SLS bead blasting should leave parts clean, but sometimes it leaves something behind. On the Formlabs forum, an operator two weeks into using a Fuse Blast found a “tacky” white residue on parts coming out of the tumbler. It felt like a woodworker’s tack cloth, and they had to re-blast each part by hand before dyeing.
Why does SLS bead blasting leave residue on parts?
In this case, fine SLS powder and broken-down glass media had packed in between the tumbler liner and the drum, and kept leaking back onto parts. Wiping the liner didn’t help. When the operator finally removed it, the residue was “piled on thick” behind it after about two weeks of mild use.
What fixed it?
A new liner, plus a switch to Formlabs’ Polishing System and its plastic media. Months later, the operator reported no further residue. Their routine is now a standard blast cycle to knock off powder, with rinse pressure raised to 55 psi, followed by a 10 to 15 minute polish. Another user who had the same residue said it improved after lowering blast pressure to 25 psi, keeping rinse at 40 psi. They suspected glass media wearing down the lining. Both noted that support had suggested raising pressure instead, so treat pressure as something to test, not a fixed answer.
What does Formlabs specify?
- Only use 200 to 300 µm (50 to 70 mesh) glass media or Formlabs Polishing Media. Other media can damage the machine.
- Use 30 psi with glass media. Formlabs says higher pressure isn’t needed except for Nylon 12 GF, and it may damage parts.
- Use 60 psi with Polishing Media.
- Run one media type at a time, and empty the hopper before switching.
What should a bureau take from this?
Inspect parts with a clean glove before they go to dyeing or packing. Add the liner to your maintenance checks. One commenter put a replacement liner at about $350. If you run both glass and polishing media, budget for the changeover, since the machine runs one type at a time.
Related on the Solvi blog: Depowdering SLS and MJF Parts: When Is Automation Worth It?; Should You Dye MJF Parts Black or Vapor Smooth Them?; SLS Powder Cleanup: How to Keep Dust Under Control.
Sources: Formlabs forum “Blast Residue from tumbler on parts” thread; Formlabs: Cleaning printed parts with the Fuse Blast; Formlabs: Adding blasting media to the Fuse Blast; Formlabs: Switching blasting media types.