KANBAN SHARING AND OPTIMIZATION IN BOSCH

PRODUCTION SYSTEM

Pedro Salgado and Leonilde Varela

Department of Production and Systems, School of Engineering, University of Minho, Gualtar Campus, Braga, Portugal

Keywords: Kanbans, Cellular manufacturing system, Information and resource sharing, Optimization, Bosch

production.

Abstract: Information sharing and optimization is a key factor for effective knowledge management, which is based

on data exchange, communication and technological infrastructures and standardization, being essential in

order to remain competitive in the today’s global market scenario. In this context, human functions are also

relevant, and in this work we refer to the interaction of both in the optimization of Bosch Production

System. Therefore, the aim of this paper consists on presenting the minimization of kanbans, when sharing

this information in a proposed cellular manufacturing environment in Bosch production, in order to enhance

workflows and material and work in process management as well as human interactions and production

performance and productivity.

1 INTRODUCTION

Knowledge management (KM) is concerned with

the analysis and technical support of practices used

in an organization to identify, create, represent and

enable the adoption and leveraging of good practices

embedded in organizational processes. Effective

knowledge management is an increasingly important

source of competitive advantage, and a key to the

success of contemporary organizations.

KM focuses on some core components including:

people, processes and technology and an important

concern aims at taking an organizational focus, in

order to optimize organization aspects and

workflows.

In order to accomplish effective KM information

sharing (IS) is a key element. Increasingly important

information is enabled through kanbans technology

implementation, and in this paper we aim at

optimizing it, in order to enable an improved

knowledge management scenario in Bosch

production.

Information sharing and optimization is a key

factor for effective knowledge management, which

is based on data exchange, communication and

technological infrastructures and standardization,

being an essential element to remain competitive in

the today’s global market scenario. In this context,

human functions are also relevant, and in this work

we refer to the interaction of both in the optimization

of Bosch Production System (BPS). Therefore, the

aim of this paper consists on presenting the

minimization of kanbans, when sharing this

information in a proposed cellular manufacturing

environment in Bosch production, in order to

enhance workflows and material and work in

process management as well as human interactions.

Kanban, a Japanese word, means a board or card

with visual information. In TPS (Toyota Production

System) kanbans are used to conduct the information

flows in the manufacturing system in order to pull

the material flows from upstream to downstream.

The operations of various types of kanban systems

were documented thoroughly by Monden (1993) and

published even before the TPS has caught the

attention of the majority of U.S. manufacturers.

In order to better summarize this contents, this

paper is structured in 5 sections. Next, in section 2

we will briefly refer to Lean a Just-in-time (JIT)

management and related technologies. In section 3

we present a literature review about some work

carried out in this areas and in section 4 the

implementation of kanbans and related technologies

to Bosch production is briefly described and some

important advantages are pointed out comparing the

proposed scenario with the existing one. Finally, in

section 5, some conclusions are reached.

Salgado P. and Varela L..

KANBAN SHARING AND OPTIMIZATION IN BOSCH PRODUCTION SYSTEM.

DOI: 10.5220/0003102600810091

In Proceedings of the International Conference on Knowledge Management and Information Sharing (KMIS-2010), pages 81-91

ISBN: 978-989-8425-30-0

 2010 SCITEPRESS (Science and Technology Publications, Lda.)

2 LEAN AND JIT MANAGEMENT

Levy (1997) defines lean production as "a tightly

coupled flexible system" centered on JIT, delivery

and low inventories. To achieve this requires the

elimination of defects, supply production problems

and other delays in the product pipeline. It also

requires high levels of responsiveness to changes in

demand from customers. To this end, continuous

improvements are necessary in component quality,

in production control, reduction of lead times (as

well as lot sizes and set-up times) and shortening of

product development cycles.

To work effectively lean production requires a

high coordination between suppliers and customers,

rapid flows of products and information and JIT

deliveries.

It is difficult for a modern manufacturing system

to make the many different kinds of available

products in low quantities, with high quality and low

cost at just the right time. Moreover, in order to

survive in the global competitive market

manufacturing enterprises must increase their

productivity and profitability through greater shop

floor agility. As the manufacturing environment

from mass production through to flexible and lean

manufacturing moved towards an agile

manufacturing philosophy, there was a drastic

impact on all manufacturing-related activities (Kidd

P.T., 1995, Cheng K., 1998). Therefore,

manufacturing systems must adapt themselves at an

ever-increasing pace to incorporate new information

technology and new products as well as new

organizational architectures.

A kanban system facilitates lean principles in a

simple and effective way. While reportedly

successful in many manufacturing firms, the

conventional kanban systems using physical cards

suffer from human errors, limited tracking

capability, and so on. To make the information flow

leaner, software providers add new features to their

existing programs for manufacturing systems to

computerize kanban activities. As Web-based

technologies advance rapidly, developing an entirely

Web-based kanban system appears to be feasible and

promising.

Kidd (1995) established that a kanban system

typically performs efficiently and effectively in shop

floor control when the demand is repetitive and

stable. It also applies to adjacent suppliers,

customers, and even within a global supply chain to

facilitate just-in-time (JIT) delivery (Cheng K., et al,

1998).

In the past decade, lean manufacturing concepts

have shown significant influence in the way jobs are

performed. Eliminating non-value added activities in

response to customer’s true demand, i.e., value,

makes manufacturers leaner and eventually stronger

in the marketplace.

Levy (1997) summarized lean thinking into

value, value stream, flow, pull, and perfection.

Among them, the pull concept is the key to carrying

out a smooth flow of value stream. It aligns

production targets throughout the system with end

customer’s demand and hence minimizes inventory

and work-in-process (WIP).

As lean manufacturing gains popularity globally,

the impact of implementing pull or kanban system

becomes clearer. Mortimer (2008) summarized the

major advantages of implementing pull system,

including: (1) shorter lead time, and hence, higher

flexibility to demand changes; (2) reduced levels of

inventory and other wastes: (3) capacity

considerations that are restricted by the system

design, and (4) inexpensive to implement. Moreover,

Hirano (2009) compared the pull-and-push systems

in terms of production planning and control and

conclude that pull system is more efficient, easier to

control, more robust, and more supportive of

improving quality. In general, implementing kanban

system for pull concept contributes to a higher level

of customer satisfaction by providing products with

lower cost, shorter lead time, and more stable

quality, while the supplier enjoys a more

manageable production environment with lower

WIP and inventory.

From the viewpoint of implementing kanban

system in practice, the “paper card” system is known

to be simple and effective, and requires little

investment.

Fax and e-mail are commonly used as the means

of dispatching kanbans among distant sites, when

delivering physical kanban is no more considered

efficient. For production control, the number of

kanban can be adjusted within a range to meet the

capacity requirements. Using demand leveling, the

pull system remains stable when demand fluctuates

in a certain range. When the product variety,

demand fluctuation, capacity requirement, or

distance between facilities drops out of the

acceptable range, the kanban system becomes too

complicated and difficult to manage. As a result,

mistakes arise, and significant workforce can be

wasted on managing and maintaining the kanban

system.

Beside the effectiveness of information delivery,

visibility is another critical issue of the paper-based

KMIS 2010 - International Conference on Knowledge Management and Information Sharing

kanban system. Within a workstation or production

cell, the conventional kanban system enhances

visibility of workflows by the paper cards.

“Seeing” the flow of value stream is the key to

building a lean system. Information technologies

provide the tools that can greatly enhance the

visibility of a kanban system. Therefore, e-kanban

system with real-time data transaction and

monitoring becomes the natural solution for

eliminating the weaknesses of the kanban systems.

While reportedly successful in many

manufacturing firms, the conventional kanban

systems using physical cards suffer from human

errors, limited tracking capability, and so on. To

make the information flow leaner, software

providers add new features to their existing

programs for manufacturing systems to computerize

kanban activities. As Web-based technologies

advance rapidly, developing an entirely Web-based

kanban system appears to be feasible and promising.

Ohno (1988), Monden (1993), and Slack (2007)

stated that a kanban system, when well applied in

organizations has as main advantages: eliminating

waste, enhancing control levels in the shopfloor,

through the decentralization and simplification of

operational processes; lead time reduction;

improvement of the company’s reactive capacity to

its clients; stock level adjustment to regular

oscillation of demand; reduced wip stock;

elimination of intermediate and safety stock; and

production lot size reduction and all these aspects

and advantages motivated this work.

2.1 JIT and Kanban Calculation

“The JIT production system is a market-oriented

production system that rests entirely on the

foundation of serving client needs. JIT, or "Just in

Time" refers to the timing of production flow; goods

are delivered to the manufacturing lines just in time

to be used, just in the immediately quantities and

just to the production process that need them. Saying

"in time" is not enough, since parts can arrive at

processes a week or to two prior to their use and still

be there "in time". That is why the most important

word in Just-In-Time is the first word "just". Goods

need to arrive within minutes, not days or weeks, of

their use on the production line. Only then can we

eliminate waste in such forms as overproduction,

waiting for late deliveries and excess inventory”

(Hirano, 2009)

In the literature several different kanbans

calculation formulas exist, namely the ones put

forward by Shingo (1989), and Monden (1993).

In the opinion of Shingo (1989), the

determination of the number of kanbans is far away

from being as important as the improvement of the

production system in order to minimize the number

of kanbans. Shingo (1989) presents a simple formula

for the determination of the number of kanbans

necessary:

(1)

K = number of kanbans;

Q = quantity of products in batch production;

α = minimum security stock level;

n = quantity of products transported on a pallet.

Monden (1993) presented a wider formula for

kanbans calculation:

(2)

k = number of kanbans;

d = demand on the planned period;

te = waiting time, defined from the time since the

necessity of production is defined until

effective production starting time;

tf = time it takes to produce a container (one

kanban) of products;

β = safety factor (around 15%);

c = container capacity.

3 LITERATURE REVIEW

In the late 1980s and early 1990s, researchers started

to intensively investigate the mechanism and

benefits of kanban systems. Various studies were

carried out, such as simulation analysis, analytical

modeling, system re-design, and so on (Askin, R. G.,

et al, 1993, Slack, 2007).

Various types of kanban systems and related

techniques have been developed at Toyota (Monden,

Y., 1993, Shingo, S., 1989). The system can be

applied internally on a shop floor and also externally

between distant facilities.

E-kanban systems have been developed based on

existing ERP (enterprise resources planning)

systems, electronic data interchange (EDI)

connections, and web-based technology (Cheng, K.,

et al., 1998, Wan, H. et al, 2007, Ming P. T. and

James T. Lin, 2004). In order to support the kanban

activities, providers of ERP systems started to

extend their products with pull or kanban modules.

A few other e-kanban systems have also been

developed recently by software providers, including

Datacraft Solutions, eBots, SupplyWorks, among

others (Monden, Y., 1993).

KANBAN SHARING AND OPTIMIZATION IN BOSCH PRODUCTION SYSTEM

Even Toyota, the creator of the kanban system,

has adapted an e-kanban system for sending external

pulling signals to distant suppliers (Ohno, T., 1988).

The paper presented by Ming P. Tsai and James

T. Lin (2004) presents advantages, limitations, and

challenges of web-based kanban systems. They

developed an experimental program based on

popular web programming platform and technology,

based on PHP+MySQL. The server-executed

program features cross-platform compatibility, real-

time tracking and performance monitoring, and

greatly enhanced information contents compared to

physical kanbans.

Therefore, human errors were minimized by the

automated transactions; nevertheless, the interfacing

and data maintenance still required further research

efforts (Hung-da Wan, F. Frank Chen, 2007).

Rothenberg (2004) reported that some printing

companies that implement the Lean Production

methods have been successful using the 'pull' or

kanban in some specific segments of their business.

Generally, in business it is important to implement a

kanban system to produce only the quantity ordered,

and managing production under Just-in-time

principles.

Lean and JIT technology can also greatly profit

from cell systems and Hyer (1984) collected data on

20 U.S. firms. A detailed questionnaire was

employed to gather information on the costs and

benefits of cellular manufacturing. A large majority

of the respondents reported that the actual benefits

from implementing cellular manufacturing met or

exceeded their expectations. Specific savings

generally occurred in reductions of lead times,

throughput times, queuing times, setup times, work

in process, labor costs, material handling costs, and

in easier process plan preparation.

4 BPS AND KANBANS

The main activity of Bosch Car Multimedia

Portugal, Lda. Is the production and assembly of

car-radios. The production process of this enterprise

is, in general, divided in two main areas: An upper

level, composed by the automatic insertion area of

components and an area for storing the material

needed in this area.

The lower level is composed by the manual

components insertion area and by several storage

areas.

The automatic components insertion area

integrates several assembly lines, which are

dedicated to the production of Pressed Circuit

Boards (PCB), namely: Main Boards, Switch

Boards, Antennas and Tuners.

The production process starts in the automatic

components insertion area, where the automatic

assembly of the PCBs takes place, after which it

passes to the final assembly, where the manual

components insertion process is carried out in PCBs.

4.1 Existing Scenario

The production programming is performed in the

Bosch Production System (BPS) in two steps. First

an annual plan is established and next a monthly

based plan is prepared. Based on these plans, the

daily production programming is determined in

detail. The information about the daily production

programming is managed by the kanban system, by

using information cards. Through this system, which

is based on pull production principles, the previous

process produces just the quantity to be used in the

subsequent process, therefore, eliminating the

necessity of planning the production on all

production processes and thus avoiding

overproduction.

In the BPS, the type of kanbans used for caring

out this work was the cards attached to the material

containers.

The material received from the storage area is

removed from the supplier package and put in

standard boxes, which are passed to the production

lines by the “Milkrun”. The kanban card goes

attached to the boxes, identifying them.

In the entry point of each production line, in the

automatic components insertion area there is a

kanbans board, as illustrated in Figure 1, where the

batches of each product are defined and a rule about

production planning.

Figure 1: Kanban board.

This kanbans board is divided in three important

areas. One area refers to the composition of the

batch for each product, indicated by letter A.

KMIS 2010 - International Conference on Knowledge Management and Information Sharing

Another is the kanbans buffer (B) and finally the

planning ruler, indicated by a letter C.

The kanban systems works as follows: first each

time kanbans arrive to the board, coming from

production they are inserted in the batch

composition area of the corresponding product.

Next, at the time the number of batches is reached,

i.e., when this area is full, for a given product, the

cards are placed in an existing box (buffer). In this

same box there is a red line, and once it is reached

indicates that someone responsible has to pay

attention to this information (Figure 2).

Figure 2: Product lot size.

Once the kanbans are put into a box they are used

based on the First In First Out rule, so that the first

kanban inserted into the box is also the first one

coming out from it.

After being removed from the buffer, the kanbans

are put into the programming ruler placed on the

bottom of the board, where the production

programming of the three daily production periods is

expressed, based on the production times referred on

each kanban. This ruler is divided into several 5

minutes based spaces. Notice that the kanbans

distribution on the programming ruler is performed

by a production line worker each time a new work

period starts.

Figure 3: Kanban flow in the production line.

After all the previously described steps, the

kanban follows to the production line, being

attached to a container on the end of the line, from

which it follows to the supermarket, where it is

going to wait for being necessary on the manual

insertion area. Once the containers are transported to

the final assembly area the kanbans are placed back

on the board in order to start a new production cycle.

Figure 3 illustrates the kanban and the PCB flows in

the production line.

In order to illustrate the kanban calculation let us

consider an example about a PCB product, which we

are going to refer as a “Type I”. The daily based

requisites (PR) of this product are around 1560

units/day, which corresponds to the quantity that

BPS has to produce on a daily basis.

The standard number of pieces (SNP) is 120

units. This means that one box with 120 units will

correspond to a kanban.

Production is based on a model that includes

three work periods per day (24 hours = 1440

minutes), including intervals of 90 minutes

(including breaks) and intervals of 187 minutes,

including stopping periods, namely due to line

stopping, due to technical problems or related to

quality requisites. This conducts to an effective

production time (NPT) of 1163 minutes (1440 min –

90 min – 187 min = 1163 min).

The processing time of one piece is 30 minutes

and the production line cycle time is 15 seconds.

Let us consider a client that needs the product

type I every day. So, the quantity removed within

the period (WA) for the products are: 1560

units/day. The recharging time (RT loop) for the

product type I is of 830 minutes.

Table 1 presents the values previously referred.

Table 1: Product type I main values (a).

Based on the values presented in Table 1 we can

now calculate the values of RE, LO, WI, TI and SA,

shown in Table 2.

Table 2: Product type I main values (b).

The time gap coverage (TI) is zero, due to

inexistence of difference between the time shift

model of the customer (Tc) and the supplier (Ts).

The value of withdrawal peak coverage (WI) is also

zero once the quantity removed in the periods; the

KANBAN SHARING AND OPTIMIZATION IN BOSCH PRODUCTION SYSTEM

withdrawal amount

(WA) is the same as the lot size

(LS).

Therefore, we have 35 kanbans for the product

type I and 33 kanbans of product type II.

Based on a demand on the first month of 24.780

units, the number of kanbans necessary at the end of

the month will be 554 units. Next we present a

graphic expressing the number of kanbans necessary

at the end of each month on a six month period.

Figure 4: Number of kanbans for six months.

At the end of the six months period the total

number of kanbans necessary was 2.936 kanbans.

The Kanban system is an information system to

control harmoniously the production quantities in

every process (Monden 1983).

The term kanban has sometimes been used as

being equivalent to “JIT planning control” or even to

the whole of JIT, However, kanban controlled is a

method for operationalizing a pull-based planning

and control system. It is sometimes called the

“invisible conveyor” which controls the transference

of material between the stages of operations (Slack

et al, 2007).

Figure 5: Kanban example.

Shingo (1989) stated that the determination of

the number of kanbans is yet very far away from

being as important as the improvement of the

production system in order to minimize the number

of kanbans.

Besides that, several formulas have been put

forward for determining the number of kanbans

which consider forecast factors, namely demand

forecast, and also products processing and waiting

times between processes.

The BPS formula used to calculate kanbans (K) is as

follows:

(3)

Where,

RE = (PR×RTloop) / (NPT×SNP

)

(4)

, If LS>SNP

(5)

, Only if WA>LS, else WI=0

(6)

(7)

(8)

RE - replenishment time coverage

LO - lot size coverage

WI - withdrawal peak coverage

TI - time gap coverage

SA - safety coverage

Tc - shift time model of customer (minutes);

Ts - shift time model of supplier (minutes).

PR – requirement per period [pieces/period];

RT loop – replenishment lead time [minutes];

NPT – working time [minute/period];

SNP – standard number of parts per kanban [pieces];

LS – lot size [pieces];

WA – withdrawal amount [pieces/period];

ST – safety time (hours);

At the entry point of each production line, in the

automatic insertion area is planned to exist a laser

machine for printing codes (bar code 1D and data

matrix code 2D). In the existing scenario only three

lines are already integrating the laser machine, but in

the future, in order to enable the BPS to satisfy the

total demand, a total of 12 lines, and each one

integrating a laser machine will be necessary to

implement. These codes are important for enabling

the operators to identify the PCBs, in the on going

processing along the processing system, and in the

screening and programs selection on machines in the

automatic and in the manual insertion areas,

therefore contributing to the improvement of

production control and to the final product quality.

These lines are characterized as common

production lines, where the product enters on the

beginning of the line and subsequently passes from

one work centre to the next one, without skipping or

re-entering any one, and maintaining, therefore, a

typical straight forward production flow (Baker e

Trietsch, 2009, Black, J. T., 1991).

Due to some relevant inconveniences detected on

the existing BPS lines there was a need to propose

another kind of production system to supply the

automatic insertion area, which is going to be

described in the next section. Figure 8 shows the

location of the production lines, which are 7 and

KMIS 2010 - International Conference on Knowledge Management and Information Sharing

each one includes the laser machines as well as a

common local stockage area.

Figure 6: Production line phases.

Figure 7: Kanban-line system layout.

4.2 Proposed Scenario

The existing BPS scenario composed by production

lines revealed some significant disadvantages for the

company, namely in terms of the high investment

that had to be made for acquiring the 12 laser

machines. Another disadvantage about the lines

arises from the lack of flexibility of those production

systems, as they do not enable to rapidly adapt to

changes in order to satisfy different kind of client

demands and different products, and the consequent

changes on the product design and processing

requirements (Black, 1991).

Another problem arises from the fact that if one

machines stops working this may cause the complete

production stopping (Slack et al, 2007).

Therefore, the company presented a new

proposal, which considers modifying the production

system to a cellular manufacturing system. In this

kind of system instead of having one laser machine

per line, and 12 lines, we only have to integrate 7

lines, disposed as a cell, and the corresponding 7

laser machines. So, we reduce in 5 lines and 5 laser

machines, in the new scenario. Therefore, the

company has to buy only 4 new laser machines, to

complete the 7 necessary for serving the automatic

insertion area, as 3 of them already exist. So, in case

of maintaining the production lines scenario the

company would have to buy more 9 laser machines,

instead of 4, which would represent a big investment

requirement.

The proposed cell configures typical

characteristics of manufacturing cells, including

some typical aspects that characterize the so called

just in time cells (JITC) and the quick response

manufacturing cells (QRC).

The JIT cells are well known under the scope of

JIT principles and objectives, namely, zero defects,

zero setup times, zero stocks, zero extra

manipulations, zero breakdowns, and zero deadlines

and also unit lot sizes (Singh, N. et al, 1996).

Nowadays it is convenient to use JIT cells, as

they are wel suited for integrating group technology

features and principles (Suri, R., 1998), therefore,

being able to adapt very well to products families

production, which is quite adequate in the BPS, in

order to fulfil the requirements of producing PCBs

product families. PCBs belonging to a same family

share several kind of similarities, namely related

with, processing and manipulation requirements, up

to geometrical and dimensional and/or materials

related similarities.

Once BPS faces a growing necessity to satisfy a

wider range of product specifications and

differences, it turns out increasingly more important

to be able to easily and fast adapt and change the

production system and processes in shorter time

periods and this flexibility and quick response are

some of the most relevant characteristics enabled by

manufacturing cells (MC). (Hyer, N., 1984).

Moreover, MC also enable reaching better product

quality levels at the same time as productivity is

maintained at competitive levels and material

transportations and stock levels are minimized

(Singh, N. et al, 1996).

Regarding the relation with clients, this kind of

manufacturing environment also suits very well, as

cellular the quick time model also aims at enabling

reduced production and delivery times of products

combined with offering a widened range of product

differences, in order to meet the costumers needs

and product specifications, in increasingly more

reduced due dates (Suri, 1998, Slack et al, 2007).

The proposed layout for the automatic insertion

area is presented in Figure 9 and shows the location

of the proposed manufacturing cell. As we can

observe, this proposal led to the need of an

additional area of about 529 m2, for implementing

the cell.

KANBAN SHARING AND OPTIMIZATION IN BOSCH PRODUCTION SYSTEM

Figure 8: Cell.

Figure 9: Automatic insertion area layout.

When the final assembly need material coming

from automatic insertion area the containers placed

in the stockage area, located at the end of the

automatic insertion lines are transported, through

milkruns, to the final assembly, were the final PCBs

processing step takes place. Therefore, only when

the containers are transported to final assembly

kanbans are released in order to go back to the

kanbans board and start a new cycle.

In a similar way, when the automatic insertion

area requests material to the cell the materials

grouped in the local storage area (the so called

supermarket) located at the end of the manufacturing

cell, are transported to the lines, where the automatic

components insertions in the PCBs takes place.

Therefore, every time a kanban returns from the

supermarket to the board it is incorporated in the

corresponding product area in order to constitute a

new product batch. Once the product batch level is

reached the corresponding cards (kanbans) are put

on its buffer, which is a box, where the cards are

being removed accordingly to the FIFO rule.

After being removed from the buffer, the

kanbans are placed into a programming rule, located

at the bottom of the kanban board, where the

production programming is establisher for a rage of

three daily working periods, based on the production

times referred on each kanban. After leaving the

programming ruler the kanban follows through the

whole line and cell being attached to a container at

the end of line and the cell and moving towards the

supermarket, where it waits until it is necessary in

the automatic and in the manual components

insertion areas.

Figure 10: Cell kanban system.

In order to enable to establish a better data

comparison the same PCBs example used for the

line case is going to be used for the proposed

cellular manufacturing case.

In the proposed scenario only the NPT and the

RT loop values are different. This is due to proposed

manufacturing cell environment, which enables

setup and processing time’s reduction. Therefore,

the net production time (NPT) increases but the

replacement time reduces and at the end we obtain a

reduced product processing time (25 minutes) and

cycle time (9 seconds), as shown in Table 3.

Table 3: Cell parameters calculation

With these values we were able to calculate the

associated RE, LO, WI, TI and SA values as

follows.

Table 4: Cell kanbans calculation

As we can observe in Table 4, the number of

kanbans reduced from 35 kanbans to 30 kanbans.

This corresponds to reducing 5 kanbans per day and,

therefore, a reduction of 100 kanbans per month (20

working days), maintaining the product demand.

Thus, in a range of 6 months we are able to obtain a

significant reduction of around 600 kanbans.

The kanbans reduction is due, on one hand, to

the increase on the NPT and to the reduction on the

cell replenishment time.

KMIS 2010 - International Conference on Knowledge Management and Information Sharing

Ohno (1988) referred that the number of kanbans

reduction led to the reduction of the intermediate

and final stocks levels, enabling a better adjustment

to the regular demand variation. Moreover, Shingo

(1996) stated that eliminating stocks reduces down

to 40% on labour costs.

For the proposed cell scenario the same forecast

analysis was carried out as for the line case, based

on the same product data, covering a range of 6

months, and the results obtained are expressed in

Figure 11, which shows that at the end of this

planned period a total of 2.581 kanbans was

obtained.

Figure 11: Number of kanbans in the proposed cell.

Comparing the results obtained for the proposed

cellular manufacturing system with the existing line

system we can observe that the total number of

kanbans reduced significantly. At the end of the six

months period analysed, the number of kanbans

reduced from 2.936 in the line scenario down to

2.581 (less 355 kanbans) in the cell scenario.

Figure 12: Total number of kanban comparison.

In Figure 12 we can observe the variations of the

number of kanbans, along the six month period, in

both scenarios simultaneously for a better

comparison. Therefore, we were able to obtain a

reduction of around 12 % of the number of kanbans

necessary in the proposed cell scenario at the end of

the six months (from 2.936 to 2.581). This is mainly

due to the increase of the net production time (NPT)

and to the reduction of the replenishment time (RT

loop) in the proposed cell system.

As shown in Figure 12 it is expectable that

product demand suffers some variations from month

to month. Therefore, when a demand increase occurs

is it normal to also have an increase in the number of

kanbans necessary, and vice versa. Ohno (1988)

stated that fluctuations of around 10 to 30% may be

managed without significant changes on the number

of kanbans necessary. Nevertheless, the real

implementation is the most reliable indicator and the

kanbans calculations will change accordingly to the

company’s nature.

On the other hand, regarding the production

system itself, Black (1998) already stated that the

main advantage, even in terms of the umber of

kanbans, arises from the implementation of cellular

manufacturing systems, instead of production lines,

mainly due to it’s increased flexibility, i.e., the

greater capacity that this kind of production system

presents to quickly react to changes, namely the ones

caused by externally imposed changes, where

variations on the demand is included, and also

internal ones, related to product project changes and

changes due to an increased variety of products.

The advantages derived from cellular

manufacturing in comparison with traditional

manufacturing systems in terms of system

performance have been widely discussed by Askin et

al (1993) and Singh (1996). These benefits have

been established through simulation studies,

analytical studies, surveys, and actual

implementations and they can be summarized as

follows:

• Setup time is reduced. A manufacturing cell is

designed to handle parts having similar shapes

and relatively similar sizes. For this reason,

many of the parts can employ the same or

similar holding devices. Generic fixtures for

the part family can be developed so that time

required for changing fixtures and tools is

decreased.

• Lot sizes are reduced. Once setup times are

greatly reduced, small lots are possible and

economical. Small lots also smooth production

flow.

• Work-in-process (WIP) and finished goods

inventories are reduced. With smaller lot sizes

and reduced setup times, the amount of WIP

can be reduced. Askin et al (1993), showed that

the WIP can be reduced by 50% when the

setup time is cut in half. In addition to reduced

setup times and WIP inventory, finished goods

inventory is reduced. Instead of make-to-stock

systems with parts either being run at long,

fixed intervals or random intervals, the parts

KANBAN SHARING AND OPTIMIZATION IN BOSCH PRODUCTION SYSTEM

can be produced either just-in-time in small

lots or at fixed, short intervals.

• A reduction in flow time is obtained. Reduced

material handling time and reduced setup time

greatly reduce flow time.

• Tool requirements are reduced. Parts produced

in a cell are of similar shape, size, and

composition. Thus, they often have similar

tooling requirements.

• Throughput times are reduced. In a job shop,

parts are transferred between machines in

batches. However, in CM each part is

transferred immediately to the next machine

after it has been processed. Thus, the waiting

time is reduced substantially.

As a result of these characteristics, product

quality is also improved: As the parts are transported

individually from one work center to another within

the cell, the feedback is immediate and the process

can be stopped whenever any errors may occur.

5 CONCLUSIONS

Summarizing the above results presented with the

study performed we may highline that several kind

of advantages were able to be reached throughout

the implementation of the proposed work. These

advantages are mainly related to wip and inventory

costs reduction, throughout decreasing the number

of kanbans necessary, under the scope of Lean and

JIT production principles, with are being used in

Bosch Production System.

Another important improvement obtained was

due to the proposed cellular manufacturing system

scenario, instead of the existing line system.

Therefore, it is possible to enhance the production

system, by improving the production flow and

consequently the production tasks management.

Moreover it is possible to simplify materials

acquisition and storage. Besides that, material

handling and control is also simplified.

As a final conclusion we may state that kanbans

sharing and minimization was possible through a

manufacturing system layout change and

improvement, by transforming lines to cellular

manufacturing system. Thus, improving several

other related aspects in the BPS, related to a better

production system arrangement and materials and

production flow, also enabling to facilitate the

production planning and control tasks and material

acquisition, storage, manipulation and control.

Moreover, this study consists on another

contribution in the Lean, JIT and kanban domain

showing that these principles enable to better control

production process, enabling better tasks

performance and enhance productivity and

production quality in manufacturing environments,

by enabling better work integration among

operators, through a closer interaction and

information and responsibility sharing, which is a

clear achievement within the proposed

manufacturing cell. As a consequence, reduced

production time and material and wip flow is also

reached, through the reduction of waste and

distances between work centres within the

manufacturing system, which was also visible in the

proposed manufacturing cell.

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