Laser surface treatment using customised heat source profiles

The work aims to extend and improve existing conduction limited laser surface treatment techniques (laser transformation hardening and laser surface meltingrý) by applying a simple analytical model to design laser experiment using customised beat source profiles. A general methodology for optimising the laser surface treatment by customising the heat source profile was proposed. Through identifying surface property to be achieved, analysing the required microstructural changes, examining the necessary surface temperature distribution and applying a custornised heat source profile, a desired surface mechanical property can be obtained. A simple analytical model was used to design the heat source profiles and to calculate the temperature distribution within and outside the beam illumination region. The model based on the summation of a continuous series of point sources traversing on a semiinfinite workpiece. Laser surface treatment experiments were conducted using high power C02 laser on BS 080A40 carbon steel, BS 817M40 low alloy steel and BS grade 250 pearlitic grey cast iron. Customised heat source profile beams were produced using a diffractive optical element (DOE) mirror as the final turning mirror. A circular "near Gaussian", a square "top hat" and four complex beam heat source profiles, namely: "CU, "CLT' and "CIM', were used in the research. Experimental and theoretical analyses were made to compare the HAZ shape and dimension, microstructure and hardness value produced using traditional and customised heat source profiles. The results showed that the model predicted well the temperature distribution in the workpiece with satisfactory.