Comparison of Sheared Edge Zones Developed in Electromagnetic and Quasistatic Dieless Perforation Sagar Pawar , Sachin D. Kore, and Arup Nandy (Submitted November 27, 2018; in revised form January 12, 2020) Electromagnetic (EM) perforation is a high-strain-rate shearing process of making holes in the workpiece by using an electromagnetic force. This process overcomes the disadvantages of conventional or quasistatic processes. In this work, the comparative study of the quality of holes perforated by the EM dieless per- foration process and quasistatic dieless perforation process has been carried out and the differences are reported. This study allows one to understand the physical phenomena that happen during the perforation by the pointed and concave punch as well as the type of failure like the formation of petaling, plugging and softening or hardening of the material. The sheared edges are characterized using microscope, scanning electron microscopy (SEM) and microhardness analysis studies. Among interesting observations, it has been noticed that the smooth sheared depth, rollover depth, burr height and fracture depth are more in quasistatic dieless perforation. No significant change in hardness is observed in the case of quasistatic perforation, while in EM perforation, more than 50% increase in hardness is observed. The SEM obser- vation has revealed that in both the perforation cases, ductile dimple growth is the prominent failure mode. The results obtained during this study show the capability of electromagnetic perforation to obtain per- forated holes with better surface finish and material properties over the quasistatic perforation process. Keywords dieless perforation, electromagnetic forming, high-strain-rate perforation, quasistatic process 1. Introduction Electromagnetic (EM) forming process is a high-strain-rate process, and it is used to deform a large-size part and the materials with low formability. In the electromagnetic forming and perforation process, the electromagnetic force is used for the forming and perforation of tubes. It is a high-strain-rate shearing process, and it overcomes various disadvantages of conventional or quasistatic processes, like large rollover depth, the formation of burrs. EM perforation can be used for the shearing of lightweight materials like aluminum, magnesium which are difficult to shear by conventional processes and have a large demand in automobiles and aerospace industries. Many researchers have studied electromagnetic manufacturing pro- cesses and their advantages over other conventional processes (Ref 1, 2). The different applications of electromagnetic forming can be achieved by different geometries and arrangements of the coil and the workpiece (Ref 3). The length of the coil and capacity of capacitor bank decides the efficiency of forming processes. The longer length of the coil and the smaller capacity of the capacitor are more efficient (Ref 4). The EM field present at the middle of the coil is maximum, and hence the deformation obtained at the middle of the workpiece is also more (Ref 5). The various deformed shapes of the tube can be achieved by changing the relative position of the coil and workpiece (Ref 6). For concentrating the magnetic field and hence the deformation in the required region, field shaper, a single-turn coil is used (Ref 7). In the current work, the coil is designed for the electromagnetic perforation. Experiments on the punch-less electromagnetic shearing process were conducted by Golowin et al. (Ref 8). The authors validated the finite-element simulated results with experiments. The detailed investigation shows that the EM perforation of tubes has not been reported, and there is a need for a comparison of the process. Some researchers have compared different high-strain-rate perforation processes with conven- tional or quasistatic perforation, and they concluded that the burrs and slivers could be eliminated from the sheared part using the high-strain-rate process. The importance of high- strain-rate processes over the quasistatic strain rate process has been studied by Gotoh et al. (Ref 9). The punch speeds of 10 and 0.1 mm/sec were used for the high-strain and the quasistatic shearing process, respectively. The quality and appearance of the sheared-off edge were improved with the increase in punch speed. A typical mechanically sheared edge shows the different zones. During the shearing process, initially, the punch engages the tube, and it pushes the material downward. Hence, it draws the material and creates a small depression on the parent sheet as shown in Fig. 1, which is termed as ‘‘rollover.’’ With the increase in the clearance value in die punching, rollover area also increases (Ref 10). After the initial stage, punch continues to penetrate, and it shears the upper part of the material, creating a burnished area before the remaining material along the thickness, which is fractured or separated completely. Jana et al. reported secondary-crack, well-known defect in the case of low-speed blanking, and it was observed that secondary shear disappears under high-speed conditions (Ref Sagar Pawar and Arup Nandy , Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India; and Sachin D. Kore, School of Mechanical Sciences, Indian Institute of Technology Goa, Ponda, Goa 403401, India. Contact e-mail: s.pawar@iitg.ac.in. JMEPEG ÓASM International https://doi.org/10.1007/s11665-020-04636-w 1059-9495/$19.00 Journal of Materials Engineering and Performance