CNC machine tools are high-precision automation equipment, which is expensive. In order to ensure long-term safe and stable operation of machine tools, and to play a greater role, it is necessary to pay attention to the maintenance methods of CNC machine tools and the troubles and troubleshooting methods that are prone to occur.
In recent years, CNC machine tools have been widely used in manufacturing, and have become the key equipment for enterprise production, bringing great benefits. However, the advanced, complex and intelligent features of CNC machine tools also make the maintenance requirements of CNC machine tools. Higher, the number of faults that occur increases, and the diagnosis is more difficult.
1 Reasonable use of CNC machine tools
1.1 Workplace selection of CNC machine tools
(1) Avoid direct sunlight and other heat radiation, avoid too humid or excessive dust, try to use in air-conditioned environment, keep room temperature around 20 °C. Because China is in a temperate climate, affected by the monsoon, and the temperature difference is large, for high precision and expensive CNC machine tools, it should be used in air-conditioned rooms. (2) Avoid places with corrosive gases. Corrosive gases tend to deteriorate electronic components, cause poor contact, or cause short-circuiting of components, affecting the normal operation of the machine. (3) Keep away from equipment with high vibration (such as punching machines, forging equipment, etc.). For high-precision machine tools, anti-vibration measures (such as anti-vibration ditch) should also be used. (4) Keep away from strong electromagnetic interference sources and make the machine work stable.
1.2 The power supply CNC system of CNC machine tools has strict requirements on power supply. Generally, the working voltage is 220V±10%. For the power supply conditions in China, for qualified enterprises, special line power supply or voltage regulators can be used for CNC machine tools to reduce the influence of poor power supply quality and provide a strong guarantee for the normal operation of the CNC system.
1.3 CNC machine configuration The appropriate automatic programming system is manually programmed for a part program that is not too complicated or has a small amount of programming. It is simple and easy. When the workpiece is more complicated (such as cam or multi-dimensional space surface), the manual programming cycle is long (several days or weeks), the precision is poor, and it is easy to make mistakes. Therefore, the rapid and accurate programming of the program becomes an important part of improving the utilization rate of CNC machine tools; for this reason, conditional users are better equipped with the necessary automatic programming system to improve programming efficiency.
1.4 CNC machine tools are equipped with the necessary accessories and tools In order to fully utilize the machining capabilities of CNC machine tools, necessary accessories and tools must be provided. Don't spend hundreds of thousands of dollars to buy a CNC machine tool, which affects the normal operation of the whole machine due to the lack of a tens or hundreds of accessories or tools. Since the unit price of the accessory purchased separately by the contract is much higher than the unit price of the accessory supplied with the host, the conditional enterprise tries to purchase the consumable parts and other accessories when purchasing the host.
1.5 Preparation before processing Before processing, it is necessary to review the CNC machining process of the workpiece. Pay attention to the preparation of production technology (including CNC machining process analysis, engineering programming, tooling and tool configuration, raw material preparation and trial cutting) to shorten Production preparation time, fully improve the use efficiency of CNC machine tools.
Reasonably arrange various workpieces suitable for machining on CNC machine tools, and arrange the beats required for CNC machine tool processing.
1.6 Prepare for maintenance and repair to establish a high-level maintenance team. The complete transfer of the saved equipment is generally divided into three areas:
(1) In the initial operation area, the failure rate is high and the fault curve is on the rise. Most of the failures in this area are caused by design and manufacturing and assembly defects. (2) In the normal operation area, the fault curve approaches the level and the failure rate is low. The fault in this area is usually an accident caused by poor operation and maintenance. (3) In the aging zone, the failure rate is large in this area, and the fault curve rises rapidly. The main reason is the long running, the aging of the parts and the excessive wear.
2.2 The classification of faults is divided into mechanical and electrical categories according to the structure; according to the fault source, it is divided into two categories: mechanical fault and control fault; for its numerical control system, it is divided into hardware fault, software first check control system to see if the program can run normally. Whether the display and other function keys are normal, whether there is any alarm phenomenon, etc.; if the motor is not checked, the motor can be preliminarily judged to be in the mechanical aspect, and the transmission link is mainly checked. When checking the drive link, the motor should be de-energized. Check the machine manually and with a watch.
3. Common fault analysis of CNC system
(1) Position loop. This allows the CNC system to issue control commands and compare it with the feedback value of the position detection system to further complete the key aspects of the control task; it has a high operating frequency and is connected to the peripherals, which is prone to failure. Common faults are: 1) Position control loop alarm: It may be that the measurement loop is open, the measurement system is damaged, and the position control unit is damaged internally. 2) Movement without command, may be excessive drift, positive feedback, malfunction of the position control unit, and damage of the measuring component. 3) Measuring component failure, generally showing no feedback value; the machine tool can't return the reference point; the high-speed leak pulse generates an alarm, the possible reason is that the grating or the read head is dirty; the grating is broken.
(2) The pressure fluctuation is too large or caused by a voltage shock. The poor quality of the regional power grid will bring voltage overrun to the machine tool, especially the instantaneous overrun. If there is no special voltage monitor, it is difficult to measure. Pay attention when looking for the cause of the malfunction, and some are damage caused by special causes. 2) The surface of the workpiece does not meet the requirements during machining. When the circular interpolation axis is reversing, the boss appears, and the motor crawls or vibrates at a low speed. This type of fault is generally caused by improper adjustment of the servo system, and the gain systems of the axes are not equal or related to the motor. If the match is not appropriate, the solution is to optimize the adjustment. 3) The fuse is blown, or the motor is overheated, and even burned out. This type of fault is usually caused by excessive mechanical load or jam.
(3) Power section. The direct result of power failure or failure is that the system is shut down or destroyed due to large fluctuations in power supply, poor quality, and high frequency pulse type interference, plus human factors (such as sudden power failure, etc.). Can cause power failure to be out of control or damage. Furthermore, some of the operating data, setting data, and processing programs of the numerical control system are generally stored in the RAM memory, and are maintained by the backup battery or lithium battery of the power supply after the system is powered off. Therefore, the downtime is relatively long, and the power or memory may be unplugged, which may cause data loss and make the system inoperable.
(4) Programmable controller logic interface. The logic control of the CNC system (such as tool magazine management, hydraulic start, etc.) is mainly realized by plc. It is necessary to collect the status information of each control point (such as breaker, servo valve, indicator light, etc.), which has various signals from the outside world. The source and the actuator are connected, the change is frequent, the possibility of failure is more, and the fault type is more.
(5) Others. Due to environmental conditions, such as interference, temperature, humidity exceeding the allowable range, improper operation, and improper parameter settings, it may cause downtime or malfunction. Failure to remove the circuit board according to the operating procedures, or static-free protection measures, may also cause downtime or even damage the system.
4 Troubleshooting methods for common faults
(1) Initialize the reset method. Under normal circumstances, due to the system alarm caused by transient fault, the hardware reset or the power of the switch system can be used to clear the fault in turn; if the system working storage area is chaotic due to power failure, plugging or unloading the circuit board or battery undervoltage, the system must be initialized. Clear, clear data should be recorded before clearing; If the fault is still not eliminated after initialization, hardware diagnosis is required.
(2) Parameter change, program correction method. The system parameters are the basis of the system function. If the parameter settings are incorrect, the system may be faulty or a function may be invalid. Sometimes due to user program errors can also cause downtime, this can be checked by the system's block search function, correcting all errors and ensuring normal operation.
(3) Adjustment and optimization adjustment method. The adjustment is simple and easy, and the system fault can be corrected by adjusting the potentiometer. By adjusting the speed factor and integration time of the speed regulator, the servo system can be used to the most common troubleshooting method.
(4) Improve the power quality method. Currently, a regulated power supply is generally used to improve power supply fluctuations. For high frequency interference, a comprehensive integration of capacitive filtering is available. The coordinated development of various disciplines will strongly promote the expansion of SHPB technology application and the improvement of SHPB testing technology.
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