Chapter 29
Injection Molding

There’s a point where craftsmanship meets automation.

Where every shot is a commitment to precision.

That point is rubber injection molding.

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The process begins as the rubber compound, usually supplied in strips or preforms, is fed into the injection unit. Inside a temperature-controlled barrel, a plunger or rotating screw plasticizes and pressurizes it until it reaches the right flow behavior.

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When the mold closes, the system acts in a single calibrated stroke. Material is injected through runners and gates into the cavities. There, under controlled heat and pressure, vulcanization begins.

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Moments later, the mold opens, the part is ejected and the cycle repeats.

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Injection presses come in two main forms.

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Vertical presses: compact, gravity-assisted and ideal for insert molding.

Horizontal presses, by contrast, dominate fully automated lines and are often used for TPEs and liquid injection systems.

But the real power of injection molding lies in repeatability: faster cycles than compression or transfer, consistent surface finish and flash that can be dramatically reduced, especially with well-designed venting and cold-runner tooling.

It’s the process built for stable dimensions, high output and repeatability across thousands or millions, of cycles.

Modern presses take it further. Sensors, closed-loop controls, robotic demolding and full traceability optimize each cycle and log every parameter in real time.

Pressure, temperature, injection profile, cure time: nothing is left to chance.

From automotive plugs to appliance gaskets, from high-volume connectors to precision seals, injection molding delivers accuracy, speed and reliability at scale.

But even here, success depends on the mold: balanced runners, venting, gating, shrinkage control. No press, no matter how advanced, can overcome flawed tooling.

That’s why, when tolerances are tight, volumes are high and consistency is non-negotiable, injection molding becomes the gold standard.

And when that gold standard still isn’t enough, when you need near zero-flash finishes, medical-grade purity and full automation, you step into the world of LIM: Liquid Injection Molding.