1、 1 Deep Drawing With Internal Air-Pressing to Increase The Limit Drawing Ratio of Aluminum Sheet Young Hoon Moon*t, Yong Kee Kang, Jin Wook Park, Sung Rak Gong Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University The effects of internal air-pressing on deep draw
2、 ability are investigated in this study to increase the deep drawability of aluminum sheet. The conventional deep drawing process is limited to a certain limit drawing ratio(LDR) beyond which failure will occur. The intention of this work is to examine the possibilities of relaxing the above limitat
3、ion through the deep drawing with internal air-pressing, aiming towards a process with an increased drawing ratio. The idea which may lead to this goal is the use of special punch that can exert high pressure on the internal surface of deforming sheet during the deep drawing process. Over the ranges
4、 of conditions investigated for AI-1050, the local strain concentration at punch nose radius area was decreased by internal air-pressing of punch, and the deep drawing with internal air-pressing was proved to be very effective process for obtaining higher LDR. Keywords: Deep Drawing, Internal Air-Pr
5、essing, Limit Drawing Ratio(LDR), AI-1050 1. Introduction Aluminum alloy sheets are inferior in press formability compared to the mild steel sheets. Most of the aluminum alloys have an r-value(plastic anisotropy value) between 0.7 and 1.0.Nonetheless, even though the r-values for the aluminum alloys
6、 are only about half of steel(Roger, 1991), they show, under the right circumstances, quite satisfactory drawing 2 behavior. Among the aluminum alloys some noticeable differences in forming behavior on the stamping shop floor have been observed(Roger, 1991； Lange, 1985) because the relationship betw
7、een the material, die design and test parameters, etc., versus the deep drawability may change with alloy systems. While many of the general metallurgical and die design principles that promote enhanced deep drawing are understood, the researches to improve the formability of aluminum sheet are stil
8、l insufficient. Deep drawing is a process for shaping flat sheets into cup-shaped articles without fracture or excessive localized thinning. t First Awhor Corresponding Author, E-mail: yhmoonhyowon.pusan.ac.kr TEL: +82-51-510-2472； FAX: +82-51-512-1722 Engineering Research Center for Net Shape and D
9、ie Manufacturing, Pusan National University, Pusan 609-735, Korea.(Manuscript Received August 7, 2000； Revised January 30, 2001) The design and control of a deep drawing process depends not only on the workpiece material, but also on the condition at the tool-workpiece interface, the mechanics of pl
10、astic deformation and the equipment used. The equipment and tooling parameters that affect the success or failure of a deep drawing operation are the punch and die radii, the punch and die clearance, the press speed, the lubrication and the type of restraint to metal flow(Hrivnak and Sobotoba, 1992；
11、 Date and Padmanabhan, 1992； Yossifon and Tisosh, 1991； Thiruvarudehelvan and Loh, 1993； Kawai et al., 1992； Johnson and Mellor, 1983). To establish the geometry of a part that can be successfully and economically fabricated from a given material, it is essential to know the limit to which the part
12、material can be formed without reaching failure. 3 This forming limit depends, in addition to the shape change and process conditions, on the ability of a material to deform without failure. The limiting drawing ratio(LOR), is commonly used to provide a measure of the drawability of sheet metal, bei
13、ng the ratio of maximum blank diameter to punch diameter under the drawing limit without failure(Thomas and Dadras, 1981； Leu, 1997； Chen and Sowerby,1996). It is well recognized that a high plastic anisotropy value(r-value) clearly indicated a better drawability, by inducing a high resistance of a
14、sheet to thinning. But there is no single material parameter which satisfactorily describes the drawing behavior. In this work, the effect of internal pressing on the formability of aluminum sheet is investigated to increase the LOR of aluminum alloys. Figure 1 is a schematic of a cup die, showing t
15、he punch, die and blank holder, and a partially formed cup. The punch is on the down stroke and is just beginning to draw the sheet-metal blank into the die cavity. If the blank size has been chosen correctly, the metal will work harden sufficiently to overcome the combined strength of the remainder
16、 of the blank metal and friction between it and the blank holder and the part will be successfully made. However, if the blank is too large, the part will break when the tensile strength is exceeded. The first deformation of the blank occurs between the die radius and the punch-nose radius part, since this is the part that is not supported by friction with the tooling components. The metal in this section is increasing in area as it thins out and losing
