| TA15 alloy is a middle-temperature titanium alloy that widely used in aviation, but its high strength, low modulus characteristics make its rebound phenomenon serious in the precision machining process. Heat treatment sizing technology is based on the principle of high temperature stress relaxation, which makes the internal stress of the workpiece to the limit after placing a long time in high temperature experiment. So, the workpiece will be in a low-stress state at room temperature, which can greatly reduce the rebound and make the workpiece’s accuracy improved greatly. In this paper, we will study the influencing factors of heat treatment sizing precision on the post-welded TA15 titanium alloy thin-walled cone piece. And through research result to guide the design of the heat treatment process for thin-walled cone piece and the die sizes.In this paper, first of all, we will simulate the laser welding process for TA15 alloy thin-walled cone piece in Abaqus finite element software. During the welding process simulation, using the birth-death element technology to simulate the weld metal deposition and connection. At the meantime, setting the dynamic film exchange surfaces with the birth-death element. Using the above processing method, we verify the weld shape and weld stress distribution of laser welding of titanium alloy that have published on related literature, finding that parabola rotating body heating source model describes the laser welding heat energy distribution better than double ellipsoid heating source model. At the same time, it also indicates the laser welding simulation model set up above is correct. Subsequently, conducing the laser welding simulation for the TA15 alloy cone piece, we find that the welding residual stress and deformation are mainly concentrated in the center of the weld seam and the affected area that ranges 10 mm from weld seam. Somet hing have to say that the residual stress values of the weld seam and the affected area are as high as 500 to 900 MPa, the integrated, longitudinal, radial, lateral deformation displacements of that also one by one up to 2.8mm, 1.6mm, 1.25 mm, 0.45 mm.According to the stress relaxation curve of TA15 alloy under the 600℃,650℃,700℃ temperature that reported in literature, we set up a three-stage constitutive equation at different temperatures based on fast, transitional and slow relaxation rates. And then importing the written constitutive relation subroutines to high temperature cyclic stress relaxation model to simulate the relaxation behavior, finding that transient stress relaxation, unloading springback agree well with the experimental and theoretical computation results, which says the constitutive relation of the TA15 alloy achieve a success in analog computation.By using the verified stress relaxation constitutive subroutine to study the influencing factors of heat treatment sizing precision, such as pre-deformation, shaping temperature, mould thickness, and the deformation degree of workpiece. The results showed that: with the increase of pre-deformation at room temperature, heat treatment sizing precision will first increase and then reduce, and the optimum deformation is the deformation of standard thermal bulging; for the factors of temperature and mould thickness, the greater the value, the higher correction shape accuracy,which the temperature factor affects significantly, the mould thickness factor affects little; and the deformation degree of workpiece has no effect on the heat treatment sizing precision. By using the above research results, we d esign the heat treatment sizing temperature is 700℃and keep the temperature for 5000 s, pre-deformation is 2.528 × 10-2× and corresponding mould size.Under the above process parameters, we take the heat treatment sizing to the post-weld TA15 alloy thin-walled cone piece, and find that the heat treatment sizing result can meet the workpiece machining precision. |
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