Suppose if this is a hot plastic material. When it’s cool down shrinking can take place in two opposite direction. Is it correct to say hole size will increase in this case?
I was given shrinkage allowance for this plastic material is 0.1~0.2 inch.
While it doesn't seem intuitive, I believe that the entire part shrinks about its centroid as if it is scaled, so the hole actually gets smaller. This has been discussed quite a few times on the forum and one good example is listed in the "MORE LIKE THIS" list on the right column of this thread. This is the thread I'm referring to:
Re: Plastic Shrinkage Rate - Does the donut hole get smaller?
I believe that the entire part shrinks about its centroid as if it is scaled,
Jim Wilkinson is right, all dimensions will be smaller by default (rule of thumb), including the hole diameter.
However plastics can have anisoptropic properties (different properties for different directions), and it is also depending on the processing of the plastic; pressure, supports, cooling rate, uniform cooling and so on.
Some plastics do even have a negative coefficient of expansion for a certain direction.
Fortunately Solidworks can set diffrent shrinkage parameters for different directions.
Actually it is better to speak about "thermal expansion" than "shrinkage", because the mass does not change while the temperature changes..
Thanks for the good explanation.
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