DFA, DFM, & DFMA 2 DFA, DFM, & DFMA 2

Lecture 8
Working for the environment
© J. Jeswiet
DFA, DFM, & DFMA 2

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

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

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, Jack 2001

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

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

Reduce locating/alignment operations –
manual/time consuming
Assemble from
Top
http://www.hfmgv.org/rouge/tour.asp#

From BDI Promo
So in which industries can DFMA be used ?

The concept of DFMA has been introduced.
However, there are many
more methods and the
following is a list
compiled as part of a
study* 1,2 of the use of
formal design methods
within industry: industry
* 1 Gouvinhas & Corbett, 1999, The
use of design Methods within
production machinery companies,
IMECHE J. of Engineering
Manufacture, vol 213, Part B, pp
285 – 293.
* 2 Seliger Production Innovation
– Industrial Approach, Annals of
CIRP, 2001, vol. 2.

Flow chart for
typical steps taken using DFMA techniques are:
Design concept
DFA
Selection of materials
and processes and
Early cost estimates
Best design concept
DFM
prototype
Suggestions for
simplification
of product structure
Suggestions for more
economic materials, processes
and environmentally friendly materials
Detail design
for minimum
manufacturing
costs
production

The The Advantages of of Applying DFMA
1. DFMA provides a systematic procedure for analyzing a proposed
design from the point of view of assembly and manufacture.
The result is simpler more reliable products which are less
expensive to assemble and manufacture.
2. Any reduction in the number of parts in an assembly produces a
snowball effect on cost reduction because of drawings and
specifications that are no longer needed; reduced overheads.
3. Dialogue is encouraged between design and manufacturing
engineers giving the teamwork an attitude necessary to
concurrent engineering.
Companies reporting large savings with DFMA are:
Bombardier - Canadair Regional Jet Nacelles
NCR - new point of sales terminals.
Brown and Sharpe - measurement equipment

A typical product to which DFMA analysis can be applied is:
We will now look at Design rules for Manual Assembly.
Assembly

PROCEDURE FOR THE ANALYSIS OF MANUALLY ASSEMBLED PRODUCTS
STEP 1. Obtain the best information about the product or assembly; useful
items are:
engineering drawings
exploded 3-D views
existing version of the product [for a redesign]
a prototype
STEP 2. Imagine how the assembly would be dismantled, or for a redesign
do it with an actual part.
Note: this is an important step for later DFD analysis.
If the assembly contains subassemblies, treat these as parts first.
STEP 3. Set up a worksheet with cells for appropriate entries
part name, number of parts, theoretical part count, handling time,
insertion time, assembly time, assembly cost
STEP 4. Begin assembling, or re-assembling the product.
Complete each row on the sheet. The column for the minimum theoretical
number of parts is a critical step in this process.
The estimated handling times and insertion times are obtained from the
Boothroyd and Dewhurst tables.

STEP 5. When all of the rows have been completed (reassembled in effect), the
assembly time column is added to give a total estimated assembly time.
The estimated assembly cost column is also added to give a total estimated
assembly cost.
The theoretical minimum column is also summed.
STEP 6. The design efficiency is calculated.
Where N min = the theoretical part minimum
E ma
N .
min t a
t ma
t a = the theoretical, lowest assembly time for one part
This is an ideal minimum
t ma = the estimated assembly time to complete assembly of
the actual product

The Pen Example
• Take the pens apart
• Determine the minimum theoretical parts
• Check assembly time
• Cost to assemble $50/hr rate
– Now vs minimum time
• Efficiency = Min. Parts* Min. Time/Actual
Time

Handling & Insertion
• Handling Time Factors
– Orientation
–Part Size
– Ease of Handling
• Insertion Time Factors
– Type of Fastening
– When secured

Orientation
AXIS OF INSERTION
Rotating a part about its axis of insertion: how many possible orientations are
there?
The more symmetric a part, the easier it is to install it, quickly and accurately.
When a part is not
symmetric, obvious
external features
make orientation
easier for the
operator.
infinite
orientations
limited
orientations

One of the principal geometric design features that affects times required to grasp
and orient a part is symmetry.
Experience shows there are two distinct operations in this:
1. Alignment of the axis of the part that corresponds to the axis of insertion
- called alpha rotation, α.
2. Rotation of the part about its axis of insertion
- called beta rotation, β.
0 instead of infinity
β
α

Then, a plain square prism which is to be inserted into a square hole would
first have to be rotated about an axis perpendicular to the insertion axis.
This rotation will be repeated every 180 degrees and therefore has an alpha, α
symmetry of 180 degrees.
The square prism would then have to be rotated about the axis of symmetry for
the part but in the beta direction. This give a beta, β, symmetry every 90 degrees.
Note: if the square prism were inserted into a round hole it would have 180 o α
symmetry and infinite or 0 β symmetry.
Its has been found that the
best single parameter to
describe overall symmetry is
simply the addition of alpha
and beta, α + β, giving the
total axis of symmetry.
tables have been derived for
total axis of symmetry.

Estimated Handling Times
How
handled
Total
axis
of
symmetry
Size of Part
Time used later
Source: Design for Assembly, © Boothroyd &
Dewhurst 1983

Estimated Handling
Time Table
Total axis of
symmetry
Size of Part
Time used later
How
handled
Source: Design for
Assembly, © Boothroyd &
Dewhurst 1983

Estimated Insertion Times
Effort Required
Fastening
& Securing
View
Source: Design for Assembly, © Boothroyd &
Dewhurst
1983
Time used later

Estimated InsertionTimes
Source: Design for
Assembly, © Boothroyd &
Dewhurst 1983
Effort Required
Fastening
& Securing
View
(obstructed vs
unobstructed)
Time used later

Case Study:
Pneumatic
Piston

Estimated Handling
Time Table
Source: Design for
Assembly, © Boothroyd &
Dewhurst 1983

Estimated Handling
Time Table
Source: Design for
Assembly, © Boothroyd &
Dewhurst 1983

Pneumatic Piston worksheet
Part/subassembly Number Min # Handling Insertion Operator Operation
or operation of items parts sec per item sec per item time, sec cost, cents
1 main block 1 1 1.95 1.5 3.5 4.8
2 piston 1 1 1.5 2.5 4.0 5.6
3 piston stop 1 1 1.5 1.5 3.0 4.2
4 spring 1 1 1.84 1.5 3.3 4.6
5 cover 1 0 2.36 6.5 8.9 12.3
6 screw 2 0 1.8 8 19.6 27.2
7 4 42.3 58.7
Labour cents Design eff = 0.28
rate,$/hr /sec 28%
50 1.39

Thank you for your attention
Thank you for your attention