HVOF & Thermal Spray Masking: CAM Vector Prepress & Shadow Tolerance Guide

Learn how to engineer precision mechanical and laser-cut shadow masks for supersonic thermal spray processes (HVOF, HVAF, Plasma Spray). Master plume divergence geometry, edge feathering mitigation, and CAM DXF mask offsets.

1. Supersonic Thermal Spray & Masking Fundamentals

High-Velocity Oxy-Fuel (HVOF), High-Velocity Air-Fuel (HVAF), and Cold Spray (CSAM) propel molten or solid-state powder particles at supersonic velocities ($500 - 1200\text{ m/s}$) to create ultra-dense, wear- and corrosion-resistant coatings (e.g. WC-Co-Cr, Inconel 718, MCrAlY). When coating critical landing gears, turbine blades, or pump shafts, non-spray regions must be protected with rigid shadow masks.

2. Shadow Effect Physics & Penumbra Equations

Because the thermal spray plume diverges from the nozzle axis with a half-angle $\theta_{div}$ ($3^\circ - 8^\circ$), any standoff gap between the mask and substrate creates a tapered shadow zone (penumbra):

Mask Shadow Blur Radius:
  R_blur = d_mask * tan(theta_div)   [mm]

Where:
  d_mask    = Gap between mask underside and substrate (mm)
  theta_div = Plume divergence half-angle (deg)

3. Knife-Edge Mask Chamfer Design & Toolpath Prepress

Flat $90^\circ$ mask edges reflect supersonic shockwaves, creating severe turbulence and oversized buildup beads along the mask perimeter. Hardened steel masks (Toolox 44, AISI D2, or hardened copper) must feature a $30^\circ - 45^\circ$ knife-edge chamfer facing the spray gun.