Available online at ScienceDirect. Procedia Engineering 81 (2014 )

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1 Available online at SieneDiret Proedia Engineering 81 (214 ) th International Conferene on Tehnology of Plastiity, ICTP 214, Otober 214, Nagoya Congress Center, Nagoya, Japan Streth press bending of AZ31 magnesium alloy extruded square tube Osamu Hasegawa a, *, Ken-ihi Manabe b, Tsutomu Murai a Tokyo Metropolitan College of Industrial Tehnology,1-1-4,Higashiooi,Shinagawa-ku,14-11, Japan b Tokyo Metropolitan University,1-1,Minami-Osawa,Hahioji-shi, , Japan Japan Siene and Tehnology Ageny, -3,Yonbanho, Chiyoda-ku, ,Japan Abstrat The results of the experimental study on bending behaviour of AZ31 magnesium alloy extruded square tube under streth press bending are presented. Craking with bukling ours at ompressive side, but we an bend AZ31 tube at room temperature by means of applied axial tension during forming. The mehanism of bending behaviour of AZ31 magnesium alloy tube has been examined from the point of view of the position of neutral axis aording to the mehanial properties under tension and ompression and flow stress dependeny on strain rate The Published Authors. by Elsevier Published Ltd. by This Elsevier is an Ltd. open aess artile under the CC BY-NC-ND liense Seletion ( and peer-review under responsibility of Nagoya University and Toyohashi University of Tehnology. Seletion and peer-review under responsibility of the Department of Materials Siene and Engineering, Nagoya University Keywords: AZ31 magnesium alloy extruded square tube; Press bending behaviour; Room temperature; Dependeny on strain rate 1. Introdution In transportation systems, light metals that an be easily reyled must be used for the weight redution of automotive outer panels, energy absorption strutures, suspension parts, and so on. As an example, magnesium alloys are used for parts of the steering wheel, instrument panel, and seat struture. In order to use lightweight bent tubes in transportation systems, we have studied methods that prevent raking, bukling, and ross-setional distortion under press bending in 6 series aluminum [1] and AZ31 magnesium alloy extruded tubes [2]. In this study, a bendability improvement method for the press bending of AZ31 magnesium alloy extruded square tube is presented. We have applied wing-type dies [3] to streth press bending, whih an restrain raking at the * Corresponding author. Phone.: ; fax: address: hasegawa@s.metro-it.a.jp Published by Elsevier Ltd. This is an open aess artile under the CC BY-NC-ND liense ( Seletion and peer-review under responsibility of the Department of Materials Siene and Engineering, Nagoya University doi:1.116/j.proeng

2 Osamu Hasegawa et al. / Proedia Engineering 81 ( 214 ) ompressive side with axial tension [4]. Furthermore, we have onfirmed the effet of high strain rate on the bendability of AZ31 tube. Nomenlature R p Punh profile radius R Bending radius H Height of ross-setion of tube W, W 1 External and internal width of ross-setion of tube t Initial thikness of tube t t,t Outside and inside thikness of tube after bending t' (t t - t )/2 n Strain hardening exponent t, Average flow stress of tension side and of ompression side m Ratio of axial tensile stress to tensile strength of tubes (based on nominal stress) Position of neutral axis in the ross-setion at bending entre of tube y Co-ordinate for the height of ross-setion of tube 2. Experiment 2.1. Material Two kinds of AZ31 magnesium alloy square tubes, whih were extruded under different billet temperatures (623 K and 723 K), were used. In this paper, they are referred to as TP3 and TP4, respetively. The ross-setional shapes and dimensions are shown in Fig. 1. H t W t W = H =3mm t =2.mm 2.2. Tension and ompression test Fig. 1. Cross-setional shape and dimensions of square tube. Tension tests were performed in the room temperature with JIS13B test piees. The n-value was derived at a strain range from.2 to.3. Compression tests were performed with test piees that were ut from a square tube and finished with parallel end surfaes by a milling mahine. The ross-head speeds were and mm/min in both tension and ompression tests for the investigation of the strain rate effet. Before the high strain rate ompression test, there was a gap of over 2 mm between the ompression tool and the test piee Press bending experiment The bending dies are shown in Fig. 3. They were set on a 3 kn apaity press mahine. Bending is exeuted at room temperature. Bending onditions are shown in Table 1. Wing-type dies were used, whih had their positions of support (i.e., the distane between the support plane of the tube and the rotational support of the wing) designed to obtain about 3% strain in the length of the 3 mm region of the square tube.

3 2186 Osamu Hasegawa et al. / Proedia Engineering 81 ( 214 ) (a) (b) R p =1 Wing-type die Punh Profile support surfae Rotational enter of wing 3 Fig. 2. Press bending setup. (a) Appearane of bending die at lower dead point and (b) main parts and dimensions of tooling. Table 1. Bending onditions. Punh stroke per minute (spm) 6 Punh profile radius R p (mm) 1 Bending radius R (mm) 12 Ratio of bending radius and profile height R /H 4. Target bending angle (degree) 4 Total learane between die and material (mm). Kinemati visosity of lubriant on punh and dies (mm 2 s -1 ) 63 Temperature R.T. Internal mandrel without

4 Osamu Hasegawa et al. / Proedia Engineering 81 ( 214 ) Experimental results 3.1. Material Mehanial properties of material derived from tension and ompression test are shown in Table 2. There is no different between TP3 and TP4 remarkably, but strength fator of TP3 is slightly higher than TP4. Under high strain rate, both of materials have higher tesile proof stress and ompressive maximum stress. As a result, they have higher average flow stress in the ompressive side under high strain rate. Apperane of speimens after tests are displayed in Fig. 3. Table 2. Mehanial properties of material used. tension (JIS13B) Cross head speimen speed (mmmin -1 ) TP3 TP4 ompression Cross head speimen speed (mmmin -1 ) TP3 TP4 * = n, ** G.L.=2mm n * value F * Proof stress.2 (MPa) Value (MPa) Proof stress.2 (MPa) Tensile strength B (MPa) 22 Maximum stress MAX (MPa) Average flow stress t (MPa) strain range 24(.17) 24(.17) 24(.18) 24(.17) Average flow stress (MPa) strain range 12 ( (.11) 11 ( (.12 Breaking Elongation (%) Strain at maximum stress ** (%) b d a Fig. 3. Appearane of speimens after tests. (a) TP3 tension, (b) TP3 ompression. () TP4 tension and (d) TP4 ompression.

5 2188 Osamu Hasegawa et al. / Proedia Engineering 81 ( 214 ) Press bending The appearanes of the AZ31 alloy square tubes after press bending are displayed in Fig. 4. In the photograph, (a) and () are bent tubes of the same bending radius (R =12 mm) and target bending angle (4 degrees) under three-point press bending without axial tension. By applying axial tension, raks are prevented from ourring on the ompressive side ((b) and (d)). However, sine a mandrel was not used, bukling (i.e., wrinkling on the ompressive flange) and sagging (on the tensile flange) did our. a b d Fig. 4. Appearane of speimens after press bending. (a) TP3 without axial tension, (b) TP3 streth bending, () TP4 without axial tension and (d) TP4 streth bending. 4. Disussion It is known that the neutral surfae shifted toward the tensile side after bending beause the tensile and ompressive flow stresses and strains at the ompressive side inreased, and therefore, raking ourred on the ompressive side [4]. From the results of this study, it has been larified that raking was restrained by means of axial tension beause of the tendeny of the neutral surfae position to shift toward the ompressive side and the derease in the ompressive strain level in the press bending of AZ31 square tube. If the neutral surfae shifted a distane from the initial position, whih is the entroid of the ross setion, then an be expressed theoretially using the following formula based on the equilibrium fores at the ross setion of the square tube. It is assumed that thikening and thinning of wall our only at ompressive flange and at tensile flange eah other. 1 t H / 2 t t t t t W / 2t 1 m B H tt t W1 2t The oeffiient m is the ratio of tensile stress to tensile strength of the material. We substitute eah value to the formula (1), when m=.4t t =1.9 and t =2.1, we an obtain value, = -11. The absolute value is too large, but we an onfirm the tendeny of the neutral surfae position to shift onsiderably toward the ompressive side, against =7 (experimental value is ) under m=, without axial fore. (1)

6 Osamu Hasegawa et al. / Proedia Engineering 81 ( 214 ) Conlusions We an bend AZ31 magnesium alloy extruded square tube without raking by means of streth press bending applying wing-type dies under bending onditions of room temperature and R /H = 4.. The mehanisms of bendability enhanement are listed as follows. (1) AZ31 alloy has relatively high ompressive flow stress under high strain rate. (2) There is the tendeny that the neutral surfae position is shifted toward the ompressive side by the flow stress, thikness deviation of ross setion and the axial tension. Referenes [1] O. Hasegawa, H. Nishimura: Improvement methods of bending auray for 6 series aluminum alloy extruded shapes in press bending, Pro. ICAA7 (2), [2] O. Hasegawa, K. Manabe, N. Inoue, H. Nishimura: Effet of forming temperature on press bendability of AZ31 magnesium alloy tube, J. JSTP, 48-6 (27), (in Japanese). [3] O. Hasegawa, K. Manabe, H. Nishimura: Effet of wing-type die in Press bending of aluminum alloy extruded shapes, J. JILM, 7-6(27), (in Japanese). [4] O. Hasegawa, K. Manabe, T. Murai, H. Nishimura: Pro. 62nd JSTP (211), (in Japanese).