Shrinkage Compensation Calculator

Calculate mold cavity dimensions to compensate for plastic shrinkage in flow, cross-flow, and thickness directions. Assesses warpage risk and tolerance feasibility.

Inputs

Nominal length (mm)

Nominal width (mm)

Nominal height (mm)

Shrinkage, flow dir (%)

Shrinkage, cross-flow (%)

Shrinkage, thickness (%)

Part tolerance (mm)

Tab to move between fields

Results

Mold length (mm)

101.52

Mold width (mm)

50.92

Mold height (mm)25.51

Length compensation (mm)1.52

Width compensation (mm)0.92

Height compensation (mm)0.51

Volumetric shrinkage (%)5.21

Anisotropy ratio1.2

Warpage risk (1-3)2

Tolerance feasible (0/1)0

How to Use This Calculator

Enter Nominal length (mm), Nominal width (mm), and Nominal height (mm).
Set Shrinkage, flow dir (%), Shrinkage, cross-flow (%), and Shrinkage, thickness (%).
Adjust Part tolerance (mm) as needed.
Review Mold length (mm) and Mold width (mm).
Use Mold height (mm) and Length compensation (mm) to inform your decision.

How the result changes with Nominal length (mm)

Nominal length (mm)	Mold length (mm)	Mold width (mm)
1,000	1,015.23	50.92
3,500	3,553.3	50.92
6,500	6,598.99	50.92
9,000	9,137.06	50.92

What each input means

Nominal length (mm): Desired final part length (flow direction).
Nominal width (mm): Desired final part width (cross-flow direction).
Nominal height (mm): Desired final part height (thickness direction).
Shrinkage, flow dir (%): Shrinkage rate in flow direction. PE 1.5-3%, PP 1-2.5%, ABS 0.4-0.7%.
Shrinkage, cross-flow (%): Shrinkage rate perpendicular to flow. Often 10-50% higher than flow direction.
Shrinkage, thickness (%): Shrinkage rate in part thickness direction.
Part tolerance (mm): Required dimensional tolerance on the finished part.

What each result means

Mold length (mm): Required mold cavity length to achieve nominal part length.
Mold width (mm): Required mold cavity width.
Mold height (mm): Required mold cavity height (depth).
Length compensation (mm): Amount the mold is oversized in length.
Width compensation (mm): Amount the mold is oversized in width.
Height compensation (mm): Amount the mold is oversized in height.
Volumetric shrinkage (%): Total volume reduction from mold to part.
Anisotropy ratio: Cross-flow / flow shrinkage ratio. >1.3 indicates high warpage risk.
Warpage risk (1-3): 1 = low, 2 = moderate, 3 = high warpage risk.
Tolerance feasible (0/1): 1 = tolerance is achievable, 0 = shrinkage variation may exceed tolerance.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Nominal length (mm) = 100, Nominal width (mm) = 50, Nominal height (mm) = 25, Shrinkage, flow dir (%) = 1.5 = 7 input(s) provided
Calculate Mold length
Mold length = nominalLength / (1 - sFlow)
101.523 = 101.523
Calculate Mold width
Mold width = nominalWidth / (1 - sCross)
50.916 = 50.916
Calculate Mold height
Mold height = nominalHeight / (1 - sThick)
25.51 = 25.51
Calculate Length compensation
Length compensation = moldLength - nominalLength
1.523 = 1.523

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