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DNC solves tape storage problems.

Using a distributed NC system helps a valve manufacturer manage storage of more than 12,000 active tape files.

With more than 12,000 part programs requiring in excess of 200 sq-ft of storage space in the tool crib, a valve manufacturer was starting to run out of space for tool storage. When a customer ordered spare parts, the operator had to file and retrieve programs from the tool crib, and then load them into the machine tools, resulting in wasted production time.

While the company's tape filing system was logical and efficient, the sheer number of tapes began to overwhelm the limited storage facilities. So they turned to DNC to free up floor space and make the programmers' and operators' time more productive.

Why so many programs?

Anchor/Darling Valve Co manufactures valves used in power generation, oil transfer, and other applications. Manufactured parts include a tremendous amount of spares, that are typically run in lot size quantities of one or two, and have to be made quickly for power plant customers.

Parts are generally spherical shapes that mount inside cast-valve housings, such as threaded valve stems and disks that expand or contract to control liquid flow. sizes range from a few inches to several feet long and materials can be either carbon or stainless steels, brass, or hard facing materials like Stellite. The combination of new valve orders and spare parts orders resulted in a tape library of more than 12,000 programs. The company expects that this number will grow to 20,000 in just two years. This volume of tapes is what drove the company to DNC.

DNC-how does it work?

Distributed or direct numerical control eliminates the use of tapes in both NC and CNC machinery; machining instructions are transmitted directly from a computer to the machine tool. With a DNC system, it is possible to serve multiple machines from a single source.

When Anchor/Darling first attempted to implement a DNC system, the supplier was unable to consistently transfer programs to the eight machine tools in the factory. The valve company wanted to use the DNC to run seven CNC lathes and one CNC vertical drilling center, with a variety of controllers, including: Giddings & Lewis, General Electric, Cincinnati Milacron, Fanuc, and Allen Bradley. In addition to the variety of control types, all controls were of various vintage.

For a successful DNC application, the supplier had to provide a low-cost interface that would work with both newer and older controls, and also interface with a Schlumberger Ltd CAD/CAM system for the generation of new part programs. After the initial attempt at DNC proved unsuccessful, Anchor/Darling tried a system developed by Remex, a division of Seymour Electronics & Automation Inc.

DNC plus networking

Using a 80286 10-Mhz PC with a 30-MB hard disk, Remex mounted their DNC board in an expansion slot. The board was then connected to shop terminals located at each of the eight machine tools with RS-422 cable.

The PC basically serves as a front end to two Sun Microsystem minicomputers that are part of the CAD/CAM system and used to store part programs. After programmers had transferred all programs from tape to a 326-MB disk drive on one of the minicomputers, the PC was able to store and retrieve files, using the minicomputer as if it were its own hard disk.

To insure the integrity of machining, Anchor/Darling created a duplicate DNC file storage system on the second minicomputer. In the event the primary computer goes down, the second computer takes over. Archival program storage is on magnetic tape cassettes that run on a tape drive connected to the CAD/CAM system.

Each of the eight machines connected to the DNC system has a Remex terminal. These terminals provide backup program storage sufficient for at least one shift of operation. In addition, the system was designed to prevent the failure of any specific DNC terminal from causing downtime at other machines in the DNC network.

The DNC shop-floor terminals are installed into the space originally designated for a tape reader on the machine controls. With some of the older controls, the unit is mounted on a bracket attached to the control and interfaced behind the tape reader. Newer controls, like the Fanucs, use an existing RS-232 port to simplify connection of the DNC terminal.

Time savings, data integrity

Prior to the DNC hookup, programmers were required to punch a tape, put the tape in a folder and carry it to the tool crib, with folders stored by part number. Each folder contained a CNC tape and a setup sheet that included a hard copy of the program. Every time a new job was run, machine operators made a trip to the tool crib to retrieve the appropriate folder, then had to load the tape into the appropriate machine.

With the DNC system, the tape punching exercise is completely eliminated, saving programmers' time. At the machine, operators are no longer required to use the tape reader. While both programmer and operator still make trips back and forth to the tool crib, the DNC offered substantial time savings.

Dave Bower, Anchor/Darling's NC programming manager, estimates that a few minutes are saved by eliminating tape punching and a few more minutes are saved because the operator no longer has to load tapes. With each of eight machines using an average of two programs per day, Mr Bower believes considerable time is saved over a short period of weeks.

He points out that an operator often had to load a tape three or four times before the control would accept all of the data, further adding to unproductive time. And, on some of the older tape readers, data errors would occasionally crop up. "Unlike NC tape," says Mr Bower, "DNC never allows bad data to reach the machine."

He also believes it is easier to make program changes on the DNC's host PC, rather than at the machine control. While the operator is still free to make minor adjustments, such as feed and speed overrides, program changes are handled at the PC by an NC programmer assistant.

Added capabilities

Though the primary reason for implementing a DNC system was management of part programs, Anchor/Darling expects to use the system's capabilities even more in the future. The company plans to employ the DNC shop terminals for shop-floor data collection.

Using a standard Remex module at the host PC and each terminal, operators will log on and off of each job by keying in part numbers. Data will automatically be sent to the company's MIS computer, making information transmission more timely and eliminating potential errors that could result if shop-floor information had to be re-keyed from a job card.

As part of the expanded DNC capabilities, Anchor/Darling also expects to upgrade their CAD/CAM system to receive downloaded data from computers in the engineering department that will allow the creation of tool paths and machine instructions.

"Looking ahead, we see savings of more floor space and time, and fewer errors," says Mr Bower.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:direct numerical control
Publication:Tooling & Production
Date:Mar 1, 1991
Words:1181
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