Laser cutting of sheets for Tailored Blanks

Over the past few years there has been an enormous increase in the use of tailored blanks, especially in the automotive industry. Often the sheets for tailored blanks are shear cut, but results have been reported that the allowable sheet gap distance should not exceed 0.1 mm in order to obtain sound welds. Laser cutting the sheets may therefore be an alternative to shear cutting, if the cut kerf squareness can be kept below 0.05 mm.In a number of systematic laboratory experiments the effects of the major process parameters in laser cutting have been investigated. Each cut was quantified by the squareness, the surface roughness and the burr height. Mild steel as well as high strength steel with and with out galvanisation with thickness' of 0.7(5) and 1.25 were used.In the tests the difference in cut quality between a 5" and a 7.5" focusing lens were tested and the effect of using pulsed mode laser cutting instead of continuous wave cutting at average power settings of approximately 500, 1000, 1500 and 2000 W were analysed. Furthermore the optimum assist gas pressure and optimum cutting speeds were identified. The results showed that the highest qualities are obtained with a 7.5" focusing lens. Generally pulsed mode cutting give the best overall cut quality and result in the highest cut speeds as compared to cw mode cutting. The best cuts are obtained at an average power of 2000 W and a pulse energy of 1.42 J.Seven out of eight materials were cut with high quality with a squareness between 0.01 mm and 0.05 mm at optimum. All 1.25 mm sheets have been cut with high qualities (except galvanised mild steel) at speeds of about 8 m/min. whereas sheets of 0.7(5) mm thickness have been cut with high qualities between 12 and 17 m/min.