THE UNIVERSITY OF MANITOBA
DEPARTMENT OF MECHANICAL & INDUSTRIAL ENGINEERING
KANBAN SYSTEMS:
THE STIRLING ENGINE MANUFACTURING CELL
Submitted By:
Balram Bali 6741405
Presented to: Leon Fainstein, P. Eng.
April 17, 2003
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INTRODUCTION
The purpose of this report is to explain what a kanban system is, how it works, and how it
can be implemented. The theory will then be applied to the Stirling Engine
Manufacturing Cell and a suggestion for implementation is to be proposed. The proposal
for implementation will include explaining the requirements for a kanban system and
designing the containers required for the system. The scope of the project ends with a
summary of the report and other recommendations useful to the instructor.
WHAT IS KANBAN?
Kanban (kahn-bahn) is a Japanese word that when translated literally means “visible
record” or “visible part”. In general context, it refers to a signal of some kind. Thus, in
the 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 an
actual consumer of a finished product (external) or the production personnel at the
succeeding station in a manufacturing facility (internal). Likewise, the supplier could be
the person at the preceding station in a manufacturing facility. The premise of kanbans is
that 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 the
supplier. The container has attached to it instructions for refilling the container such as
the 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 balls
sent via pneumatic tubes from station to station.
Kanbans serve many purposes. They act as communication devices from the point of use
to the previous operation and as visual communication tools. They act as purchase orders
for your suppliers and work orders for the production departments, thereby eliminating
much of the paperwork that would otherwise be required. In addition, kanbans reinforce
other manufacturing objectives such as increasing responsibility of the machine operator
and allowing for proactive action on quality defects. However, kanbans should not be
used when lot production or safety stock is required because the kanban system will not
account 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 Materials
Requirements Planning (MRP) system. This system is based on the Planning Department
setting 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 this
system is that it relies on guessing the future customer demand to develop the schedule
that production is based on and guessing the time it takes to produce each part. Overestimation 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 mentioned
wastes throughout an organization due to the pull system that is employed. Waste can
come from over-production (inventory) and therefore, the need for a stockroom. This
waste is eliminated. Part shortages (under-production) are also eliminated. Costs are
reduced by eliminating the need for many of the purchasing personnel and the paperwork
associated with purchasing. The planning department’s workload is also reduced as they
no longer need to produce work orders.
TYPES OF KANBAN
Dual-Card Kanban
This kanban system is more commonly referred to as the Toyota kanban system as
Toyota was the first to employ this system in full scale use. It is a more useful kanban
technique in large-scale, high variety manufacturing facilities. In this system, each part
has its own special container designed to hold a precise quantity of that part. Two cards
are used: the production kanban which serves the supplier workstation and the
conveyance kanban, which serves the customer workstation. Each container cycles from
the 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 Pkanban 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) and
Drilling (customer) processes:
1.
2.
3.
4.
5.
6.
Find the note “Start here”. The C-kanban is detached and placed in a collection
box for Stock Point M.
The container that is most recently emptied in Drilling is taken to Stock Point M
and a C-kanban is attached to it.
The empty container and C-kanban are taken to Stock Point L where the Ckanban is detached and re-attached to a full container which is taken back to
Stock Point M.
The full container taken to Stock Point M had a P-kanban attached to it. Before
leaving Stock Point L, the P-kanban was detached and placed in the Stock Point L
collection box.
The P-kanban in the Stock Point L collection box are taken to Milling hourly
where they go into a dispatch box and become the list of jobs to be worked on
next at the Milling Station.
For every job that is completed, parts go into an empty container from Stock Point
L, 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 facilities
requiring less variety in their parts. Essentially, the single-card kanban system is simply
a 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 same
workstations as the dual-card example (where the stock points shown are the work
stations themselves but are shown separately for explanation purposes):
1.
2.
3.
4.
Find the note “Start here”. A container has just been emptied at the Drilling
station. The kanban is placed in the kanban collection box.
The full containers at Milling, with kanbans attached to them, are transported to
Drilling and the kanbans in the collection box are taken back to Milling.
Milling continues to fill containers depending on the demand from Drilling.
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 is
employed.
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KANBAN DEVELOPMENT
Implementing a kanban system entails four major steps (which may be slightly modified
depending on the requirements of the facility):
Step #1 is to pick the parts you would like to kanban. In general, these parts should be
used repetitively within the plant with fairly smooth production requirements from month
to month.
Step #2 is to calculate the kanban quantity. This quantity is based on the following
formula:
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 locations
tells us how many locations should have a full container to begin with. The smoothing
factor 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 standard
quantity. 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 the
following formula:
# of Containers = Kanban Quantity / # of Parts Held Per Container
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KANBAN DEVELOPMENT FOR STIRLING ENGINE MANUFACTURING CELL
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 be
easy to understand for the students using the system, easy for the instructor of the course
to manage, and the kanban containers must be easy to use. Another obvious but very
important characteristic of the kanban system is that there must be enough kits produced
to 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 by
the students. In other words, a buffer quantity must always accompany the kanban
container to accommodate the production of defective parts. This system then becomes a
modified kanban system due to the use of buffers but this change is necessary because the
course 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 previous
station will not produce a part until the following station pulls a part), the buffer is used
to compensate. Based on the past experience of the instructor, a buffer quantity of 2 is
required 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 we
would 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 the
routing 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 one
and the same based on the current setup in the machine shop. They have been included in
the routing for the purposes of completeness. Since these two stations are storage
facilities and there is an absence of a JIT system from suppliers of raw materials, we
would 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. Since
all 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 use
a kanban container between Station #7 and any previous station. Another important
observation we can make from Table #1 is that some parts have the exactly same routing
as 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 in
mind 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 in
the following table:
Parts
Combined Container # 1 Power Cylinder Displacer Bushing
Combined Container # 2 Balancer
Hub
Table 2: Parts Placed in Combined Containers
Step #2:
Piston
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 produce
1 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 use
the formula to calculate the kanban quantity between any two stations for any part even
though 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 normally
employed. In this kanban system, the container itself will act as the signal. There will
not be any card or other form of writing accompanying the container. By doing so, the
simplicity objective is satisfied further and the need to replace missing cards is
eliminated.
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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 designed
to hold 3 parts—1 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 a
container quantity of 1 is used. Naturally, the # of containers required between two
stations 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 the
kanban 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 the
containers 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, material
availability, and alternative designs. In general, however, where metal was used, a
thickness of 0.125” was assumed and where foam was used, a thickness of 1.5” was
assumed. 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 is
within the buffer part replenishment cycle. There must be a system in place to ensure
that for every part used from a buffer slot in a container, an extra part is produced to
replenish the part that was removed.
The proposed solution to this problem is that a chart be set up at the raw material storage
location with a listing of each station and containers that are outgoing from it. Each
station 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 will
know when an extra part is required to be produced for that station and they can pull an
extra part from the previous station. As soon as the buffer part is replenished, a white
sticker is placed on top of the red sticker by the student. In this manner, the cycle
continues and the buffer part quantity is maintained. A sample chart is shown in
Appendix 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 as
indicated in Table 2 and the routing for each part indicated in Table 1, we derive the
following 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 a
station and then leaving in another kanban at that same station. Since the kanban
containers for that part are designed exactly alike, the student may become confused as to
which 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 that
all the outgoing containers from a station be colored the same based on the following
chart:
Station Color
1
Red
2
Blue
3
Green
4
Yellow
5
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 kanban
signals 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 to
the Stirling Engine Manufacturing Cell. Based on the discussion of the reasons and
manner in which the kanban production system is to be input into the Stirling Engine
Manufacturing Cell, we can summarize the requirements for implementation with the
following 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 quantity
maintenance 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.
RECOMMENDATIONS
It must be noted that we never used kanban containers for transporting parts from raw
materials and transporting parts to finished parts storage. Ideally, we would want to pull
from raw materials and have finished parts pull from the previous station. However, due
the 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 proposed
kanban 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 is
more suitable to the application because of the ease allowed in purchasing these items. It
would 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
instructor’s 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 the
top plate and acts as a deterrent to the accidental placement of a bottom plate in the
container. The two buffer parts are held in the slot on the bottom which completely
surrounds 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 top
of the container. A small tab in front of the slot for preventing the buffer parts from
falling out would be recommended. Further dimensions may be acquired from the
drawing files.
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Bottom Plate Container
The Bottom Plate Container is designed with the use of 0.125” thick aluminum (or
instructor’s 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 completely
surrounds the two bottom 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 top of the container. A small tab in front of the slot for preventing the buffer parts
from falling out would be recommended. Further dimensions may be acquired from the
drawing files.
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Flywheel Container
The Flywheel Container is designed with the use of 0.125” thick aluminum (or
instructor’s 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 the
flywheel. The container is actually smaller in perimeter dimensions so as not to confuse
the container with those of the top or bottom plates. The two buffer parts are held in the
slot on the bottom which completely surrounds the two flywheels. 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 top of the container. A small tab in front of the slot
for 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 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 0.125” thick. Each cutout is
shaped as the outline of a bearing support. Further dimensions may be acquired from the
drawing files.
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Power Cylinder – Piston – Displacer Bushing Container
The Power Cylinder–Piston–Displacer Bushing 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 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 0.125”
thick. The top three cutouts are for the power cylinder and piston (since they will be
taped together) and the bottom three cutouts are for the displacer bushing. Each cutout is
shaped as the circumference of the corresponding part. Further dimensions may be
acquired 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 part
locations are to be enclosed in a boxed dome which slides 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 0.125” thick. The top three cutouts
are for the balancer and the bottom three cutouts are for the hub. Each cutout is shaped
as the circumference of the corresponding part. The extra groove in the hub cutouts are
to accommodate the shape of the hub. Further dimensions may be acquired from the
drawing 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. Fort
Wayne, IN: WCM Associates.
Schonberger, R.J. (1982). Japanese Manufacturing Techniques. New York, NY: The
Free Press.
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