I. Brief History and Trend of CNC System Development
The world’s first electronic computer was born in 1946, which shows that humans have created tools that can enhance and partially replace mental work. It has made a qualitative leap from the tools created by human beings in the agricultural and industrial societies that only enhance physical labor and laid the foundation for human beings to enter the information society.
Six years later, in 1952, computer technology was applied to the machine tool and the first CNC machine was born in the United States. Since then, traditional machine tools have produced qualitative changes. In the past half century, CNC systems have experienced two stages and six generations of development.
1.1. Numerical Control (NC) Stage (1952 to 1970)
The early computer's low computing speed had little impact on scientific computing and data processing at the time, but it could not meet the requirements of real-time control of machine tools. People have to use digital logic circuits to "build up" a machine dedicated computer as a numerical control system, known as hardware-connected numerical control (HARD-WIRED NC), abbreviated as NC (NC). With the development of components, this stage has gone through three generations, namely, the first generation of 1952--electronic tubes; the second generation of transistors in 1959--transistors; and the third generation of 1965--small-scale integrated circuits.
1.2. Computer Numerical Control (CNC) Phase (1970-present)
By 1970, the general-purpose small computer industry had appeared and was mass-produced. So it was transplanted as a core part of the CNC system, and then entered the computer numerical control (CNC) stage (the "common" word in front of the computer is omitted). In 1971, INTEL Corporation in the United States for the first time in the world to the computer's two most core components - calculators and controllers, using large-scale integrated circuit technology integrated on a chip, called the microprocessor (MICROPROCESSOR ), also known as Central Processing Unit (CPU).
By 1974, microprocessors were used in numerical control systems. This is due to the fact that small computers are so powerful that they have the ability to control a machine tool (so it was used to control multiple machine tools at the time, called a group control). It is better to use a microprocessor as an economical and reasonable tool. At the time, minicomputer reliability was also unsatisfactory. Although early microprocessor speeds and functions were not high enough, they could be solved by a multiprocessor architecture. Since the microprocessor is a core part of a general-purpose computer, it is still called a computer numerical control.
By 1990, the performance of PCs (personal computers, domestically used as microcomputers) had advanced to a very high level and could satisfy the requirements of the core components of numerical control systems. The CNC system has since entered the PC-based phase.
In short, the computer numerical control stage also experienced three generations. That is, the fourth generation of the 1970-small computer; the fifth generation of the 1974-microprocessor and the sixth generation of the 1990-based PC (PC-BASED abroad).
It should also be pointed out that although foreign countries have long been renamed Computer Numerical Control (CNC), China still uses NC. Therefore, the "CNC" that we talk about daily has essentially meant "computer numerical control."
1.3. Trends of CNC's Future Development
1.3.1 Continue to develop in the direction of the open, PC-based sixth generation
Based on the openness, low cost, high reliability, and rich hardware and software resources of PCs, more CNC system manufacturers will take this path. At least PC is used as its front-end machine to handle human-machine interface, programming, networking and other issues, and the original system assumes the task of CNC. The friendly human-machine interface that the PC machine has will be popularized to all numerical control systems. Telecommunication, remote diagnostics and maintenance will become more common.
1.3.2 Speeding up and High-precision Development
This is the need to adapt the machine to high speed and high precision.
1.3.3 Towards the development of intelligence
With the continuous penetration and development of artificial intelligence in the computer field, the degree of intelligence in CNC systems will continue to increase.
(1) Apply adaptive control technology
The numerical control system can detect some important information in the process and adjust the relevant parameters of the system automatically to achieve the purpose of improving the operating status of the system.
(2) Introduce expert system to guide processing
The skilled workers and experts' experience, the general laws and special rules of processing are stored in the system, and the expert system of artificial intelligence is established with the support of the process parameter database.
(3) Introduce fault diagnosis expert system
(4) Intelligent Digital Servo Drive
By automatically recognizing the load, the parameters can be automatically adjusted so that the drive system can operate optimally.
Second, the necessity of CNC transformation of machine tools
2.1. The necessity of micro-viewing transformation
From a microscopic point of view, CNC machine tools have the following outstanding advantages over traditional machine tools, and these advantages are derived from the power of the computer contained in the CNC system.
2.1.1 Can process complex parts such as curves and surfaces that cannot be machined by traditional machine tools.
Because the computer has superb computing power, it can instantaneously and accurately calculate the amount of motion that each coordinate axis should move at a moment, so it can be compounded into complex curves or surfaces.
2.1.2 can realize the automation of processing, and it is flexible automation, so that the efficiency can be improved by 3 to 7 times compared with the traditional machine tools.
Because the computer has memory and storage capabilities, the input program can be remembered and stored, and then automatically executed in the order specified by the program, thus achieving automation. As long as the CNC machine tool replaces a program, it can realize the automation of another workpiece processing, so that the single-piece and small batch production can be automated, so it is called "flexible automation".
2.1.3 The precision of the machined parts is high, the dispersion of the dimensions is small, and the assembly is easy. It is no longer necessary to "repair".
2.1.4 Concentration of multiple processes can be achieved, reducing the frequent handling of parts between machine tools.
2.1.5 With automatic alarm, automatic monitoring, automatic compensation and other self-discipline functions, it can realize long-term unattended processing.
2.1.6 The benefits derived from the above five articles.
Such as: reducing the labor intensity of workers, saving the labor force (one person can take care of multiple machine tools), reducing the tooling, shortened the new product trial production cycle and production cycle, can respond quickly to market demand and so on.
These superiorities are beyond the imagination of our predecessors and represent an extremely significant breakthrough. In addition, the numerical control of machine tools is still the basis for the transformation of enterprise information systems such as FMC (flexible manufacturing unit), FMS (flexible manufacturing system), and CIMS (computer integrated manufacturing system). CNC technology has become the core technology and basic technology of manufacturing automation.
2.2. The necessity of macro transformation
From a macroscopic point of view, military and civilian machinery industries in industrialized countries have begun to apply CNC machine tools on a large scale in the late 1970s and early 1980s. Its essence is to use information technology to transform traditional industries (including military and civilian machinery industries). In addition to the use of CNC machine tools, FMC, FMS in the manufacturing process, it also includes the implementation of CAD, CAE, CAM, virtual manufacturing, and the implementation of MIS (Management Information System), CIMS, etc. in product development. As well as adding information technology to its products, including artificial intelligence, etc. Due to the in-depth transformation of foreign military and civilian machinery industries (called informationization), the use of information technology has finally made their products more competitive in the international military and civilian products market. And we are about 20 years behind the developed countries in the transformation of traditional industries in information technology. For example, in China's machine tool ownership, the proportion of CNC machine tools (CNC ratio) was only 1.9% in 1995, while Japan had reached 20.8% in 1994. Therefore, a large number of electromechanical products are imported every year. This also explains the necessity of the CNC transformation of the machine tool from a macro point of view.
Third, the machine tool and the production line transformation of the NC market
3.1, the market of CNC machine transformation
Currently, the total number of machine tools in China totals more than 3.8 million units, of which the total number of CNC machine tools is only 111,400, that is, the numerical control rate of China's machine tools is less than 3%. In the past 10 years, the annual output of CNC machine tools in China is about 0.6 to 8,000 units, and the annual output value is about 1.8 billion yuan. The annual production rate of machine tools is 6%. More than 60% of China's machine tools have a service life of more than 10 years; less than 20% of automatic and semi-automatic machine tools are under 10 years old, and FMC/FMS and other automated production lines are even more accessible (60% of US and Japanese automatic and semi-automatic machine tools. the above). It can be seen that most of the manufacturing and processing equipment in most of our manufacturing industries and enterprises are traditional machine tools, and more than half of them are older machine tools with a service life of more than 10 years. The products processed by this kind of equipment generally have poor quality, few varieties, low grade, high cost and long delivery period, thus lacking competitiveness in the international and domestic markets, directly affecting a company's products, markets, benefits, and influence. The survival and development of the enterprise. Therefore, we must vigorously increase the numerical control rate of the machine tool.
3.2. Numerical control transformation of imported equipment and production lines
Since China's reform and opening up, many companies have introduced technology, equipment and production lines from abroad to carry out technological transformation. According to incomplete statistics, from the period of 1979 to 1988, there were 18,446 imported technological transformation projects in the country, totaling approximately US$ 16.58 billion.
Of these projects, most of the projects have played a proper role in China’s economic construction. However, due to various reasons, some imported projects may not be able to operate normally, or even paralyzed, equipment or production lines, which will affect the efficiency of the company and seriously impede the enterprise's difficulties. After some equipment and production lines were introduced from abroad, some were poorly digested and absorbed, spare parts were incomplete, improper maintenance, and the operation was poor; some introduced only attention to the introduction of equipment, instruments, and production lines, neglecting software, processes, and management, resulting in the failure of projects. Incomplete, equipment potential can not be played; some can not even start running, did not play its due role; some production lines of products sell well, but because of equipment failure can not meet production standards; some because of high energy consumption, product pass rate is low It caused losses; some have been introduced for a long time and require technical updates. For various reasons, some equipment not only did not create wealth, but also consumed wealth.
These equipment and production lines that cannot be used are a burden, but also a large number of stock assets. Repairing is wealth. As long as the main technical difficulties are solved and key technical problems are solved, the smallest amount of investment can be used to revitalize the largest stock assets and gain the greatest economic and social benefits. This is also a great transformation of the market.
IV. Contents and advantages of the NC transformation
4.1. The rise of foreign transformation industry
In developed countries such as the United States, Japan, and Germany, the transformation of their machine tools as a new economic growth industry has become a golden era. Due to the continuous advancement of machine tools and technology, machine tool transformation is an "eternal" topic. China's machine tool transformation industry has also moved from the old industry to a new industry dominated by numerical control technology. In the United States, Japan, and Germany, the use of numerical control technology to transform machine tools and production lines has a broad market, and a new industry has been formed for the numerical control of machine tools and production lines. In the United States, the machine tool industry is called the Remanufacturing industry. The well-known companies in the recycling industry include: Bertsche Engineering, ayton Machine Tool, Devlieg-Bullavd Service Group, and US equipment companies. The American Depot company has opened a company in China. In Japan, the machine tool transformation industry is called the Retrofitting industry. The well-known companies engaged in the conversion industry include Daxie Engineering Group, Gangsan Machinery Corporation, Chiyoda Engineering Machine Company, Nozaki Engineering Corporation, Hamada Engineering Corporation, and Yamamoto Engineering Corporation.
4.2, CNC transformation content
The main contents of the CNC transformation of machine tools and production lines are as follows:
One is to restore the original function and diagnose and recover the faults in the machine tool and production line.
The second is NC, adding a digital display device to an ordinary machine tool, or adding a numerical control system, and transforming it into an NC machine tool and a CNC machine tool;
The third is refurbishment, in order to improve the accuracy, efficiency and automation, refurbish the mechanical and electrical parts, reassemble the mechanical parts and restore the original precision; the CNC system that does not meet the production requirements is updated with the latest CNC;
The fourth is technology update or technological innovation. In order to improve performance or grades, or to use new technologies and new technologies, large-scale technological upgrades or technological innovations are carried out on the basis of the original ones, and the levels and grades are significantly upgraded and improved. .
4.3. The advantages and disadvantages of the numerical control transformation
4.3.1 Reduced Investment and Short Delivery Time
Compared with the purchase of new machine tools, it is generally possible to save 60% to 80% of the cost, the transformation costs are low. Especially large and special machine tools are particularly noticeable. General large-scale machine tool transformation, only spent 1/3 of the cost of new machine purchase, delivery time is short. However, some special circumstances, such as the production and installation of high-speed spindles and tray automatic exchange devices, are too time-consuming and costly. As a result, the cost of improvement is often increased by 2 to 3 times. Compared with the purchase of new machine tools, it can only save about 50% of investment.
4.3.2 The mechanical performance is stable and reliable, and the structure is limited
The basic parts such as the bed and pillars used are heavy and strong cast components instead of the welded components. The transformed machine has high performance and good quality and can be used as new equipment for many years. However, due to the limitations of the original mechanical structure, it is not appropriate to make a breakthrough transformation.
4.3.3 Familiar with the equipment, convenient operation and maintenance
When buying a new device, you do not know whether the new device can meet its processing requirements. Renovation is not the case, and the machine tool's processing capability can be accurately calculated. In addition, due to many years of use, the operator has already understood the characteristics of the machine tool, and the training time is short and effective in operation and maintenance. Once the modified machine is installed, full-load operation can be realized.
4.3.4 Make full use of existing conditions
You can make full use of existing foundations without having to rebuild your foundation as you would if you purchased new equipment.
4.3.5 can use the latest control technology
According to the development speed of technological innovation, the automation level and efficiency of production equipment can be improved in a timely manner, and the quality and grade of equipment can be improved. The old machine tool can be changed to the current level of machine tools.
Fifth, the choice of CNC system
There are three main types of CNC systems. When retrofitting, the selection should be based on specific conditions.
5.1 stepping motor drag open loop system
The servo drive devices of this system are mainly stepper motors, power stepper motors, and electro-hydraulic pulse motors. After the feed command pulse sent by the CNC system is controlled by the drive circuit and the power is amplified, the stepper motor is rotated, and the actuator is driven by the gear pair and the ball screw pair. As long as the number of command pulses, the frequency, and the power-on sequence are controlled, the displacement, speed, and direction of movement of the actuator can be controlled. This kind of system does not need to feedback the measured actual position and speed to the input end, so it is called an open-loop system. The displacement accuracy of the system mainly depends on the angular displacement accuracy of the stepping motor, the gear screw and other transmission components. Pitch accuracy, so the system's displacement accuracy is low.
The system is simple in structure, easy to debug and maintain, reliable in operation, low in cost, and easy to retrofit.
5.2 Closed-loop numerical control system for asynchronous motor or DC motor dragging and grating measurement feedback
The difference between this system and the open-loop system is that the actual position feedback signal measured by a position detection device such as a grating and an inductive synchronizer is compared with a given value at any time, the difference between the two is amplified and transformed, and the actuator is driven. Moving at a given speed in the direction of eliminating the deviation until the difference between the given position and the actual position of the feedback is equal to zero. The closed-loop feed system is more complex in structure than the open-loop feed system, and also has a high cost and strict requirements on the ambient room temperature. Design and debugging are more difficult than open loop systems. However, it can obtain higher accuracy, faster speed, and higher driving power than the open-loop feed system. According to product technical requirements, decide whether to use this system.
5.3. AC/DC servo motor dragging, encoder feedback semi-closed-loop numerical control system
The semi-closed-loop system detection element is mounted on the intermediate transmission and indirectly measures the position of the actuator. It can only compensate for the errors of some components inside the system loop. Therefore, its accuracy is lower than that of the closed-loop system, but its structure and debugging are simpler than the closed-loop system. When the angular displacement detecting element is integrated with the speed detecting element and the servo motor, there is no need to consider the installation of the position detecting device.
Currently there are many manufacturers of CNC systems. Famous foreign companies such as SIEMENS in Germany and FANUC in Japan; domestic companies such as China Everest Company, Beijing Aerospace Machine Tool CNC System Group, Huazhong Numerical Control Company, and Shenyang High-end CNC National Engineering Research Center .
When choosing the numerical control system, it is mainly based on various precisions that the numerical control machine wants to reach after the numerical control transformation, the power of the driving motor and the user's requirement.
Sixth, the transformation of the main mechanical components in the transformation of CNC
A new CNC machine tool is designed to achieve: a high static and dynamic stiffness; a small coefficient of friction between the pairs of movements, transmission without gaps; large power; easy operation and maintenance. The above requirements shall be fulfilled as far as the CNC transformation of the machine tool is concerned. It cannot be said that connecting the numerical control device with the ordinary machine tool has reached the requirements of the numerical control machine tool, and the corresponding transformation of the main components is also required to achieve a certain design requirement in order to achieve the intended transformation.
6.1, slide guide
For CNC lathes, the guideway should not only have general lathe guiding accuracy and craftsmanship, but also have good resistance to friction and wear and reduce the dead zone caused by frictional resistance. At the same time, it must have sufficient rigidity to reduce the influence of rail deformation on machining accuracy, and reasonable guide rail protection and lubrication are needed.
6.2, gear pair
General machine gears are mainly concentrated in the headstock and gearbox. In order to ensure the transmission accuracy, the accuracy of gears used on CNC machine tools is higher than that of ordinary machine tools. The structure must be able to achieve a gapless transmission, so when the transformation, the main gear of the machine tool must meet the requirements of CNC machine tools to ensure the machining accuracy of the machine tool.
6.3. Slide screw and ball screw
Screw drive is directly related to the precision of the transmission chain. The choice of screw depends mainly on the precision requirements of the workpiece and drag torque requirements. When the precision of the workpiece is not required, the sliding screw can be used, but the original screw wear condition should be checked, such as the pitch error, the cumulative pitch error, and the matching nut clearance. In general, the sliding screw should not be lower than 6, if the nut gap is too large, replace the nut. The use of a sliding screw is relatively low compared to a ball screw, but it is difficult to satisfy the machining of parts with higher precision.
The ball screw has low friction loss and high efficiency. Its transmission efficiency can be over 90%. It has high precision and long service life. The starting torque and the moment of movement are similar, which can reduce the motor starting torque. So it can meet the processing requirements of higher precision parts.
6.4, security protection
It must be based on security. In the transformation of machine tools, corresponding measures must be taken according to the actual situation and must not be ignored. The ball screw pair is a precision component. When working, it must prevent dust, especially chips and hard sand, from entering the raceway. An integral iron guard can also be added to the longitudinal screw. Both end surfaces of the large carriage plate and the sliding guide rail are to be sealed, and it is absolutely necessary to prevent hard granular foreign materials from entering the sliding surface and damaging the guide rail.
Seven, the main steps of NC transformation of machine tools
7.1. Confirmation of reconstruction plan
After the feasibility analysis of the transformation is completed, a modification plan can be determined for the current status of a certain machine or several machines, which generally includes:
7.1.1 Combination of Mechanical Repair and Electrical Transformation
In general, machine tools that require electrical modifications need to be mechanically repaired. It is necessary to determine the requirements, scope, and contents of the repair; also the requirements and contents for the mechanical structural transformation due to the electrical transformation; and the requirements for the interleaving time between the electrical transformation and the mechanical repair and transformation. The integrity of the mechanical properties is the basis for successful electrical transformation.
7.1.2 First, Afterwards, Partially, Globally First
When determining the transformation steps, the whole electrical part transformation should be divided into several subsystems first, such as the numerical control system, measurement system, spindle, feed system, panel control and strong power, etc. jobs. This will allow renovation efforts to reduce omissions and errors. In the work of each subsystem, it is necessary to do a relatively low-tech, high-volume work first, and then do technically demanding, demanding work, so that people's attention can be focused on key areas.
7.1.3 Select System According to Use Conditions
For a certain or a few machine tools, determine its environment, temperature, humidity, dust, power, light, and even whether there are any external conditions such as rodent damage, this choice of electrical system protection performance, anti-jamming performance, self-cooling performance , air filtration performance can provide the correct basis, so that the transformation of the electrical system has a reliable use guarantee. Of course, the choice of electrical system must consider mature products, reasonable performance, practicality, spare parts and maintenance support, function to meet current and future development requirements for several years.
7.1.4 Implementing Transformation Workers and Responsibilities
Transformation is a systematic project and staffing is very important. In addition to the quality conditions of personnel, according to the size of the project, a reasonable determination of the number and division of labor is the key. Too few people are not conducive to work, and too many people are prone to confusion. According to the separate subsystems, the responsibilities of the personnel are determined, and there are master and subsidiary times to facilitate organization and coordination. If the project adopts a form of external cooperation, it is necessary to define the division of labor and determine the technical coordinator on the premise of clear objectives.
7.1.5 Determination of Transformation Range and Period
Sometimes the transformation of the CNC machine tool electrical system does not necessarily include all of the machine's electrical system. It should be determined based on scientific determination and analysis. The period of shutdown modification is determined according to the actual situation of each company. The factors to be considered include the level of production tension, the level of personnel skills, the degree of preparation work, the size and complexity of the new system, and even the weather conditions. Don’t be overjoyed, eager to achieve success, and rush into battle, but also make reasonable arrangements to prevent delays.
7.2, technical preparation for transformation
Whether the technical preparations before the transformation are sufficient or not largely determines the success of the transformation. Technical preparation includes:
7.2.1 Preparation of Mechanical Parts
Measurements, calculations, designs, drawings, parts production, etc. of large-scale mechanical remodeling that must be carried out in order to cooperate with the electrical transformation should be completed in advance. At the same time, the parts that need to be dismantled, modified, and processed after the shutdown should be planned in advance, clear requirements must be made, and the entire transformation work must be properly connected.
7.2.2 Digestion of New System Electrical Data
The new system has many new features, new requirements, and new technologies. Therefore, you should familiarize yourself with the technical materials before the renovation, including the system principle description, circuit diagrams, PLC ladder diagrams and texts, installation and commissioning instructions, user manuals, and programming manuals. There must be sufficient time for translation (input systems), digesting, collating, and checking of the above-mentioned materials, so that the ideas are clear and clearly structured.
7.2.3 Conversion Design of New and Old System Interfaces
According to the different scope of transformation of each equipment, it is necessary to design part of the interface conversion in advance, if all the transformation, should be designed mechanical and electrical conversion interface, operation panel control and configuration, interconnection part contacts, parameter measurement points, maintenance locations, etc., require easy operation and maintenance, Reasonable, the line goes to fluent, there are few connections between medium and small, and the interference between strong and weak electricity is minimal, and there is a reasonable margin. For partial reconstruction, it is also necessary to consider the performance matching of the old and new systems, voltage polarity and size conversion, installation location, and digital-to-analog conversion. If necessary, a conversion interface must be created.
7.2.4 Technical training for operators and programmers
After the transformation of the electrical system of the machine tool, it will inevitably bring new requirements to operators and programmers. Therefore, it is very important for operators and programmers to train new system knowledge in advance, otherwise it will affect the rapid transformation of the machine tool into production. The training content should generally include the new operation panel configuration, functions, and instructions; the new system's functional scope, usage, and differences from the old system; maintenance requirements; programming standards and automated programming, and so on. The key is to understand and get through the operating instructions and programming instructions.
7.2.5 Determination of commissioning steps and acceptance criteria
After the transformation of the new electrical system, how to debug and determine a reasonable acceptance criteria is also an important part of technical preparation. The commissioning work involves mechanical, hydraulic, electrical, control, sensing, etc., so it must be carried out by the project leader and other personnel. The debugging steps can be carried out from simple to complex, from small to large, from outside to inside, and can also be performed locally first, then globally, and then after the subsystem is completed. The acceptance criteria is the assessment of the new system. When it is formulated, it must be practical and realistic. Excessive or too low standards will have a negative impact on the transformation work. Once the standard is determined, it cannot be easily modified because it involves all aspects of the entire renovation work.
7.3. Implementation of transformation
After the preparations are ready, you can enter the implementation phase of the transformation. The contents of the implementation phase are divided into chronological order:
7.3.1 Full maintenance of the original machine
After long-term use of the machine tool, there will be defects in mechanical, hydraulic, lubrication, and cleanliness to varying degrees, so the first comprehensive maintenance. Secondly, it should record the geometric accuracy and dimensional accuracy of the machine tool before it is changed. This can not only guide the transformation of the work of reference, but also at the end of the transformation for comparative analysis.
7.3.2 Optimal adjustment of reserved electrical parts
If the electrical system is partially modified, the reserved electrical parts should be maintained and optimized. Such as replacement of parts of high-voltage parts, maintenance of motors, drying and insulation of transformers, cleaning of pollution, cleaning of ventilation cooling devices, optimization of servo drive devices, update of aging wire and cable, fastening of connectors, etc. . Only fine tuning of the retained electrical parts can ensure that the rebuilt machine has a lower failure rate.
7.3.3 Demolition of the original system
The removal of the original system must be carried out carefully against the original drawings, and markings should be made on the drawings in a timely manner to prevent omission or over-demolition (partial transformation). During the demolition process, some defects in the design of new systems will also be discovered. They should be promptly supplemented and amended. The systems and parts removed should be categorized and kept in a safe place so that they can be used again in the event of an unsuccessful or partial failure. There is also a certain use value, can be used for other machine tool spare parts. Don't avoid being overwhelmed.
7.3.4 Reasonably Arrange New System Location and Cabling
According to the new system design drawings, reasonable new system configuration, including the box fixed, panel placement, line direction and fixed, adjust the position of components, sealing and necessary decoration. There must be a clear division of labor in connection work, and some people review and test to ensure that the wiring process specifications, suitable diameter, correct, reliable and beautiful.
7.3.5 Commissioning
Commissioning must be done in accordance with pre-determined steps and requirements. Debugging personnel should be calm and record at any time in order to find and solve problems. In the process of debugging, first test the safety protection system sensitivity to prevent personal and equipment accidents. The commissioning site must be cleaned up with no extraneous items; each motion coordinate carriage is at the center of the full stroke; can be loaded with no-load test, loaded first after unloaded; simulated, first simulated and real action; manual, first manually Automatically.
7.4 Acceptance and post-work
Acceptance work should be employed by relevant personnel to participate in the inspection and follow the established acceptance criteria. The post-renovation work is also very important. It is conducive to improving the technical level of the project and putting the equipment into production as soon as possible. Acceptance and post-work include:
7.4.1 Acceptance of Machine Tool Mechanical Performance
After mechanical repair and transformation and comprehensive maintenance, the mechanical properties of the machine tool should meet the requirements and the geometric accuracy should be within the specified range.
7.4.2 Acceptance of Electrical Control Functions and Control Accuracy
The various functions of the electrical control must be normal, sensitive and reliable. The control accuracy of the application accuracy of the application system itself (such as step size, etc.) is compared with that of a standard measurement instrument (such as a laser interferometer, a coordinate measuring instrument, etc.) to within the accuracy range. At the same time, it should also be compared with the various functions and accuracy of the machine before the transformation to obtain the quantitative index difference.
7.4.3 Inspection and Acceptance of Specimen
Can refer to the relevant domestic and foreign standards of CNC machine tool cutting test, in the qualified operators, programmers with the trial cutting. Specimen cutting can accept machine tool stiffness, cutting force, noise, motion trajectory, associated actions, etc. Generally, it is not suitable to use product parts as specimens.
7.4.4 Acceptance of drawings and data
After the transformation of the machine tool, the drawings (including schematics, configuration drawings, wiring diagrams, ladder diagrams, etc.), data (including various types of manuals), and transformation files (including various records before and after the transformation) shall be collected and arranged in a timely manner. Transfer to file. Maintaining complete, effective and continuous data is very important for the stable operation of the equipment in the future.
7.4.5 Summary and Improvement
Every time after the completion of the transformation, it should be summed up in a timely manner, which will not only help improve the technical staff's business level, but also benefit the entire company's technological progress.
Eight, CNC transformation of several examples
1. Transform X53 milling machine with SIEMENS 810M
In 1998, the company invested 200,000 yuan, using the German Siemens 810M CNC system, 611A AC servo drive system to carry out X, Y, Z three-axis CNC transformation of a company's X53 milling machine; retains the original spindle system and Cooling system; The modified three-axis machine uses a roller screw and gear transmission mechanism. The entire renovation work includes mechanical design, electrical design, preparation and debugging of PLC program, overhaul of the machine tool, and finally the installation and commissioning of the complete machine. After the milling machine is modified, the machining effective stroke X/Y/Z axes are respectively 880/270/280 mm; the maximum speed X/Y/Z axes are 5000/1500/800 mm/min; and the manual speed X/Y/Z axes are respectively 3000/1000/500 mm/min; machining accuracy ±0.001mm. The three-axis linkage of the machine tool can complete the processing of various complex curves or surfaces.
2. Rebuild the C6140 lathe with GSK980T and stepper drive system
In 1999, the company invested 80,000 yuan, used the GSK980T CNC system and DY3 hybrid stepping drive unit manufactured by Guangzhou CNC Equipment Factory to transform the X, Z two axes of a company's extended C6140 lathe; it retained the original Spindle system and cooling system; the modified two-axis mechanically uses a roller screw and a timing belt drive mechanism. The entire renovation work includes mechanical design, electrical design, machine overhaul, and complete machine installation and commissioning. After the lathe transformation, the effective stroke X/Z axis is 390/1400 mm; the maximum velocity X/Z axis is 1200/3000 mm/min; the manual velocity is 400 mm/min; and the manual rapid X/Z axis is 1200 /3000 mm/min; The minimum movement unit of the machine is 0.001mm.
3, transformation of the C6140 lathe with GSK980T and AC servo drive system
In 2000, the GSK980T CNC system, DA98 AC servo unit and 4-station automatic tool holder manufactured by Guangzhou CNC Equipment Factory were used to digitally transform the two axes of a C6140 lathe X and Z of the motor branch; the original spindle system was retained. And the cooling system; the modified two-axis mechanically uses the roller screw and the synchronous belt transmission mechanism. The entire renovation work includes mechanical design, electrical design, machine overhaul, and complete machine installation and commissioning. After the transformation of the lathe, the effective stroke X/Z axis is 390/730 mm; the maximum velocity X/Z axis is 1200/3000 mm/min; the manual velocity is 400 mm/min; and the manual rapid X/Z axis is 1200 /3000 mm/min; The minimum movement unit of the machine is 0.001mm.
4. Transformation of X53 milling machine with SIEMENS 802S
In 2000, the company invested 120,000 yuan to use the German Siemens 802S CNC system and stepper drive system to carry out X, Y and Z three-axis NC transformation on another company's X53 milling machine; it retained the original spindle system and Cooling system; The modified three-axis machine uses a roller screw and gear transmission mechanism. The entire renovation work includes mechanical design, electrical design, machine tool overhaul, and finally the installation and commissioning of the complete machine. After the milling machine is modified, the machining effective stroke X/Y/Z axes are respectively 630/240/280 mm; the maximum speed X/Y/Z axes are 3000/1000/600 mm/min; manual feed rate X/Y/Z The axes are 2000/800/500 mm/min; the smallest moving unit is 0.001 mm.
IX. Problems and Suggestions in CNC Transformation
After the NC transformation work of several machine tools, we found that there are many problems in the work, mainly in:
First, the responsibilities of various departments and developers are unclear and the organization is chaotic, which has seriously affected the progress of the transformation;
Second, most of the work processes and plans formulated are based on experience and are not very reasonable;
Thirdly, the training of the relevant personnel is not in place, resulting in problems such as the programming of the machine tool after the machine tool transformation, and the unskilled operation of the operator on the machine tool.
In light of the above issues, there are several suggestions:
First, the responsibilities of the employees responsible for the transformation are clear, the rewards and penalties are clear, and the enthusiasm of the employees is fully mobilized;
The second is to train a group of high-quality application and maintenance personnel, and send personnel to go out for further studies and learn advanced technologies.
The third is to pay attention to the user's use, maintenance of CNC system technology training, and establish a domestic and foreign database of CNC technology.
The world’s first electronic computer was born in 1946, which shows that humans have created tools that can enhance and partially replace mental work. It has made a qualitative leap from the tools created by human beings in the agricultural and industrial societies that only enhance physical labor and laid the foundation for human beings to enter the information society.
Six years later, in 1952, computer technology was applied to the machine tool and the first CNC machine was born in the United States. Since then, traditional machine tools have produced qualitative changes. In the past half century, CNC systems have experienced two stages and six generations of development.
1.1. Numerical Control (NC) Stage (1952 to 1970)
The early computer's low computing speed had little impact on scientific computing and data processing at the time, but it could not meet the requirements of real-time control of machine tools. People have to use digital logic circuits to "build up" a machine dedicated computer as a numerical control system, known as hardware-connected numerical control (HARD-WIRED NC), abbreviated as NC (NC). With the development of components, this stage has gone through three generations, namely, the first generation of 1952--electronic tubes; the second generation of transistors in 1959--transistors; and the third generation of 1965--small-scale integrated circuits.
1.2. Computer Numerical Control (CNC) Phase (1970-present)
By 1970, the general-purpose small computer industry had appeared and was mass-produced. So it was transplanted as a core part of the CNC system, and then entered the computer numerical control (CNC) stage (the "common" word in front of the computer is omitted). In 1971, INTEL Corporation in the United States for the first time in the world to the computer's two most core components - calculators and controllers, using large-scale integrated circuit technology integrated on a chip, called the microprocessor (MICROPROCESSOR ), also known as Central Processing Unit (CPU).
By 1974, microprocessors were used in numerical control systems. This is due to the fact that small computers are so powerful that they have the ability to control a machine tool (so it was used to control multiple machine tools at the time, called a group control). It is better to use a microprocessor as an economical and reasonable tool. At the time, minicomputer reliability was also unsatisfactory. Although early microprocessor speeds and functions were not high enough, they could be solved by a multiprocessor architecture. Since the microprocessor is a core part of a general-purpose computer, it is still called a computer numerical control.
By 1990, the performance of PCs (personal computers, domestically used as microcomputers) had advanced to a very high level and could satisfy the requirements of the core components of numerical control systems. The CNC system has since entered the PC-based phase.
In short, the computer numerical control stage also experienced three generations. That is, the fourth generation of the 1970-small computer; the fifth generation of the 1974-microprocessor and the sixth generation of the 1990-based PC (PC-BASED abroad).
It should also be pointed out that although foreign countries have long been renamed Computer Numerical Control (CNC), China still uses NC. Therefore, the "CNC" that we talk about daily has essentially meant "computer numerical control."
1.3. Trends of CNC's Future Development
1.3.1 Continue to develop in the direction of the open, PC-based sixth generation
Based on the openness, low cost, high reliability, and rich hardware and software resources of PCs, more CNC system manufacturers will take this path. At least PC is used as its front-end machine to handle human-machine interface, programming, networking and other issues, and the original system assumes the task of CNC. The friendly human-machine interface that the PC machine has will be popularized to all numerical control systems. Telecommunication, remote diagnostics and maintenance will become more common.
1.3.2 Speeding up and High-precision Development
This is the need to adapt the machine to high speed and high precision.
1.3.3 Towards the development of intelligence
With the continuous penetration and development of artificial intelligence in the computer field, the degree of intelligence in CNC systems will continue to increase.
(1) Apply adaptive control technology
The numerical control system can detect some important information in the process and adjust the relevant parameters of the system automatically to achieve the purpose of improving the operating status of the system.
(2) Introduce expert system to guide processing
The skilled workers and experts' experience, the general laws and special rules of processing are stored in the system, and the expert system of artificial intelligence is established with the support of the process parameter database.
(3) Introduce fault diagnosis expert system
(4) Intelligent Digital Servo Drive
By automatically recognizing the load, the parameters can be automatically adjusted so that the drive system can operate optimally.
Second, the necessity of CNC transformation of machine tools
2.1. The necessity of micro-viewing transformation
From a microscopic point of view, CNC machine tools have the following outstanding advantages over traditional machine tools, and these advantages are derived from the power of the computer contained in the CNC system.
2.1.1 Can process complex parts such as curves and surfaces that cannot be machined by traditional machine tools.
Because the computer has superb computing power, it can instantaneously and accurately calculate the amount of motion that each coordinate axis should move at a moment, so it can be compounded into complex curves or surfaces.
2.1.2 can realize the automation of processing, and it is flexible automation, so that the efficiency can be improved by 3 to 7 times compared with the traditional machine tools.
Because the computer has memory and storage capabilities, the input program can be remembered and stored, and then automatically executed in the order specified by the program, thus achieving automation. As long as the CNC machine tool replaces a program, it can realize the automation of another workpiece processing, so that the single-piece and small batch production can be automated, so it is called "flexible automation".
2.1.3 The precision of the machined parts is high, the dispersion of the dimensions is small, and the assembly is easy. It is no longer necessary to "repair".
2.1.4 Concentration of multiple processes can be achieved, reducing the frequent handling of parts between machine tools.
2.1.5 With automatic alarm, automatic monitoring, automatic compensation and other self-discipline functions, it can realize long-term unattended processing.
2.1.6 The benefits derived from the above five articles.
Such as: reducing the labor intensity of workers, saving the labor force (one person can take care of multiple machine tools), reducing the tooling, shortened the new product trial production cycle and production cycle, can respond quickly to market demand and so on.
These superiorities are beyond the imagination of our predecessors and represent an extremely significant breakthrough. In addition, the numerical control of machine tools is still the basis for the transformation of enterprise information systems such as FMC (flexible manufacturing unit), FMS (flexible manufacturing system), and CIMS (computer integrated manufacturing system). CNC technology has become the core technology and basic technology of manufacturing automation.
2.2. The necessity of macro transformation
From a macroscopic point of view, military and civilian machinery industries in industrialized countries have begun to apply CNC machine tools on a large scale in the late 1970s and early 1980s. Its essence is to use information technology to transform traditional industries (including military and civilian machinery industries). In addition to the use of CNC machine tools, FMC, FMS in the manufacturing process, it also includes the implementation of CAD, CAE, CAM, virtual manufacturing, and the implementation of MIS (Management Information System), CIMS, etc. in product development. As well as adding information technology to its products, including artificial intelligence, etc. Due to the in-depth transformation of foreign military and civilian machinery industries (called informationization), the use of information technology has finally made their products more competitive in the international military and civilian products market. And we are about 20 years behind the developed countries in the transformation of traditional industries in information technology. For example, in China's machine tool ownership, the proportion of CNC machine tools (CNC ratio) was only 1.9% in 1995, while Japan had reached 20.8% in 1994. Therefore, a large number of electromechanical products are imported every year. This also explains the necessity of the CNC transformation of the machine tool from a macro point of view.
Third, the machine tool and the production line transformation of the NC market
3.1, the market of CNC machine transformation
Currently, the total number of machine tools in China totals more than 3.8 million units, of which the total number of CNC machine tools is only 111,400, that is, the numerical control rate of China's machine tools is less than 3%. In the past 10 years, the annual output of CNC machine tools in China is about 0.6 to 8,000 units, and the annual output value is about 1.8 billion yuan. The annual production rate of machine tools is 6%. More than 60% of China's machine tools have a service life of more than 10 years; less than 20% of automatic and semi-automatic machine tools are under 10 years old, and FMC/FMS and other automated production lines are even more accessible (60% of US and Japanese automatic and semi-automatic machine tools. the above). It can be seen that most of the manufacturing and processing equipment in most of our manufacturing industries and enterprises are traditional machine tools, and more than half of them are older machine tools with a service life of more than 10 years. The products processed by this kind of equipment generally have poor quality, few varieties, low grade, high cost and long delivery period, thus lacking competitiveness in the international and domestic markets, directly affecting a company's products, markets, benefits, and influence. The survival and development of the enterprise. Therefore, we must vigorously increase the numerical control rate of the machine tool.
3.2. Numerical control transformation of imported equipment and production lines
Since China's reform and opening up, many companies have introduced technology, equipment and production lines from abroad to carry out technological transformation. According to incomplete statistics, from the period of 1979 to 1988, there were 18,446 imported technological transformation projects in the country, totaling approximately US$ 16.58 billion.
Of these projects, most of the projects have played a proper role in China’s economic construction. However, due to various reasons, some imported projects may not be able to operate normally, or even paralyzed, equipment or production lines, which will affect the efficiency of the company and seriously impede the enterprise's difficulties. After some equipment and production lines were introduced from abroad, some were poorly digested and absorbed, spare parts were incomplete, improper maintenance, and the operation was poor; some introduced only attention to the introduction of equipment, instruments, and production lines, neglecting software, processes, and management, resulting in the failure of projects. Incomplete, equipment potential can not be played; some can not even start running, did not play its due role; some production lines of products sell well, but because of equipment failure can not meet production standards; some because of high energy consumption, product pass rate is low It caused losses; some have been introduced for a long time and require technical updates. For various reasons, some equipment not only did not create wealth, but also consumed wealth.
These equipment and production lines that cannot be used are a burden, but also a large number of stock assets. Repairing is wealth. As long as the main technical difficulties are solved and key technical problems are solved, the smallest amount of investment can be used to revitalize the largest stock assets and gain the greatest economic and social benefits. This is also a great transformation of the market.
IV. Contents and advantages of the NC transformation
4.1. The rise of foreign transformation industry
In developed countries such as the United States, Japan, and Germany, the transformation of their machine tools as a new economic growth industry has become a golden era. Due to the continuous advancement of machine tools and technology, machine tool transformation is an "eternal" topic. China's machine tool transformation industry has also moved from the old industry to a new industry dominated by numerical control technology. In the United States, Japan, and Germany, the use of numerical control technology to transform machine tools and production lines has a broad market, and a new industry has been formed for the numerical control of machine tools and production lines. In the United States, the machine tool industry is called the Remanufacturing industry. The well-known companies in the recycling industry include: Bertsche Engineering, ayton Machine Tool, Devlieg-Bullavd Service Group, and US equipment companies. The American Depot company has opened a company in China. In Japan, the machine tool transformation industry is called the Retrofitting industry. The well-known companies engaged in the conversion industry include Daxie Engineering Group, Gangsan Machinery Corporation, Chiyoda Engineering Machine Company, Nozaki Engineering Corporation, Hamada Engineering Corporation, and Yamamoto Engineering Corporation.
4.2, CNC transformation content
The main contents of the CNC transformation of machine tools and production lines are as follows:
One is to restore the original function and diagnose and recover the faults in the machine tool and production line.
The second is NC, adding a digital display device to an ordinary machine tool, or adding a numerical control system, and transforming it into an NC machine tool and a CNC machine tool;
The third is refurbishment, in order to improve the accuracy, efficiency and automation, refurbish the mechanical and electrical parts, reassemble the mechanical parts and restore the original precision; the CNC system that does not meet the production requirements is updated with the latest CNC;
The fourth is technology update or technological innovation. In order to improve performance or grades, or to use new technologies and new technologies, large-scale technological upgrades or technological innovations are carried out on the basis of the original ones, and the levels and grades are significantly upgraded and improved. .
4.3. The advantages and disadvantages of the numerical control transformation
4.3.1 Reduced Investment and Short Delivery Time
Compared with the purchase of new machine tools, it is generally possible to save 60% to 80% of the cost, the transformation costs are low. Especially large and special machine tools are particularly noticeable. General large-scale machine tool transformation, only spent 1/3 of the cost of new machine purchase, delivery time is short. However, some special circumstances, such as the production and installation of high-speed spindles and tray automatic exchange devices, are too time-consuming and costly. As a result, the cost of improvement is often increased by 2 to 3 times. Compared with the purchase of new machine tools, it can only save about 50% of investment.
4.3.2 The mechanical performance is stable and reliable, and the structure is limited
The basic parts such as the bed and pillars used are heavy and strong cast components instead of the welded components. The transformed machine has high performance and good quality and can be used as new equipment for many years. However, due to the limitations of the original mechanical structure, it is not appropriate to make a breakthrough transformation.
4.3.3 Familiar with the equipment, convenient operation and maintenance
When buying a new device, you do not know whether the new device can meet its processing requirements. Renovation is not the case, and the machine tool's processing capability can be accurately calculated. In addition, due to many years of use, the operator has already understood the characteristics of the machine tool, and the training time is short and effective in operation and maintenance. Once the modified machine is installed, full-load operation can be realized.
4.3.4 Make full use of existing conditions
You can make full use of existing foundations without having to rebuild your foundation as you would if you purchased new equipment.
4.3.5 can use the latest control technology
According to the development speed of technological innovation, the automation level and efficiency of production equipment can be improved in a timely manner, and the quality and grade of equipment can be improved. The old machine tool can be changed to the current level of machine tools.
Fifth, the choice of CNC system
There are three main types of CNC systems. When retrofitting, the selection should be based on specific conditions.
5.1 stepping motor drag open loop system
The servo drive devices of this system are mainly stepper motors, power stepper motors, and electro-hydraulic pulse motors. After the feed command pulse sent by the CNC system is controlled by the drive circuit and the power is amplified, the stepper motor is rotated, and the actuator is driven by the gear pair and the ball screw pair. As long as the number of command pulses, the frequency, and the power-on sequence are controlled, the displacement, speed, and direction of movement of the actuator can be controlled. This kind of system does not need to feedback the measured actual position and speed to the input end, so it is called an open-loop system. The displacement accuracy of the system mainly depends on the angular displacement accuracy of the stepping motor, the gear screw and other transmission components. Pitch accuracy, so the system's displacement accuracy is low.
The system is simple in structure, easy to debug and maintain, reliable in operation, low in cost, and easy to retrofit.
5.2 Closed-loop numerical control system for asynchronous motor or DC motor dragging and grating measurement feedback
The difference between this system and the open-loop system is that the actual position feedback signal measured by a position detection device such as a grating and an inductive synchronizer is compared with a given value at any time, the difference between the two is amplified and transformed, and the actuator is driven. Moving at a given speed in the direction of eliminating the deviation until the difference between the given position and the actual position of the feedback is equal to zero. The closed-loop feed system is more complex in structure than the open-loop feed system, and also has a high cost and strict requirements on the ambient room temperature. Design and debugging are more difficult than open loop systems. However, it can obtain higher accuracy, faster speed, and higher driving power than the open-loop feed system. According to product technical requirements, decide whether to use this system.
5.3. AC/DC servo motor dragging, encoder feedback semi-closed-loop numerical control system
The semi-closed-loop system detection element is mounted on the intermediate transmission and indirectly measures the position of the actuator. It can only compensate for the errors of some components inside the system loop. Therefore, its accuracy is lower than that of the closed-loop system, but its structure and debugging are simpler than the closed-loop system. When the angular displacement detecting element is integrated with the speed detecting element and the servo motor, there is no need to consider the installation of the position detecting device.
Currently there are many manufacturers of CNC systems. Famous foreign companies such as SIEMENS in Germany and FANUC in Japan; domestic companies such as China Everest Company, Beijing Aerospace Machine Tool CNC System Group, Huazhong Numerical Control Company, and Shenyang High-end CNC National Engineering Research Center .
When choosing the numerical control system, it is mainly based on various precisions that the numerical control machine wants to reach after the numerical control transformation, the power of the driving motor and the user's requirement.
Sixth, the transformation of the main mechanical components in the transformation of CNC
A new CNC machine tool is designed to achieve: a high static and dynamic stiffness; a small coefficient of friction between the pairs of movements, transmission without gaps; large power; easy operation and maintenance. The above requirements shall be fulfilled as far as the CNC transformation of the machine tool is concerned. It cannot be said that connecting the numerical control device with the ordinary machine tool has reached the requirements of the numerical control machine tool, and the corresponding transformation of the main components is also required to achieve a certain design requirement in order to achieve the intended transformation.
6.1, slide guide
For CNC lathes, the guideway should not only have general lathe guiding accuracy and craftsmanship, but also have good resistance to friction and wear and reduce the dead zone caused by frictional resistance. At the same time, it must have sufficient rigidity to reduce the influence of rail deformation on machining accuracy, and reasonable guide rail protection and lubrication are needed.
6.2, gear pair
General machine gears are mainly concentrated in the headstock and gearbox. In order to ensure the transmission accuracy, the accuracy of gears used on CNC machine tools is higher than that of ordinary machine tools. The structure must be able to achieve a gapless transmission, so when the transformation, the main gear of the machine tool must meet the requirements of CNC machine tools to ensure the machining accuracy of the machine tool.
6.3. Slide screw and ball screw
Screw drive is directly related to the precision of the transmission chain. The choice of screw depends mainly on the precision requirements of the workpiece and drag torque requirements. When the precision of the workpiece is not required, the sliding screw can be used, but the original screw wear condition should be checked, such as the pitch error, the cumulative pitch error, and the matching nut clearance. In general, the sliding screw should not be lower than 6, if the nut gap is too large, replace the nut. The use of a sliding screw is relatively low compared to a ball screw, but it is difficult to satisfy the machining of parts with higher precision.
The ball screw has low friction loss and high efficiency. Its transmission efficiency can be over 90%. It has high precision and long service life. The starting torque and the moment of movement are similar, which can reduce the motor starting torque. So it can meet the processing requirements of higher precision parts.
6.4, security protection
It must be based on security. In the transformation of machine tools, corresponding measures must be taken according to the actual situation and must not be ignored. The ball screw pair is a precision component. When working, it must prevent dust, especially chips and hard sand, from entering the raceway. An integral iron guard can also be added to the longitudinal screw. Both end surfaces of the large carriage plate and the sliding guide rail are to be sealed, and it is absolutely necessary to prevent hard granular foreign materials from entering the sliding surface and damaging the guide rail.
Seven, the main steps of NC transformation of machine tools
7.1. Confirmation of reconstruction plan
After the feasibility analysis of the transformation is completed, a modification plan can be determined for the current status of a certain machine or several machines, which generally includes:
7.1.1 Combination of Mechanical Repair and Electrical Transformation
In general, machine tools that require electrical modifications need to be mechanically repaired. It is necessary to determine the requirements, scope, and contents of the repair; also the requirements and contents for the mechanical structural transformation due to the electrical transformation; and the requirements for the interleaving time between the electrical transformation and the mechanical repair and transformation. The integrity of the mechanical properties is the basis for successful electrical transformation.
7.1.2 First, Afterwards, Partially, Globally First
When determining the transformation steps, the whole electrical part transformation should be divided into several subsystems first, such as the numerical control system, measurement system, spindle, feed system, panel control and strong power, etc. jobs. This will allow renovation efforts to reduce omissions and errors. In the work of each subsystem, it is necessary to do a relatively low-tech, high-volume work first, and then do technically demanding, demanding work, so that people's attention can be focused on key areas.
7.1.3 Select System According to Use Conditions
For a certain or a few machine tools, determine its environment, temperature, humidity, dust, power, light, and even whether there are any external conditions such as rodent damage, this choice of electrical system protection performance, anti-jamming performance, self-cooling performance , air filtration performance can provide the correct basis, so that the transformation of the electrical system has a reliable use guarantee. Of course, the choice of electrical system must consider mature products, reasonable performance, practicality, spare parts and maintenance support, function to meet current and future development requirements for several years.
7.1.4 Implementing Transformation Workers and Responsibilities
Transformation is a systematic project and staffing is very important. In addition to the quality conditions of personnel, according to the size of the project, a reasonable determination of the number and division of labor is the key. Too few people are not conducive to work, and too many people are prone to confusion. According to the separate subsystems, the responsibilities of the personnel are determined, and there are master and subsidiary times to facilitate organization and coordination. If the project adopts a form of external cooperation, it is necessary to define the division of labor and determine the technical coordinator on the premise of clear objectives.
7.1.5 Determination of Transformation Range and Period
Sometimes the transformation of the CNC machine tool electrical system does not necessarily include all of the machine's electrical system. It should be determined based on scientific determination and analysis. The period of shutdown modification is determined according to the actual situation of each company. The factors to be considered include the level of production tension, the level of personnel skills, the degree of preparation work, the size and complexity of the new system, and even the weather conditions. Don’t be overjoyed, eager to achieve success, and rush into battle, but also make reasonable arrangements to prevent delays.
7.2, technical preparation for transformation
Whether the technical preparations before the transformation are sufficient or not largely determines the success of the transformation. Technical preparation includes:
7.2.1 Preparation of Mechanical Parts
Measurements, calculations, designs, drawings, parts production, etc. of large-scale mechanical remodeling that must be carried out in order to cooperate with the electrical transformation should be completed in advance. At the same time, the parts that need to be dismantled, modified, and processed after the shutdown should be planned in advance, clear requirements must be made, and the entire transformation work must be properly connected.
7.2.2 Digestion of New System Electrical Data
The new system has many new features, new requirements, and new technologies. Therefore, you should familiarize yourself with the technical materials before the renovation, including the system principle description, circuit diagrams, PLC ladder diagrams and texts, installation and commissioning instructions, user manuals, and programming manuals. There must be sufficient time for translation (input systems), digesting, collating, and checking of the above-mentioned materials, so that the ideas are clear and clearly structured.
7.2.3 Conversion Design of New and Old System Interfaces
According to the different scope of transformation of each equipment, it is necessary to design part of the interface conversion in advance, if all the transformation, should be designed mechanical and electrical conversion interface, operation panel control and configuration, interconnection part contacts, parameter measurement points, maintenance locations, etc., require easy operation and maintenance, Reasonable, the line goes to fluent, there are few connections between medium and small, and the interference between strong and weak electricity is minimal, and there is a reasonable margin. For partial reconstruction, it is also necessary to consider the performance matching of the old and new systems, voltage polarity and size conversion, installation location, and digital-to-analog conversion. If necessary, a conversion interface must be created.
7.2.4 Technical training for operators and programmers
After the transformation of the electrical system of the machine tool, it will inevitably bring new requirements to operators and programmers. Therefore, it is very important for operators and programmers to train new system knowledge in advance, otherwise it will affect the rapid transformation of the machine tool into production. The training content should generally include the new operation panel configuration, functions, and instructions; the new system's functional scope, usage, and differences from the old system; maintenance requirements; programming standards and automated programming, and so on. The key is to understand and get through the operating instructions and programming instructions.
7.2.5 Determination of commissioning steps and acceptance criteria
After the transformation of the new electrical system, how to debug and determine a reasonable acceptance criteria is also an important part of technical preparation. The commissioning work involves mechanical, hydraulic, electrical, control, sensing, etc., so it must be carried out by the project leader and other personnel. The debugging steps can be carried out from simple to complex, from small to large, from outside to inside, and can also be performed locally first, then globally, and then after the subsystem is completed. The acceptance criteria is the assessment of the new system. When it is formulated, it must be practical and realistic. Excessive or too low standards will have a negative impact on the transformation work. Once the standard is determined, it cannot be easily modified because it involves all aspects of the entire renovation work.
7.3. Implementation of transformation
After the preparations are ready, you can enter the implementation phase of the transformation. The contents of the implementation phase are divided into chronological order:
7.3.1 Full maintenance of the original machine
After long-term use of the machine tool, there will be defects in mechanical, hydraulic, lubrication, and cleanliness to varying degrees, so the first comprehensive maintenance. Secondly, it should record the geometric accuracy and dimensional accuracy of the machine tool before it is changed. This can not only guide the transformation of the work of reference, but also at the end of the transformation for comparative analysis.
7.3.2 Optimal adjustment of reserved electrical parts
If the electrical system is partially modified, the reserved electrical parts should be maintained and optimized. Such as replacement of parts of high-voltage parts, maintenance of motors, drying and insulation of transformers, cleaning of pollution, cleaning of ventilation cooling devices, optimization of servo drive devices, update of aging wire and cable, fastening of connectors, etc. . Only fine tuning of the retained electrical parts can ensure that the rebuilt machine has a lower failure rate.
7.3.3 Demolition of the original system
The removal of the original system must be carried out carefully against the original drawings, and markings should be made on the drawings in a timely manner to prevent omission or over-demolition (partial transformation). During the demolition process, some defects in the design of new systems will also be discovered. They should be promptly supplemented and amended. The systems and parts removed should be categorized and kept in a safe place so that they can be used again in the event of an unsuccessful or partial failure. There is also a certain use value, can be used for other machine tool spare parts. Don't avoid being overwhelmed.
7.3.4 Reasonably Arrange New System Location and Cabling
According to the new system design drawings, reasonable new system configuration, including the box fixed, panel placement, line direction and fixed, adjust the position of components, sealing and necessary decoration. There must be a clear division of labor in connection work, and some people review and test to ensure that the wiring process specifications, suitable diameter, correct, reliable and beautiful.
7.3.5 Commissioning
Commissioning must be done in accordance with pre-determined steps and requirements. Debugging personnel should be calm and record at any time in order to find and solve problems. In the process of debugging, first test the safety protection system sensitivity to prevent personal and equipment accidents. The commissioning site must be cleaned up with no extraneous items; each motion coordinate carriage is at the center of the full stroke; can be loaded with no-load test, loaded first after unloaded; simulated, first simulated and real action; manual, first manually Automatically.
7.4 Acceptance and post-work
Acceptance work should be employed by relevant personnel to participate in the inspection and follow the established acceptance criteria. The post-renovation work is also very important. It is conducive to improving the technical level of the project and putting the equipment into production as soon as possible. Acceptance and post-work include:
7.4.1 Acceptance of Machine Tool Mechanical Performance
After mechanical repair and transformation and comprehensive maintenance, the mechanical properties of the machine tool should meet the requirements and the geometric accuracy should be within the specified range.
7.4.2 Acceptance of Electrical Control Functions and Control Accuracy
The various functions of the electrical control must be normal, sensitive and reliable. The control accuracy of the application accuracy of the application system itself (such as step size, etc.) is compared with that of a standard measurement instrument (such as a laser interferometer, a coordinate measuring instrument, etc.) to within the accuracy range. At the same time, it should also be compared with the various functions and accuracy of the machine before the transformation to obtain the quantitative index difference.
7.4.3 Inspection and Acceptance of Specimen
Can refer to the relevant domestic and foreign standards of CNC machine tool cutting test, in the qualified operators, programmers with the trial cutting. Specimen cutting can accept machine tool stiffness, cutting force, noise, motion trajectory, associated actions, etc. Generally, it is not suitable to use product parts as specimens.
7.4.4 Acceptance of drawings and data
After the transformation of the machine tool, the drawings (including schematics, configuration drawings, wiring diagrams, ladder diagrams, etc.), data (including various types of manuals), and transformation files (including various records before and after the transformation) shall be collected and arranged in a timely manner. Transfer to file. Maintaining complete, effective and continuous data is very important for the stable operation of the equipment in the future.
7.4.5 Summary and Improvement
Every time after the completion of the transformation, it should be summed up in a timely manner, which will not only help improve the technical staff's business level, but also benefit the entire company's technological progress.
Eight, CNC transformation of several examples
1. Transform X53 milling machine with SIEMENS 810M
In 1998, the company invested 200,000 yuan, using the German Siemens 810M CNC system, 611A AC servo drive system to carry out X, Y, Z three-axis CNC transformation of a company's X53 milling machine; retains the original spindle system and Cooling system; The modified three-axis machine uses a roller screw and gear transmission mechanism. The entire renovation work includes mechanical design, electrical design, preparation and debugging of PLC program, overhaul of the machine tool, and finally the installation and commissioning of the complete machine. After the milling machine is modified, the machining effective stroke X/Y/Z axes are respectively 880/270/280 mm; the maximum speed X/Y/Z axes are 5000/1500/800 mm/min; and the manual speed X/Y/Z axes are respectively 3000/1000/500 mm/min; machining accuracy ±0.001mm. The three-axis linkage of the machine tool can complete the processing of various complex curves or surfaces.
2. Rebuild the C6140 lathe with GSK980T and stepper drive system
In 1999, the company invested 80,000 yuan, used the GSK980T CNC system and DY3 hybrid stepping drive unit manufactured by Guangzhou CNC Equipment Factory to transform the X, Z two axes of a company's extended C6140 lathe; it retained the original Spindle system and cooling system; the modified two-axis mechanically uses a roller screw and a timing belt drive mechanism. The entire renovation work includes mechanical design, electrical design, machine overhaul, and complete machine installation and commissioning. After the lathe transformation, the effective stroke X/Z axis is 390/1400 mm; the maximum velocity X/Z axis is 1200/3000 mm/min; the manual velocity is 400 mm/min; and the manual rapid X/Z axis is 1200 /3000 mm/min; The minimum movement unit of the machine is 0.001mm.
3, transformation of the C6140 lathe with GSK980T and AC servo drive system
In 2000, the GSK980T CNC system, DA98 AC servo unit and 4-station automatic tool holder manufactured by Guangzhou CNC Equipment Factory were used to digitally transform the two axes of a C6140 lathe X and Z of the motor branch; the original spindle system was retained. And the cooling system; the modified two-axis mechanically uses the roller screw and the synchronous belt transmission mechanism. The entire renovation work includes mechanical design, electrical design, machine overhaul, and complete machine installation and commissioning. After the transformation of the lathe, the effective stroke X/Z axis is 390/730 mm; the maximum velocity X/Z axis is 1200/3000 mm/min; the manual velocity is 400 mm/min; and the manual rapid X/Z axis is 1200 /3000 mm/min; The minimum movement unit of the machine is 0.001mm.
4. Transformation of X53 milling machine with SIEMENS 802S
In 2000, the company invested 120,000 yuan to use the German Siemens 802S CNC system and stepper drive system to carry out X, Y and Z three-axis NC transformation on another company's X53 milling machine; it retained the original spindle system and Cooling system; The modified three-axis machine uses a roller screw and gear transmission mechanism. The entire renovation work includes mechanical design, electrical design, machine tool overhaul, and finally the installation and commissioning of the complete machine. After the milling machine is modified, the machining effective stroke X/Y/Z axes are respectively 630/240/280 mm; the maximum speed X/Y/Z axes are 3000/1000/600 mm/min; manual feed rate X/Y/Z The axes are 2000/800/500 mm/min; the smallest moving unit is 0.001 mm.
IX. Problems and Suggestions in CNC Transformation
After the NC transformation work of several machine tools, we found that there are many problems in the work, mainly in:
First, the responsibilities of various departments and developers are unclear and the organization is chaotic, which has seriously affected the progress of the transformation;
Second, most of the work processes and plans formulated are based on experience and are not very reasonable;
Thirdly, the training of the relevant personnel is not in place, resulting in problems such as the programming of the machine tool after the machine tool transformation, and the unskilled operation of the operator on the machine tool.
In light of the above issues, there are several suggestions:
First, the responsibilities of the employees responsible for the transformation are clear, the rewards and penalties are clear, and the enthusiasm of the employees is fully mobilized;
The second is to train a group of high-quality application and maintenance personnel, and send personnel to go out for further studies and learn advanced technologies.
The third is to pay attention to the user's use, maintenance of CNC system technology training, and establish a domestic and foreign database of CNC technology.
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