The production of hollow-ware by deep drawing and bulge forming.

摘要

Results of a study of the production of hollow-ware byuddeep-drawing and bulge forming are presented. Axisyrnrnetricaludand asymmetrical shapes were successfully produced from softudaluminium flat blanks in one stroke of a punch. The processudconsists of drawing, ironing and bulging inside a closed dieudcavity. The constituent operations are studied individually.udIn deep drawing without a blank-holder, an approach toudconvex type die design is presented. The investigationudevaluates the effect of die profile geometry on the drawingudperformance. Three dies of the second degree spiral type,oneudnear to the tractrix shape and the other two with largerudradius of curvature, are considered. The materials testedudinclude mild steel, stainless steel, soft aluminium and brass.udThe drawing process through tractrix, exponential spiral,udsecond degree spiral and conical type dies is analysed usinguda numerical solution formulated earlier and the theoreticaludresults on the punch load and the strain development are comparedudwith the experimental results. Good correlation isudobtained on the development of strains. The theoreticaludprediction of the punch load is reasonably good except forudmild steel which is highly anisotropic. It is shown that byudmodifying the die profile, the 'punch load can be significantlyudreduced. The reductions predicted by theory are inudgood agreement with experiment which means that optimum dieuddesign for minimum load is possible. udIn ironing of cups, using soft aluminium blanks, it wasudfound that punch speeds in the range 7-45 rom/sec haveudnegligible effect on the drawing load. The ironing loaduddecreases slightly as the speed increases in this range.udThe reduction is more significant with higher degrees ofudironing. Measurement of ironed cup wall thickness showedudthat thickness variations are attributed to planar anisotropyudof the blank and geometrical errors in tooling.udFree bulge forming is used as a simplified approach toudclosed die forming. The bulge profile modes under differentudloading conditions of internal pressure and axial force, theudeffect of the unsupported cup length and the effect of theudcup wall thickness on the bulge ratio were investigated usinguda specially designed test rig. For bulging of as deep-drawnudcups, the bulge ratio increases with increase of cup walludthickness, and it decreases with increase of length. Forudbulging of annealed cups the length effect is negligible andudthe bulge ratio increases slightly with increase of cup walludthickness.udThe procedure used in producing different hollow-ware.udshapes is described together with typical failure examples.udThe thickness reduction and bulge ratio distributions areudshown and comparison is made between annealed and as deep-drawnudcups.