What seemed like a good idea for Ford plants in 1994 has become standard practice in 2002.

Eight years ago, the automaker installed its first automated storage and retrieval system (AS/RS) for car bodies at its plant in Wixom, Mich. The idea was to support lean manufacturing by sequencing car bodies in the AS/RS between paint and assembly operations. The system provides an accumulating buffer and allows Ford to change the build order of the cars before they proceed down the line. Additionally, cars can be sequenced to better match deliveries from suppliers.

Since the first system, ten others have been placed in Ford facilities throughout North America. The most recent ones are at plants in Louisville and Kansas City (HK Systems, 800-457-9783, www.hksystems.com). An additional system will soon be installed at a second Kansas City facility, due to begin operations next July.

This approach has allowed Ford to improve its manufacturing flow and timing to the manufacturing floor, save floor space that had been used to hold parts and materials inventories, and improve labor management and line balancing.

'We've had a huge savings in floor space at the facilities,' notes Bob Fish, who manages in-line vehicle sequencing (ILVS) materials handling and logistics from Ford's headquarters in Dearborn, Mich. 'We have been able to shrink the space needed lineside for parts. And it has eliminated picking from storage in the plants and the double-handling that goes with that.'

Sequencing with the AS/RS also allows Ford to perform assemblies with greater variations and complexities that offer more vehicle options to customers. These variations are now delivered from the supplier directly to the line, rather than requiring Ford to store and pick a wide diversity of parts.

The benefits of sequencing do not stop with Ford. 'Sequencing also helps our suppliers become leaner,' adds Tracy Basing, Ford facility engineer for IVLS systems in Dearborn. 'By working to a firm six-day schedule, we give suppliers the ability to manufacture in sequence and lean out their factory too.'

Prior to moving to its new lean systems, Ford sent out a broadcast message to local suppliers for all parts required for scheduled assembly. This put considerable pressure on suppliers to make certain that parts arrived when needed, otherwise it could potentially hold up the production line.

But when Ford made the move to just-in-time manufacturing, it had to make sure of two things. Parts and components had to arrive on time from suppliers, and the facility's production systems had to learn to operate with greatly reduced in-house inventories.

'If a supplier was not close to us, we had to have stock on hand and then pick it out of our stored inventory,' says Basing.

The former process also required Ford to hold about two days of inventory in-house. The AS/RS now provides an accumulation point for car bodies that permits the build order to change depending on the supplies received. This has allowed a reduction in the on-hand inventory to only about two hours.

Ford now transmits information daily to its suppliers about specific cars that will be built during the following six days, creating a firm six-day build schedule. The supplier is given an exact window of time for when and how much sequenced material should arrive at the assembly plant to match the production schedule.

'We tell them what we will build and in what order,' explains Fish. 'It pushes more of the sequencing work to our suppliers and provides a much more stable supply.'

Although the size and exact configuration of the AS/RS differs plant to plant, the general function of the staging systems is the same at all facilities.

'The AS/RS acts like an accumulation bank, holding several hours of production. It also allows units which have been taken out of sequence or otherwise delayed in the manufacturing process to catch up and take their proper position in the final assembly queue,' says Basing.

Car bodies are welded together in the body shop and moved on skids by conveyor to the AS/RS. Upon arrival, the bodies are picked up by a storage/retrieval machine outfitted with forks and lifted to an open slot in the unit. Storage within the AS/RS is in aisles of racks eight or nine levels high and about 80 feet tall. Each of the three to seven aisles in a Ford system has its own storage/retrieval (S/R) machine. The unit is designed so that the S/R machines can access car bodies from racks on either side of the aisle. This also allows a neighboring S/R machine to retrieve car bodies if a machine in an adjacent aisle goes down for repairs.

The car bodies, still on the skids, are placed into assigned rack positions and held there. The systems at the various Ford plants hold anywhere from 300-480 bodies. Once a car body is deposited, the storage/retrieval machine then looks at the established build sequence, pulls the next needed body from its storage location, and places it onto a takeaway conveyor that serves the assembly line. The sequenced bodies are next conveyed though the various assembly stations where they meet up with parts delivered in sequence from suppliers.

'Having the AS/RS as an accumulating buffer has added a lot of stability to the process,' says Basing. 'Their reliability has been very good and we have even been able to add onto the systems as they have been running. That is quite a feat.'

Since there is less inventory in the plant, it is easier to make line changes and engineering redesigns. The sequencing process also helps Ford to schedule its labor. For example, it takes more personnel to build a convertible than a standard sedan. By proper sequence planning, labor can be better balanced. This allows the proper attention a more complex build requires, which, in turn, improves quality.

Click on the icon to read how General Motors also uses an AS/RS for sequencing at the Lansing Grand River Cadillac plant.