There are many factors to consider when creating an injection-molded part. From design, to creating prototypes, to mold-filling, plenty can go wrong during the injection-molding process. Even once you have a complete piece, it may not turn out right. Bubbles, blisters, sinks, and voids are common issues that cause a part to be rejected.
Some issues to watch for:
- Inadequate venting
- Material flow pattern design
- Gas traveling across the part surface during the fill or pack stage
- Melt flow issues
- Venturi effect
- General-purpose screws with dimensions of 18:1 L/D or lower
- Insufficient plastic
- Gate location
In the following slideshow, we’ll look at each of those defects and issues, and some tests and solutions to help address them.
Plastic Defects: How to Avoid Common Injection Molding Part Rejection from Prospector from UL
Have you encountered any of these issues in your injection-molding projects? Please share your questions and experience with a comment below.
Further Reading:
- Eliminate Bubbles, Voids, Sinks & Blisters
- Overcoming Plastics Injection Molding Problems
- Troubleshooting FlipChart for Plastic Injection Molding
Looking for plastic materials for your injection-molding project?
Find technical data and order samples from global suppliers in Prospector – see the current listings in our plastics database.
About the Author
| John Bozzelli Injection Molding (IM) Solutions 1019 Balfour St. Midland, MI 48640-3227 Phone: 989-832-2424 Fax 989-832-8743 Email: john@scientificmolding.com www.ScientificMolding.com |
John Bozzelli is a graduate of Marietta College (BS) and Ohio University (MS). His studies were interrupted for a stint in Vietnam (US Army, Purple Heart; Silver Star). Twenty years in Dow Plastics provided extensive experience in polymer synthesis, development, production, and processing. John has been a seminar leader with RJG Associates, Injection Molding Magazine, University of Wisconsin Milwaukee, General Polymers and John Klees. Competent in resin characterization and analysis, his specialty is practical, hands-on injection molding training with both small and large machines. National recognition has come through ten patents, over 60 papers covering plastics, processing, machine specifications, and over 12 years on the national seminar circuit. Feature articles such as the “Productivity”; by Plastics World and ”Scientific Molding” by Injection Molding Magazine October, November and December 1997, have highlighted a couple of exemplar case histories. Check out the August 2001 issue for applications of The Universal Set Up Sheet.John is the initiator of Scientific Injection Molding and teaches the plastic’s point of view for design and processing with a passion you will remember. Take some of your valuable time to learn practical molding techniques that improve your profits tomorrow while eliminating the state of ”fire fighting“ currently found in many molding facilities. Let us keep plastic manufacturing strong in North America. |
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I glad to read and learned something else about voids, blisters and wich is the differnece betwen bubbles and voids
Regards
Hello , this is Hilario Orta From Vuteq Mexico , do you have Information about training in apparience defects ? how to control valve gates molds , we make very visible parts ( Doors for cars ) and some times we have some questions,. Thanks in advance for your support
Thanks for the guide. We have an issue that we found a combination of back pressure and screw speed was the fix for our blisters. The base resin was an ABS with dye. IF the screw speed is too fast the material blistered and too slow the dye did not mix well. After a few attempts we found a good combination of settings and have run great ever since.
Colorado
Hello I ran into a problem with a thick part ran out of NYLATRON GS, I even try to run it with a foaming agent and the results were negative. Our next step is to increase the gate size and to vent a core pin that is also a shut off pin.
Please advise.
Thank you