Useful Tips

Tact time


Tact time - the entire time of production (for example, one shift), divided by the speed at which the consumer requires the receipt of goods. Suppose that if a consumer wants to receive 240 gizmos every day, and the plant operates 480 minutes a day (that is, one shift), then the tact time is two minutes. If the consumer wants the company to develop two products a month for him, then the tact time is two weeks. Tact time sets the speed of production, which must exactly match the current demand. The tact time in production is similar to the frequency of beats of a human heart.

Cycle time is the time required to complete one operational cycle. When the cycle time of each operation in the process becomes exactly equal to the tact time, a flow of single products occurs.

Line / operation balancing - integrating the principle of cycle time into standard operations of a production line in order to achieve maximum efficiency. Aligning the time of all operations within the same line or process.

Basic rules of balancing:

Rebalanced operations should not be loaded exactly at the tact time (VT = Tm), there should always be a small reserve of 5-10%, depending on the stability of the process in case of unforeseen problems and to avoid overloading workers.

First, it is necessary to get rid of those actions that do not create value. Any actions that can be discarded immediately (rearrange the table or rack and get rid of movements, replace the tool and reduce the time of any action, etc.) should be excluded before the balancing itself begins.

The movement of work (operations) between operators should begin from the beginning of the technological chain, that is, first, under the cycle time, it is necessary to load the very first operator, passing the work of the second one to it (or vice versa to unload). Further, after the first operator is loaded, and its loading is confirmed, it is necessary to proceed to the second, loading it under the tact time by transferring operations from the third operator, etc. The movement during balancing should always be carried out from the beginning of the technological chain, and the redistributed operations must be confirmed by trial runs, i.e. monitoring the performance of the new sequence in practice and solving problems.

The transfer of individual actions is carried out between adjacent operations, and the resulting time reserve (if any) should remain on the last operation (closest to the Customer) to give greater maneuverability in solving problems. The transfer of individual actions is carried out, as a rule, from related operations (operators) in accordance with technology, safety regulations, etc.

You can calculate the required number of staff rounding up.

Despite its simplicity, it is sometimes impossible to rebalance or completely balance the loading of all operations for the cycle time, which may be due to limitations of technology, equipment, etc. In any situation, you can find a logical rational solution. For example, if the cycle time of a certain operation obviously exceeds the estimated tact time, this “bottleneck” can be eliminated by allocating two workers to perform one operation. If two workers perform one operation in parallel, respectively, and the rhythm of work is maintained, it is only necessary to ensure that the loading of these workers remains aligned with the working time of the beat. But this is an extreme and not desirable solution from the point of view of lean, because instead of motivating managers to solve problems, such methods discourage them, on the contrary, encouraging problem solving only by attracting additional resources.

Examples. Determine the beat time in minutes

1) Given: Demand - 960 ed. per month. Month - September 2011 (September 1, the plant does not work). The working week is 5 days. The working day is 8 hours. TTm =10 min.

Determine the beat time in minutes.

Solution: The number of working days in September on the calendar is 21.

Number of working minutes: 21x8x60 = 10080min.

Define the beat time: TT= 10080: 960 = 10.5min.>TTm= 10min

2) Given: Demand - 1200 ed. per month. Month - October 2011 The working week is 4 days. The working day is 8 hours. TTm =10 min.

Determine the beat time in minutes.

Solution: The number of working days in October on the calendar is 17.

Number of working minutes: 17x8x60 = 8160min.

Define the beat time: TT= 8160: 1200 = 6.8 min.

The tact time should be clearly consistent with the level of demand, as it is demand that sets the speed or rhythm of the entire company.

Indeed, the work of all divisions of the company should be aimed at ensuring the fulfillment of the cycle time of the assembly site or conveyor, which means that parts and assemblies for assembly should be delivered on the basis of the “exactly on time” principle.

Lean manufacturing requires that between operations or types of work with an “on-time” system:

- queues were not formed, i.e. waiting for processed parts to wait for them to be processed in the next operation,

- no interoperational reserves were created (just in case) in order to ensure the subsequent operation in case of any failure in the previous operation.
A continuous flow system will work on an “exactly on time” principle if every employee and every mechanism (machine) is absolutely reliable. They should be ready:

- start work at any time,

- do the job right the first time,

- get the right product the first time.
The system is designed so that it can only be in two states: “everything works” or “nothing works”.

In order to achieve this it is necessary:

- so that people in the production team are true professionals in several areas and can replace each other,

- the equipment must always be maintained in a fully operational state,

- all work in the areas should be standardized (moreover, the work team itself should standardize the work, since only she knows how best to do this work),

- all workers (operators) should be trained in how to monitor the work of machines (machine tools) and control their work in terms of quality of execution,

- everywhere, “bye-yok” methods should be developed that do not allow the transfer of low-quality products to the next operation or stage of production,

- 5S principles should be implemented at all workplaces,

- "transparency" of the flow should be ensured, while each participant in the process should:

o see what happens

o understand all aspects of the process,

o be able to assess the state of the process at any time.
To do this, it is necessary to use means of visual control of the production process: stands, electronic displays or Andon boards (in Japanese).

The “just in time” system works well with relatively small fluctuations in demand from face value. However, even with these fluctuations in demand, it must be borne in mind that the change in tact time TT on the conveyor, depending on demand, leads to a change in the rhythm of the entire company. Changes in demand should immediately affect all production processes, i.e. there should be an adjustment TT throughout the value chain.

Consider the case when several products of the same type are manufactured in a stream. Although the products are of the same type, they are somewhat different from one another, therefore, in their manufacture it is necessary to re-equip equipment, for example, punching and molding presses.

Example: there are products: A, B, C and D, per month they need to be made 20,000 pieces. (A-8000, B-6000, S-4000, D-2000), in the month of 20 work shifts, work is carried out in 2 shifts. Each day it is required to produce the following number of products: A-400, B-300, S-200 and D-100. Since the products need to be made daily, then every day it will be necessary to readjust the press 4 times. One changeover is required - 22min. In this case:

TT = (2x8x60 - 22x4): (400 + 300 + 200 + 100) = 0.87min.

Consider how the pulling process is carried out:

The operation of the entire stream is initiated by the assembly section, since he gets a product release schedule. For example, product A is on the assembly, as soon as product A ends on the assembly, the trolley on which the product A was delivered from the welding section returns to the welding section with a kanban card and the welding section proceeds to manufacture article A in the quantity indicated on the card Kanban This is the only signal (command) to start work on the welding site.

In turn, the welding section takes the workpieces from the container, which was delivered from the forming section, as soon as the workpieces in the container end from the forming section, this container with the kanban card is sent to the forming section. This is a signal to start work on the molding area. And so on. (We will consider work on the Kanban system in more detail later.)

The “just in time” system with respect to traditional planning works as if from “bottom to top”, namely: each operation upstream of the assembly starts working only when it receives a command from a downstream operation.

In this case, production should work on the principle of:

“Do not do anything until it is required; when it is required, do it very quickly!”

Those who were in Japanese factories that introduced the Kanban system note its simplicity and effectiveness - no one is in a hurry, but everything is done on time. There are no stocks of materials and components, however, the required amount of materials and components is always at hand, replenishment occurs as they are used up, all suppliers respond promptly to replenishment requirements. The Kanban system brings huge benefits.

Trying to introduce the kanban system at home, they often encounter enormous difficulties, which is connected with the peculiarities of their enterprises, the mentality of workers, the peculiarities of the work of suppliers, the nomenclature of products, etc.

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1 How did the term “Tact Time” originate?

Initially, the word “measure” in German meant “size” or “rhythm” and was used in music. In the 30s of the last century in the German aviation industry, tact time began to denote the period of time after which the aircraft moved from one production stage to another.

In the United States, a tact time appeared a decade later, along with the assembly line production of aircraft at the Ford Motor Co. assembly line in Willow Run, USA.

At Toyota, the concept of tact time has been used since the 50s of the last century.

2 Calculation of the cycle time

In the organization, for each process of manufacturing a product or providing a service, the tact time should be calculated. The tact time is calculated by the formula:

[math] T_ <такт>= frac<><дост>>[/ math] where [math] T_<такт>[/ math] - tact time,
[math] T_<дост>[/ math] - available production time for a certain period (for example, shift, day, month, etc.),
[math] V [/ math] - the volume of consumer demand for this period.

2.1 Examples

The shift duration is 8 hours. During the shift, 4 breaks of 10 minutes are provided. In this case, the production time will be equal to the duration of the shift minus the duration of the breaks = 8 hours for 60 minutes minus 4 breaks for 10 minutes = 440 minutes or 26400 seconds.

The demand for products per month is 10560 pieces. There are 20 business days in a month. In this case, the demand in units per day will be: 10560 divided by 20, we get 528 units per day.

Now we can calculate the beat time. We divide the production time into demand during the day, divide 26400 seconds by 528 pieces - we get 50 seconds.

This means that every 50 seconds one unit of production must move on to the next stage of production. Or that every 50 seconds we must ship one unit of production to our customers. If we are talking about the service sector, this means that every 50 seconds another client receives our service.

3 What is the tact time used for?

The cycle time is always used with the cycle time, the value that is measured. Based on these two quantities, two very important questions can be answered.

First, is the production process productive enough to meet consumer demand? Or, in other words, does our production manage to fulfill all the orders that come from our customers.

Also, with the help of tact time, the following question can be answered: can our production process provide increased demand during the peak period?

In addition, using the tact time, you can answer the following questions:

  • What size should the batch be in order for the process to meet demand with the existing readjustment time?
  • What productivity should each production cell or each production site work with?