What is Overmolding?
Overmolding is a process where a single part is manufactured using two or more materials in a combination to protect sensitive components or give a better look and feel to the final product. The first material is called substrate, which is covered by the second material - overmold. The covering materials are usually thermoplastics or elastomers.
It is assumed that the reader is familiar with the basics of injection molding. If not hover on the topics below:
Plastic Injection Molding
Injection molding is a process of manufacturing diverse types of parts by injecting molten material into the mold. The raw material is fed into the heated barrel, where it gets molten and transferred to the mold cavity. Primarily, plastic materials are raw materials, so the process is also called plastic injection molding.
Micro Injection Molding
Micro molding is also a sub-branch of injection molding used to produce tiny, high-precision thermoplastic parts and components with tolerance in microns.
Technologies Used for Overmolding
There are mainly three technologies used for overmolding: insert or single-shot molding, two-shot or multi-shot molding, and low-pressure injection molding.
1. Insert Molding
Insert molding, also known as single-shot molding, is the most generally utilized process in which a pre-molded insert is put into a mold and the TPE (thermoplastic elastomer) is shot over it. The benefit of insert molding is that it is a bit faster than conventional injection molding. The reason is that insert molding offers the molding of two plastic materials simultaneously. Apart from this, the tooling costs related to insert molding are also lower.
2. Two-shot Molding
In two-shot molding (or multi-shot molding), complicated molded parts are produced from two unique materials, and the product reaches its final form in two related and subsequent steps. The molding machines consists of two or more barrels, and two materials are shot during the same cycle. The first material is fed to the barrel to create the first form of product, which then enters the second barrel for the final build. The advantage of two-shot molding is that the part quality is higher and labor costs are lower.
3. Low-Pressure Molding
Because the electronic industry is growing continuously, so the need for electronic manufacturers to protect weak and fragile components has become imperative. Accordingly, low-pressure molding, developed by Hankel Corporation in 1970, started playing a vital role in the encapsulation of delicate electronic parts, replacing the need for traditional potting processes. This advanced encapsulation process of weak electronic components involves an overmolding process that is carried out using low pressure and temperature and involves less time.
With the increasing need for printed circuit boards (PCBs) and their protection, low-pressure molding has gained ground manufacturing components in automotive, medical, industrial, and lighting industries. A protective mechanism for LED lights can be considered as a glaring application of low-pressure molding.
Benefits of Overmolding
Overmolding process is consistently finding expansion in its use, along with the following benefits:
1. Reduced Assembly and Secondary Operations Costs
While using overmolding for manufacturing parts, there is no need for secondary or additional operations. First of all, the overmolding process eliminates the need for extra adhesives and fasteners. Secondly, it does not need any further operation to get the product to its final form. All these factors hugely reduce costs, time, and the need for labor.
2. Improved Product Quality and Reliability
Overmolding is a highly reliable process since the final product provides users with the ultimate convenience of rubberized and firm grip tools like handheld products and toothbrushes. Consequently, the ergonomics of the product get improved. The over-molded part has a protective layer of thermoplastic that makes it flexible, durable, and highly resistant against external forces.
3. Higher Flexibility of Design
Manufacturing of multi-materials in a single of multi-colors and complex assembly design is easy to achieve with overmolding. Overmolding process ensures rigid assembly and proper alignment of mating parts. Therefore, the quality of the product and the requirement of seamless and compliant designs become easily achievable.
Overmolding Applications Across Industries
Overmolding has diversified applications across myriads of industries. Before moving to the specialized applications of overmolding, here are some of its generalized applications:
1. Generalized Applications of Overmolding
Cable assemblies are a magnificent application of overmolding. Cables manufactured using the overmolding process need to face high-pressure wash downs, extreme weathers, persistent sanitation, exposure to debris and dust, and frequent strain flexes.
Other common examples of overmolding include military equipment, solar energy panels, medical equipment, consumer electronics, and diverse industrial applications.
2. Specialized Applications of Overmolding
a) Medical Industry
Medical injection molding has considerable applications in the field of medicine. Overmolded medical devices comprise rigidity and toughness of one material and an ergonomic and soft feel of other material. The flexible and sturdy exterior of molded parts reduces the chances for abrasion, protects the rigid substrate from any external impact, keeps user hands safe from an infusion of vibrations, and offers excellent water-resistant properties to save from corrosion. The over-molded medical instruments include:
Handles of ambulance defibrillator
Lure fitting or tubing
The market size for molded equipment in the medical field is $1.38 billion. It is expected to grow with a CAGR of 8.2% by the end of 2027.
b) Automotive industry
By now, overmolding is used to make prototypes, handles, accessories attached with dashboards, and molded parts under the car hood.
Thermoplastic Overmolding for Structural Composite Automotive (TOSCAA) project has revolutionized the use of over-molded parts in the automotive industry. This consortium is headed by the SGL carbon fibers and Land Rover, Jaguar, Nifco, LMAT, AMRC, and the University of Nottingham. Collectively, all these partners have collected £2 million with the focus of making cars lighter, durable, and swifter.
In 2016, the global market size of molded parts in the automotive industry was $1.67 billion and $3.29 billion by the end of 2025.
Wire overmolding is one of the significant applications of overmolding in the field of electronics. Many parts in the electronics field are over-molded to make them durable, flexible, and shear resistant. However, insert molding is also excessively used for manufacturing a single part with the combination of two materials.
PCBs, circuit boards, thermostats, and wires are widely put under the overmolding process to become strong against external factors. Electronic silicon overmolding is now opening new domains for further expansion of overmolding in the field of electronics.
As indicated by some statistics, the market size of molded parts in the electronics industry would have reached $1.11 billion by the end of 2029.
The toys industry overwhelmingly relies on the use of plastic molded parts. The over-molded components used in toys provide the demanded safety against external stresses. Furthermore, a vast number of industries are using molded parts manufacturing following products:
Dolls and action figures
Models and crafts
Nonelectric puzzles and games
For example, Microplastic is a leading toy industry that uses molded parts to manufacture toys. It generated a revenue of $30 million in the past year.
Overmolding Process Complexity Overview, Equipment Needed, and Innovation
Overmolding is a bit complex but easy-to-understand process. Along the same lines, here are some of the points to describe complexity overview, equipment needed, and innovation regarding the overmolding process:
Overmolding is a bit more complex than conventional molding. The first thing that makes it more complicated is the right choice of over-molded material on the substrate. At the same time, it also needs to be taken care of whether the over-molded part is sitting correctly on the substrate or not.
Nonetheless, robot-work or machines are capable enough to eliminate all these concerns. If this job is done manually, all these apprehensions will remain the same.
Characteristics of Molding and Inserting
Inserting is a manufacturing process that combines two materials to make a single material, while molding is a simpler process that follows straightforward steps. The procedure of inserting and molding has already been discussed in one of the above sections.
However, some factors make inserting and molding a hard-to-reach process, including flowlines, sink marks, warping, short shots, burn marks, and jetting.
Demolding is referred to as the removal of molded parts from die or mold. It can either be done manually or using compressed air.
Eliminating a casting from a mold and a mold from a model is known as demolding. Demolding of the manufactured part might be a little complex if it is not adequately molded. Closing the mold and repeating the process is not a solution, and the component becomes a wastage.
But then again, wastage is genuinely minor in the overmolding process as it uses calculated and pre-defined parameters like low pressure and temperature to encapsulate naturally weak components. Subsequently, overmolding yields less wastage. Similarly, the application of automatic demolding reduces manual effort.
Latest Innovation in Overmolding
Overmolding is evolving day by day, and its use is becoming more frequent due to the mainstreaming of the following innovations:
Micro-overmolding in the field of the medical industry
Overmolding electronic control units in the electronic industry
Manufacturing of the flattest control unit with seven millimeters only
Latest transmission control system
Overmolding has become a globally renowned and adopted method for manufacturing parts that are usually vulnerable to external stress. Using overmolding has expanded in every significant field like the medical instrument industry, automotive industry, electronic industry, and household product manufacturing industry. Although the process has certain complications, it is still the most appropriate way to protect weak and frail parts.
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