The origin and development of CNC background?

In 1946, the world's first electronic computer was born, which shows that mankind has created a tool that can enhance and partially replace mental labor. It and human beings in agriculture, industrial society to create those who only enhance the physical labor tools, compared to a qualitative leap, for human beings to enter the information society laid the foundation.

Six years later, that is, in 1952, computer technology was applied to machine tools, the birth of the first CNC machine tools in the United States. Since then, the traditional machine tool has produced qualitative changes. Nearly half a century, the CNC system has experienced two stages and six generations of development.

1.1, numerical control (NC) stage (1952-1970)

Early computer computing speed is low, the impact of scientific computing and data processing at the time is not yet large, but can not adapt to the requirements of real-time control of machine tools. People had to use digital logic circuits "built" into a machine tool-specific computer as a numerical control system, known as hardware connected to the numerical control (HARD-WIRED NC), referred to as numerical control (NC). With the development of components, this stage has gone through three generations, namely, the first generation in 1952 - electron tubes; 1959, the second generation - transistors; 1965, the third generation - small-scale integrated circuits.

1.2, computer numerical control (CNC) stage (1970 to the present)

By 1970, general-purpose minicomputer industry has appeared and mass production. So it will be transplanted as the core components of the CNC system, from now on into the computer numerical control (CNC) stage (the computer should be in front of the "general" two words omitted). To 1971, the United States INTEL company in the world for the first time the two most core components of the computer - operator and controller, using large-scale integrated circuit technology integrated on a chip, called the microprocessor (MICROPROCESSOR), also known as the central processing unit (referred to as CPU).

By 1974 microprocessors were used in CNC systems. This is because the minicomputer is too strong to control a machine tool capacity is rich (so then used to control multiple machine tools, called group control), not as economical and reasonable as the use of microprocessors. And the reliability of small machines at that time is not ideal. Early microprocessor speed and functionality is not high enough, but can be resolved through the multiprocessor structure. Because the microprocessor is the core component of a general-purpose computer, it is still called computer numerical control.

By 1990, the performance of the PC (personal computer, domestic customary microcomputer) has developed to a very high stage, can meet the requirements as the core components of the CNC system. CNC system has entered the PC-based stage.

In short, the computer numerical control stage has also experienced three generations. That is, in 1970, the fourth generation - minicomputer; 1974, the fifth generation - microprocessor and 1990, the sixth generation - PC-based (known as PC-BASED abroad).

It should also be noted that, although foreign countries have long been renamed computer numerical control (i.e., CNC), and our country is still accustomed to call the numerical control (NC). So our daily talk of "numerical control", in essence, has been referred to as "computer numerical control".

1.3, the trend of future development of CNC

1.3.1 Continue to open, PC-based sixth-generation direction

Based on the openness of the PC, low-cost, high-reliability, hardware and software resources, etc., more manufacturers of CNC systems will embark on this path. At least use the PC as its front-end machine to deal with the human-machine interface, programming, networking and communications, etc., by the original system to undertake the task of CNC. PC has a friendly human-machine interface, will be popularized to all the CNC system. Remote communication, remote diagnosis and maintenance will be more common.

1.3.2 To high-speed and high-precision development

This is to adapt to the machine tool to high-speed and high-precision direction.

1.3.3 Intelligent direction

With the continuous penetration and development of artificial intelligence in the field of computers, the degree of intelligence of the CNC system will continue to improve.

(1) the application of adaptive control technology

The CNC system can detect some important information in the process, and automatically adjust the relevant parameters of the system to achieve the purpose of improving the system's operating state.

(2) the introduction of expert systems to guide the processing

The experience of skilled workers and experts, the general and special laws of processing into the system, supported by a database of process parameters, the establishment of an expert system with artificial intelligence.

(3) Introduction of fault diagnosis expert system

(4) Intelligent digital servo drive

can automatically identify the load, and automatically adjust the parameters, so that the drive system to obtain the best operation.

Second, the necessity of machine tool CNC transformation

2.1, the micro look at the necessity of transformation

From a microscopic point of view, CNC machine tools than traditional machine tools have the following outstanding superiority, and all of these superiority are from the power of the computer contained in the CNC system.

2.1.1 Complex parts such as curves and surfaces that cannot be machined by conventional machines can be processed.

Because computers have superior computing power, they can instantly and accurately calculate the amount of motion that each axis should instantly move, so they can be compounded into complex curves or surfaces.

2.1.2 The automation of machining can be realized, and it is flexible automation, so that the efficiency can be increased by 3 to 7 times compared with traditional machine tools.

Because the computer has the memory and storage capacity, can be input program to remember and store, and then automatically according to the order of the program to execute, thus realizing automation. CNC machine tools as long as the replacement of a program, you can realize the automation of another workpiece processing, so that single-piece and small batch production can be automated, so it is known as the realization of the "flexible automation".

2.1.3 Processed parts of high precision, small size dispersion, so that the assembly is easy, no longer need to "repair".

2.1.4 Can realize the concentration of multiple processes, reducing the parts in the machine tool between the frequent transfer.

2.1.5 With automatic alarm, automatic monitoring, automatic compensation and other self-regulating functions, thus realizing unattended processing for a long time.

2.1.6 Benefits derived from the above five.

Such as: reduce the labor intensity of workers, labor savings (a person can look after more than one machine tool), reduce the number of fixtures, shorten the cycle of trial production of new products and production cycle, can be a rapid response to market demand and so on.

These superiority is unimaginable before, is an extremely significant breakthrough. In addition, machine tool CNC or the implementation of FMC (Flexible Manufacturing Cell), FMS (Flexible Manufacturing System) and CIMS (Computer Integrated Manufacturing System) and other enterprise information transformation basis. CNC technology has become the core technology and basic technology of manufacturing automation.

2.2, the macro look at the necessity of transformation

From a macro point of view, the military and civilian machinery industry in industrially developed countries, at the end of the 70's and early 80's has begun to large-scale application of CNC machine tools. The essence is that the use of information technology to traditional industries (including military and civilian machinery industry) to carry out technological transformation. In addition to the use of CNC machine tools in the manufacturing process, FMC, FMS, but also in product development in the implementation of CAD, CAE, CAM, virtual manufacturing, and in the implementation of production management MIS (Management Information System), CIMS and so on. As well as in its production of products to increase the content of information technology, including artificial intelligence. As a result of the use of information technology on foreign military and civilian machinery industry to carry out in-depth transformation (known as information technology), and ultimately make their products in the international military and civilian market competitiveness greatly enhanced. And we in information technology transformation of traditional industries than the developed countries about 20 years behind. Such as China's machine tool ownership, the proportion of CNC machine tools (CNC rate) to 1995 only 1.9%, while Japan in 1994 has reached 20.8%, so every year there are a large number of mechanical and electrical products imported. This also illustrates the need for machine tool CNC transformation on a macro level.

Third, machine tools and production line CNC transformation of the market

3.1, machine tool CNC transformation of the market

China's current total number of machine tools more than 3.8 million units, of which the total number of CNC machines only 113,400 units, that is, China's machine tool CNC rate of less than 3%. In the past 10 years, China's annual output of CNC machine tools is about 0.6 to 0.8 million units, the annual output value of about 1.8 billion yuan. The annual output of machine tools CNC rate of 6%. China's machine tool service age of more than 10 years accounted for more than 60%; 10 years below the machine tool, automatic/semi-automatic machine tools less than 20%, FMC/FMS and other automated production lines are more than a handful of (U.S. and Japan automatic and semi-automatic machine tools accounted for more than 60%). It can be seen that most of our manufacturing industry and enterprise production, processing equipment, the vast majority of traditional machine tools, and more than half of the service age of more than 10 years of the old machine tools. With this equipment, the products processed out of the prevailing poor quality, few varieties, low grade, high cost, long delivery period, thus the lack of competitiveness in the international and domestic markets, directly affecting the products of an enterprise, the market, efficiency, affecting the survival and development of enterprises. So we must vigorously improve the CNC rate of machine tools.

3.2, imported equipment and production line CNC transformation market

China since the reform and opening up, many enterprises from abroad to introduce technology, equipment and production lines for technological transformation. According to incomplete statistics, from 1979 to 1988 in 10 years, the country's introduction of technological transformation projects there are 18,446, about 16.58 billion U.S. dollars.

Most of these projects have played their due role in China's economic construction. However, some of the introduced projects due to various reasons, the equipment or production line can not operate normally, or even paralyzed, so that the benefits of the enterprise is affected, and the seriousness of the enterprise into a difficult situation. Some equipment, production lines from abroad after the introduction, some digestion and absorption is not good, spare parts are not complete, improper maintenance, the result of poor operation; some of the introduction of the introduction of only pay attention to the introduction of equipment, equipment, production lines, ignoring the software, technology, management, resulting in incomplete projects, equipment potential can not be played; some can not even start the operation, did not play the role it should have been; there are some production lines of the product market is very good, but because of equipment failure can not meet the production standards. Some production lines have good sales, but because of equipment failure can not meet production standards; some because of high energy consumption, low product qualification rate and cause losses; some have been introduced for a long time, the need for technological updating. For various reasons, some equipment not only did not create wealth, but consumed wealth.

These can not use the equipment, production line is a burden, but also a number of large stock of assets, fixed is wealth. As long as the main technical difficulties to find out, solve the key technical problems, you can minimize the investment to revitalize the largest stock of assets, for the greatest economic and social benefits. This is also a great remodeling market.

Fourth, the content and advantages and disadvantages of CNC transformation

4.1, the rise of foreign transformation industry

In the United States, Japan and Germany, and other developed countries, their machine tool transformation as a new economic growth industry, business is booming, is in the golden age. As machine tools and the continuous progress of technology, machine tool transformation is a "timeless" subject. China's machine tool transformation industry, but also from the old industry into a new industry based on CNC technology. In the United States, Japan, Germany, with CNC technology to transform machine tools and production lines have a broad market, has formed a machine tool and production line CNC transformation of the new industry. In the United States, the machine tool transformation industry is called machine tool regeneration (Remanufacturing) industry. Engaged in the regeneration of the industry's famous companies are: Bertsche Engineering Company, ayton machine tool company, Devlieg-Bullavd (Takpo) Services Group, US equipment companies. The U.S. Depot has opened a company in China. In Japan, the machine tool conversion industry is called machine tool modification (Retrofitting) industry. Engaged in retrofitting the industry's famous companies are: Okuma Engineering Group, three mechanical companies in the Gang, Chiyoda Engineering Company, Nozaki Engineering Company, Hamada Engineering Company, Yamamoto Engineering Company and so on.

4.2, the content of CNC transformation

The main content of the CNC transformation of machines and production lines are as follows:

One is to restore the original function of the machine tool, the production line there are faults in the part of the diagnostic and restoration;

The second is the NC, the ordinary machine tool with a digital display device, or add a numerical control system, transformed into NC machine tools, CNC machine tools;

The second is NC, digital display device, or add a numerical control system, transformed into NC machine tools, CNC machine tools. machine tools;

Third is renovation, in order to improve the accuracy, efficiency and automation, the mechanical and electrical parts of the renovation, the mechanical part of the reassembly and processing, to restore the original accuracy; CNC system does not meet the production requirements of the CNC with the latest CNC update;

Fourth is the technological update or technological innovation, in order to improve the performance or grade, or in order to use the new technology, new technology. On the basis of the original larger-scale technological renewal or technological innovation, a substantial increase in the level and grade of the renewal and transformation.

4.3, the advantages and disadvantages of CNC transformation

4.3.1 Reduce the amount of investment, short delivery

Compared with the purchase of new machine tools, you can generally save 60% to 80% of the cost of transformation of low-cost. Especially large, special machine tools, especially obvious. General transformation of large-scale machine tools, only to spend 1/3 of the purchase cost of new machines, short delivery time. But some special circumstances, such as high-speed spindle, pallet automatic exchange device production and installation of too labor-intensive, costly, often the transformation cost 2 to 3 times, compared with the purchase of new machine tools, can only save about 50% of the investment.

4.3.2 Stable and reliable mechanical performance, structural constraints

The use of the bed, columns and other basic parts are heavy and strong casting components, rather than the kind of welded components, after the transformation of the machine tool performance is high, good quality, and can continue to be used for many years as the new equipment. But by the original mechanical structure of the limitations, it is not appropriate to make breakthroughs in the transformation.

4.3.3 Familiarize yourself with the equipment, easy to operate and maintain

When you buy new equipment, you do not know whether the new equipment to meet its processing requirements. Retrofit is not, you can accurately calculate the processing capacity of the machine tool; in addition, due to years of use, the operator of the machine tool characteristics have long been understood, in the operation and maintenance of the training time is short, quick results. Transformation of the machine tool once installed, you can realize the full load operation.

4.3.4 Make full use of the existing conditions

The existing foundation can be fully utilized, and do not need to re-construct the foundation as in the case of purchasing new equipment.

4.3.5 Adoption of the latest control technology

According to the speed of development of technological innovation, can be timely to improve the level of automation and efficiency of the production equipment, improve the quality of equipment and grade, the old machine tools into today's level of machine tools.

V. Selection of CNC systems

There are three main types of CNC systems, the transformation, should be selected according to the specific circumstances.

5.1, stepper motor drag open loop system

The servo drive of the system is mainly stepper motor, power stepper motor, electro-hydraulic pulse motor. The feed command pulse sent by the numerical control system, controlled by the drive circuit and power amplification, so that the stepping motor rotation, through the gear and ball screw sub drive execution parts. As long as the number and frequency of command pulses and the sequence of energization are controlled, the displacement, speed and direction of motion of the executive parts can be controlled. This system does not require the measured actual position and speed feedback to the input, so it is called open-loop system, the displacement accuracy of the system is mainly determined by the angular displacement accuracy of the stepper motor, gear screw and other transmission components of the pitch accuracy, so the system's displacement accuracy is low.

The system has a simple structure, easy debugging and maintenance, reliable operation, low cost, easy to modify the success.

5.2, asynchronous motor or DC motor drag, grating measurement feedback closed-loop CNC system

The difference between this system and the open-loop system is that: the grating, inductive synchronizer and other position detection devices measured by the actual position of the feedback signal at any time compared with the given value, the difference between the two amplified and transformed to drive the actuator at a given speed in the direction of eliminating deviation The difference between the two values is amplified and transformed to drive the actuator to move in the direction of eliminating the deviation with the given speed until the difference between the given position and the actual position of the feedback is equal to zero. The closed-loop feeding system is more complex than the open-loop feeding system in terms of structure, cost, and strict requirements on the ambient room temperature. Design and commissioning are more difficult than open-loop systems. However, it can obtain higher precision, faster speed and greater drive power than open-loop feeding system. According to the technical requirements of the product, decide whether to use this system.

5.3, AC / DC servo motor drag, encoder feedback semi-closed-loop CNC system

Semi-closed-loop system detection element installed in the middle of the drive parts, indirectly measuring the position of the executive part. It can only compensate for the error of some components within the system loop, so its accuracy is lower than that of the closed-loop system, but its structure and commissioning are simpler than the closed-loop system. In the angular displacement detection element and speed detection element and servo motor as a whole without considering the installation of the position detection device.

The current production of CNC system manufacturers are more companies, foreign companies such as Germany SIEMENS, Japan FANUC company; domestic companies such as China Everest, Beijing Aerospace Machine Tool CNC Systems Group Corporation, Huazhong CNC company and Shenyang High-grade CNC National Engineering Research Center.

The choice of CNC system is mainly based on the CNC transformation of the machine tool to achieve a variety of precision, drive motor power and user requirements.

Six, CNC transformation of the main mechanical components of the modification of the discussion

A new CNC machine tool, in the design to achieve: high static and dynamic stiffness; the friction coefficient between the movement of the vice is small, the transmission of gapless; power; easy to operate and maintain. Machine tool CNC transformation should try to meet the above requirements. Can not think of CNC devices and ordinary machine tools connected together to achieve the requirements of CNC machine tools, but also the main components of the corresponding transformation to achieve certain design requirements, in order to obtain the expected transformation purposes.

6.1, sliding guideway vice

For CNC lathes, the guideway should be in addition to ordinary lathe guiding accuracy and craftsmanship, but also have good friction, wear characteristics, and reduce the dead zone due to frictional resistance. At the same time, there should be enough stiffness to reduce the guide deformation on the impact of machining accuracy, there should be a reasonable guide protection and lubrication.

6.2, gears

General machine tool gears are mainly concentrated in the spindle box and gearbox. In order to ensure transmission accuracy, CNC machine tools used on the gear precision level are higher than ordinary machine tools. In the structure to be able to achieve backlash-free transmission, and thus the transformation, the main gears of the machine tool must meet the requirements of the CNC machine tool to ensure machine tool machining accuracy.

6.3, sliding screw and ball screw

Screw drive is directly related to the transmission chain precision. The selection of the screw mainly depends on the precision requirements of the workpiece and the drag torque requirements. When the precision of the processed parts is not high, the sliding screw can be used, but the original screw wear should be checked, such as pitch error and pitch cumulative error and matching nut clearance. In general, the sliding screw should not be less than 6 levels, nut clearance is too large to replace the nut. The sliding screw is less expensive than the ball screw, but it is difficult to meet the higher precision parts processing.

Ball screw friction loss is small, high efficiency, its transmission efficiency can be more than 90%; high precision, long service life; start-up torque and movement torque is close to reduce the motor start-up torque. Therefore, it can meet the requirements of higher precision parts processing.

6.4, safety protection

Effectiveness must be based on the premise of safety. In the machine tool transformation according to the actual situation to take appropriate measures, must not be ignored. Ball screw is a precision component, work to prevent dust, especially chips and hard sand into the raceway. In the longitudinal screw can also be added to the overall iron plate shield. Large drag plate and sliding guide contact with the two end surfaces should be sealed, absolutely prevent hard particles of foreign matter into the sliding surface damage guide.

Seven, the main steps of machine tool CNC transformation

7.1, the transformation of the program to determine

After the feasibility analysis of the transformation through, you can determine the transformation program for a certain machine tool or a number of machine tool conditions, generally include: