Kanban, one of the primary Lean tools, is an inventory management system that relies on real-world inventory consumption (demand) to trigger replenishment signals (supply). Click here to read more about kanban.
A kanban board manages kanban cards that are waiting for an order of replenishment parts. Click here to read about kanban cards.
Carefully design your kanban boards
A kanban board has about 3 dozen pegs, hooks, or other ways to hold kanban cards.
- 31 pegs labeled 1 to 31, for the 31 dates that can occur in a month
- Additional pegs for other circumstances
- “Stock out” – cards that have zero on-hand inventory, even if a supplier order is not late
- “Past due” – cards that were due prior to today
- Items that are out of stock should be on the “Stock out” peg
- “Next Month” – cards that are due in more than one month
- “2+ months out” – cards due in more than two months, if lead times approach 8 weeks or more
- “Waiting to be scanned” – this is only required if cards are not scanned at the board
In keeping with kanban’s mission to be a visual system, kanban boards are located where the cards live, and cards live where items are used, at point of use.
- Boards should be easy to access, easy to reach, and in good lighting
- If possible, process kanban cards at the board (i.e., put a scanner there) so they don’t leave the area
- Kanban boards are “sized” to handle the number of cards expected to be hanging at any given time. Break-a-bin cards spend a large portion of their life on the kanban board, while empty-a-bin cards spend more time on the shelf. Click here to read about trigger timing.
- For EaB items
- For 2-card solutions, expect about half of the cards to be on the board
- For multi-card solutions, expect all but 1 or 2 cards to be on the board, unless the item has a really high card count
- For 1-card solutions, the card will be randomly on the board based on each item’s characteristics
- For BaB items
- For 2-card solutions, expect both cards to be on the board a good percentage of the time
- For multi-card solutions, expect all but 1 card to be on the board
- For 1-card solutions, the cards will be randomly on the board, as described above
- For EaB items
Board count & location
In order to know how many boards we need and where tey should be placed, weneed to estimate how many cards a particular board needs, versus how many it can physically hold.
- 31 date pegs equates to ~22 workdays and 9 weekends, so 22 pegs hold all the cards for a 5-day workweek cell.
- Adjust the number of “active” pegs if the cell works more than 5 days per week.
- Determine how many cards fit on one peg. Don’t overload the pegs! Please minimize the risk that cards will fall off.
- Calculate how many cards belong to this board’s span of control, which is the sum of card count for all kanban items assigned to this board.
- Estimate how many cards could be on the board at one time, based on card count and break-a-bin or empty-a-bin trigger timing.
- Divide the number expected cards on the board by 22 pegs to see if the count per peg is less than how many can fit on a peg.
Kanban board process
- When a kanban card is scanned or processed, the due date for the new order is determined by [today’s date + standard lead time in workdays], skipping any holidays (“H”) during that period. Write the due date in some kind of erasable marker on the back of the card, so that date is available when the kanban board is audited.
HINT: Lead times are always in workdays. Why? Think about an order that is placed on a Thursday. If the plant works 5 days per week, a 3-day lead time that is processed on Thursday is due on Tuesday because three days from Thursday is [Friday-Monday-Tuesday]. If we use calendar days instead of workdays, an item with a 3-day lead time that is processed on Thursday is due Sunday [Friday-Saturday-Sunday], but Sunday is not a work day for many plants. Therefore, putting lead times in calendar days only works if 1) the site works 7 days per week and so do all external suppliers, or 2) every lead time is an even number of weeks. Since these conditions are rarely true (I’ve never seen it), lead times must be in workdays.
- Each of the numbered pegs from 1 to 31 stands for a date. Place the card on the board based on its calculated due date.
- If today is May 5thand card is due on the 12th, the “12” peg on the kanban board stands for May 12th so we hang it on the 12 peg.
- If today is May 5thand the card is due June 1st, hang it on the “1” peg.
- If today is May 5thand the card is due on June 14th but “14” stands for May 14 so it goes on the “Next Month” peg.
- For really long lead times, there is a peg for due dates that are farther out than one month. If today is May 5thand the card is due on July 12th, the “12” peg is May so one month out is June and July is 2 months out – hang it on “2+ months out.”
- The kanban board is updated at the beginning of every workday. The “Today” marker is moved to today’s date and cards that were due yesterday that did not arrive are moved to the “Past Due” peg.
- Throughout the workday, the board is kept in sync with card activities. Items that drop to zero are moved from the numbered peg to the “Stock Out” peg. Cards that are processed to place a new order are hung on the appropriate peg, as described above.
HINT: Cards on the pegs labeled Past due, Stock Out, or To Be Scanned are acted on at least twice per shift. Cards never wait more than 4 hours!
- Instruct external and internal suppliers to put the due date on the packaging for the order, so the associated card can be quickly located on the board Match the correct card to incoming parts and put both in the correct storage location.