Investigation of material deformation mechanism in double side incremental sheet forming

• Tool position/supporting force result varied deformation behavior and formability.
• Slave tool introduces “stress triaxiality drop”, which increases the DSIF formality.
• Tool squeezing increases formability more obviously under plane-strain condition.

Double side incremental forming (DSIF) is an emerging technology in incremental sheet forming (ISF) in recent years. By employing two forming tools at each side of the sheet, the DSIF process can provide additional process flexibility, comparing to the conventional single point incremental forming (SPIF) process, therefore to produce complex geometries without the need of using a backing plate or supporting die. Although this process has been proposed for years, there is only limited research on this process and there are still many unanswered open questions about this process. Using a newly developed ISF machine, the DSIF process is investigated in this work. Focusing on the fundamental aspects of material deformation and fracture mechanism, this paper aims to improve the understanding of the DSIF process. Two key process parameters considered in this study include the supporting force and relative position between master and slave tools. The material deformation, the final thickness distribution as well as the formability under varying conditions of these two process variables are investigated. To obtain a better understanding from the experimental results, an analytical model has been developed to evaluate the stress state in the deformation zone. Using the developed model, an explicit relationship between the stress state and key process parameters can be established and a drop of stress triaxiality can be observed in the double contact zone, which explains the enhanced formability in the DSIF process. Based on the analytical and experimental investigation, the advancements and challenges of the DSIF process are discussed with a few conclusions drawn for future research.