Abstract
In milling, the dynamic behavior of the tool center point is crucial for estimating surface quality of the workpiece as well as the process stability behavior. Experimental-analytical receptance coupling can be used for predicting the tool tip dynamics but requires accurate analytical modelling of the holder-tool assembly. This includes the reliable identification of the holder-tool joint properties as well as the correct modelling of the fluted segment of end mills. However, the modelling effort associated with accurately representing the dynamic behavior of the fluted segment is significant. In addition, the joint identification requires a reference tool tip frequency response function of the tool assembly clamped in the machine spindle. This is inefficient and can also lead to incorrect estimation of joint properties. This paper provides an efficient method for joint identification and fluted section modelling using an offline, free–free excitation approach. The objective of this paper is to enable a direct comparison of the dynamic behavior of the freely constrained analytical tool assembly model with that of the real freely constrained tool assembly. The comparison of displacement to force frequency response at certain points on the tool assembly allows for the identification of tool model parameters such as the joint properties and effective diameter of the fluted segment. The comparability is realized by extending the analytical holder-tool beam model to include the receptance model of the standard spindle-holder interface. In this study, as an example, a thermal shrink-fit holder-tool beam model is extended to include an HSK-A63 interface. Subsequently, frequency response functions at two points on the real freely constrained tool assembly are measured in order to identify the joint stiffness and effective diameter of the fluted segment using the corresponding proposed formulations. The updated holder-tool model is then coupled with a 4-axis milling machine and validated. Despite the reduced modelling effort, a good prediction accuracy could be achieved for different holder-tool combinations.
Highlights
The relative dynamic compliance behavior between the workpiece and tool determines significantly the allowable material removal rate without instability, surface quality as well as achievable form accuracy [3]
In [16], the Receptance Coupling Substructuring Analysis (RCSA) approach was first proposed for tool coupling where the spindle-side displacement to force receptance was obtained experimentally and the milling tool was simplified as an analytical Euler-Bernoullie beam element
This paper proposes the extension of the beam model of the holder and tool or blank such that this model can be updated using experimentally obtained frequency response function (FRF) of the tool assembly in freely constrained state
Summary
The relative dynamic compliance behavior between the workpiece and tool determines significantly the allowable material removal rate without instability, surface quality as well as achievable form accuracy [3]. The analytical beam model of the holder-tool assembly is extended by coupling the interface end of the holder with the receptance (or compliance) matrix of the interface This augmentation allows for a direct comparison of analytical calculated FRFs with the FRFs obtained experimentally in freely constrained state. These FRFs can be used for updating different parameters (complex stiffness, effective beam diameter, etc.) of the analytical holder-tool model. Using an appropriate receptance coupling formulation, the effective diameters of the fluted segments of end mills with different number of teeth and helix angle are obtained and the tool tip FRF predictions in a 4-axis machine tool are validated
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