Laser welding is applied to joining blank sheets for car body parts in automotive products. With this technology, the formability of the laser welded joint is important because laser welding produces very hard and brittle weld beads on steel sheets which have high formability.In this research, several kinds of ultra-low carbon and low carbon steel sheets (thickness: 0.70-0.8mm, tensile strength: 290-445MPa) used in car body parts were butt-welded with a CO2 laser under various welding conditions to change the weld metal chemistry and bead shape. After welding, the weld bead width and weld metal hardness were measured. The strength and formability of the welded joint were estimated by the tensile test and Erichsen test.The higher tensile strength steel gave a harder weld metal because of higher contents of alloying elements. The hardness of the weld metal hardly affected the tensile property of the welded joint. Welded joints with harder weld metal, however, showed lower Erichsen values. This problem should be improved by feeding a suitable filler wire into the molten metal.Weld bead width also affected the formability of welded joints. Welded joints with wide beads showed low Erichsen values. Thus, the formability of laser welded joints was strongly dependent on weld bead properties such as hardness and bead width.
Finishing process in foundry industries is difficult to be automated, thus, it is usually done manually with a grinder or hammer. CO2 laser beam cutting and heat treatment seem useful as finishing processes and are expected to reduce the need of physical labor in the industry. In consideration of applying CO2 laser beam cutting and heat treatment to deburring of spheroidal graphite cast iron, fundamental experiments have been done in the present paper. Removing characteristics of fins and thickness of genertated heat affected zone are obtained for various operation conditions. Heat affected zone is always generated; the thickness is dependent upon the operation conditions. It can be reduced to 20 μ m under the conditions of 200 W, 25 mm/min and 490 kPa of O2 assist gas. Furthermore, the heat affected zone is heat treated with CO2 laser beam. The hardness of MHV 380–420 is obtained under the conditions of 900 Wand 500 mm/min. This heat treated zone can be smoothed more easily than the original zone; these processes are applicable to the deburring of spheroidal graphite cast iron.
