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Building Lean Systems

Takt Time

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German engineers helped Japan build aircrafts in 30s.Takt is a German word for a musical meter.

In TPS; Customer demand dictated the pace ofoperations on the shop floor.

Takt Time: The concept of linking (external)customer demand to (internal) production resources.

It is expressed in terms of the time available to makeone unit to keep pace with customer demand.

Origin of Takt Time

per PeriodDemand

per PeriodTimeAvailableTimeTakt

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An operator can not be overloaded. Apply time studies to lowerthe time or breakdown the task.

Loading each operator close to 100 percent may lead to infinitequeue if the workload is highly variable (negative).

keep operators loaded close to 100% to motivate them to find

creative ways to reduce their cycle time to takt time (positive). If the operators are underutilized, work expands to fill the time

available (negative).

takt time goes down when demand increases. Then someoperator may become overloaded.

Subdivide tasks more finely, to load each operator close takttime. However, that would uniformly underutilize each operator.

A better alternative is to have the first two operators loaded withtasks that add up to the takt time, leaving the third under-loaded.

Load Balancing?

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The third operator could help if the others fall behind. S/he couldbe located at the end of the cell to perform material handling.

Takt Time is a Measure of External Demand

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If each operator is paced to takt time, over production willbe automatically limited. Limiting overproduction preventsfrequent stops and starts that inhibit a smooth flow.

It's best to buffer variation with capacity, not inventory.

It is incorrect stating that a machine has a takt time of fiveminutes. Takt time is a measure of external demand; ithas nothing to do with machine capacity. Takt is time perpiece, not pieces per time.

Enterprise should match its (internal) resources to meet

the (external) customer demand. takt time applies better to a flow shop, may not be very

relevant in job shop, but still useful to determine thenumber of operators.

Takt Time is a Measure of External Demand

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How often should takttime be changed?

Too Frequent Chaos Not flexible to change Missed opportunities,

Inventory buildup

Distinguish between noise and real trends.

Takt time could be reevaluated if the demand exceedsthe set production rate for 5 consecutive days (RunTest).

At Dell Assembly takt time is 15 secs per

computer. It is accomplished through (capacity)running multiple assembly lines

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Internal vs. External Takt Time

80

90

100

110

120

130

0 5 10 15 20 25 30

Day

Demand

Production

Takt Time allows to smooth external demandvariation

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Average Labor Content

Average labor content is the minimum number ofworkers to sustain operations.

Demand percentages for Hungama, Inc., Tasks

RUNS RAPS RAINS RERUNS

Jobs/Day 4 12 6 18% of Total 10% 30% 15% 45%

Operation times for Hungama, Inc. in (Minutes)

RUNS RAPS RAINS RERUNS

Distribution 58 50 44 28

Underwriting 43 40 23 19

Rating 72 65 68 75

Policy writing 67 0 55 50

Total Labor 240 155 190 172

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Average Labor Content

minutes1040

400

Demand

tyAvailabiliNetTimeTakt

k

1i

)Modelforcontentlabor)(TotalModelof(%ContentLaborAverage ii

TimeTakt

ContentLaborAverageReqirementManpowerMinimum

Average labor content = 0.10 (240) + 0.30 (155) + 0.15 (190) + 0.45(172) = 176.4 min

186.1710

176.4ReqirementManpowerMinimum

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Average Labor Content

ALC for Distribution = (0.10 x 58) + (0.30 x 50) +(0.15 x 44) + (0.45 x 28) = 40 minutes.

Since Takt time is 10 min, the minimum number ofoperators allocated to Distribution task will be 4.

(40/10 = 4)

ALC T T M LR

Distribution 40 10 4

Underwriting 28.3 10 3Rating 70.7 10 7

Policy writing 37.5 10 4

Total 176 10 18

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Practice Pleasant Valley Health ClinicThe Pleasant Valley Health Clinic treats patients withrespiratory illnesses. It classifies patients according tofour different types of respiratory problems (commonlyreferred to as Diagnostic Related Groups, or DRGs):Bronchiolitis (BRO), Pneumonia (PNE), Pharyngitis (PHA)and Sinusitis (SIN). The average number of patients

treated per day are summarized below. The clinic workstwo shifts, from 7:00 am to 3 pm and from 3 pm to 11pm. During a shift, the staff are provided a half hourlunch break and two rest breaks of 15 minutes each.

BRO PNE PHA SIN

Patients / Day 15 24 25 36

Fraction of total 0.15 0.24 0.25 0.36

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Pleasant Valley Health Clinic Task DurationsEach patient typically requires 4 process steps: Check-In(includes weigh-in, blood pressure check, etc.), Evaluation(by a physician), Testing (X-Rays, administering ofrespiratory instruments like Pulse Oximeters, etc.), andAssessment (diagnosis and future scheduling). The average

task time for each process (in minutes) is given below:Time (mininutes) BRO PNE PHA SIN

Check-In 30 30 30 30

Evaluation 20 15 10 12

Testing 45 40 15 15

Assessment 15 15 10 10

Work Content 110 100 65 67

Aggregate

30

13.42

25.5

11.95

80.87

Tasks 1, 3, and 4 are typically handled by RNs. Task 2 ishandled by a physician. For simplicity, we assume that thearrival rates of patients are constant through both shifts.

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Takt Time for Pleasant Valley Health ClinicAverage Work Content = 80.87 minutes.

Daily demand; BRO: 15, PNE: 24, PHA: 25, SIN: 36. A total of100.

Time available in a day: 2 shift @ 8 hrs less 0.5 (lunch) - 0.5(2 breaks) = 14 hours = 840 minutes

Takt time = Time Available / Daily Demand= 840/100 = 8.40 minutes / reques

Min. # of RNs required = 80.87/8.4 = 9.627 10