Proceedings of COBEM 2005 18th International Congress of Mechanical Engineering Copyright © 2005 by ABCM November 6-11, 2005, Ouro Preto, MG RESIDUAL STRESS ON STAINLESS STEEL A304 TUBE DRAWN WITH FIXED PLUG Frederico Ozanan Neves Universidade Fedral de São João del Rei fred@ufsj.edu.br Sergio Tonini Button Universidade Estadual de Campinas sergio1@fem.unicamp.br Abstract. Tubular components that present compressive residual stresses in their inner surface can be used as mechanical parts to improve their resistance to torsion and bending cyclic stresses. Tube drawing with internal plug can induce this kind of residual stresses. The main objective of this work is to present a cold drawing tool set designed to generate these compressive residual stresses within stainless steel A304 tubes, and concurrently reduce the drawing loads. This work also presents an indirect experimental procedure to determine these stresses, since the conventional x-ray diffraction method used to measure them demands a planar surface. Tube drawing was simulated by the finite element method. Experimental tests with the tube drawing tool set were also carried out with fixed plugs to analyze the influence of the lubricant, drawing speed and lubrication regimes on the drawing load. Experimental results were compared to numerical results to validate these models and to define the best drawing conditions. These results showed that the x-ray diffraction method used in this work is reliable to determine the residual stresses. It was also shown that the tube drawing tool set was efficient to reduce the drawing load and to generate compressive residual stresses in the inner surface of the drawn tubes. Keywords: Tube drawing, Residual Stresses, Lubrication, Analytical Methods, Finite Element Method. 1. Introduction Wire drawing is an important metalworking process because it can produce parts with good finished suface and improved mechanical properties. Tube drawing can be carried out with or without an internal tool. In the second case, the tool is used to provide a better-finished surface than the obtained without internal tool (Avitzur, 1983). It can be supposed that this tool will induce compressive residual streess in the inner tube surface. Tubes with residual compressive stress on its inner surface can be used as mechanical element such it is more resistant to torsion and bending cyclic stresses (Blazynski, 1986, Brethenoux, 1996). In this work we present a tool set which proved to be able to promote an efficient lubrication in the tools-workpiece interface, reducing drawing force and creating a tube internal surface with compressive residual stress. To analysis residual stress we used the x-ray diffraction method (He, 2003). However, the method is applied to planar surfaces, which is not the case of the tube internal surface. Therefore we proposed an indirect experimental procedure to evaluate the residual stress. A piece of tube after drawing was cut of on its longitudinal axis, and then deformed by flat tools to be planed (Prevey, 1986). The residual stress induced by this procedure was simulated by the Finite Element Method (FEM) and the numerical result was added to the results obtained by x-ray diffraction method in order to obtain a prediction of residual stress. The tube drawing with fixed plug was simulated by the Finite Element Method to obtain a prevision of the residual strees. The results were compared to those obtained by the indirect method previously presented (Karnezis and Farrugia, 1998, Pospiech, 1998). Experimental test were carried out with different drawing speeds, lubrication regimes and lubricants. The results statistically analyzed showed the best condition to reduce drawing force, combined to higher compressive residual stress. 2. Methods and materials 2.1. FEM simulation Tube drawing process was simulated with the software MSC.Superform 2002 using a 3D finite element model as shown in Fig. 1. Tubes with dimension 10 x 1.5 mm (diameter x thickness) were drawn to three diferent area reduction, using four die angles for each reduction. In all simulations, the wall thickness was reduced from 1.5 mm to 1.4 mm. A quarter piece of tube 100 mm long was modeled using a number of 3200 brick elements with 8 nodes to define the mesh. This length was tested in order to obtain the steady-state condition. The die geometry presented a 30º half entry angle, a 15º half exit angle and bearing length of 0.4 times the outlet dameter.