Kanban Types

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T HE U NIVERSITY OF M ANITOBAD EPARTMENT OF M ECHANICAL & I NDUSTRIAL E NGINEERING

K ANBAN

SYSTEMS

:T HE STIRLING E NGINE M ANUFACTURING C ELL

Submitted By:Balram Bali 6741405

Presented to: Leon Fainstein, P. Eng.

April 17, 2003

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I NTRODUCTION

The purpose of this report is to explain what a kanban system is, how it works, and how itcan be implemented. The theory will then be applied to the Stirling EngineManufacturing Cell and a suggestion for implementation is to be proposed. The proposal

for implementation will include explaining the requirements for a kanban system anddesigning the containers required for the system. The scope of the project ends with asummary of the report and other recommendations useful to the instructor.

W HAT I S K ANBAN ?

Kanban ( kahn-bahn ) is a Japanese word that when translated literally means visiblerecord or visible part. In general context, it refers to a signal of some kind. Thus, inthe manufacturing environment, kanbans are signals used to replenish the inventory of items used repetitively within a facility. The kanban system is based on a customer of a

part pulling the part from the supplier of that part. The customer of the part can be anactual consumer of a finished product (external) or the production personnel at thesucceeding station in a manufacturing facility (internal). Likewise, the supplier could bethe person at the preceding station in a manufacturing facility. The premise of kanbans isthat material will not be produced or moved until a customer sends the signal to do so.

The typical kanban signal is an empty container designed to hold a standard quantity of material or parts. When the container is empty, the customer sends it back to thesupplier. The container has attached to it instructions for refilling the container such asthe part number, description, quantity, customer, supplier, and purchase or work order number. Some other common forms of kanban signals are supplier replaceable cards for cardboard boxed designed to hold a standard quantity, standard container enclosed by a

painting of the outline of the container on the floor, and color coded striped golf ballssent via pneumatic tubes from station to station.

Kanbans serve many purposes. They act as communication devices from the point of useto the previous operation and as visual communication tools. They act as purchase ordersfor your suppliers and work orders for the production departments, thereby eliminatingmuch of the paperwork that would otherwise be required. In addition, kanbans reinforceother manufacturing objectives such as increasing responsibility of the machine operator and allowing for proactive action on quality defects. However, kanbans should not beused when lot production or safety stock is required because the kanban system will notaccount for these requirements.

Push vs. Pull System

The kanban system described is a pull system. Traditionally, a push system is and has been employed. The push system is also more commonly known as the MaterialsRequirements Planning (MRP) system. This system is based on the Planning Departmentsetting up a long-term production schedule which is then dissected to give a detailed

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schedule for making or buying parts. This detailed schedule then pushes the production people to make a part and push it forward to the next station. The major weakness of thissystem is that it relies on guessing the future customer demand to develop the schedulethat production is based on and guessing the time it takes to produce each part. Over-estimation and under-estimation may lead to excess inventory or part shortages,

respectively.

One of the major reasons kanbans are used is to eliminate or reduce the above mentionedwastes throughout an organization due to the pull system that is employed. Waste cancome from over-production (inventory) and therefore, the need for a stockroom. Thiswaste is eliminated. Part shortages (under-production) are also eliminated. Costs arereduced by eliminating the need for many of the purchasing personnel and the paperwork associated with purchasing. The planning departments workload is also reduced as theyno longer need to produce work orders.

T YPES O F K ANBAN

Dual-Card Kanban

This kanban system is more commonly referred to as the Toyota kanban system asToyota was the first to employ this system in full scale use. It is a more useful kanbantechnique in large-scale, high variety manufacturing facilities. In this system, each parthas its own special container designed to hold a precise quantity of that part. Two cardsare used: the production kanban which serves the supplier workstation and theconveyance kanban, which serves the customer workstation. Each container cycles fromthe supplier workstation to its stockpoint to the customer workstation and its stockpoint,and back while one kanban is exchanged for another. No parts are produced unless a P-kanban authorizes it. There is only one C-kanban and one P-kanban for each container and each container holds a standard quantity (no more, no less).

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The following diagram more clearly explains this process using the Milling (supplier) andDrilling (customer) processes:

1. Find the note Start here. The C-kanban is detached and placed in a collection box for Stock Point M.

2. The container that is most recently emptied in Drilling is taken to Stock Point Mand a C-kanban is attached to it.

3. The empty container and C-kanban are taken to Stock Point L where the C-kanban is detached and re-attached to a full container which is taken back toStock Point M.

4. The full container taken to Stock Point M had a P-kanban attached to it. Beforeleaving Stock Point L, the P-kanban was detached and placed in the Stock Point Lcollection box.

5. The P-kanban in the Stock Point L collection box are taken to Milling hourlywhere they go into a dispatch box and become the list of jobs to be worked onnext at the Milling Station.

6. For every job that is completed, parts go into an empty container from Stock PointL, and a P-kanban is attached. The full container is then moved back to Stock Point L.

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Single-Card Kanban

The single-card kanban system is a more convenient system for manufacturing facilitiesrequiring less variety in their parts. Essentially, the single-card kanban system is simplya dual-card kanban system with the absence of the production kanban and designated

stock points. This system is demonstrated using the following diagram and the sameworkstations as the dual-card example (where the stock points shown are the work stations themselves but are shown separately for explanation purposes):

1. Find the note Start here. A container has just been emptied at the Drillingstation. The kanban is placed in the kanban collection box.

2. The full containers at Milling, with kanbans attached to them, are transported toDrilling and the kanbans in the collection box are taken back to Milling.

3. Milling continues to fill containers depending on the demand from Drilling.4. Empty containers are collected from Drilling periodically.

Due to the inherent simplicity of the single-card kanban system and its applicability to the purposes of this report, the remainder of the report shall assume this technique isemployed.

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K ANBAN DEVELOPMENT

Implementing a kanban system entails four major steps (which may be slightly modifieddepending on the requirements of the facility):

Step #1 is to pick the parts you would like to kanban. In general, these parts should beused repetitively within the plant with fairly smooth production requirements from monthto month.

Step #2 is to calculate the kanban quantity. This quantity is based on the followingformula:

Kanban Quantity = Weekly Part Usage * Lead Time * # of Locations * Smoothing Factor

The weekly part usage is, as the name implies, the quantity of the part under consideration used per week. The lead time is given by the supplier. The usual

manufacturing facility lead time is 5 working days per week. The number of locationstells us how many locations should have a full container to begin with. The smoothingfactor is used to account for seasonal fluctuations in demand. It is a constant determined

by the ratio of the fluctuating demand to the regular demand.

Step #3 is to pick the type of signal and container to be used which holds a standardquantity. The container should aid visual identification, ease of storage, and count of material at the point of use.

Step #4 is to calculate the number of containers. This calculation is performed using thefollowing formula:

# of Containers = Kanban Quantity / # of Parts Held Per Container

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K ANBAN DEVELOPMENT FOR STIRLING E NGINE M ANUFACTURING C ELL

Design Requirements

There are several requirements for the design of the kanban system in the Stirling Engine

Manufacturing Cell. The main requirement is simplicity. The kanban system must beeasy to understand for the students using the system, easy for the instructor of the courseto manage, and the kanban containers must be easy to use. Another obvious but veryimportant characteristic of the kanban system is that there must be enough kits producedto supply all of the students in a class by the end of the term.

There must also be some allowance in the kanban system for errors that will be made bythe students. In other words, a buffer quantity must always accompany the kanbancontainer to accommodate the production of defective parts. This system then becomes amodified kanban system due to the use of buffers but this change is necessary because thecourse is used to teach students about manufacturing systems and errors are bound to

occur. Since there is no extra time for students to stop production altogether, as may be possible at a manufacturing facility when a defective part is produced (the previousstation will not produce a part until the following station pulls a part), the buffer is usedto compensate. Based on the past experience of the instructor, a buffer quantity of 2 isrequired along with each kanban container.

Step #1: Pick The Parts To Kanban

For the purposes of the Stirling Engine Manufacturing Cell, it was assumed that wewould kanban all of the manufactured parts. However, by analyzing the routing of each

part, some very useful information can be derived and visualized. Table 1 charts therouting for each of the parts throughout the various stations in the cell.

Table 1: Routings for Kanban Parts

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Table 1 shows RM and Station #7 are used by many of the parts. These stations are oneand the same based on the current setup in the machine shop. They have been included inthe routing for the purposes of completeness. Since these two stations are storagefacilities and there is an absence of a JIT system from suppliers of raw materials, wewould not actually use a kanban container between this station and the customer (the

station requiring parts from RM. A similar reasoning can be applied to Station #7. Sinceall parts are being delivered to Station #7 (a storage facility) from the previous station,there is no container traveling back to the previous station. Therefore, we would not usea kanban container between Station #7 and any previous station. Another importantobservation we can make from Table #1 is that some parts have the exactly same routingas other parts. Due to the simplicity objective stated previously, we can combine the

parts with the same routing to the same kanban container. However, it must be kept inmind that if the routing of any of the parts in this container was to change, the container itself must be modified. The parts we will combine in the same container are indicated inthe following table:

Combined Container # 1 Power Cylinder Displacer Bushing PistonCombined Container # 2 Balancer Hub

Parts

Table 2: Parts Placed in Combined Containers

Step #2: Calculate the Kanban Quantity (for each part)

The Kanban Quantity was dictated by the course instructor as being 1 regardless of the part we use and the station we are at. Considering the fact that we would like to produce1 complete Stirling Engine per week, it is reasonable to assume that 1 of each part should

be completed by the end of each week. Based on our knowledge, it is still possible to usethe formula to calculate the kanban quantity between any two stations for any part eventhough this quantity is already given. This is done as follows:

Kanban Quantity = Weekly Part Usage * Lead Time * # of Locations * Smoothing Factor = 1 (Part Used / Week) * 1 (Week) * 1 (Location with Full Container) *

1 (Zero Fluctuation in Demand)= 1

As you can see, the result agrees with the quantity dictated by the instructor.

Step #3: Pick the Type of Signal and a Standardized Container

The type of signal to be used is also a modification of the kanban system normallyemployed. In this kanban system, the container itself will act as the signal. There willnot be any card or other form of writing accompanying the container. By doing so, thesimplicity objective is satisfied further and the need to replace missing cards iseliminated.

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Since the kanban quantity is 1, the standardized container is limited to holding 1 part.Due to the buffer quantity requirement indicated earlier, each container must be designedto hold 3 parts1 for the kanban part and 2 for the buffer quantity.

Step #4: Calculate the Number of Containers in Each Kanban

Once again, this calculation is quite obvious when a Kanban Quantity of 1 with acontainer quantity of 1 is used. Naturally, the # of containers required between twostations becomes:

# of Containers = Kanban Quantity / # of Pieces Held Per Container = 1 / 1= 1

The above four steps were used to demonstrate the general requirements for all of thekanban that are used within the Stirling Engine Manufacturing Cell.

Design of Containers

Six containers were to be designed: Top Plate, Bottom Plate, Flywheel, Bearing Support,Displacer Bushing / Power Cylinder / Piston, and Balancer / Hub. The designs and their application are explained further in Appendix A. The dimensions for each of thecontainers have generally not been specified on the drawings because the end container design is bound to be changed by the course instructor based on the cost, materialavailability, and alternative designs. In general, however, where metal was used, athickness of 0.125 was assumed and where foam was used, a thickness of 1.5 wasassumed. The complete details of the dimensions used will be available to the instructor as the drawing files of each of the containers will be submitted along with this report.

Buffer Quantity Maintenance System

One of the major areas where problems can occur using the kanban system proposed iswithin the buffer part replenishment cycle. There must be a system in place to ensurethat for every part used from a buffer slot in a container, an extra part is produced toreplenish the part that was removed.

The proposed solution to this problem is that a chart be set up at the raw material storagelocation with a listing of each station and containers that are outgoing from it. Eachstation will be equipped with red and white stickers. Every time a part from the buffer of a container is used, a red sticker will be placed in the chart for that station and container.Thus, every week, the instructor and students at the station missing the buffer part willknow when an extra part is required to be produced for that station and they can pull anextra part from the previous station. As soon as the buffer part is replenished, a whitesticker is placed on top of the red sticker by the student. In this manner, the cyclecontinues and the buffer part quantity is maintained. A sample chart is shown inAppendix B.

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Net Requirements

Each process (station) has its own requirements for the kanban assigned to it. First of all,it is important to know the number of incoming and outgoing containers from each

station. Based on grouping of parts with the same routing in one kanban container asindicated in Table 2 and the routing for each part indicated in Table 1, we derive thefollowing quantities of incoming and outgoing kanban for each of the stations:

Table 3: (a) Outgoing Container, and (b) Incoming Container Requirements

As we can clearly see from the above two charts, some parts have kanban going to astation and then leaving in another kanban at that same station. Since the kanbancontainers for that part are designed exactly alike, the student may become confused as towhich container is the incoming kanban and which one is the outgoing kanban. In order to alleviate this problem, we color-code the containers. The proposed convention is thatall the outgoing containers from a station be colored the same based on the followingchart:

Station Color

1 Red

2 Blue

3 Green

4 Yellow5 Violet

6 Black

Table 4: Container Colors per Station

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SUMMARY

This report began with an explanation of what kanban systems and the types of kanbansignals that are commonly used. Following a discussion of the workings of a push and

pull system, the two different types of kanban systems, single and dual-card kanban

systems were described.

The next step was to show the steps to developing a kanban system and then apply it tothe Stirling Engine Manufacturing Cell. Based on the discussion of the reasons andmanner in which the kanban production system is to be input into the Stirling EngineManufacturing Cell, we can summarize the requirements for implementation with thefollowing chart:

Table 5: Summary of Kanban Development Requirements

The design for each container is provided in Appendix A and the drawing files will be provided to the instructor for further examination of dimensions. A buffer quantitymaintenance system using red and white stickers to indicate used and replenished parts,respectively, was proposed to keep track of buffer part use and replenishment of these

parts. The chart is provided in Appendix B.

R ECOMMENDATIONS

It must be noted that we never used kanban containers for transporting parts from rawmaterials and transporting parts to finished parts storage. Ideally, we would want to pullfrom raw materials and have finished parts pull from the previous station. However, duethe manner in which parts are supplied and stored, this just-in-time process would not be

possible. Currently, too many parts get stockpiled before kitting begins. The number of raw materials stored in the beginning is actually much higher than that required at that

time. Thus, introducing a MRP system at these stations in conjunction with the proposedkanban system would be recommended.

Another consideration that was not included in this report was the kanban of the nuts,screws and other kitting materials. It was found that the current two-bag inventory ismore suitable to the application because of the ease allowed in purchasing these items. Itwould help further if the kitting operation was somewhat more organized.

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Appendix A:Drawings of Kanban Containers

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Top Plate Container

The Top Plate Container is designed with the use of 0.125 thick aluminum (or instructors material of choice). The part to actually be used is held in place at the top of the container. The protrusion at the top of the container restricts lateral movement of thetop plate and acts as a deterrent to the accidental placement of a bottom plate in thecontainer. The two buffer parts are held in the slot on the bottom which completelysurrounds the two top plates. The hiding of this slot underneath the top of the container acts as a physical deterrent to using the buffer parts before using the part held at the topof the container. A small tab in front of the slot for preventing the buffer parts fromfalling out would be recommended. Further dimensions may be acquired from thedrawing files.

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Bottom Plate Container

The Bottom Plate Container is designed with the use of 0.125 thick aluminum (or instructors material of choice). The part to actually be used is held in place at the top of the container. The two buffer parts are held in the slot on the bottom which completelysurrounds the two bottom plates. The hiding of this slot underneath the top of thecontainer acts as a physical deterrent to using the buffer parts before using the part held atthe top of the container. A small tab in front of the slot for preventing the buffer partsfrom falling out would be recommended. Further dimensions may be acquired from thedrawing files.

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Flywheel Container

The Flywheel Container is designed with the use of 0.125 thick aluminum (or instructors material of choice). The part to actually be used is held in place at the top of the container. The protrusion at the top of the container restricts lateral movement of theflywheel. The container is actually smaller in perimeter dimensions so as not to confusethe container with those of the top or bottom plates. The two buffer parts are held in theslot on the bottom which completely surrounds the two flywheels. The hiding of thisslot underneath the top of the container acts as a physical deterrent to using the buffer

parts before using the part held at the top of the container. A small tab in front of the slotfor preventing the buffer parts from falling out would be recommended. Further dimensions may be acquired from the drawing files.

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Bearing Support Container

The Bearing Support Container is designed with the use of 1.5 thick foam. The buffer part locations are to be enclosed in a boxed dome which slides into the 0.5 deep groovesurrounding the buffer parts. The user may slide out the box-dome if the use of a buffer

part is required. The dome will act as a physical reminder to the user only to use the partslocated outside of the buffer area on the right in the above picture. The box-dome willideally consist of a see-through plastic material that is 0.125 thick. Each cutout isshaped as the outline of a bearing support. Further dimensions may be acquired from thedrawing files.

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Power Cylinder Piston Displacer Bushing Container

The Power CylinderPistonDisplacer Bushing Container is designed with the use of 1.5 thick foam. The buffer part locations are to be enclosed in a boxed dome whichslides into the 0.5 deep groove surrounding the buffer parts. The user may slide out the

box-dome if the use of a buffer part is required. The dome will act as a physical reminder to the user only to use the parts located outside of the buffer area on the right in the above

picture. The box-dome will ideally consist of a see-through plastic material that is 0.125thick. The top three cutouts are for the power cylinder and piston (since they will betaped together) and the bottom three cutouts are for the displacer bushing. Each cutout isshaped as the circumference of the corresponding part. Further dimensions may beacquired from the drawing files.

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Balancer Hub Container

The Balancer-Hub Container is designed with the use of 1.5 thick foam. The buffer partlocations are to be enclosed in a boxed dome which slides into the 0.5 deep groovesurrounding the buffer parts. The user may slide out the box-dome if the use of a buffer

part is required. The dome will act as a physical reminder to the user only to use the partslocated outside of the buffer area on the right in the above picture. The box-dome willideally consist of a see-through plastic material that is 0.125 thick. The top three cutoutsare for the balancer and the bottom three cutouts are for the hub. Each cutout is shapedas the circumference of the corresponding part. The extra groove in the hub cutouts areto accommodate the shape of the hub. Further dimensions may be acquired from thedrawing files.

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Appendix B:Buffer Quantity Replenishment Chart

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Insert Excel Worksheet Here

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REFERENCES

Rubrich, L. & Watson, M. (1998). Implementing World Class Manufacturing. FortWayne, IN: WCM Associates.

Schonberger, R.J. (1982). Japanese Manufacturing Techniques. New York, NY: TheFree Press.

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