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 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

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

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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