DED Arc & Plasma Hardfacing Vector CAM Prepress Guide: Toolpaths, Bead Overlap & Dilution Control

Master the engineering principles of plasma transferred arc (PTA) and wire arc hardfacing overlays: optimize bead overlap stepover, control dilution, and generate flawless robotic CAM vector toolpaths.

1. Hardfacing Overlay Physics & Toolpath Strategy

Direct Energy Deposition (DED) Arc and Plasma Transferred Arc (PTA) hardfacing are the industry-standard processes for protecting mining equipment, dredging cutters, continuous caster rolls, extrusion screws, and valve trim from severe abrasion, impact, and high-temperature corrosion. Unlike standard welding, hardfacing prioritizes controlled dilution with the base metal and uniform deposit thickness.

When creating CNC robotic or gantry CAM vector toolpaths for hardfacing, three critical parameters must be synchronized:

1. Linear Heat Input ($HI$): HI = η · (V · I · 60) / (v · 1000) in kJ/mm. Excessive heat input increases base metal dilution, washing out valuable tungsten carbide (WC) or chromium carbide ($M_{7}C_{3}$) precipitates into the melt pool.
2. Stepover Pitch ($p$): p = W × (1 - Overlap%/100). An overlap of 45%–55% ensures planar surface profile. Insufficient overlap leaves valleys that accelerate erosive channeling, while excessive overlap causes steep sidewall humping.
3. Dilution Ratio ($D\%$): D% = A_sub / (A_sub + A_clad) × 100%. For PTA cladding, dilution is kept under 5%–12%, whereas for FCAW/GMAW it ranges between 15%–25%.

2. Process Comparison Matrix

3. CAM Vector Toolpath Optimization for Hardfacing

To eliminate thermal cracking and arc strike defects on heavy industrial components, vector CAM toolpaths must follow strict geometric rules:

• Continuous Serpentine Rasters: Avoid start-stop cycles. Every arc start introduces porosity, and every crater stop creates a stress riser prone to cross-checking cracks. Utilize tangent lead-in/lead-out loops with continuous torch motion.
• Oscillation Weave Vectors: Programmable linear or trapezoidal weave vectors ($f = 0.5 - 2.5 ext{ Hz}$) provide wider single-pass coverage ($W = 15 - 35 ext{ mm}$), lowering cycle time and reducing inter-pass boundary defects.
• Sub-Micron Vector Formatting: Robotic welding controllers require smooth, tangentially connected arcs (G02/G03) rather than segmented chord approximations to maintain constant torch velocity and uniform bead profile.