Prediction of Thermal Distortions by a Newly Developed Dimensionless Model

D. Landek, , D. Lisjak, T. Lübben:
New challenges in heat treatment and surface engineering – conference in honour of prof. Božidar Liščić (09 – 12 June 2009, Dubrovnik – Cavtat, Croatia)

Investigations of transformation free cooling processes of long cylindrical workpieces in a gas nozzle field conducted at project SFB 570, at research Centre for Distortion Engineering University of Bremen, Germany, indicated a specific behavior of the dimensional changes. It is find that the dimension changes are correlated to only a few dimensionless numbers which are created by the following parameters: shape and dimensions of component, its initial temperature, temperature of the quenching media, heat transfer coefficient, heat conductivity, heat capacity, density, thermal expansion coefficient, Young´s modulus, Poisson´s ratio, yield strength and strain hardening behavior. The mentioned material’s properties were selected form from literature from a group of 29 austenitic stainless steels, and they are statistically analyzed. The mechanical response of steel on the transformation free cooling process is analyzed by the kinematic strain-hardening model by using the commercial FEM program SYSWELD. The relative changes of the component dimensions are analyzed in dependence of five autonomous dimensionless numbers with theirs interactions in aim to find the proper equations for prediction of unavoidable distortions in a transformation free cooling. For definition of these equations a standard method of regression analysis and a novel method known as genetic algorithm analysis are used. This new conception of predicting unavoidable distortions depended of specified material and process parameters by dimensionless numbers are proposed as the “FL3 model”.

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