"Design for Time," Feature Article, Sept. 2002

designed for time

Eliminate five screws, save 40 seconds, multiply by 10 million: A computer's new development path pays off.

This article was prepared by staff writers in collaboration with outside contributors.

When the Dell Computer Corp. in Round Rock, Texas, decided to redesign the chassis for its computers, the company set ambitious goals. It wanted one family of chassis to serve its Optiplex, Precision, and Dimension product lines. It also wanted 25 percent less assembly time than the previous chassis, the Optiframe, and wanted it easier to service.

Introduced in 1997, the Optiframe design had reduced assembly time an average of 32 percent from earlier frames. It was so easy to put together that Dell could postpone constructing several new factories.

"We knew that to reach our goal for the new product, we had to completely transform the chassis design," said Bradley Keup, a senior technical strategist at Dell.

In a Dell computer motherboard, a metal plate, called a tempan, holds the board rigid for shipping and installation. The one-piece solution that eliminates a screw reduces the potential for damage.

The chassis had to come in three sizes and had to accommodate the characteristic variations of the three Dell desktop PC product lines. The design team's name for the new frame family was "Transformer." In the end, the chassis design reduced assembly times by 25 to 40 percent, depending on the configuration of the PC.

Dell calls its approach to product development Design for X. The "X" can stand for manufacturing, logistics, ergonomics, service, or just about any other practical consideration. Teams comprise mechanical engineers and experts from other parts of the business, including logistics, shipping, and the supply chain.

They start by listing most of the features of a new design, and then look at the product's expected life, from manufacturing through warranty service. The teams chart their progress along a defined product development path.

"Back in 1997 and 1998, during development of the Optiframe chassis, DFX was still taking shape even as we applied it," Keup said. "Now it's a thoroughly mapped-out process with mandatory stage gates."

One of the goals was to find ways of reducing assembly times and touches, or manual operations.

The team used analysis software called Design for Assembly, which guides engineers through a series of steps to create a numerical index of design efficiency. DFA software, developed by Boothroyd Dewhurst Inc. of Wakefield, R.I., raises questions about the design or function of parts—for example, whether one moves with respect to another.

"A key goal was eliminating fasteners," said Dwight Stimson, a senior DFX engineer. "If you look at a DFA analysis, you'll see that every screw you design out of a product reduces assembly time by approximately eight seconds."

Nearly all Dell PCs require at least one CD or DVD drive and one floppy drive. Each component requires four screws to hold it in place, taking a total of 32 seconds per device.

The tempan is an L-shaped metal plate that screws to the underside of the motherboard.

During development of the Optiframe chassis, the team had considered assembly without tools. One idea was to design components—the internal drives and so forth—with rails that could snap into bays on the chassis.

At that time, the idea was impractical because it would require discarding tools that had several years of life left. When it came to the new Transformer frames, however, Dell had already committed to new tooling.

Dell developed a patented design using shock-absorbing material for the rails. Suppliers agreed to fasten the rails onto the components, so the screws for those parts were moved to an earlier stage of manufacture.

There was one more screw that the team could eliminate. The motherboard in the Optiframe had fitted into a number of built-in hooks, with a single screw to keep it secure. The software targeted that screw and guided the search for alternatives.

"Actually, we had a number of challenges to overcome," Keup said. "Motherboards face damage in shipping, installation, and use. They are awkward to handle. It's very common for an operator to damage the EMI shielding just by picking up a motherboard. The board must be kept rigid for shipping and when it is placed in the PC."

One-Piece Solution

The mechanical engineers and the DFX team devised a one-piece solution that eliminated a screw while reducing the potential for damage. Dubbed a "tempan," it is an L-shaped metal plate that the supplier screws to the underside of the board. The tempan protects the board and its EMI shielding during shipping and handling. It latches into holes on the motherboard base of the chassis, holding the board both secure and rigid. A single motherboard/ tempan design fits all three chassis sizes.

Another targeted task involved routing the integrated drive electronics cables inside the chassis and plugging them into the appropriate components. "Once you start combining features, it's hard to stop," Stimson said. "The Transformer design included the cable routing and allowed us to receive the cables preinstalled by the supplier. Plus, we color-coded the cables to make plugging them in even easier for both the factories and service."

Shipping experts contributed to analyses that reduced the risk of damage in handling. The team modified PC features that were likely to break on impact, then selected a thin, compressible packing foam that could absorb impacts from either dropping or bumping.

The new design decreased overall packaging size. According to Keup, "If we shrink the packing box by a half-inch in height or width, we can save hundreds of thousands of dollars in outbound freight costs."

The Transformer chassis opens without tools and locks in place at a 90- degree angle for assembly or service. Front of the PC is behind the hinge.

The different sizes of the final design share parts, reducing inventory and tooling expenses. The integrated cabling in the chassis offers a similar drop in purchasing, storing, and kitting, or outside assembly. It also augments the freight savings from the reduced packing box size. Additionally, the parts integration saves labor and floor space. Because features are common across all three desktop product lines, Dell has been able to standardize its assembly training.

Overall service time for PCs has been reduced 20 to 30 percent. Replacement motherboards are delivered from suppliers with tempans already installed. The other components arrive with rails in place. A service call involves toolless entry and part installation.

Dell still uses four screws in one area of in-plant assembly. Because hard drives become obsolete rapidly, it was not practical for Dell to purchase a large inventory of hard drives with the rails pre-installed. Operators in the build cell of the Dell factories use torque-driven nut drivers to fasten rails onto the hard drives, using two screws per rail. The minimum time for fitting hard drives with rails is 32 seconds.

Cutting those 32 seconds may be a place to start when the time comes to design the next generation of chassis. "We are exploring an automated system for rail installation," Stimson said.