1. Causes of abnormal treatment precision failure
The causes of the failure of abnormal machining precision are very hidden and difficult to diagnose. abnormal; The engine The operating state is abnormal, that is to say that the electrical and control parts are abnormal; In addition, preparing treatment procedures, selecting human tools and factors can also lead to abnormal treatment accuracy.
2. Principles of diagnostic for defect of CNC machine tools
1. The external machine-tool then internal CNC is a machine tool which integrates the machines, the hydraulics and electrically, so that the occurrence of its faults will also be reflected by these three. Maintenance personnel must first check from the outside to the inside, and try to avoid disappointing and unravel at will, otherwise they will widen the defect, which makes you lose the precision of the machine tool and reduce performance.
2. First mechanics then electrical. Before troubleshooting, first pay attention to the troubleshooting of mechanical defects, which can often achieve twice the result with half of the effort.
3. First static, then move. Out. For destructive faults, the danger must be eliminated before lighting up.
4. First simple then complex. Often, once simple problems resolved, difficult problems can also become easier.
3. Method of diagnostic for defects of the CNC machine
1. Intuitive method: (Look, ask, ask and touch) Question – Phenomenon of failure of machine tools, treatment status, etc.; , etc.
2. Parameter verification method: The parameters are generally stored in RAM. Depending on the defect characteristics.
3. Isolation method: Some defects are difficult to distinguish if they are caused by the CNC part, the Servo system or the mechanical part, and the isolation method is often used.
4. Similar switching methods use spare plates with the same function to replace the suspected models of being defective, or of exchange of models or units by the same function to each other.
5. Functional program test method: write a few small programs to all the instructions of G, M, S, T and functions.
4. Examples of diagnosis of defect and processing of the accuracy of abnormal treatment
1 and 1 Mechanical failure causes abnormal machining precision
Fault phenomenon: A SV-1000 vertical machining center adopts a frank system. During the machining process of the connection connecting rod, it was suddenly found that the anomaly of the power supply of the Z axis was caused by at least 1 mm of cutting error (direction of steering Z).
Troubleshooting: During the investigation, we learned that the flaw was happening suddenly. The machine-tool is jogging and each axis works normally under the operation of manual input data, and the reference point is normal, without any alarm prompt, the possibility of hard defects in the electrical control part is eliminated . The following aspects must be inspected one by one.
Check the blocks of the machining program that run when the tool-tool is precisely abnormal, in particular the compensation for the length of the tool, rereading and calculating the machining coordinate system (G54-G59) .
In jogging mode, the Z axis is moved several times, and after having seen, touched and hearing, the state of motion is diagnosed, and it is found that the noise of direction Z is abnormal, in particular jogging Fast, which makes the noise more obvious. From this, we judge that there may be hidden dangers in mechanical aspects.
Check the precision of the Z axis of the tooltip. Use a hand-handled pulse generator to move the Z axis (adjust its magnification on the 1 × 100 gear, that is to say each change stage, the engine feeds 0.1 mm) and Use the dial counter to observe the movement of the movement of the Z axis. After the one -way movement remains normal, the forward movement is used as a starting point for each stage of the impulse change, the real distance of the movement of the axis z of the machine d = d1 = d2 = D3 =… = 0.1 mm, indicating that the engine works well and that the positioning precision is also good. Return to the real movement of movement of the tool-tool, it can be divided into four stages: (1) The movement distance of the machine D1> D = 0.1 mm (slope greater than 1); (2) It is represented as D1 = 0.1 mm> D2> D3 (the slope is less than 1); (3) The machine mechanism has not really moved, showing the most standard opposite gap; Fixed value (the slope is equal to 1) and it comes back to the normal movement of the tool-tool. Regardless of how the opposite difference is offset, it shows that, with the exception of the compensation for the step (3), other changes still exist, in particular the step (1) seriously affecting the accuracy of Machining of the machine tool. It has been noted in compensation that the greater the gap compensation, the more the distance to move in the stadium (1).
The above inspection shows that there are several possible reasons: first, there is an anomaly in the engine, secondly, there is a mechanical defect, and thirdly, there is a gap in the lead screw. To further diagnose the defect, the engine and the lead screw have been completely disconnected and the engine and the mechanical parts were inspected respectively. The inspection result was that the engine was operating normally; In normal circumstances, the bearing should be able to feel the ordered and smooth movement.
Troubleshooting: After the disassembly inspection, it was found that the bearing was indeed damaged and that the bullets fell. The machine tool returns to normal after replacement.
2. The inappropriate control logic leads to an abnormal treatment accuracy
Failure phenomenon: machining center produced by a manufacturer of Shanghai machine tools, the system is frank. 1.2 mm. As part of the manual data input method, run a program in the G54 coordinate system, namely “Goog90g54x60.oy70.of150;”; “, after the operation of the monitoring tool, the value of coordinate value Mechanics displayed on the monitor is (axis x) “-1025.243”, record under this value. Then, in manual mode, activate the machine to the tool to any other position and run the program block earlier under the manual data input function. , which is the same as the previous execution. On the screen is different (unstable). A careful inspection of the X axis was carried out using a dial table and found that the real error in the mechanical position was fundamentally the same as the error displayed by the numbers, so it was believed That the cause of the fault was that the repeated positioning error of the X axis was too large. The opposite space and the positioning precision of the X axis are verified to reward the error value and the result is not effective. Therefore, there is a doubt that there are problems with the network scale and the parameters of the system. But why such a big mistake occurs, but no corresponding alarm information appears.
Troubleshooting: Modify the logical control program of the machine machine automaton, that is to say when the X axis is released, the X axis is activated first, then the X axis is released ; The X axis is tight first. Machine failure after setting is resolved.
3. The machine-tool position problem leads to abnormal machining precision
Fault phenomenon: A vertical CNC milling machine made in Hangzhou is equipped with the KND-10M system in Beijing. During jogging or treatment, an abnormal Z axis is found.
Fault diagnosis: The inspection revealed that the Z axis moved from top to bottom and that there was a certain gap. When the engine begins, there is an unstable noise and an uneven strength when the Z axis is moved to jogging mode, and it thinks that the engine is rushing more seriously; not shake. The analysis considers that there are three reasons for failure: one is that the reverse clearance of the lead screw is very large; unequal force. But there is a problem to note that there is no jig when stopping, and the movement from top to bottom is uneven, so the problem of the operation of the abnormal engine can be eliminated. Consequently, the mechanical part is diagnosed first, and no anomaly is found during the diagnostic test, in tolerance. Using the elimination rule, the only thing that remains is the problem of the belt. The inside of the belt, which was obviously due to an unequal force. caused an uneven force.
Troubleshooting: simply reinstall the engine, align the angle, measure the distance (the engine and the Z axis bearings), and the (length) of the belt must be uniform. In this way, the movement of the Z axis is uneven and the noise and the jig are eliminated, and the treatment of the Z axis returns to normal.
4. System parameters are not optimized and the engine works abnormally
The parameters of the system which lead to an abnormal machining precision mainly include the supply units of the machines, the bias of zero points, the reverse deviation, etc. For example, the Frank CNC system has two food units: metric and imperial systems. During the machine repair process, local treatment often affects changes in the shift and the zero point difference, and the appropriate adjustments and modifications must be made after the treatment of the defect; The actual value of the parameter can also be caused by severe mechanical wear or the connection position.
Fault phenomenon: A vertical CNC milling machine made in Hangzhou is equipped with the KND-10M system in Beijing. During the processing process, abnormal precision of the X axis was found.
Fault diagnosis: The inspection revealed that there was a certain gap in the X axis and that there was instability at the start of the engine. When you touch the engine of the X axis with your hands, I think that the engine pulls hard and that the traction is not obvious when stopping, especially in jogging mode. The analysis considers that there are two reasons for the fault: one is that the reverse release of screw is important;
Troubleshooting: Use the KND-10M system settings to debug the engine. First of all, compensate for the existing difference, then adjust the parameters of the servo system and the parameters of the impulse deletion function, eliminate the jig from the X axis and restore the machining accuracy of the Machine-tool for normal.
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