Numerical Simulation And Optimization Of Ring Rolling Process For Ti₃Al-Nb Based Alloy

Ring rolling technology has outstanding advantages in such aspects as synthesistechnique and economic benefits. Ti₃Al-Nb based alloy is a kind of high temperaturestructural material with excellent comprehensive properties such as high elasticmodulus, low density, good mechanical property and oxidation resistance at hightemperatures. Thus, Ti₃Al-Nb based alloy ring has favorable applicative prospects in thearea of fuel engines in aviation, aerospace and the automotive industry. However, thecharacters of ring rolling process such as nonlinearity, time-variant and unstability caneasily lead to defects such as face sunken, oval and cracks during rolling Ti₃Al-Nbbased alloys. In this paper, the ring rolling process of Ti₃Al-Nb based alloy wasnumerically simulated and the parameters were optimized by using DEFORM-3Dsoftware. The results can provide reference for the practical production of Ti₃Al-Nbbased alloy rings.The motion mathematical model of the ring and each roll have been establishedaccording to the ring rolling theory and the characteristics of ring. The material modelof Ti₃Al-Nb based alloy was established based on the data of compression test withconstant temperature and strain rate. The size of Ti₃Al-Nb based alloy finished ring wasΦ580×Φ500×100mm, and the size of ring billet was Φ445×Φ340×105mm. The ringrolling process of Ti₃Al-Nb based alloy had been simulated by using DEFORM-3Dsoftware. The change of geometry, evolution law of the temperature field as well asstrain field and force parameters in rolling process of ring were studied. The resultsshow that “fishtail” defect exists in the process of rolling. The temperature graduallydecreased from the center area to surface area. The highest temperature zone is thecenter area. The temperature of head face is slightly higher because of the effects ofaxial rolling. The temperature of corner area is the lowest. The distribution of equivalentstrain field is not uniform. Equivalent strain gradually decreased from the outer area tocenter area. The equivalent strain of corner area is always largest, and that of the centerarea is the lowest. The force of core roll increased rapidly from zero to2.59×105N whenthe ring gone into the groove. The force is leveling off after entering the phase of stablerolling.In this paper, a L18orthogonal experiment is designed based on the analysis of theinfluence of ovality, rolling force, rolling torque on process parameters. How muchfactors as temperature of billet rolling, drive roll rotation speed, core roll feeding speed, angle of guide roll, drive roll friction coefficient, axial roll friction coefficient influenceon ovality, rolling force and rolling torque are studied. The results show that axial rollfriction coefficient influences ring of ovality most, and the temperature of billet rollinghad a significant impact on the rolling force and torque.According to the optimization design, the optimal parameters are obtained asfollows: the temperature of billet rolling is1100℃, drive roll rotation speed is1.8182rad/s, core roll feeding speed takes piecewise values1-0.8-0.6mm/s, angle ofguide roll is75°. drive roll friction coefficient should be higher（0.85）, and axial rollfriction coefficient is preferable to be lower（0.3）.