Pulling hair out! Problem with material webbing.

[xncrman]

Please I Need Help.....

I am having problems with webbing of the ABS when pulling parts on a new mold. I have followed troubleshooting guides by reducing heat, dwell and added a round base plate which all helped but still have webbing in one place. My mold and draft need to be much in the shape it's in. Any suggestion?

[judleroy]

Try putting a piece of screen between your mold and the baseplate. II'm not sure if it will help in your case but its easy to try.

[xncrman]

Thanks, I use screen like you mentioned on all molds and vacuum box.

[Senna]

Your standoff is the wrong size and shape. Try a taller standoff block... one that closely replicates the outline of you plug base without creating a negative draw... also make the height of the standoff slightly taller than the tallest web your are experiencing. What you are wanting to do is have the webs end up at the standoff/table interface... so raising the plug up out of the web propagation zone is your cure.

Senna

[xncrman]

Success! Thanks Senna for the advise. I now have a complete part that can be trimmed to meet my final spec's and move on the the adjacent connecting part. i am sure glad I found the cnczone. Thanks again for the quick response.

[Senna]

Great! Glad you were able to achieve success!

I agree... CNCzone is a really terrific resource!

Senna

[trophy]

What do you call a standoff.
I thought webbing was caused by too much material and was fixed by reducing the size of the plastic sheet that is being formed.

[gordoncapucine]

hi senna, i have face the same webbing problems. You have made some advice. could you explain in a more layman terms. What is a standoff?
thanks, waiting for tour professional advice

[trophy]

If I may answer.
It is the base under the shape that is being formed.
If that is not an option I have driled several holes around the base where the webs are and applied the vacuum before the plastic comes completely sealed around the edges so it tends to pull the plastic down into the corners. It is a fine time between just right and too late for when the vacuum is applied.
Having said all tha,t I pull vac from a central hole under the mould and do not use a wire mesh or the likes.
Bear in mind you need big tank volume to do that.
Hope that helps.

[gordoncapucine]

Thank you trophy.

Also, would like to check, the PET turned an opaque white at some parts after the casting. these parts were harder/stiffer than the transparent part. was this caused by over stretching of the PET during the heating?

I also understand that overheating worsen webbing. How do we determine how far to stretch/sag the plastic?

[trophy]

Sorry not much help on this one.
I assume you are using PETG.
Yes over heating will cause bad webbing, as for the right temperature, it's all trial and error.
Depth of sag is a good way of deciding how much to heat the plastic, more sag requires more heat.

[panic]

The white color of the PET is from overheating.You should try keep the temperature high enough but without whitening the sheet.If PET turns white cannot be vacuum properly