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Numerical-control machine-tool operations.

A single jet streaks across the sky in the ad. The headline reads, "Think of it as 75,000 parts." Thinking about the number of parts in a plane that will be produced in fairly small numbers makes clear why the great assembly lines of America's factories are only one source of manufactured goods.

The number of items to be produced determines how the production is done. 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 to be made, a skilled worker, such as a machinist or tool-and-die maker, will perform the entire procedure using a variety of tools. If an intermediate number of units is required, yet a third procedure might the used; the manufacture of industrial equipment, aircraft, and many other goods involves this type of producttion. Batch production--as it is called--has been done for decades by skilled machinists, tool-and-die makers, and other workers who cut or form metal or plastic using machine tools such as milling machines and lathes, because the volume of production did not justify investment in specialized machines. A disadvantage to this approach is that the possibility of mistakes increases when workers try to produce greater numbers of identical items.

During the late 1940's, kthe increasing complexity and cost of parts for aircraft led to Air Force to sponsor research at the Massachusetts Institute of Technology to develop machine tools that could 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 numerically controlled machine tool. These machines brought the benefits of automation to batch production. Different items could be made on the same machine merely by changing the program and tooling. And the chance for human error was reduced, since the machine would make each item in exactly the same way.

Numerically controlled machine tools have two major component: An electronic controller--a type of computer--and a machine tool. The controller directs the mechanisms of the machine tool through the positioning and machining described in the program for a job. A program, for example, could contain commands that cause the controoler to move a drill bit to certain spots on a workpiece and drill a hole at each spot. Many types of machine tools--milling machines, lathes, punch presses, and others--can be numerically controlled. Each can do certain types of machining. A workpiece might have to be worked on by several machines before it is finished.

Although the machining is done automatically, numerically controlled machine tools must be set up and tended properly to maximize the benefits obtained from their use. These tasks are the job of numerical-control machine-tool operators.

Nature of the Work

Numerical-control machine-tool operators held about 66,000 jobs in 1982. Most worked in industries that produce durable goods, such as metalworking machinery, aircraft, and construction equipment.

The duties of operators vary among employers. In some shops, operators merely tend one machine. In others, however, operators might program and tend machines, operate more than one machine at a time, or operate 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, and load the program into the controller. The machine tool cannot "see" the workpiece; it moves and operates in relation to a fixed starting point. Therefore, if the operator positions the workpiece incorrectly, all subsequent machining will be wrong. Operators also must secure the workpiece to the worktable correctly, so the piece does not move while it is machined. When setting up and running a job, operators must install the proper tools in the machine. Many numerically controlled machines are equipped with automatic tool changers, so operators have to load several tools in the proper sequence. The time an operator needs to position and secure the workpiece and load the tools may be only a few minutes or it may be several hours, depending on the size of the workpiece and complexity of the job.

The way a program is loaded into a controller depends on how it is stored. If the program is stored on tape, it must be run through a tape reader that transmits the program to the controller. Increasingly, machine-tool controllers are connected to minicomputers. Operators load programs that are stored on disk or tape directly into the controller via 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-control machine operators debug the program. Others have tool programmers monitor the first run.

Once a job is properly set up and the program has been checked, the operator monitors the machine as it operates. Some jobs require frequent loading and unloading, several tool changes, or constant attention to insure that the machining is proceeding properly. For other jobs, the machine can run unattended for hours. In these cases, the operators may set up other machines, finish or inspect completed parts, or do other tasks. Operators check the finished part using micrometers, gauges, or other precision inspection equipment to insure that it meets specifications.

Working conditions generally are good in machine shops. Because of the hazards connected with operating machine tools, machines have guards and 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-fitting clothes or jewelry that might get caught in the machines. The job requires stamina because operators stand most of the day and may lift moderately heavy workpieces onto the work table. Numerical-control machine operators generally work 40 hours a week; however, overtime is common during periods of high manufacturing activity. In some shops, operators may have to work evening or night shifts.


Operating numerically controlled machine tools generally is not an entry level job. Employers prefer to fill these jobs with machine-tool operators or shop helpers who have some experience in machine-tool operation and have demonstrated good work habits and mechanical aptitude. Courses in shop math and blueprint reading may improve an employee's chances of being selected for an operator job.

Working under a supervisor or an experienced operator, trainees learn to set up and run one or more kinds of numerically controlled machine tools. Trainees usually learn the basics of their job within a few weeks. However, the length of the training period varies with the number and complexity of the machine tools the operator will run and the individual's ability. If the employer expects operators to write programs, trainees may attend programming courses offered by machine tool 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 and Machining Association. This rate is about the same as the average hourly earnings for all production workers in manufacturing but slightly lower than the hourly rates of skilled machining workers such as machinists and tool-and-die makers. Numerical-control machine-tool operators may advance to supervisory jobs. Operators who get sufficient training in numerical-control programming can move to the higher paying job, tool programmer.

Job Outlook

Employment of numerical-control machine-tool operators is expected to increase faster than the average for all occupations through the mid-1990's. In addition to openings arising from growth in demand for these workers, many openings are expected to occur as operators transfer to other fields of work, retire, or die.

Numerically controlled machine tools have been available since the 1950's. Their use has been limited, however, because many firms have been unwilling to invest in an unfamiliar technology. Increasing competition from foreign companies has forced American manufacturers of metal-working, industrial, and transportation equipment to adopt numerically controlled machine tools and other equipment that enables them to control costs and improve quality. In addition to being used as stand-alone equipment, numerically controlled machines are increasingly being used as part of flexible machining systems. In these systems, automated material handling equipment moves workpieces through a series of work stations. At each work station a robot loads the piece onto a numerically controlled machine and removes it when the machining is complete. The workpiece is then moved to the next work station for further processing.

The increased use of numerically controlled machines is expected to raise the demand for operators. Improvements to these machines may keep employment from growing as rapidly as the number of machines, however. The use of adaptive controls--sensors that automatically monitor and adjust machine operations--can be expected to shorten the time an operator must spend monitoring the machine. Improvements to the controllers and the software for parts programming also are likely to increase operator productivity and limit the rate of employment growth somewhat.

Employment of numerical-control machine-tool operators may fluctuate from year to year because this occupation is concentrated in industries that are sensitive to changes in the level of economic activity. A drop in the demand for aircraft, machinery, or other equipment lessens the need for operators and may result in layoffs or shortened workweeks.
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Title Annotation:application and employment opportunities
Author:Nardone, Tom
Publication:Occupational Outlook Quarterly
Date:Mar 22, 1985
Previous Article:Computer-aided design.
Next Article:Office automation.

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