The development of science and technology has put forward the requirements of high precision and high complexity for mechanical products, and the upgrading of products is also accelerating. This not only puts forward the requirements of precision and efficiency for machine tools, but also puts forward the versatility and Flexibility requirements. CNC machine tools are a new type of automated machine tool for this requirement. CNC machine tools integrate microelectronics technology, computer technology, automatic control technology, servo drive technology and precision mechanical technology, which are typical products of high mechatronics. It is an important part of mechatronics and an important indicator of the level of modern machine tool technology. CNC machine tools represent the mainstream of the world's machine tool technology advancement, and are an important indicator for measuring the level of mechanical manufacturing technology. They play an important and fundamental role in advanced manufacturing technologies such as flexible production and computer integrated manufacturing. Therefore, how to use CNC machine tools is a very important issue. Since CNC machine tools are expensive and expensive equipment, their maintenance cannot be ignored.
First, CNC machine tools
1. The concept of CNC machining
The working principle of CNC machine tools is to carry out various operations required for the machining process (such as spindle shifting, workpiece loosening and clamping, feeding and retracting, driving and stopping, automatic shutdown of coolant) and steps and workpiece shape. The size is represented by a digital code. The digital information is sent to the numerical control device through a control medium (such as a punched tape or a magnetic disk). The numerical control device processes and calculates the input information, and issues various control signals to control the servo system of the machine tool or Other drive components allow the machine to automatically machine the required workpiece. Therefore, the key to CNC machining is the acquisition of machining data and process parameters, namely CNC programming. CNC machining generally includes the following contents:
(1) Analyze the drawings to determine the parts that require CNC machining;
(2) Using graphics software (such as CAXA manufacturing engineers) to shape parts that require CNC machining;
(3) According to the processing conditions, select appropriate processing parameters to generate machining trajectories (including roughing, semi-finishing, finishing trajectories);
(4) Simulation test of the trajectory;
(5) generate a G code;
(6) Passed to the machine tool for processing.
2. Characteristics of CNC machine tools
(1) Highly flexible
Machining parts on CNC machine tools depends mainly on the machining program. It is different from ordinary machine tools. It is not necessary to manufacture or replace many tools and fixtures. It is not necessary to adjust the machine frequently. Therefore, CNC machine tools are suitable for occasions where parts are frequently replaced. It is suitable for the development of single-piece, small batch production and new products, shortening the production preparation cycle and saving the cost of a large number of process equipment.
(2) High processing accuracy
The machining accuracy of CNC machine tools can generally reach 0.005~0.1mm. The numerical control machine tool is controlled in the form of digital signals. Each time the numerical control device outputs a pulse signal, the moving parts of the machine tool move by one pulse equivalent (generally 0.001mm), and the machine tool advances. The average error of the backlash and the screw pitch of the transmission chain can be compensated by the numerical control device. Therefore, the positioning accuracy of the numerically controlled machine tool is relatively high.
(3) Processing quality is stable and reliable
Machining the same batch of parts, using the same tool and machining program under the same machining conditions on the same machine tool, the tool's path is exactly the same, the parts have good consistency and the quality is stable.
(4) High productivity
CNC machine tools can effectively reduce the machining time and auxiliary time of parts. The range of spindle speed and feed rate of CNC machine tools is large, which allows the machine tool to carry out powerful cutting with large cutting amount. CNC machine tools are now entering the era of high-speed machining, moving parts of CNC machine tools. The fast moving and positioning and high-speed cutting process reduces the turnaround time between the semi-finished products and improves the production efficiency.
(5) Improve working conditions
After the CNC machine tool has been adjusted before machining, the program is started and started, and the machine tool can automatically and continuously process until the end of the process. The operator is mainly the input of the program, editing, loading and unloading parts, tool preparation, observation of the processing state, inspection of the parts, etc., the labor intensity is greatly reduced, and the labor of the machine tool operator tends to be an intellectual work. In addition, the machine tool is generally closed, that is, clean and safe.
(6) Conducive to the modernization of production management
The machining of CNC machine tools can accurately estimate the machining time in advance, and the tools and fixtures used can be standardized and modernized. CNC machine tools use digital signals and standard codes as control information, which is easy to standardize processing information. It has been organically combined with computer-aided design and manufacturing (CAD/CAM) and is the basis of modern integrated manufacturing technology.
3. Things to be aware of when using CNC machine tools
Before using the CNC machine, you should carefully read the machine manual and other relevant information in order to operate the machine correctly, and pay attention to the following points:
(1) The operation and maintenance personnel of the machine tool must be professionals who have mastered the relevant professional knowledge of the machine tool or those who have been trained in technology, and must operate the machine tool according to the safety operation rules and safe operation regulations;
(2) Non-professionals are not allowed to open the electric cabinet door. Before opening the electric cabinet door, it must be confirmed that the main power switch of the machine has been turned off. Only professional maintenance personnel are allowed to open the electric cabinet door for power-on maintenance;
(3) In addition to some parameters that can be changed by the user, other system parameters, spindle parameters, servo parameters, etc., cannot be modified by the user, otherwise the equipment, workpiece, personal injury, etc. will be brought to the operator;
(4) After modifying the parameters, when the first machining is performed, the machine tool is tested with the machine lock and single block without the tool and the workpiece, and the machine tool is confirmed after the machine is normal;
(5) The PLC program of the machine tool is designed by the machine tool manufacturer according to the machine tool and does not need to be modified. Improper modification, operating the machine may cause damage to the machine and even damage the operator;
(6) It is recommended that the machine tool run continuously for up to 24 hours. If the continuous running time is too long, it will affect the life of the electrical system and some mechanical components, which will affect the accuracy of the machine tool;
(7) All connectors, joints, etc. of the machine tool are not allowed to be pulled or inserted, otherwise serious consequences will result.
Second, the maintenance of CNC machine tools
CNC system is the core component of CNC machine tools. Therefore, the maintenance of CNC machine tools is mainly the maintenance of CNC system. After a long period of use of the CNC system, the performance of electronic components should be deteriorated or even damaged. Some mechanical components are even more so. In order to maximize the life of components and the wear cycle of components, prevent various faults, especially vicious accidents. The occurrence of the CNC system must be routinely maintained. To sum it up, pay attention to the following aspects.
1. Formulate rules and regulations for routine maintenance of CNC systems
Determine the respective maintenance regulations based on the characteristics of the various components. If it is specified in the text where it needs to be cleaned every day (such as the input/output unit of the CNC system - the cleaning of the photoelectric reader, check whether the mechanical structure is well lubricated, etc.), which parts should be regularly inspected or replaced (such as DC servo motor brushes and The commutator should be checked once a month).
2. Open the door of the CNC cabinet and the power cabinet as little as possible
Because the air in the machine shop usually contains oil mist, dust and even metal powder. Once they fall on the printed circuit or electrical device in the CNC system, it is easy to cause the insulation resistance between components to drop, and even cause damage to components and printed circuits. Some users in the summer in order to overload the CNC system for a long time, open the door of the CNC cabinet to dissipate heat, this is an indispensable method, which will eventually lead to accelerated damage of the CNC system. The correct way is to reduce the external ambient temperature of the CNC system. Therefore, there should be a strict regulation, unless the necessary adjustments and repairs are made, it is not allowed to open the door casually, and it is not allowed to open the door during use.
3. Regularly clean the cooling and ventilation system of the CNC cabinet
Every cooling fan on the CNC system cabinet should be checked every day for normal operation. Check whether the air duct filter is blocked every six months or quarterly depending on the working environment. If there is too much dust accumulation on the filter, it needs to be cleaned up in time. Otherwise, the temperature inside the cabinet of the CNC system will be high (it is generally not allowed to exceed 55 °C), resulting in overheating alarm or unreliable operation of the CNC system.
4. Always monitor the grid voltage for the CNC system
The CNC system produced by FANUC allows the grid voltage to fluctuate within the range of 85% to 110% of the rated value. If this range is exceeded, the system will not work properly and may even cause damage to the internal electronic components of the CNC system.
5. Regularly replace the battery for memory
There are two types of memory in the CNC system produced by FANUC:
(1) A bubble memory that does not require battery retention.
(2) CMOS RAM devices that need to be held by batteries. In order to maintain the stored contents during the period when the CNC system is not powered, a rechargeable battery maintenance circuit is provided inside. When the CNC system is powered on, a +5V power supply passes through a diode to the CMOS RAM. Power supply and charge the rechargeable battery; when the CNC system cuts off the power, it is powered by the battery to maintain the information in the CMOS RAM. In general, even if the battery has not failed, the battery should be replaced once a year to ensure The system works fine. In addition, it must be noted that the replacement of the battery should be carried out under the power supply of the CNC system.
6. Maintenance of the CNC system when not in use for a long time
In order to improve the utilization rate of the numerical control system and reduce the failure of the numerical control system, the numerical control machine tool should be used at full load, instead of being idle for a long time. For some reason, when the numerical control system is idle for a long time, in order to avoid damage of the numerical control system, the following two should be noted. point:
(1) It is necessary to energize the CNC system frequently, especially in the rainy season with high environmental humidity. When the machine lock is not moving (ie, the servo motor does not turn), let the CNC system run empty. The heat of the electrical components itself is used to dissipate the moisture in the numerical control system, and the performance of the electronic device is ensured to be stable and reliable. It has been proved that in areas with high air humidity, frequent power supply is an effective measure to reduce the failure rate.
(2) When the CNC machine tool adopts DC feed servo drive and DC spindle servo drive, the brush should be taken out from the DC motor to avoid corrosion of the commutator surface due to chemical corrosion, resulting in deterioration of the commutation performance and even The entire motor is damaged.
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