CASE: Designing Toshiba's Notebook Computer Assembly Line
Toshihiro Nakamura, manufacturing engineering section manager, examined the prototype assembly process sheet (shown in Exhibit 6A.18) for the newest subnotebook computer model.
With every new model introduced, management felt that the assembly line had to increase productivity and lower costs, usually resulting in changes to the assembly process. When a new model was designed, considerable attention was directed toward reducing the number of components and simplifying parts production and assembly requirements. This new computer was a marvel of high-tech, low-cost innovation and should give Toshiba an advantage during the upcoming fall/winter selling season.Production of the subnotebook was scheduled to begin in 10 days. Initial production for the new model was to be at 150 unitsper day, increasing to 250 units per day the following week (management thought that eventually production would reach 300 units per day). Assembly lines at the plant normally were staffed by 10 operators who worked at a 14.4-meter-long assembly line. The line could accommodate up to 12 operators if there was a need. The line normally operated for 7.5 hours a day (employees worked from 8:15 A.M. to 5:00 P.M. and regular hours included 1 hour of unpaid lunch and 15 minutes of scheduled breaks). It is possible to run one, two, or three hours of overtime, but employees need at least three days' notice for planning purposes.
The Assembly Line
At the head of the assembly line, a computer displayed the daily production schedule, consisting of a list of model types and corresponding lot sizes scheduled to be assembled on the line. The models were simple variations of hard disk size, memory, and battery power. A typical production schedule included seven or eight model types in lot sizes varying from 10 to 100 units. The models were assembled sequentially: All the units of the first model were assembled, followed by all the units of the second, and so on. This computer screen also indicated how far along theassembly line was in completing its daily schedule, which served as a guide for the material handlers who supplied parts to the assembly lines. The daily schedules were shared with the nearby Fujihashi Parts Collection and Distribution Center. Parts were brought from Fujihashi to the plant within two hours of when they were needed. The material supply system was very tightly coordinated and worked well. The assembly line consisted of a 14.4-meter conveyor belt that carried the computers, separated at 1.2-meter intervals by white stripes on the belt. Workers stood shoulder to shoulder on one side of the conveyor and worked on the units as they moved by. In addition to 10 assembly workers, a highly skilled worker, called a "supporter," was assigned to each line. The supporter moved along the line, assisting workers who were falling behind and replacing workers who needed to take a break. Supporters also made decisions about what to do when problems were encountered during the assembly process (such as a defective part). The line speed and the number of workers varied from day to day, depending on production demand and the workers' skills and availability. Although the assembly line was designed for 10 workers, the number of workers could vary between 8 and 12. Exhibit 6A.18 provides details of how the engineers who designed the new subnotebook computer felt that the new line should be organized. These engineers design the line assuming that one notebook is assembled every two minutes by 10 line workers. In words, the following is a brief description of what each operator does:
I. The first operator lays out the major components of a computer between two white lines on the conveyor.
II. The second operator enters the bar codes on those components into a centralized computer system by scanning the bar codes with a hand-held scanning wand. On a shelf above theconveyor, portable computers display the operations that are performed at each station.
III. The next six steps of the assembly process involve a large number of simple operations performed by hand or with simple tools, such as electric screwdrivers. Typical operations involve snapping connectors together or attaching parts with small screws. All tools are hung by a cable above the operators, within easy reach. Although the individual operations are simple, they require manual dexterity and speed.
IV. The last two operations are the hardware and shock tests. Toprepare for the hardware test, an operator inserts a memory card into the USB port containing software designed to test different components of the computer circuitry. Because it takes nearly four minutes to load the testing software, the cycle time of this operation is longer than the other cycle times on the line. To achieve a lower cycle time for the line, the hardware test is performed in parallel on three different units. The units remain on the moving conveyor, and the tests are staggered so that they can be performed by a single operator. The shock test (the last operation on the assembly line) tests the ability of the computer to withstand vibrations and minor impacts. The computers are moved to a burn-in area after the assemblyline shock test. Here computers are put in racks for a 24-hour 25 ° C "burn-in" of the circuit components. After burn-in, the computer is tested again, software is installed, and the finished notebook computer is packaged and placed on pallets.
Tweaking the Initial Assembly Line Design
From past experience Toshihiro has found that the initial assemblyline design supplied by the engineers often needs to be tweaked. Consider the following questions that Toshihiro is considering:
1 What is the daily capacity of the assembly line designed by the engineers?
2 When it is running at maximum capacity, what is the efficiency of the line?
3 How should the line be redesigned to operate at the target 300 units per day, assuming that no overtime will be used? What is the efficiency of your new design?
4 What other issues might Toshihiro consider when bringing the new assembly line up to speed?