July 14, 2022

Checking the tonnage at mold parting line

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Looking at edge failures, and microscopic edge morphology of blends in exterior automotive applications, I tried to find the general answer to this question from mold makers and set-up techs (my best chance at the time) without much luck. I have wondered if this is one of those “the state of the art” technologies; if it one of the “leading edge proprietary craftsman” issues, or if it was considered so simple that no one would discuss it (a nuisance). I generally felt that it was one of those a “state of the art” and final fine adjustments to the mold or daily set up issues. Never quite successful in penetrating this technical area. Always thought one approach would to get my technology very close to a mold maker (seemed very difficult though). Would probably have to find an engineering school, but these mold makers are usually trained as apprentices.

Seemed there were similar issues in clearances of grained surfaces. This seemed to have a lot of effect on flow issues since they weren’t limited to the edge.

In order to know exactly what tonnage the molding machine is producing the stretch of the tie bars needs to be calculated. If the material that the tie bar is made of can be determined then the force can be calculated and the exact tonnage determined.

The easiest way to check the tonnage at mold parting line would be to use the pressure sensitive film. There are many factors that can cause the machine tonnage to change. Toggle clamps can vary the tonnage due to thermal expansion of the mold. Hydraulic clamps produce the same amount of clamp tonnage once they achieve full pressure position.

Pressure sensitive paper or die blue allows you to determine if the tonnage across the mold clamping surface is consistent. Factors that negatively affect squareness:

  • Mold construction
  • Platen surfaces
  • Clamp squareness
  • Tie bar stretch
  • Tool offset

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