Experimental and Numerical Investigations on Formability Characterization in Single Point Incremental Forming of Steel Tailor Welded Blanks /

Abstract

Manufacturing industries are seeking for new high strength, lightweight materials along such techniques and designs to optimally utilize these materials to produce quality and reliability in their products while simultaneously reducing cost and weight of the products. Tailor Welded Blanks (TWBs) employ such technique which exploits the advantages of localized strength and less material consumption resulting into lesser part weight. TWBs are largely used in Body-inWhite (BIW) of all modern automobiles. Research was conducted on TWBs produced successfully by manual TIG welding technique. Incremental Sheet Forming (ISF) is in practice with its several variants using TWBs. Material selected for the study included deep drawing quality (DDQ) steel (DC06) and stainless steel (SS) (AISI 201). Because of huge difference in both strength and hardness values of DDQ steel and SS, low formability was achieved in case of strength differential. Whereas formability achieved in the cases of same thickness and thickness differential were high since strength and hardness values were not varied much. Process parameters also affect formability to a fairly large extent. In case of same thickness, highest formability was achieved at maximum feed rate but minimum speed. In case of thickness differential, highest formability was achieved at minimum values of feed rate, speed and step depth. In case of strength differential, highest formability was achieved at minimum values of speed and step depth. Percentage thinning was used to assess formability achieved. Final thicknesses achieved during forming were verified by Cosine law. TWBs is a complex phenomenon, as compared to finite element modeling of monolithic sheets, which involves modeling of different zones generated due to the heat effect. Single Point Incremental Forming (SPIF) was used as a forming technique for TWBs produced by manual Tungsten Inert Gas (TIG) welding and experimental outcomes were compared with simulation results. FE software Abaqus® (Dynamic Explicit Solver) was used for the analysis with variable wall angle truncated pyramid as test geometry and Isotropic plasticity model as material model. Thickness profiles and state of stress and strain in all the cases were analyzed. A decrease in thickness was observed at the corners in all the cases, whereas decrease was more prominent in case of same thickness and strength differential. The symmetry of pattern on both sides with minimum and maximum values of stress towards the thinner side was observed in case of thickness differential. Variation in stress was more prominent towards the side of high-strength material along maximum value in case of strength differential. Equivalent plastic strain observed was morexi linear and higher towards the sides of thicker sheet and material having less strength in case of thickness differential and strength differential, respectively. Research investigations may be applied in similar fashion for precise study of formability characteristics of various kinds of TWBs being used in multiple industries including automotive, vessel, medical, etc.