DFA, DFM, & DFMA 2 DFA, DFM, & DFMA 2 - Department of ...

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 



Dewhurst 1983 

Effort Required 

Fastening 

& Securing 

View 

(obstructed vs 

unobstructed) 

Time used later

Case Study: 

Pneumatic 

Piston


Time Table 



Dewhurst 1983


Time Table 



Dewhurst 1983


Estimated Insertion 


Time Assembly, Time © Boothroyd & 

Time Table 

Dewhurst 1983 



Dewhurst 1983





Time Table 

Dewhurst 1983 



Dewhurst 1983





Time Table 

Dewhurst 1983 



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

CASE STUDY: controller assembly

Analysis sheet for controller assembly 

Part/subassembly Number Handling Insertion Operator Operation min Labour cents 

or operation of items sec per item sec per item time, sec cost, centspartsrate,$/hr /sec 

1 pressure regulator 1 2.0 1.5 3.5 4.8 1 50 1.39 

2 metal frame 1 1.95 5.5 7.5 10.3 1 

3nut 1 1.13 8 9.1 12.7 0 

4 reorientation 1 9 9.0 12.5 

5 sensor 1 1.95 6.5 8.5 11.7 1 

6 strap 1 1.8 6.5 8.3 11.5 0 

7 screw 2 1.8 8 19.6 27.2 0 Design eff = 

8 apply tape 1 12 12.0 16.7 0.07 

9 adaptor nut 1 1.5 10.5 12.0 16.7 0 7% 

10 tube assembly 1 3 4 7.0 9.7 0 

11 screw fastening 1 5 5.0 6.9 

12 pcb assembly 1 5.6 6.5 12.1 16.8 1 

13 screw 2 1.8 8 19.6 27.2 0 

14 connector 1 1.95 5 7.0 9.7 0 

15 ground lead 1 5.6 5 10.6 14.7 0 


17 knob assembly 1 1.95 6.5 8.5 11.7 1 

18 screw fastening 1 5 5.0 6.9 

19 plastic cover 1 1.95 6.5 8.5 11.7 0 


21 screw 3 1.8 10.5 36.9 51.3 0 

227.4 315.9 5

Design Change Item Time savings 

1 combine plastic cover with frame and eliminate 19, 20, 21 54.3 

screws & reorientation process 

2 Eliminate strap and 2 screws [provide snaps in plastic 6, 7 27.9 

frame tohold sensor if necessary] 

3 Eliminate screws holding PCB assembly 13 19.6 

[provide snaps in plastic frame] 

4 Eliminate two orientations 4, 16 18 

5 Eliminate tube assembly and 2 screwing operations 10, 11 12 

[screw adaptor nut and sensor into pressure regulator] 

6 Eliminate ground lead; unecessary with plastc shield 15 10.6 

7 Eliminate connector [plug sensor into PCB] 14 7 

Total: 149.4 

Time savings: 66%

Diaphragm 

assembly

Thank you for your attention 

Thank you for your attention

Design Rules for Manual Assembly: 

Assembly 

Note: In many cases the following rules can be used for either manual manual 

or 

robotic assembly. 

DESIGN GUIDELINES for PART HANDLING 

1. Design parts that have end to end 

symmetry and rotational symmetry 

about the axis of insertion, or strive for 

the closest available; see (a) 

2. If symmetry is not possible make it 

obvious the part is asymmetric (b) 

3. Use features that prevent jamming of 

parts (c ) 

4. Avoid features that allow 

entanglement in storage (d) 

5. Avoid parts that are slippery & delicate 

6. Avoid hazardous parts; sharp or 

splinter easily 

7. Use environmentally friendly materials

DESIGN GUIDELINES FOR 

INSERTION AND FASTENING 

This type of operation is very important 

in assembly, and therefore has many 

guidelines, all of which cannot be 

covered here. 

1. Keep resistance to 

insertion a minimum; 

chamfers are a help

DESIGN GUIDELINES for INSERTION and FASTENING 

(continued) 

2) standardize using common parts, processes and 

methods across all models and product lines 

where possible. Gives lower product cost. 

3) Use pyramid assembly, preferably from one axis 

of reference. 

4) Avoid, if possible, having to hold down parts to 

maintain orientation during any part of the 

operation. 

5. Design the part so it is located before released

DESIGN GUIDELINES for INSERTION and FASTENING (continued) 

6) When common mechanical fasteners are used the cost of the type of fastener 

used should be kept in mind. 

7) Avoid repositioning of a partially completed assembly in order to complete 

the operation 

snap 

fitting 

screwing 

plastic 

bending 

riveting

ADDITIONAL INFORMATION ABOUT SOME OF THE FOREGOING 

A great deal of research has been done on what we have seen so far and the 

experience gained has yielded many empirical equations. The following gives an 

idea of some of these relationships. 

Manual Insertion Time for both conical and curved chamfers 

For conical chamfers where the width of 45 o chamfers is W 1 

= 0.1d, the manual insertion time for a plain cylindrical peg, t i 

is given by: 

t i = -70 ln(c) + f(chamfers) + 3.7L+ 0.75d 10 -2 s 

or t i = 1.4L + 15 10 -2 s ; whichever is larger and where 

f(chamfers) equals one of the following: 

-100 [no chamfer], -220 [chamfer on hole], -250 [chamfer on 

peg], -370 [chamfer on peg and hole] 

For example for D = 20 mm, d = 19.5 mm, L = 75 mm, with 

chamfers on both the peg and hole: 

c = (20-19.5)/20 = 0.025 

t i = -70 ln(0.025) - 370 + 3.7(75)+ 0.75(19.5) = 181 10 -2 s 

t i = 1.4(75) + 15 = 120 10 -2 s 

To be conservative choose the higher value, 181 10 -2 s 

c is the diametral 

clearance 

c 

( D d) 

D

ADDITIONAL INFORMATION (cont’d) 

Effects of restricted access and vision on initial engagement of screw:

Torx

ADDITIONAL INFORMATION (cont’d) 

Holding parts in place

ADDITIONAL INFORMATION (cont’d)

ADDITIONAL INFORMATION (cont’d)

The following references were used for the DFMA 

presentations: 

PRODUCT DESIGN for MANUFACTURE and ASSEMBLY; Boothroyd, Dewhurst and 

Knight; © 1994 Marcel Dekker 

1999 International Forum on DFMA; Newport Rhode Island 

DESIGN for ASSEMBLY; Myrup, Kahler and Lund; © 1983 IFS Publications 

DESIGN for ASSEMBLY: a designers handbook 2 nd edition; © 1983 Boothroyd and 

Dewhurst 

Internet References 

http://engineer.gvsu.edu/vac/dfa.html…. 

http: //www.design-ivcom/about.html… 

http:www.tue.nl/tm/rave/ce/dfma-2.html….. 

http:// clear.lakes/~eltechno/TVAsfd.html…. 

http://sun.mpce.stu.mmu.ac.uk/pages/projects/dfe18/report18.html…. 

http://rolf.ece.curtain.edu.au/~clive/jit/jit.htm…. 

http://www.dfma.com/news/panel.html…. 

http://www.danfoss.com/…. 

http://www.ssd.gu.se/kid/swe/ssd0350.html…

Active websites which has DFMA study results 

http://www.dfma.com/news/panel.html 

http://www.dfma.com/news/cibacorn.html 

http://www.machinedesign.com/afiles/indexA.html 

http://www.dfma.com/news/Herrera.html

DFA, DFM, & DFMA 2 DFA, DFM, & DFMA 2 - Department of ...

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