Drawing process of thin walled tubes used to fabricate catheters and stents for medical applications was studied. Medical use needs accurate dimensions and a smooth finish of the inner and outer surfaces. This paper deals with 316L stainless steel tubes which are manufactured by means of cold drawing with or without inner plug (mandrel drawing and hollow sinking, respectively). To improve the quality of the finish of the tubes, numerical modelling can be used. In this way, a thermomechanical study of the drawing process is proposed to determine experimentally the physical parameters. This study proposes to evaluate the different parameters of the constitutive equations, of the thermal and friction models using specific experimental tests or using an inverse analysis on the drawing process. These parameters are validated by analysing other tube drawings. Finally the importance of physical parameters fit on drawing limits is emphasised, using a Cockcroft-Latham failure criterion.
Drawing process is used in manufacturing thin-walled tubes, while reducing progressively their wall thickness and their inner and outer diameters. In this paper a stainless steel 316LVM is studied with one drawing process: hollow sinking. This study gets into different issues including elastoplastic behaviour, thermomechanical coupling, contacts, friction and numerical convergence. Experimental drawings are realized on a testing bench where forces, dimensional data and temperature are recorded. In a first approach, tensile tests lead us to use an elastoplastic constitutive equation with an isotropic hardening law. In simulations, an axisymetric steadystate thermomechanical model is used. Numerical results are compared with experimental results. Finally, in spite of some defaults, this study shows that finite element modelling is able to foresee accurately the thermomechanical behaviour of a tube during a drawing process. A better understanding and modelling of the thermomechanical behaviour of materials will improve the FEM simulation results.
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