Warm Deep Drawing Research Articles

Finite element simulation of warm deep drawing of aluminium alloy sheet when accounting for heat conduction

The deformation behaviour and the temperature change in cylindrical deep drawing of an aluminium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and the heat conduction finite element methods. The comparison with the experimental results shows that the forming limits and the necking sites are successfully predicted by the simulation. It is clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher limiting drawing ratio. The numerical as well as the experimental results show that the limiting drawing ratio in the warm deep drawing increases with the die profile radius.

ｌ０５０アルミニウム板の温間対向液圧深絞り特性

As a forming method for improving the limit of deep drawing, a warm deep drawing process with hydraulic counter pressure, which is the combination of warm deep drawing process and hydraulic counter pressure deep drawing process, is proposed. As for this forming method, the improvement of limiting drawing ratio can be expected through the control of work hardening by heating flange part and the prevention of fracture by pressing the formed side wall to a punch with hydraulic pressure. According to the experiment up to the forming temperature of 200°C, by controlling the highest hydraulic pressure so that the fracture due to excessive bulging deformation does not arise, and by forming at the forming speed of 3 mm/s or less, it is successful to improve the limiting drawing ratio of A1050–O material up to D0 max/dp=3.40 in cylindrical cups and D0 max/lp=3.59 in square cups. However, at the forming temperature of 200°C, the flange part of H24 material was softened, and the improvement of its limiting drawing ratio has not been attained. Moreover, it is elucidated also that when the warm forming of H24 material is carried out, strain figures and flow marks arise, and the surface properties of the formed products are deteriorated.

The effect of temperature and deformation rate on transformation-dependent ductility of a metastable austenitic stainless steel

Recently-published investigations into the warm deep-drawing of metastable austenitic stainless steels have suggested that increased drawing ratios may be achieved by allowing controlled transformation to martensite at a strain close to that at which instability of the austenite would otherwise occur. A so-called maximum elongation temperature (M.E.T.), the temperature at which the major principal strain is maximum, determined from tests in uniaxial tension, is usually quoted. The authors confirm that it is formation of sufficient martensite in the region of incipient instability close to the instability strain which is responsible for increased tensile ductility, but there is no unique M.E.T. for a given steel. It depends, critically, on the rate of loading. Further, the M.E.T. in the uniaxial tensile test differs from that determined from the notched tensile-, bulge-, and cupping tests, so that it is not independent of the stress system, and the M.E.T. in the uniaxial tension usually quoted in the literature, may have little relevance to sheet drawing in which the stress system is essentially biaxial. The M.E.T. determined from the biaxial tests coincided with the temperature at which the limiting drawing ratio in the Swift flat-bottomed cup test was greatest.