Calculating Cavity Pressure in Injection Molding: Tips and Considerations

In summary, the conversation revolved around calculating the pressure inside an injection mold using the coefficient of thermal expansion and volume. One person with 20 years of experience in injection molding stated that they have never needed to use the coefficient of thermal expansion to consider cavity pressure. The discussion also touched on the different stages of the injection molding process and the role of electric or hydraulic machines in determining cavity pressure. The conclusion was that the coefficient of thermal expansion is useful for mold design, but not for calculating cavity pressure.
  • #1
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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  • #2
What is your understanding of how the injection molding process works?
 
  • #3
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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Likes Chestermiller
  • #4
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.
 

1. What is the role of pressure in injection molding?

In injection molding, pressure is used to force molten plastic material into a mold cavity to create a desired shape. It ensures that the material fills the entire mold and produces a high-quality finished product.

2. How is pressure controlled in injection molding?

Pressure is controlled through the use of an injection molding machine. The machine has a hydraulic system that applies pressure to the molten plastic material, which is then injected into the mold cavity. The pressure can be adjusted based on the specific requirements of the molding process.

3. What is the ideal pressure for injection molding?

The ideal pressure for injection molding varies depending on the type of material being used and the design of the mold. Generally, the pressure used should be enough to fill the entire mold and prevent any defects, but not so high that it causes issues such as warping or flashing.

4. How does pressure affect the quality of the final product in injection molding?

The pressure used in injection molding has a significant impact on the quality of the final product. If the pressure is too low, the material may not fill the mold completely, resulting in defects such as voids or sink marks. On the other hand, if the pressure is too high, it can cause issues like warping or excessive shrinkage.

5. Can pressure be used to control the physical properties of the molded product?

Yes, pressure can be used to control the physical properties of the molded product. By adjusting the pressure, the density, strength, and other properties of the final product can be controlled. This is especially important when working with materials that have specific requirements for their physical properties.

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