Plasma Spray
Is plasma spray the same as CNC plasma cutting?
No. Plasma cutting is a metal-removal process that uses an ionized gas jet to sever material, while plasma spray is a deposition process that applies coating material onto a prepared surface.
Why is plasma spray called a cold process in some references?
The feedstock is heated to a molten or semi-molten state, but the substrate can remain comparatively cool, reducing metallurgical change and distortion compared with bulk heating processes.
What controls coating quality most on the shop floor?
Surface preparation, plasma gas selection, particle temperature and velocity, spray angle, standoff distance, and post-spray finishing control density, adhesion, and final dimensions.
Plasma spray is a thermal spray coating process that heats powder feedstock in a high-temperature plasma jet, accelerates the molten or semi-molten particles toward a substrate, and builds a protective surface layer through rapid solidification on impact. It deposits wear-resistant, corrosion-resistant, thermal-barrier, or dimensionally restorative coatings onto metals, alloys, carbides, and ceramics.
On the shop floor, plasma spray is a post-machining surface-engineering step rather than a metal-removal operation. A part is rough-machined to near-final geometry, cleaned, masked, and grit-blasted to create anchor points for the sprayed splats. The coating is then applied with a plasma torch, using argon, nitrogen, hydrogen, or helium as plasma gas. Because the substrate stays relatively cool, distortion risk is lower than with bulk heating. After spraying, the part is usually finish-ground or skim-cut to bring bores, shafts, and sealing diameters back into tolerance. Coating thickness must be treated as a controlled stock allowance, since plasma spray layers add material and are not dimensionally neutral. Complex geometries often require robotic or fixture-controlled spray paths to maintain uniform thickness across edges, radii, and thin-wall sections. This approach lets a shop keep the base component machinable while adding a specialized functional skin only where it is needed.
Poor surface preparation: Without proper cleaning and roughening, sprayed splats fail to anchor, leading to weak bond strength, edge lift, and delamination under thermal cycling or abrasion.
Overheating or poor parameter control: Incorrect standoff distance, gas ratio, or traverse speed can oxidize or over-melt the coating, increase porosity, weaken wear/corrosion performance, and distort heat-sensitive parts.
Ignoring finish stock and thickness variation: Leaving too little allowance for post-spray grinding makes parts oversize or out-of-round, especially on bores, shafts, and sealing diameters where uniform thickness is critical.