Effect of grain size on mechanical revolution of pure titanium and die cavity filling rate in hot squeezing mini spur-gear forming process

This study investigates the effect of grain size on the deformability of CP2 Titanium to form the mini spur gear in hot squeezing forming process. Experimental specimens are rods with a diameter of 5 mm and annealed with temperature in a range of 500 to 1000°C to precipitate the different initial grain sizes individually. The mechanical properties and hardness of annealed specimens are measured. A mini spur gear die with a modulus of 0.915 and 8 teeth, made of H13 steel, is prepared. The annealed specimens are inserted in die and hot squeezed to form mini spur gear with a temperature of 500°C. The experimental results show that the α-phase microstructure precipitates when the annealing temperature and holding time are 700°C and 3 hours. The specimen with average initial grain size of 154.59 μm results in the maximal elongation and die cavity-filling rate. Harnesses of addendum and dedendum circle are about 215 and 180 MPa that are higher than that of initial grain (107 MPa). The β-phase microstructure precipitates when annealing temperature reaches to 900°C resulting in brittle behavior.