Value (mathematics)

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Takt time, derived from the German word Taktzeit, translated best as meter, sets the pace for industrial manufacturing lines so that production cycle times can be matched to customer demand rate. For example, in automobile manufacturing, cars are assembled on a line, at a certain cycle time, ideally being moved on to the next station within the takt time so as to neither over or under produce. The cycle time to complete work on each station is often less than the takt time in order to ensure that the customer is never shorted of product. Although theoretically you want to match cycle time to takt time to avoid building inventories and over-sizing equipment, the reality is that demand is dynamic and never truly known and because process disruptions such as unplanned downtime can occur. Thus, in practice, it is generally understood that cycle time needs to be slightly less than takt time.

Definition

Assuming a product is made one unit at a time at a constant rate during the net available work time, the takt time is the amount of time that must elapse between two consecutive unit completions in order to meet the demand.

Takt time can be first determined with the formula:

$T=\frac{T_a}{D}$

Where
T   = Takt time, e.g. [work time between two consecutive units]
T_a = Net time available to work, e.g. [work time per period]
D = Demand (customer demand), e.g. [units required per period]

Net available time is the amount of time available for work to be done. This excludes break times and any expected stoppage time (for example scheduled maintenance, team briefings, etc.).

Example:
If there is a total of 8 hours (or 480 minutes) in a shift (gross time) less 30 minutes lunch, 30 minutes for breaks (2 × 15 mins), 10 minutes for a team briefing and 10 minutes for basic maintenance checks, then the net Available Time to Work = 480 - 30 - 30 - 10 - 10 = 400 minutes.

If customer demand was, say, 400 units a day and one shift was being run, then the line would be required to output at the rate of a minimum of one part per minute in order to be able to keep up with customer demand.

In reality, people and machines can never maintain 100% efficiency and there may also be stoppages for other reasons. Allowances should be made for these instances and thus the line will need to be set up to run at a faster rate to account for this.

Also, takt time may be adjusted according to requirements within the company. For example, if one department delivers parts to several manufacturing lines, it often makes sense to use similar takt times on all lines to smooth out flow from the preceding station. Customer demand can still be met by adjusting daily working time, reducing down times on machines and so on.

Some of the early literature uses cycle time for takt time.

Implementation

Takt time is calculated on virtually every task in a business environment. It is used in manufacturing (casting of parts, drilling holes or preparing a workplace for another task), control tasks (testing of parts or adjusting machinery) or in administration (answering standard inquiries or call center operation). It is, however, most common in production lines that move a product along a line of stations that each perform a set of predefined tasks.

Once a takt system is implemented there are a number of benefits:

• The product moves along a line, so bottlenecks (stations that need more time than planned) are easily identified when the product does not move on in time.
• Correspondingly, stations that don't operate reliably (suffer frequent breakdown, etc.) are easily identified.
• The takt leaves only a certain amount of time to perform the actual value added work. Therefore there is a strong motivation to get rid of all non value-adding tasks (like machine set-up, gathering of tools, transporting products, etc.)
• Workers and machines perform sets of similar tasks, so they don't have to adapt to new processes every day, increasing their productivity (albeit at the expense of increased boredom, burnout, and risk of repetitive stress/motion injury; see below).
• There is no place in the takt system for removal of a product from the assembly line at any point before completion, so opportunities for shrink and damage in transit are minimized.

Downsides of takt time organization include:

• When customer demand rises so much that takt time has to come down, quite a few tasks have to be either reorganized to take even less time to fit into the shorter takt time, or they have to be split up between two stations (which means another station has to be squeezed into the line and workers have to adapt to the new setup)
• When one station in the line breaks down for whatever reason the whole line comes to a grinding halt, unless there are buffer capacities for preceding stations to get rid of their products and following stations to feed from. A built-in buffer of three to five percent downtime allows needed adjustments or recovery from failures.
• Short takt time can put considerable stress on the "moving parts" of a production system or subsystem. In automated systems/subsystems, increased mechanical stress increases the likelihood of breakdown, and in non-automated systems/subsystems, personnel face both increased physical stress, which increases the risk of repetitive motion (also "stress or "strain") injury), and intensified emotional stress, and lowering motivation, sometimes to the point of increasing absenteeism.
• Tasks have to be leveled to make sure tasks don't bulk in front of certain stations due to peaks in workload. This decreases the flexibility of the system as a whole.

References

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See also

• Lean manufacturing
• Toyota Production System
• Muri

External links

• Lean Manufacturing site about Takt time
• Six Sigma site about Takt time
• Takt Time Simulator On Line
• On Line business processes simulator

Further reading

• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
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• Ohno, Taiichi, Toyota Production System: Beyond Large-Scale Production, Productivity Press (1988). ISBN 0-915299-14-3
• Baudin, Michel, Lean Assembly: The Nuts and Bolts of Making Assembly Operations Flow, Productivity Press (2002). ISBN 1-56327-263-6
• Ortiz, Chris A., Kaizen Assembly: Designing, Constructing, and Managing a Lean Assembly Line, CRC Press. ISBN 978-0-8493-7187-5