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DNC - implementation of a basic concept.

DNC--Implementation of a basic concept

Over the past decade, much has been written on factory automation and computer technology for the shop floor. Automation technologies such as CIM, FMS, LAN, SPC, and DNC have become futuristic goals for many companies. However, application of these technologies in America's metalworking shops has fallen far short of industry-wide projections. The problem, it seems, lies somewhere between the vendor's promises of utopia and the user's skepticism toward new methods.

Reluctance from small-and medium-sized shops to apply these new technologies is often a result of confusion regarding the applications and their benefits. Larger shops with in-house systems expertise may understand these advanced concepts, but feel they are too complex and too expensive to implement in a single phase. Vendors maintain, however, that the ideas are simple and users can't afford to ignore them.

Despite apprehension that exists in many metalworking shops, some have adopted a realistic attitude toward applying these new technologies. They have chosen to implement them in stages. Often, the first step in implementation of a distributed numerical control (DNC) system.

DNC, in its purest form, is intended to ensure timely delivery and organization of machine-control-data (MCD) files to NC and CNC machine tools. Even this most basic concept has been clouded with confusion.

Many DNC vendors have become "total factory data integrators" or "complete automation systems experts." They've added time and attendance reporting, process planning, electronic graphics, tool tracking, and a host of other features to their list of promises.

Unlike earlier CAD and CAM vendors who sold their products to specific departments, DNC vendors are attempting a universal sale that affects many areas in the manufacturing environment. The attempt, so far, has been unsuccessful.

The paperless factory

Electronic management and control of all manufacturing information is the basis for the "paperless factory." The concept is sound, and is certain to become a reality in some plants. However, the idea that all shops will benefits from this technology has not been widely accepted by the industry.

Many features of the paperless factory offered by DNC vendors are either duplications of existing organizational mechanisms, or radical applications of new technology.

For instance, the value of an E-size blueprint reduced to the size of a 10" screen is questionable in shops where operators are accustomed to seeing, feeling, and doodling on their prints. Electronic travelers and process sheets streamline operations, but are useful only in areas equipped with CRTs. The paper traveler won't become extinct until all shop locations, including rough stores, burr benches, welding booths, and manually operated machine tools, use electronic displays. Various forms of data collection and time and attendance reporting already exist in shops today. Because old habits die hard, convincing upper management that there's a better way to do things is a difficult task at best.

The prime concern of today's manufacturers is to get parts out the door. Long-range strategic planning has become a luxury that few can afford. A universal application of the paperless concept requires exchanging some time-proven methods with untested theories. The fault lies not in the theories themselves, but in the lack of proof that they will actually increase the flow of parts out the door.

Many shops have found that if DNC is viewed in its basic form, it becomes more than justifiable. In some cases, it becomes a necessity.

DNC at Delta

The Technical Operations Center for Delta Air Lines, located in Atlanta, GA, is one such case. With more than 42 acres of hangar, shop, and office space, and approximately 5000 employees, the facility is used to maintain Delta's fleet of aircraft. By 1995, their present fleet of 435 planes is expected to grow to more than 800, and the operations center must meet the increased demands.

At Delta, more than 50 shops work on specific aircraft components. A large machine shop equipped with manual machine tools, as well as 11 NC/CNC machines, serves as a support to other areas. CAD/CAM technology has been implemented to generate tapes and support documents for the shop.

To meet increasing demand for tapes, the NC support staff installed a MicroVAX 3500, running Calma DDM software. Three workstations are linked via DECnet/Ethernet to the MicroVAX, and this, in turn, is networked to a series of VAX 2000s running Medusa CAD software in a tool-design area.

The MicroVAX is used to enter design data from original equipment suppliers such as Boeing and Lockheed. In addition, it retrieves data files for Delta-designed parts from the Medusa system.

Even before a DNC system could be installed, the Delta NC support group felt that it was imperative to organize all part and reference numbers. Strict FAA regulations require close tracking of repairs to aircraft parts. A PC-based system running dBase III was employed to assist with this task.

Delta uses an internal documentation number as a repair order. Once a work order enters the department, it is logged into the system and quickly cross-referenced to work centers, NC-tape-file numbers, tooling, and setup-document numbers. A label containing these references is printed automatically and affixed to the work order and FAA papers. These papers follow the part through the shop during the re-work process.

The installation of a DNC system was the next logical step to deliver MCD and support files to the machines. An existing library of some 2500 tapes, with a combined length of more than 20 miles, was increasing everyday. This increase was becoming a burden to maintain.

According to Bob Davies, Delta's machine shop foreman, the situation was critical. "With Delta's growth over the past two years, we reached the point where we had to eliminate time spent on handling paper tape." He added, "DNC became almost a necessity."

Davies, along with David Price, NC programmer, began a six-month evaluation of systems from five vendors. They selected a SHOPNET II DNC system from the Numeridex CAM Div of Automation Intelligence.

The SHOPNET II system provided Delta with the features it sought. Easy to operate, the system has a track record of reliability, and can handle the facility's present requirements with expansion capabilities for future demands.

Price explained, "When we were conducting our evaluation of systems, our prime considerations were size of shop-floor stations and ease of use. SHOPNET II stations were small enough to mount anywhere, and our operators felt comfortable using the system after just a few days."

The system uses a PC-based library and a single cable supporting Ethernet that runs into the shop area. Stations are placed at each machine. These serve as interfaces between individual controllers and the network. Two controllers are older and are not equipped with serial I/O ports. They are interfaced behind-the-reader (BTR), allowing the station to emulate the normal paper-tape reader. The stations also serve as editors and local storage devices, and can initiate file transfers to and from the library.

The DNC library has been linked to the MicroVAX and serves as a gateway to the DECnet LAN. MCD files now can be stored on the MicroVAX and retrieved directly from shop-floor stations. In addition, rush jobs can be sent directly from the office to targeted machines.

Changes made in the shop are handled efficiently. Price explains, "If tape files are edited by the operator, they're sent back to the SHOPNET II library. Edited files are tagged by the DNC system and then run against the master through a file-comparison routine. All changes are highlighted. If the changes are logical, they are incorporated into the master for future runs." With the tape problem solved, tooling/setup sheets became the next target.

MCD and corresponding files now are downloaded to shop-floor stations sequentially. Operators use small printers driven by the station to create current tooling/setup sheets for the job being run. These sheets could be edited in the stations, but for now, notes and changes are made by hand.

If setup sheets are changed, the operator may use small sketches and notations and turn them in. This becomes Delta's form of documentation to verify each job before it is run again.

Price notes, "We haven't totally eliminated paper in the process, but this method is fast, and now we have everything in hand as far as what's going on out there."

The original system consisted of seven machines and has been expanded twice to handle a total of 11 machines. Plans call for the addition of three more machines within the next year.

According to Davies, installations and expansion has gone without incident. "It took only three or four days to install the system, and within two weeks everyone felt comfortable using it. The transition went very smoothly."

Davies and Price agree that the DNC system has become an integral component in the manufacturing scheme at Delta. "The system has been totally reliable," stresses Price. "It was installed in April 1988 and we've never had a station failure in a year and a half of three-shift operation." Davies adds, "We've been very happy with the SHOPNET II system."

Despite what some experts claim, DNC can be justified by eliminating the paper-tape process alone. Hours spent by support personnel in punching, storing, and sorting tapes add up quickly.

Delta calculated that 470 hours/year were spent in this function. Added to the cost of tape and storage cabinets, they were able to justify the entire DNC system with a payback of 30 months.

In addition to this, Delta identified 520 hours of operator and machine time that were lost every year while tapes were being located in the shop. Had these figures been considered, payback for the system would have been less than 12 months.

Delta has taken that first calculated step toward factory automation, but is doing it on its own terms. Delta is gleaning technology and advice from a variety of vendors, and adapting it to where it will prove most beneficial without disrupting the business at hand.

When Davies considered where the Operations Center had been 18 months ago, he noted, "We used to have someone on the staff to match jobs with tapes, get tapes to the storage area, and update the tapes. Now we do all that electronically, and we have future plans to expand our present capabilities." These plans include using laser printers in the shop area to send graphic files from the Calma system directly to where they are needed.

Although Delta's Operation Center is large, the machine shop is not. It is a typical small- to medium-size shop that is adopting basic DNC to solve basic problems. Delta is just one example of over 35 shops that have streamlined their operations during the past year with installation of a SHOPNET II system.

Dixie Numerics

Although Delta's main concerns related to the number and organization of MCD files, sometimes just the size of the files warrants a DNC system. This is the case with Dixie Numerics, a highly successful job-shop operation located five miles from Delta's facility.

As with many job shops, Dixie manufactures numerous parts in a one-shot mode. That is, they cut parts and may never use the same tape again, so MCD file organization and maintenance are not prime concerns. However, the shop manufactures complicated forging dies from point-to-point data files derived from a variety of CAD/CAM systems.

Like Delta, Dixie Numerics originally turned to CAD/CAM to assist in the tape-generation process. NICAM IV and NICAM V PC-based CAM systems from Numeridex and a Micro Engineering Solution 3000 CAD system were implemented in stages. The combination of three systems gives Dixie complete flexibility to work with various input formats from numerous customers. This input may come in blueprint, APT source file, CLfile, IGES, or even hand-sketched formats.

Supporting three-, four-, and five-axes NC/CNC machines in the die business requires a tremendous amount of data. Dixie found that some tapes were reaching 5000 to 7500 feet, and required more than eight hours to punch. Walkable magnetic tape storage devices were tried with some success, but proved too fragile in the shop environment. DNC was the logical choice.

Dixie installed a SHOPNET II system in mid 1989 to accommodate six machines. Since then, the system has been expanded to 10 machines, with more to be added in the future.

Fred Hatcher, Dixie's operations manager, has been pleased with the system. He says, "The system is efficient, fast, and well organized. We load programs down to the machines in less than ten seconds. These same programs are sometimes over 30,000 lines of code and represent about 8000 feet of paper tape."

Since the initial installation, Dixie has placed the DNC file server on a plant-wide ARCNET LAN, running Novell distribution software. Now MCD files can be directly loaded onto the DNC system from any of the CAD/CAM systems. The pathway to the shop floor has been opened and will be expanded as the need arises.

Attaining the goal

The success of shops such as Delta and Dixie Numerics that have implemented DNC systems often goes unnoticed. It is lost in the hype used by "factory integrators" and "automation experts" who attempt to sell concepts without delivering solutions.

It's time that both vendor and customer sit across the table from each other and discuss the realities of DNC systems. Establishing an honest relationship is necessary because both are trying to survive in competitive businesses, and both are in business to make a profit.

The application of advanced technology in American metalworking shops has been much slower than in some parts of the world. Although some shops have taken the first small steps, others are still floundering in confusion. Technology suppliers, and DNC vendors in particular, are flooding industry with products and promises--often with little regard to the user's application.

DNC vendors should return to the role of problem solvers rather than feature sellers. DNC should be viewed as piece of the solution rather than as a cure-all that can be applied to any situation. The real solution most likely will involve products and services from a number of vendors, installed over time, and designed to meet the automation plans of the total facility.

Existing shop-floor procedures for time reporting, data collection, automated inspection, scheduling, etc can't be ignored by vendors. If features such as these are proposed, vendors should be prepared to detail and justify how they will replace or complement established procedures and policies. Until these chores are done, no DNC system should be sold.

The DNC-selection process involves responsibilities on the user's side as well. Requests for proposals (RFPs) should not include features that are not justifiable, practical, or applicable to your shop. Identify specific problems and future goals while keeping in mind acceptable budgets and time frames. Recognize that the installation of a DNC system affects many departments, and success of the project depends on everyone's early involvement.

Also, keep in mind that, unless your company is willing to serve as a test site, you need to have DNC vendors prove their claims. Demand to visit one or more sites where your proposed features are currently implemented. Ask existing customers about system performance, installation, service, and conformance to original expectations.

The concept of the paperless factory in the US is an ideal not yet achieved. However, one day it will be a reality. Since each metalworking shop is unique in its own way, steps toward achieving the ideal also will be unique. A calculated, justifiable implementation of basic DNC has proved to be a step toward the ideal. Not a cure-all, DNC is only a tool for the task at hand-getting parts out the door.

PHOTO : One of Delta's 50 specialized shops for reworking aircraft components.

PHOTO : Delta found that SHOPNET stations could be installed quickly and conveniently. A large

PHOTO : keypad and function keys help operators feel comfortable.

PHOTO : Rush jobs can be sent directly from the SHOPNET library in the programming office to

PHOTO : targeted machines on the shop floor.

PHOTO : Job requests are keyed-in by the operator. MCD and setup files are downloaded in seconds.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:distributed numerical control
Author:Knight, Dennis
Publication:Tooling & Production
Date:Feb 1, 1990
Previous Article:Supported inserts cut off instead of breaking off.
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