Injection molding is a popular rapid prototyping process employed in the mass production of many materials. There are many types of injection molding. For example, we have insert molding and overmolding. Each type has its mechanism of action, although they are in the same group. However, this article will take a closer look at the overmolding process, a specific process within the injection molding used across many industries to create parts made from multiple materials.
First, it will introduce the overmolding process, how to use it, its benefits, and its applications. By going through this article, you will know about injection molding and overmolding and why the overmolding process is important.
What Is Overmolding?
Traditional injection molding is a manufacturing process that involves the injection of molten materials into a mold cavity to create a solid product. However, there are different approaches within the realm of injection molding which product designers or prototype designers use to make complex products. Of the many ways involved in injection molding products, a prominent with wide application industrially is the overmolding process.
Overmolding injection molding process involves adding material (overmold) to an existing part or structure called the substrate. The overmolding process typically uses a rigid substrate (such as metal, plastic, or glass) and rubber or thermoplastic as the overmold material. You can use a variety of materials for the overmold. However, most overmolds are softer and more flexible than the substrate. You can also mix the overmold with other agents such as colorants, foaming agents, etc., to get the desired effect upon completion.
From the definition, the injection overmolding involves the combination of two types of material:
- Substrate: Metal, plastic, glass, etc.
- Overmold material: rubber or thermoplastic such as TPE
Also from the definition, you will know the difference between overmolding and injection molding. We will further discuss both materials later in the course of the article.
How Does Overmolding Process Work?
If an injection molded part is to be over-molded, the process is fairly straightforward. The substrate is molded first, using conventional injection molding. Alternatively, the substrate can be made using CNC machining. When the substrate is complete, it is then placed into a new mold. The overmold material, often a resin, is then injected into the new mold, bonding with the substrate.
Bonding between the two materials in the injection overmolding comes to be in two key ways. The substrate and the overmold material can become chemically or mechanically bonded in the injection molding process. Product designers or manufacturers can enhance mechanical bonding by integrating undercuts into the design, which causes the substrate and overmold to lock into place.
Substrates can be fully covered with the overmold material or partially covered to add visual or functional features to the final product. A good example of visualizing the overmolding process is the common hammer. The metal tool, often made from steel, usually has an over-molded plastic layer on the handle. Consequently, the hammer has better handling and grip.
Choosing The Right Material for the Overmolding Process
In each application area, the injection overmolding is applicable in a few basic configurations:
- Plastic substrate with plastic overmold
- Metal substrate with plastic overmold
- Plastic substrate with rubber overmold and
- Metal substrate with rubber overmold.
In each case, you can use many material combinations. However, some are more compatible than others. Compatibility is important in the overmolding process to create the chemical and mechanical bonds between the CNC machined or injection molded substrate and the over-molded layer. Incompatible materials can result in improper bonding or product deformation after the completion of the overmolding process.
However, compatibility also depends highly on the substrate you are working on. For example, when working with a metal substrate, there are many compatible plastic or rubber materials for overmolding. However, you should watch out for incompatible combinations when working with a plastic substrate. Commonly used varieties of plastics for overmolding include a substrate made from ABS (acrylonitrile butadiene styrene) or PC (polycarbonate) and an over-molded feature made from TPU (thermoplastic polyurethane) or TPC (thermoplastic copolyester).
To determine whether a combination of polymers is ideal for overmolding, it is important to consult with a professional overmolding service. This is because most of these businesses have close ties to material suppliers. Therefore, it will enable you to know whether a pair of materials are compatible or not before moving into production.
When to Use Overmolding?
It’s essential to consider the unique requirements of the overmolding process while designing parts. While overmolding is a highly versatile manufacturing method, there are several situations where it may make sense to use a different process.
Overmolding is best for producing a large number of identical parts at speed. For those with interest in manufacturing a small number of niche products, the upfront costs of overmolding may not be worth it in the long run. With overmolding, tooling expenses can be high in comparison to standard injection molding. This cost comes from the extra material needed to make both the substrate and overmolded tools and the precision needed for part alignment during the injection overmolding.
Application of Overmolding Process
The applications of the overmolding process are practically limitless as we encounter overmolded products every day. However, below are some applications of the process.
· Hardware Tools
The injection overmolding is a common technique applicable in manufacturing many hardware tools. For example, screwdrivers, pliers, wrenches, hammers, tape measuring devices, pocket knives, blades, etc. The overmolding process is of importance here because of the grip it offers the hardware tools. Without an overmolded handle, handling most of these hardware tools would be difficult. You can employ different plastics as overmold for the substrate. The common ones are plastics.
· Surgical Devices
Overmolding process is widely applicable in the medical industry due to the need for precision and product safety. Depending on the materials used for substrate and overmold, tools made using the process are sterile and easily cleaned to prevent any form of contamination. Examples of surgical devices made by injection overmolding include syringes, patient monitors, needles, catheters, dilators, soft-touch buttons, etc.
· Everyday Household Items
Due to the features that the overmolding process impacts on its products, e.g., improvement in grip, ease of use, and cleanliness, it is no surprise you find the process useful in making different household items. Examples of household items made using the overmolding process include toothbrushes, kitchen utensils, portable electric fans, mirrors, pens, multi-port chargers, shampoo bottles, reusable food containers, etc.
Another importance of overmolding is visible in making kitchen utensils, cookware, and food containers. Plastics are overmolded on the cookware parts to make grip easy and improve on insulating properties. Therefore, it increases the safety of the consumer.
Injection overmolding is ideal for producing products requiring up to tens of thousands of parts. For customers requiring mass production in the millions of parts, overmolding can also offer an effective prototyping process. At RapidDirect, we have extensive knowledge of the injection molding process and can help you achieve the best results for your product. Among our injection molding services are rapid prototype tooling, production tooling, family molds, multi-cavity molds, and, of course, overmolding.
On a tight schedule? Get in touch with us about your injection molding project and get an online quote to you in under two hours. Our production is efficient and effective, but our eyes for beauty and quality are like no other.
The Benefits of the Overmolding process
When working with injection molding, there are many benefits to overmolding. Some of these advantages come into play during the manufacturing process, and others are related to the quality and function of the end-use product.
· Reduce The Need for Secondary Operations
Looking at the former category, the overmolding process can reduce the need for secondary operations when making a multi-material component. For instance, rather than producing two separate parts made from different materials and assembling them manually using glue or screws, overmolding enables you to create a single part from multiple materials seamlessly.
· Improve Production Cost
The need for fewer steps has a knock-on effect on production costs, and the overmolding process is considered a highly cost-effective injection molding process.
· Improve Product Aesthetically and Functionally
In terms of post-manufacturing benefits, the injection overmolding can improve the look, feel and function of products. It can, for example, add cushioned, soft or non-slip grips to handheld products, improving ergonomics and overall function. These soft coatings can also offer safety benefits, absorbing shock or vibrations.
Companies can also use overmolding to visually improve products, adding different colors, including brand signature hues, to their products. Overmold aesthetic features can boost consumer appeal for products and provide a competitive edge.
Overmolding process is a vital rapid prototyping and production process used in many industrial and domestic capabilities. This article talks about overmolding and its relation to injection molding. It then introduced the benefits of using the process and its application.