July 14, 2022

Analysis of Problems Caused by Non-uniform Wall Thickness

blog aco mold

Problems resulted from a non-uniform wall thickness of a plastic injection molded part are more than imagined. This article tries to analyze typical defects resulting from the part design using non-uniform wall thickness. Hopefully, a common sense of the most important principle of part design is uniform part thickness can be established.

Sink marks or hollow
Sink marks and shrinkage occurs most frequently in bulge area (including ribs, snap, etc.), the wall thickness equivalent in these area is greater than the thickness of the ribs and the panel (see Figure below).
Wall thickness

When the injection mold start to cool down, the green area solidify first, the red area continue to cool done, it will suck in the other area and it becomes to be sink mark or sink hollow.

To avoid these failures, the wall thickness of the bulge area design at 50 to 75% of the wall thickness is preferably. By CAE simulation, you can forecasts the shrinkage on bulge area with different wall thickness designed to understand the different effects on sink marks or shrinkage.

Uneven wall thickness cause air trap
If wall thickness is uneven and the difference is large, melt flow will obtain favor to fill the thicker wall zone with smaller plastic flow resistance first. If the thin-wall area is surrounded by thick wall area, the air in thin wall area filled will be surrounded and trapped. the air trapped inside will be Oxidation, and even burnt.

Uneven wall thickness cause weld line
During the injection process, slower and faster cooling create different melt flows, weld line will be formed while the melt flow met, the weld line is not just cause obvious appearance defect but also very fragile.

Uneven wall thickness cause deformation
Picture below show a cell phone case made in PC+ABS, main wall thickness is only 1/3 of the side wall, the difference is huge, the shrinkage on different area is different so the internal stress created cause deformation.
Cell phone case

Related Blogs

blog aco mold
Gas Assisted Injection Molding Chairs
Gas Assisted Injection Molding chairs have been produced successfully for the last 20 years. My company (Aco Mold) has recently supplied gas assisted molding equipment for a customer in Brazil...
blog aco mold
What is Mould Shrinkage?
Mould shrinkage can be manipulated by nearly all process variations- melt temps, cooling temps, in. pressures and hold pressures, injection speeds and so on, as well as gate location and...

Table of Contents

Tell us your request right now and contact us today about getting started on your next project together!


Or Fill Out The Contact Form Below:

Support Your Business with Better Molding Solution

Contact Info
Copyright © 2023, ACO Mold. Terms of Service and Privacy Policy. All rights reserved.  Powered by ACO MOLD.
1 1.png

Join Our Network

Please email to sales@acomold.com
or fill out the contact form below: