Experimental verification of a numerical model of a vertical machining centre

The Machine Technology Department has developed an optimization method of machine tool bodies relying on the combined techniques of the finite element method and genetic algorithms. The method was applied in the optimization process of selected bodies of a newly designed milling machine centre. We can say that a new concept of designing of machine tool frames has been proposed because up till now, frames are designed using an analogy or an experimental method, simplified analytical models (for example, a column is modeled as a beam) or making use of experienced designers only. Because of complexity of typical machine tool frames analytical models are used very rarely. The use of numerical models of frames needs not only experience in the design process but in CAE systems (FEM, CAD) as well. In the literature there is little information about results of the optimization of frames of machine tools and there is no information about the results of experimental verification of optimized frames for machine tools. For that reason an experimental prototype of a new milling machine centre was made of metal and then verified in the course of the scientific investigation. The paper presents a numerical model of two key bodies of a milling machine centre together with simulation and experimental investigation results. In the case of stiffness indicator values, for which the displacement is measured during the experimental investigation amounted up to several or more μm, the conformity of results was satisfactory, i.e. the results varied no more than 10-15%. Yet, for cases where stiffness indicators amounted up to several thousand N/μm the discrepancies were 100% and more. The direct reason for such significant differences was the high uncertainty of measurements related to extremely minute displacements. The measuring process in a workshop environment at the level of 1 - 2 μm with uncertainty less than 1 μm is technically difficult to conduct thus entailing significant measuring errors.