Understanding Short Shots in Injection Molding

a plastic injection molding shop

Like every manufacturing process, plastic injection molded parts can come out with defects and issues that require troubleshooting. While there can be many quality issues, one of the most common problem is the short shots where the mold doesn’t fill completely.

Here, we discuss what a short shot is how to avoid it.

What is a short shot?

When the mold stops short of entirely filling the mold cavity, it leaves thin areas or voids and creates a deficient product. These holes are commonly found at the edges of the final product or in very thin areas of the mold – the last places a mold would usually fill. It’s one of the most common plastic injection molding issues because short shots can form due to many reasons. For example, they fall into three major categories:

§  Issues with the injection machine

§  Issues with the mold design

§  Issues with the plastic selection

Here’s how you can avoid short shots in injection molding:

How to avoid short shots?

Check your machine

See what’s going on with your injection machine. Are there any restrictions on your feed throat? Is there sufficient material in your hopper? This could be a slide gate getting closed or elevated feed throat temperatures. There’s one more potential cause: the machine may be undersized for the part.

In many cases, we see the tool and frame fit, but the material can’t be injected at the required speed. If you try to force a situation like this, other processing issues may occur.

custom plastic injection molding

Check your vents and tool

See if there’s any build-up in your vents. Build-up creates pressure in the tool. If the vent isn’t easily visible, you can also look for marks or burns on the tool.

You should check how the material is filling the tool. If a balance tool creates different short shots, ensure drops and tips aren’t contaminated from any previous run. One great solution could be a purge compound.

Check your heats

One of the major causes of short shots is heat on your tool, screw, and barrel. This may occur due to two reasons: not reading the proper temperature or thermocouple breaking off. Don’t make any processing changes until you double-check your heats.

PTMS offer all kinds of top-quality plastic injection molded parts

PTMS is a professional plastic injection molding company in China, offering valuable project solutions to worldwide customers.

Give them a call now for more information on their plastic injection molding price!

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