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Getting into DNC.

Getting into DNC

Have you been thinking about converting from use of punched tapes for your NC and CNC machine tools, to distribution of part programs over a DNC network? You can find several good reasons for doing so--easier program editing, less machine downtime, better program management, and others.

There's a catch, though. If you handle the project incorrectly, you may fail to justify the DNC installation, lose machine production time, pay too much for what you get, or botch opportunities for productivity gains in the future. To help you avoid these undesirable results, we asked seven industry experts for advice on how to plan and implement DNC systems. Here's a report on what they say.

1. Define your goals. This caveat has a vague, obvious sound to it, like highway signs that urge, Drive Safely. Our experts emphasize, however, that this is the first and most important step you should take.

A goal that's paramount to many prospective users is eliminating punched tapes and all their attendant problems and shortcomings. That may or may not be a legitimate goal for your company.

"Start by asking yourself how many parts you run per machine per shift," says Bert Casties, president of RWT Corp, Mt Prospect, IL. "If you run just one part a month, DNC is not justifiable. The cost of having a man move the tape is probably less than the cost of a computer system.

"On the other hand, if you run many parts and have a large turnover of tapes, eliminating them will save the valuable time of programmers and machine operators. Eliminating long tapes, such as those used in aerospace for profiling mills, may be especially worthwhile. Managing large numbers of long tapes can be difficult, costly, and subject to errors."

Ed Down, national sales manager for Numeridex Inc, Wheeling, IL, says elimination of tapes is no longer the common goal it used to be. More important, he says, is the fact that DNC can help you increase machine productivity.

"If you can move the right NC programs to the right machines at the right times, you boost machine uptime. Say you save 10 min each tim e you load a program, and do that several times a day. With a machine burden rate of about $100/hr, you don't have to save too many 10-min increments to realize a sizeable savings."

Gaining more and better performance from old NC machine tools is a worthwhile goal, too, says Jerry Williams, DNC applications manager with Highland Technology Inc, Jessup, MD. "We see many vintage machine tools that are real work-horses," he comments. "They may have CNC on them, but the computers are no longer supported by their original vendors.

"As long as these machines are still accurate, there's no sense in retiring them. Adding DNC gives extra memory, enabling you to change programs quickly and do more short runs. That in turn enables you to provide just-in-time service, thereby making your company more competitive."

2. Set a priority of goals, and look ahead. Eliminating punched tapes may be a high-priority goal for Company A, but better program management or easier editing may come first for Company B. Look at all the different benefits you'd like to realize from DNC, and then list them in order of importance.

"The definition of better program management differs from one company to the next," observes Richard Eshleman, director of marketing for Allen-Bradley Co's Industrial Automation Systems Div, Cleveland, OH. "A lot depends on frequency of program change. If you have a stable situation with few changes, a simple, manual, PC-based DNC system may fill the bill.

"On the other hand, if you must change programs frequently, you may want to take the operator out of the loop and go to an automated system. Here programs are uploaded and downloaded automatically, according to demands of a production scheduling program. The important thing is to figure out what will pay off for you, and set priorities accodingly."

When prioritizing goals, ask yourself if later on you may want to use the DNC network for functions in addition to handling NC programs. Such functions may include collection and transmission of shop labor data, SPC data, setup information, electronic travelers, and others.

"Put yourself in the position of an operator, programmer, or foreman. Imagine yourself working through a typical day or week, and think ahead," says Tim Miller, sales and marketing director for Remex Div, Seymour Electronics & Automation Inc, Fullerton, CA. "For instance, a couple of years from now, you may want to install a CAPP (computer-aided process planning) system and show setup sheets at the machines. Will you want grapics for that, and if so, how elaborate should the graphics be? Or, do you need graphics display only?

"Eliminating paper documents and drawings can be quite expensive. If all you really need is to provide a simple 2-D operations drawing to an operator, for exaple, a printer or plotter near the machines may be a suitable solution. It would also be a much less expensive solution than putting a graphics terminal at every machine.

"And don't put the cart before the horse," says Miller. "Make sure you know how and in which formats your graphics images will be created before you put graphics on the shop floor. This issue is constantly in a state of flux."

3. Make sure your CAD/CAM works well. "Don't go into DNC if you have a CAD/CAM environment that's unstable," cautions Bert Casties. "You don't want to put up with panic at the programming level.

"DNC doesn't improve NC programming; there's no synergy between the two systems. So if your CAD/CAM system isn't producing good part programs reliably and consistently, fix it before tackling DNC."

4. Review justification. With their new capabilities for carrying many kinds of information, today's DNC systems provide functionally and benefits not previously available--but at a price, of course. It's advisable to put dollar figures on as many of these functions and benefits as possible.

"One of our prospective customers says he never runs the same part twice," Bert Casties relates. "He maintains it's faster for him to make paper drawings and simply hand them to his machine operators. For him, eliminating paper tape would not be justifiable, but he may be able to justify some sort of shop network on the basis of better shop-data management.

"Every prospective user of DNC should be aware that the computer is not always the best solution to a given problem. In fact, in some cases a computer system may be counterproductive. Going 'paperless' is not the way of the future for all companies."

But it can and should be the way of the future for many companies. "In shops and factories where there's a lot of paperwork, most of it is out of date," maintains Terry Beadle, manager of shop floor systems for Cimlinc Inc, Elk Grove Village, IL. "Using a full-featured DNC system gives major paybacks, especially where there are many engineering changes, small lots, and a big mix of models.

"Use of DNC also helps ensure that correct, up-to-date NC programs go to the proper machines, and on time. This has a strong impact not only on machine and labor productivity, but also on scrap rates."

Ed Down recommends that you look at all possible benefits from DNC in your particular situation, then try to quantify them. "Add up the number of machine tools, tape changes per day, and time spent for program loading, unloading, transporting, and so on," he says. "Assign dollar figures to these factors, and use your totals to persuade company financial people that DNC is justifiable.

"Many of DNC's benefits are intangible and hard to quantify. Some you won't realize until you actually install a system, gain experience with it, and learn its capabilities. Nonetheless, it's helpful to get company management involved in the justification process, and use whatever firm numbers you have to make your case.

"Incidentally, in our experience, full payback on a typical DNC system has never taken more than one year."

5. Qualify a vendor. "When selecting a DNC system vendor, look for his ability to tailor a system to your particular needs," says Steve Couch, DNC systems engineer with Greco Systems Inc, El Cajon, CA. "Make sure he has broad experience with many types of machine tools, and can readily interface DNC with them."

To that Ed Down adds, "Watch out for sellers of general-purpose networks. Some have never even seen a machine tool, don't know unusual RS-232 protocols, and don't really understand interfacing."

It's important, say the experts, to anticipate a long-term relationship with your DNC supplier. "Determine whether or not the vendor's system is open enough to allow for expansion," says Terry Beadle. "Openness includes an ability to accept other brands of equipment."

Tim Miller advises that you check out the vendor's customer and their DNC installations. "In addition, visit the vendor's own plant," he says. "See how well organized they are. Try to determine whether or not they have ample supplies of spare DNC equipment and parts, and adequate documentation for them. Make a judgment on whether or not their product line and philosophy will allow them to grow with you."

6. Involve all concerned. When planning a DNC system, it's vital that you get all concerned persons involved in the process, says Steve Couch. "Bring in your NC programmers, foremen, superintendants or shop floor managers, and machine operators," he advises. "In addition, involve people from accounting and financial planning. Show them how the system will save money and yield a fast payback and high ROI. Get these people on your side at the outset."

Failure to involve system users may cause the project to fail, cautions Terry Beadle. "If you leave NC programmers and machine operators out of the planning process," he says, "they'll resent it. This leads to underutilization or even rejection of the system.

"On the other hand, input from prospective users results in a better system design. Further, if users take part in planning, they'll feel ownership toward the system. It becomes their system, and they'll make it work well."

7. Select system specs. As you evaluate features of various systems, look for certain specific attributes. Among these are adequate error detection and correction, documentation, spare parts, and a relatively standard type of network.

"The hardware and software at both ends of a cable should be able not only to detect errors, but also to recover from them," Tim Miller stresses. "Most CNCs detect parity errors, but can have substitution errors. This means you may waste a lot of time tracking down sources of errors. High-quality DNC systems automatically reset and resend data, even if there's a hit on the line."

Ready availability of spare parts, documentation, and personnel for troubleshooting should be requirements for vendor qualification, he adds. "If you need a custom interface, make sure its specs are communicated back to the vendor plant, documented, and backed up with spares.

"It could be your system requirements call for graphics. If so, look for a graphics format that's in the public domain, not a proprietary format. Also, try to avoid proprietary networks. There are a few good nets built to common standards. Take care, though, to select a net than can withstand a shop's electrically noisy environment."

8. Determine technical requirements. To do this, conduct a detailed inventory of machine tools and control units to be included in the DNC system. "We need more than machine makes and model numbers," says Tim Miller. "We need details on the NC and CNC units, particularly their tape readers and serial ports.

"At least 70 percent of machine tools in use today require behind-the-tape reader (BTR) interfaces before they can be hooked up for DNC. That percentage includes many CNC machines only four or five years old that were shipped with serial ports for output only. The fact that a CNC has RS-232 doesn't automatically mean it has an input port.

"If a serial port is not bidirectional, we need the make and model number of the tape reader. To get this, you must open the control box and read the number stamped on the reader chassis. There are literally hundreds of versions of similar but not identical readers requiring specific BTRs.

"A word of caution here," he adds. "Beware of a DNC vendor who says he can interface correctly with any machine without looking at the control boxes. A reputable vendor will be willing to come in and check the boxes free of charge. Failure to do so may lead to problems later."

9. Plan system implementation. Answer questions such as, Which files will you store? How will you label and store them? Do you want to keep a separate library for each machine? Should you put all tapes on the DNC system at one time, or as needed?

"Don't forget to plan how you'll manage program files while the DNC system is being installed," says Ed Down. "When a machine is being wired up, it's not producing parts."

10. Build incrementally. "We usually advise our customers to have an over-all DNC plan for the entire shop, but bring the machine tools onto it in groups," Ed Down says. "Bring in one, two, or three machines at a time. You may install wiring for the entire shop all at once, but don't commit and tie up all machines on a new system."

Terry Beadle, too, advises that you start with a small number of machines. "When these machines are on line, evaluate the DNC system, get comfortable with it, and work out bugs. Equally important, determine what you want in the final, complete DNC system."

Bert Casties advises you to start small and slowly. "Begin by handling NC programs only. Take 12 to 18 months to integrate DNC into shop operations, production engineering, and CAD/CAM. We find it takes at least a year for users to become confident that when you press a key, the right thing will happen, and it will happen the same way it did last time.

"Once you're comfortable with DNC, you can start eliminating travelers, process sheets, and other paperwork. Don't try to do this at the same time you're introducing DNC, however. That would be throwing too much technology at people at one time."

11. Plan ahead for CIM. Elimination of tapes, better NC program management, higher machine productivity--these and other benefits make use of DNC worthwhile. But the potential built into today's DNC systems means that eventually they can bring you even more and greater benefits of full computer-integrated manufacturing (CIM). To achieve these added benefits, however, you need to recognize and plan for them.

"Look ahead to a system capable of expanding to, or fitting into, a complete company loop," says Tim Miller. "The loop goes from order entry, production planning, and scheduling, through NC programming and the tool room, to machine tools, quality and production control, and on to company financials.

"Properly and fully implemented, a DNC system becomes a CIM system. It carries data on job status, scrap rates, and quality levels. It gives managers rapid updates, perhaps at intervals of only 10 minutes or less. It logs and relays data on machine performance, downtime, maintenance, and other factors.

"Further, a DNC system can carry standard forms and drawings, eliminating much paperwork. And with appropriate sensors and other input devices such as bar-code readers, a DNC system does this with little or no keyboarding by operators."

After all that advice and stargazing, you may wonder if DNC is actually worth all the time, expense, and bother required. Steve Couch answers in part by telling about a small mold and die shop in Southern California that does custom work on four NC machine tools.

"We put in a 4MB hard disk, BTRs, and machine interfaces," he says. "The owner estimates his little DNC system payed for itself in four months, producing savings at an annual rate of $144,000. That comes strictly from moving programs quickly, eliminating loss of tapes, boosting machine uptime, and acquiring a way to edit programs more conveniently and accurately."

CIM? Perhaps later. Right now, this small shop simply enjoys higher profits. 2101
COPYRIGHT 1989 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Title Annotation:distributed numerical control; pointers from seven experts
Author:Quinlan, Joseph C.
Publication:Tooling & Production
Date:Feb 1, 1989
Words:2710
Previous Article:Steel VRAs - debate and compromise.
Next Article:Insert update - the right tool boosts profits.
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