Precision Extrusion Using Tool for Counter Pressure

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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.