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Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel

Published: August 13th, 2019



1Department of Health and Beauty, Shu Zen College of Medicine and Management, 2Department of Mold and Die Engineering, National Kaohsiung University of Science and Technology

Here, we present a friction stir spot welding (FSSW) protocol on dual phase 780 steel. A tool pin with high-speed rotation generates heat from friction to soften the material, and then, the pin plunges into 2 sheet joints to create the lap joint.

Friction stir spot welding (FSSW), a derivative of friction stir welding (FSW), is a solid-state welding technique that was developed in 1991. An industry application was found in the automotive industry in 2003 for the aluminum alloy that was used in the rear doors of automobiles. Friction stir spot welding is mostly used in Al alloys to create lap joints. The benefits of friction stir spot welding include a nearly 80% melting temperature that lowers the thermal deformation welds without splashing compared to resistance spot welding. Friction stir spot welding includes 3 steps: plunging, stirring, and retraction. In the present study, other materials including high strength steel are also used in the friction stir welding method to create joints. DP780, whose traditional welding process involves the use of resistance spot welding, is one of several high strength steel materials used in the automotive industry. In this paper, DP780 was used for friction stir spot welding, and its microstructure and microhardness were measured. The microstructure data showed that there was a fusion zone with fine grain and a heat effect zone with island martensite. The microhardness results indicated that the center zone exhibited a greater degree of hardness compared with the base metal. All data indicated that the friction stir spot welding used in dual phase steel 780 can create a good lap joint. In the future, friction stir spot welding can be used in high-strength steel welding applied in industrial manufacturing processes.

Friction stir welding (FSW) was first reported in 1991 at TWI, Abington, UK1. In 2003, Piccini and Svoboda determined a superior method of enhancing the advantages of FSW called friction stir spot welding (FSSW) for use in commercial automobile manufacturing processes2. The FSSW method involves creating a spot lap joint with no bulk area melting. The most important development for the use of FSSW has been in aluminum alloys as Al alloys deform in the welding process under high temperature conditions. The first successful example was in the automotive industry, where FSSW was used in manufacturing the entire rear door of ....

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1. Material preparation

NOTE: Machine the 1.6 mm thick DP780 sheets into 40 mm x 125 mm coupons. The FSSW joints are designed as lap shear specimens for the mechanical tests. Join two 125 mm by 40 mm sheets with a 35 mm by 40 mm overlap following RSW standard NF ISO 18278-2; 2005. A geometry design polycrystalline diamond tool with a truncated cone shoulder. The geometry design is shown in Figure 1a. The diameter of the pin is 5 mm; the length is 2.5 mm, and the sho.......

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There is a diagram in Figure 3 that demonstrates that the friction stir spot welding process is comprised of 3 parts: plunging (Figure 3e), stirring (Figure 3f), and retracting (Figure 3g). In our research, the welding spot could be generated. The penetration depth is one factor that was evaluated. In Figure 6a, the FSSW creates the keyhole .......

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The plunging stage is the most important during the FSSW process. Without enough friction heat coming from the shoulder of the pin to soften the workpiece, the pin will fracture. Tool geometry, rotation speed, dwell time, and tool penetration depth26 parameters of the FSSW process play a critical role in determining the joint integrity. TPD and tool geometry27 particularly have an important effect on the weldability and joint properties was reported.

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We thank Dr. K. C. Yang in the China-Steel Company for material support and wish to express our gratitude to Mr. L.D. Wang, C. K. Wang, and B. Y. Hong at the MIRDC for assistance with the experimental FSSW. This research was supported by the Metal Industries Research and Development Centre, Kaohsiung, Taiwan, ROC.


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Name Company Catalog Number Comments
anvil MIRDC made by MIRDC
DP780 China steel Corporation CSC DP780
stir spot welder machine MIRDC made by MIRDC

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