Where is CNC Equipment Most Efficient?
CNC is the abbreviation for Computer Numerical Control. Simply stated, it is the use of a computer interfaced with a machine tool to generate tool paths controlled by a motor instead of a person using hand wheels. It has been incorporated into virtually every type of machine tool, including lathes, mills (both horizontal and vertical), Swiss screw machines, EDM (electrical discharge machines), punch presses, and almost every other type of metal working machines.
In its early development, CNC equipment required a substantial investment in manpower training, financing, and support, both on the part of management and shop personnel. Advances in computer technology and widening of the market place have now changed that, and most machining job shops cannot be competitive without CNC equipment.
When three-axis milling or complicated tool paths are necessary, it is virtually impossible to be competitive without CNC. Cams with splines can be machined in lots of 3-6 pieces, dispelling the myth that CNC is for high production only. Once a program is written and proven, the balance of the parts produced are controlled in both quality and speed more easily than with manual machining.
The mention of these three words has weakened the knees of most job shop owners or managers. The concept is here to stay, for better or for worse, and one way to adjust is to increase productivity and reduce downtime. CNC machines have helped in both these areas since the programs, once produced, are stored and ready for immediate re-use. Set-ups are quicker and more consistent, since it does not matter who set up the last run; the information is documented and each run should be consistent with previous runs. In our own operation, our customers have gone from turning inventory 3 times a year to 6 turns per year.
Many production-oriented job shops often avoided bidding on prototypes because they either did not have the personnel or they felt they could not be competitive with shops which specialize in prototype work. In our own operation we began to manufacture prototypes with the hope of getting the advantage on the production run. We have found that in most cases prototypes run on CNC equipment not only are profitable but also provide an accurate cycle time for the part in volume production. The parts are also an accurate representation of production quality, and we can give our customers "value engineering" feedback before the design is finalized.
Probably the biggest reason for seeking out CNC machining methods is the critical shortage of skilled machinists. Close to tolerance work, where the "touch" or "feel" a skilled machinist developed was so important, can now be controlled by a person of lesser skill by inserting a computer- controlled tolerance offset to make corrections quickly and accurately.
There is some resistance to any new technology, and CNC machining is no exception. If you are planning to implement CNC equipment in your plant there must be a total commitment from everyone deeply involved. An excellent paper on this subject is available from Ingersoll Engineers, a consulting firm in Rockford, IL, titled "Manufacturing Technology."
Remember drill jigs? In many shops they have been eliminated because drilling operations have been transferred to CNC mills. One advantage of drilling on a CNC mill is that the machine runs virtually unattended, leaving the operator free to complete secondary operations, such as deburring or tappng, or to load a second or third machine. The machine cycles the operation for the most part, ensuring constant efficiency regardless of the skill of the operator.
Drilling and milling on CNC can also eliminate multiple set-ups and orientation problems. If a slot has to be milled at 90 to a cross-drilled hole, this can be done in one operation and one clamping.
Ferrous and non-ferrous metals, alloys, carbon, wood, substrates and plastics are all capable of being machined using CNC. Usually the only limitation is the hardness or brittleness of the materials and their ability to be sized and toleranced by chipmaking processes.
The accuracy and speed of CNC machining are breaking new boundaries every day with more sophisticated and powerful equipment. In the past a hardened shaft with 32 micro finish, 0.0005" tolerance, and concentricity requirements of 0.001" would have involved three services: the initial blank turned on a lathe, a heat treat operation, and a final grind. With today's technology and advanced tooling, such as ceramic inserts, this part can be finished at one CNC work station, starting with a pre-hardened blank, thereby eliminating the cost and possible scrap incurred in handling this part at three separate locations. Delivery is easier to control, and expediting one vendor instead of three saves the purchase personnel time and money.
It costs nothing to find out if a particular part can be more economically machined by CNC equipment, as compared to using automatics. Or, if you are in the habit of sending prototype parts to specialty shops not equipped with CNC, get a CNC shop to quote them.
It is advisable for your engineering department to discuss dimensions, tolerances, part design and function, material, hardness, etc., with the job shops you are working with. Machining technology is constantly improving. What could not be done yesterday may be Possible today.
Often, a minor relaxation of specifications or modification of part design, with neither affecting part function, may make it possible to produce a part in one continuous operation, at one source, providing cost reductions which can be significant.
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