Metal flow hysteresis behavior and shape control strategy during porthole die extrusion of micro heat pipe

The shape control strategy of micro grooves is still unclear and challenging during the porthole die extrusion of grooved micro heat pipe (MHP). Through the simulation and experiment of porthole die extrusion of a MHP profile, the metal flow hysteresis behavior within micro features and the effect of ram speed and extrusion temperature on it and the resulting forming integrity was elucidated. Innovatively, Taguchi design and variance analysis (ANOVA) were introduced to determine their influence magnitude on the metal flow uniformity calculated by simulation results. The main findings are given below. The metal flow hysteresis derives from part feature size effect. The negligible friction-affected area during conventional extrusion severely slows down the metal flow within micro features during the MHP profile extrusion, which is due to the surge in the area ratio of the friction-affected area to the region in which it is located. Neither ram speed nor extrusion temperature can change the distribution of the friction-affected area. However, increasing ram speed multiplies the metal flow hysteresis and severely reduces the forming integrity, whereas extrusion temperature has little effect. Following this strategy, batch extrusion of the profile with micro-grooved width of 0.27 ± 0.02 mm was achieved in industrialized conditions.