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Plastic Injection Mold Quality

The "Quality" of a plastic injection mold can be looked at 2 ways. The injection mold lacks "quality" if there is a defect in injection mold making. The injection mold is built to a "quality" level based upon the budget and needs of the customer.

The Society of Plastics Engineers outlines plastic injection mold standards from Class 105 to Class 101 based on the tolerances the finished part needs to achieve and the number of parts the plastic injection mold needs to produce.

Each class has a specific list of features and characteristics that allow the plastic injection mold to achieve the desired number of shots.

There is no difference in part quality from a class 105 or 101 tool. Errors in injection mold making that lead to defects in parts are errors in injection mold making not a reflection of standard to which the injection mold is built.
  • Class 101: exceeding one million cycles.
  • Class 102: not to exceed one million cycles.
  • Class 103: not to exceed 500,000 cycles.
  • Class 104: not to exceed 100,000 cycles.
  • Class 105: not to exceed 500 cycles.
When 2 injection mold shops in the same area quote on the same injection mold to the same standards the pricing is usually within a few dollars. The difference in quoted prices comes from one company quoting a class 104 injection mold and another quoting a class 102 injection mold for the same part.

The quality plastic injection mold tooling should be the one that attends the customer requirements. There are many kind of injection molds. If you need a short cycle it must have conditions to give you a short cycle. If you need good surface quality in your product, the injection mold must be done with good steel and must have a good polish or treatment. In fact your question is a little bit subjective.
The good quality of injection mold depends of your expectations, and you must specify it when you are buying a plastic injection mold.

Many plastic injection mold makers can attempt to make your mold but any small error makes the mold useless and impossible to fix. Also, injection mold shrinkage can be different on the various part axis (x,y,z) and can make the part not function properly. You have two choices:
1) go with an experienced gear design molder who may even tell you your project is too high tolerance for success or make you aware that you can succeed but only with expensive tooling and exacting production control..
2) you can work with lower cost inexperienced plastic injection mold makers and have a project with all kinds of problems and final failure. I have done both, even a simple polycarbonate ring gear we made, had a host of production problems before we got it right.

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