Why Plastic Deforms After Machining?
Why does plastic deform after machining? When we machine plastic, we can sometimes see the parts change shape or twist after a while. We understand this can be problematic, especially for applications that require high precision. But what causes this phenomenon?
A common reason plastic parts deform is the internal stresses within the material. These stresses can arise during manufacturing, for example, during extrusion when the plastic is formed. If the plastic isn't machined correctly, these internal stresses can remain and create problems later.
Internal Stresses from Extrusion
During extrusion, the plastic is subjected to various types of stresses, such as thermal and mechanical stresses. These can lead to deformation. If the plastic isn't handled correctly, these stresses can remain. For example, HDPE and UHMWPE may be more prone to developing internal stresses during extrusion.
Asymmetrical machining can also cause deformation. When we machine plastic parts, we can unintentionally create an imbalance in the material, which, in turn, can cause it to twist. A part cut with a circular saw may be more likely to deform if it isn't symmetrical.
Annealing as a Solution
One way to reduce internal stresses in plastic parts is through annealing. This means heating the plastic to a specific temperature and then cooling it down slowly. This can help reduce internal stresses and improve the material's properties. PA6 and POM-C, for example, can benefit from annealing to reduce stresses.
When the plastic is heated, the molecules begin to move more freely. This helps reduce internal stresses and improve the properties. When the plastic is then cooled down slowly, the molecules can return to their original position, which increases stability.
The Material's Specific Properties
Different plastics have different properties. PA, for example, is sensitive to moisture and can swell if exposed to too much moisture. This can cause deformation. POM is more stable and less sensitive to moisture.
Another important factor is hardness. UHMWPE has a hardness of 65° Shore D, which affects its behavior during machining. If we don't consider the hardness, we can unintentionally create problems.
What Can We Do to Avoid Plastic Parts from Deforming?
Choosing the right material is crucial. HDPE may be a better choice than PA for some applications. It's also important to machine the parts correctly, by using symmetry and avoiding asymmetry.
- Choose the right material.
- Machine the parts correctly.
- Use annealing to reduce stresses.
- Consider the hardness and the material's properties.
By following these tips, we can reduce the risk of plastic parts changing shape. If we've already produced parts that have deformed, we may need to machine them again or manufacture new ones.
We hope this article has given you a better understanding of why plastic parts deform and how you can avoid it. Don't hesitate to contact us if you have more questions. We're happy to help!
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Why Plastic Deforms After Machining