Thermal Spray & Cold Spray Masking Vector DXF CAM Prepress Guide

Thermal Spraying (HVOF, Plasma, Arc) and Supersonic Cold Spray Additive Manufacturing (CSAM) are high-performance surface engineering and solid-state 3D repair processes used on aerospace turbine casings, landing gear hydraulic actuators, oil & gas drill collars, and defense electronics. This guide covers shadow mask edge chamfer geometry, robot scan raster stepover, and production DXF CAM toolpath generation.

Supersonic Deposition Physics & Shadow Mask Geometry

In Cold Spray Additive Manufacturing (CSAM), solid metallic powder particles ($15 - 45\,\mu ext{m}$) are accelerated through a converging-diverging de Laval nozzle to supersonic velocities ($600 - 1,100 ext{ m/s}$) using heated nitrogen or helium carrier gas. Upon impact with the substrate, severe plastic shear deformation breaks surface oxide films, creating dense, metallurgical solid-state bonds with zero melting and negligible residual thermal stress.

To restrict coating buildup strictly to repair zones while protecting precision bearing journals and machined threads, reusable metallic shadow masks are positioned over the component:

• Mask Edge Chamfer Angle ($ heta_{ ext{mask}} = 20^\circ - 30^\circ$): Straight 90° mask apertures cause particle stagnation and severe localized wedge buildup that tears the coating edge upon mask removal. A $20^\circ - 30^\circ$ outward relief chamfer ensures clean coating boundary delineation.
• Standoff Air Gap ($h_{ ext{gap}} = 0.10 - 0.25 ext{ mm}$): A microscopic clearance gap between the shadow mask underside and the substrate prevents micro-fretting and eliminates coating bridging across the mask boundary.
• Robotic Overtravel Lead-In Vectors: Spray plume deposition follows a Gaussian bell-curve distribution. Robotic CAM toolpaths must extend raster scans $1.5 imes ext{spot diameter}$ beyond mask edges before reversing direction.

Engineering Standards & Process Parameter Reference

CAD/CAM Shadow Mask & Robot Vector Toolpath Rules

• Hardened Tool Steel Mask Inserts: For high-volume CSAM or HVOF production lines, fabricate shadow masks from hardened D2 tool steel (58–62 HRC) or hard-anodized 7075 aluminum cut via CNC waterjet or 5-axis wire EDM.
• Continuous Serpentine Raster Infill Vectors: Generate robotic spray toolpaths using continuous serpentine raster infill with smooth G2 corner turnaround loops outside the mask boundary to maintain constant gun velocity across the target area.
• Stepover Pitch Calibration (50%–65% Overlap): Set raster lane spacing to $P_{\text{step}} = 0.40 - 0.50 \times D_{\text{spot}}$ to overlap adjacent Gaussian deposition tracks and achieve $\pm 5\,\mu\text{m}$ overall coating thickness uniformity.
• Multi-Directional Cross-Hatch Stacking: Rotate the robot raster scan vector angle by 90° between consecutive spray passes (Pass 1: Horizontal 0°, Pass 2: Vertical 90°) to eliminate directional grain anisotropy and maximize coating shear bond strength.