A viewer watching Tested’s Fuse 1 demo paused at the printer screen. It read 183 °C, plus 10 °C, for 193 °C total. They’d thought nylon prints above 230–240 °C. How could it work so much cooler? It’s a good question, because SLS print temperature means something different from a nozzle setting.
Why does an SLS printer run nylon at under 200 °C?
Because the heaters don’t melt anything. They keep the powder just below its melting point, and the laser adds the last bit of energy only where the part goes. Formlabs’ melting guide describes it this way: the printer fuses powder by heating it to “a point just below its melting temperature.” If it goes over that point, the powder melts across the bed and you get a brick.
For a sense of scale, Sinterit lists a melting point of 185 °C for its PA12 Smooth. A bed in the 180s is sitting right under that line, which is the whole idea.
So why does FDM nylon need 240 °C or more?
An extruder has to melt the filament completely and push it through a small nozzle, quickly enough to keep up with the toolhead. Prusa’s material guide lists nozzle temperatures for PA of 240–285 °C. That’s a flow problem. Powder in an SLS bed doesn’t have to flow anywhere. Its grains just need to fuse to their neighbors.
Why is the SLS print temperature margin so tight?
Because a degree or two changes the result. Formlabs’ bed temperature offset moves in 0.25 °C steps across a ±5 °C range, and its tuning plaques are printed only 1 °C apart. Too hot and you get melting or surface defects. Too cool and parts can curl, which is why Formlabs lists an improperly tuned bed temperature as one cause of curling.
What does that mean on the shop floor?
Treat the bed temperature reading as the most important number on the screen. Formlabs says the temperature is measured by the printer’s IR sensor, so a dirty sensor reads low and the machine overheats to compensate. If parts suddenly come out glossy or welded together, clean that sensor before you touch the offset.
Related on the Solvi blog: SLS Cooldown: How Hot Can You Unpack a Build?; SLS Orange Peel: Why It Happens and How to Fix It; SLS Nylon Yellowing: Why White Parts Turn Yellow.
Sources: YouTube: Formlabs Fuse 1 demo (Tested), viewer question; Formlabs: Melting (SLS); Sinterit PA12 Smooth data; Prusa filament material guide; Formlabs: Curling (SLS).