| High speed machining (HSM) offers tremendous capabilities for discrete part manufacturing because it can provide high material removal rates (MRR) in metals, plastics, and composites with good surface finish. To realize these benefits, stability lobe diagrams, which define regions of stable cutting as a function of spindle speed and axial depth of cut, can be used to select appropriate cutting conditions. Computation of these diagrams requires that the dynamics of the cutting system (the machine, spindle, holder, and tool assembly) be known. Typically, impact testing (i.e., exciting the structure with an instrumented hammer and recording the response with a linear transducer) is used to record the required tool point frequency response. However, due to the diversity of tool holders and tools available to end users, it can be prohibitively time-consuming to perform impact testing for each possible combination. Further, it is difficult to measure the responses of (1) small tools using traditional methods; and (2) spindles during high speed rotation. The former is necessary for new micro-milling applications, while the latter is required because the at-speed response for some spindles can differ from the nonrotating response.;This study provides a method to address these situations. The tool tip response for a given machine-spindle-holder-tool assembly is predicted by coupling a spindle measurement with finite element models of the holder and tool using the method of receptance coupling substructure analysis (RCSA). RCSA enables a user to analytically couple arbitrary tool-holder combinations to an archived spindle response. Therefore, the user must perform only a single test on the spindle in question. Given this information, the tool point response for any tool-holder can be performed via a 'virtual impact test'. Comparisons of predictions and experimental results are provided for (1) micro-tools; and (2) macro-scale tools coupled to a spindle that exhibits changing dynamics with spindle speed. |
