Study On Deformation Mechanism And Technique Of Titanium Alloy Rod During Three-Roll Hot Continuous Rolling Process

Titanium and Titanium alloy is a kind of new metal material developed in1990's. It is not only characterized by high melting point, high specific strength,high temperature resistance as well as corrosion resistance, but alsonon-magnetic and toxic-free. It is widely used in the area of aerospace, marine,bioengineering, livelihood and others. The market for small-sized titanium alloyrod is becoming more and more demanding in recent years. However, there existsome disadvantages of titanium alloy, such as complicated technology,lowaccuracy, low rolling yield and high energy consumption in the manufacturingprocess. In order to make titanium alloy become a popular metal, it is veryimportant to decrease its cost. Therefore, an important subject which aims atintegrating equipment, developing sustainable smelting technology and loweringcost variety is facing in titanium industry.This subject originated from province young research program of Shanxi isto develop a short and near-shape machining technique for titanium alloy rod.Compared with open-train mill, the continuous rolling process of Y-type cancelsrepeated heating (soaking), annealing and repair grinding. Compared withtwo-roll mill, it increases efficiency of roll. Meanwhile, the requirement ofsmall-batch and multi-variety of titanium alloy rod production is met.However, the deformation characteristics are significantly differentbetween titanium and steel, aluminum as well as copper. Especially for titaniumrod of strength and subsequent machining requirement, the pass design has animportant influence on quality and rolling yield. Therefore, in this paper thedeformation behavior of TC4alloy has been researched systematically, thecontinuous rolling process has been simulated by FEM software, pass designmodel for small-sized titanium alloy has been established, and experiment hasalso been done on self-development Y-type mill.Main contents are as follows.(1) Take TC4alloy as the study subject, this study conducts compressiontests on TC4alloy by Gleeble-1500thermal simulator and examines TC4alloy's deformation behavior and flow stresses. The constitutive equationscorresponding to the peak and stable stresses have been determined respectivelyusing regression method. Furthermore, taking into the strain account, the flowstress equation has also been established by combining exponentially hardeningand softening function. The simulated results are believed to be important todevelop production, optimize process and improve quality of TC4alloy rod.(2) Pass system of "flat triangle–round" is applied not only because theflat triangle workpiece is relatively stable in round groove, but also the differentdiameter round rod could be produced from round groove. Based on theestablished flow stress equations, continuous rolling process of TC4alloy oneight Y-type mills has been virtually simulated using ANSYS software.Extension and spread deformation have been analyzed. Temperature, equivalentstress as well as equivalent strain of different deformation zone and rolling forceof per mill have been illustrated. The whole rolling process is smooth withoutcrack, edges and folds, which shows that the proposed rolling process isfeasible.(3) It could be concluded from FEM simulation above, the TC4alloy rod iscompressed from six directions and its surface and interior temperature,resistance deformation, spread and continuous rolling constant changeconstantly in hot rolling process. Furthermore, considering the compact distanceof the adjacent stands (no more than1m) and multi-stand (more than20stands)during rod rolling, the stability of continuous rolling is very easy to beinfluenced and even interrupted due to the slight fluctuation of the mentionedparameters. Therefore, there is a significant need to engage in research ongroove design so as to ensure the stability of the continuous rolling andproduction accuracy of titanium alloy. In this paper, a new groove design modelfor Y-type process of TC4rod has been established, whose difference from thetraditional pass design lies in avoiding fill ratio of groove.(4) By combining FEM with orthogonal test, spread model for TC4alloyrod has been established, and experiments have also been done on modelmachine. It provides theoretical foundation for flat triangle and round groove design. By analyzing contact zone shape of workpiece and roller, three-rollrolling force model for TC4alloy rod has been modified based on constitutiveequations. And experiments have also been done on model machine. The resultshave shown that the difference between calculated value and measured value isin the allowable range.(5) Computer aided pass design software for continuous rolling titaniumalloy is developed using MATLAB function of calculation and logic deduction,which is suit to all of pass types of Y-type mill including flat triangle, round andarc triangle. It can calculate many parameters for pass, workpiece andmechanics, etc. Numerical results are outputted by EXCEL and multi-passgrooves are drawn by AUTOCAD. Pass design for Φ12mm TC4alloy rod hasproven the validity of CARD. With friendly interface and simple operation, theCARD software could be used to shorten period, improve efficiency andaccuracy of pass design.