Manufacturing · 7 minute read
Metal FFF sintering shrinkage: calculate the correct green-part scale
Bound-metal filament parts are printed oversize because debinding and sintering reduce their dimensions. The useful calculation is the inverse of the retained fraction—not simply 100% plus the expected shrinkage.
Use the inverse shrinkage formula
If linear shrinkage is 16%, the sintered part retains 84% of its green dimension. The required scale factor is therefore 1 ÷ 0.84 = 1.190476, or approximately 119.05%.
Scaling to 116% is not enough: 116% multiplied by the retained 84% produces only 97.44% of the intended final dimension. Inverse scaling is what returns the nominal target after shrinkage.
Calculate the green dimension from the desired final part
Required green dimension equals desired sintered dimension ÷ (1 − shrinkage fraction). A final 100 mm feature at 16% shrinkage therefore needs a nominal green dimension of about 119.05 mm.
Keep adequate calculation precision, but do not mistake a precise nominal value for a guaranteed tolerance. Printing, debinding, furnace loading, gravity and geometry can all introduce distortion.
Keep X/Y and Z compensation separate
Supplier workflows can specify different example compensation in the build plane and the vertical axis. Averaging those values into one percentage can make every axis wrong in a different direction.
For example, Forward AM’s current general guide reports averages of 16.6% shrinkage in X/Y and 19.3% in Z for its documented process, rounded to about 120% and 124% scale. These are workflow values—not universal constants. Use the current material and processing-partner guidance as a starting point, then maintain separate measured factors for X/Y and Z.
Measure coupons from the real process
Measured linear shrinkage equals 1 − sintered dimension ÷ green dimension. Record the printer, orientation, material batch, debinding route, furnace cycle and measurement method with each coupon so the result is reusable.
Repeat measurements across representative batches and geometries before applying a factor to valuable parts. Nominal scale compensates for average contraction; it does not model sag, warping, support interaction or local feature behaviour.