PM Calculations

How to Calculate Powder Fill, Compaction Tonnage, and Sinter Shrinkage

Work through the five core PM formulas with real units and numbers: fill weight, compaction tonnage, green density, shrinkage allowance, and yield.

Start with fill weight, because every downstream number depends on it. Fill weight = finished part mass / (1 - total loss fraction), then divided by nothing else since apparent density sets fill depth. For a 24.0 g finished FC-0208 part with 2.5% combined machining and sinter loss, you need 24.0 / 0.975 = 24.6 g of green mass. Fill depth = green mass / (apparent density x die cavity area). At 3.0 g/cm3 apparent density and a 4.90 cm2 cavity, depth = 24.6 / (3.0 x 4.90) = 1.67 cm. The Powder Fill Weight calculator handles the loss stack so you do not compound rounding across five steps.

Compaction tonnage is projected area times required pressure, unit-converted carefully. Iron powder for structural parts compacts at 400 to 700 MPa; pick 550 MPa for a target green density near 6.9 g/cm3. Tonnage (metric) = pressure (MPa) x projected area (mm2) / 9810. A part with 490 mm2 projected area needs 550 x 490 / 9810 = 27.5 tonnes. Add 10 to 15% for ejection and press deflection, so specify a 32-tonne press minimum. Run this through Compaction Tonnage before you commit tooling, because underspecifying press capacity by even 5 tonnes forces you to drop density.

Green density ties pressure to strength and dimensional control. Green density = green mass / (compacted volume). Measure volume from part height after compaction times cross-section: a 24.6 g slug pressed to 3.56 cm3 gives 6.91 g/cm3, or about 88% of iron's 7.87 g/cm3 pore-free density. Every 0.1 g/cm3 of green density costs roughly 40 to 60 MPa more pressure in the 6.6 to 7.1 g/cm3 band, and the curve flattens hard above 7.1. Use Green Density to back-calculate the pressure you actually need instead of over-pressing and cracking tools.

Shrinkage allowance controls whether the sintered part hits print. Linear shrinkage = (green dimension - sintered dimension) / green dimension. Iron-copper mixes with 2% Cu often grow 0.1 to 0.3%, while high-copper or bronze systems shrink 0.5 to 2.0%. To hit a 25.00 mm sintered bore with 0.8% shrinkage, size the green bore at 25.00 / (1 - 0.008) = 25.20 mm. The die must be cut to green plus spring-back. Feed your alloy's measured shrinkage factor into Shrinkage Allowance rather than a handbook nominal, because press density shifts shrinkage by 0.1 to 0.2 points.

Powder loss rate is a mass balance you must run per lot, not per year. Loss fraction = (powder issued - good part mass shipped) / powder issued. A cell issuing 1,000 kg that ships 1,000 good parts at 24.0 g each accounts for 24.0 kg as product; if 6.0 kg went to setup scrap, spillage, and rejects, loss = 6.0 / 1000 = 0.6% just in handling, separate from the sinter burn-off of lubricant at 0.5 to 0.9%. Powder Loss Rate separates recoverable spill from unrecoverable oxidized fines so you charge fill weight correctly.

Sinter furnace capacity determines throughput and feeds every cost model downstream. Capacity (parts/hr) = belt width x tray packing density x belt speed / part footprint, bounded by the hot-zone residence time your alloy needs. FC-0208 typically wants 20 to 30 minutes at 1120 C. A 610 mm belt running 150 mm/min through a 3.0 m hot zone gives 20 minutes residence; at 8 parts across and 40 mm pitch that is roughly 1,200 parts/hr. Sinter Furnace Capacity checks residence against speed so you do not starve the sinter to chase output.

Part yield closes the loop from powder to shippable pieces. Yield = good parts out / (green parts pressed). If you press 1,000 greens, lose 12 to cracks and edge chips before sinter, and reject 18 at final gauging, yield = 970 / 1000 = 97.0%. World-class structural PM runs 97 to 99%; anything under 95% means tooling wear or a density window that is too tight. Part Yield lets you translate a scrap count straight into the extra fill weight and press strokes you must plan, which is exactly the input the cost estimate needs.

Published 2026-07-01.