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Modern Design and Manufacturing
一、The Computer and Manufacturing
The computer is bringing manufacturing into the Information Age. This new tool, long a familiar one in business and management operations, is moving into the factory, and its advent is changing manufacturing as certainly as the steam engine changed it 100 years ago.
The basic metalworking processes are not likely to change fundamentally, but their organization and control definitely will
In one respect, manufacturing could be said to be coming full circle. The fist manufacturing was a cottage industry: the designer was also the manufacturer, conceiving and fabricating products one at a time. Eventually, the concept of the interchangeability of parts was developed, production was separated into specialized functions, and identical parts were produced thousands at a time .
Today, although the designer and manufacturer may not become one again, the functions are being drawn close in the movement toward an integrated manufacturing system.
It is perhaps ironic that, at a time when the market demands a high degree of product diversification, the necessity for increasing productivity and reducing coats is driving manufacturing toward inegration into a coherent system, a continuous process in which parts do not spent as much as 95% of production time being moved around or waiting to be worked on .
The computer is the key to each of these twin requirements. It is the only tool that can provide the quick reflexes, the flexibility and seed, to meet a diversified market. And it is the only tool that enables the detailed analysis and the accessibility of accurate data necessary for the integration of the manufacturing system.
It may well be that, in the future, the computer may be essential to a company’s survial. Many of today’s businesses will fade away to be replaced by more-productive combinations. Such more-productive combinations are superquality, superproductivity plants. The goal is to design and operate a plant that would produce 100% satisfactory parts wich good productivity.
A sophisticated, competitive world is requiring that manufacturing begin to settle for more, to become itself sophisticated. To meet competition, for example, a company will have to meet the somewhat conflicting demands for greater product diversification, higher quality, improved productivity , higher quality, improved productivity and prices.
The company that seeks to meet these demands will need a sophisticated tool, one that will allow it to respond quickly to customer needs while getting the most out of its manufacturing resources.
The computer is that tool.
Becoming a “superquality, superproductivity” plant requires the integration of an extremely complex system .This can be accomplished only when all extremely complex system. This can be accomplished only when all elements of manufacturing-design, fabrication and assembly, quality assurance, management, materials handing-are computer integrated.
In product design, for example, interactive computer-aided-design(CAD) systems allow the drawing and analysis tasks to be performed in a fraction of the time allow the drawing and analysis tasks to be performed in a fration of the time previously required and greater accuracy. And programs for prototype testing testing and evaluation further speed the design process.
In manufacturing planning, computer-aided process planning permits the selection, from thousands of possible sequences and schedules,of the optimum process.
On the shop floor, distributed intlligence in the form of microprocessors controls, runs automated loading and unloading equipment, and collects data on current shopconditions.
But such isolated revolutions are not enough. What is nended is a totally automated system, linked by common software from front door to back.
Essentially, computer integration provides widely and instantaneously available, accurate information, improving communication between departments, permitting tighter control, and generally enhancing the overall quality and efficiency of the entire system.
Improved communication can mean, for example, designs that are more producible. The NC programmer and the tool designer have a chang to influence the product designer, and vice versa.
Engineering changes,can be reduced,and those that are required can be handled more efficiently.Not only dose the computer permit them to be specicified more quickly, but it also alers subsequent users of the data to the fact that a change has been made.
The instantaneous updating of production-control data permits better planning and more-effective scheduling . Expensive equipment, therefore, is used more productively, and parts move more efficiently through production, reducing work-in-process coats.
Product quality, too, can be improved. Not only are more-accurate designs produced, for example,but the use of design data by the quality-assurance department helps eliminate errors due to misunderstandings.
People are enabled to do their jobs better.By eliminating tedious calculations and paperwork—not to mention time wasted searching for information—the computer not only allows workers to be more productive but also frees them to do what only human being can do: think creatively.
Computer integration may also lure new people into manufacturing. People are attracted because they want to work in a modern, technologically sophisticated enviroment.
In manufacturing engineering, CAD/CAM decreases tool-design,NC-programming, and planning times while speeding the response rate, which will eventually permit in-hous staff to perform work that is currently being contracted out.

二、Numerical Control
One of the most fundamental concepts in the area of advanced mannufacturing technologies is numerical control(NC). Prior to the advent of NC, all machine tools were manually operated and controlled. Among the many limitations associated with manual control machine tolls. Perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the peoduct is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.
Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instrutions. Rather than operating a machine tool, an NC technician writes a program that issues operating a machine tool, an NC technician weites a program that issues operational instructions to the machine tool.
Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines,they can produce parts more uniformly, they are fastre, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:
1.Electrical discharge machining.
2.Laser cutting.
3.Electron beam welding.
Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible form an economic perspective using manually controlled machine tools and processes.
Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U.S.Air Force.
The APT(Automatically Programmed Tools)language was designed at the Servomechanism laboratory of MIT in 1956. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different form those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.
A major problem was the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instuctions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.

This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the progtammed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper tape, which solved the problem of frequent tearing and breakage. However, it still left two other problems.
The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instuctions,it was necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape though the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC asociated with punched paper and plastic tape.
The devslopment of a concept known as direct numerical control(DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control, machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host computer. When the hoet computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control.
The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microcomputers. These two technologies allowed for the development of computer of computer numerical control (CNC). Whit CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stord at each individual machine tool. It also allows programs to be devsloped off-line and downloaded at the individual machine tool. CNC solved the probiems associated with downtime of the host computer, but it introduced another problem known as data management. The same program might be loaded on ten different microcomputers with no communication among them. This problem is in the process of being solved by local area networks that connect microcomputers for better data management.

三、Programmers
Skillful part-programmers are a vital requirement for effective utilization of NC machine tools. Upon their efficiency of those machines and the financial payback of the significant investment in the machines themselves, the piant’s NC-support facilities, and the overhead costs involved.
Skillful NC part-programmers are scarce. This reflects not only the general shortage of experienced people in the meyalworking industries but also the increasing demand for programmers as industry turns more to the use of numerically controlled machines to increase the capability, versaility, and productivity of manufacturing.
On an industry-wide basis,the obvious answer is to create new programmers by training them-and there are a number of sources for such training. But first,what qualifications should programmers have, and what must programming trainees learn?
According to the National Machine Tool Builder’s Assn booklet “Selecting an Appropriate NC programming Method,”the principal qualifications for manual programmers are as follows:
Manufacuring Experience Programmers must have a thorough understading of the capabilities of the NC machines being programmed, as well as an understanding of the basic capabilities of the other machines in the shop. They must have an extensive knowledge of, and sensitivity to, metalcutting principles and practices and practices, cutting capabilities of the tools, and workholding fixtures and techniques. Programmers properly trained in these manufacturing-engineering techniques can significantly reduce production costs.
Spatial Visualization Programmers must be able to visualize parts in there dimensions, the cutting motions of the machine, and potential interferences between the cutting tool, workpiece, fixture, or the machine itself.
Mathematics A working knowledge of arithmetic, algebraic, trigonometric, and geometric operations is extremely important. A knowledge of higher mathematics, such as advanced algebra, calculus,etc, is not normally required.
Attention to Details It is essential that programmers be acutely observant and meticulously accurate individuals. Programmers errors discovered during machine setup can be very expensive and time-consuming to correct.
“Manual programmer,” the booklet nots elsewhere, “requires the programmer to have more-detailed knowledge of the machine and contril, maching practices, and methods of compution than dose computer-aided programming. Computer-aided programming, on the other hand, requires a knowledge of the computer programming language and the computer system in order to process that language. In general, manual programmer is more tedious and demanding because of the detail involved. In a computer –aided programming system, this detail knowledge is embodied in the computer system(processor, postprocessor etc).”
Experts in the NC and training fields typically agree on these qualifications and requirements-adding such subsidiary details as a knowledge of blueprint reading, machinability of different metals, use of shop measuring instruments, tolerancing methods, and practices.
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