Experimental and numerical study of friction in free bulging 304 stainless steel seamed tube using elastic pad

In recent years, rubber pad forming process has conferred many advantages, such as high flexibility, good surface quality and lower manufacturing costs. RPF has been widely used in automotive, aerospace and military industries. In the present research, numerical and experimental analysis of free bulging 304 stainless steel seamed tube, using a polyurethane elastic pad has been studied. First, 3D simulation of seamed tube bulging using the finite element ABAQUS/Explicit 6.12 software by several frictional conditions has been performed. An incompressible hyperelastic pad has been modeled by Mooney-Rivlin constitutive equation and the elastic-plastic behavior as a more progressive ductile damage criterion FLD for steel tube were assumed. In the experimental activity, compression test of rubber was carried out according to ASTM D575-91 standard and compressive stress-strain curve and the Mooney-Rivlin constants were determined. Forming of meshed tubes by using elastic pad with different lubricating systems has been conducted up to onset of bursting in the seam weld and longitudinal, hoop and thickness strains were measured. Results showed that friction, especially between rubber and tube plays the main role in controlling wrinkles, increasing the bulge depth, reducing the forming load and friction dissipation energy of the process. Also, it was observed that the intact parts without any wrinkles were formed using nylon lubricant between tube and rubber and drawing oil between tubes and die.