Top Tips For Preventing Plastic Part Defects

April 15, 2018

Injection molding has made the plastic manufacturing industry much more efficient, but these parts don’t always turn out the way they should. If you understand what these issues are and what is causing them, you can work with your injection molder to identify and resolve them before they occur.

What Causes these Defects?

There are a few things that can cause defects in your plastic parts:

1. Something could be wrong with the mold. When this is the case, all of the parts made from that particular mold may be defective and need to be recalled.
2. Another issue is the way the material is processed while in the mold. If done incorrectly, the plastic may not set right and create complications.
3. Finally, the material may also be at fault. If it’s not the best material for the part, it may result in poor quality or defective pieces.

All of these different parts of the process need to be checked regularly to prevent these defects from occurring.

Mold Design or Improper Maintenance

Most of the issues caused by problems with the mold design or improper maintenance will fall into one of these four categories:

Jetting – Jetting occurs when a line of the plastic cools too quickly or slowly than the plastic around it. This is caused by poor design and can usually only be corrected by making a new mold.
Warping – When the plastic part comes out distorted or warped, it’s likely due to the cooling system. If the plastic isn’t cooled correctly within the mold, it warps.
Drag Marks – If the part is released from the mold with scratches on it, something is wrong with the ejector system or draft angles of the part. It was likely a faulty design and will have to be replaced or have tool work done to address the issue.
Short Shot – A short shot occurs when there’s not enough plastic injected into the mold to properly fill it.

Plastic Resins or Other Additives

These issues are caused by something being wrong with the resin or other types of plastic being used to create the parts.

Streaks – If the color has streaks running through it, it often means that the resins or dyes weren’t properly mixed. The colorant must be uniformly blended into the resin for a solid color.
Delamination – This issue results in a layer of flaky resin on the surface of the piece. When it occurs, it likely means that the resin had accumulated moisture or some other contaminant on its surface before being melted and injected into the mold.
Embedded Debris – If you see some odd/foreign materials embedded into your parts, you likely need to clean the barrel of your injector mold. It may have debris in it that is contaminating the resin.
Marks or other Streaks – If you notice silver colored streaks or marks in the plastic near the area where it’s injected into the mold, moisture is likely to blame. The resin may have been stored in an area where it absorbed too much moisture.

Resin Processing

Once injected into the mold, the resin goes through processing. There are several issues that can occur during this stage:

Blistering – If the resin isn’t cooled correctly or is exposed to a large amount of heat, it can cause bubbles (or blisters) to form.
Burn Marks – When the mold isn’t ventilated properly, or the resin is left in too long—it can burn. You will see brown or black spots on the resin.
Flow Marks – This issue results in discoloration or wavy lines in the resin. It’s caused by the material being injected too slowly. This causes the resin to cool faster than it should.
Stress Cracks – Also called stress crazing, this occurs when the resin is overexposed to extremely high temperatures.
Degradation – This type of defect results in the resin is losing some of its durability, flexibility, or other property. Often, the degradation occurs to the property that was most important, causing the created part to fail when used.
Dealing with these Issues

Many of these issues are not only common but also relatively easy to address. Working with an expert plastic injection molder is often the best way to avoid many of these problems. Plastic Injection professionals have regular maintenance and cleaning schedules set to prevent these problems.

If you’re looking to partner with an experienced injection molding company, New Berlin Plastics is a great choice. We pride ourselves on having experienced professionals who will work with you to create the perfect parts.