Research on the Measurement of Thermal Deformation of Tools on High-speed Machining Centers Based on Image Processing Technology

Abstract

In order to improve the efficiency of high-speed machining center and shorten its warm-up time, it is realistic and feasible to measure the thermal deformation of the machine tool system and then improve the machining accuracy of the machine by means of compensation. In this paper, a model XKA714B/A CNC milling machine and a 10mm diameter ball-head milling tool are selected. A high-speed camera is used to capture the gray level images of the tool when the machining center spindle speed is working at 1000 r/min. Using MATLAB software, the image edge extraction is coarsely localized by Canny algorithm, and sub-pixel fitting edge detection method is used to precisely locate the tool edge profile. The least-squares method is applied to fit the tool tip circular curve so as to calculate the thermal deformation during the tool preheating process. The results showed that there is a certain connection between the thermal deformation of the tool and the machine running time during the preheating process of the machine tool. That is, in the initial stage of machine operation, the tool axial thermal deformation is larger. In the 6th to 26th min, the tool thermal deformation gradually becomes smaller. At the 26th minute of preheating, the tool deformation reached more than 96% of the total deformation and the deformation rate leveled off. The axial deformation of the tool was measured to be 130.2 um at this time. Inputting the measurement results into the machining center tool holder control system as the compensation value will shorten the machine warm-up and thermal balance time so as to ensure its machining accuracy, which is of practical significance to improve machining efficiency and reduce cost in the actual production process.

Selected Aspects of Precision Machining on CNC Machine Tools

“…As a result, geometric error in the X direction of CNC machine movement was significantly reduced; however, the proposed compensation model did not consider the effect of cutting parameters and thermal expansion of CNC machine units, as well as cutting tool thermal expansion [23,24]. However, Zhao et al found that the thermal elongation of the cutting tool during the warming-up of a machine tool can reach up to 130 µm in the axial direction [25]. These findings were proved with finite element modeling (FEM) in Ansys software based on measuring spindle unit temperature with thermocouple sensors.…”