Machining Material

Problems In The Use Of CNC Machine Tools

Problems In The Use Of CNC Machine Tools

The numerical control machine tool adopts a digital control system, which can realize multi-axis linkage, realize the processing of three-dimensional shapes, and process parts with complex geometric shapes, which is very popular among people. In recent years, with the widespread application of CNC machine tools, people have a good understanding of CNC technology, and can also eliminate some common faults, thereby improving the utilization rate of the machine tool, but it is still more difficult for some uncommon faults . The following introduces several examples encountered in the maintenance of CNC machine tools in recent years for your reference.

As we all know, rotary encoders or grating rulers are generally used as position feedback components on CNC machine tools. Each time the machine is turned on, it needs to find a reference point to determine the coordinate point of the machine, which is what we often say “return to zero.” After the rotary encoder fails, the “zero return” operation is generally not possible, and an alarm will be issued because the correct reference point cannot be found. The following are some special faults encountered.

Fault phenomenon 1. A CNC lathe made in Taiwan uses the FANUC-0 system. When the tool touches the workpiece during processing, it will generate a 400# alarm (that is, a servo alarm).

Diagnosis and exclusion Check that the processing procedure is correct, check that the mechanical transmission parts of each axis are not obstructed, and the movement is flexible. The diagnostic parameters show that the X axis is overloaded, so check all parts of the motor, but they are normal, and the power supply voltage and the brake coil voltage are also normal. The cables and connectors of all parts are also normal. Replacing the servo unit, axis card and power supply unit still cannot eliminate the fault. Later, contact the manufacturer to replace the encoder in the motor, and the fault is eliminated.

Trouble phenomenon 21 A Swiss turning unit using Siemens SINUMERIKSYSTEM 840C, the X axis can not return to the reference point after starting, the X axis can decelerate but not stop during the “zero return” process, the maximum stroke of each action does not exceed 40mm, until it is pressed Hard limit, the panel coordinate value is abrupt, the display value is very large, and the “X AXIS SW LIMITSWITCH MINUS” alarm is displayed at the same time.

Diagnosis and exclusion Check that the parameter settings in the machine tool are correct, that the cable connection and other peripheral devices have not found a fault, and the machine tool can operate in manual mode and can display coordinate values. The machine tool can be positioned, indicating that the grating ruler should not be damaged. Check that the grating ruler is a German “HEIDENHAIN” product. After understanding that the zero return method adopted by the HEIDENHAIN grating ruler is different from other companies’ products, in order to avoid finding a reference point in a large range, The reference mark is coded according to the distance, and a scribe track is added beside the grating line. The reference position can be found by two adjacent reference marks, that is, within 40mm (or 80mm, depending on the scale model) Find the “zero point”. After removing the shield of the machine tool, it was found that the oil mist entered the grating ruler due to the long use time, the zero mark was blocked, and there was no zero pulse output, so that the machine tool could not find the zero point. Because the device is maintenance-free, contact the manufacturer for replacement and the fault is eliminated.

Symptom 3 One machine cannot return to the correct reference point.

Diagnosis and exclusion This machine tool adopts FANUC-0M system. There is no deceleration bumper on the machine tool, but only a hard limit stop device. The working principle of machine tool “return to zero” is clear to everyone. Generally, the movement is set in the axial direction. After the zero switch is decelerated, the CNC system will be set as the reference point of the machine tool according to the first zero pulse received after leaving the zero switch (there are three ways to return to zero). After contacting the manufacturer, the fault was resolved in the following manner. After starting the machine, manually move the shaft to the hard limit position. After eliminating the “limit alarm”, shake the shaft to 5mm away from the limit switch. After changing the parameters 20 and 21, turn off the machine. After turning on the machine, the fault is eliminated.
For the machine tool failure caused by the sudden power failure, interference or misoperation, we do not have to perform cumbersome operations in order. Sometimes, as long as we master the basic rules, we can solve them in an easy way.

The tool change mechanism of a general CNC machine China tool is composed of 4 parts: the cutter head is pushed out, the cutter head is rotated, the cutter head is pushed in, and the cutter head is clamped. When the tool changer has a disordered tool or the tool fails to be positioned and clamped, it can be recovered manually by following the above steps, but it is quite troublesome. In fact, sometimes as long as we observe carefully, we can discover the law.

Symptom 4 The cutter head is in place after turning but is not clamped

Diagnosis and exclusion According to the electrical schematic diagram of the machine tool, find the corresponding solenoid valve wiring. The machine tool I/O display indicates that the machine tool’s cutter head is in place, but it cannot be clamped. Open the electrical cabinet to find the solenoid valve wiring into which the cutter head is pushed. It can be seen from the relay that it is currently in the unpowered state. Find a temporary line to quickly connect the solenoid valve to solve the problem.

Therefore, to deal with the failure of CNC machine tools, we must consider both its versatility and its particularity. After the fault occurs, both must be considered carefully in order to solve the problem accurately and quickly.

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