Ultrasonic Butt Welding of Aluminum, Aluminum Alloy

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Ultrasonic butt welding of aluminum, aluminum alloyand stainless steel plate specimens

Jiromaru Tsujino *

, Kazuaki Hidai, Atsushi Hasegawa, Ryoichi Kanai,Hisanori Matsuura, Kaoru Matsushima, Tetsugi Ueoka

Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

Abstract

Welding characteristics of aluminum, aluminum alloy and stainless steel plate specimens of 6.0 mm thickness by a 15 kHz ul-trasonic butt welding system were studied. There are no detailed welding condition data of these specimens although the joining of these materials are required due to anticorrosive and high strength characteristics for not only large specimens but small electronicparts especially. These specimens of 6.0 mm thickness were welded end to end using a 15 kHz ultrasonic butt welding equipmentwith a vibration source using eight bolt-clamped Langevin type PZT transducers and a 50 kW static induction thyristor poweramplier. The stainless steel plate specimens electrolytically polished were joined with welding strength almost equal to the materialstrength under rather large vibration amplitude of 25 l m (peak-to-zero value), static pressure 70 MPa and welding time of 1.03.0 s.The hardness of stainless steel specimen adjacent to a welding surface increased about 20% by ultrasonic vibration. 2002 ElsevierScience B.V. All rights reserved.

Keywords: Ultrasonic welding; Ultrasonic butt welding; Welding of aluminum and stainless steel; Welding of stainless steel specimens; Hardnessdistribution of welded part

1. Introduction

Welding characteristics of stainless steel and alumi-num plate specimens of 6.0 mm thickness by a 15 kHzultrasonic butt welding system were studied. There areno detailed welding condition data of these specimensalthough the joining of these materials are required dueto anticorrosive and high strength characteristics for notonly large specimens but small electronic parts especially.Aluminum and stainless steel specimens, and stainlesssteel specimens of 6.0 mm thickness were welded end toend using a 15 kHz ultrasonic butt welding equipmentwith a vibration source using eight bolt-clampedLangevin type PZT transducers of 70 mm diameter and a50 kW static induction thyristor power amplier. Thealuminum, aluminum alloy and stainless steel platespecimens were joined with almost equal to aluminum

strength. The stainless steel plate specimens electrolyti-cally polished were joined with welding strength almostequal to the material strength under rather large vibra-tion amplitude of 25 l m (peak-to-zero value), staticpressure 70 MPa and welding time of 1.03.0 s.

From the results of measurements of hardness adja-cent to the welded part, hardness of aluminum wasfound to decrease near the welded surface. Hardnessof stainless steel decreases at the areas approximately2 mm away from the welded surface but increases byapproximately 20% near the welded surface. The increasein hardness due to ultrasonic vibration was found inwelding of these materials, which was on contrary to thephenomenon of decreasing hardness due to ultrasonicvibration observed in many industrial applications.

The combinations of aluminumstainless steel andstainlessstainless steel specimens were reported as thatthe materials are possible to join each other by ultra-sonic welding, but there were no report about weldingconditions of large specimens with welded strength nearto the material strength excepting small specimens.Using the butt welding equipment, as an example, theobtained required vibration velocity is real value without

Ultrasonics 40 (2002) 371374www.elsevier.com/locate/ultras

*

Corresponding author. Tel.: +81-45-481-5661; fax: +81-45-491-7915.

E-mail addresses: [email protected], [email protected](J. Tsujino).

0041-624X/02/$ - see front matter 2002 Elsevier Science B.V. All rights reserved.PII: S 0 0 4 1 -6 2 4 X(0 2 )0 0 1 2 4 -5


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slippage such as a conventional ultrasonic lapped weld-ing equipment. The obtained data in this paper are fun-damental welding conditions for joining ring or spotshape parts of the products such as small and thin motorsof hard disk drive and the others. Of course, adequatewelding equipments must be developed for special ap-

plications including complex vibration systems.

2. Conguration of a butt welding equipment

Fig. 1 shows an arrangement of an upper and a lowerwelding tip, welding specimens and clamping vices forultrasonic butt welding of specimens end to end. Theultrasonic butt welding system consists of a 15 kHzpowerful ultrasonic vibration source, an upper passivevibration system and a welding frame with hydraulicstatic pressure sources to clamp the welding specimens.The vibration source was driven by a 50 kW static in-duction thyristor power amplier [14]. The driving sidespecimen is clamped by a metal vice for avoiding thefatigue failures by transverse vibration of the specimen ata transverse nodal position where was carefully chosenfor the material and dimensions of the welding speci-mens. The clamping position is shown in Fig. 1.

The welded surfaces were driven to vibrate parallelto each other by welding tips and were welded togetherend to end. The welding specimens used were 6-mm-thick and 1020-mm-wide aluminum (JISA1100P, JI-SA5052P) and stainless steel (SUS304P) plates. Thewelding surfaces were nished to be at by a milling

machine. The specimens were degreased and cleaned bychlorothene and given no further treatment.

3. Welding characteristics

Fig. 2 shows (1) upper view, (2) side views and (3)cross-sections of the welded (a) aluminumstainless and(b) stainless steelstainless steel specimens. The weldedsurface of aluminumstainless steel is linear, and thin

burrs are produced only at the side of the aluminumspecimens because the hardness of aluminum is less thanthat of stainless steel. The welded surface are difficultto observe in the cross-section of the completely joinedstainless steel specimens but some cracks are found indefectively joined specimens.

Fig. 3 shows broken conditions of welded aluminumalloy-stainless steel and stainless steel specimens aftertensile test.

The relationship between welding tip vibration am-plitude and weld strength of 6-mm-thick and 20-mm-wide aluminum and stainless steel specimens is shownin Fig. 4. The welding tip vibration amplitude is alteredfrom 17 to 27 l m (peak-to-zero value). The staticclamping pressure at the welding surface is 20 MPa andthe welding time is maintained at 2.0 s. The weldstrengths obtained are near to the aluminum specimensstrength over all vibration amplitude range. Electricinput power was approximately 4 kW.

Fig. 1. 15 kHz ultrasonic butt welding equipment using an upper and alower welding tips, and hydraulic vices for clamping welding specimensand inducing static pressure to welding surface.

Fig. 2. Welded conditions of 6-mm-thick, 10-mm-wide stainless steelplate specimens. (1) Upper view, (2) side view and (3) cross-section of welded 6-mm-thick, 10-mm-wide (a) aluminum alloystainless steeland (b) stainless steel plate specimens.

Fig. 3. Broken conditions of welded specimens after tensile strengthtests. (a) Aluminum alloystainless steel specimen and (b) stainlesssteel specimen.

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The relationship between welding tip vibration am-

plitude and weld strength of 6-mm-thick and 10-mm-wide stainless steel specimens is shown in Fig. 5. Thewelding tip vibration amplitude is altered from 18 to 30l m (peak-to-zero value). The static clamping pressure atthe welding surface is 70 MPa and the welding time ismaintained at 3.0 s. The maximum weld strength about450 MPa is obtained under vibration amplitude 23 l m.

Hardness distributions are measured by a Vickersmicro-hardness tester along the cross-sections of thewelded specimen at the upper, center and lower partsacross a welding surface. Fig. 6 shows the hardnessdistribution along a weldment section across a weldedsurface of 6-mm-thick aluminum alloy and stainless steelspecimens. A decrease in hardness of the aluminumspecimen adjacent to the welded surface is noted, whilethat on the stainless steel side is observed in the area 2mm away from the welded surface and an increase inhardness is noted adjacent to the welded surface. Theincrement is largest along the central part of the sectionas compared with the upper and lower parts, which areclose to a clamping vice, due to heat conduction. The

maximum increment of hardness measured is over 20%in the stainless steel specimen. Fig. 7 shows the hardnessdistribution of 6-mm-thick stainless steel specimens. Thedecrease and increase in hardness are also noted adja-cent to the welded surface of the stainless steel specimen.

The increase in hardness is observed for the rst time,which is contrary to the decreases in hardness beingnoted in various high-power ultrasonic applications.

Fig. 8 shows the relationship between the tempera-ture, the heating time and the hardness of the stainlesssteel specimen, which was measured after heating in thefurnace. The hardness of the stainless steel increasesaccording to rather low heating temperature and shorttime due to the aging effect of stainless steel.

The hardness of the stainless steel specimen increasesslightly as temperature increases to 950 C, decreases in

Fig. 4. Relationship between vibration amplitude, input power andweld strength of 6.0-mm-thick and 20-mm-wide pure aluminum andelectrolytically polished stainless steel plate specimens.

Fig. 5. Relationship between vibration amplitude, input power andweld strength of 6.0-mm-thick and 10-mm-wide stainless steel platespecimens.

Fig. 6. Hardness distributions along a cross-section of a 6.0-mm-thickand 10-mm-wide welded aluminum alloystainless steel specimen atupper, center, lower parts. Welding time: 1.0 s.

Fig. 7. Hardness distributions along a cross-section of a 6.0-mm-thickand 10-mm-wide welded stainless steel specimen at upper, center, lowerparts. Welding time: 2.5 s.

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the range between 950 and 1000 C, and then increaseswhen the temperature exceeds 1200 C [5].

In the absence of ultrasonic vibration and staticpressure, the increase in hardness of stainless steelspecimens could be attributed to such high temperaturerise of over 1200 C at the weldment. However thehardness increase effect should actually ascribed mainlyto the vibration as no visible light emission due to thehigh temperature rise at the welded part was observed.In fact, the maximum temperature rise directly mea-sured from the thermo-electromotive force among alu-minum, copper and steel was only 441 C [4].

4. Conclusion

Welding characteristics of stainless steel and alumi-num plate specimens of 6.0 mm thickness by a 15 kHzultrasonic butt welding system were studied.

Aluminum and stainless steel specimens, and stainlesssteel specimens of 6.0 mm thickness were welded endto end using a 15 kHz ultrasonic butt welding equip-ment with a vibration source using eight bolt-clampedLangevin type PZT transducers of 70 mm diameter anda 50 kW static induction thyristor power amplier. Thealuminum, aluminum alloy and stainless steel platespecimens were joined with almost equal to aluminum

strength. The stainless steel plate specimens electrolyti-cally polished were joined with welding strength almost

equal to the material strength under rather large vibra-tion amplitude of 25 l m (peak-to-zero value), staticpressure 70 MPa and welding time of 1.03.0 s.

Hardness of aluminum was found to decrease nearthe welded surface. Hardness of stainless steel decreasesat the areas approximately 2 mm away from the welded

surface but increases by approximately 20% near thewelded surface. The phenomenon of increasing hardnessdue to ultrasonic vibration was observed although onlydecreasing hardness was noted in previous studies. Thehardness increasing effect may be applied to the partialhardening of materials due to vibration; in contrast, thehardness decreasing effect may be applied to the relax-ation of residual stress at the welded metal surface.

The combinations of aluminumstainless steel andstainlessstainless steel specimens were reported as thatthe materials are possible to join each other by ultra-sonic welding, but there were no report about weldingconditions of large specimens with welded strength nearto the material strength excepting small specimens asyet. Using the ultrasonic butt welding equipment, as anexample, the required vibration velocities revealed inthis paper are real values without slippage between thewelding tip and the upper specimen in the case of aconventional ultrasonic lapped welding equipment. Theobtained data are fundamental welding conditions for joining ring or spot shape parts of the products such assmall and thin motors of hard disk drive and the others.Of course, adequate welding equipments must be de-veloped for special applications including complex vi-bration systems.

References

[1] J. Tsujino, T. Ueoka, Ultrasonic butt welding of aluminum,anticorrosive aluminum and copper plate specimens, in: Proc. IEEE1988 Ultrasonics Symp., IEEE, New York, 1989, p. 496.

[2] J. Tsujino, T. Ueoka, Y. Susaki, M. Ogawa, Y. Hirasawa, Y.Fujita, Jpn. J. Appl. Phys. 32 (1993) 2441.

[3] J. Tsujino, T. Ueoka, I. Watanabe, Y. Kimura, T. Mori, K.Hasegawa, Y. Fujita, T. Shiraki, M. Motonaga, New methods of ultrasonic metal welding, in: Proc. IEEE 1993 Ultrasonics Symp.,IEEE, New York, 1994, p. 405.

[4] J. Tsujino, T. Ueoka, Y. Asada, S. Taniguchi, Y. Iwamura, Jpn.J. Appl. Phys. 37 (1998) 2996.

[5] J. Tsujino, T. Ueoka, T. Kashino, F. Sugahara, Jpn. J. Appl. Phys.38 (1999) 4254.

Fig. 8. Relationship heating time and hardness of 6-mm-thick stainlesssteel specimen under temperatures of 350, 400 and 500 C.

374 J. Tsujino et al. / Ultrasonics 40 (2002) 371374

Ultrasonic Butt Welding of Aluminum, Aluminum Alloy

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