Variations of the Injection Molding Process

Variations of the Injection Molding Process

There are three types of injection molding presses in use today:  electric, hydraulic, and hybrid. The hydraulic press has superior clamping pressure and accounts for a majority of the injection molding presses used in the industry. Electric presses are faster, more accurate, more environmentally friendly, and quieter than their counterpart, the hydraulic press. Due to their inherent advantages, electric presses are going to continue to increase in popularity. Lastly, hybrid presses combine features from both the electric press and the hydraulic press, which includes the clamping pressure of a hydraulic press along with the accuracy and energy efficiency of an electric press. 1 Molding process variations include multi-shot, gas and water assist, and structural foam.

Multi-shot injection molding is a process where two or more materials are molded within a single cycle. Figure 1.2 shows an example of a multishot rotary platen injection molding setup. The vast majority of multi-shot parts involve a thermoplastic material and an elastomer. Another form of the multi-shot molding is spin stack molding. The first material is molded and the entire mold rotates to the next stage where the second material is molded. The most recent advancement in multi-shot molding is referred to as “in-mold assembly.” This is a method of molding multiple parts capable of independent movement in one cycle. Examples include valves, air vents, and locking mechanisms. Multi-shot may also be used to create soft-touch surfaces on products.