1. 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.

2. The topic for today is DFA, DFM & DFMA
DFA/DFM/DFMA is supposed to:
From the BDI website
Boothroyd & Dewhurst Institute website

3. 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

4. Progression of the development of DFMA: how it developed
DFA
DFM
DFMA
DFE
DFD
DFA = design for assembly
DFM = design for manufacture
DFE = design for Environment
DFD = design for disassembly
DFS = design for service
DFSS = design for six sigma
DFX = design for X
DFS
DFSS
DFX’s

5. Product Costs Highest impact on reducing cost – reducing parts
From the BDI website
Boothroyd & Dewhurst Institute website

6. Cost Reduction Opportunities
DFA
simplifying &
reducing
DFM
DFMA
From the BDI website
Boothroyd & Dewhurst Institute website

7. Model T Early DFA Shipping crates for floorboards Paint colour
Assembly Line
Operating Door
Choke

8. Results of Ingersoll-Rand project with DFMA
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

9. 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

10. 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

11. Boothroyd and Dewhurst look at this as follows:
From the BDI website
Boothroyd & Dewhurst Institute website

12. 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)

13. Ways to Use DFMA Concurrent Engineering
Reduce Manufacturing & Assembly Costs
Reduce Time to Market
Reduce Design Costs
Etc.
Benchmarking Competitors Products
Analyzing Supplier Costs
Most contracts have a clause to reduce costs annually

14. Manual Hard Automation Soft Automation Types of Assembly
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

15. DFA Guidelines 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
Critical orientation – obvious – see & fit
Non-critical orientation – fit in any direction
Ensure access & visibility
Easy part handling
Assemble from top
Reduce locating/alignment operations – manual/time consuming

16. 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.

17. 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:

18. Proposed design of a motor drive assembly

19. Application of the three criteria gives:

20. 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

21. 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.

22. 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

23. 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.

24. 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.

26. Boothroyd and Dewhurst do one thing at this point that is particular to their DFMA analysis.
They calculate the “Manual Assembly Efficiency, Ema”
This is done with the equation:
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.

27. As an example: the design efficiency for the motor drive is, where
Nmin = 4 parts,
tma = 160 sec,
ta = 3.5 sec
Then and Ema = 8.8%

28. It can be seen that those parts that didn’t meet the criteria for the minimum part count involved a total assembly time of seconds

29. Redesigned motor after analysis;
two motor mount screws have been kept

30. Results for DFA analysis for redesign of Motor drive assembly

32. At the end of the changes due to DFMA are:

33. DFA Guidelines 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
Critical orientation – obvious – see & fit
Non-critical orientation – fit in any direction
Ensure access & visibility
Easy part handling
Assemble from top
Reduce locating/alignment operations – manual/time consuming

34. Reduce number of different parts - Standardize parts
One Time Costs
Tooling
Design/Development
Contacting / Vendor Selection
Product Testing
Continuous Costs
Material
Assembly
Inventory
Inspection

35. Simplification of Assembly
Easier = faster
Less opportunity for mistakes
Easier to automate

36. Reduction Number of Processes
Less steps = faster
Less material handling = less damage
Less operations = less opportunity for defects
Value Added processes in ~ remove Non-Valued Added steps

37. Left to right: simplest, low cost to most parts hardest to assembly
Less Fasteners especially screws & bolts
Left to right: simplest, low cost to most parts hardest to assembly
Boothroyd & Dewhurst Inc, 1999

38. Reduce Tangling / Nesting
Takes time to separate
Requires people
Hard to automate
Hugh Jack, 2001

39. So What?
How does this fit it in with MECH 424?
How does this fit into Engineering?

40. Orientation Critical orientation – obvious – see & fit
Non-critical orientation – fit in any direction

41. Ensure Access & Visibility

42. Easy part handling
Size
Weight
Shape
Sharp edges
Sticky
Tangled & Nested
etc.

43. Reduce locating/alignment operations – manual/time consuming
Assemble from Top

44. Thank you for your attention