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Unacceptable processing accuracy? The forgotten “machine tool warm-up”

Postview: 656 Date: May 16, 2019

The factory uses high-precision CNC machine tools (machining centers, EDM, wire walking, etc.) for high-precision machining. Do you have such experience and the processing accuracy is not qualified? The machining accuracy of the first piece is often not good enough when the machine is turned on every morning; the first batch of parts that are turned on after a long vacation are often very unstable, and the probability of failure during high-precision machining is extremely high, especially the position accuracy.

Factories without experience in precision machining often blame equipment quality problems for this unstable accuracy. And factories with experience in precision machining will attach great importance to the ambient temperature and the thermal balance of the machine tool. They are very clear that even high-precision machine tools can obtain stable processing accuracy only under a stable temperature environment and thermal equilibrium. The situation of high-precision machining production is required after starting the machine. Preheating the machine tool is the most basic knowledge of precision machining.

Why do you need to warm up the machine?

The thermal characteristics of CNC machine tools have an important influence on the machining accuracy, accounting for almost half of the machining accuracy. The main shaft of the machine tool, the guide rails and screws used in the XYZ moving shaft parts will be heated and deformed due to the load and friction during the movement, but the final deformation accuracy in the thermal deformation error chain is the main shaft and the XYZ moving shaft parts. Table displacement.

The machining accuracy of the machine tool in a long-term stop state and a thermal equilibrium state is quite different. The reason is that the temperature of the spindle and the motion axes of the CNC machine tool is maintained at a fixed level after a period of operation, and With the change of processing time, the thermal precision of CNC machine tools tends to be stable, which shows that it is very necessary to preheat the spindle and moving parts before processing. However, the preparation of the “warm-up exercise” of the machine tool has been ignored or unknown by many factories.

How to preheat the machine?

If the machine is on hold for more than several days, it is recommended to preheat for more than 30 minutes before high-precision machining; if the machine is on hold for only a few hours, it is recommended to preheat for 5-10 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 XYZ axis from the lower left corner of the coordinate system to the upper right corner, and repeatedly walking diagonally.
During execution, a macro program can be written on the machine tool to allow the machine tool to repeatedly perform the warm-up action.

After the machine tool is fully warmed up, the dynamic machine tool can be put into high-precision machining production, and you will get stable and consistent machining accuracy.

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