Plastic injection molding inspection guide

What to expect in this article

  • Tool design
  • Ejector pin positioning
  • Machine set – up tool change over
  • Required inspection equipment
  • First off inspection report

Start with tooling design

What is tool design?

Every plastic part designed to be injection molded needs to be produced from a tool also known as a die. These tools need to be designed using computer-aided design (CAD) software and the design engineers need to have a full understanding of how to design a tool that will produce the required part to specification.

What level of detail to check for?

Every part is different, therefore every tool would be different, and however, there are some common aspects to all tools that should be relatively standard. These standard parts of the tool design are important, however, we should be checking for more specific detail which includes the following

  • Gate type, position and size
  • Balanced runner system
  • Ejector pin position
  • Any sliders or moving cores
  • Mold flow analysis (if carried out)

Ejector pins

Ejector pins apply force to eject apart from the mold and it is important that the position and size of the ejector pins is taken into consideration during the design stage

Machine set – up checklist

What is the machine set – up?

Every time a new job is run, there is the need to do a changeover of tools. This means taking the current tool out of the molding machine and placing the next required tool into the machine. This set – up process should be carried out in the absolute any mistakes or errors.

This is why a checklist should be followed.

A set – up that has errors can lead to sluggish cycles, high scrap rats, tool damage, flawed parts, rework, an unsteady process and delayed product de delivery.

Ultimately, this all leads to higher reject rates!

Inspection equipment required

What is equipment is required?

Plastic injection molded parts are produced for numerous reasons and application, some can be cosmetic where tight tolerances are less important than the surface finish, whereas others are heavily reliant on tight tolerance dimensions being correct every time.

Must have equipment?

Molded plastic components would need inspection even it is just the first of sample for approval, the following list measuring equipment is a must in any injection molding supplier QC area:

  • 3 coordinate measuring machine (CMM)
  • Set of micrometers
  • Vernier calipers
  • Slip gauges (slip blocks)
  • Surface table
  • Height gauge
  • Dial test indicators (DTI)

First of the sample report

What is a first off sample report?

The first off sample report is a report that records the physical measured dimensions from a product that has been molded from the first pre – production conditions and to measure a number of sample on every dimension to enable verification that the parts are being molded to specification.

Note

There are different names or terms for this report, but they all refer to the same thing. It is a confirmation process to verify parts and/or materials are compliant to all requirements and specification detailed on the blueprint, quality standard and all related standards.

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