Product Lifecycle Management (PLM) System for
Shipbuilding Industry Automation of the process of conversion of Engineering BOM to Manufacturing BOM
S.Abhilash Sharma
Final year Dual Degree student,
Dept of Ocean Engineering and
Naval Architecture,
IIT Kharagpur,
Kharagpur, India
O.P.Sha
Professor,
Dept of Ocean Engineering and
Naval Architecture,
IIT Kharagpur,
Kharagpur, India
Rajiv Sharma
Assistant Professor,
Dept of Ocean Engineering,
IIT Madras,
Chennai, India
Abstract— PLM (product life-cycle management) has become
something like „a magic wand‟ for various industries because of
its capability to integrate different product modules via online
network through the product‟s complete life-cycle, and hence
providing one window access; thereby making the whole
processes of product conception, design and manufacturing,
delivery, maintenance and disposal integrated with a reduction in
product development time and cost. However, heavy industries
(i.e. shipbuilding) are different from consumer product industries
because of high customisation in design process, and engineering
software, widely varying scales of operations and less
compatibility between different design and production processes,
e.g. ship production is planned in activity driven network
scheduling system in general, and is assumed more as a
construction process or assembling process rather than a
production process.
One of the key elements of PLM is the Product Data Model
(PDM), which is also termed as the Bill of Material in many
shipyards. Bill of Material is a list of all the materials used to
make the product. Different requirements will require different
BOMs to be made by different departments. In shipbuilding
industry a major problem is developing the manufacturing BOM
(M-BOM) from the engineering BOM (E-BOM). This is because
the E-BOM is structured in a “systems based” manner to suit the
designer, whereas the M-BOM has to follow a “block/zone” based
hierarchy as the shipbuilding process is an assembly of
intermediate products. At present the conversion of E-BOM to
M-BOM is done manually by utilizing the experience of shipyard
personnel. Automation of this process will lead to considerable
decrease in the design process time and hence in overall delivery
time too.
In this paper we present the development and the basic building
concepts for a PLM system for shipbuilding industry and a case
study in “Automation of Conversion of E-BOM to M-BOM”
Keywords; Engineering BOM (E-BOM); Manufacturing BOM (M-
BOM); BOM conversion; PLM Module; E-BOM to M-BOM
I. INTRODUCTION
In the present era where the demand for new ships is on the
rise, shipyards need to be competitive. To maintain their
competitive edge over the others, shipyards are continuously
trying to produce more economical ships within less period of
time. In this endeavour, most of the shipyards are now relying
on product life-cycle management (PLM) systems.
A PLM system has been in existence for a long time, in
most of the manufacturing sectors and primarily acts as the
common platform between the various software resources
being used by the industry and allows for easy exchange of
data across these systems.
Designing is primarily a decision-making process in which
the designer decides the various aspects and attributes of the
product. Integrating the various processes and managing the
resources of an industry across a common platform in real
time helps the designer make more informed decisions and
thus leads to an effective design in lower time.
But in light of the shipbuilding industry, PLM has more
requirements than a general manufacturing industry. This
difference arises primarily due to the nature of the
shipbuilding industry, which is quite different from a general
manufacturing industry. Unlike an assembly line production
prevalent in most of the manufacturing segments, shipbuilding
industry, owing to its high level of customization is forced to
follow a unit assembly production. Thus the PLM system for
the shipbuilding industry should be able to integrate the
processes and resources of different product types.
Similarly, the design work in the shipbuilding industry is
iterative where most of the work needs to be repeated to get a
detailed design. Because of this nature of iterative work, the
design process of the ship takes a lot of time. At present, many
of the shipyards are trying to use the data of the previous
vessels built to reduce the iterative work of design. This is also
one of the fundamental requirements of the PLM system from
the shipbuilding industry's perspective.
PLM system collects the information regarding a product
throughout its lifecycle for future use. Lifecycle of a product
refers to the lifetime of the product which starts from the
conception of the design and ends at the dismantling or reuse
of the product. At every stage, the information regarding the
product is stored into the PLM system. The system should be
effective in extracting the required and relevant information
from the existing information of the previous vessels built so
that the iterative work of the design spiral is reduced.
The overall objective of a PLM system is to streamline the
design and production processes and to achieve economic
designs within lesser time. Thus any bottleneck in the present
design and production processes needs to be dealt by the PLM
system, in order to achieve the competitive edge.
Figure 1 puts together all the functional requirements of a
PLM system for the shipbuilding industry. Thus the
fundamental requirements of a PLM system to be applicable to
shipbuilding industry are:
1. Collecting and storing the ship data in a specific
format which can be used in future.
2. Reuse of previous ship design data to reduce the
iterative work.
3. Sharing information in real time from various
software systems in the shipyard to a common
platform to help the designer make more informed
decisions.
Figure 1: A PLM system for the shipbuilding industry
Figure 2: System Based Hierarchy of an Engineering BOM
4. Provide a scheduling and planning system which can
account for the various lead time offsets in the
shipbuilding processes and make amends to the
schedule.
5. Streamlining of the bottleneck processes to achieve a
lower lead time.
At present most of the shipyards are looking into the
different approaches to achieve the integration between the
various resources and processes of a shipyard. But the major
bottleneck is still in dealing with the Bill of Material. Bill of
Material (BOM) is a hierarchical list of all the constituent
components and materials of a ship. The hierarchy of the
BOM differs across the various departments of the shipyard.
The design department requires a BOM based on a system
based hierarchy, whereas the manufacturing department
requires BOM based on product oriented hierarchy. A ship is
composed of many systems, like the hull structure, outfitting
equipment, ballast water systems, fresh water systems,
electrical cables, HVAC, piping equipment, etc. The design
department divides the ship design work into the designing of
each of the above systems. Thus a group of designers will
always be working on any one particular system of the ship.
Hence it is necessary that the BOM for a designer be
organized in a system based hierarchy.
A typical system based hierarchy is shown in Figure 2.
The second level of the hierarchy in Fig. 2 represents the
division of work of a particular system design among
designers.
The manufacturing department, on the other hand does
not assemble the vessel in a system based manner. Instead, it
adopts a product/block/zone oriented approach to assembly.
The ship as a whole is divided into many interim products like
grand blocks, which are further divided into blocks,
assemblies, subassemblies and finally into the components.
The assembly process starts with assembling the components
to form subassemblies, assemblies and blocks. The blocks are
assembled together to form grand blocks, which are then
assembled to form the entire ship. A typical hierarchy of a
manufacturing BOM is shown in Figure 3. A manufacturer if
provided with a BOM which is organized in a system based
hierarchy would not be able to use the information efficiently.
This is because any particular interim product, like a block
would include components across various systems and would
not provide a complete list of all the components required to
assemble the block.
Thus, there is a necessity to convert the bill of material
developed during the design phase to a form suitable for the
manufacturing department. The design bill of material, also
known as the engineering BOM (E-BOM) needs to be
converted into manufacturing BOM (M-BOM). At present, in
most of the shipyards, this conversion of engineering BOM
into manufacturing BOM is done manually by experienced
manufacturing personnel. To build more ships, economically
and within a less period of time it is imperative that this
conversion process be automated.
Figure 3: Product/Block Oriented Hierarchy
In this paper, a solution for the automatic conversion of
engineering BOM to manufacturing BOM has been suggested.
Section II discusses more about the structure and architecture
of a Shipbuilding PLM system. Section III is a case study
about the automatic conversion of E-BOM to M-BOM and
discusses more about the problem statement and the approach
being used by this paper to solve the problem. Section IV
provides an illustrative example of a sample data on which
this approach has been used. Section V highlights the
conclusions and proposed future works.
II. PLM FOR SHIPBUILDING INDUSTRY
A Product Lifecycle Management (PLM) is a process of
managing the product information over its entire lifecycle. The
lifecycle is a timeline which starts with the conception of the
product (in this case the ship), includes its design, planning,
manufacturing, operation, maintenance and dismantling. It
centers on the ship rather than the shipyard which builds the
ship. A general idea of a PLM system for shipbuilding
industry has been presented in this paper. More information
regarding this architecture and system modules are available
in the works of Kim [3]
.
A PLM system may be thought to be composed of two
major sub-systems, viz. BOM management system and the
process engine.
The BOM management system is composed of two
components:
1. Resource tier data
2. BOM template
The resource tier data is a database storing the BOM data
and its attributes. The data may include components,
drawings, material planning schedule, drawing schedule,
assemblies, blocks, grand blocks, etc. These attributes could
be dimensions of the part or assembly or block, its weight,
volume, etc. Table 1 demonstrates a hypothetical example of
the fields of a database and the data stored therein. B13 and
B21 are blocks while the A11 is an assembly product. As can
be seen, the resource tier data does not have any hierarchical
information. Both block and assembly information is stored in
the same database. The resource tier data may also include
scheduling information, drawing plans, components, etc.
Table 1: Example of the fields of Resource Tier Data
Data
ID
Length in
meters
Breadth in
meters
Depth in
meters
Weight in
tonnes
B13 20 10 10 50
A11 5 5 7 12
B21 22 12 10 65
The hierarchy information is stored in the BOM template.
The BOM template stores the entire hierarchy of the ship
components. A schematic is shown in Figure 4. The BOM
template stores only the hierarchy and does not have any
information about the data associated with the hierarchy. So it
is possible that two sister ships share the same hierarchy but
the data associated with the hierarchy would be different.
When the construction of a new ship commences, a search
of the previous ship data is run to find a reference ship which
is close to the new ship design particulars. These particulars
could be ship type, dimensions, deadweight, speed, block
coefficient, etc. Once the reference ship is decided the
Figure 4: The hierarchy information which is stored in BOM Template
integrated BOM database of this ship is copied and refined to
suit the requirements of the new vessel. So the design process
involves adding new data to replace the old ship data wherever
required. This refinement of the data of the database continues
till the end of the manufacturing design. At the end of the
design, the final integrated BOM for the new ship is obtained
which can further be used while designing more ships in the
future.
The various other functions of the BOM management
system are:
1. Estimation of material demand (amount of material)
2. Preparing exact manufacturing schedule (time)
3. Deciding enough margin for placing Purchase Order
Requisition (POR)
4. Helping designer generate exact design data
5. Effective collaboration in design and manufacturing
Material demand, manufacturing schedule and placing a
POR are all a part of planning and scheduling process.
Planning process is composed of three stages:
1. Main event date
2. Mid-term schedule
3. Daily schedule
The main events are Contract signing, Keel laying,
Launching and Delivery. They are shown in a timeline below
in Figure 5.
Once the main events are decided the mid-term scheduling
is done. In the mid-term scheduling, all the activities related to
manufacturing of the ship are planned. At the end of the mid-
term scheduling the knowledge of how much material would
be required and at what time it would be needed is known.
Mid-term scheduling is shown in the Figure 6. The arrows
indicate the position on the timeline when new material and
equipment would be needed by the production people.
The mid-term schedule is quite important from the design
perspective. The next step is to develop the material plan
(MP). The MP provides the details of the ordering plan i.e.
when to order for the material and equipment. From the MP,
the drawing plan (DP) is generated. Drawing plan is the
schedule of completion dates of different drawings of a ship.
The planning process time line for design and manufacturing
side are shown in Figure 7 and Figure 8 respectively.
The POR is the process through which the order for
material and equipment is placed in a shipyard. This is
basically a designer‟s work. But the information for placing a
POR follows from the Material Plan (MP). Only after the MP
has been finalized can the POR for the steel plates or stiffener
be placed.
Figure 5: Main Events Timeline
Figure 6: Mid-term Scheduling
The POR data gives an estimate of the amount of material
ordered and their expected date of arrival. The POR is placed
on the basis of an “estimate” of how much material would be
needed. But the actual usage of the material is, in most cases,
different from the estimated value.
Figure 9: Project Management Module
Figure 7: Time Line of Planning Process from Manufacturing perspective
Figure 8: Time Line of Planning Process from Design perspective
Shipyards are continuously trying to achieve an estimation
of material which is very close to the actual usage. If a
shipyard overestimates, then it is forced to bear the excess cost
of the extra material. On the other hand if the shipyard
underestimates their material demand, the production process
would be halted temporarily. This will lead to delay in
schedule. Thus it is very important for the shipyard to be able
to estimate the exact material demand.
At present the estimations during contract stages are up to
80% accurate. Mid-term schedule estimates have higher
accuracy rates of around 90-95%. By using the design process
requirements of similar previous ships the PLM system
provides an accurate estimate of the material demand at
different phases of the manufacturing.
Another important aspect is the judging of the margin time
for each POR. There might be some delays in the delivery of
the material and equipment, which would lead to increased
delays in production. Thus the PLM system keeps a record of
the previous delays in order delivery of various suppliers to
assist the designer place the PORs at appropriate times. The
system also keeps track of the difference in the delivery times
of different components to aid the designer in placing a POR
at the right time.
Similarly, a designer preparing a drawing does not have the
complete information regarding the item under consideration.
Consider an example where Designer A is making the drawing
for Block E13. Suppose this drawing requires some input from
the E/R outfit drawings. But say Designer B making the E/R
outfit drawings has not yet completed his work. In this case
Designer A has incomplete information. A PLM system helps
the designer by providing him some previous ship reference
data. Since shipyards produce many ships per year, it is not
possible for the designer to search for the reference data on his
own as the manual search takes a long time. The PLM system
helps in automating this search and thus saves on design time.
Figure 10: Task representation in Project Management Module
Block E11
Block Z
Block X Block Y
Figure 11: Adjoining Blocks of Block E11
Figure 12: Definition of Activities in Process Management Module
To be able to effectively handle the planning and extracting
information the PLM systems are equipped with a process
engine. This process engine is a part of the PLM system and is
composed of two parts:
1. Project management module
2. Process management module
The Project Management Module consists of projects. A
project is a set of all the tasks related to one or a series of
ships. Each of these projects is composed of various tasks or
works. A task or work refers to a single drawing of a particular
ship component or a POR for one part or to a specific design
task. The Project Management Module maps all the tasks on a
timeline and defines the relations between the tasks.
Figure 9 represents a particular scenario of the Project
Management Module. In this figure each of the blue boxes
represents a task or a work. The horizontal axis is the time
line. These tasks are taken from the mid-term schedule and
represented in the above form. The Project Management
Module establishes the relationships between these tasks. It
does not define the nature of relationship but only defines the
existence of a relationship between two tasks.
The Process Management Module extends the definition of
tasks to the next level. All the tasks listed in the Project
Management Module are defined in the Process Management
Module. In the Project Management Module each of the tasks
is a process which was represented as a single unit. But each
task is also a set of activities which need to be performed
sequentially. The Process management module defines these
processes and the activities of a task. Consider the example
shown in Figure 10 which shows the task of preparing the
drawings of Block E21. The definition of the activities and
processes is shown in Figure 12.
The Process Management Module also consists of the
workflow engine which executes the activities and processes
defined in a particular task. Consider the example given in
Figure 12 where the processes and activities of preparing the
drawings of Block E21 have been mentioned. The first step is
the extraction of the relevant reference data from the existing
resources and providing it to the designer. The various
reference documents to be extracted might be Building
specifications, Block division, General Arrangement,
Machinery Arrangement, Engine Room outfitting drawings,
Drawings of the Blocks E81, B51, B12 (adjacent blocks –
Figure 11), Other documents (as per requirement) etc.
Thus when a designer logs into his system the PLM system
provides him with the requisite reference data. The next
activity is the initiation of the CAD program where the
designer would prepare E11 block diagram, E11 nesting plan,
E11 hole plan, E11 outfitting etc. Once the designer has
submitted the drawings, the PLM system would automatically
direct the drawings for inspection which would verify the
drawings. Once the inspection is over the final drawings need
to be updated in the product data model. This updating the
product data model is an automatic process and needs no
manual intervention. Thus the next process calling upon the
data for Block E21 would also include the drawings of Block
E21.
Thus the Process Management Module not only defines a
task but also assigns the processes of a task, controls the
product data and defines the logic of the processes involved.
The BOM management system and Process Engine
together constitute the PLM system which effectively helps in
reducing the design time as well as design cost. The next
section proposes a module for PLM system which would
streamline the process of conversion of E-BOM to M-BOM
which is presently done manually by experienced personnel of
a shipyard.
III. AUTOMATION OF CONVERSION OF ENGINEERING BOM
TO MANUFACTURING BOM
A. Problem Statement
Shipbuilding is primarily an assembly activity which
involves the assembly of various components to form interim
products and the assembly of these interim products yields the
final ship. The production is therefore product oriented or in
other words focuses specifically on a particular interim
product at all times. Hence the manufacturing personnel need
a BOM which is structured in a product oriented hierarchy.
On the other hand the design involves breaking up the ship
into its constituent systems and designing each of these
systems and their components individually. A designer at all
times would be working on a specific system of a ship viz.
hull, outfitting, piping, ballast water systems, fresh water
systems, electrical cables, HVAC etc. Therefore, a designer
requires the BOM to be oriented in a system based hierarchy.
In terms of the data, both the engineering BOM and the
manufacturing BOM share the same components at the lowest
levels of hierarchy. Essentially a plate or a stiffener is a part of
the hull structure from a designer‟s point of view. At the same
time it is a part of a particular block too. Thus, the components
in both the BOMs are same with the difference only in the
grouping of these components and their hierarchy. Thus
conversion of engineering BOM to manufacturing BOM is
essentially re-grouping the components in the engineering
BOM into interim products keeping in mind the assembly
process. Thus the problem statement of automation of the
conversion of engineering BOM to manufacturing BOM is
primarily a re-grouping problem.
Automation of this conversion process will ensure lesser
design time as compared to the manual process which takes a
long time. It will also lead to lesser cost as this process saves
on the manpower being utilized for the designing process.
B. Solution Approach
As already mentioned before, the solution lies in providing
an algorithm which can efficiently re-group the components of
the engineering BOM into the groups of the manufacturing
BOM. The algorithm must however decide on how to group
the various constituents and how many groups are to be
formed. A solution to a similar problem in a manufacturing
sector was proposed by Wang and Li [4] [5]
. They developed an
algorithm to decide the assembly groups of a product on the
basis of assembly sequence.
Consider a product which has eleven components, each
numbered from 1 to 11. The physical connectivity between
each of these 11 components is shown in Figure 13. This
figure is known as the connectivity graph of the product.
Each of the nodes represents a component and the link
between two components denotes the “physical” connectivity
between the two components. Thus, from the figure we can
see that component 5 and 6 are connected to each other
physically but component 1 and 10 are not connected to each
other, even though all the 11 components are a part of the
same product.
Once the connectivity graph has been obtained, a
connectivity matrix for the same is defined. The connectivity
matrix will always be a symmetric matrix, with all the
diagonal elements as zeros. This is because no component is
assumed to be connected to itself. Connectivity between two
nodes is represented by 1 while the absence of connectivity is
represented by 0. Each node necessarily must have a
connection to at least one other node in the graph i.e. the
matrix cannot have any row or column with only zeros.
Let the connectivity matrix be represented by M. If there
are n nodes in the connectivity graph, the size of M would be
n x n. For representing the connectivity between node 5 and
node 6 the value of M (5, 6) and M (6, 5) are both set to 1.
(5 , 6 ) (6 , 5 ) 1M M (1)
Since there is no connectivity between node 1 and node 10,
the corresponding matrix values are set to 0.
(1,1 0 ) (1 0 ,1) 0M M (2)
The connectivity matrix for the connectivity graph shown
in Figure 13 would be:
(3)
The next step is the decomposition of the assembly into
sub-assembly groups. This process starts by finding the
articulation points in the connectivity graph.
An articulation point of a graph is defined as the node
which when removed will fragment the graph into two
separate sub-graphs. For example, consider the node 1 to be
removed from the graph and all the links with node 1 to be
broken. This will lead to two separate sub-graphs {5, 6} and
{2, 3, 4, 7, 8, 9, 10, 11} which do not have any common
nodes. Thus node 1 is an articulation point.
On the hand if node 2 is removed from the graph. It can be
seen that the connectivity throughout the graph still exists and
there are no sub-graphs. Thus node 2 is not an articulation
point.
In the given example there are four articulation points {1 4
7 8}. Based on the articulation points, the 11 components are
grouped to form sub-graphs of the original connectivity graph.
Each of the groups formed represents a sub graph of the
original connectivity graph and none of these groups can be
further decomposed further i.e. there are no articulation points
within the sub-graph. The sub-groups formed are:
Figure 13: Connectivity Graph
Group 1 = {1 5 6}
Group 2 = {1 2 3 4}
Group 3 = {4 7 8}
Group 4 = {7 10 11}
Group 5 = {8 9}
The hierarchy is shown in Figure 14. This division results
in the formation of a 3 level product hierarchy which is
product oriented.
In the actual manufacturing process, the product is divided
into smaller interim products on the basis of ease of division.
An interim product must have minimum connections to other
interim products to make it suitable for independent
concurrent assembly. A block which has a large number of
connections to other blocks would be difficult to assemble
independently as it shares many connections and managing
each of them is difficult. On the other hand if a block is
connected to only one other block, it is possible to assemble it
independently without much consideration for its connectivity
to other blocks. Since the articulation points in a graph are
single elements connecting two sub-graphs, the groups formed
by the algorithm share the same concept of least connections
to other sub-graphs. Thus, the groups formed by the algorithm
are similar to those formed on the basis of ease of division.
There is a minor difference which needs to be accounted for
while adopting this model for the Hull Block Construction
Method (HBCM). The connectivity in case of HBCM does not
indicate physical connectivity. Instead it indicates a structural
connectivity. The method described above finds the
articulation points in the connectivity graph where the
structure can be divided into separate parts. In case of the
structural components of a ship, the division into blocks is
done at a structural joint so that the assembly of these blocks
does not cause a structural weakness at the joint. For this
reason it is necessary that for the HBCM only the structural
connectivity be considered. The algorithm when applied to
structural members provides accurate results only for a
structural connectivity matrix. An example to differentiate the
Product
Group 3 Group 4 Group 5 Group 1 Group 2
1
5
6
1
2
3
4
7
8
7
10
11
8
9
4
Figure 14: Initial Product Oriented BOM
Figure 15: Panels of a typical bulk carrier
structural and physical connectivity has been provided in the
next section.
The structural connectivity is relevant only in the case of
HBCM. For other components such as the piping, outfitting,
HVAC ducts etc a physical connectivity is sufficient to
provide the product oriented hierarchy. This is because the
aim of the breaking up the piping and outfitting structures into
smaller zones does not have any structural issues related to it.
The next section provides an illustration where the present
model has been applied to relevant data for shipbuilding.
IV. ILLUSTRATIVE EXAMPLE
Consider the cargo hold of a typical bulk carrier shown in Figure 15. The problem is to find the different groups into which the components must be grouped as per the above approach and compare its closeness to the actual grouping done in the shipyards.
The typical grouping adopted by a shipyard is shown below in Table 2.
Table 2: Typical grouping from shipbuilding point of view
Sl. No. Group No. Component Elements
1 1 1, 2, 3, 4
2 2 4, 5, 7
3 3 6, 7, 8
4 4 8, 9, 10, 11, 12, 13
5 5 13, 14, 15
6 6 14, 16, 19
7 7 17, 18, 19, 20
For the sake of simplicity and limiting the BOM to only two levels, the assembly groups are assumed to be individual components. The individual assembly groups are numbered as shown in the Figure 15. There are 20 panels defined for this cargo hold. A uniform longitudinal extent is assumed for each of the panels shown. Similarly the floors connecting the various panels have not been included in the calculations as they would not be articulation points and would only be extra nodes connecting different panels.
The various panels under consideration have been listed in Table 3. To apply the approach suggested above, the first step
18 17
20
19 16 14
15
13
12 11
9 10
8
6
7 5
2 3
4
1
Articulation Point
Not an Articulation Point
Figure 16: Connectivity Graph for the cargo hold of the bulk carrier
is to define a connectivity graph between all the panels. Each of the panels would be a node in the connectivity graph. As already mentioned in the previous section, connectivity between these nodes is defined by a structural connectivity instead of physical connectivity. Thus there would not be any connectivity between panel 7 and panel 9 even though there is weld line connectivity between the two. On the other hand, panel 8 and 9 share a structural continuity and are considered to be connected in the connectivity graph. The final connectivity graph is shown in Figure 16.
On the basis of this connectivity graph the articulation points are evaluated. The violet nodes are the articulation points in Figure 16 and the green nodes are not the articulation points. On the basis of these articulation points the groups are formed. The various groups obtained by the application of the algorithm are listed in Table 4.
Table 3: List of panels of cargo hold under consideration
Sl. No. Panel No. Panel Description/ Location
1 1,20 Deck
2 2, 18 Upper Hooper Tank Side Shell
3 3, 17 Inner Upper Hooper Tank
4 4, 19 Tween
5 5, 16 Side Shell
6 6, 15 Lower Hooper Tank Side Shell
7 7, 14 Inner Lower Hooper Tank
8 8, 13 Longitudinal Girder Double Bottom
9 9, 11 Tank Top
10 10, 12 Bottom Shell
It can be seen that the groups generated by the algorithm (listed in Table 4) and the groups decided by a typical shipyard (listed in Table 2) are much in agreement. This shows that the algorithm is quite successful in generating most of the groups.
Table 4: The groups generated from the algorithm.
Sl. No. Group No. Group Elements
1 1 1, 2, 3, 4
2 2 4, 5
3 3 5, 7
4 4 6, 7, 8
5 5 8, 9, 10, 11, 12, 13
6 6 13, 14, 15
7 7 14, 16
8 8 16, 19
9 9 17, 18, 19, 20
V. CONCLUSION AND FUTURE WORKS
This method does not consider the assembly lead time into the grouping methodology. Thus even though the initial Manufacturing BOM has a product oriented hierarchy, it is not clear that this BOM will result in the minimum assembly lead time.
To overcome this problem one can try to perform a critical path analysis with the initial groups formed by the algorithm. Based on this analysis, decision can be taken to merge one or more groups to improve the assembly lead time of the product.
Similarly this method can be applied only to the lower most level of the BOM, because the assembly groups produced after the application of the Wang and Li algorithm cannot be further divided into smaller sub-assembly groups
An approach to overcome this problem might be in trying to apply the same method repeatedly over the groups formed. Thus once the initial groups have been formed out of the components, a similar process is repeated with the group as a whole being considered as a component for the next level. This way a hierarchy can be continued in a bottom to top approach till the final hierarchy has the entire ship in a single group.
Application of these developments would result into a manufacturing BOM which would provide the entire hierarchy and be efficient from the product assembly lead time perspective.
VI. REFERENCES
[1] M. Grieves (2005), „Product Lifecycle Management: Driving the Next Generation of Lean Thinking’ McGraw-Hill, 1st Edition, Oct 2005, pp 141-143
[2] HHI (2009), „Hyundai Heavy Industries Shipbuilding Division Selects Siemens PLM Software Technology to Implement Innovative Digital Shipyard‟, Siemens PLM Software News and Press Release
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