Effect of the Initial Shape of L-angle Member into Bending Properties on Push-Through Bending of Aluminum Extrusion Section

Transcription

1 Effect of the Initial Shape of L-angle Member into Bending Properties on Push-Through Bending of Aluminum Extrusion Section Hidemitsu Hamano, and Hisaki Watari Abstract Push-through bending of an aluminum extruded section is a relatively new bending method. Since this method realizes complete three-dimensional bending, many studies on the bending properties of simple cross-section with circular and square pipes have been reported. This report describes the push-through bending properties on 7 system aluminum extruded section with an industrially practical asyetrical cross section. We analyze an effect of the initial deformation of materials to bending accuracy and bending properties of nonuniform cross-sectional material which was removed by cutting. As a result of study, it was found that in order to bend materials accurately with.1 x -3-1 or less curvature on push-through bending, the distance of the gyro die must be controlled to accuracy of.5. Camber and twist tend to occur in the bending member when push-through bending is performed on a material with an asyetrical cross section. In order to prevent these irregular deformations, it is necessary to move the gyro die in the direction perpendicular to the bending direction and then rotate the die. The dimensional accuracy after bending is significantly influenced by the dispersion of initial deformation. In particular, when the initial deformation scatter of materials significantly differ in the antiplane direction of bending, there is a tendency for the slippage amount to increase with the push-through bending. Even in the case of materials with a nonuniform cross section, a part of which was intermittently cut in the extrusion direction, localized neck due to push-through bending was not observed in this experiment. Thus, a smooth bending member was obtained. Accordingly, it was confirmed that a bending member with a nonuniform cross section can be easily bended without cutting after performing 3D bending on materials. Keywords aluminum extrusions, push-through bending, tube forming, forming condition, I. INTRODUCTION ECENTLY, The development of environmentally friendly Rhybrid automobiles and fuel-cell-powered vehicles has been accelerated. Space frames and sub frames constructed using an aluminum extruded section are frequently used for the Hidemitsu Hamano is a Senior Researcher of JFE Technology Research Centre, Edobori, Nishi-ku, Osaka 55 2 Japan, ( hidemitsu_hamano@yahoo.co.jp). Hisaki Watari has been working as a full time Professor at the Department of Mechanical System Engineering, Graduate School of Science and Technology, Gunma University, 29-1 Hon-cho, Ota, Gunma Japan. ( watari@gunma-u.ac.jp). The research topics are manufacturing technology for light weight metals, such as aluminum and magnesium alloys. bodies of these types of automobiles [1]. However, the extruded section is rarely used in the straight form and the materials are often subjected to complex bending or hydroforming after bending [2]. In most cases of bending, for example rotary draw bending, stretch bending and press bending, a desired shape is realized by pressing the work piece in a die. Thus, a complete three-dimensional (3D) free curve shape is hard to obtain [3]. Meanwhile, push-through bending uses a pair of dies which fit the cross section of the work piece and can process it into various 3D free curve shape through a single process when the machine is operated under NC control; it is an excellent method [4]. Therefore, even though push-through bending is a relatively new processing method, many studies on the bending properties of simple cross-sectional with circular and square pipes have been reported [5-7]. We have studied the effect of mechanical properties of work pieces, lubricants, processing conditions and the dies on bending properties in the case of push-through bending using a square pipe shaped aluminum extruded section [8-9]. In this work, using a practically applicable A7 system aluminum extruded section with an asyetrical cross section (L-angle member), we studied the effect of the initial deformation amount of materials on the bending accuracy of push-through bending and the bending properties of nonuniform cross-sectional materials, a part of which was removed by cutting. II. EXPERIMENTS A. Experimental equipment Fig. 1 shows a schema of push-through bending. In this processing method, a long work piece is passed through fixed and gyro dies, and pushed from behind. Then, by moving the gyro die upward, downward, left and right, and inclining it at certain angles, the work piece is bent into the desired shape. Movements of all five axes of the gyro die and movements of the work piece in the push-through bending direction under NC control enable the realization of a complicated bending shape. The characteristics of this processing method are that the gyro die can be simultaneously bent in upward, downward, left and right directions, complete 3D bending is performed and the work piece can be processed into a shape with a continuously changing curvature unlikely in the case of rotary draw bending 38

2 which processes the work piece into a shape with only a single curvature. In addition, with a pair of dies, various bending shapes are possible, which allows the material design to be changed to some extent. The cost of dies is low. Furthermore, by inserting a mandrel into a thin-walled tube, changes in the cross-sectional shape and decrease in the thickness of the material can be prevented. The main specifications of the bending machine used in this study are shown in Table 1 and a photograph is shown in Fig. 2. The material in the photograph is an A6N1 aluminum extruded section with a cross section of 13 x 83 and thickness of 6. The total length of the equipment was approximately 2 m. The dimensional accuracy of the bending member is heavily dependent on the operational accuracy of the gyro die. This equipment with a repeat operational accuracy of within twelve μm is a highly accurate machine. Die Support Mandrel θb Fig.3 Cross-section of L-angle member () B. Tested materials Fig. 3 shows the L-angle member (hereafter, referred to as non-cut material) used in the experiment. It is difficult to accurately cut a part of the material which is bent three-dimensionally such along the designated shape. Therefore, we performed push-through bending on a straight material, a part of which was already cut, and studied whether or not a nonuniform cross-sectional bending member could be obtained. Fig. 4 shows a nonuniform cross-sectional material (hereafter, referred to as cut material) a part of which was intermittently cut in the extrusion direction. The mechanical properties of the A775-T73 test specimen are a proof stress of 67 MPa, tensile strength of 663 MPa and elongation of.2%. Pusher Sample Fixed die Distance of dies: L Stroke of gyro die: y Fig.1 Schema of push-through bending TABLE I SPECIFICATION OF BENDING MACHINE Length of the usable section / ~6 Largest section size / 2 2 Maximum applied force /kn 39 Maximum bending force /kn 57 Maximum bending torque /kn m 16 Fig. 4 Measurement of cut part in non-uniform cross-sectional material (cut material) () Fig. 5 Curvature of bent material (-1) 1 o Fixed die Z Material (No-cut) Y X Fig.2 Appearance of machine Fig.6 Measurement coordinate and bending direction 39

3 C. Experimental methods In this experiment, a bending material with continuously changing curvature as shown in Fig. 5 was used as the subject in order to study the bending properties related to the practically bent material. However, since the situation under which the curvature changes continuously is difficult to illustrate, the curvature when the longitudinal direction was divided into 16 parts is shown in Fig. 5. The Y direction is the basic bending direction, but since the cross section is moved asyetrically around the midpoint of the figure, when the die is bent in the Y direction, camber in the Z direction and twist around the X axis develop as shown in Fig. 6. Accordingly, in this study, the movement of dies was controlled such that the gyro die was prograed to be moved in the Z direction, camber and twist were prograed to be reduced by rotating the gyro die around the X axis and a continuously changing two-dimensional (2D) curvature was realized. The bending angle of the die θ b which was added to the stroke with the gyro die y was determined to be.6 y degrees. The distance between the fixed die and the gyro die L was. The push-through speed of the material was 63 /s. III. RESULTS AND DISCUSSION A. Effect of the stroke with of a gyro die on the curvature The curvature of the bending member used in this study was.1 x -3-1 or less, therefore first using non-cut material, the effect of the stroke with a gyro die on the curvature was studied. As shown in Fig. 7, y=9.~9.2 was optimal for obtaining the targeted curvature (.8~.1 x -3-1 ), however, Fig. 7 reveals that a slight difference in the stroke with a gyro die greatly changes the curvature. Thereby, in order to obtain the bending material shown in Fig. 4, the stroke with a gyro die was prograed to be controlled to intervals of.5 B. Effect of the initial deformation amount of extruded section on the bending accuracy Since the extruded section employed in this study was subjected to annealing, solution heat treatment and artificial aging, twist as the initial deformation rarely occurred, but camber in the Y direction which was the extrusion direction and Curvature ρ / Stroke of gyro die Y / Fig.7 Effect of Stroke of gyro die in the curvature Defference between materials and straight line / Difference between targeted and actual dimensions / No.1 Y direction -6 No.1 Z direction -8 No.2 Y direction No.2 Z direction Fig.8 Initial deformation in each measurement positions No.1 Y direction No.1 Z direction No.2 Y direction No.2 Z direction Fig. 9 Difference between targeted and actual dimensions in each measurement positions Before bending After bending Fig. Change into angle of cross section in non-cut material Angle of cross section /deg In the Z direction which was perpendicular to the Y direction occurred. Material No. 1 shown in Fig. 8 represents materials with little initial deformation in either Y or Z direction, whereas No. 2 represents materials with a large initial deformation amount in both Y and Z directions, both of which were non-cut materials as explained previously. In particular, Fig. 8 shows 3

4 that the initial deformation amount of material No. 2 in the Z direction was large and the material was camber by. at maximum. Fig. 9 shows the dimensional differences between the targeted dimensions and the actual dimensions of the bending member in the Y and Z directions on push-through bending by the same program. Material No. 1 with an initial deformation had a small difference at ±2 or less in Y and Z directions, whereas the difference of material No. 2 for which push-through bending was performed increased in both Y and Z directions above the initial deformation amount. We considered that this occurred because the program was developed with the presupposition that a material with good linearity as material No. 1 could be used, thereby, the difference between the targeted and actual dimensions of material No. 2 with a large initial deformation amount increased after push-through bending. Contrary to this condition, if the program were developed based on the presupposition that material No. 2 would be used, the difference of material No. 1 for which bending was performed would be large. Accordingly, in order to reduce the difference of the bending member, rather than improving the initial linearity (deformation amount) of a work piece, maintaining the difference of the work piece from the initial linearity to a constant value is essential. Meanwhile, the angle of cross section in the L-angle member after bending remains almost unchanged before bending as shown in Fig.. The difference between the initial angle and the angle after bending was approximately 1 at maximum. This tendency was similarly observed in both materials No.1 and No. 2. Fixed die A Part Fig.11 Distribution of equivalent strain of cut material by FEM analysis Fig.12 Appearance of bended cut materials Difference betwwen targeted and actual dimensions / Position from edge of material / Fi 13 Diff b d d l Fig.13 Difference between targeted and actual dimensions in each measurement positions Angle of cross section / deg No.3 Befor bending No.3 After bending No.4 Befor bending No.4 After bending 88. Fig.14 Change into angle of cross section in cut material C. Effect of bending accuracy on cut materials (nonuniform cross-sectional materials) Since the cut materials shown in Fig. 4 present discontinuous flexural rigidity in the longitudinal direction, it is highly likely that a smooth curvature representing a continuous change of the curvature will not be obtained if the bending process is carried out without adjustment. Therefore, we studied the bent shapes of materials in the longitudinal direction and the equivalent strain using DEFORM which is a widely used software for the finite element method (FEM); the results are shown in Fig. 11. As indicated by the part labeled A in Fig. 11, there is a part which was approximately.1 higher than the surrounding distortion, but no local deformations are observed in the entire shape. This is because a web plate which governs flexural rigidity induces uniform deformation, even if some strain distribution occurs on the flange plate since the basic cross section is L-shaped. According to the results of Fig. 11, it was confirmed that plastic deformation occurred from inside a fixed die. Fig. 12 shows the appearance of cut materials subjected to push-through bending. Similar to the results of numerical analysis, a bending member presents a smooth curvature at the 311

5 discontinuous cross section of a cut area. Fig. 13 shows the difference from the targeted dimensions at seven cut materials with relatively small initial deformation; the cut materials were subjected to push-through bending following the same programs. Figs. 13 and 9 reveal that the difference of cut materials from the targeted dimensions after being bent was greater than that of non-cut materials. We considered that this was because the flexural rigidity of the cut materials was smaller than that of the non-cut materials. Meanwhile, as predicted by numerical analytical results in Fig. 11, the angle of L-shaped cross section when the cut materials were subjected to push-through bending remained almost unchanged. Fig. 14 shows changes in the angle of L-shaped cross-section before and after bending in materials No. 3 and No. 4 with relatively smaller initial deformation amounts. Even after push-through bending, changes in the angle remained within.5. REFERENCES [1] H. Yoshida, H. Ikeda, K. Shibue, Y. Nishimura, Sumitomo Light Metal Technical Reports, 38-1 (1997), [2] K. Kaida, K. Hirano, T. Fujii, M. Yoshida, R&D Kobe Steel Engineering Reports,47-2 (1997),17-2. [3] M. Hino, R&D Kobe Steel Engineering Reports,47-2 (1997),2-5. [4] H. Hamano, JETI,47-2(1999),3-5. [5] M. Murata, Journal of the JSTP (1997) [6] M. Murata, Journal of the JSTP (1996) [7] M. Murata, J. Jpn. Inst. Light Met.46-12(1996) [8] H. Hamano, H. Nishimura, Y. Hagiwara, Y. Nagai, Journal of the JSTP (21) [9] H. Hamano, H. Nishimura, Y. Hagiwara, Y. Nagai, K. Aoki, Journal of the JSTP (21) IV. CONCLUSION As a practical example of cross-sectional shapes in push-through bending, an A775 extruded section with an asyetrical cross section (L-angle member) was used. Then, the bent shape of the extruded section with a uniform cross section and that of the extruded section with a non-uniform cross section, a part of which was continuously removed in the extruded direction, were studied. The following conclusions were drawn. (1) To bend the material by.1 x -3-1 or less on push-through bending, the stroke with a gyro die must be controlled to intervals of.5. (2) When asyetrical cross-sectional shaped materials are subjected to push-through bending, camber and twist occur in the bending member if a gyro die is simply moved in the bending direction. To prevent this irregular deformation, the gyro die must be moved in the direction perpendicular to the bending direction and it must be rotated. (3) Dimensional accuracy of the material after bending is greatly influenced by scattering the initial deformation amount. In particular, when the initial deformation amounts of materials heavily are uneven in the bending antiplane direction, there is a tendency for the difference between targeted and actual dimensions to increase with push-through bending. (4) In the case of a non-uniform cross-sectional material, a part of which was intermittently cut in the extrusion direction, localized neck due to push-through bending was not observed in this experiment. A smooth bending member was obtained. Accordingly, it was confirmed that a bending member with a non-uniform cross section can be easily bended without cutting after performing 3D bending on materials. 312