July 14, 2022

Sink Mark Defects of an Injection Molded ABS Part

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Overview of assembled ABS parts
This is a wine opener product, the housing part was molded in ABS and multiple colors; metal parts were coated in multiple colors too, it is exterior critical product, it has to be looking good. so during DFM phrase, exterior related details are our focus, see next how we did it.

Invisible parting line
Clarify the core/cavity side, parting line must be invisible by following the contour of the geometry

Sub gate, interior gate mark
To hide the gating mark, we need to do sub gate like this, the extra feature was created to bridge the melt flow into the cavity, the trouble is we have to trim it off from the parts flush after injection molding.

Wall thickness analysis
The major issues we had is the wall thickness is too heavy partially, this would lead to shrinkage marks defects on exterior surface, we proposed to change the wall thickness to 1.7-2.5 mm, unfortunate our proposal was denied by the customer due to functionality requirement

Hi Carl, a molded part should have even wall thickness so it can be controlled to lead one result: good surface. Those heavy wall material cannot be controlled, melt flow, temperature etc. when we proposed to change it In DFM before mold making, we know it will be surface defects but we don’t know what it would like exactly, unfortunately advise was not taken. I think the right direction to approach would be taking our advice now to optimize the design. If your point is about producing it again without modifying the part design, my answer is no, you can have the injection mold and do the production somewhere else. Please be sure that we have good willingness to cooperate but things need to be on right track.

First trail sample of the injection molded parts
This is our first trail sample, sink mark defects on exterior surface as expected.

Hi Tim,
Thank you very much for your note, we appreciate you reaching back out to us. We understand that we may have to make some changes with the design to achieve our desired results, and we are currently looking into options. If you or Pete has any ideas for us, we would love to hear any of your thoughts. We will keep you posted on any changes we are considering so you can evaluate if you believe they will work.
I also want to say thank you for your flexibility, responsiveness, and overall professionalism. We really appreciate the level of service you have provided us, and it’s invaluable to have a partner that we trust and know will work with us on our issues as we continue to ramp up production.
Feel free to add anything else here that I may have left out.
Thanks and we will be in touch soon.

Changed parts design
To resolve the sink mark defects, we changed the part design by reducing material where was designed too thick at the first place, the new samples after mold modification come out nicely at the second time trail.

Final injection molded parts
This is the final molded parts, and assembled product

Packed ABS parts for shipping
Assembled and packed, ready for shipping

Our customer is happy with ACO Mold.

Thank you so much for the Christmas note.
We really appreciate how well you have treated our company, and you have helped us achieve our best year ever in 2019!
We are excited to continue our relationship in the New Year, and we just placed a new order today for additional metal, 2000 units. Assuming it is ok with you, we will have your team build 2000 grip side A/B and center screws, and we will have the springs and corkscrews sent directly to you for assembly.

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