Understanding Clamp Force and Clamp Geometry in Plastic Injection Moulding

 In this blog, RJG will go into detail on what clamp force is, why proper clamp force matters, what clamp geometry is, and the importance of optimal clamp geometry.

We recently wrote a blog post about the 8 Key Parameters in Injection Molding Process Optimisation to Avoid Defects, but there was one that we didn’t mention: clamp force. Clamp force and geometry play a pivotal role in the injection moulding process and can significantly impact how efficient (or not) a process is.

What is Clamp Force?

Clamp force is applied to the mould halves in a plastic injection moulding machine to keep them securely closed during the injection phase. It is the force required to resist the pressure exerted by the molten plastic material as it fills the mould cavity. Proper clamp force ensures that the mould remains tightly sealed, preventing issues like a flash, where excess plastic escapes from the mould, and maintaining dimensional accuracy in the final product.

The Significance of Proper Clamp Force:

1. Preventing Part Distortion: Insufficient clamp force can lead to part distortion as the mould may not withstand the pressure of the injected plastic. This can result in part variation and scrap.
2. Prolonging Mould Life: Adequate clamp force is crucial for extending the life of the mould. Properly clamped moulds experience less wear and tear, reducing maintenance and replacement costs.
3. Minimising Flash: Maintaining the correct clamp force helps prevent flash, which occurs when molten plastic escapes from the mould cavity. Flash wastes material, leading to scrap, additional steps to remove the excess material, or shipping bad parts.
4. Ensuring Consistency: Consistent clamp force is essential for achieving uniformity in the moulded parts. It helps produce identical components with minimal variations, meeting stringent quality standards.
5. Maintain Proper Venting: Air is trapped inside the cavity when the mould closes. Vents allow this air to escape but are too small for plastic to fit through. Proper clamp force ensures these tiny vents are not crushed under too much pressure. If that does happen, you end up with either a burn (the air compresses under pressure and creates a dieseling effect) or a non-fill (the plastic cannot fill the space of the cavity occupied by trapped air).

Conclusion:

In plastic injection moulding, the combination of clamp force and clamp geometry is a critical factor in maintaining effective and efficient processes. Achieving the right balance ensures the production of high-quality, dimensionally accurate plastic parts while maximising the life of the moulds.

Read more from RJG here.

RJG
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