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Insert molding is a variation of injection molding that includes a metal piece or pieces that have the molten plastic formed around them. The mold is typically crafted from steel due to the increased pressure necessary for parts of a comparable size from the necessity of the plastic to flow around the inserts.

Insert molded parts have applications that conventionally injection molded parts are unable to accomplish. The addition of the metal insert into the mold adds a new dimension that can be used to achieve new goals. Some potential uses for the metal pieces include use as leads for electronic devices or as bushings that can then be used to further secure the mold piece.

Prior to being being formed into the piece in the mold, the plastic is in the form of nurdles that will be processed within the press in order to be extruded into the mold.

Pre-injection plastic

General Overview of Insert Molding

For the majority of instances that occur with insert molding being used as a production technique, the overall process is quite similar to Injection Molding. The process begins when Nurdles of plastic are transfered into the rear of the molding press. The press then uses a rotating screw of decreasing diameter to melt the pellets by increasing the pressure that is exerted. The molten plastic is then extruded into the mold and travels through the sprue and fills the mold cavities. The rate of injection and the temperature of the plastic contribute to the ability of the plastic to solidify in the best manner and to reduce the number of voids present in the part. After a predetermined amount of time, based on the type of plastic and desired material qualities, the mold is opened and the parts are ejected. These parts then pass through a set of quality control inspections designated by the customer, and finally the part is ready to be shipped to the customer.

Differences from Injection Molding

Although the two processes are similar, there remain several distinct differences in both production and the product created. The most readily apparent difference between the two is the size of the parts created. Injection molding is primarily used for large, single composition pieces. The most important difference between the two is that injection molding solely involves the use of one or more plastics while insert molding does the same and also has metallic components placed in the mold to create parts both of the polymer and metal. Insert molding, on the other hand, is primarily used for small pieces that have multiple materials involved in their creation. Additionally, as a function of the difference in size of the part, the clamp force required for the press is typically higher for injection molded parts because of the additional pressure required for the plastic to evenly flow throughout the mold.

Automation

Similar to processes with injection molding, insert molding has also benefited greatly from the inclusion of automated components as part of the production process. An advantage of using automated components is that the smaller size of parts allows a mobile inspection system that can be used to examine multiple parts in a decreased amount of time. In addition to mounting inspection systems on automated components, multiple axial robots are also capable of removing parts from the mold and place them in latter systems that can be used to ensure quality of multiple parameters. The ability of automated components to decrease the cycle time of the processes allows for a greater output of quality parts. Specific instances of this increased efficiency include the removal of parts from the mold immediately after the parts are created and use in conjunction with vision systems. The removal of parts is achieved by using robots to grip the part once it has become free from the mold after in ejector pins have been raised. The robot then moves these parts into either a holding location or directly onto an inspection system, depending on the type of product and the general layout of the rest of the manufacturer's production facility. Visions systems mounted on robots are also an advancement that has greatly changed the way that quality control is performed in insert molded parts. A mobile robot is able to more precisely determine the accuracy of the metal component and inspect more locations in the same amount of time as a human inspector.

References

• Callister, William D, Materials Science and Engineering: An Introduction, John Wiley and Sons
• Injection Molding Machine from plastics.inwiki.org