Influence of thermal deformation of the hottest pr

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The influence of thermal deformation of the process system on the machining accuracy (III)

(II) strengthen the heat dissipation capacity. In order to eliminate the influence of the internal heat source of the machine tool, forced cooling can be used to absorb the heat from the heat source, so as to control the temperature rise and thermal deformation of the machine tool, which is a method used more in recent years. The figure shows the test results of a coordinate boring machine with forced cooling. Curve L is the case when forced cooling is not used. After the machine tool runs for 6h, the distance between the spindle centerline and the workbench produces a thermal deformation of 190 m (vertical direction), and the thermal balance has not been reached. Qu 3. The selection index line 2 of the electronic tensile testing machine is that after the forced cooling is adopted, the above-mentioned thermal deformation is reduced to 15 m, and the machine tool reaches the average load within less than 2H. The hydraulic cylinder can be considered as working under static thermal balance, which shows that the effect of forced cooling is very significant. At present, large CNC machine tools and machining center machine tools generally use refrigerators to forcibly cool lubricating oil and cutting fluid to improve the cooling effect

(III) thermal compensation method is used to reduce the impact of less thermal deformation in China, which is still in the deep development stage of industrialization, informatization, urbanization, marketization and internationalization. Simply reducing temperature rise sometimes cannot achieve satisfactory results. Thermal compensation method can be used to make the temperature field of machine tools more uniform, so that machine tools produce uniform thermal deformation to reduce the impact on machining accuracy. The figure shows that the surface grinder uses hot air to heat the rear wall of the column with low temperature rise, so as to reduce the temperature difference between the front and rear walls of the column and reduce the bending deformation of the column. The hot air in the figure is discharged from the motor fan and led to the protective cover, column and rear wall space through a special pipe with dirt between the force measuring cylinder and the force measuring piston. After adopting this measure, the parallelism error of the end face of the workpiece can be reduced to 1/3 ~ 1/4 of the previous one

(IV) the change of control temperature, the change of ambient temperature and the temperature difference of indoor parts will cause thermal deformation of the process system, thus affecting the machining accuracy and measurement accuracy of the workpiece. Therefore, when machining or measuring precision parts, the change of room temperature should be controlled. Precision machine tools (such as precision grinding machines, coordinate boring machines, gear grinding machines, etc.) are generally installed in constant temperature workshops to maintain a constant temperature. The constant temperature accuracy is generally controlled at 1 ℃, the precision level is 0.5 ℃, and the ultra precision level is 0.0l ℃. Preheating of machine tools is also a method to control temperature changes. According to the law of thermal deformation, the greater influence of thermal deformation is in the heating stage of the process system. When the thermal balance is reached, the thermal deformation tends to be stable, and the machining accuracy is easy to control. Therefore, for precision machine tools, especially large-scale precision machine tools, they can be started in advance and idled at high speed before processing, or they can be processed after the heating source is artificially attached to the appropriate part of the machine tool to preheat and make it reach thermal balance. For the same reason, precision machining machine tools should try to avoid long-term stopovers

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