Dissimilar joining of aluminum and steel is one of the fundamental techniques for achieving weight reduction in the automotive industry. Self-piercing rivets have been widely adopted for the aluminum-steel lap joint because of its simplicity and high joining strength. In this study, the joining quality of the aluminum-steel joint produced by self-piercing rivets is investigated depending on the strength and thickness of the aluminum sheet. Four different tensile strengths (228, 305, 320, and 326 MPa) of aluminum are considered in this study, which corresponds to Al5052-H32, Al5754-H18, Al5083-H32 and Al6061-T6. For the thickness variation test, Al5052-H32 sheets with a thickness of 1.2, 1.5, 2.0, 2.5 mm are used. The SPR joint quality was quantified with cross-sectional visual analysis and tensile lap shear test. In aluminum(top)-steel (bottom) SPR joint, it was observed that the joint load increased with increasing aluminum strength up to 320 MPa. Nevertheless, the thickness of top aluminum was found to not affect the joint strength between the thickness of 1.5 ~ 2.5 mm. In steel(top)-aluminum(bottom) SPR joint, it was found that joint strength did not change with aluminum strength but increased with increasing aluminum thickness.

The automotive vehicle is made through the following processes such as press shop, welding shop, paint shop, and general assembly. Among them, the most important process to determine the quality of the car body is the welding process. Generally, more than 400 pressed panels are welded to make BIW (Body In White) by using the RSW (Resistance Spot Welding) and GMAW (Gas Metal Arc Welding). Recently, as the needs of light-weight material due to the CO 2 emission issue and fuel efficiency, new joining technologies for aluminum, CFRP (Carbon Fiber Reinforced Plastic) and etc. are needed. Aluminum parts are assembled by the spot welding, clinching, and SPR (Self Piercing Rivet) and friction stir welding process. Structural adhesive boning is another main joining method for light-weight materials. For example, one piece aluminum shock absorber housing part is made by die casting process and is assembled with conventional steel part by SPR and adhesive bond. Another way to reduce the amount of the car body weight is to use AHSS (Advanced High Strength Steel) panel including hot stamping boron alloyed steel. As the new materials are introduced to car body joining, productivity and quality have become more critical. Productivity improvement technology and adaptive welding control are essential technology for the future manufacturing environment.

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Additive manufacturing of novel metals has received much attention as an alternative to traditional subtractive manufacturing because of its high material efficiency (cost reduction in terms of material efficiency or the Buy-to-Fly ratio), shorter lead time and higher design flexibility (new design possibilities). When compared with the laser and powder additive manufacturing, the arc and wire additive manufacturing is known to have higher material efficiency, higher deposition rate, and cheaper investment and maintenance. Therefore, in this work, we used cold metal transfer (CMT) gas metal arc welding (GMAW) for arc and wire additive manufacturing of STS 316L and perform a parametric study. It was found that the cooling time for the interpass temperature to cool down to 350℃ is dependent on the number of the deposition layer and the travel speed. We also investigate the effect of the travel speed, the travel direction, the contact tip to work distance (CTWD) and number of the deposition layer on the characteristics of the deposited sample. The spatial inconsistencies of the tensile strength and the hardness are observed to increase as the travel speed is increased. Finally, we find that anisotropic metallurgical properties are observed throughout the deposited STS 316L.