Last October Detroit Diesel, a division of Daimler, unveiled the DD15—a new heavy-duty diesel engine ready to set new efficiency standards for the industry.

The engine manufacturer spent five years and $1.5 billion to develop the new 6-cylinder engine, which displaces 14.8 liters and is available in all Daimler Trucks North America products. Designed as an international engine, the DD15 will eventually be manufactured by Daimler Trucks in Germany, Japan and the United States.

To manufacture the new engine, Detroit Diesel invested $275 million to refurbish and retool its 3-million-square-foot manufacturing plant in Redford, Mich. That project included new materials handling and storage processes to support the lean manufacturing line.

“If you look back to 2003 when we began designing the new engine, we were a traditional manufacturing facility with no well-defined storage locations,” says Chris Russell, material flow engineering supervisor. “To produce the DD15, we had to create a central warehouse area, with narrow-aisle high bay storage to free up space for the new assembly line.”

The central warehouse area takes up just 30,000 square feet, considerably less than the 80,000 square feet of space that was previously used throughout the plant. Some of that space is available for other manufacturers that lease space from Detroit Diesel. “At any given time, as much as a third of the plant is utilized by mall tenants who lease from us,” says Russell. “One of our goals is to not only free up more space for our products, but also to open up space for manufacturing tenants.”

In addition, Detroit Diesel implemented a kanban system to pull material to the line on a just-in-time basis rather than store parts and components at the line.

One of the keys to making these new processes work was a series of specially designed carts (Topper Industrial, 262-886-6931, www.topperindustrial.com) that are used with tuggers and automatic guided vehicles (AGVs) to deliver parts and components to the line just in time, and in some cases, in sequence (see p. 24 for a description of the carts). In place of a traditional assembly line, the AGVs route the engines from one workstation to the next during the manufacturing process.

While Detroit Diesel is still ramping up production of the DD15, the manufacturer is already seeing productivity rise. “We have improved our on-time delivery of parts from the storage area to the line,” says Russell. “And we're seeing improvements in quality.”

The new engine line created an opportunity to implement lean manufacturing processes at Detroit Diesel. To support manufacturing, the materials flow team set out a number of materials handling goals. They included:

• Shortening the distance between the receiving docks, the storage area for parts and components, and the point of use. To meet this goal, Detroit Diesel created a centrally located 30,000 square foot warehouse area with very narrow aisle, high bay storage. Prior to that, most inventory was stored on the floor and positioned throughout the warehouse. Once the location for the storage area was established, Detroit Diesel relocated the receiving area adjacent to the warehouse. That sped up the receiving and putaway time. “The receiving area was quite a distance from the central warehouse,” says Russell. “We did an analysis that proved we could justify the cost of putting in a new receiving dock with productivity improvements.”
• Establish a fork-truck-free environment on the manufacturing floor for improved safety. While lift trucks are still used at the receiving dock, it took quite a bit of lift truck traffic moving one pallet load of material at a time to support manufacturing operations. Going to tuggers allowed operators to deliver three loads per trip—that freed up one driver from that area. Not only is there less vehicle traffic, Russell says tugger drivers have more visibility and can stop more easily, creating a safer work environment.
• Support production to minimize non value-added work. In addition to reducing lift truck traffic, tuggers had two other advantages: Drivers don't have to get off the tuggers, and parts are at the same spot for operators on the line every time. What's more, Detroit Diesel implemented a system to deliver some parts in the same sequence as the engines being manufactured on the line. Sequenced parts are delivered on custom gravity conveyors that run parallel to the AGVs that route motors between workstations.

Enable 100% inventory accuracy. The manufacturer employs a warehouse management system (WMS) that supports dynamic storage to make most efficient use of the storage locations and to track the location of inventory in real time.

The last, and possibly most important, goal was to establish robust and efficient replenishment systems along the whole process chain.

The most important change was philosophical: The facility transitioned from a push system, where lift truck drivers managed the delivery of parts to the line, to a pull system, where parts were delivered as requested by workstation operators.

“Previously, our lift truck drivers had a milk run; they went to a storage area, picked up parts and delivered the material to the line based on their schedule,” Russell explains. “We wanted to decouple those processes.”

That decoupling led to the implementation of a kanban system to pull bulk materials through the system on a just-in-time basis. That, in turn, drove important materials handling changes.

In the new system, palletized materials are delivered to each work area on a cart. Each cart has a cardholder on the side with information about where the cart is stored and where it's delivered. The cart also has a simple flag that resembles the flag on an old-fashioned mailbox. When the operator on the line uses the last part on a cart, the flag is raised. That signals to the tugger driver that more material is needed. The driver returns the empty cart to a staging area; unloads any dunnage; and drops the card off in a mailbox. Later, that card will be retrieved and scanned by a warehouse operator, triggering replenishment.

Transitioning to a kanban system not only reduces the amount of inventory stored at the line, it also reduced the number of times production was slowed because a work cell was out of stock. “We recognized that in a lean environment, we could no longer have employees managing their own stock, or deciding when to deliver parts to the line,” says Russell. “We couldn't risk shutting down the line.”

One year after Detroit Diesel unveiled the new engine design, the line is producing about 50 engines a day, with capacity to produce as many as 300 engines a day. As production ramps up, Russell's team intends to implement an electronic kanban system that will automatically send a signal when a part is ready for replenishment.

While still not at full production, Russell says the new system is already delivering improvements. “During implementation, we began tracking things like the hours per engine, which is a measure of how efficiently we are manufacturing, and first-time through, which is whether all of the parts were on hand to produce a finished engine the first-time through, even if we didn't shut down the line,” he says. “We are seeing improvements on all of those measures.”