When you’re buying molded parts made from different types of plastics, it’s crucial you know about some of parts defects that can lower the quality of the molded plastic parts. If you know the sources of the defects and flaws they can cause, you can work in conjunction with your plastic injection molding company to maintain the highest standard of quality during production.
Three Main Sources of Defects
Majority of the defects is caused due to three sources:
- The mold itself
- Processing of the plastics in the mold
- The plastics or resins being used to make the part
Even though these are the main sources of plastic parts defects, there are many other factors that contribute to the defects.
Problems That Occur Due to the Mold
Some of the problems or defects that arise due to an issue with the mold design include:
- Flash: Also known as burrs – this refers to a protrusion that extends outwards. Usually occurs due to a problem with the mold design, but can also occur because of lower clamping force or damage to the mold.
- Drag Marks: When the plastic part is ejected from the mold, it gets scratched due to an issue with the ejector system or when the system is not aligned properly. Read more on fixing ejector marks in your injection mold.
- Warping: Sometimes, the plastic part can be distorted in appearance. This happens when the cooling system of the mold is not working properly, causing the plastics to cool unevenly. Typically, hot-runner systems offer more consistent quality at higher volumes. Learn more about the differences between hot runner and cold runner injection mold systems.
Defects From Improper Processing
Defects that can arise from improper processing of the plastics are as follows:
- Bubbles or Blisters: When plastics are exposed to too much heat or are not cooled sufficiently it results in blisters, which are nothing but raised imperfections.
- Cold Slugs: This is a small uneven area on the plastic part that develops when the plastic is not heated properly, causing it to adhere to the molded part.
- Depressions or Hollows: When the plastics are exposed to uneven heating or cooling, they develop depressions or sink marks. These marks can also occur because of too much pressure being exerted by the press.
- Stress Cracks: If the polymer is exposed for too long to high temperatures, the resultant plastic part will develop stress cracks.
- Burn Marks: You can easily identify burn marks because of the brown or black marks on the plastic part. These marks are nothing but carbon deposits, which develop due to inadequate ventilation or heating the mold for too long. Learn more from our post: Plastic Injection Molding Burns – Causes & How to Fix It.
Flaws Associated with the Plastics
The plastic parts can develop defects due to the plastics or additives being used. These defects include:
- Discoloration: If the feed zone and hopper have not been cleansed and flushed properly, the residual color in them can affect the new plastic part being molded.
- Color Streaks: If the plastics and colorants are not mixed thoroughly, it leads to random color streaks on the parts.
- Splay marks: Silver or white streaks appearing on the surface of the part. Read more about splay defects in our specific article: Plastic Injection Molding Defects: Splay
- Particulate Contaminants: When foreign material is present in the barrel of the press, it finds its way into the molded plastic part, causing formation of flecks.
- Delamination: If the resin pellets contain moisture or are contaminated, you will find the plastic parts have a flaky surface appearance.
If you want to avoid most of these defects, it is necessary to inform your plastic injection molding company to make changes to the mold, plastics and/or processing. You can easily ensure you get perfect and flawless plastic parts by working with an injection molder who is experienced and has the knowledge to work with different types of plastics.