Overmolding is an injection molding process where you cast a layer of resin (usually a rubber-like plastic known as TPE) over an already molded or machined material to give it properties it doesn’t singlehandedly possess.
Although this process is cost-effective and helps to provide excellent adhesion between materials, it requires proper planning. For example, the machinist has to pick the right materials to carry out the part’s function and attain maximum adhesion. This is one of the reasons why the machinist has to plan the overmolding design guide properly.
Due to the complexity of the design, you need to be careful when making the overmold design. This article will help give useful tips on the principles you should consider when making your overmolding design guide.
Factors to Consider Before Overmold Design
When starting your overmolding design guide, you must consider a few factors that will help make the design turn out successfully. Examples of such factors include:
Part Function
Designing an overmolding part starts with fully comprehending the function of the part. To be able to do this, you should ask yourself some questions about the part such as:
1. What is the intended goal for the part?
Understanding why you want to design the part is very vital to the design part. Due to the wide application of overmolding, knowing your product’s goal is essential in knowing the process to use. For example, if you plan to mold a seal on a water-resistant case, a water-proof seal is the product’s goal.
2. What type of exposure will the part face?
You should also consider the type of exposure your product will face in the ‘line of duty’ before making the design. For example, if the part will face harsh radiation like UV light, you can use specific plastics for this type of product.
3. Why are you overmolding the part?
The reason you’re using overmolding for the part will also help determine how complex the design should be. For example, when making a TPE overmolding design guide for a TPE (rubber-like) to be cast on a handle, the intended use of such contraption is either for vibration absorption, ergonomics, grip, or comfort. Answering this question satisfactorily will help choose the right material and map out your overmolding design guide properly.
4. Do you plan to make the part on a large scale?
If you plan to take the production on a large-scale basis, you also have to consider this when making your overmolding design guide. For example, an overmolding part meant for vibration dampening will have a thick wall, which will require more material and take a longer cycle time to produce each part. Making such a product could be very expensive, but it might be worth the price if you only want a few pieces.
After ensuring your part’s function fits in with your design, the next step is to examine the stance in which you will use it and how that will affect its physical features. The four common scenarios in which we use overmolding products include:
- Adding Grip to a Substrate
Products such as drills, garden hoses, or kitchen utensils need an amount of grip to help the user control the product even in wet conditions. In these scenarios, the best way to add grip to these products is by casting a rubber-like plastic over their handles. This type of process might not require much material and only requires low-quantity production most times.
- Comfort
When adding grip to a substrate, it also serves as a source of comfort when using the product. So, this scenario is similar to the former in most cases. The most popular example of products that combine both scenarios is the rubber grips on bicycle handles. This scenario also requires minimal materials and only require low-scale production in most cases.
- Sealing
Making an overmolding product for this scenario will require a longer cycle time and more material. These seals usually have water-resistant properties and need to achieve maximum adhesion with the substrate. Before designing this type of part, you have to find the material which would give the best adhesion with the substrate and provide the best water-proof capabilities.
- Vibration Dampening
This type of use requires the most material and has the longest cycle time. This is because the TPE part to be produced has to be thick enough to absorb the substrate’s vibrations you want to cast it on. Clients apply this scenario to high-energy machines like pumps and drills.
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