Failure Analysis and Maintenance of CNC Cutting Machine System

1. Processing size or precision errors are too large:
There are a lot of bugs in there, and they behave differently when they appear on various devices. For example, when a CNC lathe comes in diametrically, it may be smaller. What inspections need to be done before the CNC cutting machine starts? There are many errors on the vertical axis of the machining center. A gradual downward decrease in size is common, but an upward increase in size also exists. On the horizontal axis, there will often be some small wrong glitches, and some conditions will change frequently, which, for better or worse, can make the size of the part difficult to control. There are several cases where errors in CNC cutting machines are malfunctioning, but there are no alarms:
1) The geometric error of the machine tool is too large, and the mechanical precision of the machine tool cannot meet the requirements.
2) The CNC system of the machine tool is relatively simple. No errors are detected in the system, so no alerts are displayed in the event of a machine failure.
3) Errors that occur in the machine tool are not in the range predicted by the design, so errors are not detected when they occur.
Since most CNC machine tools use a semi-closed loop system, the actual position of the machine tool cannot be detected.
4) The coupling structure of the lead screw and the motor has different frequency and possibility of failure. The phenomenon after the failure occurs is different. Some dimensions will only increase in the negative direction, but certain positive and negative directions may change elastic connections. The increase in the negative direction is large, and both failures in the middle using key connections will occur.
5) The zeroing of the electrical system of the machine tool is improper, and the zeroing cannot be guaranteed to be consistent. The error of this kind of fault is generally very small. In addition to the general failure caused by the poor deceleration switch, the deceleration distance when returning to zero will also cause the zero point to deviate. In some systems, there is a "delete count" on the monitoring page, which is recorded and checked frequently to catch problems in time.
6) When the machine tool is moving, due to overshoot, the machining accuracy and machining size error are too large. If the acceleration/deceleration time constant is too small, the motor current has formed saturation, resulting in overshoot of the servo motion, which may cause the processing accuracy and processing size of the system to become larger. At this time, the processing error can be eliminated by adjusting the parameters of the servo drive, thereby improving the motion performance of the axis.
7) When tool nose radius compensation is used, G41 and G42 cannot be used correctly during reverse rotation, or G41 and G42 cannot be modified.
8) The relative position and bearing number of the tool and workpiece are not set correctly.
9) The tool is incorrect, or the tool nose radius is not considered during machining.
Case 1:
Fault phenomenon: After the machining center has been in operation for 9 months, the machining size in the Z-axis direction is unstable, the size is too poor, and irregular, and there is no alarm or difference between the display and the servo drive.
Fault analysis: The machining center of the CNC cutting machine is a CNC system imported from abroad, and the screws are directly connected. The failure analysis may be due to the coupling coupling screw being loose, causing the coupling to slip between the roller screws or the servo motor. After carefully checking the Z axis, it was found that the fastening screw of the coupling 6 was loose and tightened. After securing the screws, proceed to troubleshooting.
2. Two-axis simultaneous milling roundness
There are two general cases of roundness tolerance: one is the axial deformation of the circle; the other is the axial deformation of the circle. The other is an oblique ellipse, that is, an ellipse oriented at 45 degrees.
1) The axial deformation of the arc is caused by the poor positioning of the machine tool due to the mechanical adjustment of the machine tool or the improper compensation of the lead screw gap of the machine tool. Every time the machine tool is processing, an arc overrun will occur. degree error.
2) When the tilt ellipse error occurs, it is usually caused by the excessive position deviation of each axis. By adjusting the gain of each axis, the motion performance of each axis can be improved. The kinematic characteristics of each axis are relatively close. In addition, if the gap between the mechanical transmission pair is too large or the gap compensation is not suitable, it may also cause failure.
3. When two axes are connected to mill a circle, there will be protrusions on the arc.
When the arc cutting passes through the quadrant at a certain angle (0, 90, 180, 270 degrees), the motor needs to be reversed, and due to mechanical friction, recoil and other reasons, the speed cannot be continuous, resulting in arc protrusion.
4. When processing a lathe, the G02 and G03 processing paths are not circular or the arc data error is reported
1) The parameter setting is wrong, such as the machining plane selector is wrong.
2) The radius programming input of X-axis programming is the diameter value, and the diameter
• Enter radius values during programming
5. Automatic running time reporting program instruction error
1) There is an illegal address word in the program
2) Fixed loop parameter setting error
Case 1:
Fault phenomenon: When the machining center is machining a full circle, the machining size in the X-axis direction is incorrect and the size is too poor. There is no alarm or abnormality on the display and servo drive.
Fault analysis: The machining center is a household numerical control system. Screws connect directly. According to the fault analysis, the reason may be that the positioning accuracy of the axis is not good due to the mechanical adjustment of the machine tool, or the screw clearance of the machine tool is not properly compensated, resulting in a roundness error of the machine tool every time it rotates. Overrun. Re-adjust the level of the machine and make adjustments, check the parameters of the machine, and find that the backlash compensation of the machine shaft is zero. The clearance of the X-axis is measured by a dial gauge. The actual measured value exceeds 0.003 mm, the X-axis of the machine tool has been adjusted, and the software compensation function of the system is used to eliminate the gap of the X-axis, and the entire circle is processed again for inspection, and the fault has been eliminated. For more detailed information on CNC cutting machines and welding robots, please click