Are There More Options Than Just Kanban Cards?
Luckily, the answer to the above question is a resounding yes. The kanban signal can be anything that makes sense to your production operation and conveys a clear replenishment signal. As with the kanban cards, always put the signal in the path of the material flow and have a plan for getting the scheduling signals back to the production operations. Some of the more common methods (and variations of these options) are discussed below to give you ideas for your own implementation:
Faxbans (or e- mails )
These options and their variations are by no means the only options available. When looking at possible designs, open yourself and your team to all possibilities. Be creative ”invent new options of your own or springboard off of our suggestions to create your own variation. (By the way ”send us a picture and description of any new ones you create or any new variations of our suggestions. We also want to keep expanding our knowledge.)
Whenever possible, your kanban signal should rely on the most reliable sensor ”your eyes. This form of kanban signal, called a "look-see," consists of visual signals such as floor markings or signs that tell you at a glance when to replenish the item. The basic rule with a look-see signal is that if you can see the yellow signal, then it's time to replenish the item. The red, or danger, signal is also integrated into this scheme. Look-see signals greatly aid in the implementation of the kanban supermarkets discussed in Appendix B. Figure 5-5 shows an example of a look-see scheduling signal.
Figure 5-5: Look-See Scheduling Signal.
A special case of the look-see signal is the use of containers as the signal. The container is specifically marked to show the part number and the production quantity. When the container returns to the production process, it goes back into the queue. When you have accumulated a certain quantity of containers, this constitutes the yellow scheduling signal. The production operator will know what and how much to put into the container based on the information or standards set for the specific part number. Figure 5-6 shows a container used as a kanban signal.
Figure 5-6: Container Used as a Kanban Signal.
Under very limited conditions, you can also set up a look-see kanban using warehouse racks. The racks can be painted or numbered to correspond to provide look-see signal. However, unless visibility can be maintained , this option can be tough to manage in a quick scan mode due to the typical size of racks. Forget this option if you are trying to cover several rows of racks or have conditions that hinder seeing the top rows. Instead, consider the card option discussed in the next section.
Another special case of the look-see signal is flow lanes. The flow lanes offer visual management of production material while managing stock rotation at the same time. Flow lanes are essentially aisles that the product travels down toward the production process. The product enters the flow lane from the back and moves forward in its lane. You will interpret the schedule signals just like any other look-see kanban.
The lanes, while very visual, can be hard to keep straight if you make them too long. This problem can be avoided by putting guides in the aisles (as shown in Figure 5-7) or using flow racks (as shown in Figure 5-8).
Figure 5-7: Flow Lanes with Guides to Control Movement of Containers.
Figure 5-8: Flow Racks Allow the Containers to Move Forward with Use of Gravity.
The guides are typically angle iron strips , sheet metal frames , or rails that have been attached to the floor. The guides allow the containers to move only in the specified direction.
The flow racks (or angled roller conveyors) use gravity to move the containers forward as the previous container is removed from the flow lane. The roller conveyor is readily available and can be found in most material handling or industrial sales catalogs. However, as the flow racks get longer and the containers get wider and heavier (such as pallet size), then the price tag for the flow racks can get very big.
If floor storage space is in short supply, flow racks can be purchased as stacked rows. This option will require you to answer a number of questions about container size and weight. Therefore, if stacked flow racks have appeal , contact a material handling specialist for assistance.
One other item to consider when setting up your flow lanes is to be sensitive to the number of rows from which product can be pulled. You may defeat the stock rotation benefit if you allow too many choices, as for example if the operators withdraw the containers closest to their operation, leaving the material staged further away to age. There is no stock answer for this, but use common sense and talk with your operators.
The kanban boards are a variation on the kanban cards. Instead of the cards, the board simply utilizes magnets, plastic chips, colored washers , etc. as the signal. The objects represent the items in inventory. However, instead of chasing cards around the building, you are moving the objects around on a board. The movement of the objects corresponds to the production and consumption of full containers of product. The process works like this:
As a container of product is completed and moved into inventory, an object gets moved into the inventory section of the board.
When the container is consumed or moved to a staging area for consumption, then an object gets moved into the awaiting production section of the board.
To determine what gets produced next, you look at the board and follow the rules.
Figure 5-9 graphically shows an example of the movement of objects on a kanban board. Notice how only the bottom of the board contains the red, yellow, and green signals? This allows for only one scheduling signal ”even though the number of colored cells in the top and bottom sections is equal. Figure 5-10 shows a picture of a kanban board that uses magnetic pieces for scheduling signals.
Figure 5-9: Kanban Board Set-Up and Operation.
Figure 5-10: Kanban Using a Magnetic Board for Scheduling Signals.
The pieces used to the show board status and product movement are not limited to magnets. In fact, kanban boards using chips, washers, etc. can actually simplify movements on the board. The simplification comes from collapsing the "awaiting production" area of the board, as shown in Figure 5-11.
Figure 5-11: Kanban Using Plastic Chips.
Kanban boards work best when two conditions exist in the relationship of inventory storage and the production process:
The board can be positioned in the path of the flow of all the material to the customer (similar to the card system)
The board can be positioned so that the production process can see it and follow the visual signals
If these conditions can be met, then the board works wonders. It is visual and provides an up-to-date schedule status. It also eliminates one of the major objections to the kanban cards ”people forget to return the cards to the card racks. The board also makes it easy to add and subtract containers. In fact, if these two conditions can be met, then we recommend boards as our first choice for a scheduling signal.
A two-card kanban system works well in situations where product rotation is also an issue. This system, which is a hybrid of the kanban board and the kanban card racks, uses two companion kanban cards to signal location and product age. It is typically used for large items where flow racks are not utilized. The two-card system works like this:
When product is produced or received from a vendor, two cards are pulled from a kanban card rack and filled out:
One kanban card goes with the container
The second kanban card goes into a special first-in, first-out (FIFO) box.
Whenever a container of this product is needed, a material handler goes to the FIFO box and pulls out the bottom card.
The material handler then goes to the location written on the card and pulls this product for the production operation.
The material handler then takes both cards and places them in the kanban card racks, which show the schedule signals for production or reorder.
This system, if maintained, allows pallet size items to flow while managing product rotation. It works especially well when used for floor stacked items. As you might suspect, detailed rules and training play a large part in the success of this kanban system. Figure 5-12 shows the FIFO box used for this kanban. Figure 5-13 shows an example of the cards used for a two-card kanban.
Figure 5-12: FIFO Box Used for the Two-Card Kanban System.
Figure 5-13: Example of the Cards Used for a Two-Card System.
Faxbans (or E-mails)
Faxbans (or their twenty-first-century cousin ”e-mail) are just a special variation of the kanban card system. They are used to order replenishment of products within large plants, from off-site ware- houses , or from vendors . This system works as follows :
You set up a preset replenishment notification time with the recipient (for example, 12 PM each day).
You then look at your requirements and fax or e-mail the order before the appointed time.
The recipient then fills the order and delivers it at agreed-to time and intervals (for example, at 7 AM the next day for the previous day's 12 pm order).
The system is a means of communicating usage requirements over a predetermined interval. The delivery times are typically short ”under one week and, more than likely, under one day. The system helps cut down on the time wasted trying to manage purchasing organization bureaucracies, which allows for shorter lead times. The system requires preplanning and coordination. Because this system is faceless, make sure you plan on backup personnel to keep it going during absences and vacations .
The format of the fax sheet (or e-mail) should be agreed to by both parties. This sheet becomes the vehicle for communication and it should not be subject to interpretation. The typical sheet includes date, time, routing instructions, part numbers , and order quantity. These sheets should be preprinted or set up as a template on a word processor program to control uniformity and speed up the information transfer process. It is also helpful to include an area on the form for special information or instructions. Figure 5-14 shows an example of a typical faxban sheet.
Figure 5-14: Typical Faxban Sheet.
Electronic kanban is a term many people use when trying to avoid kanban implementation. They try to pass off their MRP systems as a kanban system because they are keeping their inventory levels at four to five days. However, as previously stated, a kanban only exists when production is based on usage (or demand). Therefore, since forecast systems do not meet this requirement, MRP scheduling systems do not meet the requirements to be called a kanban.
With this differentiation out of the way, we can now discuss what an electronic kanban really is. A true electronic kanban is a high-tech version of the faxban. It automatically transmits requirements or allows suppliers to access the customer's inventory status and ship replacement material. These systems are not conceptually difficult, but implementation can be complex. The systems are typically developed by larger companies that want to simplify their ordering process. They tend to be one of a kind and are tailored to a single company and its applications. Participating suppliers must be able to log into the system to receive the data. Therefore, the implementing company must be ready to provide assistance to their vendors.
Earlier in the chapter we discussed using racks as a look-see signal. At that point we said this was a limited option and to use racks only if the area in question was manageable.
However, racks are an effective storage method that should not be avoided as a candidate for implementing kanbans when paired with an effective control mechanism. Racks simply need to have a companion tracking system to allow easier visual management of the storage space.
Any of the previously mentioned systems will work with the rack storage. The kanban cards, kanban boards, two-card system, or electronic kanban will help maintain status of the production items kept in the storage racks. With special emphasis on layout of the scheduling system, product rotation can also be integrated into the kanban structure.
However, as your storage space grows, we especially recommend using some sort of electronic kanban to maintain inventory levels. The summation capability and review format allow for easier transmittal of replenishment orders while still allowing you to manage visually. Again, the uniqueness of these applications can sometimes lead to the need for outside programmers for implementation; for example, cost can be an issue!
The move/production kanban was first introduced by Toyota to handle kanbans between work centers. This kanban utilizes a production kanban to signal production and a move kanban to order material from storage. This kanban is very useful when one work center supplies common parts to numerous other work centers.
To explain the sequence, envision two work centers, A and B:
Work center A supplies work center B.
The parts from work center A are stored in a warehouse or supermarket until needed by work center B.
In a move/production kanban, when work center B needs another container of parts, it removes the move kanban card from the container and sends it to the warehouse. At the warehouse, a production kanban card is removed from the full container and replaced with the move kanban card from work center B. The production kanban card is then sent to work center A to authorize production of more parts. The full container with a move kanban is sent to work center B. Figure 5-15 shows this relationship.
Figure 5-15: Move/Production Kanban Steps.
Note that the system can be confusing and needlessly complicated when a work center supplies only one work center. However, when this work center supplies multiple work centers, it can be very useful. Figure 5-16 shows the relationship of one work center supplying multiple work centers.
Figure 5-16: Move/Production Kanban with One Work Center Supplying Multiple Work Centers.