Numerical and experimental research of the effect of friction on cold extrusion internal thread process

Cold extruded internal thread is a kind of green processing method with many advantages. However, the torque is greater than cutting, if the lubrication effect is not ideal, it can easily cause excessive wear and even breakage of taps. With the intention of mitigating the frictional wear of the tap in the forming process, this paper studied the effect of friction between extrusion taps and workpieces on the forming quality through simulation and experiment. The effects of friction factor on extrusion torque, extrusion temperature, effective strain, forming work and metal flow velocity were analyzed separately. The results indicate that the extrusion torque, extrusion temperature and forming work increased with the increase of friction factor. In addition, the effective strain increased and then decreased with the increase of friction factor. The metal flow velocity at the crest and root decreased with the increase of the friction factor. Finally, the lubricating properties of the four lubricants were analyzed in the experiments. The results showed that all the lubricants used in the experiment were able to reduce the extrusion torque, among which the industrial white oil had the best torque reduction performance, with a torque reduction of 32.9% compared with dry extrusion.