Numerical-control machine-tool operations Essay

A single jet streaks across the sky in the ad. The headline reads,”Think of it as 75,000 parts.” Thinking about the number ofparts in a plane that will be produced in fairly small numbers makesclear why the great assembly lines of America’s factories are onlyone source of manufactured goods. The number of items to be produced determines how the production isdone.

If tens of thousands of identical items are to be made,specialized machines and assembly line that can be tended by semiskilled and unskilled workers will be used. If only one or a few items are tobe made, a skilled worker, such as a machinist or tool-and-die maker,will perform the entire procedure using a variety of tools. If anintermediate number of units is required, yet a third procedure mightthe used; the manufacture of industrial equipment, aircraft, and manyother goods involves this type of producttion. Batch production–as itis called–has been done for decades by skilled machinists, tool-and-diemakers, and other workers who cut or form metal or plastic using machinetools such as milling machines and lathes, because the volume ofproduction did not justify investment in specialized machines.

Adisadvantage to this approach is that the possibility of mistakesincreases when workers try to produce greater numbers of identicalitems. During the late 1940’s, kthe increasing complexity and cost ofparts for aircraft led to Air Force to sponsor research at theMassachusetts Institute of Technology to develop machine tools thatcould be programmed to make parts of different dimensions automatically;the programs, or instructions for the machine, were a series of numbers.The result was the development in 1952 of the first numericallycontrolled machine tool. These machines brought the benefits ofautomation to batch production. Different items could be made on thesame machine merely by changing the program and tooling. And the chancefor human error was reduced, since the machine would make each item inexactly the same way. Numerically controlled machine tools have two major component: Anelectronic controller–a type of computer–and a machine tool. Thecontroller directs the mechanisms of the machine tool through thepositioning and machining described in the program for a job.

Aprogram, for example, could contain commands that cause the controolerto move a drill bit to certain spots on a workpiece and drill a hole ateach spot. Many types of machine tools–milling machines, lathes, punchpresses, and others–can be numerically controlled. Each can do certaintypes of machining. A workpiece might have to be worked on by severalmachines before it is finished. Although the machining is done automatically, numericallycontrolled machine tools must be set up and tended properly to maximizethe benefits obtained from their use. These tasks are the job ofnumerical-control machine-tool operators.

Nature of the Work Numerical-control machine-tool operators held about 66,000 jobs in1982. Most worked in industries that produce durable goods, such asmetalworking machinery, aircraft, and construction equipment. The duties of operators vary among employers. In some shops,operators merely tend one machine. In others, however, operators mightprogram and tend machines, operate more than one machine at a time, oroperate more than one type of machine.

Although the operators’duties may vary, they generally involve the tasks described below. Working from written instructions or directions from supervisors,operators must position the workpiece, attach the necessary tools, andload the program into the controller. The machine tool cannot”see” the workpiece; it moves and operates in relation to afixed starting point.

Therefore, if the operator positions theworkpiece incorrectly, all subsequent machining will be wrong.Operators also must secure the workpiece to the worktable correctly, sothe piece does not move while it is machined. When setting up andrunning a job, operators must install the proper tools in the machine.Many numerically controlled machines are equipped with automatic toolchangers, so operators have to load several tools in the propersequence.

The time an operator needs to position and secure theworkpiece and load the tools may be only a few minutes or it may beseveral hours, depending on the size of the workpiece and complexity ofthe job. The way a program is loaded into a controller depends on how it isstored. If the program is stored on tape, it must be run through a tapereader that transmits the program to the controller. Increasingly,machine-tool controllers are connected to minicomputers. Operators loadprograms that are stored on disk or tape directly into the controllervia the computer. Programs must be corrected, or debugged, the first time they run.If the tool moves to the wrong position or cuts too deeply, for example,the program must be changed. some employers have numerical-controlmachine operators debug the program.

Others have tool programmersmonitor the first run. Once a job is properly set up and the program has been checked, theoperator monitors the machine as it operates. Some jobs requirefrequent loading and unloading, several tool changes, or constantattention to insure that the machining is proceeding properly. Forother jobs, the machine can run unattended for hours. In these cases,the operators may set up other machines, finish or inspect completedparts, or do other tasks. Operators check the finished part usingmicrometers, gauges, or other precision inspection equipment to insurethat it meets specifications.

Working conditions generally are good in machine shops. Because ofthe hazards connected with operating machine tools, machines have guardsand shields that minimize the exposure of operators to moving parts.Still, operators must follow safety rules and wear protective equipment,such as safety glasses and earplugs. They cannot wear loose-fittingclothes or jewelry that might get caught in the machines. The jobrequires stamina because operators stand most of the day and may liftmoderately heavy workpieces onto the work table. Numerical-controlmachine operators generally work 40 hours a week; however, overtime iscommon during periods of high manufacturing activity. In some shops,operators may have to work evening or night shifts. Training Operating numerically controlled machine tools generally is not anentry level job.

Employers prefer to fill these jobs with machine-tooloperators or shop helpers who have some experience in machine-tooloperation and have demonstrated good work habits and mechanicalaptitude. Courses in shop math and blueprint reading may improve anemployee’s chances of being selected for an operator job. Working under a supervisor or an experienced operator, traineeslearn to set up and run one or more kinds of numerically controlledmachine tools.

Trainees usually learn the basics of their job within afew weeks. However, the length of the training period varies with thenumber and complexity of the machine tools the operator will run and theindividual’s ability. If the employer expects operators to writeprograms, trainees may attend programming courses offered by machinetool manufacturers. These courses last 1 to 2 weeks. Earnings and Advancement In 1982, numerical-control machine-tool operators earned about$8.70 an hour, according to a survey by the National Tooling andMachining Association. This rate is about the same as the averagehourly earnings for all production workers in manufacturing but slightlylower than the hourly rates of skilled machining workers such asmachinists and tool-and-die makers.

Numerical-control machine-tooloperators may advance to supervisory jobs. Operators who get sufficienttraining in numerical-control programming can move to the higher payingjob, tool programmer. Job Outlook Employment of numerical-control machine-tool operators is expectedto increase faster than the average for all occupations through themid-1990’s. In addition to openings arising from growth in demandfor these workers, many openings are expected to occur as operatorstransfer to other fields of work, retire, or die. Numerically controlled machine tools have been available since the1950’s. Their use has been limited, however, because many firmshave been unwilling to invest in an unfamiliar technology.

Increasingcompetition from foreign companies has forced American manufacturers ofmetal-working, industrial, and transportation equipment to adoptnumerically controlled machine tools and other equipment that enablesthem to control costs and improve quality. In addition to being used asstand-alone equipment, numerically controlled machines are increasinglybeing used as part of flexible machining systems. In these systems,automated material handling equipment moves workpieces through a seriesof work stations. At each work station a robot loads the piece onto anumerically controlled machine and removes it when the machining iscomplete. The workpiece is then moved to the next work station forfurther processing. The increased use of numerically controlled machines is expected toraise the demand for operators. Improvements to these machines may keepemployment from growing as rapidly as the number of machines, however.

The use of adaptive controls–sensors that automatically monitor andadjust machine operations–can be expected to shorten the time anoperator must spend monitoring the machine. Improvements to thecontrollers and the software for parts programming also are likely toincrease operator productivity and limit the rate of employment growthsomewhat. Employment of numerical-control machine-tool operators mayfluctuate from year to year because this occupation is concentrated inindustries that are sensitive to changes in the level of economicactivity.

A drop in the demand for aircraft, machinery, or otherequipment lessens the need for operators and may result in layoffs orshortened workweeks.


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