Among the primary reasons you always want to contract with reputable, high-quality injection molding professionals like our team at EnviroTech Custom Injection Molding is our ability to avoid various failures in the injection molding process. We have decades of experience providing quality custom injection molding products to meet exact specifications, with design engineers who know all the possible failure types during this process and how to avoid them.
Such failures can range from minor surface defects all the way to serious issues that impact the safety and functionality of the product. They’re generally caused by one of three broad culprits: Processing issues, material use or storage, or design and maintenance concerns. Here are some of the failure modes possible within each category, plus how we’ll help you avoid them.
Processing Issue Failures
In most cases, failures can be avoided by properly adjusting the molding process based on the resin involved and other factors. Some of the failure issues that can be avoided through this process include:
- Flow lines: Flow lines are a wavy pattern that might appear in a different shade than its surrounding area in narrow areas of the molded item. They don’t usually impact functionality, but are unsightly and will not be acceptable for many consumer products. They can be avoided by increasing injection speed and pressure, plus by rounding corners and relocating mold gates to prevent lines from forming.
- Warping: Warping takes place when different parts of a component shrink at uneven rates, generally due to cooling that happens too fast. We ensure this doesn’t happen with a long, gradual cooling process and non-shrink materials.
- Burn marks: Usually due to trapped air or overheating, burn marks are easily prevented by lowering melt and mold temperatures, reducing injection speed and widening gas vents to allow air to escape.
- Air pockets (vacuum voids): These are trapped air bubbles that may show up based on improper molding pressure.
- Sink marks: Small depressions in surfaces that should be flat, generally caused by cooling that’s too slow. We increase holding pressure and time to allow for proper cooling to avoid this.
- Jetting: Deformation based on an initial “jet” of molten material into the mold cavity, often showing up as a squiggling line. To avoid this, you must reduce injection pressure.
- Weld lines: When two or more polymer fronts collide, weld lines may appear – this can be avoided with increased temperature and proper injection speed and pressure.
Material Use or Storage Failures
Other failures may be related to the material used to begin with, or how the material is stored ahead of production. Examples include discoloration, which involves issues of leftover resin pellets and improper purging, or delamination, where thin layers of the product’s surface are peeling off. Both these are easily avoided with proper cleaning and temperature control steps.
Design or Maintenance Failures
Finally, poor mold design or improper maintenance may lead to certain failure modes as well. A short shot, for instance, is a case where molten material doesn’t fully fill into the mold cavity, leading to an incomplete part – this can be avoided by a better mold design with wider channels or gates, plus increasing speed and pressure. Another issue is called flash, which refers to excess molding material on the edge of a component. Again, preventing this is all about properly-designed molds for the right fit, plus proper clamping force and pressure.
For more on the kinds of failure modes possible in plastic injection molding and how they’re avoided by our pros, or to learn about any of our custom injection molding services, speak to the staff at EnviroTech Custom Injection Molding today.
