Laser Peening without Coating (LPwC) CAM Prepress Guide

1. Principles of Laser Peening without Coating (LPwC)

Laser Peening without Coating (LPwC) is an advanced surface enhancement technology developed for nuclear power plant reactor vessel bottom head J-groove welds, steam turbine blade attachments, and aerospace turbine discs. Unlike conventional laser shock peening which requires black protective tape or paint, LPwC introduces high-irradiance pulses ($I_0 = 2 - 8\,\text{GW/cm}^2$) directly through a laminar water confinement curtain onto the bare substrate, inducing deep compressive residual stresses ($> 1.5\,\text{mm}$) that prevent Stress Corrosion Cracking (SCC) and fatigue failure.

2. Raster Toolpath Strategies & Coverage Saturation

In CAM vector generation for multi-axis robotic LPwC:

• Spiral & Serpentine Raster Grids: Apply continuous spiral toolpaths to prevent localized thermal accumulation. Maintain uniform pitch $P = d_{\text{spot}} \times (1 - O_v)$.
• Water Nozzle Co-axial Alignment: Robotic toolpaths must maintain a continuous $90^\circ \pm 5^\circ$ surface-normal trajectory to ensure the water confinement film remains smooth and free of turbulence bubbles.
• Edge Feathering: Progressively reduce pulse energy or increase stepover pitch at boundary transitions to avoid sharp residual stress gradient discontinuities.