Neranuch Usamith1 and Purit Thanakijkasem1,*
1Division of Materials Technology, School of Energy, Environment and Materials King Mongkut’s University of Technology Thonburi
126 Pracha Uthit Rd., Bangkok 10140, Thailand
Keywords: Tube hydroforming, Shape distortion, SS304 bellow, Springback.
Abstract
This work was aimed to study tube hydroforming of SS304 bellows. A recent review on hydroforming can be seen in [1]. A springback effect in hydroforming process of SS304 was discussed by using Hill theory in [2]. The tube material in this work was SS304 with the initial thickness of 0.4 mm. Two shapes of the bellows were studied. In addition, different processing conditions were explored to optimize the process. Finite element analysis was conducted to study the process. The applied pressure and the gap spacing dominantly affected the formability.
A significant shape distortion was found. The main source of shape distortion is springback in the material. Two different material models were applied to observe the prediction effectiveness in springback prediction. The simulation agreed well with the experiment
The main variables were the part shape, i.e., Shape1 = S1 and Shape2 = S2, and the processing conditions, i.e., the applied pressure (P) and the gap spacing (G). For formability issue, both shapes were observed at different pressures and gaps as shown in Fig. 1.
(a) (b)
(c) (d)
Figure 1: Formability from G = 5.96 mm at (a) S1 and P=10 MPa, (b) S1 and P=15 Mpa, (c) S2 and P=10 MPa, and (d) S2 and P=15 MPa.
To observe the effect of the gap spacing, P = 15 MPa was chosen because a lower pressure was typically desired in real manufacturing. Fig. 2 showed SP from MAT37 and MAT125 for S1 and S2 at G = 5.96, 6.5, 7.0, 7.5, 8.0 mm. The estimated SP from MAT125 was larger than that from MAT37. Shape2 caused less sprinback amount when compared to Shape1.
39
Tube hydroforming (THF) process can successfully produce the bellow of interest with the right combination of the processing conditions through analysis and design with FEA. FEA as a part of CAE is an important tool to explore the forming window. Springback is an important problem needed to be solved for products under a high commitment. For this bellow, a kinematic model like YU is needed to analyze and design a proper THF process.
Figure 2: Springback from P=15 MPa and G = 5.96, 6.5, 7.0, 7.5, 8.0 mm.
REFERENCES
[1] Lee M.G., Korkolis Y.P., Kim J.H., 2015, Recent developments in hydroforming technology, Journal of Engineering Manufacture, 229 (4), pp. 572-596.
[2] Sun Z., Lang L., 2017, Effect of stress distribution on springback in hydroforming process, The International Journal of Advanced Manufacturing Technology, 93, pp. 2773-2782.
40
9th INTERNATIONAL CONFERENCE ON TUBE HYDROFORMING (TUBEHYDRO 2019) November 18-21, 2019, Kaohsiung, Taiwan T1-2
Experimental Investigation of Tube Drawing Process with Diameter Expansion
Shohei Kajikawa1,*, Hikaru Kawaguchi1, Takashi Kuboki1, Isamu Akasaka2, Yuzo Terashita2 and Masayoshi Akiyama3
1 Department of Mechanical and Intelligent Systems Engineering, The University of Electro-Communications,
1-5-1 Chofu Gaoka, Chofu-shi, Tokyo, 182-8585, Japan
2 Miyazaki Machinery Systems Co., Ltd., 1 Nii, Kaizuka-shi, Osaka, 597-8588, Japan
3 Akiyama Mechanical Engineering Consulting,
2-7-306 Tanaka Sekiden-cho, Sakyo-ku, Kyoto-shi, Kyoto, 606-8203, Japan Keywords: Drawing, Flaring, Tube expansion, Thickness reduction.
Abstract
Thin-walled tubes, which is used for various machine components, contribute reduction in size and weight of various machines for environmental protection. The thin-walled tube is manufactured from rather thick-walled raw tubes by multi-pass drawing which is the conventional cold working of tube, and determines many properties of the tube [1]. However, many drawing passes are needed for manufacturing very thin-walled tubes. This is because the tube tends to fracture in the drawing process when the thickness reduction is too large for one drawing pass. Therefore, production cost increases with the increase of the number of the drawing passes.
This paper proposes a tube drawing method with diameter expansion for manufacturing thin-walled tubes effectively. In the proposed method, the tube end is flared by plug pushing into the tube in first process, and then the tube is expanded by drawing the plug in axial direction while the flared end was chucked in second process. Because the tube wall stretches biaxially in axial and hoop direction, the thickness should be reduced effectively compared to the conventional drawing with the diameter shrink. In this study, forming limit, thickness reduction and deviation were investigated by a series of experiments in the proposed method.
At first, effects of the tube material and flaring shape on maximum flaring ratio Ef_max were
0 0.2 0.4 0.6 0.8 1
0 1 2 3 4 5
Maximum flaring ratio Ef_max
Initial thickness t0[mm]
AA1070 (Taper)
STKM13C (Taper) STKM13C (Taper-straight)
Buckling Crack α
dp d0
di0t0
Tube
Plug Holder
dif
(a) Set-up
(b) Flaring shape
dp≒dif
Only taper Taper-straight ls
(c) Defect mode and maximum flaring ratio Ef_max Figure 1: Investigation about effect of tube material and flaring shape on maximum flaring
ratio Ef_max.
41
investigated by the experiment as shown in Fig. 1. Initial diameter d0 of the tube was 30 mm, and half angle α of the plug was 12°. Flaring shapes were two types, which were only taper and taper-straight, as shown in Fig. 1 (b). Taper-straight shape was needed for the next drawing process, and the plug pushed until the straight length ls achieved to 20 mm in the case of taper-straight. Ef_max was defined as a maximum value before defect occurrence. Fig. 1 (c) shows the defect mode and Ef_max. The defect mode changed by the tube material. Buckling, which appeared at the cylinder portion near the holder, was easy to occur when an aluminum tube of AA1070 was used. Crack, which appeared at the flared edge, occurred when a steel tube of STKM13C was used. Ef_max increased with an increase in the tube initial thickness t0. In addition, Ef_max of taper-straight shape was lower than that of only taper shape. This is because the tube wall bent between the taper and the straight portion, and then the outside of the tube wall was stretched biaxially in the axial and the hoop direction.
The experiment of the expansion drawing was carried out using the tube which was flared to the taper-straight shape as shown in Fig. 2 (a). Initial diameter d0 and half angle α of the plug were 30 mm and 12°. It was possible to produce the thin-walled tubes successfully, but the tube cracked due to biaxial stretching in axial and hoop direction when the expansion ratio Ed was too large as shown in Fig. 2 (b). Fig. 2 (c) shows the effect of Ed on the thickness reduction γ and thickness deviation λ of the drawn tube. γ increased with the increase in Ed. Maximum thickness reduction γ_max were 0.29 at the maximum expansion ratio Ed_max of 0.31 when AA1070 was used, and this value of γ_max was higher than that of the conventional drawing with diameter shrink [2]. The increase in λ by the drawing was small in the range of Ed=0~0.23, but λ drastically increased when the local thinning appeared at the tube wall due to too large expansion such as Ed=0.31. Therefore, Ed should be set appropriately for producing the tube which λ is low.
Figure 2: Investigation about effect of expansion ratio Ed on thickness reduction γ and deviation ratio λ in drawing.
REFERENCES
[1] Kuboki, T., Tasaka, S., Kajikawa, S., 2017, Examination of working condition for reducing thickness variation in tube drawing with plug, COMPLAS XIV, Conference proceedings.
Barcelona, pp. 63-71.
[2] The Japan Society for Technology of Plasticity, 2017, Drawing -Drawing Technologies for Bar, Wire and Tube-, Corona Publishing, Tokyo, in Japanese.
Plug Shaft
Chuck Core
Flared portion dp
α
Tube t
(a) Schematic diagram of drawing
Success Crack
(b) Appearance of typical drawn tube
0 0.1 0.2 0.3
0 0.1 0.2 0.3 0.4
Thickness reduction ratio γ Thickness deviation ratio λ
Expansion ratio Ed AA1070, γ
STKM13C , γ
AA1070, λ
STKM13C, λ
(c) Thickness reduction and deviation of tube
42
9th INTERNATIONAL CONFERENCE ON TUBE HYDROFORMING (TUBEHYDRO 2019) November 18-21, 2019, Kaohsiung, Taiwan T1-3