Adding non-plastic components to molded plastic parts is an effective way to increase strength, functionality and performance. The process, which is also known as overmolding or insert molding, involves encapsulating an non-plastic element in molten plastic, creating an extremely strong bond between the two materials that reduces the need for soldering or adhesives in the final product and can eliminate or minimize assembly costs and lead times.
Insert molding can be used with a variety of metals, including brass, stainless steel and copper. It is a popular choice for creating plastic overmetal parts such as threaded metal tubes and brackets, reducing stress on the joined plastic piece while also providing an aesthetic finish. In addition, insert molded metals can support greater torque and tensile strength than traditional heat staking or brazing techniques, and are more suitable for low-volume production runs.
The basic principles of insert molding are similar to those of plastic injection molding, with the insert inserted into a plastic mold before the molten resin is injected and allowed to take shape. This creates a single unified part that is free of failure points like loose halves and misalignment. This is an important advantage over other types of assembly methods such as post-molding and soldering, resulting in lower manufacturing costs and higher quality products.
A key difference between insert molding and other injection molding processes is that it can be used with both polymer and metal elements, allowing designers to incorporate features into plastic products not possible through the traditional molding process. However, when designing a product that requires an insert, it’s essential to understand the limitations of this method in order to maximize its effectiveness.
One important consideration is that the inserts used must be manufactured using a separate process, such as CNC machining, before being used in an insert molded unit. This can make the overall unit more expensive than a plastic-only product, and it’s important to factor in the cost of the metal inserts when considering whether or not this method is appropriate for your project.
The other major consideration when considering insert molding is the selection of the right plastic for your product. This is especially important if you’re working with an insert made of metal, as the wrong material can cause unwanted side-effects and compromise the integrity of your finished product. Plastics with low shrink rates, such as nylons and polycarbonates, are generally more suitable for this type of molding than materials with high shrink rates, such as PP and PE. Additionally, it’s important to keep in mind that the insert must be able to withstand the temperatures and pressure of the injection molding process. For instance, brass and copper are generally preferred over steel as they are less prone to warping or distortion during the injection process. When possible, automation equipment can be used to load the inserts into the mold, which will help lower the piece price by lowering labor costs and increasing production speeds.