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Overmolding from rapid prototyping to production

What is overmolding? How does overmolding work? What is the overmolding process?

The overmolding process is used in a variety of industries and manufacturing. The process involves a technique called injection molding, but high-end prototypes can also be made through polyurethane casting. This type of injection molding helps to mold two or more layers of material together.
The process facilitates plastic overmolding as well as rubber overmolding.
Overmolding is helpful in industries that need to rapidly prototype various industrial machine parts. The process is also handy if custom parts are made by covering plastic or rubber with other materials such as metal.
Overmolding is a multi-step injection molding process in which two or more components are molded on top of each other. Overmolding is sometimes called overmolding because it is a two-step process.
First, the base component (also called the substrate) is molded and cured. Overmolded substrates are typically made of plastic. Then, the second layer is molded directly over the first layer to form a single solid piece. Overmolding is often used to make plastic parts with rubber handles. For example, the overmolding process for an overmolded toothbrush involves forming a base layer of plastic handle and a top layer of rubber (making the toothbrush less slippery to hold).

How does overmolding work?

The result of the overmolding process is a machine part or assembly created by joining two or more materials into one. The materials used can be the same material or different materials. The combinations of materials are almost endless.
To better understand how a process works, we need to understand the two components of a process. Each overmolding project is divided into two parts. The first part of the process is the substrate and the second part is the overmolding.
The substrate is your base material. It can be any type of various materials. Your overmolding is a secondary material. It is the material you want to “cover” the substrate.
In some cases, there may be two or more overmolding in the process. The amount of overmolding all depends on the desired end product and the creativity of the manufacturer.

Limitations of overmolding

We’ve talked a lot about the benefits of overmolding, but as we all know, nothing is perfect. So on the other hand, overmolding also has a slight disadvantage.

  1. The initial cost of setting everything up is very high. Initial prototyping, design, testing, tooling requires significant capital and human expertise.
  1. Overmolding follows all injection molding rules, so any designed part should be compatible with injection molding. Since the molds are made of aluminum or iron, making design changes becomes extremely difficult.
    Plastic can be added to the substrate by cutting out steel or aluminum to make the tool cavity larger.

Conversely, when you want to remove plastic, you need to reduce the size of the tool cavity by adding aluminum or any other compatible metal.
This is a difficult thing to do and can sometimes result in the entire part being scrapped or worse. This will lead to cost overruns and damage the entire manufacturing cycle.

The benefits of overmolding

Overmolding offers many benefits. You can manufacture products in multiple materials and/or colors with relative simplicity. Overmolding also uses fewer man-hours (and therefore costs less) than other manufacturing methods that require transferring the part to a completely different mold or machine. Overmolding reduces the need for product assembly because parts are fabricated on top of each other, resulting in a stronger, more durable overall design.
For large production runs and/or products with colored and multi-layer designs, overmolding is often the best manufacturing method, but you need to be aware of some limitations. Similar to injection molding, the upfront cost of overmolding is prohibitive. Making and modifying molds from metal is time-consuming and expensive, and the dial-in of the overmolding machine is complicated. This means you need to produce a lot of parts to distribute these costs. 
Pro tip: 3D printed parts or molds for overmolding can save you a lot of time and money during the prototyping stage.

Custom Plastic Parts

One of the advantages of overmolding is that it allows custom plastic parts to be designed and created for almost any type of industry. Manufacturers can manufacture plastic-plastic or metal-plastic overmolded products with high dimensional quality.
Some of the products manufactured through overmolding technology include handles, handles, knobs, electronic components, molds, bottle caps, automotive parts, and virtually any other type of consumer or industrial product. Customers can propose different designs for overmolded products as long as the raw materials/resins used are compatible with each other.

Improve product performance

While the most common resins used in injection molding have good properties—waterproof, chemical-resistant, durable—adding another material can greatly improve the performance of the final product. Overmolded products are of higher quality because they have the advantage of two materials that the industry uses for different types of applications.
For example, a large number of hardware tools are made of plastic and rubber. Some typical components of hardware tools include plastic housings, rubber handles, and cutting/machined parts. In this case, the plastic housing is overmolded with a rubber handle made of silicone, styrene-butadiene rubber (SBR), nitrile rubber, etc. 
Overmolded rubber greatly improves tool ergonomics by increasing grip and preventing unwanted slippage by the end user. This also increases the safety of the product, especially when the main tool parts have sharp edges that can cut or pierce.

Reduce manufacturing costs

As mentioned earlier, overmolding is done in one cycle time. This means that the process is accelerated as there is no two- or multi-part assembly. Since overmolding eliminates the post-assembly stage, they are able to reduce manufacturing costs and speed up the overall process. This results in shorter lead times and faster distribution of the final product to different tiers of suppliers/manufacturers for OEM or aftermarket use.
As manufacturing costs decrease, injection molding companies can increase their production capacity. They also reduce the raw material waste that can result during assembly – i.e. by cutting and removing redundant/unwanted parts. Likewise, the costs passed on to consumers are reduced as costs are reduced.

Overmolding can no longer be ignored

You no longer need to wonder “What is the overmolding process?” Everything you ever wanted to know about overmolding is probably in this article. We’ve covered how it works, what to look for in the material, and we’ve even highlighted the benefits of the process for you and your team.
If you have any questions about overmolding, or how it can help your business develop prototypes, please contact us today. Our team of experts is here to help you. We look forward to doing everything we can to help you take your business to the next level with overmolding.

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