The Weldability of Stainless Steel with Solid State Laser
Examensarbete för masterexamen
Materials engineering (MPAEM), MSc
Laser welding can offer many advantages over conventional welding when used in the right applications. Some of these advantages include smaller heat affected zone (HAZ) and lower thermal stresses, narrow weld seams with smooth surfaces reducing or even eliminating additional steps of refining work, high strength coupled with low weld volume, high welding speeds relative to conventional welding and easy integration potential to name a few. Laser welding even with its obvious benefits faces a lot of skepticism among manufacturers; especially sub suppliers who could benefit the most from committing to laser welding. Conventional welding have established and proven guidelines and standards within the manufacturing industry, techniques quantifying for example the throat measure. Laser welding lacks universal measures or guidelines aside from data and documentation provided by the producer of laser welding systems. The weldability of the stainless steel EN 1.4301 (AISI 304) sheets of 1.5 mm thickness has been investigated. The goal has been to achieve a method that can be applied also in future investigations of other alloys. Iteration of welding parameters has been made in order to find optimized welding parameters. Butt joint welded test specimens with geometrical tolerance deviations were manufactured to investigate the process sensitivity against tolerance deviation. To characterize the influence on the mechanical properties a series of ASTM standardized mechanical tests were performed. Tests include tensile testing, bend testing and hardness testing on metallographically prepared cross-sections. Computer simulations of the heataffected zone were made using the numerical computing environment MATLAB. Results show a local increase in peak hardness of approximately 28-43%. Bend testing results show that even with this local increase of the peak hardness, ductility is not critically affected. Bend testing was performed without fracture or presence of surface irregularities but for one sheet. In this case the specimens had the most extreme tolerance deviation in the specimen series, giving rise to incomplete welding and severe stress concentration. Tensile tests results show no significant effect on tensile strength and elongation at break for specimens with tolerance deviations up to 150 μm. Larger tolerance deviations showed an abrupt drop in both tensile strength and elongation at break.
Materialvetenskap , Produktion , Mekanisk tillverkningsteknik , Övrig bearbetning/sammanfogning , Materials Science , Production , Mechanical manufacturing engineering , Other processing/assembly