当内压力为P(工作压力)时,在凹模的内表面切向应力最大(拉应力)。凹模一般采用冷锻模具钢制造,这类模具钢承受压应力的性能较好,当有拉应力存在时,模具容易损坏。为此对凹模采用施加予应力的方法,使其产生的压应力抵消其拉应力,这是防止凹模开裂的有效方法。 When the internal pressure is P (working pressure), the tangential stress is maximum (tensile stress) on the inner surface of the die. Die commonly used cold forging die steel, die steel to withstand compressive stress better performance, when there is tensile stress, the mold easily damaged. For this reason, the method of applying stress to the die is adopted to make the compressive stress produced by the die counteract the tensile stress, which is an effective method to prevent the die from cracking.