The world manufacturing industry is shifting, China is gradually becoming the world processing plant. The United States, Germany, South Korea and other countries have entered the high technology-intensive era of industrialization and development and microelectronics era, steel, machinery, chemicals and other heavy industries are gradually transferring to developing countries. China's current economic development has passed the early stage of development, is in the middle of the development of heavy industry.
The next 10 years will be the best period for the development of China's machinery industry. The United States, Germany's heavy chemical industry development period continued for more than 18 years, the United States, Germany, South Korea, four countries heavy chemical industry development period continued for an average of 12 years, we estimate that China's heavy chemical industry development period will continue for at least 10 years, until 2015. Therefore, in the next 10 years, as China's heavy chemical industry process, China's enterprise scale, product technology, quality, etc. will be greatly improved, domestic machinery products to enhance international competitiveness, and gradually replace imports, and accelerate exports. At present, the machinery industry in the central molecule industry such as ships, railroads, containers and container cranes manufacturing has benefited from the international industrial transfer, and will continue to benefit; power station equipment, construction machinery, beds, etc. will benefit from the industrial transfer to accelerate the export process
Keywords : numerical control, industrialization, development of knives, machine tools
Catalogue
Chapter 1 The emergence of numerical control machine tools
Chapter 1 CNC machine tools< /p>
Chapter 2 Development of CNC Machine Tools
2.1 Development of CNC System 1
2.2 Development Trend of Machine Tools 2
Chapter 3 Classification of CNC Machine Tools
3.1 Classification According to Machining Process Methods 4
3.1.1 CNC Machine Tools of Metal Cutting Classes 4
3.1.2 CNC Machine Tools of Special Machining Classes CNC Machine Tools 4
3.1.3 Plate Processing CNC Machine Tools 4
3.2 Classification According to the Control of Motion Trajectory 5
3.1.2 Point Control CNC Machine Tools 5
3.2.2 Linear Control CNC Machine Tools 5
3.2.3 Profile Control CNC Machine Tools 5
3.3 Classification According to the Characteristics of Driving Device 6
3.3.1 Open-loop Control CNC Machine Tools 6
3.3.2 Closed-loop Control CNC Machine Tools 7
3.3.3 Semi-Closed-loop Control CNC Machine Tools 7
3.3.4 Hybrid Control CNC Machine Tools 7
Chapter 4: Craftsmanship and Tooling Cutting of CNC Turning
4.1 Reasonable Selection of Cutting Volume 9
< p>4.2 Reasonable selection of cutting tools 94.3 Reasonable selection of fixtures 10
4.4 Determination of machining routes 10
4.5 The link between machining routes and machining allowances 10
4.6 Points for fixture installation 10
Chapter 5: Tips for using the first sentence of a program and controlling dimensional accuracy
5.1 The first sentence of a program Tips for Using G00 11
5.2 Tips for Controlling Dimensional Accuracy 12
5.2.1 Modifying Tool Complements to Ensure Dimensional Accuracy 12
5.2.2 Semi-finishing to Eliminate the Effect of Screw Backlash to Ensure Dimensional Accuracy 12
5.2.3 Programming to Ensure Dimensional Accuracy 12
5.2.4 Modifying Programs and Tool Complements to Control Dimensions 13
5.2.4 Modifying Programs and Tool Complements to Control Complementary control of dimensions 13
Chapter 6 CNC Technology
6.1 Overview of the electrical control system of CNC machine tools 14
6.2 Electrical control of CNC machine tool motion coordinates 16
Conclusion
Acknowledgments
References
Chapter 1: The emergence of the CNC machine tool
In the machinery manufacturing industry Not all product parts have a large batch, single and small batch production of parts (batch size of 10 to 100 pieces) accounted for more than 80% of the total amount of machining. Especially in the shipbuilding, aerospace, aviation, machine tools, heavy machinery and defense industry is so.
In order to meet the multi-species, small batch automated production, there is an urgent need for a flexible, versatile, flexible automated machine tools that can apply to frequent changes in the product. CNC machine tools are born and developed in this context. It for a single piece, small batch production of precision complex parts to provide automated means of processing.
According to the national standard GB/T8129-1997, the definition of digital control of machine tools: digital control device (referred to as CNC device), in the operation process, the continuous introduction of digital data, so as to achieve automatic control of a production process, called digital control, referred to as CNC. With computer control of processing functions, called computer numerical control (computerized numerical , abbreviated CNC).
Numerical control machine tools, even if the use of numerical control technology, or machine tools equipped with a numerical control system. From the application, CNC machine tools is the machining process requires a variety of operations (such as spindle speed, loose workpiece, feed and retract, drive and stop, select tools, supply cutting fluid, etc.) and steps, as well as the relative displacement between the tool and the workpiece are digitized code to represent the digital information through the control medium into the special or general-purpose computers, computers process the input information with The computer processes and calculates the input information and issues various instructions to control the servo system of the machine tool or other actuating elements, and the machine tool automatically processes the required parts.
Chapter 2 The development of CNC machine tools
2.1 The development of CNC systems
From the first CNC machine tools in 1952, the CNC system has gone through two phases and six generations of development, its six generations refers to the electronic tube, transistor, integrated circuits, minicomputers, microprocessors, and general-purpose CNC systems based on industrial PCs. Among them, the first three generations for the first stage, called as a hardware connection to the numerical control, referred to as the NC system; the latter three generations for the second stage, ride the computer software numerical control, referred to as the CNC system.
2.2 The development trend of the machine
The general development trend of CNC machine tools is process centralization, high-speed, high-efficiency, high-precision, as well as easy to use, improve reliability and so on.
(1) process concentration In the late 1950s, on the basis of general CNC machine tools developed CNC machining centers, that is, automatic tool changer CNC machine tools with their own tool magazines. In the machining center machine tool, the workpiece once clamped, the machine tool manipulator can automatically change the tool, continuous processing of the workpiece for a variety of processes.
Currently, the machining center machine tool magazine capacity can reach more than 100 tools, automatic tool changing device tool change time is only 0.5 ~ 2 seconds. Machining center machine tool so that the process is concentrated in a machine tool to complete, reduce the process due to the dispersion of the workpiece multiple installation caused by the positioning error, improve the machining accuracy, but also reduces the number of machine tools and footprint, compressed semi-finished goods inventory, reduce the auxiliary time between processes, effectively improve the productivity of CNC machine tools and CNC machining of the economic benefits.
(2) high speed, high efficiency, high precision
High speed, high efficiency, high precision is the goal of machining, CNC machine tools because of its expensive, in the above three aspects of the development is more prominent.
(3) easy to use
CNC machine tool manufacturers to establish a friendly human-machine interface, improve the reliability of CNC machine tools as a major aspect of improving competitiveness.
1) processing and programming is convenient
Manual programming and automatic programming has been used for decades, there has been significant development in manual programming, the development of a variety of machining cycles, parameter programming and in addition to straight lines, arcs other than a variety of interpolation functions, CAD/CAM research and development, technically speaking, can be a substitute for manual programming. But a set of applicable CAD / CAM software plus computer hardware, a larger investment, learning, mastery time is longer, for most of the simple workpiece is very uneconomical.
In recent years, the development of a graphical interactive programming system (WOP, also known as workshop-oriented programming), very popular with users. This programming method does not use G, M code, but with the help of graphic menus, enter the entire graphic block and the corresponding parameters as machining instructions to form a machining program, similar to the traditional way of thinking when machining. Graphical interactive programming method in the development of standards, it is possible to become a variety of models of CNC machine tools unified programming method.
2) use
CNC machine tools generally use color CRT for man-machine dialogue, graphic display and graphic simulation. Some CNC machine tools will be used to manuals, programming guides, lubrication guides, etc. deposited in the system **** user access.
Chapter III Classification of CNC machine tools
3.1 Classification of CNC machine tools according to the method of machining process
3.1.1. metal cutting CNC machine tools
With the traditional lathe, milling, drilling, grinding, gear processing corresponding to the CNC machine tools CNC lathes, CNC milling, CNC drilling, CNC grinding, CNC gear machine tools and so on. Although these CNC machine tools in the processing process method is very different, the specific control mode is also different, but the action and movement of the machine tool are digitally controlled, with a high degree of productivity and automation.
In the ordinary CNC machine tool with a tool magazine and tool changer becomes a CNC machining center machine tool. Machining center machine tools to further improve the degree of automation and productivity of ordinary CNC machine tools. For example, milling, boring, drilling machining center, which is based on the CNC milling machine to increase the capacity of a larger tool magazine and automatic tool changer formed, the workpiece after a clamping, can be a box parts on all sides or even most of the five-sided machining process for milling, boring, drilling, expanding, hinging, and tapping threads and other multi-processing, especially suitable for the processing of box type parts. Machining centers can effectively avoid positioning errors caused by multiple installation of the workpiece, reducing the number of machine tools and floor space, shorten the auxiliary time, greatly improving production efficiency and processing quality.
3.1.2 special processing CNC machine tools
In addition to cutting CNC machine tools, CNC technology is also used in a large number of CNC EDM wire cutting machine tools, CNC EDM molding machine tools, CNC plasma arc cutting machine tools, CNC flame cutting machine tools, as well as CNC laser processing machine tools.
3.1.3. Sheet metal processing CNC machine tools
Commonly used in sheet metal processing CNC machine tools are CNC presses, CNC shearing machines and CNC bending machines.
In recent years, a large number of other machinery and equipment in the use of CNC technology, such as CNC multi-coordinate measuring machine, automatic drawing machine and industrial robots.
3.2 Classification according to the control of the movement trajectory
3.2.1. point control CNC machine tools
Precise positioning of the position, in the process of moving and positioning without any processing. Machine tool numerical control system only controls the coordinate value of the end of the trip, does not control the movement trajectory between the point and the point, so there is no connection between the movement of several coordinate axes. Several coordinates can be moved to the target point at the same time, or each coordinate can be individually sequential movement.
This type of CNC machine tool mainly includes CNC coordinate boring machine, CNC drilling machine, CNC punching machine, CNC spot welding machine and so on. Point control CNC machine tool CNC device is called point CNC device.
3.2.2 Linear control CNC machine tools
Linear control CNC machine tools can control the tool or table to the appropriate feed rate, along the direction parallel to the coordinate axis of linear movement and cutting, feed rate according to the cutting conditions can be varied within a certain range.
Linear control of simple CNC lathe, only two coordinate axes, can be processed stepped axis. Linear control of CNC milling machine, there are three coordinate axes, can be used for milling and processing of the plane. Modern combination of machine tools using CNC feed servo system, drive power head with multi-axis box axial feed for drilling and boring processing, it can also be considered a linear control CNC machine tools.
CNC boring and milling machines, machining centers and other machine tools, it is the speed of each coordinate direction of the feed movement can be adjusted within a certain range, both point and linear control of the function of machining, this type of machine tool should be called point/linear control of CNC machine tools.
3.3.3 Contour control CNC machine tools
Contour control CNC machine tools are able to control the displacement and speed of two or more motions in a continuous manner, so that the synthesized planar or spatial trajectory can meet the requirements of the part contour. It can not only control the coordinates of the starting and ending points of the moving parts of the machine tool, but also control the speed and displacement of each point of the entire machining contour, so that the workpiece can be machined into the required contour shape.
Commonly used CNC lathe, CNC milling machine, CNC grinding machine is a typical contour control CNC machine tools. CNC flame cutting machine, EDM machine tools and CNC plotter also uses a contour control system. The structure of the contour control system is more complex than the point/linear control system, which requires constant interpolation in the machining process, and then the corresponding speed and displacement control.
Nowadays, the control functions of computer numerical control devices are realized by software, and adding contouring control functions will not bring about an increase in cost. Therefore, in addition to a few specialized control systems, modern computer numerical control devices have contour control functions.
3.3 Classification according to the characteristics of the drive device
3.3.1 Open-loop control of CNC machine tools
This type of control of CNC machine tools is its control system does not have a position detection element, the servo drive components are usually reactive stepping motor or hybrid servo stepping motor. The CNC system sends out a feed command, the drive circuit power amplification, drive stepping motor rotation angle, and then through the gear reduction device to drive the screw rotation, through the screw nut mechanism is converted into a moving part of the linear displacement. The moving speed and displacement of the moving part are determined by the frequency and number of input pulses. The information flow of this type of CNC machine tool is unidirectional, i.e., after the feed pulse is sent out, the actual moving value is no longer fed back, so it is called open-loop control CNC machine tool.
The open-loop control system of CNC machine tools has a simple structure and low cost. However, the system does not monitor the actual displacement of the moving parts, nor can it perform error correction. As a result, stepping motor out-of-step, step angle error, gears and screws and other transmission errors will affect the accuracy of the machined parts. The open-loop control system is only suitable for small and medium-sized CNC machine tools that do not require very high machining accuracy, especially simple and economical CNC machine tools.
3.3.2 Closed-loop control of CNC machine tools
The actual displacement of the table is detected, the measured actual displacement value is fed back to the CNC device, compared with the input command displacement value, and the difference is used to control the machine tool, so that the moving parts move in accordance with the actual required displacement, and ultimately realize the precise movement and positioning of the moving parts. Theoretically, the motion accuracy of the closed-loop system mainly depends on the detection accuracy of the detection device, and also has nothing to do with the error of the transmission chain, so its control accuracy is high. Figure 1-3 shows the closed-loop control CNC machine tool system block diagram. In the figure, A is a speed sensor, C is a linear displacement sensor. When the displacement command value sent to the position comparison circuit, if the table does not move, there is no feedback, the command value makes the servo motor rotation, through the A will be the speed feedback signal sent to the speed control circuit, through the C will be the actual displacement of the table back to the position comparison circuit with the displacement command value, with the difference between the comparative value for position control, until the difference is zero. This type of control of CNC machine tools, because the machine table into the control link, it is called closed-loop control of CNC machine tools.
Closed-loop control CNC machine tools have high positioning accuracy, but debugging and maintenance are more difficult, the system is complex, high cost.
3.3.3 Semi-closed-loop control CNC machine tools
Semi-closed-loop control CNC machine tools are equipped with angular displacement current detecting devices (such as photoelectric encoder, etc.) in the servo motor's axle or CNC machine tool's transmission screw, which indirectly detects the actual displacement of the moving parts through the detection of the rotating angle of the screw, and then feeds back to the numerical control device and corrects for the error. The rotational speed of the servo motor can be indirectly detected by means of the speed measuring element A and the photoelectric encoder disk B. The actual displacement of the table is then deduced, and this value is compared with the commanded value, and the difference is used to realize control. Since the table is not included in the control loop, it is called semi-closed-loop control CNC machine tool.
Semi-closed-loop control CNC system debugging is more convenient, and has good stability. At present, most of the angle detection device and servo motor are designed as a single unit, which makes the structure more compact.
3.3.4 Hybrid control CNC machine tools
The combination of the characteristics of the above three types of CNC machine tools, the formation of hybrid control CNC machine tools. Hybrid control CNC machine tools are particularly suitable for large or heavy CNC machine tools, because large or heavy CNC machine tools require high feed rate and quite high precision, its transmission chain inertia and torque is large, if you only use the full closed-loop control, the machine tool transmission chain and the table are all placed in the control of the closed-loop, the closed-loop debugging is more complex. Hybrid control system is divided into two forms:
(1) open-loop compensation type. Its basic control selection of stepper motor open-loop servo mechanism, in addition to an additional correction circuit. The feedback signal of the linear displacement measuring element mounted on the table is used to correct the error of the mechanical system.
(2) semi-closed-loop compensation. It is a semi-closed-loop control to achieve high-precision control, and then mounted on the table linear displacement measuring element to realize the full closed-loop correction, in order to obtain the unity of high speed and high accuracy. Among them, A is the speed measuring element (such as speed generator), B is the angle measuring element and C is the linear displacement measuring element.
Chapter 4 CNC lathe process and tooling cutting
CNC lathe machining process is similar to that of the ordinary lathe, but because the CNC lathe is a one-time clamping, continuous automatic machining to complete all the turning process, and therefore should pay attention to the following aspects.
4.1. Reasonable selection of cutting volume
For efficient metal cutting, the material to be processed, cutting tools, cutting conditions are three major elements. These determine the machining time, tool life and machining quality. Cost-effective machining is bound to be a reasonable choice of cutting conditions.
The three elements of cutting conditions: cutting speed, feed and depth of cut directly cause tool damage. Along with the increase in cutting speed, the tip temperature will rise, will produce mechanical, chemical and thermal wear. A 20% increase in cutting speed reduces tool life by 1/2.
The relationship between feed conditions and wear behind the tool arises on a very small scale. However, with high feed, the cutting temperature rises and the back wear is high. It is smaller than the effect of cutting speed on the tool. The effect of depth of cut on the tool is not as large as the cutting speed and feed, but in the tiny depth of cut cutting, the material being cut produces a hardened layer, which also affects the life of the tool.
Users should choose the cutting speed according to the material to be machined, hardness, cutting condition, material type, feed, depth of cut and so on.
The most suitable machining conditions are selected on the basis of these factors. Regular and steady wear to achieve life is the ideal condition.
However, in practice, the selection of tool life is related to tool wear, the size change of the machined size, surface quality, cutting noise, machining heat and so on. When determining the machining conditions, it is necessary to study according to the actual situation. For difficult-to-machine materials such as stainless steel and heat-resistant alloys, you can use coolants or choose a rigid blade.
4.2. Reasonable selection of tools
1) When rough turning, choose tools with high strength and good durability in order to meet the requirements of large back-eating and large feed in rough turning.
2) For fine turning, choose a tool with high precision and good durability to ensure machining accuracy.
3) In order to reduce the time of tool change and facilitate tool setting, machine tool and machine clamped inserts should be used as much as possible.
4.3. Reasonable selection of fixtures
1) Try to use general fixtures to clamp the workpiece, avoid the use of special fixtures;
2) The parts positioning reference overlap, in order to reduce positioning errors.
4.4. Determine the machining route
The machining route refers to the CNC machine tool machining process, the tool relative to the part's trajectory and direction.
1) It should be able to ensure the machining accuracy and surface roughness requirements;
2) It should try to shorten the machining route and reduce the tool empty travel time.
4.5. The link between machining route and machining allowance
At present, under the condition that the CNC lathe has not yet reached the popularization of the use of CNC lathe, the excessive allowance on the blank should generally be arranged for machining on the ordinary lathe, especially the allowance that contains the forged and cast hard skin layer. If you must use CNC lathe processing, you need to pay attention to the flexible arrangement of the program.
4.6. Clamp installation points
Currently, the hydraulic chuck and hydraulic clamping cylinder connection is realized by the tie rod, hydraulic chuck clamping points are as follows: first of all, use the moving hand to remove the hydraulic cylinder on the nut, remove the pull tube, and from the back end of the spindle, and then use the moving hand to remove the chuck fixing screws, can be removed from the chuck.
Chapter 5, the first sentence of the program and the control of dimensional accuracy techniques
5.1, the first sentence of the program to use G00 techniques
Currently, we have access to the textbooks and technical books on CNC turning, the first sentence of the program are to establish the coordinate system of the workpiece, i.e., G50 Xα Zβ as the first sentence of the program. According to this instruction, a coordinate system can be set up so that a point of the tool in this coordinate system for the coordinate value of (Xα Zβ) (this paper, the origin of the workpiece coordinate system are set in the right end face of the workpiece). Using this method to write the program, after the tool, the knife must be moved to the established position set by the G50 can be processed, to find the position of the process is as follows.
Numerical control systems are very perfect self-diagnostic capabilities, the daily use of more attention to strictly in accordance with the provisions of the operation, and the daily maintenance