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 shoulder width is 10 mm. The real tool pin is shown in Figure 1b.
<ol>
	<li>Safety guidelines
	<ol>
		<li>Use devices such as a hood or baffle, goggles, and gloves for protection.</li>
		<li>Stand behind the hood or the baffle. Wear goggles and gloves to prevent splash contact or heat damage.</li>
	</ol>
	</li>
	<li>FSSW machine setting
	<ol>
		<li>Manufacture all joints using an MIRDC-made friction stir welder machine.</li>
		<li>Record the Z axial force and penetration depth during each joining operation using the embedded data acquisition (DAQ) system.</li>
	</ol>
	</li>
	<li>Parameter settings
	<ol>
		<li>In this study, use the following parameters: a tool pin rotation speed of 2,500 rpm, 4 s of tool pin dwell time, and a rate pf 0.5 mm/s of tool pin plunge into the sheet.</li>
		<li>Optimize the parameters for the operator. The range of the rotation speed is 1,000- 2,500 rpm. The range of the dwell time can be from 2-10 s, and the plunge rate can be 0.1-0.5 mm/s.</li>
	</ol>
	</li>
</ol>
2. Procedure
NOTE: The work space is shown in Figure 2. All the manufacturing procedures are completed in the work space. Before the procedure, the welding process sequences are comprised of a combination of tool rotations and penetration depths, as well as a series of sequences including preheating, plunging, dwelling, retracting, and post heating. All steps are shown in Figure 3 in the form of a work flowchart.
<ol>
	<li>DP780 workpiece preparation
	<ol>
		<li>Before the welding process, ensure that there are no impurity substrates contaminating the workpieces. Use knitted micro-fiber fabrics to wipe the surface of the workpiece to eliminate any small particles.</li>
	</ol>
	</li>
	<li>Place the DP780 workpiece, and clamp 2 DP780 sheets (size: 125 mm x 40 mm) with an overlap of 35 mm. Fix the clean workpieces on an anvil to prevent shifting.</li>
	<li>Ensure that the pin is clean to prevent impure substrate contamination. Use knitted microfiber fabrics to wipe the surface of the tool pin to eliminate small particles.</li>
	<li>Fix the pin with a clamp on the machine.
	<ol>
		<li>Screw on the tool pin tightly again for tool pin clamping.</li>
		<li>Pay attention to the pin clamping step. Ensure that the pin is clamped tight in the machine to avoid danger. The rotating tool is surrounded by a nonrotating clamping ring with which the workpieces are pressed firmly against one another before and during welding by applying a clamping force. The illustration shown in Figure 3a notes the clamp ring used to fix the tool pin. After this step, the production is shown in the flowchart.</li>
		<li>Ensure safety.</li>
		<li>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 1 minute. The speed can accelerate from 100 to 1,000 rpm within 1 minute (Figure 3b).</li>
	</ol>
	</li>
	<li>Machine settings
	<ol>
		<li>Use the following parameters: a rotational speed of 3,000 rpm, a dwell of 4 s, and a plunge rate of 0.5 mm/s (Figure 3c).</li>
	</ol>
	</li>
	<li>Calibrate the welding location (Figure 3d and the real product shown in Figure 4a).
	<ol>
		<li>Set the pin in the stir spot welder machine. The gap between the pin and the workpiece is smaller than 5 cm to calibrate the joint location. After the location is confirmed, move onto the welding process.</li>
	</ol>
	</li>
	<li>During welding, wear goggles and gloves to avoid injury.
	<ol>
		<li>Begin the welding process with the tool under high-speed rotation to plunge the tool pin into the workpiece. The tool shoulder contacts the workpieces and stops the rotation and retracts the pin.</li>
	</ol>
	</li>
	<li>Plunging
	<ol>
		<li>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 into the workpieces under a high-speed rotation and the shoulder contacts the workpieces at a high angular speed (Figure 3e). The real product is shown in Figure 4b.</li>
	</ol>
	</li>
	<li>Stirring
	<ol>
		<li>As the plunged tool pin continues stirring in the workpiece, soften the interface of the pin and the material from the friction heat to create the grain. When the shoulder of the tool pin comes into contact with the top of the workpiece, 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 (see Figure 3f.) The real product is shown in Figure 4c.</li>
	</ol>
	</li>
	<li>Retracting
	<ol>
		<li>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 (Figure 3g). The real product is shown in Figure 4e.</li>
	</ol>
	</li>
	<li>Remove the workpieces.
	<ol>
		<li>Turn off the machine power.</li>
		<li>After the welding is finished, remove the workpieces from the anvil. Observe the samples for cracks and lack of fusion.</li>
		<li>Remove the tool pin.</li>
		<li>After the procedure, remove the tool pin from the clamp ring. The appearance of the tool pin is observed and checked (Figure 5).</li>
	</ol>
	</li>
</ol>
3. Mechanical property evaluation
<ol>
	<li>Microscopy examination of the FSSW welds (Figure 3h)
	<ol>
		<li>Microscopic sample preparation</li>
		<li>Measure the cross-sectional area of the bonded region using an optical microscope image and a secondary electron image analysis. Prepare the microscopic samples using grounded silicon carbide paper with a grit size ranging from 200 to 2,000 starting with a grit size of 200 and increasing in sequence. Polish the samples with 0.03% alumina and etch with a 4% nital solution for 7&#8211;10 s at room temperature.</li>
		<li>Microscopy observation</li>
		<li>Observe and characterize the microstructures using optical microscopy and scanning electron microscopy. Use a voltage of 20 kV, and a working distance of 10 &#956;m. From the optical microscopy, any tiny crack line or lack of a fusion zone can be determined. Use scanning electron microscopy to analyze the martensite and austenite distribution and the grain size.</li>
	</ol>
	</li>
	<li>Microhardness
	<ol>
		<li>Verify the microhardness experiments more than 3 times. The values were too small to clearly denote the standard deviation.</li>
		<li>Press the Vickers diamond indenter with a 300 g test load sample and 0.5 mm per test.</li>
		<li>Conduct the microhardness testing of the DP780 steel sheet using a microhardness testing machine with a 300 g load and a holding time of 15 s. The microhardness testing revealed the hardness distribution and the individual hardness values in the stir zone, the thermomechanical affect zone, the heat affected zone, and in the base metal of the welds.</li>
	</ol>
	</li>
</ol>

<ol><li>Mazda. Mazda Develops World’s First Aluminum Joining Technology Using Friction Heat. , Available from:
 <a target="_blank" href="https://www2.mazda.com/en/publicity/release/archive/2003/200302/0227e.html">https://www2.mazda.com/en/publicity/release/archive/2003/200302/0227e.html</a> (2003).</li>
<li>Piccini, J. M., Svoboda, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+pin+length+on+Friction+Stir+Spot+Welding+%28FSSW%29+of+dissimilar+Aluminum-steel+joints%5BTitle%5D)+AND+%22Procedia+Materials+Science%22%5BJournal%5D)">Effect of pin length on Friction Stir Spot Welding (FSSW) of dissimilar Aluminum-steel joints.</a> Procedia Materials Science. 9, 504-513 (2015).</li>
<li>Iwashita, T. Method and Apparatus for joining. , USA patent US6601751B2 (2003).</li>
<li>Allen, C. D., Arbegast, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Evaluation+of+Friction+Spot+Welds+in+Aluminium+Alloys%5BTitle%5D)+AND+%22SAE+Technical%22%5BJournal%5D)">Evaluation of Friction Spot Welds in Aluminium Alloys.</a> SAE Technical. , No 2005-2001-1252 (2005).</li>
<li>Feng, Z., et al. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aFeng%2C+Z+%22Friction+Stir+Spot+Welding+of+Advanced+HighStrength+Steels+-+a+Feasibility+Study%22">Friction Stir Spot Welding of Advanced HighStrength Steels - a Feasibility Study</a>. , SAE 2005 Congress, SAE-International, Detroit, MI, Technical Paper No 2005-2001-1248 (2005).</li>
<li>Miles, M. P., Nelson, T. W., Steel, R., Olsen, E., Gallagher, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+friction+stir+welding+conditions+on+properties+and+microstructures+of+high+strength+automotive+steel%5BTitle%5D)+AND+%22Science+and+Technology+of+Welding+and+Joining%22%5BJournal%5D)">Effect of friction stir welding conditions on properties and microstructures of high strength automotive steel.</a> Science and Technology of Welding and Joining. 14 (3), 228-232 (2009).</li>
<li>Feng, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Friction+stir+spot+welding+of+advanced+high-Strength+steels-a+feasibility+study%5BTitle%5D)+AND+%22SAE+Technical+Paper+Series+2005-01-1248%22%5BJournal%5D)">Friction stir spot welding of advanced high-Strength steels-a feasibility study.</a> SAE Technical Paper Series 2005-01-1248. , (2005).</li>
<li>Santella, M., Hovanski, Y., Frederick, A., Grant, G., Dahl, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Friction+stir+spot+welding+of+DP780+carbon+steel%5BTitle%5D)+AND+%22Science+and+Technology+of+Welding+and+Joining%22%5BJournal%5D)">Friction stir spot welding of DP780 carbon steel.</a> Science and Technology of Welding and Joining. 15 (4), 271-278 (2010).</li>
<li>Saunders, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Joint+strength+in+high+speed+friction+stir+spot+welded+DP+980+steel%5BTitle%5D)+AND+%22International+Journal+of+Precision+Engineering+and+Manufacturing%22%5BJournal%5D)">Joint strength in high speed friction stir spot welded DP 980 steel.</a> International Journal of Precision Engineering and Manufacturing. 15 (5), 841-848 (2014).</li>
<li>Khan, M. I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Resistance+and+friction+stir+spot+welding+of+DP600%3A+a+comparative+study%5BTitle%5D)+AND+%22Science+and+Technology+of+Welding+and+Joining%22%5BJournal%5D)">Resistance and friction stir spot welding of DP600: a comparative study.</a> Science and Technology of Welding and Joining. 12 (2), 175-182 (2007).</li>
<li>Sarkar, R., Sengupta, S., Pal, T. K., Shome, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microstructure+and+Mechanical+Properties+of+Friction+Stir+Spot-Welded+IF%2FDP+Dissimilar+Steel+Joints%5BTitle%5D)+AND+%22Metallurgical+and+Materials+Transactions+A%22%5BJournal%5D)">Microstructure and Mechanical Properties of Friction Stir Spot-Welded IF/DP Dissimilar Steel Joints.</a> Metallurgical and Materials Transactions A. 46 (11), 5182-5200 (2015).</li>
<li>Yang, X. W., Fu, T., Li, W. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Friction+Stir+Spot+Welding%3A+A+Review+on+Joint+Macro-+and+Microstructure%2C+Property%2C+and+Process+Modelling%5BTitle%5D)+AND+%22Advances+in+Materials+Science+and+Engineering%22%5BJournal%5D)">Friction Stir Spot Welding: A Review on Joint Macro- and Microstructure, Property, and Process Modelling.</a> Advances in Materials Science and Engineering. 2014, 11(2014).</li>
<li>Esther, T. A., Stephen, A. A. Trends in Welding Research 2012: Proceedings of the 9th International Conference. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aEsther%2C+TA+%22Materials+Characterisation+of+Friction+Stir+Processed+6082+Aluminum+Alloy%22">Materials Characterisation of Friction Stir Processed 6082 Aluminum Alloy</a>. DebRoy, T., et al. , ASM Press. Chicago, IL. 548-551 (2012).</li>
<li>Ghosh, P. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Influence+of+Weld+Thermal+Cycle+on+Properties+of+Flash+Butt+Welded+Mn-Cr-Mo+Dual+Phase+Steel%5BTitle%5D)+AND+%22ISIJ+International%22%5BJournal%5D)">Influence of Weld Thermal Cycle on Properties of Flash Butt Welded Mn-Cr-Mo Dual Phase Steel.</a> ISIJ International. 33 (7), 807-815 (1993).</li>
<li>Schultz, R. A. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aSchultz%2C+RA+%22Metallic+materials+trends+for+north+American+light+vehicles%22">Metallic materials trends for north American light vehicles</a>. , American Iron and Steel Institute. Michigan, US. Power point presentation of great designs in steel seminar (2007).</li>
<li>Horvath, C. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aHorvath%2C+C+%22Material+challenges+facing+the+automotive+and+steel+industries+from+globalization%22">Material challenges facing the automotive and steel industries from globalization</a>. , American Iron and Steel Institute, Michigan, USAmerican Iron and Steel Institute. Michigan, US. Power point presentation of great designs in steel seminar (2007).</li>
<li>Pouranvari, M., Marashi, S. P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Critical+review+of+automotive+steels+spot+welding%3A+process%2C+structure+and+properties%5BTitle%5D)+AND+%22Science+and+Technology+of+Welding+and+Joining%22%5BJournal%5D)">Critical review of automotive steels spot welding: process, structure and properties.</a> Science and Technology of Welding and Joining. 18 (5), 361-403 (2013).</li>
<li>Khan, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Welding+behaviour%2C+microstructure+and+mechanical+properties+of+dissimilar+resistance+spot+welds+between+galvannealed+HSLA350+and+DP600+steels%5BTitle%5D)+AND+%22Science+and+Technology+of+Welding+and+Joining%22%5BJournal%5D)">Welding behaviour, microstructure and mechanical properties of dissimilar resistance spot welds between galvannealed HSLA350 and DP600 steels.</a> Science and Technology of Welding and Joining. 14 (7), 616-625 (2009).</li>
<li>Ma, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microstructure+and+fracture+characteristics+of+spot-welded+DP600+steel%5BTitle%5D)+AND+%22Materials+Science+and+Engineering%3A+A%22%5BJournal%5D)">Microstructure and fracture characteristics of spot-welded DP600 steel.</a> Materials Science and Engineering: A. 485 (1), 334-346 (2008).</li>
<li>Hilditch, T. B., Speer, J. G., Matlock, D. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+susceptibility+to+interfacial+fracture+on+fatigue+properties+of+spot-welded+high+strength+sheet+steel%5BTitle%5D)+AND+%22Materials+%26+Design%22%5BJournal%5D)">Effect of susceptibility to interfacial fracture on fatigue properties of spot-welded high strength sheet steel.</a> Materials & Design. 28 (10), 2566-2576 (2007).</li>
<li>Yan, B., Zhu, H., Lalam, S. H., Baczkowski, S., Coon, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spot+Weld+Fatigue+of+Dual+Phase+Steels%5BTitle%5D)+AND+%22SAE+Technical+Paper+Series+2004-01-0511%22%5BJournal%5D)">Spot Weld Fatigue of Dual Phase Steels.</a> SAE Technical Paper Series 2004-01-0511. , (2004).</li>
<li>Wilson, R. B., Fine, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fatigue+behavior+of+spot+welded+high+strength+joints%5BTitle%5D)+AND+%22SAE+Technical+Paper+Series+1981-02-01%22%5BJournal%5D)">Fatigue behavior of spot welded high strength joints.</a> SAE Technical Paper Series 1981-02-01. , (1981).</li>
<li>Sun, X., Stephens, E. V., Khaleel, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+fusion+zone+size+and+failure+mode+on+peak+load+and+energy+absorption+of+advanced+high+strength+steel+spot+welds+under+lap+shear+loading+conditions%5BTitle%5D)+AND+%22Engineering+Failure+Analysis%22%5BJournal%5D)">Effects of fusion zone size and failure mode on peak load and energy absorption of advanced high strength steel spot welds under lap shear loading conditions.</a> Engineering Failure Analysis. 15 (4), 356-367 (2008).</li>
<li>Pouranvari, M., Mousavizadeh, S. M., Marashi, S. P. H., Goodarzi, M., Ghorbani, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Influence+of+fusion+zone+size+and+failure+mode+on+mechanical+performance+of+dissimilar+resistance+spot+welds+of+AISI+1008+low+carbon+steel+and+DP600+advanced+high+strength+steel%5BTitle%5D)+AND+%22Materials+%26+Design%22%5BJournal%5D)">Influence of fusion zone size and failure mode on mechanical performance of dissimilar resistance spot welds of AISI 1008 low carbon steel and DP600 advanced high strength steel.</a> Materials & Design. 32 (3), 1390-1398 (2011).</li>
<li>Hsu, T. -I., Wu, L. -T., Tsai, M. -H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Resistance+and+friction+stir+spot+welding+of+dual-phase+%28DP+780%29%E2%80%94a+comparative+study%5BTitle%5D)+AND+%22The+International+Journal+of+Advanced+Manufacturing+Technology%22%5BJournal%5D)">Resistance and friction stir spot welding of dual-phase (DP 780)—a comparative study.</a> The International Journal of Advanced Manufacturing Technology. , (2018).</li>
<li>Piccini, J. M., Svoboda, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+the+tool+penetration+depth+in+Friction+Stir+Spot+Welding+%28FSSW%29+of+dissimilar+aluminum+alloys%5BTitle%5D)+AND+%22Procedia+Materials+Science%22%5BJournal%5D)">Effect of the tool penetration depth in Friction Stir Spot Welding (FSSW) of dissimilar aluminum alloys.</a> Procedia Materials Science. 8, 868-877 (2015).</li>
<li>Aissani, M., Gachi, S., Boubenider, F., Benkedda, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Design+and+Optimization+of+Friction+Stir+Welding+Tool%5BTitle%5D)+AND+%22Materials+and+Manufacturing+Processes%22%5BJournal%5D)">Design and Optimization of Friction Stir Welding Tool.</a> Materials and Manufacturing Processes. 25 (11), 1199-1205 (2010).</li>
<li>Zhang, Y. N., Cao, X., Larose, S., Wanjara, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Review+of+tools+for+friction+stir+welding+and+processing%5BTitle%5D)+AND+%22Canadian+Metallurgical+Quarterly%22%5BJournal%5D)">Review of tools for friction stir welding and processing.</a> Canadian Metallurgical Quarterly. 51 (3), 250-261 (2013).</li>
<li>Nandan, R., DebRoy, T., Bhadeshia, H. K. D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Recent+advances+in+friction-stir+welding+%E2%80%93+Process%2C+weldment+structure+and+properties%5BTitle%5D)+AND+%22Progress+in+Materials+Science%22%5BJournal%5D)">Recent advances in friction-stir welding – Process, weldment structure and properties.</a> Progress in Materials Science. 53 (6), 980-1023 (2008).</li>
<li>Tang, W., Guo, X., McClure, J., Murr, L., Nunes, A. C. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aTang%2C+W+%22Heat+Input+and+Temperature+Distribution+in+Friction+Stir+Welding%22">Heat Input and Temperature Distribution in Friction Stir Welding</a>. 7, (1998).</li>
</ol>

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 ...

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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 ...

generating-lap-joints-via-friction-stir-spot-welding-on-dp780-steel

Research

JoVE Journal

Engineering

6.9K Views.  Shu Zen College of Medicine and Management. De gewichtsreductie eisen in de auto-industrie hebben geleid tot een toenemende interesse in ronde gewrichten en de geavanceerde hoge sterkte staal, of AHSS. Ahss-lasverbindingen hebben echter uitdagingen voor procesbetrouwbaarheid. De voordelen van wrijving roer spot lassen, of FSSW, in vergelijking met weerstand spot lassen zijn een lagere lastemperatuur, geen plons, en hoe meer stabiliteit in het productieproces.Het aantonen van de procedure zal Cheng Chia-Ping en Hsu Hao, afgestude...

Video: Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel

Origami Inspired Self-assembly of Patterned and Reconfigurable Particles

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two dimensional (2D) structures. These technologies are mature, offer high precision and many of them can be implemented in a high-throughput manner. We leverage the advantages of planar lithography and combine them with self-folding methods1-20 wherein physical forces derived from surface tension or residual stress, are used to curve or fold planar structures into three dimensional (3D) structures. In doing so, we make it possible to mass produce precisely patterned static and reconfigurable particles that are challenging to synthesize.
In this paper, we detail visualized experimental protocols to create patterned particles, notably, (a) permanently bonded, hollow, polyhedra that self-assemble and self-seal due to the minimization of surface energy of liquefied hinges21-23 and (b) grippers that self-fold due to residual stress powered hinges24,25. The specific protocol described can be used to create particles with overall sizes ranging from the micrometer to the centimeter length scales. Further, arbitrary patterns can be defined on the surfaces of the particles of importance in colloidal science, electronics, optics and medicine. More generally, the concept of self-assembling mechanically rigid particles with self-sealing hinges is applicable, with some process modifications, to the creation of particles at even smaller, 100 nm length scales22, 26 and with a range of materials including metals21, semiconductors9 and polymers27. With respect to residual stress powered actuation of reconfigurable grasping devices, our specific protocol utilizes chromium hinges of relevance to devices with sizes ranging from 100 &mu;m to 2.5 mm. However, more generally, the concept of such tether-free residual stress powered actuation can be used with alternate high-stress materials such as heteroepitaxially deposited semiconductor films5,7 to possibly create even smaller nanoscale grasping devices.

We describe experimental details of the synthesis of patterned and reconfigurable particles from two dimensional (2D) precursors. This methodology can be used to create particles in a variety of shapes including polyhedra and grasping devices at length scales ranging from the micro to centimeter scale.

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two ...

Chemistry

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

Experimental Procedure for Warm Spinning of Cast Aluminum Components

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to improve material properties. With a wide array of processing parameters which can affect both the shape attained and resulting material properties, this type of processing is notoriously difficult to commission. A simplified, light-duty version of the process has been designed and implemented for full-size automotive wheels. The apparatus is intended to assist in understanding the deformation mechanisms and the material response to this type of processing. An experimental protocol has been developed to prepare for, and subsequently perform forming trials and is described for as-cast A356 wheel blanks. The thermal profile attained, along with instrumentation details are provided. Similitude with full-scale forming operations which impart significantly more deformation at faster rates is discussed.

An experimental protocol for instrumented warm rotary forming of cast aluminum alloys employing a bespoke industrially scaled apparatus is presented. Experimental considerations including thermal and mechanical effects are discussed, as well as similitude with full-scale processing of automotive wheels.

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to ...

A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional experimental approaches, such as out-of-plane and in-plane tests, are not applicable to the determination of forming limits when heating and rapid cooling processes are introduced prior to forming for tests conducted under hot stamping conditions. A novel in-plane biaxial testing system was designed and used for the determination of forming limits of sheet metals at various strain paths, temperatures, and strain rates after heating and cooling processes in a resistance heating uniaxial testing machine. The core part of the biaxial testing system is a biaxial apparatus, which transfers a uniaxial force provided by the uniaxial testing machine to a biaxial force. One type of cruciform specimen was designed and verified for the formability test of aluminum alloy 6082 using the proposed biaxial testing system. The digital image correlation (DIC) system with a high-speed camera was used for taking strain measurements of a specimen during a deformation. The aim of proposing this biaxial testing system is to enable the forming limits of an alloy to be determined at various temperatures and strain rates under hot stamping conditions.

This protocol proposes a novel biaxial testing system used on a resistance heating uniaxial tensile test machine in order to determine the forming limit diagram (FLD) of sheet metals under hot stamping conditions.

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional ...

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A ...

Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It is intended as a practical and reproducible procedure to identify macroscopic cracks at an early stage and monitor crack propagation during fatigue tests. It consists of strain field measurements at the weld using DIC. Images are taken at fixed load cycle intervals. Cracks become visible in the computed strain field as elevated strains. This way, the whole width of a small-scale specimen can be monitored to detect where and when a crack initiates. Subsequently, it is possible to monitor the development of the crack length. Because the resulting images are saved, the results are verifiable and comparable. The procedure is limited to cracks initiating at the surface and is intended for fatigue tests under laboratory conditions. By visualizing the crack, the presented procedure allows direct observation of macrocracks from their formation until rupture of the specimen.

Digital image correlation is used in fatigue tests on a resonance testing machine to detect macroscopic cracks and monitor crack propagation in welded specimens. Cracks on the specimen surface become visible as increased strains.

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It ...

Rapid Manufacturing of Thin Soft Pneumatic Actuators and Robots

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with an ultrathin form factor using a heat press and a laser cutter machine. The method starts with the lamination of thermoplastic polyurethane (TPU) sheets using a heat press for 10 min at the temperature of ~93 &#176;C. Next, the parameters of the laser cutter machine are optimized to produce a rectangular balloon with maximum burst pressure. Using the optimized parameters, the soft actuators are laser cut/welded three times sequentially. Next, a dispensing needle is attached to the actuator, allowing it to be inflated. The effect of geometrical parameters on the deflection of the actuator are studied systematically by varying the channel width and length. Finally, the performance of the actuator is characterized using an optical camera and a fluid dispenser. Conventional fabrication methods of soft pneumatic actuators based on silicone molding are time consuming (several hours). They also result in strong but bulky actuators, which limits the actuator&#8217;s applications. Moreover, microfabrication of thin pneumatic actuators is both time-consuming and expensive. The proposed manufacturing method in the current work resolves these issues by introducing a fast, simple, and cost-effective fabrication method of ultrathin pneumatic actuators.

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with a thin form factor. The fabrication method starts with lamination of thermoplastic polyurethane (TPU) sheets followed by laser cutting/welding of a two-dimensional pattern to form actuators and robots.

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with an ultrathin form factor using a heat press and a ...

Micromechanical Tension Testing of Additively Manufactured 17-4 PH Stainless Steel Specimens

This study presents a methodology for the rapid fabrication and micro-tensile testing of additively manufactured (AM) 17-4PH stainless steels by combining photolithography, wet-etching, focused ion beam (FIB) milling, and modified nanoindentation. Detailed procedures for proper sample surface preparation, photo-resist placement, etchant preparation, and FIB sequencing are described herein to allow for high throughput (rapid) specimen fabrication from bulk AM 17-4PH stainless steel volumes. Additionally, procedures for the nano-indenter tip modification to allow tensile testing are presented and a representative micro specimen is fabricated and tested to failure in tension. Tensile-grip-to-specimen alignment and sample engagement were the main challenges of the micro-tensile testing; however, by reducing the indenter tip dimensions, alignment and engagement between the tensile grip and specimen were improved. Results from the representative micro-scale in situ SEM tensile test indicate a single slip plane specimen fracture (typical of a ductile single crystal failure), differing from macro-scale AM 17-4PH post-yield tensile behavior.

Presented here is a procedure for measuring fundamental material properties through micromechanical tension testing. Described are the methods for micro-tensile specimen fabrication (allowing rapid micro-specimen fabrication from bulk material volumes by combining photolithography, chemical etching, and focused ion beam milling), indenter tip modification, and micromechanical tension testing (including an example).

This study presents a methodology for the rapid fabrication and micro-tensile testing of additively manufactured (AM) 17-4PH stainless steels by combining ...

Surrogate Model Development for Digital Experiments in Welding

The manufacturing industry heavily relies on welding processes to join materials, forming integral components across various sectors. Many aspects will influence the quality of the weld and finally affect the structure integrity of the weldment. Welding-induced residual stress, a consequence of the thermal cycling inherent in these processes, significantly impacts the structural integrity and performance of fabricated components. Understanding and predicting this residual stress is crucial for enhancing the reliability and durability of welded structures. However, quickly assessing a welding setup in digital experiments presents significant challenges, as a traditional simulation may be time-consuming. This research outlines the application of a workflow to construct an artificial neural network-based surrogate model to predict welding-induced residual stress. The model is built using data automatically generated from finite element simulations through Python scripts based on macro functions. Unlike traditional methods that rely on manual preprocessing and finite element simulations, this approach significantly reduces the time and effort required for simulation setup and data extraction, enhancing overall efficiency. By ensuring that all simulation steps are performed consistently through macro functions, the method eliminates human-induced variability, leading to improved reproducibility. Furthermore, the automation of data generation makes it possible to create extensive datasets necessary for training machine learning models, overcoming the limitations of labor-intensive traditional techniques. The workflow contains four main steps: build a standard weld finite element simulation and validate the finite element simulation results against experimental data; develop scripts for large dataset generation using a macro function that records the preprocessing and postprocessing steps of the finite element simulation; use the scripts to generate the required data; develop surrogate models and test their performance. The artificial neural network demonstrated high accuracy in predicting stress levels, closely aligning with simulation results on the test dataset and a relative root mean square error of 0.0024.

This protocol outlines a general workflow for constructing an artificial neural network for welding simulation using datasets generated automatically through Python scripts with macro functions. The workflow is validated against a benchmark case involving single-pass, straight-line welding. The surrogate model's predictive accuracy shows a strong agreement with finite element simulations.

The manufacturing industry heavily relies on welding processes to join materials, forming integral components across various sectors. Many aspects will ...

Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel

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