This article summarizes the common faults of CNC grinding machines, and then analyzes the causes of the faults according to the fault phenomena combined with the faults that occurred in the field tracking test, and proposes solutions.
Common Faults and Solutions of CNC Grinding Machines
Abstract: This article summarizes the common faults of CNC grinding machines, and then analyzes the causes of the faults according to the fault phenomena combined with the faults that occurred in the field tracking test, and proposes solutions.
Keywords: CNC guide rail grinder; fault phenomenon; solution
In the context of economic globalization, customers' requirements for product performance and quality are constantly increasing, and the structure and function of products are becoming more and more complex, so the precision and production efficiency of mechanical products are also put forward higher and higher requirements. Especially in the fields of automobiles, ships, aerospace, military and other fields, the precision requirements of mechanical workpieces and molds are getting higher and higher, and the shapes are becoming more and more complex. In order to meet the processing needs of modern manufacturing industry, CNC machine tools not only came into being, but also developed in the direction of high processing accuracy, stable processing quality, good flexibility and suitable for complex product manufacturing.
At the same time, the market also puts forward higher requirements on the quality indicators of CNC machine tools such as reliability, stability and life. Therefore, my country formulated the CNC machine tool reliability assessment standard in 2009: GB/T23567.1-2009. According to the content of the standard, a 2000-hour on-site tracking statistical test was conducted on multiple CNC guide rail grinders produced by a machine tool factory. The following analyzes the common faults of CNC grinders and the faults that occurred in the reliability test and proposes solutions for reference.
1. CNC system failures and maintenance skills
With the enhancement of the functions and technologies of modern CNC systems, the trouble-free working time of CNC systems has also been greatly improved, but CNC systems occasionally still have some faults. Common faults in CNC systems can be divided into two categories: software faults and hardware faults. Software faults are caused by errors in the processing program, problems with machine tool data, or some parameters are not set properly. This type of fault can be checked and analyzed through the prompts of the alarm information. After the problem is found, the corresponding program can be modified to eliminate the fault.
Hardware failure, as the name implies, is that the CNC machine tool cannot operate normally due to damage to the hardware module of the CNC system. The hardware modules of the CNC system include CPU module, memory module, display module, measurement module, PLC interface module, power module, display, etc.
For hardware failures of CNC machine tools, you only need to find the problematic module and repair or replace it to eliminate the fault.
2. Servo system failure and maintenance skills
The servo system is a feedback control system that compares the input given value with the output measured value through the command pulse, and uses the compared deviation value to automatically adjust the system to eliminate the deviation. The servo system is the key actuator of the CNC machine tool. Therefore, the failure of the servo system is an important part of the entire CNC machine tool failure.
The following lists some typical servo system failures and discusses the common failure forms and diagnostic methods of the servo system.
(1) Reference point return failure: Common failures of machine tool reference point return can generally be divided into two types: unable to find the reference point and unable to find the reference point accurately. The former is mainly caused by the failure of the signal of the reference point deceleration switch or the zero mark pulse signal (including the signal not being generated and lost during transmission). When troubleshooting this type of failure, you must first understand the machine tool reference point return method, and then analyze it in accordance with the fault phenomenon; the latter is often caused by improper setting of the reference point switch block position, and the fault can be eliminated by re-adjusting the block position.
(2) Servo motor does not rotate: Because the CNC system sends an enable control signal to the feed drive unit in addition to the speed signal. Therefore, the reasons for the servo motor not rotating are: CNC system failure, enable signal failure, feed drive unit failure, servo motor failure. Solution: Check whether the CNC system has signal output, whether the signal is connected to the motor and the servo motor itself.
(3) Position error: When the servo axis movement exceeds the position tolerance range, the CNC system will generate an alarm for excessive position error, including following error, contour error and positioning error. The main reasons are: the system setting tolerance range is too small, the servo system gain setting is improper, the position detection device is contaminated or damaged, and the feed transmission chain cumulative error is too large.
3. Hydraulic system failure and maintenance skills
As an important part of the mechatronic system, the hydraulic system has an important impact on the performance and reliability of the CNC machine tool. The hydraulic system works in a closed environment. Its common fault types include: large vibration and abnormal noise: it is a comprehensive manifestation of system failure. The analysis is based on the fault data bit, focusing on the main fault points such as changes in hydraulic oil characteristics, hydraulic pump oil suction process, and hydraulic pump blockage. The main causes of this fault are serious hydraulic oil pollution, poor sealing of pipes and joints, etc.
Insufficient pressure or large fluctuations: the main manifestation of this fault is that the load does not move or stops from time to time. The analysis mainly starts from the hydraulic pump, hydraulic circuit leakage, and hydraulic actuator cylinder string. The main causes of this fault are hydraulic oil pollution, poor sealing of pipes and joints, improper assembly and sealing of hydraulic cylinders, etc. Unstable flow: this fault is mainly manifested in the speed of the actuator being fast and slow.
The starting point and cause of this fault analysis are similar to the previous fault. Component failure: this fault is mainly caused by the failure of components such as hydraulic pumps, control valves, and hydraulic cylinders under normal oil circuit conditions. It can be analyzed from the mechanical structure of the components and their working mode. The main causes of this fault are hydraulic oil pollution, poor component assembly, and improper user maintenance.
4. Failure and maintenance skills of auxiliary devices of grinding machines
CNC grinding machines have many special auxiliary devices, such as grinding wheel spindle, grinding wheel automatic balancer, grinding wheel dresser, etc. Its common failures are: Grinding wheel spindle failure: Grinding wheel spindle failure can generally be divided into mechanical failure, control part failure
, inverter failure and electric spindle failure. Its common failure phenomena include no feedback of spindle speed, abnormal grinding wheel speed, spindle overload, and spindle stopping before reaching the working speed. Grinding wheel automatic balancer failure: The grinding wheel balancer starts the balancing function and automatically balances the grinding wheel. When the grinding wheel balance does not meet the requirements, the machine tool will alarm and stop the grinding wheel rotation. Its failure phenomenon is often that the grinding wheel spindle stops and the spindle does not start.
5. Conclusion
The complex and diverse structures of CNC machine tools lead to a variety of failures. And failures play an important role in the reliability analysis and improvement of CNC machine tools. As we all know, high-reliability CNC machine tools can reduce the production costs of users and the after-sales costs of manufacturers, with obvious economic benefits. At the same time, they can also promote the development of national industry. Therefore, in the actual production, manufacturing and maintenance process, enterprises should pay attention to the collection of fault data and ensure the comprehensiveness and integrity of the data during the collection process.