing to maintain appropriate machine and mold temperatures or allowing for variances in the time taken for the injection molding process. Ideally, the molding process should run automatically, with the operator only intervening in cases of error. Mold Design Problems Several mold issues may lead to sink marks developing: Improper gate placement is a common cause of sink marks. Typically, this is the issue if the mold has an insufficient number of gates or if the main gate is placed away from the part’s thickest wall. If a junction forms between a mating wall and another wall, the secondary wall should be between 60% and 70% of the mating wall’s thickness. If it isn’t, shrinkage can lead to sink marks developing. Material suppliers often provide data for gate and runner dimensioning. Failure to follow these directions can lead to the manufacturer having smaller gates or runners than required. Failing to maintain a balance between rib and wall thickness can be a problem. If the rib is too high relative to the thickness of the wall, sink marks may occur. How to Prevent Injection Molding Sink Lines Thankfully, manufacturers can use several techniques to prevent the formation of injection molding sink marks. Adjust Pack and Hold Times Pack and hold pressures are one of the most common causes of sink marks. Increasing the pack and hold pressure in the cycle may help to increase the amount of material sent to the thicker sections of the mold. Getting enough material into these areas with enough pressure ensures the material’s molecules don’t pull on themselves and get rid of the sink lines. Change Melt Temperature Ensure the melt temperature is within the material manufacturer’s recommended range. If the temperature is too high, the melt takes longer to cool, and sink marks can form. Adapt the Mold Design Ideally, all areas of the mold should allow for the creation of a part with nominal wall thickness. However, this isn’t always possible if a part needs thicker walls. In these cases, creating multiple thinner sections in the thick area or coring out the thick wall can solve sink mark issues. Corners are also a problem with injection molding. Rounding the inner and outer corners prevents increased thickness from occurring due to the joining of two walls. Avoid Excessive Mold Temperatures If a mold’s temperature is too high, the gate may take longer to seal. As mentioned, a gate that doesn’t seal presents an opportunity for melt to exit the mold, increasing the possibility of sink marks. Manufacturers can contact the material manufacturer to discover the ideal mold temperature range they should abide by. Balance Rib and Wall Thickness Melt follows the path of least resistance, meaning it will fill the thicker wall sections before moving to thinner rib sections. The thicker wall sections cool faster, causing sink marks to form if the rib sections are too high. Avoid making a rib height that is more than three times the thickness of a part’s wall. The following diagram demonstrates how this can occur: Use the Seven Degree Rule Implement a seven-degree slope at the base of any ribs built into the part’s design. This allows the mold to pack the melt more uniformly, thus preventing surface blemishes link sink marks. Adjust the Boss Design Bosses are reinforced posts that hold screws or inserts. Incorrect boss design can lead to sink marks because each boss represents additional mass. Following these steps ensures proper boss design: Make the boss’s wall thickness equal to the hole’s inner diameter Use the seven-degree rule at the base of the boss Don’t place bosses directly against outer wall sections Conduct a Thickness Analysis In their study Visualization of potential sink marks using thickness analysis of finely tessellated solid model , Masatomo, I, et al, proposed an interesting method of extracting sink marks from a part’s surface. Using finely tessellated polyhedral models of the part, the researchers found that the amount of shrinkage likely to occur is proportional to the part’s thickness. Using the sphere method, they calculated the thickness of the polygons in the tessellated model, allowing them to extract sink marks. The study is found at the above link and may represent a novel way to counter sink marks. Use External Gas-Assisted Injection Molding External gas-assisted injection molding (EGAIM) is often used to reduce sink marks in amorphous polymer parts. However, Sheofei, J, et al, discovered that it can also be used when working with crystalline polymers in their study Reducing the Sink Marks of a Crystalline Polymer Using External Gas-Assisted Injection Molding . Prevent Sink Marks Injection molding sink marks are visual defects that affect a part’s aesthetic and structural qualities. By taking steps to remedy the issues causing these marks, manufacturers make products that offer greater commercial viability and increased quality.

Injection molding is a precise process, meaning many things can go wrong. Everything from operator error to minor issues with the mold design can cause problems for the part’s aesthetic or structural integrity. Injection molding flow lines are one such issue. This article explains what they are, how they occur, and the techniques manufacturers can use to avoid them. What Are Injection Molding Flow Lines? Flow lines often appear as a wavy pattern on the surface of a plastic part, though several other patterns may occur. They usually display a slightly different color to the rest of the part and are more likely to appear on narrow sections of the item. There are four main types of injection molding flow lines: Type No. 1 – Snake Lines Snake lines occur when a jet effect is created as the melt enters through a gate and into the mold cavity. The resulting line looks like a snake and appears on the product’s surface. Type No. 2 – Wave Lines Inconsistent melt flowing speeds tend to cause wave lines. The melt slows down or speeds up, leading to the melt wandering and causing wavy lines. Type No. 3 – Radiation Lines If the melt sprays as it enters the cavity via a gate, it becomes radial on the part’s surface. A radial line is usually the result. Type No. 4 – Fluorescent Lines Stress and pressure created by the melt’s flow results in a luster appearing on the product. This defect looks similar to a firefly, hence the name fluorescent lines. What Is the Difference Between Weld Lines and Flow Lines? Weld lines tend to occur at spots where flows meet at different temperatures. This results in inconsistent cooling that leaves a line on the part’s surface where the two flows met. Injection molding flow lines also often occur as a result of inconsistent cooling. However, in this case, manufacturers can have a single consistent flow of hot melt that reaches cooler melt inside the mold, leading to the creation of lines. What Causes Injection Molding Flow Lines? The causes of flow lines break down into four key categories, each of which has various issues that can affect it: The Injection Molding Process The Mold The Material The Operator The Injection Molding Process Faults with the injection molding process can cause an array of issues. Either the holding pressure or injection pressure isn’t high enough to press the solidified melt against the mold’s surface, leading to flow lines that match the melt’s flow direction. If the cycle time is too short, the melt may not be heated sufficiently within the barrel. With a low melt temperature, the material can’t be compacted during pressure holding and flow lines occur. This issue is often linked to improper residence time, which also leads to the melt being held in the barrel for too short a time. A low barrel temperature leads to a low melt temperature. These temperatures affect the holding and injection pressure by ensuring it won’t be high enough to hold solidified layers of the melt against the mold’s surface. The nozzle is the final heating zone inside the barrel. It passes heat to the melt. If the nozzle isn’t heated appropriately, the melt temperature decreases and causes the previously mentioned pressure issues. The Mold Mold design is a key aspect of injection molding. Flow lines can occur if any of the following affect the mold: A runner, gate, or sprue that is too small for purpose creates more flow resistance. When combined with low injection pressure, this problem leads to decreasing melt speeds and can cause flow lines. The cooler the mold, the faster the material temperature drops as the melt is injected. Rapid temperature decreases lead to flow lines occurring as hot melt is poured on top of cool solidified material. Blockages can occur if the mold isn’t adequately vented. Flow lines occur because the melt front can’t push the solid material layer against the mold. The Material Issues with the material used can also lead to injection molding flow lines. If a mold cavity has a large flow length to thickness ratio, the material should have a low enough viscosity to ensure a consistent flow. If it doesn’t, the material's lack of fluidity leads to a slow melt flow that causes the previously mentioned cooling and pressure issues. Failure to increase the material’s lubricant content in line with the flow length to wall thickness ratio can cause flow lines. The larger this ratio becomes, the more lubricant content is required. The Operator Operator errors can lead to flow lines occurring in a part. For example, if an operator mistimes the door switching process for the injection molding machine, this creates irregular heat loss that the machine has to try and compensate for. A lack of temperature uniformity occurs, creating cold spots in the mold that causes flow lines. How to Prevent Injection Molding Flow Lines The methods to prevent injection molding flow lines vary depending on the type of lines occurring in a part. Snake Lines For snake lines, the following techniques may help to reduce or prevent their appearance: Reducing the melt injection rate can prevent the jet effect and expand the flow of the melt, leading to superior surface quality. Ensuring the gate depth is equal to the cavity depth allows an expanding flow that prevents snake lines. Setting the gate close to the cavity wall can allow a manufacturer to use the wall as a barrier that prevents a jet from forming. Adjusting the mold gate angle to between 40 and 50 degrees can also achieve this cavity wall barrier. Wave Lines Several changes to the mold design or its temperature can prevent wave lines from forming: Melt fluidity increases as the mold’s temperature rises. This is beneficial for crystalline polymers, as it leads to a more uniform flow that reduces wave patterns. Maintaining uniformity in the product’s thickness prevents wave lines. Prominent edges and corners in a mold core lead to melt flow resistance. Changing these prominent edges and corners may aid flow stability. Combining low-speed injection with the maintenance of high pressure levels ensures melt flow stability. Radiation Lines Preventing spray issues is the key cause for concern with radial lines. These techniques can help a manufacturer reduce spray: Changing the gate to a fan shape may restore the melt’s elasticity prior to it entering the mold cavity. This prevents melt fracturing, which reduces radiation lines. Extending either the main runner or nozzle lengths the melt’s flow path before it reaches the mold cavity. This increases the melt’s degree of elastic failure, preventing spray and the formation of radiation lines. Slowing the injection speed also increases the elastic melt’s flow time, again increasing the degree of elastic failure. Fluorescent Lines Fluorescent lines tend to occur at the narrowest points of the part. These narrow points stretch the flow, creating internal stress that leads to flow lines. These solutions may prevent fluorescent lines: Increasing the mold temperature reduces internal stress by relaxing macromolecules and reducing the flow’s molecular orientation. This reduces the appearance of fluorescent lines on the product’s surface. Maintaining consistent part thickness reduces fluorescent lines. Kucukoglu, A, et al, emphasize this in their paper A Study for Detecting Flow Lines on The Aesthetic Plastic Parts During Design Phases as Using Material Flow Analysis Programs . They note that uniform part thickness prevents warpage and the shrinkage balance effect. Combining medium-speed injection with medium pressure slows the solidification of the melt per unit volume. Internal stress decreases to reduce the appearance of fluorescent lines. Applying heat treatment to a part, such as baking in an oven or boiling the part in hot water, intensifies macromolecule movement. This shortens the part’s relaxation time and reduces fluorescent lines. Tackle Injection Molding Flow Lines Injection molding flow lines are a key concern because there are several types, each with a variety of potential causes. Manufacturers can prevent flow line formation by tweaking their molds, processes, and machines based on the part’s requirements.

The injection molding process allows manufacturers to rapidly create parts. The process involves using a mold into which a melted material, called a melt, is poured. The design of that mold is critical to the part’s visual and structural integrity. Mistakes in the design of a mold can lead to an array of defects, including warping, sink marks, and flow lines. This article aims to help manufacturers avoid the poor mold design choices that lead to compromised parts by sharing some key injection mold design tips. Tip No. 1 – Maintain Uniform Wall Thickness for Molded Parts Managing the injection molded part’s wall thickness is key to quality design. A lack of uniformity in wall thickness can cause the melt to warp as it cools into a solid shape. This results in sink marks that have a negative visual impact on the part. Maintaining consistency in wall thickness helps to avoid the creation of sink marks. Of course, it’s not always possible to have the same wall thickness throughout the whole part. If a wall needs to be thicker, it should be no more than 15% thicker than the nominal wall used for the part. Additionally, wall thickness varies depending on the material used to make the part. The following are recommended wall thicknesses for the most common injection molding materials: · ABS: 1.143 mm – 3.556 mm · Acetal: 0.762 mm – 3.048 mm · Acrylic: 0.635 mm – 12.7 mm · Liquid Crystal Polymer: 0.762 mm – 3.048 mm · Long-Fiber Reinforced Plastics: 1.905 mm – 27.94 mm · Nylon: 0.762 mm – 2.921 mm · Polycarbonate: 1.016 mm – 3.81 mm · Polyester: 0.635 mm – 3.175 mm · Polyethylene: 0.762 mm – 5.08 mm · Polyphenylene Sulfide: 0.508 mm – 4.572 mm · Polypropylene: 0.889 mm – 3.81 mm · Polystyrene: 0.889 mm – 3.81 mm · Polyurethane: 2.032 mm – 19.05 mm Tip No. 2 – Follow the Guidelines for Avoiding Sink Marks Beyond maintaining consistent wall thickness, manufacturers can prevent sink marks by ensuring the proper placement of ribs, gates, and screw bosses. There are three guidelines to follow: · Avoid placing any ribs, gates, or screw bosses on the rear side of cosmetic surfaces; · Rib bases should be no more than 60% of the wall’s thickness; · A rib’s height should be no more than three times the wall’s thickness. Tip No. 3 – Save CAD Design Files in an Appropriate Format Injection mold design tips aren’t limited to the physical manufacturing of the mold. Even something as simple as the computer-aided design (CAD) file format a manufacturer uses when designing the mold can affect its quality. For example, let’s assume a manufacturer creates a CAD design and saves it in the .STL file format. While this may be fine for 3D-printed molds intended for temporary use, this file format has a problem. It reveals the mold’s surface as a series of triangles linked together to create polygonal shapes. As a result, this file format isn’t ideal if a mold or part has precise curves. This triangular representation can also cause issues when defining wall thickness. In this scenario, using a STEP file created by a CAD program like Inventor or SOLIDWORKS is the better option due to this file type’s increased precision. The point is that even a well-designed mold may be subject to unintentional flaws if an inappropriate file type is used for the design. Tip No. 4 – Try to Eliminate Undercuts The term undercut refers to any part feature that prevents straight ejection of a part at the mold’s parting line. Using undercuts in a mold increases its complexity, leading to a higher possibility of part defects. Ideally, the mold designer should eliminate the use of undercuts. However, that isn’t always possible, especially if the part requires a pick-out, side action, or sliding shutoff. In these cases, the manufacturer may be able to mitigate undercut-related issues by using pass-through cores or by adjusting the mold’s draft angles and parting line to facilitate easier ejection. Eliminating undercuts is also one of the most important injection mold design tips for manufacturers that wish to reduce costs. Using undercuts creates higher tooling costs because the mold requires more pieces. Tip No. 5 – Add Draft Angles for Injection Molded Parts Creating parts that have vertical walls can cause problems with injection molding. The part may get stuck as it contracts upon cooling. This leads to the manufacturer having to apply more force to eject the part, which can damage both the mold and the machine’s ejector pins. Using draft angles can solve this problem. Draft angles allow manufacturers to design the walls of a part with a slight slant, facilitating easier ejection in the process. Draft angles are usually added at the end of part design. Typically, the angle is two degrees for most parts. However, any walls with near-vertical requirements should have a 0.5-degree angle. Shutoff surfaces and faces with light textures need three-degree angles, while any face with a medium texture usually requires a draft angle of five degrees or more. Tip No. 6 – Arrange Polymer Flow from Thick to Thin Sections A manufacturer may need to design injection molded parts with thicker sections, which enhance the strength and structure of the part. In these cases, maintaining uniform wall thickness isn’t possible. The problem this creates is that the melt loses pressure and temperature as it flows through the mold. Improper design can lead to the melt flowing through a thin section and into a thick one, resulting in incomplete filling. One of the simplest injection mold design tips to overcome this problem is to position gates at the thicker sections of the part design. This ensures the melt fills the thick sections before flowing into the thin ones, creating a stronger part. Tip No. 7 – Don’t Forget About Ejection Applying inappropriate ejection force can damage the mold, part, and machinery used in the injection molding process. Manufacturers must balance ejection force over the part’s surface area, taking mass and thickness into account in the process. This prevents the part from breaking or warping during ejection. Furthermore, the manufacturer may have to account for the need to clear plastic from the gate in the event of a short shot. This issue can be remedied by placing stripper plates or extra ejector pins in the area surrounding the gate. Tip No. 8 – Attach Bosses to Side Walls and Ribs A boss is a cylindrical feature that is molded into a part. Its typical function is to receive a pin or screw. Manufacturers may use bosses for parts that come in a collection of parts that require assembly. Bosses shouldn’t be freestanding. It’s good practice to attach bosses to ribs or side walls, which ensures the part’s structural integrity. A freestanding boss could snap or break easily because it doesn’t have appropriate support. Design with Confidence With these injection mold design tips, manufacturers have some guidance on how to design a mold that produces reliable and high-quality parts. Details are critical when creating a mold. Even small design flaws can lead to visual defects and issues that affect a part’s structural integrity.

In injection molding , wall thickness is one of the most crucial design elements. Selecting the appropriate injection molding wall thickness ensures the manufacturer optimizes the part’s appearance and moldability. It also improves the mold’s performance, leading to lower manufacturing costs. Most manufacturers use the prototyping stage to test different wall thicknesses and their impacts on the resulting part. Nevertheless, there are some best practices most manufacturers follow to ensure they select the appropriate injection molding wall thickness. This article examines those best practices, the issue of wall uniformity, and explains why uniformity is so important when designing a mold. The Importance of Uniformity in Injection Molding Wall Thickness Uniformity ensures that every wall used for a part is of the same thickness. The most important benefit is that uniform wall thickness ensures consistency when making multiple parts. Manufacturers don’t have to worry about changing flow or cooling rates when the melt moves from thick to thin walls or vice versa. Instead, they get consistent flow and cooling. Maintaining uniform thickness also improves the part’s stress distribution, minimizes shrinkage, and generally allows manufacturers to save money when creating their molds. What Can Happen if Injection Molding Wall Thickness Isn’t Uniform? If a manufacturer doesn’t maintain uniform wall thickness, they must account for variations in thickness in their design and the way they inject melt into the mold. Failure to do that can lead to an array of issues: · Warping may occur if the part experiences uneven shrinkage as a result of varying wall thickness. This usually presents as twists and bends in the part. · Sink marks tend to form on the thickest sections of uneven walls. These small crates occur due to the melt not being able to fully cool inside the mold. · Uneven wall thicknesses can cause varying flow rates, leading to the creation of flow lines . · If the melt is intended to flow from a thin section into a thick one, short shots may cause issues. A short shot happens when the melt cools prematurely in the thin section of the mold, which prevents the melt from flowing into the thicker section. · Uneven wall thicknesses create cooling challenges. The melt in the thicker areas of the part takes longer to cool than that in the thinner areas. The aforementioned short shot issues can occur because of this. However, inconsistent cooling times can create other visual defects and may lengthen the manufacturing process. The Best Practices for Selecting the Appropriate Wall Thickness It isn’t always possible to maintain uniform injection molding wall thickness for a part. But even in those cases, manufacturers have several best practices to follow that can account for variances and help them achieve as much uniformity as possible. Understand the Melt Material’s Wall Thickness Guidelines The material used for the melt plays a huge role in determining a part’s ideal wall thickness. Every material is different, with some having lower tolerances for thickness than others. The following is a useful at-a-glance guide for some of the most common melt materials: · ABS: 1.143 mm – 3.556 mm · Acetal: 0.762 mm – 3.048 mm · Acrylic: 0.635 mm – 12.7 mm · Liquid Crystal Polymer: 0.762 mm – 3.048 mm · Long-Fiber Reinforced Plastics: 1.905 mm – 27.94 mm · Nylon: 0.762 mm – 2.921 mm · Polycarbonate: 1.016 mm – 3.81 mm · Polyester: 0.635 mm – 3.175 mm · Polyethylene: 0.762 mm – 5.08 mm · Polyphenylene Sulfide: 0.508 mm – 4.572 mm · Polypropylene: 0.889 mm – 3.81 mm · Polystyrene: 0.889 mm – 3.81 mm · Polyurethane: 2.032 mm – 19.05 mm Staying within these recommendations ensures the manufacturer avoids cooling and flow rate issues. If Wall Thickness Varies, Make It Gradual Uniformity isn’t always possible, especially if some areas of a part are thicker than others. In these cases, manufacturers must manage the transition from thick to thin or vice-versa carefully. Changes in wall thickness should be gradual because sudden changes can cause cooling issues. The example of shifting straight from a thin wall to a thick wall applies, as this sudden change can lead to the previously mentioned short shots. Follow the Wall Uniformity Best Practices There are several general best practices that manufacturers use to achieve uniform wall thickness: · Regardless of variances, all walls should fall within the recommended thickness range for the material used. · Use ribs to strengthen tall walls. · Place radiuses on inside corners to strengthen them and alleviate the stress that causes warping. · Avoid sharp corners, long unsupported areas, and poorly designed bosses. · Keep draft consistent to avoid creating unnecessary internal stress. A good rule of thumb is to use one degree of draft for every inch of cavity depth. Use Coring or Gussets to Avoid Sink Marks and Shadowing Intelligent tweaks to a part’s geometry can alleviate the stress created by suboptimal wall thickness. For example, a manufacturer may use coring for parts shaped like dumbbells. This technique is similar to coring an apple, as it involves removing cross-sections of the material while keeping the sturdy core in place. Coring can help to prevent sink marks and reduces material wastage. Furthermore, using gussets reinforces long and thin walls, such as those required for box lids. This prevents shadowing, which happens if one area of the part cools faster than another. Understand the Material’s Key Properties The material’s recommended injection molding wall thickness isn’t the only material consideration a manufacturer must account for. They must also consider the attributes of the intended product when selecting the material to use. Key questions for these considerations include: · Can the material be painted or can the manufacturer add colorant to the melt before injection? · Does the part need a high ultraviolet light or chemical resistance? · Is the part intended to be subjected to extreme temperatures? · Should the part be able to flex when under a heavy load? · Will the part be used in an electromagnetic environment? Knowing the answers to these questions ensures the manufacturer selects an appropriate melt material. With the material selected, they can then adapt the part’s design to account for that material’s recommended wall thickness. Follow the Adjacent Wall Thickness Rule The adjacent wall thickness rule states that the thickness of one wall should be no less than 40-to-60% of any wall adjacent to it. Going below this percentage range creates thin sections of a part that may be subject to short shots. Furthermore, manufacturers must follow this rule while staying within the melt material’s recommended injection molding wall thickness guidelines. Avoid Wall-Related Problems here are many issues for a manufacturer to consider in injection molding. Wall thickness is among the most important because sudden variations in thickness can create visual and structural defects. Maintaining uniformity throughout is ideal. When that isn’t possible, the manufacturer must design for manufacturability by using the best practices in this article to account for wall thickness variations.