At present, the automatic tool changer (ATC) of the machining center has two common types of tool change. One is that the tool is directly exchanged from the tool magazine by the spindle, and the other is to rely on the manipulator to complete the exchange of the tool on the spindle and the tool magazine. The first tool change method is suitable for small machining centers, the tool magazine is small, the tools are few, the tool change is simple, and it is easy to find and eliminate in time when the tool is broken. The second tool change method is a more complicated one in terms of structure and movement. This article takes the Vcenter-80 type machining center as an example to analyze and deal with the phenomenon of broken tool.
1. Analysis of the tool change action of the machining center
Here, the ATC data exchange, transfer, storage and tool number storage are omitted, and the tool change action is briefly described as follows: CNC tool change command (M06) → tool sleeve down → down into position → manipulator rotation → rotation deceleration → rotation In place (X4.7) → spindle tool release → release in place → robot rotation → rotation deceleration → rotation in place → spindle tool clamping → clamp in place (X2.5) → manipulator reverse → machine home position, tool change is completed. Among them, the fast and slow speed of the manipulator is realized by the frequency converter, and when the motor rotates, the mechanical cam is driven to realize the rise and fall of the manipulator.
2. Knife drop failure
The knife-off failure phenomenon occurs for a long time. At the beginning, it occasionally appears once, once a month, or even once every two or three months. It is caused by accidental factors and does not attract enough attention. It slowly appears once or twice a week. At the same time, it is accompanied by the situation that the knife on the spindle is not in place. Later, it slowly evolved into a shift with multiple failures, which seriously affected the production schedule and caused waste products. Observe carefully that there are two cases of tool drop failure, one is the tool drop after the processing of this step is completed, and the other is that the tool step is not processed at all and the tool falls on the workbench. During the machining process, the tool change action is executed and the action sequence is normal, so there is no alarm phenomenon when the tool is dropped, the tool is installed (installed on the spindle), and the operator only checks the workpiece or hears the abnormal sound of the tool. Only when the fault occurs will there be a lot of waste products in the automatic processing production line due to the loss of the knife.
3. Failure analysis and treatment
- (1) Check the manipulator to execute the ATC tool change troubleshooting steps, and stop the manipulator at the vertical limit position. Check the two claws on the manipulator arm and the springs supporting the claws and other accessories. No problems were found, indicating that the robot grips the tool tightly, and the knife will not fall when the robot rotates.
- (2) Check the tool clamping situation. According to the analysis of the phenomenon that the knife has a wrong installation on the main shaft, it may be that the disc spring in the inner hole of the main shaft cannot clamp the tool, so that the knife is not installed properly, or even the tool is not installed . Disassemble the inside of the main shaft, and found that the disc spring is broken. So all disc springs were replaced. No problems occurred during the test run. After running one shift, the knife fell again.
During the running of the program, the following situation was found: when the spindle tool clamping is not in place, or even there is no clamping action, the manipulator rotates and the tool is dropped. According to the sequence of tool change action in the previous article, analyze the malfunction of the spindle tool clamping in-position travel switch and cause the tool drop fault. Open the PLC ladder diagram, monitor the travel switch (input is X2.5), press the travel switch repeatedly, and it is found that the phenomenon of X2.5 being “0” occurs three times out of more than 20 presses, and presses simultaneously After X2.5 can’t change from “1” state to “0 state”, the phenomenon occurs twice. According to the above, the stroke switch is damaged. This switch is OMRONZC-Q2255, replaced with domestic CXW5-11Q1, and the test run is normal. One week later, the operator still reported the phenomenon of knife drop, of course, the frequency of occurrence is less, which means that the problem of knife drop has not been completely eliminated. (4) The fault treatment is repeated for two hours, and the tool is automatically changed hundreds of times. Finally found a fault: in the case of the robot is not in place, the tool on the spindle is loose, the robot does not grasp the knife, and the phenomenon of knife drop occurs, which shows that the magnetic sensor switch in place is malfunctioning. Replace the switch E2E-CR8C1, the fault phenomenon still exists. Check the PLC ladder diagram, the input point of this switch is X4.7. X4.7 in the ladder diagram is the normally open point. When the switch is inducted, the state is “0”, when it is not inducted, the state is “1”. Its logic state is opposite to that of common inductive switches.
When X4.7 is disconnected, it will also cause the status of X4.7 to be “1”, so check the connection of X4.7 and find that the terminal at the rear of the electromagnetic induction switch is loose at X4.7. Whenever the tool is changed automatically, The slight vibration caused by a series of manipulator cam movements makes the X4.7 line disconnected. In this way, when the manipulator is not in place, the sensor switch that releases the tool is still sensed, but because it is in the disconnected state, X4.7 is “1” state, then when the machine is not in place, the tool is loosened and a tool drop fault occurs. In this case, the tool drop failure is a tool that has been cut in a machining step and then dropped. The above mentioned is a failure in which the tool is dropped without any machining step.
