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Rubber Injection Molding 

What is Rubber Injection Molding?

Rubber injection molding is similar to rigid plastic injection molding, except that the materials being used have flexibility and elasticity to make parts that require adaptability in their environments. These rubber-like materials are durable and can be produced in a variety of shore values, making them useful for many applications. Some applications of rubber injection molded parts may include electrical overmolding, seals, stoppers, soft-touch grips, baby bottles, and other pliable parts. 

Although multiple flexible materials are available for rubber molding, the two primary types used are TPE and LSR. For the sake of simplicity, this article will only discuss these two main competitors. 

Thermoplastic Elastomer (TPE)

TPE, or Thermoplastic Elastomer, is a rubber-like thermoplastic that uses the same equipment and production method as rigid plastic injection molding. This involves feeding TPE pellets through a hopper and barrel where they are melted and injected into the mold. Once cooled enough to retain its shape, the part is ejected from the mold, and the next cycle begins. 

Because it is a thermoplastic and, therefore, its particles are not chemically bonded, it can be remelted and remolded repeatedly without change to its mechanical properties. This makes it easily recyclable. TPE is also processed at a lower temperature, and the average mold for this material may be heated to only 70-120°F, meaning that it takes less energy to manufacture than LSR and other thermoplastics. This lower temperature also contributes to a shorter molding cycle time, which can be as little as 20 seconds depending on part size and design. 

While TPE has many advantages, including its remoldability, these can be also be areas of weakness. TPE will deform and melt at elevated temperatures, including those found in high heat applications. For this reason, it is best to use this material only in moderate temperatures to avoid part warp or failure. Likewise, TPE will deform under continuous stress. 

Liquid Silicone Rubber (LSR)

LSR, or Liquid Silicone Rubber, is a rubber thermoset that is most commonly injection molded, but it requires different equipment than rigid plastic injection molding due to the nat