Calculating Cavity Pressure in Injection Molding: Tips and Considerations

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Discussion Overview

The discussion revolves around calculating the pressure inside an injection mold during the injection molding process. Participants explore various factors influencing cavity pressure, including machine type and operational stages, as well as the relevance of the coefficient of thermal expansion.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks assistance in calculating cavity pressure, mentioning the coefficient of thermal expansion and volume.
  • Another participant questions the understanding of the injection molding process, implying that a foundational knowledge is necessary for meaningful discussion.
  • A participant with extensive experience in injection molding states they have never used the coefficient of thermal expansion for cavity pressure calculations and requests more details about the problem.
  • It is noted that cavity pressure depends on whether an electric or hydraulic machine is used and the stage of the injection process, with specific conditions for the first and second stages outlined.
  • One participant argues that the coefficient of thermal expansion is not relevant for calculating cavity pressure, suggesting it is more useful for mold design rather than pressure calculations during the packing phase.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of the coefficient of thermal expansion in calculating cavity pressure, with some emphasizing its lack of importance while others believe it should be considered. The discussion remains unresolved regarding the best approach to calculating cavity pressure.

Contextual Notes

Participants have not reached a consensus on the role of the coefficient of thermal expansion in this context, and there are varying assumptions about the types of machines and stages involved in the injection molding process.

marcus1944
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Im currently trying to calculate the pressure inside an injection mold. Does anyone have experience with similar problems? I need to use coeficient of Thermal expansion and volume. please help .
 
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What is your understanding of how the injection molding process works?
 
In 20 years of injection moulding I have never needed to use the coefficient of thermal expansion in consideration of cavity pressure. Please state your problem with more detail so that we can give a meaningful answer.
 
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Depends on if you are using an electric machine or a hydraulic machine and what stage you are in. If you are in the 1st stage then the cavity pressure should be zero as the polymer hasn't reached the end of the cavity yet. If you are in 2nd stage then I need to know if it is an electric machine or a hydraulic machine. If it is electric then the cavity pressure will typically be whatever you set your pack stage too. If it is a hydraulic machine then you need to take your set pack pressure and multiply it by your screws intensification ratio (get this information from the machine manual or ask your maintenance guy).

Not sure where you are going with the coefficient of thermal expansion. This information will not give you cavity pressure as you are packing the cavity out with plastic in a confined space. The coefficient of thermal expansion is great for designing the mold, but not for calculating cavity pressure.
 

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