DESIGN FOR ASSEMBLY
1
OBJECTIVES OF DESIGN FOR ASSEMBLY (DFA)
The aim of DESIGN FOR ASSEMBLY (DFA) is to simplify the product so
that the cost of assembly is reduced. However, consequences of applying
DFA usually include improved quality and reliability, and a reduction in
production equipment and part inventory. These secondary benefits often
outweigh the cost reductions in assembly.
2
OBJECTIVES OF DESIGN FOR ASSEMBLY (DFA)
DFA recognizes the need to analyze both the part design and the whole
product for any assembly problems early in the design process.
We may define DFA as "a process for improving product design for easy
and low-cost assembly, focusing on functionality and on assembly - ability
concurrently."
3
HISTORY OF DESIGN FOR ASSEMBLY (DFA)
The practice of DFA as a distinct feature of designing is a relatively recent
development, but many companies have been essentially doing DFA for a
long time. For example, General Electric published an internal
manufacturing handbook in the 1960's as a set of guidelines and
manufacturing data for designers to follow.
These guidelines embedded many of the principles of DFA without ever
actually calling it that or distinguishing it from the rest of the product
development process.
It wasn't until the 1970's that papers and books on the topic began to
appear.
4
WHAT WILL DFA ACHIEVE?
5
% of influence on production cost
WHY IS DFA IMPORTANT?
6
REASONS FOR NOT IMPLEMENTING DFA
See the next slide
See the second next slide
7
UGLY BABY SYNDROME
8
I PREFER DESIGN RULES
9
TRENDS DRIVING PRODUCT DEVELOPMENT TODAY
10
EVOLUTION OF DESIGN PROCESS
11
IMPORTANCE OF REDUCING PART NUMBER
12
ELIMINATED PARTS ARE NEVER
13
INFLUENCE OF REDUCING THE NUMBER OF PARTS
ON THE PRODUCT QUALITY
14
INFLUENCE OF REDUCING THE NUMBER OF PARTS
ON THE PRODUCT QUALITY
15
THE PENALTY OF LATE IMPLEMENTATION OF DFA
16
THE PENALTY OF LATE IMPLEMENTATION OF DFA
17
SELECTION OF ASSEMBLY METHOD
Manual assembly
Automatic assembly
Robotic assembly
18
SELECTION OF ASSEMBLY METHOD
Relative costs per unit of different assembly methods by type and
production volume.
19
SELECTION OF ASSEMBLY METHOD
Typical production volumes for each type of assembly method
20
MANUAL ASSEMBLY GUIDELINES
•
Eliminate the need for workers to make decisions or adjustments
•
Ensure accessibility and visibility
•
Eliminate the need for assembly tools and gauges (self-locating parts)
•
Minimize the number of different parts - use "standard" parts
•
Minimize the number of parts
•
Avoid or minimize part orientation during assembly (symmetrical parts)
•
Prefer easily handled parts that do not tangle or nest within one another
Many such products are sold as "ready-to-assemble" kits or
require that assembly be shifted to cheaper labor markets.
21
AUTOMATED ASSEMBLY GUIDELINES (HARD AUTOMATION *)
*The main difference here is that assembly is performed by machines instead of by humans.
Reduce the number of different components by considering
does the part move relative to other parts?
must the part be isolated from other parts (electrical, vibration, etc.)?
must the part be separate to allow assembly (cover plates, etc.)?
Use self-aligning and self-locating features
Avoid screws/bolts
Use the largest and most rigid part as the assembly base and fixture
Perform assembly in a layered, bottom-up manner
22
AUTOMATED ASSEMBLY GUIDELINES (HARD AUTOMATION *)
Use standard components and materials
Avoid tangling or nesting parts
Avoid flexible and fragile parts
Avoid parts that require orientation
Use parts that can be fed automatically
Design parts with a low centre of gravity
23
ROBOTIC ASSEMBLY GUIDELINES (SOFT AUTOMATION)
Design the part so that it is compatible with the robot's end effector *
Design the part so that it can be fed in the proper orientation.
End-effector
* The robot's last link. The robot uses the end-effector to accomplish a task. The
end-effector may be holding a tool, or the end-effector itself may be a tool. The
end-effector is loosely comparable to a human's hand.
24
AN EXAMPLE OF DFA GUIDELINES
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Minimize part count by incorporating multiple functions into single parts
Modularize multiple parts into single subassemblies
Assemble in open space, not in confined spaces; never bury important components
Make parts such that it is easy to identify how they should be oriented for insertion
Prefer self-locating parts
Standardize to reduce part variety
Maximize part symmetry
Design in geometric or weight polar properties if non-symmetric
Eliminate tangly parts
Color code parts that are different but shaped similarly
Prevent nesting of parts; prefer stacked assemblies
Provide orienting features on non-symmetries
Design the mating features for easy insertion
Provide alignment features
Insert new parts into an assembly from above
Eliminate re-orientation of both parts and assemblies
Eliminate fasteners
Place fasteners away from obstructions; design in fastener access
Make channels sufficiently wide to provide access to fastening tools; eliminate channels if possible
Provide flats for uniform fastening and fastening ease
Ensure sufficient space between fasteners and other features for a fastening tool
Prefer easily handled parts
http://deed.ryerson.ca/~fil/t/dfmdfa.html
25
JOINING DESIGN GUIDELINES
26
JOINING DESIGN GUIDELINES
MECHANICAL FASTENERS - BOLTS
BOLT
STUD
CAPSCREW
MACHINE
SCREW
THREAD
FORMING
SCREW
Common terminology
27
JOINING DESIGN GUIDELINES
MECHANICAL FASTENERS - BOLTS
28
JOINING DESIGN GUIDELINES
MECHANICAL FASTENERS - RIVETS
29
JOINING DESIGN GUIDELINES
MECHANICAL FASTENERS – SHEET METAL JOINTS
Strap seam
Single lock seam
Pittsburgh lock seam
30
JOINING DESIGN GUIDELINES
DON’T
DO
Reduce the number of fasteners
31
JOINING DESIGN GUIDELINES
DON’T
DO
Deep channels should be sufficiently wide to provide access to fastening tools.
Eliminate channel if possible
32
JOINING DESIGN GUIDELINES
DON’T
DO
Design proper spacing for easy access of a fastening tool
33
JOINING DESIGN GUIDELINES
DON’T
DO
Place fasteners away from obstructions
34
JOINING DESIGN GUIDELINES
DON’T
DO
impossible
Provide flats for fastener faces
35
JOINING DESIGN GUIDELINES
DON’T
DO
Snap-fits are great
for plastic parts
Minimize part count by incorporating multiple functions into single parts
36
JOINING DESIGN GUIDELINES
DON’T
DO
Design open enclosures to permit assembly in open space,
not in a confined spaces.
Do not burry important components
37
JOINING DESIGN GUIDELINES
DON’T
DO
Standardize to reduce part variety
38
JOINING DESIGN GUIDELINES
DON’T
DO
Modularize multiple parts into sub-assemblies
39
JOINING DESIGN GUIDELINES
DON’T
DO
Parts should easily indicate orientation for insertion
40
HANDLING DESIGN GUIDELINES
41
HANDLING DESIGN GUIDELINES
DON’T
DO
Maximize part symmetry
42
HANDLING DESIGN GUIDELINES
DON’T
DO
Eliminate “tangly” parts
43
HANDLING DESIGN GUIDELINES
DON’T
DO
Prevent nesting of parts
44
HANDLING DESIGN GUIDELINES
DON’T
DO
Added
weight
For automated assembly, add weight across non-symmetries
45
HANDLING DESIGN GUIDELINES
DON’T
DO
10 mm
10 mm
8 mm
8 mm
Color code parts that are different but shaped similarly
46
HANDLING DESIGN GUIDELINES
Provide features for orienting small features
47
INSERTION DESIGN GUIDELINES
48
INSERTION DESIGN GUIDELINES
DON’T
DO
Design the mating faces for easy insertion
49
INSERTION DESIGN GUIDELINES
DON’T
DO
Insert new parts into assembly from above
50
INSERTION DESIGN GUIDELINES
DON’T
DO
Stud for easy
alignment
Stud for easy
alignment
Provide alignment features
51
INSERTION DESIGN GUIDELINES
DON’T
DO
Insert for the same direction. Do not require assembly to be turned over
52
WHAT IS WRONG?
pot.sldasm
53
WHAT IS WRONG?
clamp.sldasmt
54
WHAT IS WRONG?
two plates.sldasmt
55
WHAT IS WRONG?
angle.sldprt
56
WHAT IS WRONG?
box 01.sldasm
57
DFA GUIDELINES IN MME2259a: OUR 13 RULES
Overall Assembly
1.
Minimize overall part count
2.
Minimize the use of separate fasteners
3.
Try fixturing features on base-part
4.
Minimize repositioning during assembly
5.
Optimize assembly sequence efficiency
Part Retrieval
6.
Make component easy to retrieve
7.
Design parts designed for selected type of assembly
Part Handling
8.
Design parts with end-to-end symmetry
9.
Design parts with symmetry about the axis of insertion
10.
Design non-symmetric parts clearly asymmetric
Part Mating
11.
Design for straight-line motions of assembly
12.
Design chamfers and features that facilitate insertion and self-alignment
13.
Design for the maximum part accessibility
58
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Step (A)
Find the theoretical minimum number of components by examining each pair of adjacent
components in the design to see if they really need to be separate.
Fastening components such as bolts, nuts and clips should be included in this
accounting.
Note: Components must be separate if:
1) The design is to operate mechanically
2) The components are made of different materials
3) Assembly or disassembly would be impossible
59
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Step (B)
Find the improvement potential I.P.
NA - NT
I.P. =
× 100
NA
Where:
NA is the actual number of components
NT is the theoretical minimum number of components
60
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1 Minimize overall part count
Step (C)
Rate the product on the worksheet:
If
I.P.  10%, then current design is outstanding
If
10% < I.P.  20%, then current design is very good
If
20% < I.P.  40%, then current design is good
If
40% < I.P.  60%, then current design is fair
If
I.P. > 60%, then current design is poor
61
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Improvement potential
NA - NT
I.P. =
× 100
NA
I.P. =
15 - 1
× 100 = 93
15
Very poor design
Where:
NA is the actual number of components
NT is the theoretical minimum number of components
62
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Improvement potential
I.P. =
I.P. =
NA - NT
× 100
NA
2-1
× 100 = 50
2
Fair design
Where:
NA is the actual number of components
NT is the theoretical minimum number of components
63
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Example:
–
–
Combining two or more parts into an integrated design is one approach to minimizing
the overall component count.
Part reduction should not add costs by making the remaining parts too heavy or too
complex.
64
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Example:
Assembly efficiency of the EPSON MX80 printer.
[Ullman 1992]
Note
The MX80 is constructed from 150 separate components (or subassemblies)
that requires 185 separate operations and 30 minutes to assemble.
65
DESIGN FOR ASSEMBLY GUIDELINES
Rule 1
Minimize overall part count
Example: Assembly efficiency of the IBM Proprinter.
[Ullman 1992]
Note:
The IBM Prprinter has 32 components (or subassemblies) requiring 32 operations (one
per component) and 3 minutes to assemble.
66
DESIGN FOR ASSEMBLY GUIDELINES
Rule 2.
Minimize the use of separate fasteners.
Reasons:
– Each fastener used is one more component to handle (and may
involve many more components for the case of a bolt with
accompanying nut, washer and lock washer).
– Fasteners are not cheap.
– Fasteners are stress concentrators.
– An outstanding design will have few separate fasteners, and those it
does have will be standardized.
Note:
If more than 1/3 of the components in a product are fasteners,
then the assembly logic should be questioned.
67
DESIGN FOR ASSEMBLY GUIDELINES
Rule 2. Make minimum use of separate fasteners
Twist snap
Note:
In designing with plastics, the best way to get rid of fasteners is through snap fits.
68
DESIGN FOR ASSEMBLY GUIDELINES
Rule 2. Make minimum use of separate fasteners
Example:
Several examples of single fasterners that use pins, hooks or other
interference to help connect the components. Generally used for plastic
and sheet metal operations.
69
DESIGN FOR ASSEMBLY GUIDELINES
Rule 2. Make minimum use of separate fasteners
Example:
DON’T
DO
70
DESIGN FOR ASSEMBLY GUIDELINES
Rule 2. Make minimum use of separate fasteners
Example:
Several examples of single fasterners that use pins, hooks or other
interference to help connect the components. Generally used for plastic
and sheet metal operations.
DO
Clip and slot insertion design.
71
DESIGN FOR ASSEMBLY GUIDELINES
Rule 3. Design the product with a base component for locating other components.
– The base provides a foundation for
consistent component location, fixturing,
transport, orientation, and strength.
– Use of a single base component has
shorten the length of some assembly
lines by a factor of 2.
Meter assembly.
72
DESIGN FOR ASSEMBLY GUIDELINES
Rule 4. Don't require the base to be repositioned during assembly.
– Repositioning is both time consuming and costly.
– A product requiring more than two repositionings is considered
to be a poor design.
73
DESIGN FOR ASSEMBLY GUIDELINES
Rule 5.
Make the assembly sequence efficient
An efficient assembly sequence:
• Uses the fewest possible steps.
• Avoids risk of damaging components.
• Avoids awkward, unstable, or conditionally unstable positions for the
product, and the assembly personnel and machinery during assembly.
• Avoids creating many disconnected subassemblies to be joined later.
Note: If there are N components to be assembled, then there are potentially
N! different possible sequences to assemble them.
74
DESIGN FOR ASSEMBLY GUIDELINES
Rule 5.
Make the assembly
sequence
efficient.
[Redford and Chal 1994]
Column 1
Column 2
Column 3
Column 4
Column 5
Column 6
Column 7
Earth Pin
Neutral Pin
Plug Base
Live Pin
Fuse Clip
Cord Grip
Screws
Fuse
Cover
Insert
(operation)
Product
Cover Screw
Cord Grip
Power Plug Assembly Precedence Diagram
75
DESIGN FOR ASSEMBLY GUIDELINES
Rule 5. Make the assembly sequence efficient.
Assembly Precedence Diagrams
Column 1
Column 2
Part 1
Part 2
Part 3
Product
Part 4
Part 5
Etc.
Precedence diagram for a product with “perfect” precedence
Column 1
Part 1
Column 2
Part 2
Column 3
Part 3
……
Column N -1
Part N-1
Column N
Product
Precedence diagram for a product with worst possible precedence
76
DFA GUIDELINES IN MME2259a: OUR 13 RULES
Overall Assembly
1.
Minimize overall part count
2.
Minimize the use of separate fasteners
3.
Try fixturing features on base-part
4.
Minimize repositioning during assembly
5.
Optimize assembly sequence efficiency
Part Retrieval
6.
Make component easy to retrieve
7.
Design parts designed for selected type of assembly
Part Handling
8.
Design parts with end-to-end symmetry
9.
Design parts with symmetry about the axis of insertion
10.
Design non-symmetric parts clearly asymmetric
Part Mating
11.
Design for straight-line motions of assembly
12.
Design chamfers and features that facilitate insertion and self-alignment
13.
Design for the maximum part accessibility
77
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Three component characteristics that make retrieval difficult:
Tangling
Nesting
Flexibility
78
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Design Modifications to Avoid Component Tangling
DON’T
DO
79
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Design Modifications to Avoid Component Tangling
DON’T
DO
80
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Design Modifications to Avoid Component Tangling
DON’T
DO
81
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Design Modifications to Avoid Component Tangling
DON’T
DO
82
DESIGN FOR ASSEMBLY GUIDELINES
Rule 6
Make component easy to retrieve
Design Modifications to Avoid Component Nesting
Nesting - components jam inside each other.
DON’T
DO
Design modifications:
Change the angle of the
interlocking surfaces.
Add features to prevent
jamming.
83
DESIGN FOR ASSEMBLY GUIDELINES
Rule 7. Design components for selected type of assembly
Three types of assembly systems:
Manual assembly
used for low volume production i.e. less than 250,000 units annually
Automatic assembly
used for very high volume production (more than 2 million units annually
Robotic assembly
used for mid to high volume production (between 250,000 and million units
annually)
84
DFA GUIDELINES IN MME2259a: OUR 13 RULES
Overall Assembly
1.
Minimize overall part count
2.
Minimize the use of separate fasteners
3.
Try fixturing features on base-part
4.
Minimize repositioning during assembly
5.
Optimize assembly sequence efficiency
Part Retrieval
6.
Make component easy to retrieve
7.
Design parts designed for selected type of assembly
Part Handling
8.
Design parts with end-to-end symmetry
9.
Design parts with symmetry about the axis of insertion
10.
Design non-symmetric parts clearly asymmetric
Part Mating
11.
Design for straight-line motions of assembly
12.
Design chamfers and features that facilitate insertion and self-alignment
13.
Design for the maximum part accessibility
85
DESIGN FOR ASSEMBLY GUIDELINES
Rule 8. Design all components for end-to-end symmetry.
–
End-to-end symmetry (i.e. symmetry about an axis perpendicular to the axis of
insertion) means that a component can be inserted in the assembly either end first.
DON’T
DO
[Ullman 1992]
Note:
If a component can only be installed in the assembly in one way, then it
must be oriented and inserted in just that way; thereby requiring time and
worker (or machine) dexterity to accomplish the task.
86
DESIGN FOR ASSEMBLY GUIDELINES
Rule 9. Design all components for symmetry about their axes of insertion.
Example:
Components in column (a) have only one orientation for insertion.
However, by adding a functionally useless notch (top component) or a hole and end rounding
(bottom component), there can be two orientations.
DON’T
DO
87
DESIGN FOR ASSEMBLY GUIDELINES
Rule 9. Design all components for symmetry about their axes of insertion.
Example:
(a) Original design fits only one way into the assembly.
(b) The addition of a functionally useless opposing finger and redesign of the mating
recessed area gives the component two possible insertion orientations.
(c) Modifying the component functions can make the component axisymmetric.
DON’T
(a) Assembly fits together
only one way.
DO
(b) Two possible directions of
insertion
DO
(c) 360o rotational symmetry
88
DESIGN FOR ASSEMBLY GUIDELINES
Rule 9. Design all components for symmetry about their axes of insertion.
Example:
DON’T
DON’T
DON’T
DO
DO
DO
89
DESIGN FOR ASSEMBLY GUIDELINES
Rule 9. Design all components for symmetry about their axes of insertion.
Example:
DON’T
Difficult to Orient
DO
Preferred
90
DESIGN FOR ASSEMBLY GUIDELINES
Rule 10. Design components that are not symmetric about their axes of insertion
to be clearly asymmetric.
The goal of this guideline is to make components that can be inserted only in the way
intended. This is to avoid ambiguities in the process or the handling of the
components.
DON’T
Difficult to Orient
DO
Preferred
91
DESIGN FOR ASSEMBLY GUIDELINES
Rule 10. Design components that are not symmetric about their axes of insertion
to be clearly asymmetric.
This slot will be hard to
detect
Pin to help orientate slot
Chamfer to help
orientate slot
92
DESIGN FOR ASSEMBLY GUIDELINES
Rule 10. Design components that are not symmetric about their axes of insertion
to be clearly asymmetric.
Example: The self-alignment and nesting of parts.
This part can be
inserted in any position
DON’T
DO
These parts can
be inserted only
in one position
Hole to accept
swaged part
Hole to accept
notched part
D shaped hole
93
DESIGN FOR ASSEMBLY GUIDELINES
Rule 10. Design components that are not symmetric about their axes of insertion
to be clearly asymmetric.
Example: The self-alignment and nesting of parts.
DON’T
This part could be placed in any
orientation and would not be secured.
DO
This part has a “nest” to orientate
and help secure it.
94
DFA GUIDELINES IN MME2259a: OUR 13 RULES
Overall Assembly
1.
Minimize overall part count
2.
Minimize the use of separate fasteners
3.
Try fixturing features on base-part
4.
Minimize repositioning during assembly
5.
Optimize assembly sequence efficiency
Part Retrieval
6.
Make component easy to retrieve
7.
Design parts designed for selected type of assembly
Part Handling
8.
Design parts with end-to-end symmetry
9.
Design parts with symmetry about the axis of insertion
10.
Design non-symmetric parts clearly asymmetric
Part Mating
11.
Design for straight-line motions of assembly
12.
Design chamfers and features that facilitate insertion and self-alignment
13.
Design for the maximum part accessibility
95
DESIGN FOR ASSEMBLY GUIDELINES
Rule 11. Design components to mate through straight-line assembly, all from the
same direction
This guideline is intended to minimize the motions of assembly.
The assembly process should never require the reorientation of the base nor any other assembly motion
than straight down (i.e. down is the preferred single direction so that gravity can be used to help the
assembly process).
DON’T
Three motions required for insertion
DO
Only one motion required
96
DESIGN FOR ASSEMBLY GUIDELINES
Rule 11. Design components to mate through straight-line assembly, all from the
same direction
Assembly process of an electric motor for a washing machine. The 20 parts are assembled in
20 seconds using 3 robots.
97
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12. Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
• To make actual insertion or mating of a component as easy as possible, each
component should guide itself into place.
• Three techniques to facilitate insertion and alignment:
1)
Chamfers
rounded corners
2)
Leads smaller.
making the fromt end of the component
3)
Compliance
making the component "elastic"
98
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12. Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
Example: Use of Chamfers to ease assembly.
99
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
Example: Use of Chamfers to ease assembly.
100
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
lead
Example: Use of leads to ease assembly.
101
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
Design parts to be self-aligning as in assembly on the right.
102
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
Use funnel-shaped openings and tapered ends to facilitate insertion of parts.
103
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
DON’T
DO
Note: This component mating scheme need not have high tolerances, even if the post is
larger than the hole the components will snap together.
Use of Compliance to ease assembly.
104
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
Compliance
Mating parts that are designed to provide clearance at the point of engagement or which provide
flexibility to reduce the need of precision alignment during assembly and allow some dimensional
variation in the mating parts.
105
DESIGN FOR ASSEMBLY GUIDELINES
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
Examples of Compliant parts
106
Rule 12 Make use of chamfers, leads, and compliance to facilitate insertion and
alignment
www.spirol.com
107
DESIGN FOR ASSEMBLY GUIDELINES
Rule 13.
Maximize for the maximum part accessibility
• Assembly can be difficult if components have no clearance for
grasping.
• Assembly efficiency is also low if a component must be inserted in an
awkward spot.
• Furthermore, if both assembly and maintenance are required, then
additional room must be allowed for the repair tools to mate with the
component.
108
DESIGN FOR ASSEMBLY GUIDELINES
Rule 13.
Maximize for the maximum part accessibility
DON’T
DO
Example of modifications for tool clearance.
109
ADDITIONAL DFA GUIDELINES
Parts that are too thin or have beveled edges may shingle during feeding.
DON’T
DO
110
ADDITIONAL DFA GUIDELINES
Design parts with ends that are “flat” - i.e. orthogonal to the direction of travel.
Difficult to feed
DON’T
Preferred
DO
Larger flat
Smaller angle
111
ADDITIONAL DFA GUIDELINES
DON’T
Slot should be on the
left, but plate can be
fastened on the left
DO
Raised section prevents part
from being fastened
backwards
Bent raised section
112
ADDITIONAL DFA GUIDELINES
DON’T
DO
Oversized Fastener Holes
113
[Redford and Chal 1994]
DESIGN FOR ASSEMBLY -EXAMPLE
Original Assembly
Redesign 1
Redesign 2
114
[Boothroyd et. al. 1994]
DESIGN FOR ASSEMBLY -EXAMPLE
Original
Redesign
115
DESIGN FOR ASSEMBLY -EXAMPLE
Example: Reciprocating mechanism from a power hand saw.
Original Design – 41 parts
Redesign – 28 parts
[Boothroyd et. al. 1994]
The number of parts was reduced from 41 to 28 and assembly time from 409 to 215 seconds.
116
DESIGN FOR ASSEMBLY -EXAMPLE
Redesign
Original Design
Controller assembly
[Boothroyd et. al. 1994]
117
DESIGN FOR ASSEMBLY -EXAMPLE
Redesign
Original Design
Tool carrier
118
DESIGN FOR ASSEMBLY -EXAMPLE
Original Design
Redesign
119
POTENTIAL CONFLICT BETWEEN DFM AND DFA
Complex part, simple assembly
[Otto et. al. 1994]
Simple parts, more complex assembly
120
Design for Assembly Worksheet
Individual Assembly Evaluation for
Date
P
F
G
VG
E
COMMENTS
Overall Assembly
1. Overall part count
2. Use of separate fasteners
3. Fixturing features on base-part
4. Minimal repositioning during assembly
5. Assembly sequence efficiency
Part Retrieval
6. Component characteristics for ease of retrieval
7. Parts designed for selected assembly
Part Handling
8. Parts with end-to-end symmetry
9. Parts with symmetry about the axis of insertion
10. Non-symmetric parts clearly asymmetric
Part Mating
11. Straight-line motions of assembly
12. Chamfers and features that facilitate insertion and self-alignment
13. Maximum part accessibility
8x
Note:
6x
Evaluation score is to be used
only to compare one assembly
to alternative designs of the
same assembly
4x
2x
Total =
0x
121
x0
Overall Assembly
1 Minimize overall part count
2 Minimize the use of separate fasteners
3 Try fixturing features on base-part
4 Minimize repositioning during assembly
5 Optimize assembly sequence efficiency
x2
x6
x8
1
1
1
1
1
Part Retrieval
6 Make component easy to retrieve
7 Design parts designed for selected type of assembly
1
1
Part Handling
8 Design parts with end-to-end symmetry
9 Design parts with symmetry about the axis of insertion
10 Design non-symmetric parts clearly asymmetric
Part Mating
11 Design for straight-line motions of assembly
12 Design chamfers and features that facilitate insertion and self-alignment
13 Design for the maximum part accessibility
x4
1
1
1
1
1
1
3
2
2
3
3
54
122
P
F
G
VG
E
x0
x2
x4
x6
x8
Overall Assembly
1 Minimize overall part count
2 Minimize the use of separate fasteners
3 Try fixturing features on base-part
4 Minimize repositioning during assembly
5 Optimize assembly sequence efficiency
1
1
1
1
1
Part Retrieval
6 Make component easy to retrieve
7 Design parts designed for selected type of assembly
Part Handling
8 Design parts with end-to-end symmetry
9 Design parts with symmetry about the axis of insertion
10 Design non-symmetric parts clearly asymmetric
Part Mating
11 Design for straight-line motions of assembly
12 Design chamfers and features that facilitate insertion and self-alignment
13 Design for the maximum part accessibility
1
1
1
1
1
1
1
1
2
1
3
0
7
70
123
I.P. =
NA - NT
× 100
NA
I.P. =
20 - 3
× 100 = 85%
20
VERY BAD DESIGN
124
Overall Assembly
1 Minimize overall part count
2 Minimize the use of separate fasteners
3 Try fixturing features on base-part
4 Minimize repositioning during assembly
5 Optimize assembly sequence efficiency
1
1
1
1
1
Part Retrieval
6 Make component easy to retrieve
7 Design parts designed for selected type of assembly
1
1
Part Handling
8 Design parts with end-to-end symmetry
9 Design parts with symmetry about the axis of insertion
10 Design non-symmetric parts clearly asymmetric
Part Mating
11 Design for straight-line motions of assembly
12 Design chamfers and features that facilitate insertion and self-alignment
13 Design for the maximum part accessibility
1
1
1
1
1
1
`
6
4
1
0
2
28
125
Try fixturing features on base-part
4 Minimize repositioning during assembly
5 Optimize assembly sequence efficiency
3
1
1
1
Part Retrieval
6 Make component easy to retrieve
7 Design parts designed for selected type of assembly
1
1
Part Handling
8 Design parts with end-to-end symmetry
9 Design parts with symmetry about the axis of insertion
10 Design non-symmetric parts clearly asymmetric
1
1
1
Part Mating
11 Design for straight-line motions of assembly
12 Design chamfers and features that facilitate insertion and self-alignment
13 Design for the maximum part accessibility
1
1
1
0
3
5
5
0
56
126
127