Powder refresh rate: Powder refresh rate is the share of fresh powder mixed with recycled powder for each powder bed build, set to keep the mix within its quality limits.
In polymer powder bed processes most of the powder in a build is never fused, but it spends hours close to its melting point and ages. Reused too often, it gives rough, orange-peel surfaces and weaker parts. Shops therefore mix each build from recovered powder topped up with virgin powder at a set ratio. The right ratio depends on the material, the machine and the process; the maker’s guidance is the starting point, and MJF is designed to run at lower refresh ratios than most SLS processes.
What it means for the price
Refresh means a build consumes more powder than its parts weigh. The fresh powder a build needs is driven by the whole bed, not by the parts in it, so the true powder cost per part is higher than part mass times price per kilogram. A shop that prices only the part’s own mass undercharges, most of all on sparse builds.
Example: a build fuses 1 kg of parts but needs 2.5 kg of fresh powder to refresh the bed. Pricing powder at 1 kg understates the material cost by 60%. The figures are an example.
Common confusions
The refresh rate is not a waste rate: the recovered powder is reused, and only the share replaced is consumed. It interacts with packing density and so with build share. Read how SLS pricing and nesting work.
Go deeper: SLS pricing: build share, packing density, refresh and cool-down