Seat Time

Automotive Manufacturing & Production, Jan, 2000 by Jeff Sabatini

Johnson Controls juggles complexity, quality and variability in producing seats for the Lincoln LS.

Johnson Controls' (JCI's) Port Street facility (Plymouth, MI) assembles seats for, among other vehicles, the Lincoln LS. The LS seats are significant for two reasons. First, since they're luxury seats, they have a lot of integral features including power lumbar control, seatheaters, and side impact airbags. Second, since Ford intends to market the LS worldwide, the seats are made in both right-and left-hand drive versions, as well as having several different headrest configurations. This means that the 124 different build combinations for the LS seats makes producing them a lot more complex than just stuffing the right color cowhide.

There's also an issue of quality. With Ford's extreme scrutiny of the LS launch and expectation of world-class comfort and appearance, these seats must be consistently flawless. However, Ford's focus on initial launch quality meant lower production volumes than originally forecast. (JCI's LS seat line has a capacity of 94,000 units per year, but production forecasts for 2000 are much closer to 65,000.) Regardless of numbers, three shipments per shift, two shifts per day, have to be delivered on a just-in-time basis, in sequence, to Visteon's Chesterfield, MI, plant. Visteon builds seats in this plant for the other Lincolns built at Ford's Wixom, MI, assembly plant. All the seats are then blended, again in sequence, for shipment to Wixom.

These issues--complexity, quality and variability--usually form the basis for a "two-out-of-three-ain't-bad" situation (as in, the only way to get high quality is with low complexity). But in the case of Port St., there is a simple solution to meeting these challenges: lean production techniques.

SUPPLIERS

One key to any lean organization is having a close working relationship with its suppliers during product development. On the LS, this started when Ford entrusted JCI to devise its own benchmarking for the seating, which JCI carried out at its Comfort Engineering Center (see "Where Comfort Is an Engineering Discipline," AM&P, January 1999). While this kind of relationship may seem of little consequence to those in production, consider the following example of JCI working closely with one of its own suppliers.

A challenge in designing and building the LS seats concerned the wiring harness, supplied by Yazaki Corp. (Canton, MI). As harnesses have increased in length and complexity to accommodate all the luxury features in seats, they have become more difficult to install. Furthermore, more harness also means more potential to rattle against the seat frame, meaning more NVH issues. Bill Stamm, JCI program manager, explains that these problems were solved by Yazaki engineers developing a plastic encapsulated harness. It snaps easily into the seat track, thereby keeping the wire from making any noise.

THE LINE

The LS seat line is actually two lines: one that builds the simple rear seats and another that builds the more complicated front seats. The lines converge at their ends, where a complete set of seats is palletized and put on a rack for shipment. The lines actually have the same theoretical starting point: the broadcast from Ford that initiates the build, usually 8 to 12 hours before the seat is needed. This broadcast results in a build sheet that stays with the seat until it is installed in the vehicle and includes options, color and other information.

The seats are assembled entirely of subassembled components--tracks, foam cushions, back frames, leather covers, airbags, wiring harnesses, etc. These are all stored line-side in inventories ranging from 2 to 8 hours of supply, necessitating daily deliveries from the seven key suppliers. (JCI manages 27 suppliers in total on this project.) Stamm explains that line-side inventories are important in reducing hi-lo traffic and material handling, as well as making it easier for operators to find parts.

Operators work in "cells," which are combinations of the 16 or so discrete steps in assembly. Each cell has a measured takt time, which ensures that the line can run at an optimal speed. Right now, the line meets production demand with 45 operators; however as demand increases, more operators will be added (up to twice the current number). In this way, JCI can adapt production levels to Ford's demand. As more operators are added, work assignments in each cell are changed to reduce takt times. (The fixed parts--floor space, conveyors, fixtures, machinery--were built to maximum capacity.)

PEOPLE

"Craftsmanship" is the word Stamm uses to describe seat assembly. Which is to say that seats require a great deal of manual labor. Stretching leather and stuffing foam are tasks best mastered by human hands, rather than robots. But with humans come inherent quality challenges. While there may be an art to getting a seat cover to fit, the proper alignment of a seat back frame with the track and cushion pan needs to be absolute every time. Therefore, JCI uses poka-yoke fixtures for every significant seat component. It is worth noting that all of these fixtures were built and debugged during the initial prototype stages, leading to a higher first-run rate.