Yüksek zımba hızının, AISI 304 paslanmaz çelik iş parçası kesme yüzeyi sıcaklığı ve kalitesine olan etkisinin sonlu elemanlar yöntemiyle incelenmesi

Abstract

The main goal of the blanking process is to shear the sheet metal with minimum energy consumption and to obtain a good surface quality on the sheared workpiece. The punch speed is one of the important process parameters which have effect on both surface quality and energy consumption. In the literature, investigations and experimental works contain a gap that includes the range of speed which the mentioned works were executed either at speeds which is below high speed (lower than 5m/s) or excessively high speeds (at ballistic level). Also, studies that investigate stainless steel sheets are scarce. The purpose of this study is to thermomechanically investigate the punch speed, cutting force, cutting energy and workpiece surface quality of a 2 mm thick AISI 304 stainless steel sheet that was blanked under a constant clearance value and three different punch speeds by using experimental and finite element methods. Theory and Methods:A 2 mm thick AISI 304 stainless steel sheet was used as the workpiece material. The die diameter was taken as 10 mm. The clearance were kept constant (5% of sheet thickness) and three different punch speeds (0.1 m/s, 1 m/s and 10 m/s) were used to execute the blanking process. A hydraulic press with 30 Tons capacity, a mechanical press with 100 Tons capacity and a powder actuated HERF hammer were used to obtain required speed values. On the other hand thermo-mechanical finite element analysis of the mentioned process were done by using Deform 2D. The maximum element number (10000) which is the highest value that can be defined was used and all mesh elements were compressed at the cutting zone to reach more realistic results. Surface roughnesses of the blanks were calculated by using a profilometer. Results:The strain hardening capability of AISI 304 is well known and results showed that the cutting force and cutting energy elevated with increasing punch speeds. But when the punch speed became 10 m/s, the cutting force and energy reached to lower values than expected. It was observed that the temperature values were elevated with increasing speed. There was 241% increase in temperature values between 1 m/s and 10 m/s punch speeds. Also, it was found out that the effective stresses got localized with increasing speed. The surface roughness values showed that the best quality was obtained at higher speeds. Conclusion:Cutting force and cutting energy increased due to AISI 304's tendency to strain harden but not to expected levels because of the thermal effects in the zone . Increase in the punch speed caused the effective strain rate to rise that resulted in a sudden heat emanation at the shear zone. This heat couldn't dissipate into the material and created an adiabatic shear zone with elevated temperature. Increase in temperature softened the material thermally by lowering the materials flow stress. There occurred a 53% loss in the expected cutting force. On the other hand, the localization of the effective stresses caused the material crack early, changing the distribution of zones espec...