What Are the Different Types of Computer-Aided Manufacturing?

Computer-aided manufacturing refers to the use of electronic digital computers to control machine tools and equipment through various numerical values in the mechanical manufacturing industry to automatically complete the manufacturing processes of discrete product processing, assembly, testing and packaging. Referred to as cam.

Chinese name: Computer aided manufacturing

Foreign name: Computer aided manufacturing
Use: Computer Controlled Machining

Introduction to Computer Aided Manufacturing

Computer Aided Manufacturing Applications In addition to the narrow definition of cam, the international computer-aided manufacturing organization (cam-i) has a broad definition of computer-aided manufacturing: "Through direct or indirect interfaces between computers and the company's physical or human resources, computer technology Effectively applied to the management, control and processing operations of enterprises. "According to this definition, computer-aided manufacturing includes enterprise production information management, computer-aided design (cad) and computer-aided production, manufacturing. Computer-aided production and manufacturing include two kinds of computer control methods: continuous production process control and discrete part automatic manufacturing. This generalized computer-aided manufacturing system is also called an integrated manufacturing system (ims). The use of computer-aided manufacturing of parts and components can improve the ability to adapt to product design and variety, and increase processing speed.

CAM system and what it contains And production automation level, shorten processing preparation time, reduce production costs, improve product quality and labor productivity of mass production.

Computer Aided Manufacturing Basic Functions

In CAD / CAM system, people use computers to complete product structure description, engineering information expression, engineering information transmission and transformation, and information management. Therefore, the CAD / CAM system should have the following basic functions:

1. Modeling of products and processes How to use computer-recognized data (information) to express and describe products. Such as the description of product shape and structure, description of product processing characteristics, how to describe the mesh and boundary conditions required for finite element analysis, and so on.

2. Graphic and image processing In CAD / CAM system, graphic image is still the main expression form of product shape and structure. Therefore, how to express graphics in the computer, and perform various transformations, editing, blanking and lighting on graphics Wait processing is the basic function of CAD / CAM.

3. Information storage and management The design and manufacturing process will generate a large amount of data, such as design analysis data, process data, manufacturing data, management data, and so on. Data types include graphic images, alphanumerics, sound, video, etc .; structured and unstructured data; dynamic and static data. How to store and manage these large amounts of electronic information in CAD / CAM system is an essential function of CAD / CAM.

4. Engineering analysis and optimization calculation of volume, center of gravity, moment of inertia, etc., mechanism motion calculation, dynamics calculation, numerical calculation, optimization design, etc.

5. Engineering information transmission and exchange Information exchange includes information exchange between CAD / CAM system and other systems and information exchange of different functional modules in the same CAD / CAM system.

6. Simulation and simulation In order to check the performance of the product, it is often necessary to perform various tests and tests on the product. Special equipment and production samples are required. It is destructive, time-consuming and costly. By establishing a digital model of the product or system, computer simulation technology can be used to solve this problem. Such as machining trajectory simulation, mechanism motion simulation, collision and interference inspection of workpieces, tools and machine tools.

7. Human-computer interaction data input, selection of routes and schemes, etc., require a dialogue between human and computer. Human-machine dialogue interaction methods include software interfaces and devices (keyboard, mouse, etc.)

8. Input and output of information Input and output of information Man-machine interactive input and output and automatic input and output.

CAD/CAM Computer Aided Manufacturing CAD / CAM System Composition and Classification

CAD / CAM system consists of hardware and software systems. The hardware system refers to the physical equipment that can be touched, such as host equipment, terminal equipment, network and communication equipment, input and output equipment, numerical control processing and control equipment, and so on. Software system usually refers to the sum of programs and related documents. Software systems are generally divided into system software, supporting software and application software ^[1] .

From different perspectives, CAD / CAM systems can be divided into different types ^[1] .

From a hardware perspective , it is divided into two categories:

1. A multi-user time-sharing system with a mainframe or small computer as the host. The characteristics of the host system: 1) Peripheral equipment and user workstations are connected to the host. The user workstation has at least one graphics workstation and a set of graphics processing equipment (such as graphics terminals, graphics input and output devices, etc.) 2) Advantages: The host has strong functions and can process a large amount of information, such as analysis, calculation, and simulation. The performance depends on the software level. 3) Disadvantages: The system has strong specificity, is relatively closed, has too many terminals, the system speed becomes slow, and the price is high. In addition, the reliability of the system depends on the host (if the host fails, the entire system will be paralyzed) ^[1] .

2. Single user system of engineering workstation or microcomputer system. Features of this system: 1) Each engineering workstation or microcomputer system can independently complete various tasks required by the CAD / CAM system; 2) the price is lower; 3) the reliability is high ^[1] .

According to functional division , CAD / CAM systems can be divided into CAD, CAM, and CAD / CAM ^[1] .

1. CAD system: a system specially designed for design, which can complete various design tasks, such as modeling, meeting drawings, engineering analysis simulation and simulation, document management, etc. Does not have NC programming, machining simulation, production control and management ^[1] .

2. CAM system: It has functions such as NC programming, machining simulation, production control and management, and almost does not have functions such as modeling, meeting drawings, engineering analysis simulation and simulation ^[1] .

3. CAD / CAM system: It has all the functions of CAD and CAM, and can automatically exchange information. Has become mainstream ^[1] .

According to whether a computer network is used , CAD / CAM systems can be divided into stand-alone systems and network systems ^[1] .

Computer network: A collection of autonomous computers connected by communication lines. It includes three meanings: 1. There must be two or more computer systems with independent functions connected to each other to achieve the purpose of resource sharing; 2. The connected computers must have a channel for information exchange; 3. Information exchange between computer systems in the same network must follow a common agreement and rule, that is, an agreement ^[1] .

1. Stand-alone CAD / CAM system: with all CAD / CAM software and hardware functions. Information cannot be exchanged with other CAD / CAM. Information cannot be shared ^[1] .

2. Network CAD / CAM system: Connect each node with CAD / CAM software and hardware functions with network equipment and communication lines to form a networked CAD / CAM system. Can achieve resource and information sharing. Has become mainstream. The network structure has star, ring, bus and network. Because the bus type has the characteristics of strong compatibility, openness, and good scalability, the bus has become the mainstream ^[1] .

Development of computer-aided manufacturing

The core of computer-aided manufacturing is computer numerical control (NC for short), which is the process or system that applies computers to the manufacturing process. In 1952, the Massachusetts Institute of Technology first developed a CNC milling machine. The characteristic of numerical control is that the machine tool is controlled by the program instructions coded on the perforated paper tape. Since then, a series of CNC machine tools have been developed, including multifunctional machine tools called "machining centers".

Computer aided manufacturing simulation Automatic tool change and automatic change of working position from the tool magazine can continuously complete multiple processes such as milling, drilling, reaming, tapping, etc. These are controlled by program instructions. As long as the program instructions are changed, the machining process can be changed. This processing flexibility is called "flexibility". The programming of machining programs not only requires considerable labor, but is also prone to errors. The earliest CAM was computer-aided machining part programming. MIT researched and developed the machining part programming language APT of CNC machine tools in 1950, which is a high-level language similar to FORTRAN. The geometric definition, tool movement and other statements have been enhanced. The application of APT makes writing programs simple. This computer-aided programming is batch processing.

CAM system generally has two functions of data conversion and process automation. The scope of CAM includes computer numerical control and computer-aided process design.

In addition to the application of machine tools, CNC is also widely used for the control of various other equipment, such as punching machines, flame or plasma arc cutting, laser beam processing, automatic plotters, welding machines, assembly machines, inspection machines, automatic knitting machines, Computer embroidery and garment cutting have become the basis of CAM in various industries.

The computer-aided manufacturing system controls and manages multiple aspects of the manufacturing process through a computer hierarchical structure. Its goal is to develop an integrated information network to monitor a wide range of interconnected manufacturing operations, and control each of them in accordance with an overall management strategy. Items.

From the perspective of automation, CNC machine tool processing is a process automation process. The machining center is to automate part or all of the machining process. The direct control of the computer and the flexible manufacturing system are to complete the automatic processing of one family of parts or different families of parts. Computer-aided manufacturing is the general concept that computers enter the manufacturing process.

A large-scale computer-aided manufacturing system is a network of computer hierarchies.

Computer aided manufacturing process It consists of three or three-level computers. The central computer controls the whole world, provides processed information, the main computer manages certain aspects of work, and issues instructions and monitors the subordinate computer workstations or microcomputers. The computer workstations or microcomputers assume a single Process control or management work.

The composition of computer-aided manufacturing systems can be divided into two aspects: hardware and software: hardware includes CNC machine tools, machining centers, conveying devices, loading and unloading devices, storage devices, testing devices, computers, etc., and software includes databases, computer-aided process design, Computer-aided numerical control programming, computer-aided tooling design, computer-aided job planning and scheduling, computer-aided quality control, etc.

Computer Aided Manufacturing Basic Components

Computer Aided Manufacturing CNC System and Principles of CNC Programming

Computer Aided Manufacturing Development (1) Numerical control system

The numerical control system is the control part of the machine tool. It is generated in the manner of human-computer interaction according to the input part drawing information, process and process parameters.

CNC system functions A numerical control machining program is formed, and then the number of electric pulses is used to drive the machine tool parts to perform corresponding movements through the servo drive system. Figure 3-4-2 is a functional diagram of the CNC system.

On traditional NC machine tools (NC), the processing information of parts is stored on the NC paper tape. The information on the NC paper tape is read by the photoelectric reader to realize the processing control of the machine tool. Later developed to computer numerical control (CNC), the function has been greatly improved, all the letter readers that can be processed at one time. More advanced CNC machine tools can even remove the photoelectric reader and program directly on the computer, or directly receive information from CAPP to achieve automatic programming. The latter CNC machine tool is the basic equipment of computer integrated manufacturing system. Modern CNC systems often have the following functions:

(1) Multi-axis coordinated control;

(2) Tool position compensation;

(3) system fault diagnosis;

(4) Online programming;

(5) Parallel operation of processing and programming;

(6) machining simulation;

(7) Tool management and monitoring;

(8) Online detection.

(Two) the principle of NC programming

The so-called NC programming is the process of generating NC code automatically or under human intervention based on the geometric information of the part from CAD and the process information of the part from CAPP. Commonly used CNC codes are ISO (International Standards Organization) and EIA (American Electronics Industry Association) two systems. Among them, the ISO code is a 7-bit complement code, that is, the 8th bit is a complement bit; and the EIA code is a 6-bit complement odd code, that is, the 5th column is a complement odd bit. The purpose of complementation and supplementation is to facilitate the verification of misreading information of the paper tape reader. The general NC program is composed of program words, and the program words are composed of the address code represented by English letters and the numbers and symbols after the address code. Each program represents a special function, such as G00 for point control, G33 for constant-pitch thread cutting, and M05 for spindle stop. Generally, a CNC machining instruction is composed of several program words. For example, N012 in N012G00G49X070Y055T21 represents the 12th instruction, G00 represents the point control, G49 represents the tool compensation preparation function, and X070 and Y055 represent X and Y coordinate values , T21 indicates the tool number command. The meaning of the entire command is: rapid movement to the point (70, 55), the No. 1 knife takes the knife compensation value on the No. 2 dial. The meanings of common address codes are shown in Table 1.

function

address code

significance

Program number

Sequence number

Ready for function

Program number

Sequence number

Machine operation mode instruction

Coordinate instruction

XYZ

ABCUVW

IJK

Coordinate axis movement command

Additional axis movement command

Arc radius

Arc center coordinates

Feed function

Spindle function

Tool function

Feed speed command

Spindle speed command

Tool number command

Auxiliary function

On, off, start, stop instructions

Table indexing instructions

make up

time out

Subroutine call

repeat

parameter

PQR

Tool compensation instruction

Pause time instruction

Subroutine number designation

Canned cycle repetitions

Canned cycle parameters

Table 1 Address codes and their meanings

There are four general ways of NC programming:

(1) Manual programming; (2) Numerical control language programming; (3) CAD / CAM system programming; (4) Automatic programming.

Computer Aided Manufacturing Manual Programming

Manual programming is that the programmer manually compiles the CNC machining program of the part to be processed according to the machining program segments and instruction format specified by the CNC system. The main steps of manual programming are as follows:

(1) Process analysis of parts according to part drawings;

(2) Determine the processing route and process parameters (setting order, surface processing order, cutting parameters);

(3) Determine the tool trajectory (starting point, ending point, and movement form);

(4) Data required for computer bed movement;

(5) Writing the processing program list of parts;

(6) Perforated paper tape;

It can be seen that manual programming also includes the content of formulating technological procedures. Manual programming has been rarely used at present.

Computer aided manufacturing

The use of numerical control language programming is often called "automatic programming", this name comes from APT (Automatically Programmed Tools) numerical control programming language. In fact, it is not an automated programming tool, but it is a step further than manual programming, and it implements the "high-level programming language" to write CNC programs. The working process of this programming system is shown in Figure 3-4-3. Figure 3-4-3 CNC programming process

Programming in NC language is to use special languages and symbols to describe the geometry of the part and the trajectory, sequence and other movements of the tool relative to the part.

CAD / CAM system programming Process parameters and the like, because the numerical control language similar to the high-level computer language is used to describe the machining process, which greatly simplifies the programming process, especially the numerical calculation process, and improves the programming efficiency. A program written in a numerical control language is called a source program. After the computer receives the source program, it must first compile and then post-process the program to generate a CNC program that controls the machine tool. The commonly used NC programming language is the APT language developed by the Massachusetts Institute of Technology. APT language has rich vocabulary, many defined geometric types, and is equipped with a variety of post-processing programs. It has good versatility and is widely used. The source program of the APT language is composed of statements. There are four types of statements. Sentences are composed of vocabulary, values, and symbols according to certain grammatical rules.

1) Geometry definition statement

The general form of a geometric definition statement is: <identifier> = <special words for geometric elements> / parameters For example, the statement C1 = CIRCLE / 20, 80, 12, 5, C1 is the name of the geometric element definition, and VIRCLE is the geometric element type (Circle), 20, 80, 12, 5 represent the coordinate value and radius value of the circle center, respectively.

2) Tool movement statement

The tool movement statement is used to simulate the trajectory of tool movement during machining. In APT, three surfaces are used to define the position and movement path of the tool. This

Part faces, guide faces and inspection faces The three surfaces are the part surface (PS), guide surface (DS), and inspection surface (CS), as shown in Figure 3-4-4. The part surface is the surface formed during the tool movement; the guide surface is used to define the positional relationship between the tool and the part surface; the inspection surface is used to determine the end position of the tool for each movement. For example, TLONPS and TLOFPS indicate that the tool center is located on the part surface and not on the part surface, respectively. TLLFT indicates that the tool is on the left side of the guide surface.

Figure 3-4-4 Part surface, guide surface and inspection surface 3) Process data statement

Process data statements are used to describe process data and some control functions. For example, SPINDL / n is used, CLW is the spindle speed (n) and rotation direction (CLW), CUTTER / d is used, and r is the diameter of the cutter and the radius of the tool nose.

4) Initial statement and termination statement

The initial statement indicates the name of the program, and the end statement indicates the end of the part program. The initial statement consists of "PARTNO" and the name, and the termination statement is represented by FIN1.

Figure 3-4-5 CAD / CAM system programming

Figure 3-4-6 Automatic programming system

CAD/CAM Computer Aided Manufacturing CAD / CAM System Programming

Although the use of CNC programming is much simpler than manual programming, it still requires programmers to write source programs, which is still time-consuming. For this reason,

CAD / CAM system programming Exhibited CAD / CAM programming technology. Up to now, almost all large-scale CAD / CAM applications have NC programming functions. When using this kind of system for programming, the programmer does not need to write the NC source program, but only needs to call the part graphic file from the CAD database and display it on the screen. The multi-level function menu is used as the man-machine interface. During the programming process, the system also gives a lot of prompts. This method is convenient to operate, easy to learn, and can greatly improve programming efficiency. The general CAD / CAM system programming part includes the following basic contents: query the geometric information of the graphic elements of the processed part; process the design information; calculate the tool center path; define the tool type; define the tool position file data.

For some powerful CAD / CAM systems, it even includes a data post-processor to automatically generate CNC machining source programs and perform machining simulations to verify the correctness of the CNC programs. Figure 3-4-5 is a schematic diagram of this system.

Computer Aided Manufacturing Automatic Programming

In the above CAD / CAM system programming, the programmer still needs too much intervention to generate the CNC source program. With the development of CAPP technology, automatic programming of numerical control becomes possible. Figure 3-4-6 shows the composition of the automatic programming system. The system obtains the geometric information of the part from the CAD database, the process information of the part processing process from the CAPP database, and then calls the NC source program to generate the NC source program, and then performs dynamic simulation on the source program. For processing.

Computer Aided Manufacturing Support Environment

The supporting environment of computer-aided manufacturing can be divided into two major aspects: hardware and software. Specifically, it can be divided into computer hardware, computer software, database, network and communication.

Computer hardware generally refers to the entity of a computer. Compared with computer software, computer hardware and software together form a computer system. A computer must have both hardware and software to work.

Computer hardware can generally be divided into two parts, the host and external devices. The host usually includes an arithmetic unit, a controller, a power supply, an interface circuit, an input / output channel (bus), an internal memory, and the like. External devices usually refer to input devices, output devices, external memories, and so on.

Computer software can be divided into system software and application software. System software mainly includes computer operating system and supporting software. Supporting software generally refers to tools (or platforms) for secondary development for users, and application software refers to special software developed by users themselves.

A database is a generalized and comprehensive data collection that can provide various users to share with minimal redundancy and high independence of data and programs. It can efficiently and timely process data and provide security and reliability. .

The database system is established on the basis of a computer system. It consists of computer hardware, a database management system, users and their applications, and a database administrator.

A computer network refers to a group of computers that are geographically dispersed and have independent functions and are interconnected to form multiple computers, terminal devices, transmission devices, and network software.

Computer network is composed of two parts: hardware and software. Network hardware includes computer systems, terminal equipment, communication transmission equipment, and so on. Network software includes network operating systems, network databases, network protocols, communication protocols, communication control programs, and so on.

Data communication refers to the transmission, exchange, and processing of information. It is the third generation of communication after the telegraph and the telephone. It is not simply data communication, but organizes and systematically organizes the original information, and transmits its essence in an appropriate time and space to function.

Computer Aided Manufacturing Group Technology

Group technology is the basis of computer-aided manufacturing systems. It has developed from group processing in the 1950s to group technology in the 1960s. Group production units and group processing lines have appeared, and its scope has also expanded from simple mechanical processing to the entire product manufacturing process. After the 1970s, the group technology was combined with computer technology and numerical control technology to develop into a group technology. A flexible manufacturing system based on group technology was used to classify and encode parts using computers, and was systematically applied to product design , Manufacturing technology, production management, and many other fields, forming computer-aided design, computer-aided process design, computer-aided manufacturing, and group technology

Computer Aided Manufacturing Group Technology Colored computer integrated manufacturing system.

Group technology is a comprehensive technology involving multiple disciplines. Its theoretical basis is similarity and the core is group technology. Group technology is combined with computer technology, numerical control technology, similarity theory, methodology, and system theory to form a group technology. At the current stage, it has more characteristics of computer-aided group technology.

The group process is to group parts with similar sizes, shapes, and processes into one part family, and make processes according to the part family. This increases the batch size, reduces the variety, and facilitates the use of high-efficiency production methods, thereby improving Labor productivity has opened a way for multi-variety and small-batch production to improve economic efficiency.

The similarity of parts in terms of geometry, size, functional elements, accuracy, materials, etc. is basically similarity. Based on the basic similarity, the similarity derived in manufacturing, assembly production, operation, management, etc. is called secondary similarity or derived similarity. Therefore, secondary similarity is the development of basic similarity, and has important theoretical significance and practical value.

The basic principle of the group process shows that the similarity of parts is the basic condition for achieving the group process. Group technology is to reveal and use basic similarity and secondary similarity. It is an industrial enterprise to obtain unified data and information, obtain economic benefits, and lay the foundation for the establishment of integrated information systems.

Part information description

Entering part information is the first step in computer-aided process design. Part information description is the key to computer-aided process design. Its technical difficulty and workload are important factors affecting the efficiency of the overall process design.

The accuracy, scientificity and completeness of the part information description will directly affect the quality, reliability and efficiency of the designed process. Therefore, the information description of the parts should meet the following requirements:

(1) The information description must be accurate and complete. The so-called completeness refers to being able to meet the needs of computer-aided process design, rather than describing all the information;

(2) The description of the information should be easy to be accepted and processed by the computer, with a friendly interface, convenient use, and high work efficiency;

(3) The description of information should be easy to understand and master by engineering and technical personnel, and easy to be used by operators;

(4) Since it is a computer-aided process design, the information description system (module or software) should take into account computer-aided design, computer-aided manufacturing, computer-aided inspection and other requirements in order to enable information sharing.

Computer Aided Manufacturing Applications

cam has been widely used in aircraft, automotive, machinery manufacturing, home appliances and electronics manufacturing.

The application areas of cam include:

Parts processing of mechanical products

Mechanical product parts processing (cutting, stamping, casting, welding, measurement, etc.), component assembly, complete machine assembly, acceptance, packaging and storage, automatic warehouse control and management. In metal cutting, the basic cutting condition equation is established in the computer in advance. According to the parameters measured by the measurement system and the working condition of the machine tool, the feed rate, cutting force, cutting speed, cutting operation sequence and coolant flow rate are adjusted to ensure the parts. Under the conditions of surface finish and machining accuracy, the machining efficiency, tool wear and energy consumption are optimized.

Components and components of electronic products

Ageing, testing, and screening of electronic device components, automatic insertion of component devices into printed circuit boards, wave soldering, automatic winding of device boards, chassis wiring, and automatic testing of components, wholes, and complete machines.

Finished product inspection and quality control of various mechanical and electrical products

The finished product inspection and quality control of various electromechanical products can complete a large number of testing of complex products (such as aircraft engines, VLSI, electronic computers, etc.) that cannot be completed by manual methods.