Thermal Model

predicted vs. experiment

The goal of this project area is to provide a complete physical understanding of the laser hardening process (applied to various materials) and to develop accurate predictive models that will enable optimization of the process and its industrial applications to various engineering materials to meet precise specifications. Specific objectives of the research include:

• Find operating conditions that globally optimize laser hardening processes in order to:
  • maximize laser hardening rate
  • minimize sub-surface flaws
  • maximize surface hardness and case depth
• Investigate the underlying laser hardening mechanisms for various work materials and geometries.
• Develop a predictive transient, three-dimensional thermo-kinetic-stress model for laser hardening.
• Develop guidelines to determine the best way of performing laser hardening for various materials and geometries.
• Develop an economic analysis of laser hardening against current practice

The study of laser-hardening at Purdue is based on the simultaneous experimental and numerical investigation of the process. The experiments are performed on an integrated processing cell comprising a 4 kW direct diode laser with a rectangular beam shape and an 7axis positioning system (bottom right Figure) as well as a CO₂ and a Nd:YAG laser providing circular beams.   Modeling efforts include three-dimensional heat transfer modeling, kinetic modeling of diffusion kinetics, deformation and stress modeling.   These models are coupled together to provide comprehensive hardening results including hardness profiles, deformation and resultant residual stresses. 

Research Progress:

• Successful laser hardening of 5150H, 4140 and 1045 steel alloys has been carried out with Rockwell hardness, Rc, exceeding 60.
• A fully three dimensional thermo-kinetic-model has been developed and validated (see the middle figure below), which provides the resultant microstructure and hardness distribution.
• A back-tempering model has been developed to predict microstructure change during the tempering process and integrated with the thermo-kinetic model.   The model can be used to optimize the overlapping patterns of the laser beam to achieve the most uniform hardness distribution.
• Experimental facilities have been developed for hardening various parts with complex geometry.
• Laser hardening and nitriding capabilities of Ti6Al4V have been successfully demonstrated along with the development of a predictive thermo-diffusion model. 
• A numerical model has been developed to predict resultant residual stresses and integrated with the thermo-kinetic-tempering model.

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National Science Foundation
Purdue Research Foundation
Indiana 21st Century Research and Technolog
International Truck and Engine
Rolls Royce Corp