Parametric Study and Optimization of Pulsed Laser Thermal Micro-Forming of Thin Sheets

1. Introduction

Laser thermal micro-forming is a non-contact technique to deform a metal sheet at micro-scale using the controlled distribution of thermal stresses induced by a defocused laser beam. A precise deformation or adjustment of thin sheet metal components by continuous and pulsed laser irradiations has potential applications in micro-manufacturing, micro-machines and devices, actuators, hard disks, microelectronics components and others. Miniaturization, geometric complexity and dimensional accuracy required for fabrication of micro devices placed a huge challenge for assembly and adjustment works. The conventional mechanical methods for precision forming and adjustment are limited in giving the desired accuracy due to the spring-back and hard-tooling requirements. Moreover, fabrication of micro-parts or devices is highly sensitive to mechanical forces and particularly to the impact loads. Laser thermal micro-forming is advantageous compared to mechanical one with the limitation thermal effects for the heat sensitive materials. Therefore thermal-structural analysis in laser thermal micro-forming, parametric study and optimization of process parameters for fabrication and adjustments works is essential for its effective applications. The research work on laser thermal micro-forming or micro-adjustments carried out in the past are discussed below.

Numerical simulations of pulsed laser bending and forming thin sheet metals were carried by different researchers considering single and multiple laser pulses under different processing conditions. Qi et al. (2010) carried out experimental investigations and finite element analysis to study the effects of parameters on the laser adjustment of a rod. Laser thermal adjustments of actuators made of stainless steel and aluminum alloy were studied by investigators (Shen & Yao, 2011; Shen et al., 2012; Shen at al., 2015). Actuators with different cut-out geometries was investigated by Shen et al. 2012 considering the effects of different process parameters, and it was concluded that the effects of cut-out geometries must be considered in optimizing the process parameters. Experimental study on laser thermal adjustment of sheet metal micro-parts was carried out by Griffith et al. (2014) using pulsed modes of laser irradiations with different process parameters. It was observed that ablation of the laser irradiated sheet surface for short duration pulse was less compared to the long duration pulse heating. It was also found that type and amount of deformation was significantly influenced by both sample geometry and material properties. Folkersma et al. (2016) proposed an algorithm for alignment of micro tube through laser micro forming using statistical analysis of the previous deformation data. The proposed algorithm was validated by micro tube laser bending experiments and found to predict alignment with good accuracy. Laser forming of shaped surfaces were investigated using finite element analysis experiments and other methods by different researchers (Jovic et al., 2017; Maji et al., 2018). Deformation of the samples with the different process parameters was studied and the most significant variables were identified to affect bending and thickening in laser forming of shaped surfaces. The deformation mechanism and process parameters of thermal forming mechanism are discussed as the following.