| Powder metallurgy is a near net shape advanced manufacturing technology combining material preparation with part forming, and it includes some advantages such as energy conservation, material saving, effective, good dimension stability, high precision and so on. So it has a significant role in manufacturing industry and has gained extensive attention of domestic and foreign scholars. Nevertheless, cracks in PM compacts have a bad influnce on product performance. Causes of cracks have been investigated and classified by domestic and international scholar, but quantifiable investigation is absent. Using finite element technology to analyze and prejudge crack damage in the compacts for determining proper forming parameters is an effective method for solving crack damage.In this paper, the modified powder yield criterion was choosed and the crack damage model was obtained from the yield criterion based on plastic mechanics theory of porous material. The crack damage model expresses damage situation of the compact under the accumulated effects of stress, strain and relative density. Uniaxial compression tests of iron and aluminum compacts have made to confirm the validity and universality of the crack damage model.Using the crack damage model above, two – dimension fem numerical simulations with different technological parameters of lubrication conditions, high diameter ratios and ejection have taken to explore their influence on crack damage of compacts. The results show that: the damage during pressing is more serious than that during demoulding, and the damage reachs maximum when the compacts locate at the die lips; The improvement of lubricating condition contributes to alleviate damage in the compacts; The bigger height-diameter ratio, the more serious the damage of the compacts; Top-out demoulding mode is more reasonable than the bottom-out type.Analysis of conditions that could causing cracks during transport of the compacts have made. Mechanical performance parameters including elastic modulus, tensile strength and fracture toughnes were obtained by flattened Brazilian disc test. The results have be used for numerical simulation of annular compact clamping process to determine safe clamping parameter. |
