Under Streamline-3D’s short demo of its shot peen finish on MJF parts, a viewer asked the obvious follow-up: “What plastic media are you using? Size and type?” Nobody answered. It’s a good question, because MJF shot peening only works if the media is matched to the part.
What media does MJF shot peening use?
Plastic beads, fired with compressed air. DyeMansion, which makes the Powershot S that 3D Print UK uses for its shot peen finish, calls its process PolyShot Surfacing. Its datasheet describes beads accelerated by compressed air that even out the peaks and lows of the surface, and calls the process non-abrasive for hard plastics like PA12 and PA11. It doesn’t give a bead size.
3D Print UK, which runs a Powershot S, does. It says its shot peen media has a 0.5 mm diameter and is fired at a much higher pressure than the media in its cleaning blaster.
How is that different from bead blasting?
Bead blasting cleans. Peening reshapes the skin. 3D Print UK says the plastic media melts the surface for a split second on impact, which turns that spot glossy, and the effect builds up over a 10 minute cycle as parts tumble in a barrel. DyeMansion describes the result as semi-gloss, with better scratch resistance, and as a base for dyeing.
The cycle is short. DyeMansion lists 10 to 15 minutes as typical, with capacity for up to one full HP Jet Fusion 4200 or 5200 build job per run.
What can it damage?
Small and thin features. 3D Print UK lists the risks plainly:
Holes, grooves or cavities about 0.5 mm wide can trap the media. It suggests making engravings 0.3 mm deep, or wider than 0.7 mm, so beads don’t catch. Small pins and protruding features can break, and a fillet at the base helps without guaranteeing anything. Trailing edges under 1 mm are likely to be damaged, and parts under 10 mm can get lost in the process.
How should you quote it?
Run the part’s smallest gap through the 0.5 mm test before you offer the finish. If an engraving or slot sits near that width, either change it to 0.3 mm deep or wider than 0.7 mm, or quote a plain bead blast and dye instead.
Related on the Solvi blog: Should You Dye MJF Parts Black or Vapor Smooth Them?; SLS Bead Blasting: What Causes Residue on Parts?; Depowdering SLS and MJF Parts: When Is Automation Worth It?.
Sources: YouTube: MJF finishing, shot peen (Streamline-3D), viewer question; DyeMansion Powershot S datasheet (PDF); 3D Print UK: shot peened 3D printed parts.