Experience and practices in the management and maintenance of CNC equipment for deep hole drilling

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I. Management of CNC Equipment 1. Management models for CNC equipment The usage of CNC equipment has a direct impact on a company’s production efficiency and economic performance, and the management methods in place determine how effectively such equipment is utilized; hence, the management of CNC equipment is extremely important. In the early stages of the use of CNC equipment, due to the small number of such devices, their limited variety, and their concentration in one or two organizations, each relevant organization developed its own closed management system that integrated the management, use, and maintenance of CNC equipment. With the development of production, more and more equipment is equipped with CNC technology, making it difficult to concentrate such equipment in a single facility; many production workshops now have CNC equipment. Therefore, the aforementioned management model becomes difficult to apply. If the above approach is adopted, each unit would need to establish its own maintenance facilities and staff, which would inevitably lead to significant waste of human, material, and financial resources; moreover, the practical conditions do not permit this. Therefore, we currently adopt a modern management model in which the use of CNC equipment and CNC machining are the responsibility of the workshops, while management and maintenance fall under the responsibility of the mechanical department. 2. Basic and technical management of CNC equipment: For enterprises, owning CNC machines is a reflection of their strength; making the most of these CNC devices is highly beneficial for improving the company’s profitability. Enterprises should not focus only on the utilization rate and optimal performance of equipment; they must also pay attention to its maintenance and repair. Equipment serves as a precursor to production processes, and it is crucial for ensuring that CNC equipment can operate properly over the long term. To maintain the optimal technical condition of numerical control equipment and ensure its full effectiveness, we have focused on the following aspects in terms of equipment infrastructure management and technical maintenance: ① Establishing a dedicated maintenance unit, specifically a numerical control equipment repair room, to handle the management and repair of all numerical control equipment in the plant. They are composed of experienced senior technicians, as well as mechanical and electrical engineers with strong specialized knowledge, a sense of responsibility, and practical working skills. The unit that uses the equipment appoints a CNC equipment technician to be responsible for the daily maintenance of the CNC equipment in that unit. ②Formulate and improve rules and regulations. In light of the characteristics of CNC machines, corresponding management systems should be established gradually, such as management systems for CNC equipment, safety operation procedures for CNC equipment, operating procedures for CNC equipment, maintenance systems for CNC equipment, technical management methods for CNC equipment, maintenance procedures for CNC equipment, as well as the scope of responsibilities for electrical and mechanical maintenance technicians and workers involved in the repair of CNC equipment. This helps to make equipment management more standardized and systematic. ③Establish comprehensive maintenance records by creating records for the upkeep of CNC equipment as well as shift handover logs. Detailed records should be kept of the operation status and any faults that occur with the CNC equipment; in particular, information such as the time when a fault occurs, the affected area, the cause of the fault, the methods used to resolve it, and the process of resolution should all be carefully documented and archived. This will facilitate reference and guidance in future operations and maintenance tasks. ④Establish a basic management information database as well as a database for CNC equipment, detailing the basic characteristics of such equipment and providing fundamental data on its capabilities. This serves as a reference for the future management, utilization, product processing, adjustment, and maintenance of CNC equipment. ⑤Strengthening the acceptance process for CNC equipment: To ensure the quality of new equipment, we have enhanced the work related to its installation, commissioning, and acceptance. In particular, strict measures have been put in place for equipment acceptance, involving a thorough inspection of each item as specified in the contract, technical agreements, relevant international and domestic standards, as well as the acceptance guidelines. The acceptance criteria include: pre-reception checks at the time of leaving the factory (quality inspection during assembly at the manufacturing plant), packaging inspection before unboxing the equipment, and inspection of the appearance and quantity of components after unboxing. All accompanying documents such as user manuals, maintenance manuals, instruction sheets for accessories, system software, and related manuals must be carefully verified and properly stored; in particular, a backup of the system software is required. This facilitates the development of additional functions for future equipment, as well as the maintenance and repair of machine tools. After the machine tool is tuned, data transmission of its parameters is carried out via the RS232 interface as a backup measure. To prevent the loss of machine tool files (parameters). After installation and commissioning, the following items need to be checked: geometric accuracy, positioning accuracy and repeat positioning accuracy, CNC functions, safety and noise levels, the ability to machine standard parts, products specified by the client, the cutting power of the machine tool, and the reliability of the machine tool. During acceptance, claims regarding quality must be supported by factual evidence; strict controls and thorough inspections are required for indicators related to the important performance and precision of machine tools. For example, our factory purchased a German machining center. When checking its precision, it was found that the positioning accuracy for all five coordinates was above the acceptable limits. Upon examining the NC system program of the machine, it became clear that no compensation for positioning accuracy errors had been applied at the time of its manufacture. Faced with these facts, the manufacturer had no choice but to admit fault. Eventually, they sent people twice to adjust and compensate the coordinate accuracy until it met the specified standards. ⑥Strengthen the development of the maintenance team. CNC equipment is a high-tech product that integrates mechanics, electricity, hydraulics (pneumatics), and optics; it has a high level of technical complexity, making operation and maintenance challenging. Therefore, it is necessary to establish a high-quality maintenance team to meet the needs of equipment repair. We carry out training in various forms. First, we utilize equipment installation and commissioning to provide on-site training for operators, maintenance staff, programmers, and management personnel by the manufacturers themselves. Second, we send people out for learning and invite experts in, along with organizing visits and practical training sessions. Third, we use internal training programs to help trainees acquire equipment operation skills as well as maintenance techniques as quickly as possible. ⑦Establishing a collaboration network for CNC equipment: Given the great diversity among CNC equipment, their hardware and software configurations vary significantly, which poses many difficulties for maintenance work. To this end, we have established friendly relations with organizations that use similar CNC equipment, and regularly exchange experiences in management and maintenance as well as share information, which has played a positive role in promoting the use of CNC machines. II. Preventive maintenance of CNC equipment: As the name implies, preventive maintenance involves identifying and eliminating those factors that could cause equipment failures or make it difficult to resolve issues once a failure occurs, before such failures take place. Generally, it should include: the selection of equipment, the proper use of the equipment, and routine inspections during operation. ①From a maintenance perspective, when selecting CNC equipment, in addition to the parameters related to its usability, the parameters related to its maintainability should include the equipment’s level of advancement, reliability, and technical indicators of maintainability. Advancement refers to the technical level that equipment must possess in line with the progress of the times; reliability relates to the average time between failures and the average failure rate, especially whether the control system has passed quality inspection by **authorized institutions; maintainability involves how easy it is to repair the equipment, the availability of spare parts in the market, the completeness of technical documentation for repairs, the quality of after-sales service, the existence of adequate repair capabilities, and whether the performance-to-price ratio of the equipment is reasonable. Here, special attention must be paid to the completeness of the drawing documents, the backup of system disks, PLC program software, system transmission software, transmission methods, operation commands, etc.; none of these can be missing. Technical training for the users cannot be a mere formality; these aspects must be specified in the order contract and implemented carefully, otherwise it will cause problems in future operations. Furthermore, unless there are special circumstances, it is advisable to choose CNC systems from the same series by the same manufacturer, so as to facilitate the availability of spare parts, drawings, and related documentation. Programming and operation both have advantages, and they also contribute to the management and maintenance of equipment. ②Adhere to the proper use of equipment. Correct usage of CNC equipment is key to reducing equipment failures and extending its service life, and it plays a very important role in preventive maintenance. According to statistics, one-third of failures are caused by human error, and routine maintenance tasks such as oiling, cleaning, and inspections are carried out by the operators. The solutions involve emphasizing the importance of equipment management, usage, and maintenance, providing better training in both operational and technical aspects, improving the skills of operators so that they can quickly understand the performance of the machinery, and strictly adhering to the operating procedures and maintenance guidelines to ensure that the equipment operates in an optimal condition. ③Adhere to regular inspections during equipment operation. Given the advanced nature, complexity, and high level of intelligence of CNC equipment, its maintenance tasks are much more complex and require higher standards compared to those of ordinary equipment. Maintenance personnel should conduct regular inspections, such as checking the operation of the exhaust fans in CNC systems, whether cabinets and motors are overheating, if there are any abnormal noises or odors, whether the pressure gauges show normal readings, and whether there are any leaks in the various pipelines and connections as well as assessing the condition of the lubrication. By taking proactive measures to prevent faults and accidents, any issues that arise can be addressed promptly, thereby preventing them from developing further and reducing all avoidable losses. III. Examples of CNC Equipment Maintenance 1. Fault Diagnosis of CNC Systems ① System Self-Diagnosis: Most CNC systems come equipped with a fairly comprehensive self-diagnosis system. Whether it is a Fanuc system or a Siemens system, they are able to perform limited self-diagnosis of themselves or their interfaces during power-up initialization or while in operation. Maintenance personnel should be familiar with various alarm messages from the system’s self-diagnosis. Analyze according to the instructions to determine the scope of the fault. Locating the faulty component: for imported CNC systems, it is generally only possible to locate it at the board level. ②Soft faults in CNC systems refer to the system software of the control system and the PLC programs. Some systems write them into EPROMs that are inserted into the motherboard, while others reside on the hard disk. Once problems arise with these software programs, the system will experience total or partial disruption. Once it is determined that the issue is caused by a software fault, backup software or a replacement EPROM should be used, and the system should be tested after being initialized in strict accordance with the operating procedures. With backup files, such failures are generally not difficult to recover from. The difficulty lies in the inability to restore data due to incomplete backup software, the lack of specialized transfer equipment, or password protection set in the manufacturer’s operating procedures. ③Using PLC programs to locate interface faults in machine tools and CNC systems: Nowadays, most CNC control systems are equipped with PLC controllers, usually built-in ones. Maintenance personnel should analyze the machine tool control electrical components based on the ladder diagram, and visually observe the I/O status of the CNC system on the CRT. Through the logical analysis of the PLC program, it is easy to identify where the problem lies. Such as the self-diagnosis page in the FANUC One OT system, and the T command in the FANUC One 7M system. 2. Troubleshooting steps: ① Ask the operator about the cause of the malfunction. After a malfunction occurs, maintenance personnel should generally not rush to take action. Instead, they must carefully ask under what operating conditions the machine was in when the malfunction happened, what its symptoms were, what consequences resulted from it, and whether it was caused by a human error. Whether the fault can reoccur, etc. ②Surface and basic power supply inspections mainly involve checking for any abnormalities in the equipment, such as mechanical jams in the conveyor belts, damaged motors, or blown fuses. First, check whether the AC/DC power supply is functioning properly to narrow down the scope of the fault as much as possible. ③Analyze the drawings to determine the location of the fault. By examining the PLC ladder diagram in the drawings, it is possible to identify whether the fault lies in the mechanical, electrical, hydraulic, or pneumatic system. ④Broaden your thinking; based on empirical analysis, it is essential to broaden one’s perspective and not stick to what is outlined in the repair manuals. Repair manuals provide only a starting point, and sometimes their limitations are quite significant. For one of our factory’s FANUC OTC CNC lathes, no image appeared on the CRT after it was turned on, and the alarm light on the power supply module lit up. According to the repair manual, it was found that the 24EDC power supply shared by the CRT and the I/O interfaces had a resistance of only 1–2Ω between its positive terminal and the DC ground, whereas similar devices use a resistance of 155Ω. Per the documentation, such faults are usually related to the motherboard, and the machine would have to be sent to the manufacturer for repair. However, we thought outside the box: we first removed the M18 cable connector, but the problem persisted; then we removed the C-S14 connector, and a short circuit was detected there. After fixing this issue, the lathe returned to normal operation. 3. Examples of troubleshooting: ① In our factory’s XH716 CNC machining center, which uses a FANUC OM system, an error code 408 occurred once. It turned out to be a problem with the servo system, indicating poor feedback signals. The cable signal lines were found to be in good condition, but when the pulse encoder was connected, there was no +5V power supply. It was checked that the +5V power supply on the servo system was functioning normally; however, no power was supplied even after connecting the encoder. It was later suspected that the connection between the cable plug and the cable socket on the servo was poor. After resolving this issue, the machine returned to normal operation. This machine tool often experiences overload alarms during processing; the alarm code is 434. This is manifested by excessive current in the axis motor, resulting in overheating of the motor. The alarm disappears after about 40 minutes of shutdown, and after it operates for a while again, a similar alarm occurs. After inspection and analysis, it is determined that there is no fault with the electrical servo system; it is likely caused by an excessive load that the system cannot handle. To distinguish whether the electrical fault no longer occurs. It is confirmed that this is caused by the mechanical screw or moving parts being too tight. After adjusting the anti-loosening nut on the lead screw of the adjustment shaft, there was no noticeable effect. Later, after adjusting the wedges on the guide rail of the adjustment shaft, the load on the machine tool was significantly reduced, and the malfunction was resolved. ②The FAUNC 17M CNC 4-axis milling machine gave errors 05 and 07 upon startup; further inspection revealed that the position of axis B was out of range. Analysis indicated a problem with the feedback component of the position loop. Upon checking the internal position control board of the 17M model, it was found that one of the integrated filters was open, which caused interruptions in the feedback signals. Replacing that filter restored normal operation of the machine. ③Our factory has modified a C6140A CNC lathe on our own; the system used is HUST from Taiwan. After turning it on, it’s not possible to find the zero point. Upon analysis, the zeroing principle is as follows: during the zeroing process, the speed is reduced after pressing the zero position switch; the machine moves in the opposite direction and should stop once it reaches the zero pulse of the pulse encoder. All previous operations proceeded normally, but no zero point could be found during the decelerated return movement. It is presumed that there is no zero pulse from the pulse encoder or that the signal line is broken. After replacing the pulse encoder, the machine resumed normal operation. ④The SAJO HMC 630-P horizontal machining center is equipped with a Siemens 840C CNC system. After it was turned on, the B-axis would not move. Upon inspection, it was found that the solenoid valve for the B-axis was operating, but the PLC indicated that the B-axis was not released. It was determined that there was a problem with the pressure switch; after removing it and examining it, it was found that its contacts were damaged. Replacing the pressure switch resolved the issue. IV. Some insights on the management and maintenance of CNC equipment 1. As a type of high-precision mechanical processing equipment, CNC machines integrate various disciplines such as mechanics, electronics, and computer science; therefore, specialized management of such machines is becoming increasingly important. The main issues related to CNC equipment at present can be summarized as management, maintenance, and improvement. That is, to implement scientific management methods in order to maximize the efficiency of CNC equipment: strengthen maintenance capabilities by establishing a specialized maintenance team with expertise in mechanics, electricity, power systems, as well as computer hardware and software; improve the theoretical and technical skills of maintenance personnel, especially their ability to identify faults and resolve them, while also enhancing the technical skills of operators and programmers. 2. The maintenance of CNC equipment is actually a very complex and highly technical task. Due to the significant differences between CNC equipment and ordinary equipment, high technical skills are required from maintenance personnel. They not only need to be proficient in electrical systems but also possess knowledge in areas such as mechanics, hydraulics, and optics. Since CNC equipment represents an integrated mechatronic system, components like CNC profiling heads include sensors, A/D converters, as well as mechanical displacement devices – all of which are combined together. A broad range of knowledge is necessary to carry out this work successfully. Carefulness, diligence, confidence, responsibility, and strong technical skills are the most basic requirements. Numerical control management is a highly comprehensive engineering field that requires not only advanced equipment, but also proper equipment maintenance, as well as scientific equipment management. Over the years, based on the characteristics of our CNC equipment and our work experience, we will continue to explore new management models for such equipment in order to enable them to serve scientific research and production more effectively.