Precision Extrusion Using Tool for Counter Pressure

研究了前向棒材或齿轮、后向罐体或棒材的复合挤压。为了在加工结束时获得指定长度的齿轮，需要用倒刀控制正向挤压速度。通过控制正向挤压速度，可以在较低的挤压压力下获得具有给定挤压长度的产品。在这个过程中，可以利用模具出口处产生的反压来减少缺陷。1.控制正向挤压速度的正反向组合挤压当反压力在应变为1.0的情况下提高到坯料的流动应力量级时，端面变得完全平坦，不需要后加工。2.交替控制正反向挤压速度的正反向组合挤压由于端面不总是与工具接触，端面不可能完全平整。在不控制反挤压速度的情况下，虽然后端面平整度为0%，但采用交替控制挤压速度时，后端面平整度为80%。3.正向齿轮--反向棒材或罐体与正挤压速度控制相结合的情况下，后向棒材齿侧的欠填缺陷比后向棒材的少。在反向挤压的情况下，当应变为1.0时，反向压力为坯料流动应力的75%时，缺陷消失，当反向压力为流动应力的140%时，得到完全平坦的端面。4.受控正反向组合挤压后的反挤压，虽然正反向组合挤压和反挤压的挤压压力几乎相等，但反挤压获得了较长的正挤压部分。

Extrusion of forward bar or gear, and backward can or bar by combined extrusion is studied. To attain the specified length of the gear just at the end of the process, the forward extrusion velocity is controlled with a counter tool. By controlling the forward extrusion velocity, a product with given extruded length are obtained with a low extrusion pressure. In this process, the counter-pressure caused at the die exit can be utilized to reduce the defects.1.Forward-backward combined extrusion with control of forward extrusion velocityWhen the counter pressure is raised to the order of flow stress of the billet at the strain of 1.0, the end surface becomes completely flat and no post machining is needed.2.Forward-backward combined extrusion with alternate control of forward and backward extrusion velocitiesSince the end surfaces do not always contact with tools, the end surfaces cannot be flat completely. Although the flatness of the back end surface is 0 % without controlling backward extrusion velocity, it becomes 80% when the alternate control of extrusion velocities is employed.3.Forward gear-backward bar or can combined extrusion with control of forward extrusion velocityThe under-filling defect at the side of teeth in the case of backward bar is less than the case of backward can. In the case of backward can, the defect is disappeared when the counter pressure becomes the 75% of flow stress of the billet at the strain of 1.0, and the completely flat end surface is obtained when the counter pressure is 140% of the flow stress.4.Inverse extrusion after controlled forward-backward combined extrusionAlthough the extrusion pressures for only forward-backward combined extrusion and inverse extrusion are almost equal, the longer forward extruded part is obtained by the inverse extrusion.