Toshihiro Nakamura, manufacturing engineering section manager, is examining the prototype assembly process sheet $($shown in Exhibit $6\mathrm{.}8)$ 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 is designed, considerable attention is 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 is scheduled to begin in $10$ days. Initial production for the new model is to be $150$ units per day, increasing to $220$ units per day the following week $($management thought that eventually production would reach $300$ units per day$).$ Assembly lines at the plant normally are staffed by $10$ operators who work at a $14\mathrm{.}4-$meter$-$long assembly line. The line is organized in a straight line with workers shoulder to shoulder on one side. The line can accommodate up to $12$ operators if there is a need. The line normally operates for $7\mathrm{.}5$ hours a day $($employees work from $8$:$15$ A$.$M$.$ to $5$:$00$ P$.$M$.$ and regular hours include one 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 displays the daily production schedule, consisting of a list of model types and corresponding lot sizes scheduled to be assembled on the line. The models are simple variations of hard disk size, memory, and battery power. A typical production schedule includes seven or eight model types in lot sizes varying from $10$ to $100$ units. The models are assembled sequentially: All the units of the first model are assembled, followed by all the units of the second, and so on$.$ This computer screen also indicates how far along the assembly line is in completing its daily schedule, which serves as a guide for the material handlers who supply parts to the assembly lines.

Exhibit $6\mathrm{.}8$: Notebook Computer Assembly Process Sheet

TASK TASK TIME $($SECONDS$)$ TASKS THAT MUST PRECEDE

$1.$ Assemble Cover. $86$ None

$2.$ Install LCD in Cover. $54$ Task $1$

$3.$ Prepare Base Assembly. $24$ None

$4.$ Install M$-$PCB in Base. $36$ Task $3$

$5.$ Install CPU. $23$ Task $4$

$6.$ Install Backup Batteries and Test. $44$ Task $4$

$7.$ Install Accupoint Pointing Device and

Wrist Rest. $30$ Task $4$

$8.$ Install Speaker and Microphone. $42$ Task $4$

$9.$ Install Auxiliary Printed Circuit Board

$($A$-$PCB$)$ on M$-$PCB$.25$ Task $4$

$10.$ Prepare and Install Keyboard. $26$ Task $9$

$11.$ Prepare and Install Digital VideoDrive

$($DVD$)$ and Hard Disk Drive $($HDD$).52$ Task $10$

$12.$ Install Battery Pack. $8$ Task $11$

$13.$ Insert Memory Card. $7$ Task $12$

$14.$ Start Software Load. $8$ Tasks $2,5,6,7,8,13$

$15.$ Software Load. $286$ Task $14$

$16.$ Test Video Display. $50$ Task $15$

$17.$ Test Keyboard. $40$ Task $16$

The daily schedules are shared with the nearby Fujihashi Parts Collection and Distribution Center. Parts are brought from Fujihashi to the plant within two hours of when they are needed. The material supply system is very tightly coordinated and works well.

The assembly line consists of a $14\mathrm{.}4-$meter conveyor belt that carries the computers, separated at $1\mathrm{.}2-$meter intervals by white stripes on the belt. Workers stand shoulder to shoulder on one side of the conveyor and work on the units as they move by$.$ In addition to the assembly workers, a highly skilled worker, called a $$supporter$,$ is assigned to each line. The supporter moves along the line, assisting workers who are falling behind and replacing workers who need to take a break. Supporters also make decisions about what to do when problems are encountered during the assembly process $($such as a defective part$).$ The line speed and the number of workers vary from day to day, depending on production demand and the workers$$ skills and availability. Although the assembly line has $12$ positions, often they are not all used.

Exhibit $6\mathrm{.}9$ provides details of how the engineers who designed the new subnotebook computer felt that the new line should be organized.

Exhibit $6\mathrm{.}9$: Engineers' initial design of the assembly line

ASSEMBLY

LINE POSITION TASKS WORKSTATION

NUMBER LABOR TIME $($SECONDS$)$

$11.$ Assemble Cover. $(86)186$

$22.$ Install LCD in cover. $(54)254+24=78$

$3.$ Prepare Base Assembly. $(24)$

$34.$ Install Main Printed Circuit Board

$($M$-$PCB$)$ in Base. $(36)336+23+44=103$

$5.$ Install CPU $.(23)$

$6.$ Install Backup Batteries and Test. $(44)$

$47.$ Install Accupoint Pointing Device and

Wrist Rest. $(30)430+42+25=97$

$8.$ Install Speaker and Microphone. $(42)$

$9.$ Install Auxiliary Printed Circuit Board

$($A$-$PCB$)$ on M$-$PCB$.(25)$