DESIGN FOR MANUFACTURE AND ASSEMBLY (DFMA)
“DFM ASSIGNMENT – LOGITECH COMPUTER MOUSE”
PREPARED BY
MOHD NIZAM BIN ALI
DEPT. OF MANUFACTURING AND INDUSTRIAL ENGINEERING
FACULTY OF MECHANICAL ENGINEERING
UNIVERSITI TEKNOLOGI MALAYSIA
2010
I
LIST OF FIGURE
Page Figure 2.1 The product design phases and material selection
(Adapted from Mangonon 1999) 4 Figure 2.2 Factors influencing the material selection processes 5 Figure 2.3 Taxonomy of manufacturing processes (adapted from Groover, 1996) 8 Figure 2.4 Types of casting processes 10 Figure 2.5 Types of forging processes 10 Figure 2.6 Types of extrusion processes 11 Figure 2.7 Classification of various machining processes 12 Figure 3.1 PCB Lower Case (New Design) 13 Figure 3.2 PCB Upper Case (New Design) 13 Figure 3.3 PCB Upper Case Cover (New Design) 14 Figure 3.4 Clicker Wheel 14 Figure 3.5 Clicker Wheel Shaft Holders 15 Figure 5.1 Injection molding machine 55
II
LIST OF TABLES
Page Table 4.1 Compatibility between processes and materials 16 Table 4.2 Shapes attributes for PCB Lower Case (New Design) 17 Table 4.3 Process elimination based on 8 geometric attributes
PCB Lower Case (New Design) 18 Table 4.4 Final process selection based on process/materials combination of
PCB Lower Case (New Design) 19 Table 4.5 Compatibility between processes and materials 21 Table 4.6 Shapes attributes for PCB Upper Case (New Design) 22 Table 4.7 Process elimination based on 8 geometric attributes
PCB Upper Case (New Design) 23 Table 4.8 Final process selection based on process/materials combination of
PCB Lower Case (New Design) 24 Table 4.9 Compatibility between processes and materials 26 Table 4.10 Shapes attributes for PCB Lower Case Cover (New Design) 27 Table 4.11 Process elimination based on 8 geometric attributes
PCB Upper Case (New Design) 28 Table 4.12 Final process selection based on process/materials combination of
PCB Lower Case Cover (New Design) 29 Table 4.13 Compatibility between processes and materials 31 Table 4.14 Shapes attributes for Clicker Wheel 32 Table 4.15 Process elimination based on 8 geometric attributes
Clicker Wheel 33 Table 4.16 Final process selection based on process/materials combination of
Clicker Wheel 34 Table 4.17 Compatibility between processes and materials 36
III
Table 4.18 Shapes attributes for Clicker Wheel Shaft Holders 37 Table 4.19 Process elimination based on 8 geometric attributes
Clicker Wheel Shaft Holders 38 Table 4.20 Final process selection based on process/materials combination of
Clicker Wheel Shaft Holders 39 Table 5.1 Mould cavity pressure required depending on the product group 42 Table 5.2 PBT unreinforced and PBT reinforced process requirement 52 Table 7.1 Parts and materials requirement 60 Table 7.2 Parts attributes 61 Table 7.3 Final selection for material and processes 62
MMP 1663 DFM Assignment: Logitech Computer Mouse
1
1.0 OBJECTIVE
The objectives of the DFM assignment are:
Apply the principle of design for manufacturing for selected part in Logitech
computer mouse.
Suggested the suitable material to be used based on the part material requirement
and performance functions.
Examine the modern manufacturing operations capabilities and limitations
including machining, casting, forging, soldering, brazing, finishing, heat treating,
assembly, plastic materials processing, powder metallurgy and specialized
manufacturing processes.
Discuss the relation of the manufacturing process related to the part design and
cost.
MMP 1663 DFM Assignment: Logitech Computer Mouse
2
2.0 INTRODUCTION
2.1 Manufacturing, Design and Design for Manufacturing (DFM)
Different uses of the word manufacturing create an unfortunate confusion.
Sometimes the word is used to refer to the entire product realization process, that is, to
the entire spectrum of product-related activities in a firm that makes products for sale,
including marketing (e.g., customer desires), design, production, sales, and so on. This
complete process is sometimes referred to as "big-M Manufacturing." But the word
manufacturing is also used as a synonym for production, that is, to refer only to the
portion of the product realization process that involves the actual physical processing of
materials and the assembly of parts. This is sometimes referred to as "little-m
manufacturing."
Design (as in a design process) is the series of activities by which the information
known and recorded about a designed object is added to, refined (i.e., made more
detailed), modified, or made more or less certain. In other words, the process of design
changes the state of information that exists about a designed object. During successful
design, the amount of information available about the designed object increases, and it
becomes less abstract. Thus, as design proceeds the information becomes more complete
and more detailed until finally there is sufficient information to perform manufacturing.
Design, therefore, is a process that modifies the information we have about an artifact or
designed object, whereas manufacturing (i.e., production) modifies its physical state.
Design for manufacturing (DFM) is a philosophy and mind-set in which
manufacturing input is used at the earliest stages of design in order to design parts and
products that can be produced more easily and more economically. Design for
manufacturing is any aspect of the design process in which the issues involved in
manufacturing the designed object are considered explicitly with a view to influencing
the design. Examples are considerations of tooling costs or time required, processing
costs or controllability, assembly time or costs, human concerns during manufacturing
MMP 1663 DFM Assignment: Logitech Computer Mouse
3
(e.g., worker safety or quality of work required), availability of materials or equipment,
and so on. Design for manufacturing occurs or should occur throughout the design
process.
2.2 Consideration and Selection of Materials
After the conception of a product idea, the question that the research and
development (R&D) personnel must ask is, what would be the best material for the
product? More often this is closely followed by the question, is the material selected
easily manufacturable? In other words, what would be the best material and process
combination for developing a product that not only performs the indispensable functions
but is also economical to manufacture. A design criterion for the product based only on
either material or process has all the ingredients of a recipe for disaster. The choice of
material is a major determinant for the successful functioning and the feasible, low-cost
manufacture of any product.
Materials are at the core of all technological advances. Mastering the
development, synthesis, and processing of materials opens opportunities that were
scarcely dreamed of a few short decades ago. The truth of the statement is evident when
one considers the spectacular progress that has been made in such diverse fields as
energy, telecommunication, multimedia, computers, construction, and transportation.
It is widely accepted that the final cost of a manufactured product is determined largely at
the design stage. Designers tend to conceive parts in terms of processes and materials
with which they are familiar and, as a consequence, may not consider process and
material combinations that could prove more economical. Sometimes, the designers tend
to focus only on the cost aspect of materials and manufacturing and select a combination
of materials and processes that lead to products of substandard quality and reduced
operating life. In the long run, this not only leads to reduced brand loyalty for the product
but, in many cases, to huge financial losses as a result of litigations and product liability
lawsuits. The already difficult task of satisfying engineering and commercial
requirements imposed on the design of a product becomes even more difficult with the
MMP 1663 DFM Assignment: Logitech Computer Mouse
4
addition of legislated environmental requirements. A vital cog in this product design
wheel is the materials engineer. The optimal selection of material used to construct or
make the product should lead to optimum properties and the least overall cost of
materials, ease of fabrication or manufacturability of the component or structure, and
environmentally friendly materials.
Figure 2.1 The Product Design Phases and Material Selection (adapted from
Mangonon, 1999).
Figure 2.1 shows the various stages of the design process with their associated
activities. The material selection process consists of the property, process, and
environmental profiles concurrently considered at each phase of design. What happens if
the material selection is not considered during each stage of the design decision process?
The designer would be unaware of any problems about the availability of the final
material, the costs associated with the manufacturing processes, or the processability of
the product to be manufactured. Consider a designer who needs to design a product but
has no idea of the material from which to make it. Suppose the designer designs the
MMP 1663 DFM Assignment: Logitech Computer Mouse
5
product considering it to be a metallic, but management decides to make it of ceramics at
a later stage. The processing of a ceramic product is entirely different from that of a
metallic product. Ceramic and metallic products vary in structure, strength properties,
manufacturability, and so on. Therefore, it is critical that decisions regarding materials to
be used for manufacturing a product be made in a timely fashion (Mangonon, 1999). The
selection of an appropriate material and its conversion into a useful product with the
desired shape and properties is a complex process. The first step in the material selection
process is the definition of the needs of the product. Figure 2.2 shows the factors
affecting the material selection process:
Figure 2.2 Factors Influencing the Material Selection Processes.
a. Physical factors: The factors in this group are the size, shape, and weight of the
material needed and the space available for the component. Shape considerations
greatly influence selection of the method of manufacture. Some typical questions
considered by a materials designer are. What is the relative size of the
MMP 1663 DFM Assignment: Logitech Computer Mouse
6
component? How complex is its shape? Does it need to be one piece or can it be
made by assembling various smaller pieces? How many dimensions need to be
specified, and what are the tolerances on these dimensions? What are the surface
characteristic requirements for the product? All the factors in this category
interrelate to the processing of the material. For example, shape and size might
constrain the heat-treatment of the material. The shape of the product determines
whether casting could be used. Material consideration, to a large extent, also is
determined by the space available for the component.
b. Mechanical factors: The ability to withstand stress and strain is determined by
these factors. Strength, ductility, modulus, fatigue strength, and creep, are some
mechanical properties that influence what material needs to be used. The
mechanical properties also are affected by the environment to which the materials
are exposed. Some typical questions that designers consider while narrowing
down the material to be used are. What are the static strength needs of the
product? What is the most common type of loading to which the product would be
subjected during its use (tensile, compressive, bending, and cyclic)? Is the loading
static or dynamic? Would the product be subjected to impact loading? Does the
product require wear resistance? What temperature range must the mechanical
properties possess?
c. Processing and fabrication factors: The ability to form or shape a material falls
under the processing and fabrication factors. Casting and deformation processing
are commonly used. Typical questions that arise out of consideration of these
factors are Has the design addressed the requirements that facilitate ease of
manufacture? Machineability? Weldability? Formability? Hardenability?
Castability? How many components are to be made? What must be the production
rate? What are the maximum and minimum cross-sectional dimensions? What is
the desired level of quality for the finished product? Small objects more
commonly are investment casted, while intricate shapes are produced as casting.
Powder metallurgy, or a sintering process, is commonly used for the brittle
materials like ceramics.
MMP 1663 DFM Assignment: Logitech Computer Mouse
7
d. Life of component factors: These factors relate to the life of the materials to
which they perform the intended function. The properties of this group are the
external surface properties like oxidation, corrosion, and wear resistance and
some internal properties like fatigue and creep. The performance of materials
based on these properties is the hardest to predict during the design stages.
e. Cost and availability: With reduced lead times from design to market, there is a
tendency to jump to the first material that fits the selection profile. It is important
to note that additional effort determining the correct material helps optimize the
manufacturing costs. Also, standardization of parts and materials is related to the
cost of the final product. Special processing requirements or rare materials with
limited availability increase the final cost and affect the timely manufacture of the
product.
2.3 Economic of Material Selection
After developing a comprehensive list of requisite properties in a material,
categorize these properties according to their level of criticality. Some property
requirements may be absolute, while others may be relative. The absolute ones cannot be
compromised and should be used as a filter to eliminate the materials that cannot be used.
It is apparent that no one material would emerge as the obvious choice. Here, the
knowledge of a materials engineer and the handbook-type data need to be utilized. Also,
the cost factor of materials needs to be closely analyzed here. Cost is not a service
requirement, but it plays an important part in the selection process, both the material cost
and the cost of fabricating the selected material. The final decision involves a
compromise between the cost, producibility, and service performance.
Current market and economic trends force companies to produce low-cost, high-
quality products to maintain their competitiveness at the highest possible level. There is
no doubt that reducing the cost of a product is more effective at the design stage than at
the manufacturing stage. Therefore, if the product manufacturing cost can be estimated
MMP 1663 DFM Assignment: Logitech Computer Mouse
8
during the early design stage, designers can modify the design to achieve proper
performance as well as a reasonable cost at this stage, and designers are encouraged to
design to cost.
2.4 Selection of Manufacturing Processes
The manufacturing process is the science and technology by which a material is
converted into its final shape with the necessary structure and properties for its intended
use. Formation of the desired shape is a major portion of processing. The product
processing could be a simple, one step operation or a combination of various processes,
depending on the processability of the material used and the specifications for the
finished part, which includes surface finish, dimensional tolerances, and so forth. The
method of selecting the appropriate process is closely tied to the selection of material.
What leads to a successful manufacturing process? The performance of any
manufacturing process depends on:
a. Rate: material flow through the system.
b. Cost: material, labor, tooling, equipment.
c. Time: lead time to procure materials, processing time, setup time.
d. Quality: deviation from the target.
All these factors result from decisions made in selecting the process-material-part
combination. As designers and engineers developing a new product, at this juncture, we
already have the basic part drawing and a selection of various material-process
combinations feasible for the part. The next stage is arriving at the material-
manufacturing process combination that is technically and economically feasible. Figure
2.3 shows the taxonomy of manufacturing processes. The processes are arranged by
similarity of function. Manufacturing processes can be broadly classified into three
categories. Based on the desired outcome, they are primary, secondary, or tertiary
processes.
MMP 1663 DFM Assignment: Logitech Computer Mouse
9
Figure 2.3 Taxonomy of Manufacturing Processes (adapted from Groover, 1996)
2.5 Primary Processes
The primary process generates the main shape of the final product. The primary
process is selected to produce as many required shape attributes of the part as possible.
Such processes appear at the top of the sequence of operation for a part and include
processes such as casting, forging, molding, rolling, and extrusion.
a. Casting: Casting is the fastest way to attain simple or complex shapes for the part
from its raw material. The casting process basically is accomplished by pouring a
liquid material into a mold cavity of the shape of the desired part and allowing it
to cool. The different types of casting methods (for both metals and nonmetals)
are shown in Figure 2.4.
MMP 1663 DFM Assignment: Logitech Computer Mouse
10
Figure 2.4 Types of Casting Processes
b. Forging: Forging is a deformation process in which the work is compressed
between two dies using either impact or gradual pressure to form the part. The
different types of forging processes are shown in Figure 2.5.
Figure 2.5 Types of Forging Processes
c. Extrusion: Extrusion is a compression forming process in which they worked
metal is forced to flow through a die opening to produce the desired cross-
sectional shape. Extrusion usually is followed by a secondary process, cold
drawing, which tends to refine the molecular structure of the material and permits
sharper corners and thinner walls in the extruded section. The different extrusion
processes can be classified as shown in Figure 2.6.
MMP 1663 DFM Assignment: Logitech Computer Mouse
11
Figure 2.6 Types of Extrusion Processes
2.6 Secondary Processes
The secondary processes, in addition to generating the primary shape, form and
refine features of the part. These processes may appear at the start or later in a sequence
of processes. These include all the material removal processes and processes such as
machining, grinding, and broaching.
Machining is the process of removing material from a workpiece in the form of
chips. The term metal cutting is used when the material is metallic. Most machining has a
very low setup cost compared to the forming, molding, and casting processes. However,
machining is much more expensive for high volumes. Machining is necessary where tight
tolerances on dimensions and finishes are required.
The different machining processes are shown in Figure 2.7. It is commonly
divided into the following categories:
a. Cutting generally involves single-point or multipoint cutting tools, each with a
clearly defined geometry.
b. Nontraditional machining processes utilize electrical, chemical, and optimal
sources of energy.
MMP 1663 DFM Assignment: Logitech Computer Mouse
12
c. Abrasive machining processes are categorized under surface treatment and, hence,
are discussed as tertiary processes.
Figure 2.7 Classifications of Various Machining Processes
2.7 Tertiary Processes
The tertiary processes do not affect the geometry or shape of the component and
always appear after one or more primary and secondary processes. This category consists
of finishing processes, such as surface treatments and heat treatments. Selection of a
tertiary process is simplified because many tertiary processes affect only a single attribute
of the part.
MMP 1663 DFM Assignment: Logitech Computer Mouse
13
3.0 SELECTED PARTS
Part that are selected to be analysed in DFM as shown below:
A: PCB Lower Case (New Design)
Figure 3.1 PCB Lower Case (New Design)
B: PCB Upper Case (New Design)
Figure 3.2 PCB Upper Case (New Design)
MMP 1663 DFM Assignment: Logitech Computer Mouse
14
C: PCB Upper Case Cover (New Design)
Figure 3.3 PCB Upper Case Cover (New Design)
D: Clicker Wheel
Figure 3.4 Clicker Wheel
MMP 1663 DFM Assignment: Logitech Computer Mouse
15
E: Clicker Wheel Shaft Holder
Figure 3.5 Clicker Wheel Shaft Holders
MMP 1663 DFM Assignment: Logitech Computer Mouse
16
4.0 SUITABLE MATERIALS AND PROCESSES FOR EACH SELECTED PART.
4.1 PCB Lower Case (New Design)
Table 4.1 Compatibility between process and materials
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding Structural Form Moulding Blow Molding (Ext.) Blow Molding (Inj.) Rotational Molding Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts Hot Extrusion Rotary Swaging Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
17
Table 4.2 Shapes attributes for PCB Lower Case (new design)
No. Shapes Attributes Yes/No
1. Depression Yes
2. Uniform Wall Thickness Yes
3. Uniform Cross-Section No
4. Axis of Rotation No
5. Regular Cross-Section No
6. Captured Cavity No
7. Enclosed Cavity No
8. No Draft No
Material Requirement
A Used snap fit features (flexibility)
B Excellent of Electrical Resistivity (> 1015) µΩ.cm
C Good impact resistance
D Light weights
MMP 1663 DFM Assignment: Logitech Computer Mouse
18
Table 4.3 Process elimination based on 8 geometric attributes of PCB Lower Case
(new design).
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Al u
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding 6,2 Structural Form Moulding 6,2 Blow Molding (Ext.) 7,2 Blow Molding (Inj.)
Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM
2 Sheet Metal (Stamp/bend) 2 Themoforming
4,2 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
19
Table 4.4 Final process selection based on process/materials combinations of PCB Lower
Case (new design)
A A A A A A A A A A A B B B B B B B B B B B C C C C C C C C C C D D D D D D D D D D
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding 6,2 Structural Form Moulding 6,2 Blow Molding (Ext.) 7,2 Blow Molding (Inj.)
Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM
2 Sheet Metal (Stamp/bend) 2 Themoforming
4,2 Metal Spinning Compatible between process and materials Not applicable Normal Practices Less Common
MMP 1663 DFM Assignment: Logitech Computer Mouse
20
Based on the final process selection shown above, INJECTION MOLDING is suitable
processes to be selected. Meanwhile, THERMOPLASTICS material is selected to be used for
PCB lower case (new design). The characteristic of part chosen, such as below:
a. Part:
• Size: 115 mm x 60 mm x 25 mm
• Weight: 50 gram
b. Tolerances:
• General: ± 0.15 mm
c. Surface Finish:
• 0. 2- 0.3 µm
d. Product Life Volume
• More than 5 years
e. Process Recommended:
• Injection Molding
f. Materials:
• Thermoplastic
g. Production Volume:
• 10, 000 units
MMP 1663 DFM Assignment: Logitech Computer Mouse
21
4.2 PCB Upper Case (New Design)
Table 4.5 Compatibility between process and materials
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding Structural Form Moulding Blow Molding (Ext.) Blow Molding (Inj.) Rotational Molding Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts Hot Extrusion Rotary Swaging Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
22
Table 4.6 Shapes attributes for PCB upper case (new design)
No. Shapes Attributes Yes/No
1. Depression Yes
2. Uniform Wall Thickness No
3. Uniform Cross-Section No
4. Axis of Rotation No
5. Regular Cross-Section No
6. Captured Cavity No
7. Enclosed Cavity No
8. No Draft No
Material Requirement
A Used snap fit features (flexibility)
B Excellent of Electrical Resistivity (> 1015) µΩ.cm
C Good impact resistance
D Light weights
MMP 1663 DFM Assignment: Logitech Computer Mouse
23
Table 4.7 Process elimination based on 8 geometric attributes of PCB Upper Case
(new design).
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
24
Table 4.8 Final process selection based on process/materials combinations of PCB Upper
Case (new design)
A A A A A A A A A A A B B B B B B B B B B B C C C C C C C C C C D D D D D D D D D D
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
25
Based on the final process selection shown above, INJECTION MOLDING is suitable
processes to be selected. Meanwhile, THERMOPLASTICS material is selected to be used for
PCB upeper case (new design). The characteristic of part chosen, such as below:
a. Part:
• Size: 114 mm x 55 mm x 25 mm
• Weight: 40 gram
b. Tolerances:
• General: ± 0.15 mm
c. Surface Finish:
• 0. 2- 0.3 µm
d. Product Life Volume
• More than 5 years
e. Process Recommended:
• Injection Molding
f. Materials:
• Thermoplastic
g. Production volume
• 10, 000 units
MMP 1663 DFM Assignment: Logitech Computer Mouse
26
4.3 PCB Upper Case Cover (New Design)
Table 4.9 Compatibility between process and materials
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding Structural Form Moulding Blow Molding (Ext.) Blow Molding (Inj.) Rotational Molding Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts Hot Extrusion Rotary Swaging Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
27
Table 4.10 Shapes attributes for PCB Upper Case Cover (new design)
No. Shapes Attributes Yes/No
1. Depression Yes
2. Uniform Wall Thickness Yes
3. Uniform Cross-Section No
4. Axis of Rotation No
5. Regular Cross-Section No
6. Captured Cavity No
7. Enclosed Cavity No
8. No Draft No
Material Requirement
A Used snap fit features (flexibility)
B Excellent of Electrical Resistivity (> 1015) µΩ.cm
C Good impact resistance
D Light weights
MMP 1663 DFM Assignment: Logitech Computer Mouse
28
Table 4.11 Process elimination based on 8 geometric attributes of PCB Upper Case Cover
(new design).
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
29
Table 4.12 Final process selection based on process/materials combinations of PCB Upper
Case Cover (new design)
A A A A A A A A A A A B B B B B B B B B B B C C C C C C C C C C D D D D D D D D D D
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
30
Based on the final process selection shown above, INJECTION MOLDING is suitable
processes to be selected. Meanwhile, THERMOPLASTICS material is selected to be used for
PCB upper case cover (new design). The characteristic of part chosen, such as below:
a. Part:
• Size: 100 mm x 55 mm x 25 mm
• Weight: 30 gram
b. Tolerances:
• General: ± 0.15 mm
c. Surface Finish:
• 0. 2- 0.3 µm
d. Product Life Volume
• More than 5 years
e. Process Recommended:
• Injection Molding
f. Materials:
• Thermoplastic
g. Production volume
• 10, 000 units
MMP 1663 DFM Assignment: Logitech Computer Mouse
31
4.4 Clicker Wheel
Table 4.13 Compatibility between process and materials
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding Structural Form Moulding Blow Molding (Ext.) Blow Molding (Inj.) Rotational Molding Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts Hot Extrusion Rotary Swaging Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
32
Table 4.14 Shapes attributes for Clicker Wheel
No. Shapes Attributes Yes/No
1. Depression Yes
2. Uniform Wall Thickness No
3. Uniform Cross-Section No
4. Axis of Rotation Yes
5. Regular Cross-Section No
6. Captured Cavity No
7. Enclosed Cavity No
8. No Draft No
Material Requirement
A Good shock absorption.
B Excellent of Electrical Resistivity (> 1015) µΩ.cm
C Good impact resistance
D Light weights
MMP 1663 DFM Assignment: Logitech Computer Mouse
33
Table 4.15 Process elimination based on 8 geometric attributes of Clicker Wheel
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding 6,2 Structural Form Moulding 6,2 Blow Molding (Ext.) 7,2 Blow Molding (Inj.)
Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 1 Rotary Swaging Machining (From Stock) ECM EDM WEDM
2 Sheet Metal (Stamp/bend) 2 Themoforming 1 Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
34
Table 4.16 Final process selection based on process/materials combinations of Clicker Wheel
A A A A A A A A A A A B B B B B B B B B B B C C C C C C C C C C D D D D D D D D D D
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
35
Based on the final process selection shown above, INJECTION MOLDING processes is
suitable processes to be selected. Meanwhile, THERMOPLASTICS material is selected to be
used for Clicker Wheel. The characteristic of part chosen, such as below:
a. Part:
• Size: Ø30 mm
• Weight: 20 gram
b. Tolerances:
• General: ± 0.15 mm
c. Surface Finish:
• 0. 2 - 0.3 µm
d. Product Life Volume
• More than 5 years
e. Process Recommended:
• Injection Molding
f. Materials:
• Thermoplastic
g. Production volume
• 10, 000 units
MMP 1663 DFM Assignment: Logitech Computer Mouse
36
4.5 Clicker Wheel Shaft Holder
Table 4.17 Compatibility between process and materials
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding Structural Form Moulding Blow Molding (Ext.) Blow Molding (Inj.) Rotational Molding Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts Hot Extrusion Rotary Swaging Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming Metal Spinning
Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
37
Table 4.18 Shapes attributes for Clicker Wheel
No. Shapes Attributes Yes/No
1. Depression Yes
2. Uniform Wall Thickness No
3. Uniform Cross-Section No
4. Axis of Rotation No
5. Regular Cross-Section No
6. Captured Cavity No
7. Enclosed Cavity No
8. No Draft No
Material Requirement
A Good shock absorption.
B Excellent of Electrical Resistivity (> 1015) µΩ.cm
C Good impact resistance
D Light weights
MMP 1663 DFM Assignment: Logitech Computer Mouse
38
Table 4.19 Process elimination based on 8 geometric attributes of Clicker Wheel Shaft Holder
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
39
Table 4.20 Final process selection based on process/materials combinations of Clicker Wheel
Shaft Holder
A A A A A A A A A A A B B B B B B B B B B B C C C C C C C C C C D D D D D D D D D D
Cas
t Iro
n
Car
bon
Stee
l
Allo
y St
eel
Stai
nles
s Ste
el
Alu
min
ium
and
Allo
ys
Cop
per a
nd A
lloys
Zinc
and
Allo
ys
Mag
nesi
um a
nd A
lloys
Tita
nium
and
Allo
ys
Nic
kel a
nd A
lloys
Ref
ract
ion
Met
als
Ther
mop
last
ics
Ther
mos
ets
Sand Casting Investment Casting Die Casting Injection Moulding
6 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) Rotational Molding
Impact Extrusion Cold Heading Closed Die Forging Powder Metal Parts
3 Hot Extrusion 4,2,1 Rotary Swaging
Machining (From Stock) ECM EDM WEDM Sheet Metal (Stamp/bend) Themoforming
4,1 Metal Spinning Compatible between process and materials Not applicable Normal practice Less common
MMP 1663 DFM Assignment: Logitech Computer Mouse
40
Based on the final process selection shown above, INJECTION MOLDING processes is
suitable processes to be selected. Meanwhile, THERMOPLASTICS material is selected to be
used for Clicker Wheel. The characteristic of part chosen, such as below:
a. Part:
• Size: 20 mm x 13 mm x 13 mm
• Weight: 20 gram
b. Tolerances:
• General: ± 0.15 mm
c. Surface Finish:
• 0. 2 - 0.3 µm
d. Product Life Volume
• More than 5 years
e. Process Recommended:
• Injection Molding
f. Materials:
• Thermoplastic
g. Production volume
• 10, 000 units
MMP 1663 DFM Assignment: Logitech Computer Mouse
41
5.0 REASONS FOR THE MATERIALS SELECTIONS
5.1 Reasons for Material Selections – Thermoplastic
Thermoplastics are resins that repeatedly soften when heated and harden when cooled.
Most thermoplastics are soluble in specific solvents and can burn to some degree. Softening
temperatures vary with polymer type and grade. Because of thermoplastics’ heat sensitivity, care
must be taken to avoid degrading, decomposing, or igniting the material. Nylon, acrylic, acetal,
polystyrene, polyvinyl chloride, polyethylene, and cellulose acetate are just a few examples of the
many rigid thermoplastic resins currently available. Because of this behavior, thermoplastic also
allow production scrap such as runners and trimming to be ground and reused. Furthermore,
thermoplastic can be injected molded, extruded or formed via other molding techniques.
Unlike thermoplastics, thermosets form cross links, inter-connections between
neighboring polymer molecules that limit chain movement. This network of polymer chains tends
to degrade, rather than soften, when exposed to excessive heat. Until recently, thermosets could
not be remelted and reused after initial curing. Today’s most-recent advances in recycling have
provided new methods for remelting and reusing thermoset materials.
Based on above explanation, thermoplastic materials are chosen as material to be used in
this project. The next stage is to select the specific material among the thermoplastic materials.
MMP 1663 DFM Assignment: Logitech Computer Mouse
42
5.2 Material Selected for Thermoplastics
Table 5.1 shows some of the material applications of the thermoplastics. Selection of the
specific material to be used in producing the mouse parts is based on Table 5.1:
Table 5.1 Mould cavity pressure required depending on the product group
Application Group Examples Typical
Materials
Flow Path To
Wall Thickness
Ratio
Quality Requirement
Required Mould Cavity Mould
Consumer goods
Parts with low surface quality and dimensional requirement, simple toys
PS, PP, PE, ABS 100 - 150 Low 200 - 500
Closures
Screw caps/closures, lids and closures for pharmaceutical and cosmetics
PE, PP 30 - 100 Medium 350 – 400
Covers
Vacuum cleaner housings, bumpers, instrument panels, lawn movers, power drills
PS, PP, ABS/PC 100 -150 Medium 350 – 400
Engineering Packaging
3.5” floppy disks, CD jewel cases, video cassettes, slide frame
PS, ABS 100 - 150 Medium 350 - 400
Housings Telephone, TV, radio and computer housings
ABS, PC, PA 100 - 150 Medium 400 - 500
Optical Parts
Automotives rear lenses, mirrors, optical lenses, head lights, glasses, emergency triangles
PMMA, PC 30 - 100 High 600 – 500
Engineered Function Parts
Gear wheels, connectors, terminal strips, camera and camcorder housings
PC, POM, PBT 50 - 200 High 600 – 800
Thin wall Containers
Drinking cups, planters, yogurt cups, ice cream, containers, pails, containers
PS, PE, PP 200- 350 Medium -
MMP 1663 DFM Assignment: Logitech Computer Mouse
43
By referring to the table 5.1, one (1) application groups are suitable to be used for the
chosen Logitech computer mouse; COVERS & ENGINEERED FUNCTION PARTS. This
selected application groups of materials, there are:
a. PS b. PP c. ABS d. PC e. POM f. PBT
Polystyrene (PS)
This is probably the best known of the thermoplastics materials. It has an excellent
resistance to corrosion by most common chemicals and is unaffected by foodstuffs. It is tough
and flexible, has a high electrical resistivity, has a low density, and is easily moulded and
machined. Since it is also comparatively cheap to produce, it is not surprising that polythene
finds such a wide range of applications. Polythene is available in several different modifications
with the following properties such as:
• High hardness and dimensional stability. • Thermal dimensional stability up to 80°C. • Glossy finish. • Very good electrical insulating properties. • PS is susceptible to environment stress cracking even in air, especially with odourants.
Polystyrene is widely easy to process by means of extrusion, injection molding, extrusion
blow molding, injection blow molding and thermoforming. The good flow properties of the melt
ensure easy processing. Objects that are injection molded show orientation in the flow direction.
This can cause a decrease in mechanical strength perpendicular to the direction of flow. The
brittleness of PS can be reduced by stretching during processing and PS fibres are used for
braiding in cables. Molded items and semi finished stock can be welded and glued. Application
of the polystyrene are:
• Packaging: For cosmetics, pharmaceuticals, appliances, clocks, electronic parts, etc.
MMP 1663 DFM Assignment: Logitech Computer Mouse
44
• Household articles: Bowls, plates, beakers, plant holders, disposable cups, tumblers and
party cutlery.
• Electronics industry: Reels for film, covers for relays, insulating foils, tape cassettes
and refrigerator parts.
• Foamed and expanded components: Heat insulating sheets for the building and
automobile industry, disposable heat conserving tumblers and packaging for impact-
sensitive objects.
Polyproplene (PP)
This is similar in structure and properties to polyethylene but it has a higher temperature
tolerance. PP is polymerised from the gas propylene. PP is strong and is used for a wide variety
of mouldings where greater strength and rigidity. The higher melting point of PP as compared
make it suitable for fibre manufacture, whilst large amounts are also produced as clear film for
wrapping cigarettes and crisps. Typical properties of polypropylene are:
• Low density.
• High stiffness, hardness and strength.
• Temperature resistance up to 110°C.
• Embrittlement temperature at 0°C for homopolymers (copolymers have a lower
embrittlement temperature).
• Milky translucency.
• Electrical properties are comparable to that of PE.
• Resistant to weak inorganic acids and alkalis, alcohol and some oils and washing soda up
to 100°C.
• Susceptible to attack by strong oxidising agents and halogenated hydrocarbons. PP swells
in aliphatic and aromatic hydrocarbons such as benzene or benzine (especially at high
temperatures).
MMP 1663 DFM Assignment: Logitech Computer Mouse
45
Meanwhile, application of polypropylene consists of following criteria:
• Machine and automobile industry: Pipes for heating, ventilation fans, bellows, air
supply filters and pump bodies.
• Household articles: Components for washing machines, dishwashers and vacuum
cleaners, and cooking foils.
• Electrical applications: Cable couplings, antenna components, and cable covering.
• Transport industry: Crates, toolboxes, boxes, strapping tape, bags, rope, binder twine
and packaging films.
• Building industry: Piping, fittings and under-floor heating.
• Construction of apparatus: Piping and reaction vessels.
• General: Woven bags, carpet backing, ^-artificial grass, toys, medical syringes and
footwear parts.
Acrylonitrile/butadiene/styrene erpolymer[ABS]
Acrylonitrile/butadiene/styrene terpolymer is made up of three monomers. The most
important commercially used polymer is a graft terpolymer polymerised from polybu-tadiene and
styrene/acrylonitrile (SAN). To obtain good grafts between the SAN-matrix and the
polybutadiene particles the elastomer particles are coated with a graft coating of SAN. ABS has the
following:
• Good impact and notched impact resistance, even at low temperatures (to -40°C) • Good scratch resistance and hardness • Good toughness - can be used with metal inserts • Good shock absorption, due to the presence of butadiene which acts as a mechanical
shock absorber • Good thermal dimensional stability and cyclic temperature resistance (up to 100°C) • High surface gloss when graft polymerised. Blends have a slightly matt surface • Low water absorption • Good environmental stress cracking resistance • Good chemical resistance.
MMP 1663 DFM Assignment: Logitech Computer Mouse
46
In addition to the basic ABS types (DIN 16772) special types of ABS are
available, for instance the types which are easily electroplateable. It’s also to the
terpolymers the ABS range includes numerous polymer mixtures. Those terpolymers that
are not modified with butadiene rubber are described as AXS products. The X is the
symbol for the elastomer components. The properties of compounds of ABS with other
polymers depend on the mix ratio of the individual components. The following are
available in the trade:
• ABS/PVC alloys - ABS acts as an impact modifier and processing aid for PVC. These
alloys are self-extinguishing.
• ABS/PC blends - these blends have high impact resistance (to -50°C) and high
dimensional heat stability (up to 115°C).
• ABS/PUR blends - these materials have very high cold impact resistance. The PUR
components improve the abrasion properties. The flow properties of these blends are
excellent, rendering them suitable for the production of thin-walled injection-moulded
articles. A disadvantage of ABS is its low weathering resistance and lower transparency be-
cause of the butadiene content. The butadiene is replaced by other elastomer components
for exterior applications.
Because of its good physical properties ABS, lends itself to following technical applications:
• Electrical and audio industry: Telephones, computer housings, lamps, watch cases,
office machines, copiers, video cassettes, projectors, portable TV housings, chassis and fronts
for Hi-Fi apparatus and video camera and film apparatus.
• Automobile industry: Body parts, fan blades, air ducts, light housings, spoilers, hub caps
and instrument panels.
• Plumbing: Pipes, fittings, couplings and WC Flush tanks.
• Sport and recreation: Surfboards, chairs, technical toys, aeroplane and railway models and
chair shells.
• General: Suitcases, briefcases, hair dryer parts, hard hats for industry and mining,
Christmas tree light holders and aircraft parts.
MMP 1663 DFM Assignment: Logitech Computer Mouse
47
• Foamed articles: Portrait frames, umbrella handles, chairs, tool handles, decorative
articles and table place mats.
Polycarbonate became available in 1956 from Bayer and two years later from General
Electric. Polycarbonate is an amorphous thermoplastic with a degree of crystallisation of up to 5%
only. PC is manufactured by polycondensation from bisphenol A, which in turn is manufactured
from phenol, acetone, and phosgene. About 120 basic units make up one polymer chain. The
presence of aromatic rings in the molecular chain reduces the movement of the macromolecules
and gives the polymer rigidity and temperature resistance. PC has the following properties:
Polycarbonate (PC)
• High strength, hardness and toughness
• Temperature resistance from -150°C to 135°C and to 145°C in glassfibre reinforced grades
• Glass clear
• Good electrical insulation
• Low water absorption
• Resistant to petrol, oils, greases and saturated aliphatic hydrocarbons. It can also be
immersed in boiling water for a short period and can be sterilised at 120°C
• Not resistant to strong acids and alkalis, aromatic hydrocarbons and chlorinated
hydrocarbons nor to lengthy immersion in hot water
• Prone to stress cracking (tempering at 120°C helps to release internal stresses).
• Good weathering properties
• PC burns but is extinguished if the ignition source is removed. PC can be made fire
retardant by condensation with bisphenol A with chlorine or bromine atoms in the aromatic
ring.
The stiffness of PC can be enhanced with the addition of glass fibres up to a glass
content of 30%. The stress/strain relationship of PC is characterised by a wide strain flow
area. When reinforced with glass fibres, this disappears from improving stiffness, tensile
strength, heat deformation resistance, and compressive strength, the addition of glass fibres
MMP 1663 DFM Assignment: Logitech Computer Mouse
48
also improves the dimensional stability and reduces the burning rate of PC. The light
transmission of glass clear PC is between 80% and 90% depending on thickness.
Injection moulding, extrusion and blow moulding PC has to be dried to a moisture content
of 0,02% before processing. This is achieved by placing it in a 2cm deep layer in an oven at 120°C
for four hours. Even when the polymer is packed in an airtight container this pre-heating is
recommended. The use of a heated hopper is recommended because the polymer takes up moisture
upon cooling. Conversion temperatures are high when compared to other moulding compounds.
Heating and control elements must be capable of temperatures of at least 350°C. Follow-on
pressure in injection moulding must be as low as possible to reduce residual stresses.
Machining of articles is easily done, but care should be taken with the cooling methods
used. No oil emulsions but only air or clean water should be used. Welding is best done by
means of heated elements. Other welding methods can also be used. Tempering is required after
welding to remove stresses. Gluing is by means of solvents, solvent-based glues and reactive
adhesives. When using solvent glues it is necessary to heat the parts to higher temperatures. For
thermoforming of sheet the material must be preheated at 110°C for several hours depending
on wall thickness. For stretch forming (i.e. drape and vacuum form etc), whether by compressed
air or vacuum, the stock temperature should be 180°C to 210°C. The moulds must also be
heated to about 100°C.
Due to its excellent properties, PC is used as an engineering plastic as well as in do-1
mastic applications.
• Machines and appliances: Housings, typewriter and sewing-machine components,
computer housings, medical equipment, sight glasses, filter cases, ventilation fans and
covers, electric razors and cam discs.
• Electronics: Plugs, wall plugs, coil cores, couplings, switchgear housings, fluorescent, light
mountings and switches.
• Photographic and audio apparatus: Radio and television equipment, telephones,
compact discs, binoculars and instrument housings.
• Automotive industry: Indicators, rear lights, air ducts, ventilation and cooling grills.
MMP 1663 DFM Assignment: Logitech Computer Mouse
49
• Lighting and building industry: Lighting strips, domes, glazing, protective glazing,
balcony and bridge railings, bus and telephone shelters, greenhouse walling and ar-J
moured "glass" panels.
• Household articles: Utensils, vacuum cleaner components, bottles, canisters and
crockery.
Polyacetal [POM]
Polyacetal, also known as polyoxymethylene, has been available since 1958. It is available as
homo- and copolymers, the main difference being that the copolymers have greater thermal and
chemical stability. POM is a semi-crystalline thermoplast. The crystallinity of homopolymers is
greater than that of the copolymers and is somewhere in the region of 80%. The monomer for the
manufacture of this polymer is formaldehyde i.e. trioxane -a cyclic trimer of formaldehyde
obtained when the formaldehyde molucules form a ring structure.
In copolymers, the chains are divided by means of other monomers such as cyclic ethers, which
retard chain decomposition of the melt.
POM is characterised by high strength, hardness and rigidity over a wide temperature range.
The materials show little creep over a wide stress range even during a relatively long loading period.
Further characteristic properties of POM are as follows:
• High toughness down to -40°C
• High abrasion resistance
• Low coefficient of friction
• High heat distortion resistance
• Good electrical and dielectric properties
• Low water absorption
• Resistant to organic solvents such as alcohols, esters, ketones, as well as oils, fats, petrol,
watery bases and acids not resistant to strong acids and oxidising agents
• Resistance to weathering is poor. Sunlight has an embrittling effect on POM, but it can
be retarded by the addition of correct stabilisers. To delay the degradation of the polymer
MMP 1663 DFM Assignment: Logitech Computer Mouse
50
chain one of the best methods of protection against UV light is the addition of carbon
black.
POM is mainly processed by injection moulding, extrusion and blow moulding. With glass
reinforced POM a higher injection pressure has to be used; it is also necessary to increase the gate
cross sectional area by about 20%. Extrusion is normally done by means of single screw
machines without breaker plates and screens. In case of any machine stoppage, great care should
be exercised.
Above a temperature of 240°C and during long residence periods in machines, the
polymer decomposes to form formaldehyde which can easily be identified by its pungent smell. A
build-up of formaldehyde gas in the cylinder can cause an explosion through the feed hopper and
nozzle. Protective clothing and glasses should be worn and processing temperatures reduced.
There should be adequate ventilation. All methods of welding except HF-welding can be used. A
low rotational speed should be used in friction welding, because the POM has a low melt
viscosity and molten material might be thrown away from the work face by centrifugal force.
Gluing - Bonding by means of adhesives and solvent adhesives is feasible, but two component
adhesives require the pre-treatment of surfaces with chromic acid.
POM has very low creep combined with low frictional properties and good abrasion
resistance. This makes this material an excellent engineering plastic. Because of its high
toughness with good resilience it is used for the manufacture of snap and press fittings in machine
and appliance construction. POM is used as follows:
• Machines and appliances: Gear wheels, bushes, bearings, housings, springs, chains,
rollers, screws, nuts, pump parts, valve and control elements, snap & press fittings,
ventilation fans and slide and guide elements.
• Electronics: Isolators, small motor parts, relay components, telephone components,
radios, projectors, spools and plugs.
• Automotive: Eevers for direction indicators and covers for universal joints.
• Furniture: Edging, closing devices, hinges, handles and rollers for sliding doors and
curtains.
MMP 1663 DFM Assignment: Logitech Computer Mouse
51
• Packaging: Aerosol cans, cigarette lighters and gas cartridges.
Poly(butylene terephthalate) [PBT]
The manufacture of poly(butylene terephthalate) is very much the same as that of
poly(ethylene terephthalate). PBT is a semi-crystalline thermoplastic which has similar properties
to PET. The slightly poorer mechanical properties compared to PET are often cancelled out by the
better processing properties. The technical and physicals properties of PBT are:
• For a thermoplastic PBT has good hardness, stiffness, and strength
• High toughness, even under cold conditions
• Good friction and abrasion properties
• Good creep resistance
• Good thermal dimensional stability
• Service temperature between -60°C and 110°C (short term up to 170°C); filled
grades up to 200°C
• Naturally translucent and has a high surface gloss
• Good electrical properties including tracking resistance and dielectric performance
• Low water absorption
• Physiologically acceptable
• Similar resistance properties to PET
• Not resistant to aromatic and aliphatic hydrocarbons
• Resistant to stress cracking and weathering
• Burns with a yellow-orange sooty flame without the formation of droplets.
Due to the fact that PBT burns easily, most grades are modified with flame retar-dants. To
improve certain mechanical properties, fibre reinforcement is commonly used. This leads to
shorter cycle times, wider melt temperature ranges, faster recrystallis-ation and lower melting
points when compared to PET. The partial replacement of glass fibres with glass microspheres, or
mica, results in moulding compounds with better resistance to warpage.
MMP 1663 DFM Assignment: Logitech Computer Mouse
52
Modification by means of blends or graft polymerisation increases the notched impact
resistance of the material. For blends, PC, PA, PTFE, and TPE with a styrene butadiene base are
used. PBT compounds are described in DIN 16779.
Process - The guidelines given in regarding moisture content are also applicable to PBT. It is
preferable to pre-dry PBT granules that have become wet:
Granulate layer depth - 2 to 3 cm
Drying temperature - about 120°C
Table 5.2: PBT unreinforced and PBT reinforced process requirement
Process
PBT unreinforced
PBT reinforced
Injection moulding
Melt temperature, (°C)
Mould temperature, (°C)
Injection pressure (bar)
Shrinkage , (%)
230 to 260 60
800 to 1200 1,
0 to 2,0
250 to 270 up to 120
800 to 1200 0,4 to 1,3
Extrusion Melt temperature, (°C)
Die temperature, (°C)
250 to 280
250 to 270
5.3 Selected Materials
Base on 6 types of thermoplastic material above, the suitable material for CLICKER
WHEEL and CLICKER WHEEL SHAFT HOLDER is Poly (butylenes terephthalate)
[PBT]. This selection base on the properties PBT is suitable with part requirement and application.
The advantages of material properties compare to others is:
• high thermal stability, great stiffness, and hardness
• temperature resistance – 40° c to 100° c
• low water absorption,
• good resistance to stress cracking
• excellent anti friction
MMP 1663 DFM Assignment: Logitech Computer Mouse
53
• good dimensional stability
• low cost of material
Meanwhile, for PCB Lower Case (new design), PCB Upper Case (new design) and
PCB Upper Case Cover (new design), ABS is material to be used on producing particular parts.
This selection base on the properties ABS is suitable with part requirement and application. The
advantages of material properties compare to others is:
• Good impact and notched impact resistance, even at low temperatures (to -40°C) • Good scratch resistance and hardness • Good toughness - can be used with metal inserts • Good shock absorption, due to the presence of butadiene which acts as a mechanical
shock absorber • Good thermal dimensional stability and cyclic temperature resistance (up to 100°C) • High surface gloss when graft polymerised. Blends have a slightly matt surface • Low water absorption • Good environmental stress cracking resistance • Good chemical resistance.
MMP 1663 DFM Assignment: Logitech Computer Mouse
54
6.0 REASONS FOR THE PROCESSES SELECTIONS
6.1 Reasons for Process Selections – Injection Molding
One of the most common methods of converting plastics from the raw material form to an
article of use is the process of injection molding. This process is most typically used for
thermoplastic materials which may be successively melted, reshaped and cooled. Injection
molded components are a feature of almost every functional manufactured article in the modern
world, from automotive products through to food packaging. This versatile process allows us to
produce high quality, simple or complex components on a fully automated basis at high speed
with materials that have changed the face of manufacturing technology over the last 50 years or
so. Below is the reason for the injection processes selections for producing about 10, 000 units of
each selected parts for Logitech computer mouse product as mention before:
• Parts can be produced at high production rates.
• large volume production is possible (for this project – 10, 000 units volume of
production)
• Relatively low labor cost per unit is obtainable.
• Process is highly susceptible to automation.
• Parts require little or no finishing (good surface finish).
• Many different surfaces, color and finishes are available.
• For many shapes this process is the most economical way to fabricate.
6.2 The Injection Molding Process
Figure 5.1 shows the equipment necessary for injection molding. It consists of two main
elements, the injection molding machine and the injection mold. An injection molding machine
can be broken down into the following components:-
a. Plasticizing/injection unit,
b. Clamping unit,
c. Control system and
MMP 1663 DFM Assignment: Logitech Computer Mouse
55
d. Tempering devices for the mold.
Figure 5.1 Injection molding machine
6.3 Injection Molding Cycle
The modern day process has developed and matured significantly to the level where fully
automated, closed loop, microprocessor controlled machines are the 'norm', although in principle
injection molding is still a relatively simple process. Thermoplastic injection molding requires
the transfer of the polymeric material in powder or granule form from a feed hopper to a heated
barrel. In the barrel, the thermoplastic is melted and then injected into a mould with some form of
plunger arrangement. The mould is clamped shut under pressure within a platen arrangement and
is held at a temperature well below the thermoplastic melt point. The molten thermoplastic
solidifies quickly within the mould, allowing ejection of the component after a pre determined
period of cooling time. The basic injection molding process steps with a reciprocating screw
machine are as follows.
Mould Close and Clamping
The mould is closed within the platen arrangement and clamped using necessary force to
hold the mould shut during the plastic injection cycle, thus preventing plastic leakage over the
face of the mould. Present day molding machines range from around 15 to 4,000 metric tons
available clamping force (150 to 4000 kN).
MMP 1663 DFM Assignment: Logitech Computer Mouse
56
Many systems are available for opening/closing and clamping of mould tools, although
usually they are of two general types. Direct Hydraulic Lock is a system where the moving
machine platen is driven by a hydraulic piston arrangement which also generates the required
force to keep the mould shut during the injection operation. Alternatively, smaller auxiliary
pistons may be used to carry out the main movement of the platen and a mechanical blocking
arrangement is used to transfer locking pressure from a pressure intensifier at the rear of the
machine, which moves only by a few millimeters, through to the platen and tool.
The second type of general clamping arrangement is referred to as the Toggle Lock. In
this case a mechanical toggle device, which is connected to the rear of the moving platen, is
actuated by a relatively small hydraulic cylinder; this provides platen movement and also
clamping force when the toggle joint is finally locked over rather like a knuckle arrangement.
Injection
At this stage in the machine cycle the helical form injection screw is in a 'screwed back'
position with a charge of molten thermoplastic material in front of the screw tip roughly
equivalent to or slightly larger than that amount of molten material required to fill the mould
cavity. Injection molding screws are generally designed with length to diameter ratios in the
region of 15:1 to 20:1, and compression ratios from rear to front of around 2 : 1 to 4 : 1 in order
to allow for the gradual densification of the thermoplastic material as it melts. A check valve is
fitted to the front of the screw such as to let material pass through in front of the screw tip on
metering (material dosing), but not allow material to flow back over the screw flights on
injection. The screw is contained within a barrel which has a hardened abrasion resistant inner
surface.
Normally, ceramic resistance heaters are fitted around the barrel wall, these are used to
primarily heat the thermoplastic material in the barrel to the required processing temperature and
make up for heat loss through the barrel wall, and due to the fact that, during processing most of
the heat required for processing is generated through shear imparted by the screw. Thermocouple
pockets are machined deep into the barrel wall so as to provide a reasonable indication of melt
MMP 1663 DFM Assignment: Logitech Computer Mouse
57
temperature. Heat input can therefore be closed loop controlled with a Proportional Integral and
Derivative (PID) system. The screw (non-rotating) is driven forward under hydraulic pressure to
discharge the thermoplastic material out of the injection barrel through the injection nozzle,
which forms an interface between barrel and mould, and into the molding tool itself.
Holding Pressure and Cooling
The screw is held in the forward position for a set period of time, usually with a molten
'cushion' of thermoplastic material in front of the screw tip such that a 'holding' pressure may be
maintained on the solidifying material within the mould, thus allowing compensating material to
enter the mould as the molded part solidifies and shrinks. Holding pressure may be initiated by
one of three methods: by a set time in seconds from the start of the injection fill phase; by the
position of the screw in millimeters from the end of injection stroke; or by the rise in hydraulic
pressure as measured by a pressure transducer in the mould itself or in the injection hydraulic
system.
As the material solidifies to a point where hold pressure no longer has an effect on the
mould packing, the hold pressure may be decayed to zero; this will help minimize residual
stresses in the resultant molding. Once the hold pressure phase has been terminated the mould
must be held shut for a set period of cooling time. This time allows the heat in the molding to
dissipate into the mould tool such that the molding temperature falls to a level where the molding
can be ejected from the mould without excessive distortion or shrinkage. This usually requires
the molding to fall to a temperature below the rubbery transition temperature of the thermoplastic
or Tg (glass transition temperature). Depending on the type of plastic this can be within a few
degrees or over a temperature range. Mould temperature control is incorporated into the tool
usually via channels for pressurized water flow. The mould may be connected to a cooling unit or
water heater depending on the material being processed, type of component and production rate
required.
MMP 1663 DFM Assignment: Logitech Computer Mouse
58
Material Dosing or Metering
During the cooling phase, the barrel is recharged with material for the next molding cycle.
The injection screw rotates and, due to its helical nature, material in granule or powder form is
drawn into the rear end of the barrel from a hopper feed. The throat connecting the hopper to the
injection barrel is usually water cooled to prevent early melting and subsequent material bridging
giving a disruption of feed. The screw rotation speed is usually set in rpm which is measured
using a proximity switch at the rear of the screw. Screw rotation may be set as one constant speed
throughout metering or as several speed stages.
The material is gradually transferred forward over the screw flights and progressively
melted such that when it arrives in front of the screw tip it should be fully molten and
homogenized. The molten material transferred in front of the tip progressively pushes the screw
back until the required shot size is reached. Increased shear is imparted to the material by
restricting the backward movement of the screw; this is done by restricting the flow of hydraulic
fluid leaving the injection cylinder. This is referred to as `back pressure' and it helps to
homogenize the material and reduce the possibility of unmelted material transferring to the front
of the screw.
Mould Open and Part Ejection
When the cooling phase is complete the mould is opened and the molding is ejected. This
is usually carried out with ejector pins in the tool which are coupled via an ejector plate to a
hydraulic actuator, or by an air operated ejector valve on the face of the mould tool. The molding
may free fall into a collection box or onto a transfer conveyer, or may be removed by an
automatic robot. In this latter case the molding cycle is fully automatic. In semi-automatic mode,
the operator may intervene at this point in the cycle to remove the molding manually. Once the
molding is clear from the mould tool, the complete molding cycle can be repeated.
MMP 1663 DFM Assignment: Logitech Computer Mouse
59
6.4 Other Advantages of Injection Molding Processes
Injection molding is particularly advantageous when intricate parts must be produced in
large quantities. Although there are limitations, generally the more irregular and intricate the
parts, the more likely it is that injection molding will be economical. In fact, one major advantage
of the injection-molding method is that one molded part can replace what would otherwise be an
assembly of components. In addition, color and surface finish often can be molded directly onto
the part, so that secondary finishing operations are not necessary. Injection-molded parts are
generally thin-walled. Heavy sections and variable wall thicknesses are possible, though they are
normally not recommended.
Because thermoplastics are generally less strong than metals, they are more apt to be
found in less highly stressed applications. Housings and covers are common uses rather than, for
example, frames and connecting rods. However, thermoplastic materials are gradually being
developed with better and better strength characteristics and are increasingly finding themselves
used for moving parts and in more structural applications. The “engineering plastics,” nylon,
polycarbonate, acetal, phenylene oxide, polysulfone, thermoplastic polyesters, and others,
particularly when reinforced with glass or other fibers, are functionally competitive with zinc,
aluminum, and even steel.
MMP 1663 DFM Assignment: Logitech Computer Mouse
60
7.0 DISCUSSION
In producing a product starting from zero until a finish product is produced in the market,
a series of processes is being gone through step by step consist of DfA and DfM which runs
concurrently. The main objectives is to produce a product with the less part number, less
manufacturing processes, less lead time and for most less overall cost.
As for Logitech computer mouse product, 5 parts had to be evaluated and analysis in the
DfM methodology introduced by Boothroyd-Dewhurst. The parts are as below:
• Part 1 – PCB Lower Case (new design)
• Part 2 – PCB Upper Case (new design)
• Part 3 – PCB Upper Case Cover (new design)
• Part 4 – Clicker Wheel
• Part 5 – Clicker Wheel Shaft Holder
7.1 Material Requirement
Table 7.1 Parts and Material Requirement
Part
Part Name
Material Requirement
1. PCB Lower Case (new design) 1. Plastic materials 2. Used snap fit features
(flexibility). 3. Excellent of Electrical
Resistivity (> 1015
4. Good impact resistance ) µΩ.cm
5. Light weight
2. PCB Upper Case (new design) 3. PCB Upper Case Cover (new
design)
4. Clicker Wheel 1. Plastic materials 2. Good shock absorption 3. Excellent of Electrical
Resistivity (> 1015
4. Good impact resistance ) µΩ.cm
5. Light weight
5. Clicker Wheel Shaft Holder
MMP 1663 DFM Assignment: Logitech Computer Mouse
61
The material requirement will be used as guide in selecting the best material which suite
the part‘s design.
7.2 Parts Attributes
Table 7.2 Parts attributes
Part 1 Part 2 Part 3 Part 4 Part 5
Depression
Yes Yes Yes Yes Yes
Uniform Wall
Yes No Yes No No
Uniform Cross-Section
No No No No No
Axis of Rotation
No No No Yes No
Regular Cross-Section
No No No No No
Capture Cavities
No No No No No
Enclosed
No No No No No
No Draft
No No No No No
MMP 1663 DFM Assignment: Logitech Computer Mouse
62
7.3 Final Selection for Material and Processes
Table 7.3 Final selection for material and processes
Part 1 Part 2 Part 3 Part 4 Part 5
MATERIAL
ABS Poly (butylenes
terephthalate) [PBT]
PROCESSES
Injection Molding
After using the elimination method, above results was finalised. The final
selections also consider the part’s specifications and the design guideline which in the end
will produce a product with minimum overall manufacturing cost.
7.4 Design Guidelines
Design for ease of fabrication and assembly. Select processes compatible with the design
intent, materials and production volumes. Select materials compatible with production processes
and that minimize processing time while meeting functional requirements. Avoid unnecessary
part features because they involve extra processing effort and/or more complex tooling.
Consider the following design guidelines:
• For higher volume parts, consider castings, extrusions or other volume manufacturing
processes to reduce machining and in-machine time
• Consult with manufacturing to determine and design for solid mounting or other fixture-
locating features on the component.
• Avoid thin walls, thin webs. or similar features that will result in distortions due to
manufacturing
• Avoid undercuts that will require special operations & tools
MMP 1663 DFM Assignment: Logitech Computer Mouse
63
• Design around standard cutters, drill bit sizes or other tools
• Avoid small holes and threaded features as tool breakage and part scrap increases
Threaded Holes
• Design for full thread depth. Usually 1.5 x major diameter provides adequate holding
strength
• Drilled hole depth (to the sharp point of the tool) is recommended to be at least equal to
the full thread plus ½ major diameter, but never less than .050"
• Material thickness as measured from the bottom of the drilled hole to next surface should
not be less than the major diameter of the thread or diameter of hole, and not less than
.050".
• When material thickness allows, thru holes are preferred
Fixture/tooling material selection
When designing steel fixtures or tooling where high accuracy flatness, perpendicularity,
parallelism or true position is required, specify the material as low carbon hot rolled. This
material is very stable and will retain form much better than CRS (Cold Rolled Steel).
Flatness
Flatness should be applied with reasonable overall form tolerance as well as on a per
unit basis as a means to prevent abrupt surface variation within a relatively small area of the
feature. Depending on material thickness and application, a note can be added to design
drawing: "FLATNESS MAY BE MEASURED WITH COMPONENT IN RESTRAINED
CONDITION". Where applicable, note should include specific retraining requirements
MMP 1663 DFM Assignment: Logitech Computer Mouse
64
Internal Radii
• Always specify largest radius possible. Small diameter tools add significant cost to
manufacturing process.
• When design requires metalized plating such as nickel, silver or other, specify a CR
"Controlled Radius" as applicable (CNC manufacturing). CAD model or design for non-
standard radii. CNC machining will create a "hard corner" in that the machine will race to
a radius corner and abruptly change onto the nelct direction. The CNC change of direction
often creates "tool chatter" resulting in rough sharp edges at the radius corner. Non-
standard or CR (Controlled Radius) will result in the CNC cutter to slow down and blend a
smooth radius at the corner feature. The smooth radius feature will facilitate good
metalized plating and avoid flaking common to small sharp edges.
• When depth exceeds 5 X the diameter of the pocket radii, consult manufacturing on
alternative fabrication methods. Depths of up to 10 X are possible when machining
aluminum but, not all manufacturing facilities have capability
• For deep sharp corner cutouts that require broaching or EDM, specify radii max at all
cutout corners i.e. (4X R .008 MAX)
Dimensional Tolerancing
For surface composite curves such as, internal pockets, or other profiles that for CNC
manufacturing a continuous cutting path will be established and manufactured. Design for and
specify unilateral tolerances (+/- .010). Reason: Often the machine tools used to manufacture
the components utilize a feature called "Cutter Compensation". This allows size control
variation of the features being machined without having to control the NC program (file) to an
exact match with the cutter diameter. For a continuous path, if "X" dimension has -+0, -.005 and
"Y" dimension has +.005, -0 tolerance specified, the cutter compensation cannot be used to
control size, because adding or subtracting from cutter path input automatically invokes an error
to the dimension of the other toleranced continuous path surface. Simply, a offset is input into
MMP 1663 DFM Assignment: Logitech Computer Mouse
65
the machine relative to the cutting tool to manufacture for mid tolerance of surface ''X' at -.0025
however, this path is not compatible with the "y" surface in that the nominal offset is .0025 out
of tolerance.
Design of tolerances should be within manufacturing capabilities.
Concurrently designing for manufacturing will greatly improve product quality and
reduce fabrication costs. Consult with manufacturing early in the design process. After
completion of preliminary drawings, meet with manufacturing and review design intent,
requirements and determine manufacturing process requirements. Manufacturing should review
tolerances and determine process capabilities to meet dimensional limits. Manufacturing should
identify tolerance challenges that require design and requirements review. In general, design
should avoid unnecessarily tight tolerances that are beyond the natural capability of the
manufacturing processes. Determine when new production process capabilities are needed early
to allow sufficient time to determine optimal process parameters and establish a controlled
process. Tolerance stack-ups should be considered on mating parts. Overall assembly tolerances
should be calculated, and interface as well as clearance requirements understood. Surface finish
requirements can be established based on actual manufacturing processes employed however,
surface finish requirements should be understood and design intent accurately defined.
Simplify design and assembly so that the assembly process is unambiguous.
Components should be designed so that they can only be assembled in one way; they cannot be
reversed. Roll pins, dowel pins or offset mounting holes can be employed.
Design for components orientation and handling to minimize non-value-added manual
effort, ambiguity or difficulty in orienting and merging parts. Basic principles to facilitate parts
handling and orienting are:
• Parts must be designed to consistently orient themselves. Examples are dowel pins.
• Product design must avoid parts that can become tangled, wedged or disoriented.
• Verify clearance for assembly tooling such as hand tools and fixtures.
• With hidden features that require a particular orientation, provide an external feature, guide
MMP 1663 DFM Assignment: Logitech Computer Mouse
66
surface or design alignment fixturing or tooling to correctly orient the part.
• Design in fasteners large enough that are easy to handle and install
Design for efficient joining and fastening.
Threaded fasteners (screws, bolts, nuts and washers) can be lime-consuming to
assemble. Consider design alternatives that will reduce fastener count. Use uniform screw sizes
here practical.
However, during the manufacturing processes in the plant, there might be some
changes in the detail process plan whenever the manufacturing personnel find out that
there are still improvement can be make in order to achieve the minimum manufacturing
cost such as combining the processes or parts as well.
MMP 1663 DFM Assignment: Logitech Computer Mouse
67
7.0 CONCLUSION
By using Boothroyd-Dewhurst method in design for manufacturing, whereby material for
each part is determined by eliminating the one which does not fulfill the basic requirements. The
overall activities in DFM are achieved with the goal of selection the materials and manufacturing
processes. From this Logitech computer mouse assembly project, it’s managed to:
i. Minimizes the cost of manufacturing.
ii. Minimizes the cost of the material.
iii. Minimizes the waste in manufacturing and in the product life cycle.
iv. Maximizes the performance of the part.
v. Maximizes the safety of the product.
It come to an end of the report regarding on the DFM method in determination of the
material and related manufacturing process. For the five selected parts namely; PCB Upper Case
(new design), PCB Lower Case (new design), PCB Upper Case Cover (new design), Click Wheel
and Click Wheel Shaft Holder, base upon the argument and rationale in the discussion section, it
is being decided that the most efficient manufacturing method is injection molding process. As
for the material selection, the PCB Upper Case (new design) , PCB Lower Case (new design),
PCB Upper Case Cover (new design) will be made of ABS materials whereby Click Wheel and
Click Wheel Shaft Holder will be made from Poly (butylenes terephthalate) [PBT].
MMP 1663 DFA Assignment: Logitech Computer Mouse
68
REFERENCE:
[1] Boothroyd, G., “Product Design For Manufacture And Assembly”, 2nd
New York: Marcel Dekker Inc. 2001. 374p. Edition.
[2] Henry W. Stoll, “Product Design Methods and Practices”, New York: Marcel Dekker Inc. [3] Kjell B. Zandin, “Maynard’s Industrial Engineering Handbook”, 5th
edition, McGraw-Hill.
[4] Mark Curtis, “Boothroyd Dewhurst Design for Manufacture & Assembly’s”, Harland
Simon Automation Systems Ltd. [5] Hubert K. Rampersad, “The House of DFA”, Rotterdam School of Management,
Erasmus University.