The insert molding process is a great way to add strength, stiffness, and function to your custom plastic parts. Also known as overmolding, it involves injecting molten plastic around pre-placed inserts (usually metal) to create a strong, permanent bond. This helps reduce assembly and labor costs while improving part performance. Injection molding with inserts is a common manufacturing sub-process for automotive and electronics components, such as doors and dash panels, electrical sensors, gears, fasteners, and batteries. Additionally, medical devices, such as defibrillators and wired tracing, often use plastic-covered metal cylinders to reduce stress on the jointed parts and make them easier to sterilize for cleaning.

Inserts can be made of almost any type of material, including metal, wood, or another plastic. However, for best results, the insert should be compatible with the thermoplastic resin in which it will be encapsulated. Romeo RIM offers a large selection of stocked inserts from PEM, Dodge, Tri-Star, Spirol, and more that can be used in the overmolding process to help you achieve your desired product design.

Injection molding with inserts is a simple, two-step process. First, the inserts are placed into a customized mold. This can be done manually or robotically. Next, a molten plastic is injected into the mold and the inserts are engulfed in the molded product. The molded product is then cooled and the inserts are removed.

Because a strong mechanical bond is created between the insert and the plastic, overmolding with inserts can increase part reliability and life expectancy. It can also decrease assembly and maintenance costs, while allowing for a more compact, lightweight design.

When designing a project with inserts, many of the same considerations as standard injection molding apply. For instance, it’s important to maintain proper draft angles, keep wall thicknesses consistent, eliminate undercuts, and avoid unnecessary part features. It’s also vital to understand the load and stress that will be applied to the insert during usage and work with your injection molding partner to ensure it can withstand these forces.

Lastly, it’s important to consider the size of the insert, as well as its position within the mold. Because inserts are manually loaded at Protolabs, it’s critical that they aren’t too small to easily place with your hands—particularly if the product requires hand-held operation. A 2:1 ratio of hand clearance to insert depth is a good rule of thumb for optimal results. Additionally, inserts should be located on a side of the part that will be molded to reduce hand fatigue and prevent damage during loading and unloading. For more information on insert molding, contact the team at Protolabs today. We’d love to discuss how we can improve your product with this versatile and cost-effective manufacturing sub-process. Click here to request a quote for your upcoming project! The sooner we receive your quote request, the sooner your products can get into production. Our fast turnaround and industry-leading quality can’t be beat. See for yourself why Protolabs is the leading source for quick-turn prototyping and low-volume production services.