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How a GM plant keeps track of tools; random storage maximizes density in three vertical carousels.

How a GM plant keeps track of tools

A 200,000-sq-ft toolroom, completely modernized for machining and building auto-body production equipment, now employs men and equipment for grinding, rebuilding, measuring, storing, and tracking cutters and cutter components for 32 CNC milling machines and a seven-machien FMS. Within the toolroom is a new crib measuring just 40 ft X 35 ft. The installation is in a General Motors B-O-C (Buick-Oldsmobile-Cadillac) plant at Grand Blanc, MI.

Such efficient use of space for tool storage was gained by making use of the plant's vertical cube, through installation of three computer-operated vertical carousels, plus a dedicated tool-management system.

The cutter crib, placed into service in October, 1986, is significantly smaller than the former crib, yet serves a toolroom with several times more machining capacity.

Upgrade needed

"The new crib is part of a program to upgrade the toolroom," says a senior plant engineer. "Upgrading is being accomplished in part by switching to high-accuracy CNC machines that have automatic tool-changers and can make effective use of carbide tooling. Our project goal is to boost toolroom throughput, shorten turnaround time, and increase machining accuracy."

The upgraded toolroom supplies GM's B-O-C divisions with body-panel stamping tools, dies, and fixtures. The facility also builds fixtures for assembly, welding, and adhesive application.

Much of the work involves contour milling and 2-1/2-axis surface cutting, holemaking, and slotting. Most of the new machines are now in service; all are expected to be fully operational this year.

Carbide ups inventory

Switching from high-speed steel (HSS) to carbide tooling presented three problems. First was the ballooning inventory of components needed to build carbide tools: Bodies, inserts, supports, screws, and Caterpillar 50- and 60-taper holders for the automatic toolchangers. Previously, each cutter was a one-piece tool.

Second, carbide inserts range in cost from $3 to $200, and must be kept under tight security. And third, a number of rebuilt, assembled, and measured cutters in each part number must be stored and ready to send to the milling machines at a moment's notice. These assembled cutters include spare standards for kits on the machines, as well as special cutters that are used by all the machines and float in and out of intermediate storage in the crib.

Several methods evaluated

"In comparing various types of storage systems, two primary issues had to be faced," the engineer relates. "First was a flat-out reduction in floor space. We were restricted to only 1400 sq ft (40 ft X 35 ft) regardless of inventory, because of the toolroom layout and the need to be as close as possible to the machine tools.

"Second was a need for absolute control of inventory--to have full knowledge of what's on hand, rapid access to any cutter or part, and full protection."

Because of floor-space constraint, department engineers were driven toward looking at vertical storage systems. These offer high-density storage, and the plant's headroom ranges to 26 ft.

The system selected consists of three Model 1400 VSR vertical carousels from Spacesaver Corp, Fort Atkinson, WI. Each machine is 21 ft 6" H x 10 ft 6" W x 5 ft 11" D, and supports about 1000 plastic bin locations. In each carousel, these are spread over 78 shelves of 18" depth on 26 recirculating carriers.

Loaded into the carousels are all cutter components and all assembled cutters up to 4-1/2"-dia and 18" length. Weight of cutters and parts in each carousel ranges up to 12 tons.

"The carousels were not economically justified as stand-alones," the engineer says. "Justification was driven by space constraints, and by the projected increase in throughput and efficiency provided by our fnew CNC and FMS machines. The old crib layout and equipment never could have supported these new machines in only 1400 sq ft of floor space."

Tool management, too

Supporting the carousels is a computer-aided tool management package consisting of a host computer with CRT and printer, three slaved transaction terminals (one per carousel), and software. The computer is a multitasking, hard-disk machine with a Unix-like operating system.

Besides controlling carousel motions, the computer and terminals track tool inventory. The carousels cannot be operated except by password access through the host and terminals, or in emergencies, by keyswitch.

"All parts pass through openings at the machine countertops," the engineer explains. "Moreover, inventory can be accessed only by making a formal request through the computer. By default, therefore, we electronically track everything moving into and out of the system."

Dedicated control needed

"We needed a dedicated tool-management system, independent of the division's global inventory-control system, for two reasons," the engineer points out. "Tool management requirements in the cutter crib are much too detailed for efficient handling by a global system. Further, the global system is not designed to track intermediate storage; it has no need to know locations of reusable items moving into and out of the crib. Most of our cutter transactions involve reusables."

The dedicated tool-management system does generate recommended reorder tallies when minimum inventory levels are reached. These tallies are passed through to the division global system.

At present, all such tallies are printed. Eventually, though, the Spacesaver host will communicate with the global-system host directly. This will permit automatic preparation of purchase requisitions for tools.

Spacesaver's tool-management package is a two-layer system. Transaction terminals on the carousels are responsible only for directing movements of individual carousels. These terminals have no idea of what is stored in the carousels, but do know how to present shelves to the operator in an efficient order.

On the other hand, the host can't operate the carousels, but knows their contents, helps operators choose which bins to pick, and downloads pick lists to the slave terminals. Picking order is normally first-in, first-out (FIFO) for multiple locations of one part number. The system host also tracks inventory levels, and generates recommended reorder tallies.

Picking simplified

The crib manager, who also is a cutter grinder, retrieves items by keying in the number for fan individual cutter, component part, or cutter assembly. Or, he may key in a request for a bill of materials for all cutters and components for a job on a particular machine or the FMS.

The host then searches its memory for requested items, and presents them as a picking list on the CRT screen. Identifications of carousel and bin locations accompany each picking list.

Normally, a bin holds one part number--either a single assembled cutter, or a supply of components. Multiple locations for the same part number are dispersed throughout the three carousels, so more than one can be picked simultaneously. Such loading minimizes problems should a carousel go down.

Thought it was inteded that only one cutter be stored in each bin, the computer can handle situations in which a lack of empty bins forces small cutters to be doubled up.

After a picking list is printed, the operator edits it. For example, if he wants to retrieve a cutter or component from other than carousel No 1, he can proceed through a list of FIFO transactions for that part number until he finds one on the chosen carousel.

To carousels

Once the operator agrees with the host-generated pick list, it is sent electronically to the transaction terminals of the carousels involved. The operator steps up to the first carousel and keys in his password. The machine indexes to the proper shelf for the first item, and an LED light bar, embedded in the countertop, is turned on in front of the correct bin.

After removing the item, the operator keys an acknowledgment. The carousel then proceeds to the next item, and so on. To complete his picking, the operator carries out the same sequence at the other carousels.

In each carousel, order of part presentation to the operator is such that carrier movements are minimized. Picking can therefore be done rapidly.

Maximizes density

All bins are the same size, and bin locations are not preassigned to particular part numbers. At the same time, though, tool-management software can dedicate some locations, such as those for extra-long cutters that need to be stored sideways.

During restocking, the host picks empty bins at random, but can be forced to pick certain locations. This override feature is sometimes used for stocking parts (rather than assembled cutters), so similar parts can be located near one another. Assembled cutters take up about 70 percent of bin locations; parts take up the remainder.

"Random storage maximizes density," the engineer comments. "When all the new machine tools are installed later this year, over 3000 spare and special cutters will be floating around the toolroom. We expect that a minimum of 85 percent of the 3000 available carousel bins will be occupied at any given moment.

"Had assigned storage been chosen, a large number of bins would have to stand empty. Another problem with dedicated bins is that the mix of cutter part-numbers in storage will probably change regularly. This would require constant reassignment of bins."

Can be locked

The crib is fully staffed over two shifts, and picking and restocking are usually distributed evenly throughout the day. The third shift employs only one cutter grinder; he is not present in the crib full time. When he is absent, the carousels are locked shut to prevent unauthorized access.

"The security of having only one access window, computer-controlled movements, and lockability are definitely advantages with these carousels," the engineer states. "Each machine carries about $1-million worth of inventory. A log of all carousel transactions is retained in the host computer; this log can be printed, retained on disk, or purged, as needed."

Scheduled for future addition in the crib is a computerized tool-presetting system. This will be able to communicate with the carousel host computer and the CNC and FMS machines. The new system will greatly speed cutter changeouts, and will make the crib even more efficient.

For more information on vertical carousels, contact Spacesaver Corp, 1450 Janesville Ave, Fort Atkinson, WI 53538. Phone 414-5-5546.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Title Annotation:toolroom upgrade at General Motors Corp. Grand Blanc, MI, plant
Publication:Tooling & Production
Date:Mar 1, 1989
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