Yes, rubber can absolutely be injection molded. In fact, injection molding is one of the most popular manufacturing processes for creating custom rubber components and products at scale.
In this complete guide, as a plastic injection molding manufacturer, I’ll walk you through everything you need to know about injecting molding rubber, including:
- The benefits of rubber injection molding
- What materials work with this process
- Step-by-step how it works
- Real-world applications
- And much more
Let’s get started!
Why Choose Rubber Injection Molding?
There are several key benefits of using injection molding for rubber parts:
Extreme Consistency and Precision
The injection molding process offers industry-leading consistency. Thanks to precise computer-controlled equipment, each single component comes out identical to the one before it.
This repeatability also ensures tight tolerances to guarantee your rubber parts meet strict specifications. I’m talking precision down to the 100th of a millimeter if needed!
Ability to Produce Complex Geometries
Injection molding also provides unmatched design flexibility. You can produce rubber components in virtually any shape or configuration.
This includes parts with intrigate curves, ridges, holes, and other complex features. I’ve even seen rubber injection molded gaskets in the shape of a lion!
Short Production Times
Rubber injection molding offers very short cycle times. The entire process from raw material to finished product takes just minutes (more on this process below).
The automated nature also eliminates the need for hand assembly or other secondary operations to speed things up.
Scalability and Volume Production
Injection molding rubber is ideal for high-volume manufacturing. With an upfront investment in precision tooling, you can crank out thousands of parts per hour.
This makes per-part costs extremely low once production and tooling expenses are amortized over the entire production volume.
What Materials Work With Rubber Injection Molding?
One of the best things about injection molding for rubber is the broad range of compatible materials, including:
Silicone Rubber – Offers excellent heat resistance and flexibility. Used in seals, gaskets, medical devices, and consumer products.
Nitrile Rubber – Provides exceptional resistance to oils, grease, and fuels. Common in seals, O-rings and automotive parts.
Thermoplastic Elastomers – Combines plastic-like manufacturing properties with rubber-like flexibility. Recylable.
Natural Rubber – Made from latex. High tensile strength. Used in seals, mounts, and vibration damping applications.
Fluorocarbon Rubber – Extreme chemical and temperature resistance. Used in fuel systems and aerospace.
That’s just a small sample – there are dozens of additional rubber compounds to choose from. Work with your injection molding partner to select the optimal material for your product goals.
Step-By-Step: How Rubber Injection Molding Works
Now that you know why businesses use rubber injection molding and the material options, let’s look at the actual manufacturing process step-by-step:
1. Prepare the Rubber Material
First, raw rubber material (usually small pellets) is specially prepared for the injection molder. An additive package is blended in to achieve desired characteristics.
2. Load Material Into the Injection Machine
Next, the rubber feedstock is loaded into a large screw-style injection molding machine through a hopper.
3. Heat and Soften Material
The injection molder melts and softens the rubber with a combination of conducted heat and shear friction forces. This transforms the solid pellets into a liquid capable of flowing into the mold.
4. Inject Material Under Pressure
The machine then uses extreme hydraulic pressure – we’re talking ~15,000 PSI – to forcibly inject the molten rubber into the mold cavity. Complex channels guide material flow to completely fill the empty space.
5. Cure the Rubber
Inside the mold, additional heat and dwell time chemically crosslink polymers to transform the rubber into a solid elastic state via a process called vulcanization.
6. Cool and Eject the Part
With curing complete, cooled water is used to reduce the component’s temperature so it regains rigidity. Finally, ejector pins push the finished rubber product out of the mold.
And that’s it! After ejection, some additional trimming or finishing steps may be required. Then the component heads off to its final destination.
Real-World Applications of Injection Molded Rubber Parts
Thanks to the consistency, geometrical freedom, fast cycle times and ability to scale production up and down, injection molded rubber components are everywhere.
Here are some of the most common real-world uses and applications:
Seals and Gaskets
From oil pans to aerospace door seals, custom injection molded gaskets and O-rings create leak-proof interfaces between mechanical assemblies.
Vibration Isolation
Effective vibration damping is critical in motors, pumps, sensitive instrumentation, and vehicles. Molded isolators and bushings absorb unwanted motion.
Noise Attenuation
Unwanted noise presents huge problems in machinery and gearboxes. Injection molded rubber engine mounts, buffers and barriers block sound transmission.
Grips and Handles
Ergonomic tool handles and grips consisting of rigid cores with overmolded rubber jackets offer comfort while improving control.
As you can see, the applications leveraging molded rubber are nearly endless!
Frequently Asked Questions
Let’s wrap things up with answers to some common FAQs about injection molding rubber:
Does Rubber Injection Molding Require Special Machinery?
Yes! You can’t simply use a generic plastic injection molder. Rubber injection molding machines feature special screws, barrels and clamping force optimized for viscosity and cure rheology.
What Are Typical Tolerances for Molded Rubber Parts?
Injection molded rubber components easily achieve tolerances ranging from ±0.005 in down to ±0.002 in depending on material and part complexity. Critical dimensions can be held to ±0.001 in.
Is Secondary Machining or Finishing Required?
aside from some occasional light deflashing or debarring, injection molded rubber parts come out of the mold fully complete – no additional CNC or finishing required!
The Bottom Line
As you can see throughout this guide, injection molding is highly compatible with rubber and rubber-like materials like TPEs.
It’s a go-to manufacturing technique to achieve extreme consistency and precision even with complex geometries and tight tolerances.
So if you’re wondering “can rubber be injection molded?“, the answer is a resounding yes! Injection molding allows rubber to be transformed into an incredibly diverse set of custom components and end products.
Hopefully this overview gives you the confidence to leverage injection molding for your next rubber or TPE project! Let me know if you have any other questions.
