MANUFACTURING – INJECTION MOULDING & PLATIC CALCULATOR
Shrinkage Mold Dimension
A precise tool.
What is the Shrinkage Mold Dimension & How does it work?
In injection moulding, the part that exits the mould is slightly larger than the final cooled part because the polymer contracts as it solidifies. This phenomenon is called linear shrinkage and is expressed as a percentage of the original dimension. Accurately predicting the mould cavity size requires adding the expected shrinkage to each critical dimension of the part. The calculation is linear for most thermoplastics, allowing designers to simply scale the part dimensions by a factor derived from the shrinkage percentage. The resulting mould dimensions ensure that, after cooling, the part will meet the target size without excessive post‑processing. Using the formula below, engineers can quickly generate the required cavity dimensions for any rectangular part.
L_{mold}=L_{part}\times\left(1+\frac{S}{100}\right)
S = linear shrinkage %
Parameters
Result
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Frequently Asked Questions
What is linear shrinkage in injection molding?
Linear shrinkage is the reduction in size that occurs when a polymer cools and solidifies after being injected into a mold.
How do I calculate the mold cavity size for injection molding?
Add the expected linear shrinkage percentage to each critical dimension of the part to determine the mold cavity size.
What factors affect linear shrinkage in thermoplastics?
Factors such as material type, cooling rate, and mold design can influence linear shrinkage in injection molding.
Is linear shrinkage different for different types of plastics?
Yes, different thermoplastics have varying rates of linear shrinkage, so it’s important to use the specific percentage for the material being used.
How can I minimize linear shrinkage in my injection molded parts?
Minimize linear shrinkage by optimizing cooling conditions, using appropriate mold designs, and selecting materials with lower shrinkage rates.
What is the typical range for linear shrinkage percentages in thermoplastics?
Linear shrinkage percentages can vary widely depending on the material, but they typically range from 0.5% to 3% for common thermoplastics.
Can linear shrinkage be completely eliminated in injection molding?
While it’s challenging to eliminate linear shrinkage entirely, careful design and process control can significantly reduce its impact on part dimensions.
Results are for informational purposes only and do not constitute professional advice.