Accuracy of axial depth of cut in micromilling operations - Simplified procedure and uncertainty model

In order to maintain an optimum cutting speed, the reduction of mill diameters requires machine tools with high rotational speed capabilities. A solution to update existing machine tools is the use of high speed attached spindles. Major drawbacks of these attachments are the high thermal expansion and their rapid warming and cooling, which prevent the achievement of a steady state. Several other factors, independent on the tool-workpiece interaction, influence the machining accuracy. The cutting parameter most heavily affected is the axial depth of cut which is the most critical when using micro end mills, due to the easy breakage particularly when milling on hard materials [1]. Typical values for the errors on the control of the axial depth of cut are in the order of 50 microns, while the aimed depth of cut can be as low as 5 microns. The author has developed a machining procedure for optimal control of axial depth of cut in micromilling operations carried out in a workshop environment. Such a procedure is thoroughly described in [1] and [2] and leads to a reduction of the depth of cut error from 36.5 microns to 2.5 microns. Such accuracy has been determined as the result of machining tests. The focus of this investigation is the determination of the uncertainty of the set depth of cut, using the developed procedure, in a range of practical operating conditions and thereby the estimation of the expected accuracy of the method prior to verification of the machined parts.