Difference between production order and KANBAN of planned production

計画生産の製造指図とかんばんの違い

Production Control


The kanban when a customer said “Our production runs on kanban”.

When we visit Japanese trading companies and manufacturers in Indonesia and ask them about their business requirements for system implementation, most of them tell us that they receive “Kanban” from the customer every morning, which corresponds to the delivery instructions for sub-payment of fixed orders received at the beginning of the month.

Ideally, the supply chain between the customer, the company, and the supplier would work in tandem with each other by placing monthly orders for products and materials with the supplier, and then having the customer divide the incoming goods and materials according to the movement of the kanban.

The Kanban, which appears in the order and supply system of trading companies, is issued to each box when the order is received and paid for, as shown below.

  1. The Kanban arrived from the customer.
  2. Request for delivery of Kanban to a supplier.
  3. After digesting the kanban from the customer for the current month, we close the order and purchase orders.

On the other hand, the in-process Kanban, which has appeared in the manufacturing industry, is issued to each box for pickup and processing as shown below.

  1. Stuck in the shipping area due to misalignment
  2. It is returned to the processing area and stays in the processing area.
  3. When the processing point is reached, processing begins and the box is inserted.
  4. Back to #2.

The role of the in-process kanban may be divided into the pickup kanban (moving results), which moves around the site, and the in-process kanban (production results), which serves as production instructions.

  1. Staying in the shipping area due to stoppages in shipping (pickup kanban)
  2. Returned to the processing area (collection kanban), box picked up (collection kanban), held in the processing area (in-process kanban)
  3. When the processing point is reached, the processing starts and it is inserted into the box.
  4. Back to #2.

Whether to issue manufacturing instructions by MRP or to calculate the number of sheets

Both manufacturing instructions and kanban are based on the actual requirements, which are the result of MRP passed around by the Production Control Department based on the unofficial information, while manufacturing instructions are the realization of the production plan into a work unit (push method), while kanban method is the realization of the work unit as a result of the post-facto results because the post-process took over from the previous process only the portion used at the manufacturing site (pull method).

  • Total number of manufacturing index = actual – current status in stock + safety in stock
  • Number of kanban x box capacity = Number of processing + Number of required number per day x (kanban L/T + processing L/T + days of safety stock)

かんばん枚数The total manufacturing order quantity is the net requirements minus the current inventory from the actual requirements plus the safety stock. The total manufacturing order quantity is the result of multiplying the required number per day (kanban L/T + processing L/T + safety stock days) by the actual requirements divided by the operating days and adding the number of processing (processing lot).

The kanban flowing through the factory will stay in the following three places.

  1. Accumulated in the shipping area (Kanban L/T)
    Idle period until the canister comes off for shipping and returns to the site.
  2. Accumulation until the machining point is reached in the field (machining L/T)
    Period of time until the kanban next to the site reaches the machining point + period of time when the machining lot should be completed
  3. Plugged into an inventory lot on site or in a warehouse (safety stock)
    This is an inventory level for N days that must not be cut, and if safety stock = 0, it is the best condition to be able to operate with “no inventory without delays in delivery”.

Therefore, the theoretical monthly number of Kanban can be calculated as follows

  • Valuable
    A = Quantity of processing to be produced at one time (separate calculation required)
    B=Number required per day
    x = Number of days with safety in stock
    y = KANBAN lead time days
    z = Processing lead time days
    p = number of units
  • monthly number of KANBAN
    Roundup[{A + B x (x + y + z)} / p]

The number of days of shifts in manufacturing instructions should theoretically be the same as the number of days of Kanban calculation (days of safety stock + days of Kanban lead time + days of processing lead time).

Influence of Date Shift on Requirements Expansion and Load Calculation

The total requirements calculated by requirements expansion is the same whether MRP is executed with the date of the end of the month as the delivery date or with the date of the month as the delivery date without shifting the date of the monthly notice data received from the customer.

MRP

If the load calculation is done with the last day of the month as the delivery date, the load is calculated against the line capacity on the last day of the month, but if you look at it on a monthly basis, you can see the load against the total operating days of the month, which is the same as the total load calculated on a day-over-day basis.

However, if the load is calculated based on weekly unofficial notice, the load will be under-loaded in the first week of the month by the amount covered by the previous month, and the load will be over-loaded in the last week of the month by the amount covered by the next month, so the load calculated based on weekly unofficial notice will not be the monthly load by simply adding up the load.

Kanban method and leveling

The kanban system is designed to meet the demand for only the required quantity of what is needed, and it works well for processes that can handle small lots, such as assembly and welding. However, in order to apply kanban to processes that require lot production, such as forming and pressing, the intermediate inventory must be accumulated and consumed, and when it falls below a certain level, production requests must be made using signal kanban.

The following four conditions are necessary for the Kanban system to work

  1. Always produce the same number of products in the previous process as the next process takes back.
  2. Yield and variety leveling
  3. 100% good products
  4. The kanban works with the actual product.

A person in the next process returns the take-back kanban in units of a certain number of sheets (the number of sheets calculated by leveling) and leaves the work-in-process kanban behind, but in order to be able to cover this stably, it is necessary to have a system that can always produce the necessary items at the necessary time and in the necessary amount in any process.

In order to do so, it is necessary to eliminate the variation in production volume and the variation in the type of products, and if we produce 100 units today and 1 unit tomorrow, there will be a lot of waste in maintaining the production system (production preparation) and costs will be high.

This is the reason why the Kanban system is based on the assumption of levelized production.

Leveling and one-piece flow

This is contrasted with lot production, in which various types of products are evenly distributed and produced together, and the following are possible ways to achieve this.

  1. Single setup (external setup of internal setups and standardization of setups) shortens setup changeover time (mold change within 10 minutes).
  2. Multi-tasking (utility players who can handle multiple positions)
  3. The line is a mix of different types of products (mixed flow production)

Therefore, if the leveling is pursued, one piece will inevitably flow.

Kanban method and scheduler

MRP (Material Requirement Planning) is a push type in which production instructions are sent from the Production Planning and Inventory Control (PPIC) to each process at the same time, while the Kanban method is called the pull method because the necessary quantity of production instructions are sent from the final process to the front process based on the required quantity (Kanban) from the back process on the basis of levelized production.

At plants that use the Toyota Production System, the pick-up and delivery kanban is operated in the order of the back-end process to the front-end process, triggered by the e kanban from the customer.

In a factory where this type of kanban post-production has been established, the production scheduler will issue a daily production plan and hand it over to the factory floor and say, “Please manufacture the items on the list according to the lot”, but the operators who are fully accustomed to post-production will react with rejection and will not be able to respond.

The basic requirements of the kanban system to produce only the required amount of the necessary items are met in the back-end processes such as assembly and welding, where small-lot production is possible, and it is impossible to meet the demands of the back-end processes to produce only the required amount of the necessary items due to the high set-up load.

Therefore even in a factory where the production floor is running using the kanban method it is possible to introduce a scheduler for the front-end processes that cannot deal with postponement in detail and choose to control the intermediate inventory.