Investigation of interfacial heat transfer characterization for TC4 alloy in triple-layer sheet hot stamping process

Abstract

During the hot stamping process, heat exchange always occurs between the hot sheet and cold tools. The interfacial heat transfer in the whole forming process will not only affects the forming quality of the parts but also partially determines their post-form mechanical properties and microstructure distribution. As an essential parameter, the interface heat transfer coe cient (IHTC) is of great signi cance for the prediction of temperature elds in the nite element simulations, especially for the novel forming process named triple-layer sheet hot stamping. In this study, the triple-layer sheet heat exchange experiment is carried out to investigate the interfacial heat transfer behavior of the titanium alloy sheet in the triple-layer sheet hot stamping process. The effects of contact pressure, cladding steel sheet thickness, and contact gap on the interfacial heat transfer behavior and post-form mechanical properties of titanium alloy sheet are analyzed, and the interface heat transfer coe cient between the titanium alloy and high-strength steel sheets is calculated. The nite element model of triple-layer sheet heat transfer is established to verify the accuracy of the calculated interfacial heat transfer coe cient. The results show that the upper and lower steel sheets maintain the temperature of the titanium alloy sheets at a higher level in the triple-layer sheet hot stamping compared with the single-layer one. The temperature of the titanium alloy sheet under the single-layer hot stamping decreases from 900°C to 781.6°C after transferring, a decrease of 118.4°C. The temperature of the titanium alloy sheet only declines by 57.5°C during this period in the triple-layer sheet hot stamping process. In addition, the titanium alloy parts obtained by the triple-layer sheet hot stamping process have better mechanical properties. The IHTC increases with the increase of contact pressure and decreases with the increase of steel sheet thickness and contact gap. The accuracy of the calculated IHTC between the titanium alloy and cladding steel sheets is validated by comparing the results of the experiment and simulation. The maximum error between the simulation results and the experimental measurements is 5.5%.

Finite Element Simulation and Microstructural Evolution Investigation in Hot Stamping Process of Ti6Al4V Alloy Sheets

“…The tensile specimens were cut into bone-shaped specimens of 50 mm length and 14 mm width as shown in Figure 1 f. For better alignment with the mechanical properties of Ti6Al4V alloy during the hot stamping process, the specimens were preheated in a furnace at 800 °C for 2 min before the tensile experiment. Based on existing research, in the hot stamping forming process of titanium alloys, the deformation starting temperature is usually between 700 and 800 °C, and the temperature of the sheet material typically fluctuates around 400 °C at the end of formation [ 9 , 19 ], so the deformation temperatures were set to be 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C, and according to the real hot stamping process, the strain rates were set to be 0.1 s −1 , 0.05 s −1 , and 0.01 s −1 . Each specimen was heated to the set temperature, held for 3 min, and then subjected to the hot tensile test.…”

Effect of Heating on Hot Deformation and Microstructural Evolution of Ti-6Al-4V Titanium Alloy

“…Titanium alloys have strong deformation resistance and severe spring-back drawback that forms at room temperature, which may damage forming tools and reduce the accuracy of formed components [ 4 ]. In order to overcome the low formability at room temperature, superplastic forming (SPF) [ 5 ], hot stamping [ 6 ] and hot metal gas forming (HMGF) [ 7 ] were developed for forming complex-shaped thin-walled parts in recent years, featuring low deformation resistance and high forming precision [ 8 , 9 ]. Heating to elevated temperatures is the first and key step in hot forming processes.…”