Computer control programmers and operators use computer numerically controlled (CNC) machines to cut and shape precision products, such as automobile, aviation, and machine parts. CNC machines operate by reading the code included in a computer-controlled module, which drives the machine tool and performs the functions of forming and shaping a part formerly done by machine operators. CNC machines include machining tools such as lathes, multi-axis spindles, milling machines, laser cutting machines, and wire electrical discharge machines. CNC machines cut away material from a solid block of metal or plastic—known as a workpiece—to form a finished part. Computer control programmers and operators normally produce large quantities of one part, although they may produce small batches or one-of-a-kind items. They use their knowledge of the working properties of metals and their skill with CNC programming to design and carry out the operations needed to make machined products that meet precise specifications.
CNC programmers—also referred to as numerical tool and process control programmers—develop the programs that run the machine tools. They review three-dimensional computer aided/automated design (CAD) blueprints of the part and determine the sequence of events that will be needed to make the part. This may involve calculating where to cut or bore into the workpiece, how fast to feed the metal into the machine, and how much metal to remove.
Next, CNC programmers turn the planned machining operations into a set of instructions. These instructions are translated into a computer aided/automated manufacturing (CAM) program containing a set of commands for the machine to follow. These commands normally are a series of numbers (hence, numerical control) that describes where cuts should occur, what type of cut should be used, and the speed of the cut. After the program is developed, CNC programmers and operators check the programs to ensure that the machinery will function properly and that the output will meet specifications. Because a problem with the program could damage costly machinery and cutting tools or simply waste valuable time and materials, computer simulations may be used to check the program before a trial run. If errors are found, the program must be changed and retested until the problem is resolved. In addition, growing connectivity between CAD/CAM software and CNC machine tools is raising productivity by automatically translating designs into instructions for the computer controller on the machine tool. These new CAM technologies enable programs to be easily modified for use on other jobs with similar specifications.
After the programming work is completed, CNC setup operators—also referred to as computer-controlled machine tool operators, metal and plastic—set up the machine for the job. They download the program into the machine, load the proper cutting tools into the tool holder, position the workpiece (piece of metal or plastic that is being shaped) on the CNC machine tool—spindle, lathe, milling machine, or other machine—and then start the machine. During the test run of a new program, the setup operator, who may also have some programming skills, or the CNC programmer closely monitors the machine for signs of problems, such as a vibrating work piece, the breakage of cutting tools, or an out-of-specification final product. If a problem is detected, a setup operator or CNC programmer will modify the program using the control module to eliminate the problems or to improve the speed and accuracy of the program.
Once a program is completed, the operation of the CNC machine may move from the more experienced setup operator to a less-skilled machine operator. Operators load workpieces and cutting tools into a machine, press the start button, monitor the machine for problems, and measure the parts produced to check that they match specifications. If they encounter a problem that requires modification to the cutting program, they shut down the machine and wait for a more experienced CNC setup operator to fix the problem. Many CNC operators start at this basic level and gradually perform more setup tasks as they gain experience.
Regardless of skill level, all CNC operators detect some problems by listening for specific sounds—for example, a dull cutting tool that needs changing or excessive vibration. Machine tools rotate at high speeds, which can create problems with harmonic vibrations in the workpiece. Vibrations cause the machine tools to make minor cutting errors, hurting the quality of the product. Operators listen for vibrations and then adjust the cutting speed to compensate. CNC operators also ensure that the workpiece is being properly lubricated and cooled, because the machining of metal products generates a significant amount of heat.
Since CNC machines can operate with limited input from the operator, a single operator may monitor several machines simultaneously. Typically, an operator might monitor two machines cutting relatively simple parts from softer materials, while devoting most of his or her attention to a third machine cutting a much more difficult part from hard metal, such as stainless steel. Operators are often expected to carefully schedule their work so that all of the machines are always operating.
Work environment. Most machine shops are clean, well lit, and ventilated. Most modern CNC machines are partially or totally enclosed, minimizing the exposure of workers to noise, debris, and the lubricants used to cool workpieces during machining. Nevertheless, working around machine tools can be noisy and presents certain dangers, and workers must follow safety precautions. Computer-controlled machine tool operators, metal and plastic, wear protective equipment, such as safety glasses to shield against bits of flying metal and earplugs to dampen machinery noise. They also must exercise caution when handling hazardous coolants and lubricants. The job requires stamina because operators stand most of the day and, at times, may need to lift moderately heavy workpieces.
Numerical tool and process control programmers work on desktop computers in offices that typically are near, but separate from, the shop floor. These work areas usually are clean, well lit, and free of machine noise. Numerical tool and process control programmers occasionally need to enter the shop floor to monitor CNC machining operations. On the shop floor, CNC programmers encounter the same hazards and exercise the same safety precautions as do CNC operators.
Many computer control programmers and operators work a 40-hour week. CNC operators increasingly work evening and weekend shifts as companies justify investments in more expensive machinery by extending hours of operation. Overtime is common during peak production periods.
| 1. | Determine the sequence of machine operations, and select the proper cutting tools needed to machine workpieces into the desired shapes. |
| 2. | Revise programs and/or tapes to eliminate errors, and retest programs to check that problems have been solved. |
| 3. | Analyze job orders, drawings, blueprints, specifications, printed circuit board pattern films, and design data in order to calculate dimensions, tool selection, machine speeds, and feed rates. |
| 4. | Determine reference points, machine cutting paths, or hole locations, and compute angular and linear dimensions, radii, and curvatures. |
| 5. | Observe machines on trial runs or conduct computer simulations to ensure that programs and machinery will function properly and produce items that meet specifications. |
| 6. | Compare encoded tapes or computer printouts with original part specifications and blueprints to verify accuracy of instructions. |
| 7. | Enter coordinates of hole locations into program memories by depressing pedals or buttons of programmers. |
| 8. | Write programs in the language of a machine's controller and store programs on media such as punch tapes, magnetic tapes, or disks. |
| 9. | Modify existing programs to enhance efficiency. |
| 10. | Enter computer commands to store or retrieve parts patterns, graphic displays, or programs that transfer data to other media. |
| 11. | Prepare geometric layouts from graphic displays, using computer-assisted drafting software or drafting instruments and graph paper. |
| 12. | Write instruction sheets and cutter lists for a machine's controller in order to guide setup and encode numerical control tapes. |
| 13. | Sort shop orders into groups to maximize materials utilization and minimize machine setup time. |
| 14. | Draw machine tool paths on pattern film, using colored markers and following guidelines for tool speed and efficiency. |
| 15. | Align and secure pattern film on reference tables of optical programmers, and observe enlarger scope views of printed circuit boards. |
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