Comparative Dynamic Acceptance Tests for Machine Tools Applied to Horizontal Milling Machines

Abstract

The paper is concerned with the objective evaluation of performance improvements achieved in three successive stages of development of a horizontal milling machine. It is proposed that the dynamic quality of machine tools be measured by the coefficient of merit (c.o.m.) of the structure under consideration. This is a measure of the chatter resistance of the machine, being proportional to the maximum width of cut which is stable at all cutting speeds. The c.o.m. is obtained with the aid of vibration tests. It is derived from the ‘operative receptance’ of the system as inversely proportional to its maximum negative in-phase amplitude. After discussing the general basis of this type of acceptance test, the concepts are applied to the particular case of the evaluation of the relative performance of three successive stages of development of a horizontal milling machine. For this purpose the c.o.m. of the three machines are plotted as a function of the depth of cut, with the angle between the normal to the centre of the arc of contact and the representative cutting force as a parameter specifying tool design. These curves can be combined to show the relative improvement achieved in the second or third stages of development with respect to the former designs. The predicted performance of the three machines is verified, for one particular value of the depth of cut, by determining experimentally the stability charts of a milling process carried out on each of them. Some indirect confirmation of the validity of the proposed method for assessing machine tool performance is given by investigating its consistency.