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Dfma lab module (1)
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DESIGN FOR MANUFACTURE AND ASSEMBLY (DFMA): INTRODUCTION TO
BOOTHROYD DEWHURST SOFTWARE
Book · September 2014
DOI: 10.13140/2.1.4108.9285
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Azli Nawawi
Universiti Tun Hussein Onn Malaysia
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2. BDD 40103
DESIGN FOR MANUFACTURE AND ASSEMBLY (DFMA)
INTRODUCTION TO
BOOTHROYD DEWHURST SOFTWARE
Azli Nawawi
DEPARTMENT OF MANUFACTURING AND
INDUSTRIAL ENGINEERING
FACULTY OF MECHANICAL AND MANUFACTURING
ENGINEERING
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Contents
Introduction ............................................................................................................ 4
Importance of DFMA............................................................................................ 4
Preparation before using the DFMA software .......................................................... 4
Product details .................................................................................................... 5
Product disassembly............................................................................................ 5
Structure chart..................................................................................................... 7
Steps to use DFMA software................................................................................... 8
DFM Software ..................................................................................................... 8
DFA Software.................................................................................................... 15
Starting DFA software.................................................................................... 15
Adding parts.................................................................................................. 16
Adding manufacturing operations................................................................... 22
Adding fasteners from DFA library.................................................................. 23
Generating results ......................................................................................... 23
Preparing the report.............................................................................................. 26
Concluding Remarks ............................................................................................ 27
References........................................................................................................... 28
Appendix.............................................................................................................. 29
Appendix A........................................................................................................ 29
Appendix B........................................................................................................ 30
Appendix C ....................................................................................................... 31
Appendix D ....................................................................................................... 32
Appendix E........................................................................................................ 33
Appendix F........................................................................................................ 34
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Introduction
As the cost of materials going up, the prices of home appliances, electronic products,
automotive parts and others follow suit. This scenario put a significance amount of
tense to the manufacturers and consumers. In order to cope with the increasing cost,
manufacturers tend to use DFMA method to simplify the product design and save
some costs.
DFMA enables the customers to get the desired products with same
functionality as the original ones but with a lower cost to produce. To fulfill these
needs, this module focuses on assisting UTHM students in learning one of the
software used for performing DFMA analysis: Boothroyd Dewhurst software.
Importance of DFMA
DFMA offers some benefits such as [1]:
1. Reduction in product development cost.
2. Simplify the structure of a product.
3. Provide good design practices to the designer.
The DFMA software offers a huge savings in time and money. It will assist in the
decision making process for a product design. Another interesting point, the user has
the ability to generate several design options in order to do some comparison. This
software also has one of the most extensive libraries for product’s materials,
production processes, fasteners and additional production operations.
Additionally, this software is a great tool for forecasting and the input or
parameter can be customized in order to fit an actual manufacturing enterprise.
Preparation before using the DFMA software
In order to start using the DFMA software, the user needs to do some preparations.
i. The user needs to identify a product that will be studied in this lab. For
beginners, a product that consists of 30 to 50 parts is suitable.
ii. After the product is identified and approved by the lab instructor, the user can
start by following a flow chart in Figure 1.
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Figure 1: Overall flowchart for DFMA project
Product details
The user has to take some time to gather some information about the product. This
step is crucial because a sound DFMA analysis requires a deep understanding of a
particular product. The user will be needed to eliminate or combine a couple of parts
and from here; a deep understanding of a product is highly needed.
Product disassembly
The next step is to perform the product disassembly. During the disassembly
process, the user is advised to jot down the assembly or disassembly sequences.
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This is important for avoiding the user from forgetting the sequence of product
assembly.
Additionally, the user needs to gather the information related to each part of the
product. The information needed is as follows:
a) Name of the part.
b) Function of the part.
c) Material the part made from.
d) Manufacturing processes of the part.
e) Dimension of the part.
In the DFMA software, only two types of dimension are considered (box-shaped
and cylindrical-shaped).
a) A box-shaped part requires the dimensions of the Height (H), Width (W) and
Length (L)(refer Figure 2).
b) For a cylindrical-shaped part, the Length (L) and Overall Diameter (D) of the
part should be provided (refer Figure 3).
Figure 2: Dimensions needed for a box-shaped part
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Figure 3: Dimensions for a cylinder-shaped part
Structure chart
A structure chart must be constructed along the disassembly process. Any delay will
cause the user to forget the sequence and it will affect the whole analysis. An
example of a structure chart can be seen in Figure 4.
There are two types of parts (Sub-assembly and Part). From the figure, the
Main body is considered as the Sub-assembly because the Main body is actually the
combination of many parts (Keypad, PCB and Connector). An example of Part is the
Battery cover because it is a standalone part.
It is very crucial for the user to identify the Sub-assembly and Part correctly
because any mistake made in this stage will result in a time consuming correction
process once it entered the DFMA software.
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Figure 4: An example of a structure chart
Steps to use DFMA software
The Boothroyd Dewhurst DFMA software is divided into two main components (DFM
and DFA). DFM stands for Design for Manufacture while DFA is for Design for
Assembly.
DFM analysis needs to be done on all parts except the standard fasteners
such as screws, bolts, nuts and washers because the data regarding these fasteners
are available in the software’s library.
DFM Software
In this module, an example of product will be used for the purpose of explanation [2].
Figure 5 shows a piston-assembly design before the DFMA process. For the DFM
software explanation, the Main block (refer the most bottom part) is used as an
example.
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Figure 5: Piston-assembly design [2]
The DFM software is useful for investigating the quantitative effects on
changing a part’s material and manufacturing process [3]. The main output of DFM is
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the cost for a piece of part according to the life volume (quantity of the part to be
manufactured).
To start the DFM software, the user needs to click on an icon named DFM
Concurrent Costing. Slightly after that, the Graphical User Interface (GUI) for the
software will appear (refer Figure 6).
Figure 6: The Graphical User Interface (GUI) of DFM software
a) To change the unit, the user needs to go to ToolsSet Unit. From here, the
user can change from English units to the Metric units.
b) The user needs to key in the part’s name. Part’s number can be typed in if
available.
c) The default Life Volume value is 100,000 units. This value shows the number
of parts to be manufactured. For now, it is better to stick with the default value.
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d) The next step is to select the Envelope shape that can represent the part. If
the part has a chamber or room inside it, the user should choose the Envelope
shape with hollow characteristic.
e) The next question is the Dimension of the part. The types of dimension
needed can be referred in Figure 2 and Figure 3. Additionally, the thickness of
the part is also required.
f) The next step is to select the manufacturing process and part’s material. This
can be done by clicking Select process and material command button.
Figure 7: The GUI for selecting the process and material
g) The tips here are to select the material first and then followed by the process
(refer Figure 7).
h) Once the user clicks OK, the DFM software will calculate the cost for a unit of
the part if the total amount of production is equal to the Life Volume. As an
example, if part A is produced in the quantity of 100,000, the cost for one unit
of part A is RM X.
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i) Another useful feature of the DFM software is the user is able to adjust the
value of various parameters related to the manufacturing process, machine
parameters and process parameters (refer Figure 8)
j) The generated results can be seen at the left-bottom of Figure 8.
Figure 8: The results generated once the process and material are selected
To generate a graph, the user can go to the menu Graph. An example of a graph
generated can be seen in Figure 9.
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Figure 9: A graph generated by the DFM software
Interestingly, this software is capable of performing the analysis for more than
one material. Figure 10 shows the value for a same part made from Modified
polyphenylene oxide (plastic) and Generic aluminum alloy. It can be concluded from
the graph that the part made from aluminum costs higher. This price is for the part
made in a batch quantity of 100,000 pieces.
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Figure 10: Price comparison for a part made from plastic and aluminium
Figure 11: The price difference between a part made using different processes
(injection molding and thermoforming)
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In the same way, the user can also compare the part’s price between different
manufacturing processes (refer Figure 11). This feature is very useful for the decision
making process.
It is also worth to note that, one part should have a DFM file (analysis). As a
result, if a product has 30 parts, there should be 30 DFM analyses.
a) It is advised to divide the parts equally between group members.
b) Once all DFM analyses are completed, the user can proceed to the
DFA software. In the DFA software, the user will assemble or gather the
parts together to form the product.
c) From here, a good structure chart will be very helpful.
DFA Software
The DFA software is used evaluate the assembly process of a product. It is in this
software, where the user is suggested to eliminate or combine the parts. The main
goal of this software is to simplify the assembly process so that the time and cost can
be reduced [4].
Starting DFA software
To start the software, the user needs to click on the icon named Design for
Assembly. The GUI for the DFA software is shown in Figure 12. In the software:
a) The user can change the Units from English to Metrics in the Settings box.
b) Next, the name of the product can be typed in the Name textbox.
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Figure 12: The initial GUI for DFA software
Adding parts
There are two main ways to add parts. The user can go to Analysis menu or the
icons in Figure 13 can be used. However, it is recommended to use the icons since it
saves time.
Figure 13: Icons for adding parts
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From Figure 13:
a) The first icon is used for adding a Part in the assembly. This icon is useful if
the part has no DFM file.
b) The second icon is for adding a Sub-assembly. As seen in Figure 4, a sub-
assembly is a combination of more than one part.
c) The third icon is for adding Operations such as applying grease, soldering,
welding and others.
d) In order to add parts from the library, the fourth icon can be selected. Most of
the parts in the library are fasteners such as screws, nuts, bolts and washers.
e) The last icon (fifth) is for adding parts that come with DFM analyses. This icon
is also known as Add DFM Item. In this module, the fifth icon is used since the
DFM analyses are already available for all parts.
Once the user clicked the fifth icon, a browsing window will appear (refer Figure
14). In this window, the user needs to search for the DFM files. Only one DFM file
can be added at a time. (Note: Make sure to add the base part first)
The sequence for adding DFM files can be referred from the structure chart. An
example of structure chart is shown in Figure 4.
Figure 14: A browsing window for searching and adding DFM files
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Figure 15 shows a DFM file that is successfully added. It can be seen that the part
name (main block) is located under the main product. This shows that the main block
is the base part.
Figure 15: The first DFM file (main block) is inserted
Once a part is inserted, the user has to answer several questions related to the
part (refer Figure 16). The categories of questions are as below:
a) Definition.
b) Securing method.
c) Minimum part criteria.
d) Envelope dimensions (Can be skipped if DFM file is available).
e) Symmetry.
f) Handling difficulties.
g) Insertion difficulties.
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Figure 16: The questions related to the part
Definition related questions
In Definition related questions, the Name of the part is already inserted if the DFM file
is already added to the assembly (refer Figure 17). Moreover, an additional
identification in the form of Part number can be inserted in the system.
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Figure 17: Questions related to Part Definition
From the Figure 17, the most important question is the Item type. The user needs to
declare whether the part is actually a single part or a sub-assembly. For more
information, the user can refer Figure 4.
Securing Method
Figure 18: The answer options for the Securing method
In the Securing method category, the user has to define how the part is
secured/fixed/mounted to the base part or the part before it. As an example, the main
block (base part) will be secured later because after all parts added to the base, the
parts will be “secured later” by fasteners (screws) (refer Figure 18). If the part is a
bottle cap, the securing method will be Thread.
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Minimum Part Criteria
In the Minimum part criteria, the category of part will be selected. From here, the
potential parts to be eliminated or combined with other parts can be identified.
Figure 19: The categories of part
In the Minimum part criteria, the categories are separated by a fine line (refer
Figure 19). For a part belongs to any category above the line should not be combined
or eliminated. This is because the part is considered as an important part that
supports the product functionality. Below are the explanations of each category:
a) Base part: The first part that act as the main platform for other parts to be
assembled in. According to Figure 5, the main block is considered as the base
part.
b) Material: A part that should be made from different material compared to other
neighbouring parts. As an example, the tyre and rim of your car should not be
combined because the tyre should be made from synthetic rubber while the
rim is made of steel. If the tyre can be combined with the rim, it will also be
made from steel and your car will not have a smooth ride and a proper
stopping power.
c) Movement: A part cannot be eliminated or combined with other parts if it is
used for performing movement. A simple example will be; a door should not be
combined with the wall because the door needs to perform some movements
(open and close).
d) Assembly: Two parts should not be combined if something needs to be
inserted between the parts. As an example, the lid of your Tupperware
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container should not be combined with the container’s body or else, you will
not be able to fill the food inside the container.
A part that can be eliminated or combined falls under these categories:
e) Fastener: A part that used to combine more than two parts together such as
screws, nuts, rivets, nails and others. This part can be eliminated if it doesn’t
jeopardize the functionality and durability of a product.
f) Connector: A part that is used to connect more than two parts but does not
have a significant function.
g) Other: Any part that did not fall into any category can be described as Other.
Adding manufacturing operations
In order to add any Operation, the user can click the third icon (refer Figure 13).
Then, the software will show a library that provide a list of operations (refer Figure
20). The user can select the suitable operation from here. In the piston-assembly
example, the operation needed is to apply oil for lubricating the parts. To do that, the
user needs to choose the Material application.
Figure 20: The library for adding operations
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Another useful feature of the DFM software is the availability of parts’ library.
In this library, the parts’ are actually fasteners (screws, bolts, nuts and washers).
Adding fasteners from DFA library
To insert a fastener, the user needs to click on the fourth of Figure 13. Once the icon
is clicked, a GUI in Figure 21 will appear. In this figure, a lot of fasteners types can be
seen. It is advised for the user to get to know the types of screws on their product
before proceeding to this stage.
Figure 21: The library of fasteners
.
Generating results
Once all parts are inserted, the user can proceed with generating the results (refer
Figure 22). The results are presented in the form of charts and tables. To view the
results, the user can go to Reports menu. From here, the user can choose the type of
results to be generated.
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Figure 22: All parts have been inserted
The types of results are as below:
a) Executive Summary of DFA (refer Appendix A).
b) Executive Summary of DFMA (refer Appendix B).
c) Product Worksheet (refer Appendix C).
d) Structure Chart (refer Appendix D).
e) Analysis Totals (refer Appendix E).
f) Suggestions for Redesign (refer Appendix F).
These results show the performance of the original design in terms of manufacturing
cost, product’s cost, product’s weight, DFA index and assembly time. Logically, the
user will want to reduce the cost, weight and time. As for the DFA index, the higher is
the better. A higher index means the product is easier to be assembled.
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Another useful feature of this software is the Suggestion for Redesign (refer
Appendix F). These suggestions are very useful to improve the design of the original
product. The software might suggest for combining or eliminating some parts and
fasteners. Additionally, there will be some solutions for the handling and insertion
difficulties during the assembly process. An improved piston-assembly design is
shown in Figure 23.
From the improved design, the fasteners (screws) are eliminated and replaced
with a snap-fit mechanism. Moreover, the number of parts is also reduced. As a
result, the improved product will be faster to assemble and cheaper to produce.
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Figure 23: The improved design of a piston-assembly design [2]
Preparing the report
The final stage of this project is to prepare a report. The format for the report is
presented in Table 1.
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In the Results and Discussion, the user is needed to propose 3 design options.
Each option focuses on different set improvements which are product’s materials,
manufacturing processes and assembly processes.
In the last chapter (Conclusion), the user has to justify the percentage of
improvements for each option. The improvements are in terms of product’s weight,
manufacturing cost, assembly time and DFA index.
Table 1: Report format
Chapter Contents
Introduction What have you did?
Why it was important?
Literature Review Briefly describe about:
Definition of DFMA.
Applications of DFMA.
Methodology Please refer Fig.__
Results and
Discussion
List and discuss the DFM and DFA results for the:
Original product design.
Design Option 1: Improvement of product’s materials.
Design Option 2: Improvement of manufacturing processes.
Design Option 3: Improvement of assembly processes.
Comparison between all options above.
Please include the sketch drawing for each option of product design.
Conclusion Justify the % of improvement.
Concluding Remarks
This module provides a brief introduction of Boothroyd Dewhurst software.
This software is very useful for students who enrolled in the Design for Manufacture
and Assembly (DFMA) subject. It is worth to note that, without the software, the
decision making process might be longer because the designer needs to perform the
DFMA analysis and calculations manually.
The DFMA software will not generate a new and improved design. However,
this software will assist the user to improve a product design by suggesting some
improvements. Fortunately, this software is quite easy to learn and the user is
advised to propose several design improvement in order to construct a robust
analysis. Once the user knows how to use this software, the job for proposing new
design improvements will just be a brief. It is very interesting to “play” around with
different materials and production processes and the author believe that some user
will enjoy this learning session. Lastly, do enjoy the module! Any suggestions for
improvement are highly welcomed!
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References
[1] G. Lucchetta, et al., "Integrated design analysis for product simplification," CIRP Annals-
Manufacturing Technology, vol. 54, pp. 147-150, 2005.
[2] G. Boothroyd and P. Dewhurst, Product design for assembly: Boothroyd Dewhurst
Incorporated, 1991.
[3] B. D. Inc., DFM Concurrent Costing vol. Version 2.3. Rhode Island: Boothroyd Dewhurst Inc.,
2009.
[4] B. D. Inc., Design for Assembly vol. Version 9.4. Rhode Island: Boothroyd Dewhurst Inc., 2009.
