Toyota's JIT Revolution

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JIT in Toyota Contd...

In the traditional forecast oriented method, parts were 'pushed' to the line (Refer Exhibit III for a comparison of the Kanban philosophy with the western philosophy). At Toyota, two types of Kanban cards were used: one, to move parts from one place to another, known as the Conveyance Kanban card, and the other, to authorize the production of parts, known as the Production Kanban card. (Refer Figure I). A standard size container was used to store parts and each card was treated like a coupon. (Refer Box). Suppose a container of item X is required in work centre A. As a first step, a production Kanban card is issued to work centre A. The work centre withdraws a container of raw materials from its inventory. The container of raw materials also included a conveyance Kanban card. Work centre A removes the conveyance Kanban card from the container and sends it to the proceeding work centre where it serves as an authorization to pick up a container of raw materials.

Three types of information were exchanged using Kanban. Pick up information guided the earlier stages regarding parts to be produced for the succeeding stages. Transfer information indicated when the parts had to be produced for the succeeding stages. Production information was transmitted from the earlier stages to the later stages to inform the workers about the product mix and other operational matters.

To make the Kanban system effective and reap maximum benefits (Refer Table II) from it, Ohno framed six rules:
• Later process went to the earlier process to pick up products.
• The earlier process produced only the amount withdrawn by the later process.
• Should not pick or produce goods without a Kanban.
• A Kanban should be attached to the goods.
• 100% defect free parts were required.
• Reduce the number of Kanbans.

Table II
Advantages of Kanban

Source: ICMR

The Kanban cards were re-circulated and the number of cards controlled work-in-progress (WIP) in the system. In this way, the activities of final assembly were linked to previous operations by a chain system of card ordering that 'pulled' production through the factory.

Another important component of JIT was Heijunka (production smoothing). JIT's principle of building only the required number of items helped keep the production costs low. Heijunka helped in the accomplishment of this principle by creating a consistent production volume. Heijunka averaged the highest and lowest variations of the orders. The variations were then removed from the production schedule. This ensured that the right quantity of parts was produced with minimum workforce. Heijunka took care not only of the total volume of items but also the type of items produced and the other options.

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