Overmolding is becoming more and more popular in the injection molding industry, so do you know about overmolding? Let me talk something about the Materials Compatibility  and advantages of overmolding,

Overmolding Materials Compatibility

Materials

While there are many combinations of substrate and resin materials that are compatible, other factors affect resin choice apart from compatibility and adhesion. If you only want to cushion the substrate, the resin’s thickness is just as essential as its softness. The best way to measure a material’s softness is the flexural modulus, which is the measure of a material’s resistance to bending. The softness of the material is inversely proportional to the flexural modulus of the material.

While you can find various overmolded materials suitable for overmolding applications, some resins like Versaflex are specifically suited for overmolding processes. If your goal is to enhance a substrate’s grip, the best way to choose a resin is by determining its coefficient of friction. The coefficient of friction of a resin is directly proportional to its tactility (the degree of grip it possesses).

Principles

The type of overmolding method used for the manufacturing process is also an important factor to consider when mapping out the overmolding design guide. There are two primary overmolding methods:

1. Two-shot molding

This method involves molding the substrate using a material and rapidly overmolding it with another material. The whole process uses only a single mold and is an automated process. There are three types of two-shot molding: transfer overmolding, rotational overmolding, and core-back overmolding. The three methods utilize chemical bonding by casting the resin on a warm substrate. This technique strengthens the chemical bond. However, machinists use it only for large-scale productions above 10,000 parts due to its high operating costs.

2. Pick-n-place molding

This method uses two molds and works in batches. The first batch involves molding the substrate parts and manually placing them in the second mold. The second batch then involves injecting the resin on the molded substrate to produce the finished parts. Pick-n-place molding is more cost-effective as it is a manual process and doesn’t involve robotic machines like the former. However, it might not attain maximum adhesion and can only handle low production volumes of up to 10,000 parts.

          The Advantages of Using Overmolding

Although it requires meticulous planning and complex plastic overmolding design guidelines, it is one of the best injection molding processes. Here are a few reasons why:

1. Low Costs

Overmolding can minimize production costs. This is because it can use multiple parts to make a single product using assembly, unlike standard injection molding. Even though the mold design is expensive, it eliminates having to assemble the same part over a thousand times. With the multiple varieties of materials available for overmolding, you can always find the cost-efficient pair for your production process

2. Rapid Cycle Times

Once you create the molds for overmolding, the remaining parts of the process are faster than those that need assembly. While the two-shot molds can take months to complete parts’ production, the pick-n-place overmolding only requires a few weeks for production. However, the latter can handle larger volumes of production. In either case, after the molds’ production, the production process is sped up quickly compared to standard injection molding processes.

3. Ideal for Low-Volume Production

Pick-n-place overmolding is a perfect choice for low to mid-volume production. Although it is a more labor-intensive choice because of the manual labor involved, it doesn’t have high operating costs associated with two-shot overmolding. If you need prototypes of the product before full-scale production begins, pick-n-place overmolding is a better choice. Also, if you need to redesign the part, pick-n-place productions allow you to redesign the molds at lower costs than two-shot molds.