“Takt time”的意思、由来-开放百科全书

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Takt time

释义

Etymology
Definition
Implementation
See also
References
External links
Further reading

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Takt time is the average time between the start of production of one unit and the start of production of the next unit, when these production starts are set to match the rate of customer demand. For example, if a customer wants 10 units per week, then, given a 40-hour work week and steady flow through the production line, the average time between production starts should be 4 hours (actually less than that in order to account for things like machine downtime and scheduled paid employee breaks), yielding 10 units produced per week. In fact, takt time simply reflects the rate of production needed to match the demand. In the previous example, whether it takes 4 minutes or 4 years to produce the product, the takt time is based on customer demand. If a process or a production line are unable to produce at takt time, either demand leveling, additional resources, or process re-engineering is needed to correct the issue.

Etymology

Takt time is a borrowing of the Japanese word {{transl|ja|takutotaimu}} ({{Lang|ja|タクトタイム}}), which in turn was borrowed from the German word {{Lang|de|Taktzeit}}, meaning clock interval. The word was likely introduced to Japan by German engineers in the 1930s.^[1]

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:

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

In reality, people and machines cannot maintain 100% efficiency and there will be stoppages for other reasons. Allowances should be made for these instances, and thus the line will 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 performs 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.
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.^[2]
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), intensified emotional stress, and lowered motivation, sometimes to the point of increased 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.
The concept of takt time doesn’t account for human factors such as an operator needing an unexpected bathroom break or a brief rest period between units (especially for processes involving significant physical labor). In practice, this means that the production processes must be realistically capable of operation above peak takt and demand must be leveled in order to avoid wasted line capacity

References

1. ^{{cite web|url=https://ocw.mit.edu/courses/engineering-systems-division/esd-60-lean-six-sigma-processes-summer-2004/lecture-notes/8_1assembly_op.pdf|title=Takt Time|last1=Graban|first1=Mark|last2=Ducharme|first2=Colin|last3=Ruddick|first3=Todd}}
2. ^{{cite book |title=The Kaizen Blitz: accelerating breakthroughs in productivity and performance |last=Laraia|first=Anthony C. |author2=Patricia E. Moody |author3=Robert W. Hall |publisher=John Wiley and Sons |location=New York |year=1999 |isbn=978-0-471-24648-0}}{{Page needed|date=October 2010}}

External links

Lean Manufacturing site about Takt time
Six Sigma site about Takt time
Takt Time Simulator On Line
On Line business processes simulator
Takt Time - a vision for Lean Manufacturing

Etymology

Definition

Implementation

See also

References

External links

Further reading