One of the first steps in troubleshooting a short shot is to turn off second stage pressure and time, and make what is referred to as a fill-only part. This will give you an idea of the flow pattern of the material inside the cavity and help with the troubleshooting process.

While the machine is down, it’s a good time to give the mold surface and vents a good wipe down to make sure they haven’t been clogged by contamination.

–Verify the machine settings are correct by comparing them to the process setup document. –Make sure that there are no mechanical problems. –Check for any foreign material that could be blocking the gates and impeding flow into the cavity.

The goal is for a part to appear to be 99% full with no second stage being applied. If the part is significantly smaller than that, you will need to do a root cause analysis of the problem:

Short shots are among the most common and visually obvious quality issues most molders face. So, what causes them? How can we prevent them? And how do we troubleshoot them when they do occur?

A short shot is when a plastic injection molded part does not completely fill out—a portion of it is missing. A few issues can cause short shots, and the fix is not always straight forward.

If the short is still present, or the part is underweight, then increase the second stage pressure to drive more material into the cavity. The short will hopefully disappear and the part weight will come up.

If everything seems to be in good working order, the problem could simply be material variation. If this seems to be the cause of the short shot, then add material to the cavity.

There are many ways to prevent short shots that range from equipment to processes to material. Here are five of the most common fixes:

The ultimate goal is to follow a systematic troubleshooting procedure that allows everyone to work through the process in the same manner for the same reason to fix the problem.

You can put back the second stage pressure settings and take a look at the parts, compare them to the target part weight if you have it.

As you can see, there are many causes, so it’s often hard to pin down which one you’re battling. Unfortunately (or fortunately), there are just as many fixes to these issues depending on the root cause of the problem. But the best-case scenario, of course, is avoiding them altogether.