Precision cold forming modelling, interfacial thermal parameter investigation and tool design optimisation
Precision cold forming process modelling, thermal contact conductance and optimum shrink-fitted die with profiled interference were studied. The aims of this work have been achieved using analytical, numerical and experimental approaches to the relevant subjects. Several features of the work are presented: (i) an application of systematic modelling IDEFO language, (ii) an equivalent asperity of surface that enables FE simulation of surface deformation and (iii) a shrink-fitted die with profiled interference, which enables compensation for component-error and necessary die surface pre-stresses. Cold forming process was modelled systematically by IDEFO language in general. The most often used iterations, including design and error-compensation procedures, were constructed; basic activities, inputs, resources and constraints were defined and decomposed. These provide a general procedure for precision cold forming design and a base for the following research of this work. A thermal contact conductance (h -value) experimental investigation was conducted based on steady-temperature measurements and devices. h -value as a function of surface texture and interfacial pressure was experimentally investigated; typically, the value changes from 10 kWm⁻²K⁻¹ to 150 kWm⁻²K⁻¹ for changes in surface texture from Ra = 0.3 0.5 , um to Ra =3-5, um , depending on interfacial pressure (<180 MPa). Based on surface measurements and mathematical work, an equivalent asperity for isotropic surface was presented to represent surface geometry. Uniqueness of the equivalent asperity enables simulation of surface deformation by FE technology. Surface textures under interfacial pressure up to 300 MPa were successfully predicted by FE simulations, results being in agreement with surface measurements. h -value is defined as a function of either contact area ratio or local interfacial pressure; a FE model and an approach of integration of local h -value were dev eloped; value of h was successfully predicted by the established FE model and integration. A profiled interference for shrink-fitting die was designed for component-errors compensation and die surface pre-stress. This was achieved by considering the relationship between die pre-deflection and the profiled interference by FE simulations and a minimisation procedure. Both, the equation and minimisation procedure to determine the profiled interference were established analytically. Uniform die surface direct compensation is combined with shrink-fitted die. Component-errors can be controlled to within a few microns.