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shrinkage formulas

shrinkage formulas

shrinkage formulas

I need to know the functional diffrence between the shrinkage formulas.



(S stands for the shrinkage factor)

By functional I mean where or when to use the proper formula
Any other info about shrinkage formulas would also be helpful

RE: shrinkage formulas

The 1+S formula would be used to add shrinkage (or scale up) to a part. For instance, if the shrink is 0.003 in/in, you would multiply the dimension by 1.003 to get the number that would be used for the tool design.

The 1/(1-S) formula is used to take the shrink away (or to scale down) to give the nominal or real dimension. Since shrink is multiplicitive, you don't multiply the above example by 0.997 to take the shrink away...it would actually be 0.99701 due to the formula.

RE: shrinkage formulas

In the case of some thermoset molds, the shrinkage is very low and the mold steel is heated up. This can affect the part...in extreme cases on large parts, I have had to calculate cavity sizing based on the steel growing more than the part would shrink. In this case, you actually scale the part down. You should also take steel temps in consideration when design molds for extremely high tolerance parts.

RE: shrinkage formulas

Both formulas are usefull.   With the second one you will have more presicion.  When you need to get the right size you have to leave more material so after the test you can get the correct size.  Make sure where to leave under & over.  Remove from steel is better than weld.
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