Abstract
Laser surface hardening is becoming one of the most successful heat treatment processes for improving wear and fatigue properties of steel parts. In this process, the heating system parameters and the material properties have important effects on the achieved hardened surface characteristics. The control of these variables using predictive modeling strategies leads to the desired surface properties without following the fastidious trial and error method. However, when the dimensions of the surface to be treated are larger than the cross section of the laser beam, various laser scanning patterns can be used. Due to their effects on the hardened surface properties, the attributes of the selected scanning patterns become significant variables in the process. This paper presents numerical and experimental investigations of four scanning patterns for laser surface hardening of AISI 4340 steel. The investigations are based on exhaustive modelling and simulation efforts carried out using a 3D finite element thermal analysis and structured experimental study according to Taguchi method. The temperature distribution and the hardness profile attributes are used to evaluate the effects of heating parameters and patterns design parameters on the hardened surface characteristics. This is very useful for integrating the scanning patterns’ features in an efficient predictive modeling approach. A structured experimental design combined to improved statistical analysis tools is used to assess the 3D model performance. The experiments are performed on a 3 kW Nd:Yag laser system. The modeling results exhibit a great agreement between the predicted and measured values for the hardened surface characteristics. The model evaluation reveals also its ability to provide not only accurate and robust predictions of the temperature distribution and the hardness profile as well an in-depth analysis of the effects of the process parameters.
Highlights
Laser surface transformation hardening (LSTH) is a heat treatment process applied to mechanical part surfaces in order to reach specific mechanical properties needed to achieve specific tasks [1]
The investigations are based on exhaustive modelling and simulation efforts carried out using a 3D finite element thermal analysis and structured experimental study according to Taguchi method
The temperature distribution and the hardness profile attributes are used to evaluate the effects of heating parameters and patterns design parameters on the hardened surface characteristics
Summary
Laser surface transformation hardening (LSTH) is a heat treatment process applied to mechanical part surfaces in order to reach specific mechanical properties needed to achieve specific tasks [1]. In the overlapped area located in the middle of two overlapped laser tracks, an over-tempered zone with a lower hardness and a tempered zone with hardness that may not reach the minimum hardness requirements are observed To overcome this problem, is important to investigate other economical and efficient strategies than the traditional multi linear tracks processing approach [3] [4]. Farrahi et al and Zhou are the more recent researchers who have worked on complex patterns as alternative to multi-track approach for laser surface transformation hardening [3] [4] [5] [6] [7] They focused on analytical modeling of laser surface hardening according to various scanning patterns and showed that the maximum temperature reached using rotating patterns was lower than that achieved using zigzag patterns. The performance of the 3D FEM model is assessed using structured experimental data produced using a 3 kW Nd:Yag laser system
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