How to better use and maintain CNC machine tools

How to better use and maintain CNC machine tools

CNC machine tools reflect the mainstream of the current world machine tool technology progress, are important indicators to measure the level of mechanical manufacturing technology, and play an important basic and core role in advanced manufacturing technologies such as flexible production and computer integrated manufacturing. Therefore, how to better use CNC machine tools is a very important problem. As CNC machine tool is a kind of expensive precision equipment, its maintenance can not be ignored

I. numerical control machine tool

1. The concept of numerical control machining

the working principle of numerical control machine tool is to use digital codes to express various operations (such as spindle speed change, workpiece loosening and clamping, tool feeding and withdrawing, start-up and shutdown, automatic shutdown of coolant) and steps required in the processing process, as well as the shape and size of the workpiece, and send digital information to the numerical control device through control media (such as perforated paper tape or disk, etc.), The numerical control device processes and calculates the input information, sends out various control signals, controls the servo system or other driving elements of the machine tool, and enables the machine tool to automatically process the required workpiece. Therefore, the key of NC machining is the acquisition of machining data and process parameters, that is, NC programming. NC machining generally includes the following contents:

(1) analyze the drawings and determine the parts that need NC machining

(2) use graphic software (such as CAXA Manufacturing Engineer) to shape parts that need NC machining

(3) according to the processing conditions, select the appropriate processing parameters to generate the processing track (including rough processing, semi finishing and finishing)

(4) simulation test of trajectory

(5) generate G code

(6) transfer to machine tool for processing

2. Characteristics of CNC machine tools

(1) it is highly flexible

processing parts on CNC machine tools mainly depends on the processing program. Unlike ordinary machine tools, it does not need to manufacture and replace many tools and fixtures, and it does not need to adjust the machine tools often. Therefore, CNC machine tools are suitable for occasions where parts are frequently replaced. That is, it is suitable for single piece, small batch production and new product development, which shortens the production preparation cycle and saves a lot of process equipment costs

(2) high machining accuracy

the machining accuracy of CNC machine tools can generally reach 0.005-0.1mm. CNC machine tools are controlled in the form of digital signals. For each pulse signal output by the CNC device, the moving parts of the machine tool move by a pulse equivalent (generally 0.001mm), and the average error between the reverse clearance of the machine tool feed transmission chain and the lead screw pitch can be compensated by the CNC device. Therefore, The positioning accuracy of CNC machine tools is relatively high

(3) stable and reliable processing quality

process the same batch of parts on the same machine tool, under the same processing conditions, using the same tools and processing procedures, the tool path is exactly the same, the consistency of 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 rate of CNC machine tools is large, which allows the machine tools to carry out strong cutting with large cutting amount. At present, CNC machine tools are entering the era of high-speed machining. The rapid movement and positioning of moving parts of CNC machine tools and high-speed machining reduce the turnover time between processes of semi-finished products and improve production efficiency

(5) improve working conditions

after adjusting the NC machine tool before processing, input the program and start it, and the machine tool can automatically and continuously process until the end of processing. The operators mainly work on program input, loading and unloading parts, tool preparation, observation of processing state, part inspection, etc. the labor intensity is greatly reduced, and the labor of machine tool operators tends to be intelligent work. In addition, machine tools are generally closed processing, which is clean and safe

(6). It is conducive to the modernization of production management

the processing of CNC machine tools, which can accurately estimate the processing 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 realize the standardization of processing information. At present, it has been organically combined with computer-aided design and manufacturing (cad/cam), which is the basis of modern integrated manufacturing technology

3. Precautions in the use of CNC machine tools

before using CNC machine tools, you should carefully read the machine tool instructions and other relevant materials in order to operate and use the machine tools correctly, and pay attention to the following points:

(1) machine tool operators and maintenance personnel must be professionals who master the professional knowledge of the corresponding machine tools or personnel who have received technical training, and must operate the machine tools according to the safe operation procedures and safe operation regulations

(2) non professionals are not allowed to open the electric cabinet door. Before opening the electric cabinet door, they must confirm that the main power switch of the machine tool 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 for users to use and can be changed, users cannot modify other system parameters, spindle parameters, servo parameters, etc. without permission, otherwise it will cause equipment, workpiece, personal injury, etc. to the operator

(4) after modifying the parameters, during the first processing, the machine tool is locked with the machine tool and single program segment for trial operation without installing tools and workpieces, and the machine tool can be used after confirming that the machine tool is normal

(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 and operation of the machine tool may cause damage to the machine tool and even harm the operator

(6) it is recommended that the machine tool run continuously for up to 24 hours. If the continuous operation time is too long, it will affect the service life of the electrical system and some mechanical components, which will affect the accuracy of the machine tool

(7) all connectors and connectors of the machine tool are not allowed to be unplugged and plugged with electricity, otherwise serious consequences will be caused

II. 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 numerical control system, the performance of electronic components will be aging or even damaged, especially some mechanical parts. In order to maximize the service life of components and parts and parts wear cycle, and prevent various faults, especially malignant accidents, it is necessary to carry out daily maintenance of the numerical control system. To sum up, we should pay attention to the following aspects

1. Formulate rules and regulations for daily maintenance of CNC system

determine their maintenance regulations according to the characteristics of various components. For example, it is expressly stipulated which places need to be cleaned every day (such as the cleaning of the input/output unit of the CNC system - the photoelectric reader, checking whether the mechanical structure is well lubricated, etc.), and which parts need to be checked or replaced regularly (such as the brush and commutator of the DC servo motor should be checked once a month)

2. Try not to open the doors of numerical control cabinet and strong current cabinet

what kind of rubber tensile testing machine should we choose to do the rubber tensile test? Because the air in machining workshops generally contains oil mist, dust and even metal powder. Once they fall on the printed circuit or electrical components 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. In order to overload the CNC system for a long time in summer, some users open the door of the CNC cabinet to dissipate heat. This is an absolutely unacceptable method, which will eventually lead to accelerated damage to the CNC system. The correct way is to reduce the external ambient temperature of the numerical control system, which is the protection, maintenance and use precautions of the cold and hot shock experimental machine. Therefore, there should be a strict regulation. Unless necessary adjustment and maintenance are carried out, it is not allowed to open the cabinet door casually, let alone open the cabinet door during use

3. Regularly clean the cooling and ventilation system of the digital control cabinet

check whether each cooling fan on the numerical control system cabinet works normally every day. Depending on the working environment, check whether the air duct filter is blocked every half a year or every quarter. If the dust on the filter accumulates too much, it needs to be cleaned in time, otherwise the temperature in the CNC system cabinet will be high (generally not allowed to exceed 55 ℃), resulting in overheating alarm or unreliable operation of the CNC system

4. Frequently monitor the electric voltage used by the CNC system

cnc system produced by FANUC company, allowing the electric voltage to fluctuate within the range of 85% - 110% of the rated value. If it goes beyond this range, the system will not work normally, and even the internal electronic components of the CNC system will be damaged

5. Regularly replace the battery for memory

there are two kinds of memory in the CNC system with a profit of 73.83 billion yuan produced by FANUC company:

(1) bubble memory without battery

(2) for CMOSRAM devices that need to be maintained by battery, in order to maintain the stored content during the period when the CNC system is not powered on, a rechargeable battery maintenance circuit is set inside. When the CNC system is powered on, the 5V power supply supplies power to CMOSRAM through a diode and charges the rechargeable battery; When the CNC system cuts off the power supply, it will be powered by the battery to maintain the information in CMOSRAM. In general, even if the battery has not failed, the battery should be replaced once a year to ensure that the system can work normally. In addition, it must be noted that the replacement of the battery should be carried out under the power supply state of the CNC system

6. Maintenance of the CNC system when it is not used for a long time

in order to improve the utilization rate of the CNC system and reduce the faults of the CNC system, the CNC machine tool should be used at full load instead of being idle for a long time. For some reason, when the CNC system is idle for a long time, in order to avoid damage to the CNC system, the following two points should be paid attention to:

(1) the CNC system should be powered on frequently, Especially in the rainy season with high environmental humidity, when the machine tool is locked (that is, when the servo motor does not rotate), let the CNC system run idle. The heat of electrical components is used to disperse the moisture in the CNC system and ensure the stable and reliable performance of electronic devices. Practice has proved that in areas with high air humidity, frequent power on is an effective measure to reduce the failure rate

(2) if the CNC machine tool adopts DC feed servo drive and DC and establishes a new supply chain to meet the needs of the aviation industry, the spindle servo drive, the brush should be taken out of the DC motor, so as to avoid the corrosion of the commutator surface due to chemical corrosion, resulting in the deterioration of commutation performance, and even the damage of the whole motor