芯轴摩擦系数对推压-拉拔复合缩径的影响

推压-拉拔复合缩径工艺是管坯减径的新方法，芯轴外表面与管坯内表面之间摩擦系数对工艺有重要的影响。通过建立推压-拉拔复合缩径变形过程中变形管坯的力学模型，分析了芯轴外表面与管坯内表面之间摩擦系数对成形的影响规律。针对某载重6.5 t胀压成形汽车桥壳管件的第一道次推压-拉拔复合缩径，设定不同的芯轴摩擦系数，进行了有限元仿真，得到了芯轴摩擦系数对管坯变形的影响规律，并基于管坯传力区不失稳以及变形所需凹模推力和芯轴拉拔力较小，给出了芯轴摩擦系数的设定范围。进行了缩径实验，实验和有限元模拟的结果接近。较小的芯轴摩擦系数可能造成管坯起皱失稳，而较大的芯轴摩擦系数，有利于降低管坯轴向压应力、凹模推力和芯轴拉拔力，但可能造成管坯表面划伤。

Effects of mandrel friction coefficient on pushing-pulling necking

Pushing-pulling necking is a new method of reducing the diameter of the tube blank. The friction coefficient between the outer surface of the mandrel and the inner surface of the tube blank has an important influence on the process. The mechanical model of the deformed tube blank in the process of pushing-pulling necking was established, and the influence of the friction coefficient between the outer surface of the mandrel and the inner surface of the tube blank on forming was analyzed. With the first pass of pushing-pulling necking of a 6.5 t bulging-pressing axle housing as an example, different mandrel friction coefficients were set, and finite element simulation was carried out. The influence law of the friction coefficient of the mandrel on the deformation of the tube blank was obtained. Under the conditions that the force transmission area of the tube blank was not wrinkling and the die pushing force and mandrel pulling force required for deformation were small, the range of the friction coefficient of the mandrel was given. Diameter reduction test was carried out, and the test results were consistent with the finite element simulation results. A small mandrel friction coefficient may cause wrinkling and instability of the tube blank. While a larger mandrel friction coefficient is beneficial to reduce the axial compressive stress of the tube blank, the die pushing force, and the mandrel pulling force, but it may cause scratches on the surface of the tube blank.