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.

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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The authors have nothing to disclose.

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.
<p class="jove_cont...

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 the Mazda&#39;s RX-81,3,4.
Meanwhile, high strength steel is the dominant material of the car body, specifically dual phase steel. The literature indicates that DP600 produced with FSSW can have the same properties as the base metal, where all welding regions have similar microstructures and degrees of hardness5. FSSW methods for the use of DP steel on their microstructure of the stir zone (SZ), the thermos-mechanically affected zone (TMAZ), and the failure model of DP590 and DP600 steel have been studied by a few researchers. They observed differences in the consistency of the microstructure (ferrite, bainite, and martensite) of DP590 and DP600 steel at various rotation speeds6,7,8,9,10. Some researchers conducted comparative studies of FSSW and RSW for DP780 steel8,9. They reported that longer joining times and higher tool rotation speeds resulted in an increased bonding area for all plunges, which led to a higher shear force and shifted the mode from interfacial to pull out. They also concluded that FSSW had a higher strength than RSW. The FSSW process includes 3 steps: plunging, stirring, and retraction. The first step is plunging with a rotation tool pin close to the sheet of the lap joint and plugged into the sheet. The rotating tool shoulder in the FSSW process can generate frictional heat. In the second step, the heat can soften the sheet and facilitate plugging of the tool pin into the sheet, as well as dwell in the materials to stir two workpieces together and mix around the pin area. Finally, the pressure from the tool shoulder press on the workpieces can enhance the bonding. After the welding process, the pin can be retracted from the keyhole. The benefits of FSSW compared with RSW are a lower welding temperature, no splashing, and more stability in the manufacturing process.
Even though studies on the FSSW of advanced high-strength steels (AHSS) have been reported by various researchers, studies on the FSSW of DP590, DP600, and DP780 have focused on the microstructure and on the mechanical and failure models using various process parameters. In the present study, the FSSW of DP780 steel was considered. The protocol of the FSSW process was reported in detail, and the individual hardness in the stir zone, the thermos-mechanically affected zone, and the heat-affected zone, as well as the base metal were evaluated based on the measured microhardness.
With the continuous growth and heavy demand for weight reduction in the automotive and aerospace industries, the automotive industry has shown an increasing interest in AHSS and lap joints. For example, the conventional steel body of a car, on average, has more than 2,000 spot weld lap joints11. There are 3 common welding processes for lap joints used in the industry, including resistance spot welding, laser spot welding, and friction spot welding12. One way to decrease the weight is by using advanced high-strength steels (AHSS). The most popular materials are dual-phase and transformation-induced plasticity (TRIP) steels, which are being increasingly used in the automotive industry13,14,15,16. Because the automotive industry has increased the strength standards due to improved fuel consumption and crash energy absorption under a decreased vehicle weight, the use of different materials and welding processes is becoming an important issue.

<table>
	<tbody>
		<tr>
			<td>anvil</td>
			<td>MIRDC</td>
			<td></td>
			<td>made by MIRDC</td>
		</tr>
		<tr>
			<td>DP780</td>
			<td>China steel Corporation</td>
			<td>CSC DP780</td>
			<td></td>
		</tr>
		<tr>
			<td>stir spot welder machine</td>
			<td>MIRDC</td>
			<td></td>
			<td>made by MIRDC</td>
		</tr>
		<tr>
			<td>tool pin</td>
			<td>KINIK COMPANY</td>
			<td>DBN2B005B</td>
			<td></td>
		</tr>
	</tbody>
</table>

generating lap joints via friction stir spot welding on dp780 steel

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.

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 ...

Watch this Scientific Journal Video about Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel at JoVE.com

Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel

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 ...

The weight reduction demands in the automotive industry have generated a increasing interest in lap joints and the advanced high-strength steels, or AHSS. However, AHSS spot welding joints have challenges for process reliability. The benefits of friction stir spot welding, or FSSW, compared with resistance spot welding are a lower welding temperature, no splash, and the more stability in the manufacture process.Demonstrating the procedure will be Cheng Chia-Ping and Hsu Hao, graduate students from my laboratory. During this procedure wear goggles and gloves to prevent splash contact or heat damage. Also stand behind the hood or the baffle for protection.Manufacture all joints using a friction stir welder machine. Record the z-axial force and penetration depth during each joining operation using the embedded data acquisition system. Set a tool pin rotation speed of 25, 000 RPM, a tool pin weld time of four seconds, and a rate of 0.5 millimeters per second of tool pin plunge into the sheet.Optimize the parameters for the operator. The range of the rotation speed is 1, 000 to 2, 500 RPM. The range of the dwell time can be from two to 10 seconds and the plunge rate can be 0.1 to 0.5 millimeters per second.Before the welding process, ensure that there are no impurity substrates contaminating the work pieces. Wipe the surface of the work piece with knitted microfiber fabrics to eliminate any small particles. Place the DP 780 work pieces and clamp tWo DP 780 sheets with an overlap of 35 millimeters.Fix the clean work pieces on an anvil to prevent shifting. Ensure that the pin is clean to prevent impure substrate contamination. Use knitted microfiber fabrics to wipe the surface of the tool pin.To fix the pin with a clamp on the machine, first screw on the tool pin tightly. Pay attention to the pin clamping step. Ensure that the pin is clamped tightly in the machine to avoid danger.The rotating tool is surrounded by a non-rotating clamping ring, with which the work pieces are pressed firmly against one another before and during welding by applying a clamping force. Confirm that the high-speed rotation pin without a clamp ring loosens. When the tool pin is placed on the machine, ensure that the tool pin does not separate from the clamp during rotation for safety reasons.The tool pin uses a low-rotation rate from 10 to 100 RPM in one minute. The speed can accelerate from 100 to 1, 000 RPM within one minute. Set the machine to a rotational speed of 3, 000 RPM, a dwell of four seconds, and a plunge rate of 0.5 millimeters per second.Calibrate the welding location and the real product. Set the pin in the stir spot welder machine. The gap between the pin and the work piece is smaller than five centimeters to calibrate the joint location.After the location is confirmed, move on to the welding process. Begin the welding process with the tool under high-speed rotation to plunge the tool pin into the work piece. The tool shoulder contacts the work pieces, stops the rotation, and retracts the pin.For plunging, first turn the stir button on. When the machine warms up, confirm that the tool pin is consistently operating at a 2, 500 RPM rotation speed. Ensure that the tool pin is clamped well under the high-speed rotation at 2, 500 RPM.The pin plunges in the work pieces under a high-speed rotation and the shoulder contacts the work pieces at a high angular speed. As the plunged tool pin continues stirring in the work piece, soften the interface of the pin and material from the friction heat to create the grain. When the shoulder of the tool pin comes into contact with the top of the work piece, stop the process because the high rotation of the tool pin can generate high temperatures.It is important to wear protective gear that ensures operational safety. Draw out the tool pin in the vertical direction. After the procedure, the pin creates the key hole welding spot in the lap joint.Note that the friction stir spot weld stops in this step. Turn off the machine power. After the welding is finished, remove the work pieces from the anvil.Observe the samples for cracks and lack of fusion. After the procedure, remove the tool pin from the clamp ring. The appearance of the tool pin is observed and checked before the mechanical property evaluation as described in the text protocol.The friction stir spot welding creates the key hole in the center of the DP 780 sheets to create the joint for two sheets. The dwell depth of the key hole is measured from the sheet top to the key hole bottom surface. The dwell depth measurement values are shown, for which the setting values are two centimeters and the real values are 1.92 to 1.98 centimeters.This image shows the key hole overall view of the welding spot in the DP 780 sheet. The analyzed area contained four parts, the base metal, the heat affected zone, the thermos-mechanically affected zone, and the stir zone. The analysis of the base metal microstructure shows no change in material properties.The heat affected zone exhibits the martensite islands. The microstructures of the thermos-mechanically affected zone near the key hole are characterized by a mixture of needle-like martensite and fine acicular ferrite, whereas the stir region around the key hole reveals a fine-grain martensite and porosity. Friction stir spot welding of AHSS weld lap joints has great potential.On average, the conventional steel body of a car has more than 2, 000 spot weld lap joints. Following this procedure, materials and the design geometry of the tool pin can be performed for hard lap joints. A longer lifetime will be the demand of this process.

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Engineering

6.8K Views.  Shu Zen College of Medicine and Management. The weight reduction demands in the automotive industry have generated a increasing interest in lap joints and the advanced high-strength steels, or AHSS. However, AHSS spot welding joints have challenges for process reliability. The benefits of friction stir spot welding, or FSSW, compared with resistance spot welding are a lower welding temperature, no splash, and the more stability in the manufacture process.Demonstrating the procedure will be Cheng Chia-Ping and Hsu Hao, graduate s...