Study On Forming Limit Of Hot Gas Forming Of Double-layered Laserwelding Titanium Alloy Sheet

Titanium alloys have excellent properties and are widely used.In the aerospace industry,a kind of curved parts of large-size thin-walled cylinder is of double-layer titanium alloy structure.It is planned to adopt the hot gas expansion forming process.Due to the limitation of rolled plate size,laser welding of plate must be carried out before forming.Therefore,before forming,it is double-layer titanium alloy laser welding plate.However,there are few researches on the forming of Ti alloy laser welded blanks,and there is lack of reference materials.In this paper,based on the development of hot gas expansion of TA15 and TC2 Titanium alloy double-layer thin-walled tubular parts,the research on the forming limit and dimensional accuracy control of hot gas expansion of double-layer titanium alloy laser welded blanks is carried out to guide the hot gas expansion of double-layer thin-walled tubular parts.Based on the results of high temperature tensile mechanical properties of 3.5mm thick TA15 and 1.2mm thick TC2 Titanium alloy sheets,the experimental temperature and loading strain rate of the hot gas bulging limit of the double-layer sheet were determined.The elongation of TA15 and TC2 Titanium alloy sheets at strain of 0.001s-1 at 850 ℃ was larger and the closest.Secondly,the numerical simulation of the hot gas expansion process of TA15 and TC2 Titanium alloy double-layer plates was carried out,the gas pressure loading path to ensure the basically constant strain rate was determined,the influence of different pressure path and friction between plates on the deformation performance and wall thickness distribution was analyzed,and the forming limit diagram of double-layer plates was predicted and drawn.Then,the numerical simulation of the hot gas bulging process of TA15 and TC2 Titanium Alloy Double welded plate was carried out.The influence of different weld shapes and weld positions on the hot gas bulging deformation performance of double welded plate and the limit bulging height of non welded plate was analyzed.The forming limit diagram of double welded plate was predicted and drawn,and the influence of weld on the forming limit diagram was analyzed.Finally,to study the size change of titanium alloy double-layer plate in the process of cooling after hot expansion by means of cold die cooling,a cold die hot gas expansion experimental device was designed.The numerical simulation of the double-layer plate’s differential thermal expansion process was carried out,and the dimensional accuracy of the double-layer plate with different mold temperature and pressure relief path was analyzed,which provided a reference for the specification of the double-layer titanium alloy welded plate’s thermal expansion process.