Lecture 7
DFA, DFM, & DFMA 1
The contents of this lecture are the sole copyright of M. Ham & J. Jeswiet
They are intended for use only by students in MECH 424, Life Cycle Engineering,
Queen’s University, Kingston, ON, Canada.
Unlicensed use of the contents of this lecture outside MECH 424 is illegal.
The topic for today is
DFA, DFM & DFMA
DFA/DFM/DFMA is
supposed to:
From the BDI website
Boothroyd & Dewhurst Institute
website
What is DFA/DFM/DFMA
• DFA – how easy things go together
– DFA: Design of components taking into account how they will be
assembled together to ensure that assembly costs are
minimized.
• DFM – how easy things can be made
– DFM: Design of components taking into consideration the
processes that will be used to manufacture them to ensure that
manufacturing costs are minimized.
• DFMA – balance between ease of making & assembly
– DFMA: It is obvious that these two goals are often incompatible
and hence compromises must be made.
• Environmental factors are not directly taken into account,
improved quality = reduced waste, and thus does indirectly
impact the environment!
• DFD – how easy things take apart
Progression of the development of DFMA: how it developed
DFA
DFM
DFMA
DFE
DFD
DFA = design for assembly
DFM = design for manufacture
DFS
DFE = design for Environment
DFD = design for disassembly
DFSS
DFS = design for service
DFSS = design for six sigma
DFX = design for X
DFX’s
Product Costs
4%
24%
Labour
Overhead
Parts
72%
Highest impact on reducing cost – reducing parts
From the BDI website
Boothroyd & Dewhurst Institute website
Cost Reduction Opportunities
DFA
simplifying
&
reducing
DFM
DFMA
From the BDI website
Boothroyd & Dewhurst Institute website
Model T
Early DFA
• Shipping crates for
floorboards
• Paint colour
• Assembly Line
• Operating Door
• Choke
Example of results of DFMA application:
In 1989, Ingersoll-Rand not only cut product development time in half
but also reduced the number of parts needed.
Ingersoll-Rand cut product development time from two years to one.
The following shows the reduced number of parts:
Results of Ingersoll-Rand project with DFMA
Before
After
Compressor/
oil cooler parts
80
29
Number of
fasteners
38
20
Number of
assembly
operations
159
40
Assembly
time, min
18.5
6.5
From the BDI website
Boothroyd & Dewhurst Institute website
Ford vs. GM
(Boothrotd & Dewhurst, 1999)
• Front Bumper of Taurus (after DFA)
– 10 parts
• Front Bumper of Grand Prix
– 100 parts
• 41% productivity gap – due to ease of
assembly
• Ford’s parts fit together easier
In a survey of 89 industries who used DFMA
it was found that the following reductions were achieved, on average
100%
From the BDI website
Boothroyd & Dewhurst Institute website
Boothroyd and Dewhurst look at this as follows:
From the BDI website
Boothroyd & Dewhurst Institute website
Why were these improvements suddenly possible and not before?
modern methods of analysis
traditional view: “we design it, you build it”, (still prevalent today)
changing attitudes (more teamwork)
Ways to Use DFMA
1. Concurrent Engineering
1.
2.
3.
4.
Reduce Manufacturing & Assembly Costs
Reduce Time to Market
Reduce Design Costs
Etc.
2. Benchmarking Competitors Products
3. Analyzing Supplier Costs
1. Most contracts have a clause to reduce costs
annually
Types of Assembly
Manual
Most flexible & Most expensive
Skill of workers effects assembly times
Hard Automation
Custom tooling – only make one product
Soft Automation
Robots
More dexterity BUT dumb
DFA Guidelines
1. Reduce number of parts
2. Reduce number of different parts - Standardize
parts
3. Simplification of assembly
4. Reduction number of processes
5. Less fasteners especially screws & bolts
6. Reduce tangling
7. Orientation
1. Critical orientation – obvious – see & fit
2. Non-critical orientation – fit in any direction
8. Ensure access & visibility
9. Easy part handling
10. Assemble from top
11. Reduce locating/alignment operations –
manual/time consuming
Justification of Part
The three criteria against which a part must be
examined, as it is added to the product assembly, are:
1. during operation of the product, does the part move relative to all
other parts already assembled?
Only gross motion should be considered; small motions can be
accommodated by other means such as integral elastic elements.
2. must the part be of a different material than or be isolated from all
other parts already assembled?
Only fundamental physical needs for material differences are
acceptable.
3. must the part be separate from all other parts already assembled?
The only reason to have it separate would be that assembly or
disassembly (for maintenance reasons ONLY) of other separate parts
would be impossible.
The best way to look at this is with an example.
Consider a motor drive assembly that is required to sense and
control its position on two guide rails, as shown schematically:
Proposed design of a motor drive assembly
Application of the three criteria gives:




From the foregoing analysis it can be seen that:
 if the motor and sensor subassemblies could be arranged to snap or
screw into the base and
 if a plastic cover could be designed to snap on,
in theory, there would be only four parts needed instead of nineteen.
The foregoing was done without considering any practical limitations
Advantage in the Design Process:
The Designer and/or design team is now placed in a position of having to
justify the existence of the parts that did not satisfy the DFA criteria.
Justification comes from practical, technical or economic considerations.
For example: it could be argued that two screws are needed to secure the
the motor and one screw is needed to position the sensor because any
alternatives are impractical for a low volume operation such as this.
However the design of the screws could be improved by providing them
with “pilot points” to facilitate assembly.
Based upon the foregoing some design rules can already be established.
Some Design Rules - logical
A common theme throughout DFA, is the need to
 reduce the number of fastening devices, with screws
being the main culprit
 if screws are used, one standard size should be used
 all screw heads should be the same;
a common screw driver can then be used
 all screws should have pilot points to facilitate easier
assembly
The following change could easily be made:
 the powder metal bushings are unnecessary because the part can
be machined from an alternative material with the right frictional
characteristics, such as Nylon
The following are difficult to justify:
 separate stand-offs
 end plate
 cover
 the six screws
We started with this.
Before going further it is necessary to have estimates of
 assembly times
 costs
Techniques are available to make these estimates but will not be dealt
with here.
Suffice it to say we can estimate the times and costs shown in the next
table.
Boothroyd and Dewhurst do one thing at this point that is particular to
their DFMA analysis.
They calculate the “Manual Assembly Efficiency,
This is done with the equation: E ma  N min
Ema”
ta
t ma
Where Nmin = the theoretical part minimum
ta = the theoretical, lowest assembly time.
this is an ideal minimum
tma = the estimated assembly time to complete assembly of
the actual product
It should be noted these criteria are applied without taking general
design considerations into account.
As an example:
the design efficiency for the motor drive is, E ma  N min
where
Nmin = 4 parts,
tma = 160 sec,
ta = 3.5 sec
Then Ema
35
.
 4
and
160
Ema = 8.8%
ta
t ma
It can be seen that those parts that didn’t meet the criteria for the
minimum part count involved a total assembly time of 120.6 seconds
Table 1
no.
base
1
bushing
2
motor sub
1
motor screw
2
sensor sub
1
set screw
1
stand-off
2
end plate
1
end plate screw
2
plastic bus
1
thread leads
reorient
cover
1
cover screw
4
theoretical assembly assembly
part count time, sec cost (cents)
1
3.5
2.9
0
12.3
10.2
1
9.5
7.9
0
21
17.5
1
8.5
7.1
0
10.6
8.8
0
16
13.3
1
8.4
7
0
16.6
13.8
0
3.5
2.9
5
4.2
4.5
3.8
0
9.4
7.9
0
31.2
26
The assembly cost is for a
labour rate of $30 per hour
Design Efficiency =
8.8%
Time for parts deleted =
in ideal situation, sec
120.6
Time for parts deleted =
for redesign, sec
99.2
Redesigned motor after analysis;
two motor mount screws have been kept
Results for DFA analysis for redesign of Motor drive assembly
base
motor sub
motor screw
sensor sub
set screw
thread leads
plastic cover
Totals
1
1
2
1
1
1
1
0
1
0
1
7
1
4
Design efficiency =
3.5
4.5
12
8.5
8.5
5
4
46
2.9
3.8
10
7.1
7.1
4.2
3.3
38.4
26% This percentage approaches the range found,
from experience, for electro-mechanical devices
Savings in assembly cost = $
Increase in design efficiency =
0.95
348%
At the end of the changes
due to DFMA are:
DFA Guidelines
1.
2.
3.
4.
5.
6.
7.
Reduce number of parts
Reduce number of different parts - Standardize parts
Simplification of assembly
Reduction number of processes
Less fasteners especially screws & bolts
Reduce tangling
Orientation
1. Critical orientation – obvious – see & fit
2. Non-critical orientation – fit in any direction
8. Ensure access & visibility
9. Easy part handling
10. Assemble from top
11. Reduce locating/alignment operations – manual/time
consuming
Reduce number of different parts Standardize parts
• One Time Costs
–
–
–
–
Tooling
Design/Development
Contacting / Vendor Selection
Product Testing
• Continuous Costs
–
–
–
–
Material
Assembly
Inventory
Inspection
Simplification of Assembly
• Easier = faster
• Less opportunity for mistakes
• Easier to automate
Reduction Number of Processes
• Less steps = faster
• Less material handling = less damage
• Less operations = less opportunity for
defects
• Value Added processes in ~ remove NonValued Added steps
Less Fasteners
especially screws & bolts
Left to right: simplest, low cost to most parts hardest to assembly
Boothroyd & Dewhurst Inc, 1999
Reduce Tangling / Nesting
• Takes time to
separate
• Requires people
• Hard to automate
Hugh Jack, 2001
So What?
• How does this fit it in with MECH 424?
• How does this fit into Engineering?
Orientation
1.
Critical orientation – obvious – see & fit
2.
Non-critical orientation – fit in any direction
Ensure Access & Visibility
www.detnews.com/2004/project/0405/04/901-134795.htm
www.uniontire.ca/tireassfr.htm
Easy part handling
•
•
•
•
•
•
•
Size
Weight
Shape
Sharp edges
Sticky
Tangled & Nested
etc.
Reduce locating/alignment operations –
manual/time consuming
Assemble from
Top
http://www.hfmgv.org/rouge/tour.asp#
Thank you for your attention