Browsing by Author "DURAN, Deniz"
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Item ANALYSIS OF COLD EXTRUSION(2014-06-09) DURAN, Deniz; KARADOĞAN, Celalettin; ÖZDEMİR, İzzetCold extrusion is a cold forging process where product of smaller cross sectional area is obtained by compressing a billet through an aperture in the die. In this study, different facets of cold extrusion processes are investigated experimentally and numerically to a certain extent that seem to be overlooked in the existing studies. Proper material characterization that is necessary to analyse cold extrusion processes is addressed. A method for reconstruction of isothermal flow curves based on the flawed test data is proposed. An unexpected instability is observed for 16MnCr5 steel in the process range of 200-400°C, where material exhibits negative strain rate sensitivity. This instability is associated with dynamic strain aging phenomenon. The importance of the proposed method is presented for a forward rod extrusion case. The pitfall existing for a common friction identification test, namely, the double cup extrusion test, is emphasized when insufficient material data is used in the inverse analysis. Treatment of surface enlargement, a crucial tribological parameter, within FEA framework under arbitrary deformations is discussed and an alternative calculation scheme is developed. An experimental method for surface enlargement measurement is developed to verify the numerical predictions. A recently proposed, surface evolution based friction model is investigated and possible improvements are addressed. Forward rod extrusion process with multiple area reductions is examined as the proof of concept study. Following, the simulated surface roughness predictions are compared with the experimental surface topography measurements for a forward rod extrusion process.