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Plastic product Impact resistance - what can you do with the geometry

Skilled boxers have good impact resistance. They can absorb the energy of impacts with their whole body, not just one part of it, nose for instance. The same principle applies not only to material toughness, but to mechanics as well:

1: Try to distribute the energy of impacts to the whole construction. Do not maximise the stiffness of the product without a good reason. Think of the component as a spring.

2: Impact resistant materials are able to absorb energy in their internal structure. That requires bulkiness to some degree from the construction. A helmet with 0,5 mm wall thickness is not very impact resistant. Robustness is good. Don’t make the shock-absorbing elements too thin or lacy.

3: Sharp corners and notches operate as stress raisers. This goes with static loads as well, but in the case of impacts, they are merciless.

4: A rib that is meant to strengthen the product might easily reverse the intended purpose by crack propagation. Ribs should preferably be under compression rather than tension.

5: If possible, try to avoid weld lines in the areas that are exposed to shocks. The same goes for gating, too.

Did I miss something? Please add your own design tips in the comments below!

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Comments

Sander Rave
Hi Markus, I'd like to share with you some guidelines for thermoforming, in essence they also apply to other production techniques. Do you like to share your mail address with me so I can send you some input for your blog? Regards, sander.rave@sabic.com
Markus Paloheimo
Hello Sander, all material is highly appreciated. Perhaps there is something that could be shared under some article. Please use markus@plasticprop.com. Thank you, Markus
Thomas
Markus - Thanks for sharing your knowledge and experience. I found the information on designing against impact resistance to be helpful.
Markus Paloheimo
Thank you Thomas. I am happy you found it useful.
Markus
Hardik, If there is a hole, there is always a parting line. It is a common suggestion that the piston that makes the hole is in withdrawn position during the filling of the mold and then moves forward. It would definitely leave a film/burr on the product. I have never seen this implemented in practise. Anyway, if you have the critical weld line quite close to the gate and material running through the area (fronts not colliding and stopping) this will help with the strength. Good luck, Markus

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