DFA, DFM, & DFMA 1DFA, DFM, & DFMA 1

Lecture 7

The contents of this lecture are the sole copyright of M. Ham & J. JeswietThey 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

The topic for today is DFA, DFM & DFMA

From the BDIBDI website

BBoothroyd & DDewhurst IInstitute website

DFA/DFM/DFMA is supposed to:

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, Environmental factors are not directly taken into account,

improved quality = reduced waste, and thus does indirectly improved quality = reduced waste, and thus does indirectly impact the environment!impact the environment!

• DFD – how easy things take apart

DFA DFM DFMA DFE

DFS

DFD

DFSS

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

Progression of the development of DFMA: how it developed

DFX’s

Product Costs

4%

24%

72%

LabourOverheadParts

Highest impact on reducing cost – reducing parts

From the BDIBDI websiteBBoothroyd & DDewhurst IInstitute website

Cost Reduction Opportunities

DFA

DFMDFMA

From the BDIBDI websiteBBoothroyd & DDewhurst IInstitute website

simplifying simplifying &&

reducingreducing

Model T

Early DFA• Shipping crates for

floorboards• Paint colour• Assembly Line• Operating Door• Choke

In 1989, Ingersoll-Rand not only cut product development time in half but also reduced the number of parts needed.

Results of Ingersoll-Rand project with DFMA

Before After

Compressor/ oil cooler parts

8080 2929

Number of fasteners

3838 2020

Number of assembly operations

159159 4040

Assembly time, min

18.518.5 6.56.5

Example of results of DFMA applicationDFMA application:Example of results of DFMA applicationDFMA application:

Ingersoll-Rand cut product development time from two years to one.

The following shows the reduced number of parts:

From the BDIBDI websiteBBoothroyd & DDewhurst IInstitute 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 BDIBDI websiteBBoothroyd & DDewhurst IInstitute website

Boothroyd and Dewhurst look at this as follows:

From the BDIBDI websiteBBoothroyd & DDewhurst IInstitute website

modern methods of analysis

traditional view: “we design it, you build it”, (still prevalent today)

changing attitudes (more teamwork)

Why were these improvements suddenly possible and not before?

1. Concurrent Engineering1. Reduce Manufacturing & Assembly Costs

2. Reduce Time to Market

3. Reduce Design Costs

4. Etc.

2. Benchmarking Competitors Products

3. Analyzing Supplier Costs1. Most contracts have a clause to reduce costs

annually

Ways to Use DFMAWays to Use DFMAWays to Use DFMAWays to Use DFMA

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

Types of AssemblyTypes of AssemblyTypes of AssemblyTypes of Assembly

1. Reduce number of parts2. Reduce number of different parts - Standardize parts3. Simplification of assembly4. Reduction number of processes5. Less fasteners especially screws & bolts6. Reduce tangling7. Orientation

1. Critical orientation – obvious – see & fit2. Non-critical orientation – fit in any direction

8. Ensure access & visibility9. Easy part handling10.Assemble from top11.Reduce locating/alignment operations – manual/time

consuming

DFADFA GuidelinesGuidelinesDFADFA GuidelinesGuidelines

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 three criteriathree criteria against which a part must be examined, as it is added to the product assembly, are:

Justification of PartJustification of PartJustification of PartJustification of Part

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 assemblyProposed 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

The Designer and/or design team is now placed in a position of having to justify the existence of the partsjustify 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.

Advantage in the Design Process: Advantage in the Design Process:

Some Design Rules - logical

A common theme throughout DFAcommon 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, Ema”

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.

E Nt

tmaa

ma

minThis is done with the equation:

where

Nmin = 4 parts,

tma = 160 sec,

ta = 3.5 sec

As an example:

the design efficiency for the motor drive is, E Nt

tmaa

ma

min

Then and Ema = 8.8% E ma 43 5

1 6 0.

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 1theoretical assembly assembly

no. part count time, sec cost (cents)base 1 1 3.5 2.9 The assembly cost is for a bushing 2 0 12.3 10.2 labour rate of $30 per hourmotor sub 1 1 9.5 7.9motor screw 2 0 21 17.5sensor sub 1 1 8.5 7.1set screw 1 0 10.6 8.8stand-off 2 0 16 13.3end plate 1 1 8.4 7 Design Efficiency = 8.8%end plate screw 2 0 16.6 13.8plastic bus 1 0 3.5 2.9 Time for parts deleted = 120.6thread leads 5 4.2 in ideal situation, secreorient 4.5 3.8cover 1 0 9.4 7.9 Time for parts deleted = 99.2cover screw 4 0 31.2 26 for redesign, sec

Redesigned motor after analysis;

two motor mount screws have been kept

base 1 1 3.5 2.9motor sub 1 1 4.5 3.8motor screw 2 0 12 10sensor sub 1 1 8.5 7.1set screw 1 0 8.5 7.1thread leads 5 4.2plastic cover 1 1 4 3.3Totals 7 4 46 38.4

Design efficiency = 26% This percentage approaches the range found,from experience, for electro-mechanical devices

Savings in assembly cost = 0.95$ Increase in design efficiency = 348%

Results for DFA analysis for redesign of Motor drive assembly

At the end of the changes due to DFMA are:

1. Reduce number of parts2. Reduce number of different parts - Standardize parts3. Simplification of assembly4. Reduction number of processes5. Less fasteners especially screws & bolts6. Reduce tangling7. Orientation

1. Critical orientation – obvious – see & fit2. Non-critical orientation – fit in any direction

8. Ensure access & visibility9. Easy part handling10. Assemble from top11. Reduce locating/alignment operations – manual/time

consuming

DFADFA GuidelinesGuidelinesDFADFA GuidelinesGuidelines

• One Time Costs– Tooling– Design/Development– Contacting / Vendor Selection– Product Testing

• Continuous Costs– Material– Assembly– Inventory– Inspection

Reduce number of different parts - Reduce number of different parts - Standardize partsStandardize partsReduce number of different parts - Reduce number of different parts - Standardize partsStandardize parts

• Easier = faster

• Less opportunity for mistakes

• Easier to automate

Simplification of AssemblySimplification of AssemblySimplification of AssemblySimplification of Assembly

• Less steps = faster

• Less material handling = less damage

• Less operations = less opportunity for defects

• Value Added processes in ~ remove Non-Valued Added steps

Reduction Number of ProcessesReduction Number of ProcessesReduction Number of ProcessesReduction Number of Processes

Less Fasteners Less Fasteners especially screws & boltsespecially screws & boltsLess Fasteners Less Fasteners especially screws & boltsespecially screws & bolts

Left to right: simplest, low cost to most parts hardest to assembly

BBoothroyd & DDewhurst IInc, 1999

• Takes time to separate

• Requires people• Hard to automate

Reduce Tangling / NestingReduce Tangling / NestingReduce Tangling / NestingReduce Tangling / Nesting

Hugh JackHugh Jack, 2001

• How does this fit it in with MECH 424?

• How does this fit into Engineering?

So What?So What?So What?So What?

1. Critical orientation – obvious – see & fit

2. Non-critical orientation – fit in any direction

OrientationOrientationOrientationOrientation

Ensure Access & VisibilityEnsure Access & VisibilityEnsure Access & VisibilityEnsure Access & Visibility

www.uniontire.ca/tireassfr.htm www.detnews.com/2004/project/0405/04/901-134795.htm

• Size

• Weight

• Shape

• Sharp edges

• Sticky

• Tangled & Nested

• etc.

Easy part handlingEasy part handlingEasy part handlingEasy part handling

Reduce locating/alignment operations – Reduce locating/alignment operations – manual/time consumingmanual/time consumingReduce locating/alignment operations – Reduce locating/alignment operations – manual/time consumingmanual/time consuming

http://www.hfmgv.org/rouge/tour.asp#

Assemble from Assemble from TopTopAssemble from Assemble from TopTop

Thank you for your attentionThank you for your attention