機械外文翻譯 ----高強度鋼在u彎曲變形中的彎曲性和成型過程（英文）

1、Bendability and Forming Behaviour of High Strength Steel in U Bending OperationP. Kaewtatip1, N. Prasitkhetkhan1, A. Khantachawana1, V. Premanond1, R. Hato1, B. Sresomreong1, N. Koga21King Mongkut’

2、 s University of Technology Thonburi, Thailand; 2Nippon Institute of Technology, JapanSummaryIn this work, the bendability and forming behaviour of high strength steels in U bending were studied. The

3、sheet materials used in the experiments are (JIS) SAPH440 (thickness 2 mm), SPFH590 (thickness 2 mm) and SPFC780Y (thickness 1.2 mm). Firstly, minimum bend radius of each material was investi

4、gated. Next, the experiments to compare three different methods of minimizing springback were carried out. The first method is, so called; bottoming that is the reduction of sheet thickness a

5、t the bottom of the workpiece or at bended angle by 10%. The second one is bottom overbending, i.e., the method to overbend the workpiece at bottom by 6o. For this method, the punch havi

6、ng a concave bottom surface and the bottom pad having corresponded convex upper surface have been used. The last one is flange overbending, i.e., the method to overbend the flange of workpi

7、ece by 6o. This can be done by using the punch having side relief angle (taper punch). The punches and dies edge radii are 5 mm. The clearance between punch and die are determined to be

8、 the same as material thickness. Two kinds of sheet layouts were experimented, i.e., the sheets were placed in order that their rolling directions were (1) parallel and (2) perpendicular to

9、 the bend line. The results revealed that the springback angle increased with the strength of sheet material. The bottom and flange overbending methods are more effective to reduce springback t

10、han bottoming method. In addition, for bottoming method, the force required was about 8 times higher than conventional bending force.1. IntroductionNowadays, high strength steel sheets have been

11、 widely used in automobile industry in order to reduce weight of the vehicles which is strongly related to their fuel consumption rate [1~4]. However, it is generally known that the strengt

12、h of the sheets, which is relatively higher than that of the conventional carbon steel sheets, leads to their low formability and high springback of the deformed parts. Many works proposed

13、to reduce springback of the high strength steel. For examples, Mori [2] proposed to control the springback of the V bended part by utilizing CNC servo press to reduce the sheet thickness a

14、t bend angle. Next, Yamano [3] has been studied to reduce side wall curl of the draw- bended U- shape part by using so called overrun inducing- punch. Yoshida [4] studied a crash forming me

15、thod to reduce springback of the part made of high strength steel sheet. Yanagimoto [5, 6] showed that springback- free forming of high strength steel sheets could be achieved by forming the

16、 sheet at elevated temperature in the range of warm working temperature (higher than 750 K but considerably lower than hot working temperature). The methods to reduce springback used in the

17、 previous works are mostly based on bottoming and overbending principles. In this work, the experiments to compare the results of three different methods of minimizing springback were carried o

18、ut in order to verify their effectiveness in elimination the springback of high strength steel sheet. Those methods are bottoming, flange overbending and bottom overbending, respectively. In ad

19、dition, the bendability which is represented by minimum bend radius was also investigated for the sheet having the strength ranged from 440 to 780 MPa. 2. Experimental setup and MethodologyThre

20、e kinds of sheet materials, as shown in Table 1, were used in the experiment. The sheets were cut into rectangular shape with dimension of 120 x 50 mm. The workpieces have been deformed,

21、by the tools in Fig. 1(a), into U shape having dimension as shown in Fig. 1(b). The die set is shown in Fig. TA1-2 ICTP 2008 (The 9th International Conference on Technology of Plasticity)295(a) Bottom

22、ing (b) Flange overbending (c) Bottom overbending Fig. 3: Three different methods of elimination springback used in the experiments3. Results and discussions3.1. Bendabilities (minimum bend radius)The

23、 ratio of bending force required and sheet thickness for each material are shown in Fig. 4. It is clearly shown that larger forces are required for the material having higher strength and

24、for the punch having smaller edge radius. In cases of using the punch with sharp edge (RP = 0), the required forces are largest which are 1.87~1.90 times of those when using the punch hav

25、ing RP = 5 mm. The results of minimum bend radius are shown in Table 2. The deformed parts were observed by both visual method and optical microscope. Four different symbols were used to

26、 distinguish the quality of parts. The definition of each symbol is indicated below the same Table. The sample pictures, in the cases of using sharp- edge punch, corresponded to each symbol a

27、re shown in Table 3. As the results, for all three kinds of sheet materials, bending perpendicular to rolling direction is easier than bending parallel to rolling direction, as generally know

28、n. Bendabilities, which are represented by minimum bend radius, became worse with increasing of strength of materials. For SAPH440, the workpieces without fracture could be obtained although us

29、ing the punch with sharp edge (RP = 0) when bending perpendicular to rolling direction. On the other hand, SPFH590 could be successfully bended if the ratio of punch radius and sheet thickne

30、ss was larger than 0.50. Moreover, the same ratio should be larger than 0.83 in the case of SPFC780Y sheet. These might be explained by the different values of the ductility of the sheet

31、materials. The minimum bend radius is smaller for the material having higher ductility (elongation at break as shown in Table 1).3.2. Comparison of different methods of springback eliminationTh

32、e force- travel diagrams of forming SAPH440 workpieces by conventional U bending, bottoming, flange overbending and bottom overbending are shown in Fig. 5. The maximum forces required for Fig. 4

33、: Forces required for U bending of each materialR5 6oR50.1t 6oR513.710.8 9.5 7.318.514.911.2 9.724.419.816.312.9051015202530R0 R1 R2 R5SAPH440SPFH590SPFC780YPunch edge radius: RP (mm)Bending force/ Sheet t