No longer crawling at Caterpillar

An upgrade to an overworked AS/RS has increased throughput 50%.

By -- Modern Materials Handling, 4/1/2000

Not every day is easy for the engineers at Caterpillar' s Pontiac, IL plant. In fact, a recent upgrade of an automated storage and retrieval system (AS/RS) may have had some thinking about a different career path.

The challenge was to tear apart an aging AS/RS, add a new storage/ retrieval (S/R) machine, move a second one, re-locate 30% of the system' s racking, install conveyors and new control systems, and integrate all units to existing production equipment and manufacturing control software. Oh, and by the way, have it all done in a week.

Fortunately, the engineers at the plant saw the challenge as an opportunity to eliminate critical backups and downtime in a facility that has seen a 50% increase in output over each of the past 5 years.

Though completed in a very short timeframe, the overhaul of the mini-load AS/RS supporting robotic manufacturing of fuel injectors has produced big results, including a 50% increase in throughput of the system.

"Our whole goal was to increase capacity. We flat out did not have enough," says Steve Brown, manufacturing engineer in Caterpillar' s Hydraulic Injector Group.

Brown and his team, along with the AS/RS supplier and integrator (HK Systems, www.hksystems.com ), spent the week between Christmas and New Year' s Day 2000 performing the upgrade.

"We had a very small window to get it together," he says. "That was naturally challenging."

The upgraded system now supports more throughput at higher speeds, and keeps an army of manufacturing machines continuously supplied with parts. It also provides an accumulation area if an S/R machine goes down, and decreases the labor that was required during back-ups when parts had to be manually carried to assembly induction stations.

Injecting new life

Caterpillar supplies the majority of fuel injectors used in medium and heavy-duty trucks and construction equipment in the North American market. The Pontiac facility is one of three Caterpillar fuel injector component plants. Three types are manufactured in the 800,000 sq ft facility - hydraulic, electronic, and older "pump and line" products. The AS/RS upgrade was performed in the hydraulic assembly area. These injectors are sold to companies such as Navistar and Isuzu for use in their trucks and sport utility vehicles. They are also shipped to the Greenville, SC Caterpillar vehicle assembly plant.

Outside vendors supply most of the components used in the production of hydraulic injectors, however machining and finishing is performed on many of these parts in the Pontiac plant. Finished parts are placed in pre-formed plastic trays. Each tray is identified with a bar code label that is hand scanned for Caterpillar' s management software. This marries the tray to the type of part it contains.

Trays first flow to large industrial washers designed to thoroughly clean all debris and contaminates left from the finishing processes. A new washer unit was recently added to accommodate the dramatic increase in production, adding further strain to the over-burdened AS/RS located further down the line in the assembly area.

Parts are air dried as they exit the washers and are again scanned to notify the control system that each tray has completed washing. From the dryers, an overhead-mounted conveyor transports the trays toward the AS/RS, which is sandwiched between assembly lines 1 and 2 to provide a work-in-process buffer be-tween the finished machining and assembly processes.

A fixed scanner on the conveyor reads the tray' s bar code and directs it either to the AS/RS or to line 3, which is a smaller capacity area used to assemble one fuel injector model.

Parts destined for line 3 are diverted onto a conveyor spur that brings the trays to a small equipment elevator that lowers them to a staging area. From there the lightweight trays are manually moved to the assembly induction machines. Once assembly in this area is complete, the injectors are taken by wheeled cart to an outbound area near line 1.

No more back-ups

Since original installation of the AS/RS in 1989, millions of parts flow through it annually. To minimize materials handling steps, the storage aisles were positioned end-to-end so that the 2,000 rack locations are only a few short steps from the assembly machines. While that capacity was not altered with the upgrade, what has changed is the configuration of the units and the way in which the S/R machines handle materials. Before the upgrade, the system had two aisles with two very overworked S/R machines.

"We had a constant situation where aisle 2 could not keep up," explains Brown. "The system was just maxed out with capacity that would overrun the system. It would back-up all the way to the washers."

When that occurred, workers would have to transport trays manually from the washer room to the assembly machine induct areas until the S/R machines could catch up. The alternative was to shut down the washers and stop assembly. That can be especially difficult in a facility that runs 24 hrs, 7 days a week.

To resolve this bottleneck, the upgrade engineers split the storage bay in aisle 2. Half was left in place while the other half was slid farther down the space between assembly lines to create a third aisle. The S/R machine in aisle 1 was replaced with a faster-moving one, while the old unit in that aisle was relocated to service the new aisle 3.

Conveyors and fixed scanners were also added or modified to accurately deliver product to the three aisles of the AS/RS.

Today, a fixed scanner reads trays on inbound conveyors as they approach the AS/RS. The information is relayed to the control system, which determines the storage location. The conveyor then delivers the tray to that aisle' s induction station where another fixed scanner confirms delivery.

The control system next instructs the crane to pick up the tray, deliver it to the selected storage location, and slide the tray into the rack.

Since the AS/RS is adjacent to lines 1 and 2, the trays are ideally stored as close as possible to the assembly induction station that requires each type of part. This provides less crane movement on outbound deliveries.

Storage durations in the AS/RS vary depending on the parts, but most stay in the system for about 2 days.

As a part is needed by an assembly machine, the control software directs the S/R machine to retrieve the proper tray. As the tray is removed from the storage location, its bar code label is read with a scanner on the S/R machine, confirming accuracy of the pick. The tray is then delivered to one of a series of outbound windows located along the sides of the AS/RS aisle.

Parts heading to line 1 are picked up at the outbound windows by automatic guided vehicles (AGVs). These vehicles loop all the way around the assembly line, dropping off trays at the appropriate input stations.

Line 2 parts are dropped off at AS/RS windows on the opposite side from where the AGVs patrol. These are moved manually to the assembly stations. Again, the selected drop-off window is ideally only a few paces from that part' s assembly induction station.

The assembly line' s mechanized battalion builds the injectors with near military precision. Each of the 47 robots in the line has a specific task - turning the assembly to the proper orientation, lifting and inserting the proper part, or tapping it home - before passing it on to the next assembly station.

Once an injector has completed the assembly process, it is again scanned and then placed into a pre-formed pallet-size shipping tray designed to stack in layers. As many as 400 injectors comprise a full pallet load of stacked trays. The load is stretch-wrapped and loaded by lift truck onto 30 ft long pallet roll racks. The pallets enter the racks on one end and are pulled from the opposite end once a over-the-road truck is available to transport the injectors just-in-time to a vehicle assembly plant.

Upmost uptime

Completing the upgrade and getting the system back online was a daunting task. Conveyor controls and upgraded controls for the AS/RS had to be integrated with Caterpillar' s customized manufacturing software system, the room was cleaned after the upgrade, and the system tested. So far, all is working as designed.

"We are making sure it is right and are still working on the little things," adds Brown. "We have not seen any trays backing up towards the washers now, which is the main thing we have been tuned into and tells us if the system is functioning the way it should."

Upgrade at a glance

• Faster storage/retrieval machine added

Manufacturer Profile

Caterpillar, Inc.,

Pontiac, IL

Produces fuel injectors for trucks,

SUVs and construction equipment

Facility facts:

Size - 800,000 sq. ft.

AS/RS storage locations - 2,000

3 primary injector assembly lines

24 hr / 7 days week production

Suppliers:

Automated storage and retrieval system, conveyors, and control systems: HK Systems - 414-860-6715, www.hksystems.com

Automatic guided vehicles: Schlafhorst Automation - 616-393-0101, www.saiautomation.com

Lift trucks:

Caterpillar Lift Trucks - 713-365-1424, www.cat-lift.com

Fixed scanners:

Accu-Sort Systems - 215-723-0981, www.accusort.com

Hand scanners:

Symbol Technologies - 800-927-9626, www.symbol.com

Robotic assembly:

Adept Technologies - 408-432-0888, www.adept.com