Do you have the experience of using precision CNC machine tools (such as machining centers, electric discharge machines, slow wire machines, etc.) in factories for high-precision machining? When starting up every morning for machining, the machining accuracy of the first piece is often not good enough; The accuracy of the first batch of parts processed after a long holiday is often unstable, and the probability of failure during high-precision machining is extremely high, especially in terms of positional accuracy.
Factories without experience in precision machining often attribute the unstable accuracy to equipment quality issues. Factories with precision machining experience will attach great importance to the environmental temperature and the Thermal equilibrium of machine tools. They are very clear that even high-precision machine tools can achieve stable machining accuracy only under stable temperature environment and Thermal equilibrium. Preheating the machine tool is the most basic precision machining knowledge when high-precision machining production needs to be put into operation after startup.
1、 Why do we need to preheat the machine tool?
The thermal characteristics of CNC machine tools have a significant impact on machining accuracy, accounting for almost half of the machining accuracy. The guide rails, screws, and other components used in the spindle and X, Y, and Z motion axes of the machine tool will undergo temperature rise and deformation due to load and friction during movement. However, in the thermal deformation error chain, the ultimate impact on machining accuracy is the displacement of the spindle and X, Y, and Z motion axes relative to the workbench.
The machining accuracy of the machine tool in the state of long-term shutdown and Thermal equilibrium is quite different. The reason is that the temperature of the spindle and each moving axis of the NC machine tool is relatively maintained at a fixed level after running for a period of time, and as the processing time changes, the thermal accuracy of the NC machine tool tends to be stable, which indicates that it is necessary to preheat the spindle and moving parts before processing.
However, the preparation of "Warming up" of machine tools has been ignored by many factories.
2、 How to preheat the machine tool?
If the machine tool has been idle for more than a few days, it is recommended to preheat for at least 30 minutes before high-precision machining; If the idle state is only a few hours, it is recommended to preheat for 5-10 minutes before high-precision machining.
The preheating process involves involving the machine tool in the repeated movement of the machining axis, preferably through multi axis linkage, such as moving the X, Y, and Z axes from the bottom left corner of the coordinate system to the top right corner, and repeatedly walking diagonally. During execution, a macro program can be written on the machine tool to repeatedly execute the preheating action. For example, when a CNC machine tool is stopped for a long time or before high-precision component processing, based on the mathematical 3D elliptical parameter curve and the preheating machine tool space range, t is used as the independent variable, and the coordinates of the X, Y, and Z motion axes are used as the parameter variables. According to a certain increment step, the maximum range of the specified X, Y, and Z motion axes is used as the boundary condition of the parameter curve, and the spindle speed and X, Y The Z-axis feed speed is associated with the independent variable t, allowing it to continuously change within a specified range, generating a CNC program that can be recognized by the CNC machine tool. It is used to drive each motion axis of the machine tool to generate synchronous no-load motion, and accompanied by control changes in spindle speed and feed speed during the motion process.
After sufficient preheating of the machine tool, the dynamic machine tool can be put into high-precision machining production!
Post time: Aug-02-2023