| Residual stress usually exists in the plastic forming parts. It varies with thematerial properties, the shape and size of parts and the processing parameters etc. Theresidual stress in the drawing part has great influence on its fatigue life, strength andstability of size and shape. Thus, it is very necessary to evaluate the residual stress indrawing parts, and to adjust the distribution of residual stress or eliminate the negativeinfluence of residual stress.For its good comprehensive performance and cold working performance,304stainless steel sheet is suitable for making deep-drawing parts. But the drawingprocess of stainless steel parts is influenced by many factors such as drawing ratio, themold parameters (punch-die clearance, punch bottom radius and die corner radius),the blank holding force and the friction coefficient etc. Influence of the drawing ratioon residual stresses in304stainless steel cylindrical deep-drawing cups was studied inthis paper. The main research contents and achievements are as follow:1) Uniaxial tensile tests had been carried out with different deformation rates at0o,45o, and90o to the rolling direction of the304stainless steel sheet in order toobtain its mechanical properties of different directions at room temperature. Theresults showed that the yielding strength increased slightly but the tensile strengthdecreased a little with the increase of the tension rate. The deforming rates had littleeffect on the hardening process of the304stainless steel sheet. The true stress-straincurves had no significant difference in different tensile direction, which meant that304stainless steel sheet was isotropic. The Young’s modulus, yield strength andpoisson’s ratio of304stainless steel sheet were193GP,257MPa and0.28,respectively. The tensile tests provided the material properties for the formingsimulation and determining the forming process of cylindrical deep-drawing cups.2) The drawing process of304stainless steel cylindrical cup was simulated onABAQUS software. The distributions of residual stress were obtained in the wall ofcylindrical cups which were produced with drawing ratios of1.82,1.67,1.54and1.43.The simulation results showed that the maximum residual stresses in outer surfaces ofthe cylindrical cups wall (obtained with above four kinds of drawing ratios) were483.69MPa,386.61MPa,343.56MPa and312.60MPa, respectively. All appeared inthe middle of the cylindrical cups wall along the height direction. The maximumresidual stresses increased and their positions in the cups wall varies with the increase of drawing ratios.3) The deep drawing mold for forming cylindrical cups was designed andproduced. Four different drawing cups were obtained using different drawing ratios of1.43,1.54,1.67and1.82on the drawing mold. The ring specimens were cut from thecylindrical cups wall by wire electrical discharge machining. The residual stresses inouter surface of the different ring specimens (all from the height of the maximumresidual stresses) measured by nanoindentation were391.87MPa,745.30MPa,793.74MPa and1588.46MPa, respectively. They also increased with the increase ofdrawing ratios, and were greater than the corresponding numerical simulation residualstresses. The phase transition in304stainless steel after drawing can greatly increasethe residual stress, which could not be considered in numerical simulation onABAQUS software. |
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