Is it necessary to warm up the CNC machine tools when turning them on every morning?



Factories use precision CNC machine tools (machining centers, EDM, wire-cut machines, etc.) for high-precision machining. Do you have this experience: when the machine is turned on every morning for machining, the machining accuracy of the first piece is often not good enough; the first batch of parts processed after a long vacation often have unstable accuracy, and the probability of failure during high-precision machining is extremely high, especially the position accuracy.

Factories without experience in precision machining often attribute the cause of this unstable accuracy to equipment quality problems. Factories with experience in precision machining attach great importance to the thermal balance between ambient temperature and machine tools.

They know very well that even high-precision machine tools can only obtain stable machining accuracy in a stable temperature environment and thermal balance state. In the case of high-precision machining production after starting the machine, preheating the machine tool is the most basic common sense of precision machining.

1. Why do we need to preheat the machine tool?

The thermal characteristics of CNC machine tools have an important influence on machining accuracy, accounting for more than half of the machining accuracy. The guide rails, lead screws and other components used in the spindle and X, Y, and Z motion axis parts of the machine tool will heat up and deform due to load and friction during movement, but the displacement of the spindle and X, Y, and Z motion axis parts relative to the worktable is what ultimately affects the machining accuracy in the thermal deformation error chain.

The machining accuracy of the machine tool is quite different when it is stopped for a long time and in the thermal equilibrium state. The reason is that the temperature of the spindle and each motion axis of the CNC machine tool is relatively maintained at a certain fixed level after running for a period of time, and the thermal accuracy of the CNC machine tool tends to be stable as the machining time changes. This shows that preheating the spindle and moving parts before machining is very necessary.

However, the "warm-up exercise" preparation link of the machine tool is ignored by many factories.

2. How to preheat the machine tool?

If the machine tool has been idle for more than several days, it is recommended to preheat for more than 30 minutes before high-precision machining; if it has been idle for only a few hours, it is recommended to preheat for 5 to 10 minutes before high-precision machining.

The preheating process is to let the machine tool participate in the repeated movement of the machining axis. It is best to perform multi-axis linkage, such as moving the X, Y, and Z axes from the lower left corner of the coordinate system to the upper right corner, and repeatedly moving diagonally.

During execution, a macro program can be written on the machine tool to let the machine tool repeatedly perform the preheating action. For example, when the CNC machine tool is stopped for a long time or before high-precision parts processing, according to the mathematical 3D elliptical parameter curve and the preheated machine tool space range, t is used as the independent variable, and the coordinates of the three motion axes of X, Y, and Z are used as parameter variables. According to a certain incremental 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 the feed speed of the X, Y, and Z motion axes are associated with the independent variable t, allowing it to change continuously within the specified range, and generate a CNC program that can be recognized by the CNC machine tool to drive the various motion axes of the machine tool to produce synchronous no-load motion, and accompanied by the control transformation of the spindle speed and feed speed during the motion process.

After the machine tool is fully preheated, the energetic machine tool can be put into high-precision machining production!