Springback phenomenon analysis of tailor welded blank of mild steel in U-bending process Free

In sheet metal forming process, springback is one of the important problems. Springback is defined as geometrical deviation after the process. Sheet metal forming at room temperature will have both elastic and plastic deformation due to the metal characteristic of elastic-plastic. Strain distribution along the sheet thickness is relatively not homogeneous. It is also influenced by bend angle and sheet blank thickness. Therefore, variation of blank thickness in one sheet will deliver different springback compared with the constant thickness. Thickness variation in blank sheet can be found in Tailor Welded Blank (TWB). TWB is a blank sheet content of two or more plate with different properties or thickness that has been welded together. Several types of welding method can be conducted to join them, i.e., laser welding, electron-beam welding, mash welding, arc welding and friction stir welding. It is also developed to gain both strength and light materials in automotive industries. Application of TWB in automotive can reduce car weight, improve quality and reduce fuel consumption. It is usually applied in side frame, door inner panel, hood inner panel, inner-outer B-pillar, and floor pan. Among the problems arises in using TWB are springback, cracking, tearing and wrinkling.. Bending processes are commonly used in sheet metal forming production of automotive components. The present study investigates the springback phenomenon of mild steel TWB strips in U-bending process. It is focused on comparing the differences of welding types of Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW). Specimens were created by using different types of welding for both tensile and u-bending specimens. The material used was mild steel plate in 1.5 mm thickness. SMAW welding process was conducted by using wire of 2.6 mm in diameter, series E7016, current between 60-150 A, and voltage 20-30 Volt. For GTAW process, it used wire of 1.6 mm in diameter, series ER70S-6, shielded gas CO2 with velocity of 10 l/min. GMAW method was carried out by using wire of 0.8 mm diameter, series ER70S-6 and the same parameters with GMAW method. Tensile test was conducted using Gotech Testing Machine series GT-AI-7000L with the maximum load of 5000 kg. ASTM E8 was selected for tensile test standard. In the tensile test, three specimens were employed in each variation of welding method. The result of tensile test indicates that welding process influences the elasticity modulus of mild steel. The elasticity modulus of specimens of SMAW, GTAW and GMAW method were: 2800 N/mm², 3166 N/mm², and 3300 N/mm², respectively. The highest springback value of 2 mm is obtained by the specimen of GMAW. Meanwhile, the welding process of GTAW and SMAW give lower springback than the GMAW.