Jet Field Calculation Model for Laser-Assisted Atmospheric Plasma Arc Cladding

Literature Overview

Laser-assisted plasma arc cladding (LA-PAC) is an advanced hybrid cladding process that combines the high energy density and precise thermal control of laser cladding with the high deposition rate and deep penetration of atmospheric plasma arc (PTA) cladding. The interaction between the laser beam and the plasma arc creates a complex jet field — a coupled gas flow, thermal field, and electromagnetic field — that governs the melt pool geometry, dilution rate, and final cladding quality. This study presents a computational model for predicting the jet field in LA-PAC, providing engineers with a theoretical framework for process optimization and scale-up.

Process Configuration and Physical Phenomena

The LA-PAC process configuration involves a plasma arc torch and a laser head arranged in a coaxial or near-coaxial geometry. The plasma arc is generated by an atmospheric plasma power source (typically 100–300 A, 30–40 V), while the laser is a fiber laser (typically 1–6 kW, 1064 nm wavelength). Powder feedstock is injected through a nozzle positioned between or adjacent to the arc and laser beam.

The jet field in LA-PAC encompasses several interacting phenomena:

1. Plasma jet: The high-velocity plasma gas (100–300 m/s) exiting the torch nozzle creates a directed gas stream that entrains powder particles and shields the melt pool.
2. Laser-induced plume: The laser beam interacts with the atmosphere, creating a plasma plume of ionized gas and vaporized material that can reflect and scatter the laser beam.
3. Powder stream: The carrier gas (typically argon) carrying powder particles (typically 20–45 μm) forms a divergent jet that intersects the melt pool.
4. Atmospheric convection: Natural and forced convection in the surrounding atmosphere affects the thermal field and gas flow pattern.

The interaction between these jets creates a complex three-dimensional flow field that determines the powder deposition efficiency, melt pool geometry, and dilution rate.

Computational Model Formulation

The jet field model is based on a coupled solution of the Navier-Stokes equations for gas flow, the energy equation for thermal transport, and the species transport equation for powder concentration. The model assumes a steady-state, three-dimensional, compressible flow with the following governing equations:

The model domain is a rectangular volume encompassing the torch, laser head, powder nozzle, and substrate surface. Boundary conditions include:

• Inlet (plasma torch): Fixed velocity (150 m/s), temperature (15,000 K), and composition (argon plasma).
• Inlet (laser): Fixed power density (10–50 MW/m²) at the focal plane.
• Inlet (powder): Fixed carrier gas velocity (5–15 m/s) and powder mass flow rate (50–200 g/min).
• Substrate surface: Fixed temperature (initially 25 °C, rising to melting temperature during welding) and no-slip condition.
• Outlet (top and sides): Pressure outlet with backflow suppression.

Key Results and Process Parameter Influence

The computational model predicts the velocity field, temperature field, and powder concentration field throughout the cladding process. The following key results were obtained:

Velocity Field

The plasma jet creates a high-velocity core (100–200 m/s) that decays rapidly with distance from the torch axis. The laser-induced plume creates a secondary jet directed away from the focal point, with velocities of 20–50 m/s. The powder stream intersects the plasma jet at an angle of 30–45°, creating a complex recirculation zone above the melt pool.

Temperature Field

The temperature field shows a steep gradient near the substrate surface, with the melt pool reaching temperatures of 1800–2200 °C. The laser contributes a concentrated heat input at the focal point, while the plasma arc provides a broader heat distribution. The combined heat input creates a melt pool that is deeper and narrower than plasma arc cladding alone, reducing dilution.