Shrinkage allowance for patterns

  • Thread starter Ritz_physics
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In summary, when making a pattern for a casting, the bore diameter should be increased to account for shrinkage during cooling. However, the amount of change will vary depending on the material used and may require trial and error to meet required tolerances. Overall, most metals will experience a decrease in bore diameter during the casting process.
  • #1
Ritz_physics
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While making a pattern for a casting do we increase or the bore diameter of the pattern, than actually required in the casting, taking into consideration the shrinkage allowance for metal?
 
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  • #2
It depends on the material you're using to make the casting. There's a reason why Ferrari parts are made with molds made from sand.
 
  • #3
I'll put the question in a different way. If we have a hot metal ingot with a bore, after the ingot cools down, whether the bore diameter will increase or decrease?
 
  • #4
Bore diameter will decrease.
 
  • #5
pantaz said:
Bore diameter will decrease.

So this is exactly what would happen during the cooling of a similar casting, after it has solidified?
 
  • #6
Ritz_physics said:
So this is exactly what would happen during the cooling of a similar casting, after it has solidified?

Generally speaking, yes, but...
Wikipedia said:
... Some alloys will have overall linear shrinkage of up to 2.5%, whereas other alloys may actually experience no shrinkage or a slight "positive" shrinkage or increase in size in the casting process (notably type metal and certain cast irons). ...
http://en.wikipedia.org/wiki/Pattern_(casting)#Contraction_allowances_.2F_Shrinkage_allowance
 
  • #7
Ok.. anyway for most metals (the ones that contract on cooling) the bore diameter will decrease during the shrinkage of casting, right?
 
  • #8
Ritz_physics said:
Ok.. anyway for most metals (the ones that contract on cooling) the bore diameter will decrease during the shrinkage of casting, right?

Again, yes. The amount of change will depend on many things. Getting the "as cast" dimensions to meet your required tolerances may require considerable trial & error.
 

What is shrinkage allowance for patterns?

Shrinkage allowance for patterns is the amount of material added to a pattern to account for the shrinkage that occurs during the manufacturing process. This ensures that the final product is the correct size.

Why is shrinkage allowance important?

Shrinkage allowance is important because it ensures that the final product is the correct size and meets the desired specifications. Without it, the product may end up being too small after the shrinkage occurs.

How is shrinkage allowance calculated?

Shrinkage allowance is calculated by multiplying the linear shrinkage rate by the dimensions of the pattern. The linear shrinkage rate is typically provided by the manufacturer or can be determined through testing.

What factors can affect shrinkage allowance?

The type of material, the manufacturing process, and the environment in which the product is produced can all affect the amount of shrinkage that occurs. It is important to consider these factors when determining the appropriate shrinkage allowance for a pattern.

Can shrinkage allowance be adjusted?

Yes, shrinkage allowance can be adjusted based on the specific needs and requirements of the product. However, it is important to carefully consider and test any adjustments to ensure the final product meets the desired specifications.

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