CNC machine tool principle and maintenance

First, CNC machine tools

1. Concept of CNC Machining The working principle of CNC machine tools is the various operations required for the machining process (such as spindle speed change, release and clamping of workpieces, feed and retraction, start and stop, and automatic shutdown of coolant). The shape and dimensions of the steps and workpieces are represented by digitized codes. The digital information is sent to a numerical control device through a control medium (such as a perforated tape or a diskette). The numerical control device processes and calculates the input information and sends out various control signals. Control the machine's servo system or other drive components, so that the machine tool automatically processes the desired workpiece. Therefore, the key to CNC machining is the acquisition of machining data and process parameters, ie, numerical control programming. CNC machining generally includes the following contents:
(1) Analyze the drawings and determine the parts that require CNC machining;
(2) Using graphic software (such as CAXA manufacturing engineers) to shape the part that needs CNC machining;
(3) According to the processing conditions, select the appropriate processing parameters to generate the processing trajectory (including roughing, semi-finishing, finishing trajectory);
(4) simulation test of the trajectory;
(5) Generate G code;
(6) Transfer to the machine tool.

2. Characteristics of CNC machine tools
(1) Highly flexible The machining of parts on CNC machine tools mainly depends on the machining program. It is different from ordinary machine tools in that it does not have to manufacture or replace many tools or jigs, and does not require frequent adjustment of the machine tools. Therefore, CNC machine tools are suitable for frequent replacement of parts. That is, it is suitable for the development of single parts, small batch production and new products, shortens the production preparation cycle, and saves the cost of a large number of process equipment.
(2) High machining accuracy The machining accuracy of CNC machine tools can generally reach 0.005 to 0.1mm. CNC machine tools are controlled by digital signals. Each time the CNC device outputs a pulse signal, the moving part of the machine tool moves one pulse equivalent (generally 0.001). Mm), and the average error of the backlash and screw pitch of the feed chain of the machine tool can be compensated by the numerical control device. Therefore, the positioning accuracy of the numerical control machine tool is relatively high.
(3) The processing quality is stable and reliable to process the same batch of parts. In the same machine tool, under the same processing conditions, the same tool and machining program are used, the tool path of the tool is exactly the same, the consistency of the parts is good, and the quality is stable.
(4) High productivity CNC machine tools can effectively reduce the processing time and auxiliary time of parts. The range of spindle speed and feed of CNC machine tools is large, which allows the machine to carry out powerful cutting with large amounts of cutting. CNC machine tools are now entering the era of high-speed processing. , The rapid movement and positioning of the moving parts of the CNC machine tool and high-speed cutting processing reduce the turnaround time between the semi-finished products and improve the production efficiency.
(5) Improve working conditions After the CNC machine tool is adjusted before processing, the input program is started and the machine tool can automatically continue processing until the processing is completed. Operators mainly input, edit, load and unload parts, tool preparation, machining status observation, and parts inspection. The labor intensity is greatly reduced, and the machine operator's labor tends to be intellectual work. In addition, machine tools are generally closed process, ie clean and safe.
(6) Facilitate the production and management of modern CNC machine tools, can accurately estimate the processing time in advance, the use of tools, fixtures can be standardized, modern management. CNC machine tools use digital signals and standard codes as control information, and are easy to standardize processing information. Currently, they have been organically combined with computer-aided design and manufacturing (CAD/CAM) and are the basis of modern integrated manufacturing technologies.

3. Matters needing attention in the use of CNC machine tools Before using CNC machine tools, you should carefully read the machine tool instructions and other relevant information in order to operate the machine correctly, and pay attention to the following points:
(1) The machine tool operation and maintenance personnel must be professionals or technically trained personnel who have mastered the relevant machine tool professional knowledge, and must operate the machine tool according to the safety operation regulations and safety 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 machine's main power switch has been turned off. Only professional maintenance personnel are allowed to open the electric cabinet door for power overhaul;
(3) Except for some parameters that can be used by the user and can be modified, other system parameters, spindle parameters, servo parameters, etc., cannot be modified by the user, otherwise it will bring damage to the operator such as equipment, workpieces, and people;
(4) After the parameters are modified, when the first processing is performed, the machine tool shall be tested in the form of machine locks or single blocks without loading tools and workpieces. After confirming that the machine tool is normal, the machine tool will be used;
(5) The PLC program of the machine tool is designed by the machine tool manufacturer according to the needs of the machine tool and does not need to be modified. Incorrect modification, operation of the machine may cause damage to the machine, or even injure the operator;
(6) It is recommended that the machine tool run continuously for a maximum of 24 hours. If the continuous operation time is too long, it will affect the life of the electrical system and some mechanical devices, which will affect the accuracy of the machine tool;
(7) All connectors, joints, etc. of the machine tool are not allowed to be charged and inserted. Otherwise, serious consequences will occur.

Second, the maintenance of CNC machine tools CNC system is the core components of CNC machine tools, therefore, the maintenance of CNC machine tools is mainly the maintenance of CNC systems. After a long time of use, the numerical control system will deteriorate or even deteriorate the performance of electronic components. This is especially true for some mechanical components. In order to extend the lifespan of components and the wear cycle of components as much as possible, various types of failures, especially in the event of a serious accident, are prevented. When it happens, it is necessary to carry out daily maintenance of the CNC system. To sum up, pay attention to the following aspects.

1. Formulate the rules and regulations for the daily maintenance of CNC systems. Determine the respective maintenance regulations based on the characteristics of various components. As clearly stipulated where the need to clean up every day (such as the input/output unit of the CNC system - the cleaning of the optoelectronic reader, check the mechanical structure is good lubrication, etc.), which parts should be regularly checked or replaced (such as DC servo motor brush and The commutator should be checked once a month).

2. The doors of CNC cabinets and power cabinets should be opened as little as possible because the air in the machining workshop generally contains oil mist, dust and even metal powder. Once they fall on the printed circuit or the electrical device in the numerical control system, it is easy to cause the insulation resistance between the components to drop, and even cause damage to the components and the printed circuit. Some users in the summer in order to make the CNC system overload long-term work, open the door of the CNC cabinet to heat, this is an absolutely undesirable method, and ultimately will lead to accelerated damage to the CNC system. The correct way is to reduce the outside temperature of the CNC system. Therefore, there should be a strict rule, unless the necessary adjustments and maintenance, do not allow the door to open, but also does not allow open the door when in use.

3. Regularly clean the cooling ventilation system of the CNC cabinet. Check whether the cooling fans on the CNC system cabinet are working properly every day. Check whether the duct filter is clogged every six months or quarters depending on the working environment. If there is excessive accumulation of dust on the filter screen, clean it up in time. Otherwise, it will cause the temperature in the cabinet of the numerical control system to be high (generally not exceeding 55°C), causing overheating alarm or unreliable operation of the CNC system.

4. Regularly monitor the grid voltage used by CNC system
FANUC's CNC system allows the grid voltage to fluctuate within the range of 85% to 110% of the rated value. If it is beyond this range, it will cause the system to not work properly and even cause damage to the electronic components inside the CNC system.

5. Replace the battery for storage regularly
There are two kinds of memory in the CNC system produced by FANUC:
(1) Bubble memory without battery retention.
(2) A CMOS RAM device that needs to be held by a battery. In order to maintain the stored contents during the power-off of the CNC system, a rechargeable battery maintenance circuit is provided inside. When the digital control system is powered on, a +5V power supply passes through a diode to the CMOS RAM. Power supply and charging the rechargeable battery; when the CNC cuts off the power supply, the battery power supply is used instead 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 in order to ensure The system can work normally. In addition, it must be noted that the replacement of the battery should be performed under the power supply of the CNC system.

6. Maintenance of CNC system when it is not used for a long time In order to improve the utilization of CNC system and reduce the failure of CNC system, CNC machine tools should be used at full capacity instead of idle for a long time. For some reason, when CNC system is idle for a long time, To avoid damage to the CNC system, note the following two points:

(1) Always power the CNC system, especially in the rainy season when the environment is relatively humid. In the case where the machine tool is locked (ie, the servo motor does not rotate), let the CNC system run empty. The heat generated by the electrical component itself is used to disperse the moisture in the CNC system to ensure the stable and reliable performance of the electronic device. Practice has proved that frequent energization is an effective measure to reduce the failure rate in areas with high air humidity.

(2) 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 make The entire motor is damaged.