Computer英文

2016-2017学年第一学期

《机械专业英语》论文题目：计算机集成制造

系别：机电工程系

班级：机制1303班

学号：2013100318

姓名：刘拴龙

指导教师：王嘉伟

Computerintegrated manufacturing

Computer-integrated manufacturing (CIM) is the term used to describe the most modern approach to manufacturing. Although CIM encompasses many of the other advanced manufacturing technologies, it is more than a new technology or new concept. CIM is actually an entirely new approach to manufacturing a new way of doing way of doing business.

The term“computer-integrated manufacturing”was developed in 1974 by Joseph Harrington as the title of a book he wrote tying islands of automation together through the used of computers. It has taken many years for CIM to develop as a concept, but integrated manufacturing is not really new. In fact integration is where manufacturing actually began. Manufacturing has developed through four distinct stages: manual manufacturing, mechanization/specialization, automation and integration.

With the advent of the computer age, manufacturing has developed full circle. It began as a totally integrated concept and, with CIM, has once again become one. However, there are major differences in the manufacturing integration of today and that of the manual era of the past. First, the instrument of integration in the manual era was the human mind. The instrument of integration modern manufacturing is the computer. Second, processes in the modern manufacturing setting are still specialized and automated.

Another way to view the historical development of CIM is by examining the ways in which some of the individual components of CIM have developed over theyears. Such components as design, planning and production used to accomplish the processes.

Design has evolved from a manual process using such tools as slide rules, triangles, pencils, scales, and erasers into an automated process known as computer-aided design (CAD). Process planning has evolved from a manual process known as computer-aided process planning (CAPP). Production has evolved from a manual process involving manually controlled machines into an automated process known as computer-aided manufacturing (CAM).

These individual components of manufacturing evolved over the years into separate islands of automation. However, communication among these islands was still handled manually. This limited the level of improvement in productivity that could be accomplished in the overall manufacturing process . When these islands and other automated components of manufacturing are linked together through computer networks, these limitations can be overcome. Computer-integrated manufacturing has enormous potential for improving productivity in manufacturing, but it is not without problems.

As with any new philosophy that requires major changes to the status quo, CIM is not without problems. The problems associated with CIM fall into three major categories; technical problems; cultural problem; business-related problem;

These types of problems have hindered the development of CIM over the years and will have to be overcome for CIM to achieve widespread implementation.

If mechanical engineering is regarded as the process of design, development and manufacture, then one can identify a fast growing aspect known as computer aided engineering (CAE), this includes computer aided design (CAD) and computer aided manufacture (CAM). It is important to note the word “aided”in all these titles, as the engineer is till the key person.

Other aspects of CAE important to the mechanical engineer include the testing and proving of a design, often using computer-controlled test rigs with automatic data logging and processing, i.e., reading of instrument transducers, producing analogue voltage signals which are passed through an A to D interface to produce a digital signal to be stored and processed in the computer and then graphically displayed.

Process simulation is also achieved in a computer to guide design, an example being the combustion process in a petrol engine, computers are also used for control purposes, such as the engine management system in a modern motor car.

All computing systems need databases, which are akin to filing systems. Thus a database is a collection of information stored is a computer memory which may be

accessed and used in the programs being exercised. Simple examples would include section module of standard beams, the properties of a refrigerant or head loss factors for various pipe fittings.

Before considering the mechanical technology aspects of CAD, it is necessary for the designer to take account of the use of CAM methods. Such systems use computer numerically controlled machines (CNC) and these may well be operated by the CAE system postprocessor which shapes the drawing date into cutter paths, etc.

CNC machines are available for a variety of processes, including turning, milling, flame-cutting, grinding and bending. Inspection and measurement may also be computer controlled and parts may be handled and moved around by robot or automated guided vehicle (AGV), which is programmed to follow a metallic conductor on or in the factory floor. A combination of CNC, robots and AGV can be linked to from a flexible manufacturing system (FMS), controlled by one man from a single computer work station. The group name for these manufacturing methods is advanced manufacturing technology (AMT) and the design engineer must be aware of the constraints such methods place on his work.

All the new technology will be for naught if we are not able to create a more dedicated and motivated work force to operate, maintain, This process will require a change in the way we have produced goods over hundreds of years, For as long as man has relied on the factory concept, he has always worked to reduce the cost of human labor and the support systems that keep it going. Clearly, there will be a tremendous impact as our work force, undergoes the wrenching changes that will be required to restructure our production and product base. We have seen many smaller technological revolutions and their impact on the work force which then impacts the overall fabric of the society it supports.

NUMERICAL CONTROL APPLICATIONS

As with other expanding technologies, these is a tendency to consider numerical control as a final solution to a broad range of manufacturing problems; however, NC

application in certain manufacturing situations would be highly undesirable.

An NC machine is most be efficiently used in an environment that takes advantage of the inherent flexibility of NC. The precise level of control attributed to a numerically controlled capability of a human operator. For these reasons, numerical control is best suited to relatively low volume runs of complex and varied components. However, NC can also be used to produce large numbers of complex components and/or small number of simple ones.

Specific application areas for numerical range from the manufacture of knitted fabrics to the fabrication of structural members for jet aircraft. In the following sections we present a brief overview of some specific applications in which NC has been utilized.

Metal-Cutting Machine Tools

Numerical control was introduced and developed in the metalworking industry, and the largest concentration of NC equipment remains in metalworking shops. NC has been successfully implemented for milling, drilling, grinding, boring, punching, turning, sawing, and routing machines. It is interesting to note that NC has made possible the development of machines with basic capabilities that far surpass their conventional counterparts. For example, sophisticated NC milling machines maintain control over five axes of motion. Such devices can literally sculpt complex undulating surfaces which would be impossible to machine manually.

New breed of NC machine tool, called the machining center, incorporates the functions of many machines into a single device, thereby reducing work handling. It can access multiple tools to perform such operations as milling, drilling, boring, and tapping.

Automated Drafting

Automated drafting equipment is generally part of a larger computer-aided design (CAD) network. CAD system, making use of both large-scale and

minicomputers, are proliferating in the industry. Numerical control is used to translate a blueprint, drawing, or graph, which has been converted to digital format, to pen motions on an automatic drafting machine.

Effectively, an NC drafting machine is a two-axis contouring device which controls a pen or stylus as it move over drawing paper or film. Data is supplied to the drafting machine control unit through a variety of communication media. Computer generated punched or magnetic tape is the most common mode of communication.

Although the size, accuracy, and configuration of NC drafting equipment varies among manufacturers, it is not uncommon to find machines capable of producing drawings 1.5mm*2m in size with an accuracy of 0.02mm. Many sophisticated system incorporate a digitizing feature which enables a machine operator to generate computer-compatible from existing drawings.

Other Numerical Control Applications

The following paragraphs discuss some of the less familiar (although not lea important) NC application areas. As the field of programmable automation continues to evolve, NC will be used increasingly in all phases of the manufacturing process.

NC welding equipment is used to provide uniformity and accuracy in a process that is affected by many external variables. By maintaining proper electrode to material distances, feed angles, feed rates, and position accuracy, the NC welder can maintain critical fabrication requirements. High energy welding techniques that are capable of concentrating an electron beam or laser can be precisely controlled using numerical control.

The NC welding machine makes use of the same control principles as multiple-axis metal cutting machines tools. Five-axis welding machines have been used in the aerospace industry to the injection molding process and obtained an increase in production-rates and a decrease in rejects.

Flexible Machining System

FMS stands for flexible manufacturing system or flexible machining system. It is used to describe a wide range of flexible automation technologies stretching from simple cells to market demands. They are the third stage in the development toward more flexibility. The first stage is NC machine tools, and the second stage is flexible manufacturing cells(FMCs).

An FMS consists of a CNC machine tool, a work piece storage, devices for handling and changing work pieces and tools, and automatic control and supervision subsystems. Hence, the machine tool is capable of performing more than one operation automatically on more than two work pieces. Further devices may be integrated. Such manufacturing cells have experienced rapid growth in both number of suppliers and users. Their appearance and frequent application closed an important gap between the individual machine tool and interlinked systems.

An FMS contains several automated machine tools of the universal or special type as well as flexible manufacturing cells. Further manual or automated workstations may by included. These elements are interlinked by an automated work piece flow system in away that enables the simultaneous machining of different routes. Thus multi step and multi product manufacturing is possible in an FMS.

A flexible transfer line contains several automated universal or special-purpose machine tools and further automated work stations. They are interlinked by an automated work piece flow system according to the line principle. A flexible transfer line is capable lf simultaneously or sequentially machining different work pieces that run through the system along the same path. In order to balance differences in cycle time, setup times, and short breakdowns, buffers are allocated between the stations.

The cornerstone of FMS is the automatic machine tool. Machine tool design has shown a significant change within the last decade. Integration of different manufacturing processes into one machine tool allows for a reduction lf lead times. Perhaps of more importance, however, is the reduction of organizational effort. Fewer manufacturing devices also means less effort to control the whole production process.

Meanwhile the idea of combined processes has been extended to machining centers. They allow for complex turning, milling, and boring operations without setup changes. Some machine has a movable round table. Automatic change of work pieces is carried out by movable pallets. The spindle can be changed from vertical to horizontal position, and therefore allows for five-sided machining. Turning and milling tools are equipped with identical adapters. Therefore only one magazine is needed to store all tools.

The concept of bringing processes to the work piece can be expected to influence the future development of machine tools. More and more processes are integrated into a single machine, like grinding, laser treatment, or hardening.

System Integration In The Manufacturing Industry

This is precisely the case study we will follow in this section particularly emphasizing the integration of discrete islands of operations in manufacturing. In a manufacturing industry, such discrete islands of implementation fall into five classes:

https://www.wendangku.net/doc/e76906283.html,puteraided design (CAD) systems typically run on specialized graphics-oriented engines. They are mot tied to the rest of the manufacturing system, though such a connection is becoming very critical.

2.Manufacturing requirements planning (MRP) tracks orders, supplies, suppliers, and the production floor. The problem is that there are few, if any, automated links between CAD and MRP.

3.The automated shop floor ( ASF) has computer-controlled tools and robots-which cannot communicate. To overcome such limitations, General Motors requires vendors to enforce its Manufacturing Automation Protocol. An internal study demonstrated that about 40 percent of investment pays for interfaces in sprawling, incompatible environments.

4. Word processing at HQ, factories, sales offices. In manufacturing, an estimated 75 percent of all paper-based information is for internal consumption. In

some industries, like banking and insurance, this reaches 90 percent.

5. Integrated mainframe support. Every organization has a variety of incompatible mainframes and/or operating systems.

The proper system architecture will look at these live areas not as discrete islands but ad parts of a global integrated system. Neither should be considered as a technology that stands alone. Both between areas and within each area we must integrate hardware and software within the network with databases and applications. This will permit extending current applications and embedding future applications, and also controlling costs by eliminating redundant actions and extensive interfacing.

The system integration effort undertaken at General Motors by EDS runs along these lines. The stated goal is to save money by overhauling a fragmented computers and communications system. According to published information, in 1986 there have been 95 communications networks, and 106 data centers at GM. The aim of system integration is to assure one digital communications network and 18 data centers.

System integration and rationalization is not simply a technological matter, as the CIM theorists suggest. To integrate dispeace and incompatible systems we must change traditional procedure, not just throw in more money and equipment. Whenever we try to change procedures we find resistance. The larger the company and the more independent the network (as GM’s dealer network is ), the more difficult it is to turn policies and procedures around. Yet, as Figure17.1suggests, a condition for successful system integration is that it extends along functional and support lines ( hardware,software ), in the global sense of the distributed environment.

The integration effort should include both front-line operations and the back office. EDS has also taken over the back office data processing functions at GM. It consolidated the computer facilities, resulting in significant cost savings, and in better overall matching of benefits to competitive policies.

Methods Of Simulation

The impact of the computer on the technological aspects of manufacturing has been discussed in preceding sections. In this section the use of the computer as a means of investigating the manufacturing function itself will be considered, not as a component of the system but as a tool for discovery. This approach views the manufacturing process as a system, and attempts to achieve productivity and efficiency improvements through a better understanding of the manner in which these components are selected and controlled and of their interactions.

This section is restricted to discrete event simulation with the emphasis on computer-aided manufacturing, also known as flexible automation, With fixed automation the operations to be performed on a work piece are set and the same sequence of operations occurs for every work-piece. In flexible automation, the sequence of operations depends upon the work piece being processed. The system must have information identifying the individual work piece to invoke the proper operations and sequences.

Simulation depends upon the concept of a model which is an abstraction of the system under study, in the same sense that a play is an abstraction of real life. The objective is to capture the essence without the detail. There can be many different abstractions of a given system, both by level of abstraction and by content, the correct choice depending upon the modeler’s objectives.

In discrete event simulation one develops a model by describing the elements, or components, of the system, i. e. the things of which the system is the aggregate, and the manner in which these elements interact. These elements are generally known as entities. In a job shop the entities of interest might be machines, operators, and work pieces. If the system under study were a traffic system, the entities might be cars,drivers, roads, and intersections. It is generally useful to give characteristics,called attributes, to these entities to distinguish between them. In the job shop the work pieces might have attributes such as due date, weight, and length. The operator attributes might be skill level, assigned machine, pay rate, and name. Entities are usually physical but can be logical as well. For instance, a machine group

can be viewed ad a logical collection of the machines in it; first-come-first-serve is a logical entity for choosing the next work piece to be processed on a machine; and the assignment of an operator to a machine can also be viewed as a logical entity with the attributes of machine and operator.

Using the basic concepts of entities and attributes it is possible to describe a model giving a picture, or snapshot, at a point in time. The total set of information needed to describe this picture of the model is known as the system status. Simulation is the process of moving the model through time by continually updating the system status, much as one might make a movie by combining a series of snapshots. For instance, if the status of the operator is idle, an assignment to a task may be made and the operator’s status changed to busy. To do this, one must determine the rules by which the attribute changes are to be made, i. e the logical relationships which must exist before a status change can be implemented. For example, when an idle operator, a free machine, and a waiting work piece are simultaneously available, an assignment ( i. e. a status change ) can take place. It should be clear that a thorough understanding of the manufacturing system is required to develop the model and the rules for system change. Without this knowledge base the prospects of success are slim and chance dependent. .