Workpiece Coupling in Machine Tools Using Experimental-Analytical Dynamic Substructuring

Abstract

The process stability of a metal cutting operation is determined by the dynamic compliance behavior of the machine components lying within the force flux. This not only includes the cutting tool and the machine tool structure but also the workpiece. The problem of predicting the tool tip frequency response function (FRF) of a tool in a clamped state has been addressed in the literature using experimental dynamic substructuring. However, the problem of predicting the compliance behavior of a point on a workpiece, which is clamped on a machine table, has not yet been addressed comprehensively. In case of a milling machine, workpieces are often clamped using bolted joints or fixtures. In this paper, an efficient method for coupling a milling workpiece to a machining table is proposed using experimental-analytical substructure coupling techniques such that, an FRF at any point on the clamped workpiece can be predicted. This FRF can then be utilized for predicting process stability. In the proposed method, the dynamic behavior of the workpiece is simulated using a discretized model and that of the table is measured experimentally. The accurate measurement of the experimental model of the table is essential for successful substructure coupling. This includes the measurement of translational as well as rotational compliances at the coupling points. For overcoming the challenge of the measurement of rotational compliances, an alternative method using decoupling is proposed and compared with several relevant experimental techniques from the literature. Additionally, a sensitivity analysis is carried out in order to identify the most relevant compliances necessary for an accurate prediction of the dynamics in clamped state. Based on these results, a guideline for successful coupling of workpieces or fixtures with a machining table are proposed. The proposed method is implemented and validated for a workpiece clamped to a milling machine table using bolted joints.