This research was aimed at the development of production methods and tools needed to achieve a high degree of reliability and integrity of laser cladded components manufactured at high production rate. These targets can be realized by understanding the laser/materials interactions during laser cladding. In order to accomplish these targets the correlations between process conditions, clad geometry, thermal distribution and residual stress were investigated through extensive experimental and numerical researches. Several approaches and steps were taken to identify the optimal process conditions to produce satisfactory clad layers with desired hardness and low residual stresses to avoid defects and cracking. Laser cladding experiments were designed to investigate the relations between processing parameters (laser power, cladding speed and powder feeding rate) and the resulting clad geometry (clad height/width) and dilution. The relations between the processing parameters, the resulting clad geometry and dilution were analysed using response surface methods (RSM), data split and analysis of variance (ANOVA) methods. It is worth mentioning that also with the aid of an optical spectrometer the minimum effective energy can be identified. The capability of monitoring and controlling the laser cladding process with an optical emission spectrometer was investigated. Based on understanding of the interactions between laser beam, powder stream and substrate, a 2D numerical model of laser cladding was developed to simulate the clad formation and the heat transfer during laser cladding. The geometries, melt depth and depth of the heat affected zone (HAZ) of a single clad track and overlapped clad layer were computed together with their temperature distributions in COMSOL. An analytical solution was developed to calculate the residual stresses using the temperature data simulated from the developed 2D model. The relations between the cooling rates, thermal gradients, maximum residual stresses and absorbed energy were investigated and the results are discussed. During this research, many typical defects in clads and their causes were identified. Experimental solutions were found to avoid such defects.
|Qualification||Doctor of Philosophy|
|Award date||30 Oct 2015|
|Place of Publication||Enschede|
|Publication status||Published - 30 Oct 2015|