Kanban

Inventories, while lacking value-added generation for organizations, allow one or another to provide availability of the goods and services provided by them, as well as to ensure the continuity of the processes that perform them.

In this order of ideas, one of the main objectives, in terms of production control, would be to align inventories and product flow according to demand behavior.

Precisely, according to these objectives, Kanban emerges as a material control and production tool.

What is Kanban?

Kanban is a Japanese-origin word meaning card, its concept has evolved into a signal, and can be defined as a flow system that allows, through the use of signals, the mobilization of units through a production line through a pull strategy or pulling strategy.

And what is a pull system?

A pull flow system is to optimize inventories and product flow according to the actual demand behavior.

In these systems the logistics process begins with the customer’s order, and although it is the ideal system for inventory optimization, the commitment to know the demand in real time and make the chain more flexible to meet their needs is a complex bet. However, like most cutting-edge logistics practices, a large number of success stories are based on the application of a pull flow system.

Similarly, the pull flow system is applied to the production line, in which case study, customers are previous processes (internal customers), and the tool par excellence that allows to know the demand in real time and make the production line more flexible is Kanban.

So, we can conclude that Kanban pulls inventory through work centers, using cards to signal the need for another material container. Or put another way, the card is the authorization for the next production batch to occur.

Kanban Types

According to the Kanban model used by Toyota, there are basically two types of Kanban cards, these are:

  • Withdrawal kanban.
  • Production kanban.

WITHDRAWAL KANBAN

A kanban or withdrawal card specifies the reference and quantity of product that a process must withdraw from the immediately preceding process, or from its product container (small cross-process regulatory warehouses).

PRODUCTION KANBAN

A kanban or production card specifies the reference and quantity of product that a process should produce.

The operation of the Kanban system is relatively simple. Taking into account Toyota’s original model, the input system consists of a board on which we deposit the cards (signals), the board is positioned so that the operator can easily see it from its normal or usual position. Each card is associated with a container or storage unit. In case the container is empty, the card must be on the board, if otherwise full, the card must accompany the container.

So, in case the board is full of cards, it means that there are no parts left in inventory and it is important to produce units (red area of the board). If the cards are in the yellow or green area of the dashboard, it means that units are left in inventory and that it is probably not necessary to produce.

So if the vendor process starts production, take the card from the board and place it in the container where you will deposit the units corresponding to the batch. 

Once finished, it places the container in the buffer.

The client process then starts consuming the parts deposited in the buffer; Once you consume all the units in the container, you will place the card that accompanies it, on the card board, and return the container completely empty.

It should be considered that the number of cards and containers between processes are not arbitrarily defined, but are determined by the parameters of the production system, which we will address later.

To adopt kanban, production must be considered to be leveled and mixed, so that the same volumes must almost always be manufactured. This system does not allow variability of more than 15%-20% without changing the signalling parameters. In the production lines it is manufactured with a mix of products, so that different color ranges can be used by reference on the same board, so the operator will know which reference to manufacture at any time.

Advantages of using Kanban

  • Level demand with production flow: Attacks two wastes overproduction and excess inventories.
  • Improves the level of service in relation to customer compliance (internal and external).
  • Supports production planning activities.

When should Kanban be used?

Basically, Kanban should be used:

  • In production systems that have high mix of references.
  • When Lean Manufacturing is being implemented and a previous work of 5’s and SMED has been done.
  • When aiming to achieve small batches of size.
  • When you have high product inventory costs in process.

How long does it take to deploy Kanban?

The implementation of Kanban can be developed through a Kaizen event, so that it is developed by a multidisciplinary team with the active participation of production staff.

It can take between one and three months to deploy Kanban.

How to implement Kanban?

According to the implementation of the Kanban model in Toyota, the procedure for implementing Kanban is systematic and includes the following steps, in which the parameters of the production system are defined to adopt the tool:

  1. Select the references to be produced using Kanban.
  2. Calculate the number of parts per kanban (lot size).
  3. Choose the standard signal type and container type. The container may vary by reference.
  4. Calculate the number of containers per reference (production curve) and pitch sequence.
  5. Follow up (WIP or SWIP).

SELECT REFERENCES

References should be chosen according to existing product families, and it is recommended to use groups in which there is prior improvement work, such as SMED, manufacturing cells or line balances.

CALCULATE THE NUMBER OF PIECES PER KANBAN

To determine the number of parts per kanban, also known as Total Required Inventory (ITR), the following formula is applied:

Parts per Kanban (ITR) – D x TE x U x %VD

Where 

D – Demand by time horizon (e.g. and usually weeks).

TE – Delivery time in the same units of the demand horizon.

U – Number of locations (intermediate warehouses).

%VD – Demand variation level. It is obtained by the standard deviation of demand over the average demand.

For example:

You want to implement kanban between processes A and B of a production system. The material requirements of process B in the last year are as follows:

The first step is to determine the weekly demand for process B, for this we go to the average of the last year:

Monthly Average – 1542 pieces

Weekly Average (1542 x 12 months) / 52 weeks – 356 pieces per week

Demand 356 pieces a week

The second step is to determine the delivery time (TE) of the weekly demand, i.e. the 356 pieces. To do this we must consider the processing, inspection, reception, enlistment times. Let’s assume that the TE of 356 pieces is equivalent to 1 week.

Delivery time – 1 week

The third step is to determine the number of locations in the product warehouses in process, when the deployment is starting it is common to use two locations, until you reduce it to a single location. Let’s assume that a single location will be used.

Locations 1

The fourth step is to determine the variation of demand, for this we first calculate the standard deviation of demand and then divide it by the average:

%VD x 1 + (266 / 1542) – 1,1725

Now we can determine the number of parts per Kanban, or the Total Inventory Required (ITR) using the initial formula:

Parts per Kanban (ITR) x 356 x 1 x 1 x 1,1725

Parts per Kanban (ITR) – 417.4 x 418

CHOOSE THE TYPE OF SIGNAL AND THE TYPE OF STANDARD CONTAINER

There are a number of factors to consider when selecting the container for each reference, some of which are:

  • Size of the units.
  • Weight of the full container.
  • Operator load capacity.
  • Maintenance equipment available.
  • Space available.
  • Container ergonomics.

CALCULATE THE NUMBER OF CONTAINERS

The formula for determining the number of containers is very simple, for this you need to know the capacity of the containers:

Number of Containers (Total Inventory Required / Container Capacity)

For example purposes that we have been handling, suppose the container size is 20 pieces, so then:

Number of contenders (418 / 20)

Number of containers – 21

FOLLOW-UP TO WIP VS. SWIP

WIP – Product inventory in process, i.e. total inventory in the cell.

SWIP – Standard cell inventory.

WIP to SWIP – WIP / SWIP

The ideal result is equivalent to 1, i.e. the WIP is equal to SWIP.

In cases where it is greater than 1, it means that there is a lot of inventory in the cell, in case it is less than 1, it means that there is a risk that the cell will become unsused with materials. 

Kanban Principles

1. No non-compliant products are passed to the following process.

2. A kanban is removed when a process removes units from the immediately preceding process.

3. The kanban is a production order for vendor processes.

4. Nothing occurs or nothing is transported without kanban.

5. The number of kanbans should decrease over time.

1. No non-compliant products are passed to the following process.

2. A kanban is removed when a process removes units from the immediately preceding process.

3. The kanban is a production order for vendor processes.

4. Nothing occurs or nothing is transported without kanban.

5. The number of kanbans should decrease over time.

While many specialists agree that Kanban is more of a visual programming system, the truth is that Kanban is not a system where everything is put into a schedule. It is worth considering that Kanban is a production control system designed to allow the process manager to visualize production requirements in a flexible and fast manner, while ensuring that all parts or supplies are ordered or produced only if necessary

Kanban
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