Design for Manufacturing and Assembly - cbinet.com for... · Design for Manufacturing and Assembly ... DFA Analysis Worksheet ... Functional Analysis / Redesign Opportunity

Design for Manufacturing

and Assembly

Case Study

Many well-known disasters can be traced back to design changes.

Although the root cause for the source of the fire has never been determined, there

are some lessons that still apply today.

Recap: After crossing the Atlantic, the Hindenburg attempted to land in Lakehurst,

New Jersey. During the landing procedure, a fire started on the aircraft. The

aircraft was destroyed in 30 seconds. Trivia: This flight was actually a partnership

with American Airlines.

Lesson 1: The Hindenburg design contained performance and safety improvements over the previous best-in-class airships from both Germany and the UK. Even “better” can fail catastrophically.

Lesson 2: Initial assumption was that the fire was hydrogen-burning, but the flames were yellow – indicating the side and internal containment bags were burning. The obvious root cause might not be correct.

Lesson 3: The designers originally specified Rolls-Royce gasoline engines, but the manufacturer refused to buy from a UK supplier. Instead, they installed Benz diesels with a lower power-to-weight ratio. As a result, the designers had to quickly lighten the airship. They chose to skip the flame-retardant coating on the skin. Last minute changes are risky.

Source: Pat Baird, Baxter Healthcare, 2015

Design for Assembly

Definition: DFA is a method of design of products for ease of assembly

DFA focuses on the optimization of the part/system assembly

DFA is a tool used to assist the design teams in the design of products

that will transition to production at a minimum cost, focusing on the

number of parts, handling and ease of assembly.

Concerned only with reducing product assembly cost

Minimizes number of assembly operations

Individual parts tend to be more complex in design

Copyright GCI, LLC 2015


Definition: DFM is a method of design for ease of manufacturing of

the collection of parts that will form the product after assembly.

DFM focuses on optimization of the manufacturing process.

DFM is a tool used to select the most cost effective material and

process to be used in production in the early stages of product design.

Concerned with reducing overall part production cost

Minimizes complexity of manufacturing operations

Uses common datum features and primary axes


Design for Manufacturing and Assembly


Source: Boothroyd and Dewhurst, 1989

Design for Manufacturing and Assembly


Sequence of Analysis for DFMA

1. Concept Design

2. Design for Assembly

Optimize Design for Part Count

Optimize Design for Assembly

3. Design for Manufacturing

Optimize Design for Production Readiness

4. Detailed Design


10 Steps of the Design for Assembly Process


1. Gather functional requirements

2. Perform a functional analysis

3. Identify parts that can be standardized

4. Determine part count efficiencies

5. Determine the practical part count

6. Identify poka-yoke opportunities

7. Identify handling opportunities

8. Identify insertion opportunities

9. Look for ways to reduce secondary operations

10.Analyze metrics against cost and risk

Example: The CLAW


1 of 10: Gather Functional Requirements

Understand how the product works

Review the preliminary specifications and DOE

DOE for design optimization

DOE for process optimization


2 of 10: Functional Analysis


There are 3 rules for functional analysis:

1. Assume the first part (the base) is always an essential part

2. Assume fasteners, spacers, washers, o-rings, connectors and

leads are always non-essential parts

3. Liquids such as glue, sealant, lube do not count as parts

Functional Analysis


Begin by identifying each

part of The CLAW:

1. List the parts in the order of

assembly

2. Assign a part number to each

part

DFA Analysis Worksheet (courtesy of Cummins Tools)

Part

Nu

mb

er

Part Name

1 Lower Jaw Subassembly

1.1 Lower Jaw

1.2 Lower Cover

1.3 Rivet

2 Upper Jaw Subassembly

2.1 Upper Jaw

2.2 Upper Cover

2.3 Rivet

3 Spring

4 Pivot

Part

Functional Analysis


The best way to

identify all the parts

is to take the device

apart…

Rivet

Rivet

Pivot

Upper jaw

Spring

Lower jaw

Rivet

Rivet

Upper

Cover

Lower

Cover

Functional Analysis


Next, count the number of each

kind of part

- this value is known as Np

Then, count the number of

Interfaces between each part

- this value is known as Ni


Assembly Name: ____________________________

Pa

rt N

um

be

r

Part Name Nu

mb

er

of

Pa

rts

(Np

)

Nu

mb

er

of

Inte

rfa

ces

(Ni)

(pa

rt a

to

pa

rt b

= 1

)


1.1 Lower Jaw 1 6

1.2 Lower Cover 1 3

1.3 Rivet 2 4


2.1 Upper Jaw 1 6

2.2 Upper Cover 1 3

2.3 Rivet 2 4

3 Spring 1 3

4 Pivot 1 3

Totals 10 32

Part DFA Complexity

Functional Analysis


Now we’ll determine if each part is essential or non-essential, so we

can determine the theoretical minimum number of parts.



Assembly Name: ____________________________Team Name: _______________________________

Part

Num

ber

Part Name Num

ber

of P

arts

(Np)

Num

ber

of In

terf

aces

(Ni)

(par

t a to

par

t b =

1)

Theo

retic

al M

inim

um P

art

(Fun

ctio

nal A

naly

sis

Char

t)

Part

Can

be

Stan

dard

ized

(if n

ot a

lrea

dy s

tand

ard)

Cost

(Low

/Med

ium

/Hig

h)

Prac

tical

Min

imum

Par

t


1.1 Lower Jaw 1 6 Y N L Y

1.2 Lower Cover 1 3 N N L N

1.3 Rivet 2 4 N N L N


2.1 Upper Jaw 1 6 N N L Y

2.2 Upper Cover 1 3 N N L N


3 Spring 1 3 N N L Y

4 Pivot 1 3 N N L Y

Totals 10 32 1 0 0 4

Part DFA Complexity

Functional Analysis /

Redesign Opportunity

3 of 10: Can Parts be Standardized?

• Consider if each part can be

standardized

• within the assembly station

• Within the full assembly

• Within the assembly plant

• Within the corporation

• Within the industry

• Consider if each part should be

standardized

• If you answer yes to both questions,

place “Y” in the spreadsheet cell;

otherwise, place “N” Copyright GCI, LLC 2015

4 of 10: Part Count Efficiency


In step 4, we’ll determine part count efficiencies, beginning with the

theoretical part count efficiency.

Theoretical Part Theoretical Min. No. Parts

Count Efficiency = Total Number of Parts x 100

• In our example:

Theoretical Part 1

Count Efficiency = 10 x 100 = 10%

• Rule of thumb: part count efficiency goal is >60%

Continuing with Step 4, we’ll calculate the DFA Complexity Factor

Cummins metric for assessing complexity of a product design

Two Factors

Np – Number of Parts

Ni – Number of part-to-part interfaces

Smaller is better (goal is 0.0)


= 17.9

Part Cost


This is a subjective estimate

Part costs are categorized as low,

medium or high relative to other

parts in the assembly or in the

factory.

As we prepare for the next Step in the sequence, we must consider the part

cost.

5 of 10: Practical Minimum Part Count


Step 5 is to determine the practical minimum part count

This is also subjective, and requires a team assessment of practical changes and

consideration of the trade offs between part cost and assembly cost.

Consider the “Part Cost” from the previous slide.

This step answers the question, “What are we prepared to do with the design

realistically and practically?”

From our example, there are 4 practical minimum parts:

spring, pivot, upper jaw, lower jaw

Practical Part Count Efficiency

Now we have enough information to calculate the Practical Part Count Efficiency:

Practical Part Practical Min. No. Parts

Count Efficiency = Total Number of Parts x 100

• In our example:

Practical Part 4

Count Efficiency = 10 x 100 = 40%

• Rule of thumb: part count efficiency goal is >60%


Re-designed CLAW


This simple design is the result of the

theoretical part count of 1, the

consideration of cost, and the practical

minimum part count.

Don’t constrain your design to

incremental improvement unless you

have to!




Part

Nu

mb

er

Part Name Nu

mb

er o

f Pa

rts

(Np

)

Nu

mb

er o

f In

terf

aces

(N

i)

(par

t a

to p

art

b =

1)

Theo

reti

cal M

inim

um

Par

t

(Fu

nct

ion

al A

nal

ysis

Ch

art)

Part

Can

be

Stan

dar

diz

ed

(if

no

t al

read

y st

and

ard

)

Co

st (

Low

/Med

ium

/Hig

h)

Prac

tica

l Min

imu

m P

art


1.1 Lower Jaw 1 6 Y N L Y

1.2 Lower Cover 1 3 N N L N



2.1 Upper Jaw 1 6 N N L Y

2.2 Upper Cover 1 3 N N L N


3 Spring 1 3 N N L Y

4 Pivot 1 3 N N L Y

Totals 10 32 1 0 0 4

DFA Metrics 10% 40%

Goals 60% 60%0.0 -

17.9 -

Part DFA Complexity


Redesign Opportunity

General Design and Cost Considerations


Select the least expensive fastening method that allows you to meet the

specification



Where appropriate, choose self-fastening features



Symmetrical parts are easier to assemble because they don’t require

reorientation

Asymmetric Symmetric



Top-Down Assembly is preferred



Modular Assemblies are preferred

Image courtesy hitechcontrols.com



Received

Inspected

Rejected

Stocked

Outdated

Returned to Vendor

Unreliable

Recycled

Late from Supplier

Involved in a Customer Complaint

Eliminate parts that aren’t required. Eliminated parts are NEVER…

Designed

Detailed

Prototyped

Produced

Scrapped

Tested

Re-engineered

Purchased

Progressed

Audited by FDA

Examples


7 of 10: Handling (Grasp and

Orientation)


Handling time is based on: • Assembly process

• Complexity of parts

Consider: • How many hands are required?

• Is any grasping assistance needed?

• What is the effect of part symmetry on assembly?

• Is the part easy to align/position?

Handling Difficulty


Is a function of…

Part size

Part thickness

Part weight

Part fragility

Part flexibility

Part slipperiness

Part stickiness

How many hands it takes

Is optical magnification required

Is mechanical assistance required

Picture How Difficult It Is to Handle

These Parts…


Another Handling Challenge Is

Tangling or Nesting


8 of 10: Insertion (Locate and Secure)


Insertion time is based on the difficulty required

for each component’s insertion

Consider: • Is the part secured immediately upon insertion?

• Is it necessary to hold down the part to maintain

its location?

• What type of fastening process is used

(mechanical, thermal, other)?

• Is the part easy to align?

Design Self-aligning and Self-locating Parts


…and ensure the parts do not need to be held in

position in order to secure them in place

Other Insertion Challenges…


• Provide adequate access and visibility

• Avoid small clearances

• Avoid large insertion forces

• Avoid mating locations that cannot be seen easily

9 of 10: Secondary Operations

Eliminate Secondary Operations as much as possible

Instead of this….. Do this


Soldering

Gluing

Welding

Measuring

Reorienting

Screwing

Crimping

Drilling

Painting

Testing

Adjusting




Pa

rt

Nu

mb

er

Part Name Nu

mb

er o

f P

arts

(N

p)

Nu

mb

er o

f In

terfa

ce

s (

Ni)

(pa

rt

a t

o p

art

b =

1)

Th

eo

re

tica

l M

inim

um

Pa

rt

(F

un

cti

on

al

An

aly

sis

Ch

art)

Pa

rt

Ca

n b

e S

tan

da

rd

ize

d

(if

no

t a

lre

ad

y s

tan

da

rd

)

Co

st

(Lo

w/M

ed

ium

/H

igh

)

Pra

cti

ca

l M

inim

um

Pa

rt

Asse

mb

le w

ro

ng

pa

rt

/

Om

it p

art

Asse

mb

le w

ro

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wa

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ro

un

d

Ta

ng

le/N

est/

Sti

ck

to

ge

the

r

Fle

xib

le/F

ra

gil

e/

Sh

arp

/S

lip

pe

ry

Pli

ers/T

we

eze

rs/

Ma

gn

ify

ing

gla

ss

Dif

ficu

lt t

o a

lig

n/Lo

ca

te

Ho

ldin

g d

ow

n r

eq

uir

ed

Re

sis

tan

ce

to

in

se

rti

on

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str

ucte

d a

cce

ss/v

isib

ilit

y

Re

-orie

nte

d w

ork

pie

ce

Scre

w/D

ril

l/T

wis

t/R

ive

t/

Be

nd

/C

rim

p

We

ld/S

old

er/G

lue

Pa

int/

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be

/H

ea

t/

Ap

ply

liq

uid

or g

as

Te

st/

Me

asu

re

/A

dju

st


1.1 Lower Jaw 1 6 Y N L Y Y N N Y N N N N N N Y N N N

1.2 Lower Cover 1 3 N N L N N N N N N N Y N N N Y N N N

1.3 Rivet 2 4 N N L N N N N Y N N Y N N N N N N N


2.1 Upper Jaw 1 6 N N L Y Y N N Y N N N N N N Y N N N

2.2 Upper Cover 1 3 N N L N Y N N N N N Y N N N Y N N N

2.3 Rivet 2 4 N N L N N N N Y N N Y N N N N N N N

3 Spring 1 3 N N L Y N N Y Y N N Y Y N N Y N N N

4 Pivot 1 3 N N L Y N N N Y N N Y N N N N N N N

Totals 10 32 1 2 0 4 3 0 1 6 0 0 6 1 0 0 5 0 0 0

DFA Metrics 10% 40%

Goals 60% 60%

5.0

0.0 - 0.0 0.0 0.0 0.0

17.9 - 3.0 7.0 7.0

Secondary OperationsPart DFA Complexity


Redesign Opportunity Poka-yoke Handling Insertion

Now Let’s Focus on



6 questions to ask when selecting the manufacturing method:

Q1: Is hard tooling required?

Q2: Have we selected the best technology or process to fabricate parts?

Q3: Have we selected the best material needed for function and cost?

Q4: Have we looked at all the new technology that is available?

Q5: Are the parts shaped for the implementation of automation?

Q6: Is the supplier capable of meeting the specifications?

Image courtesy dmtcnc.com

Selection of Manufacturing Method

Material

Function

Cost

Fabrication Process

Hard Tooling

New Technology

Configure product with access for automation

Simplify and reduce the number of manufacturing operations


…and Finally


Understand which part features are critical to the product’s functional quality

(not every drawing call out is critical to function and quality)

Contact

Information

Roberta Goode

[email protected]

www.GoodeCompliance.com

(954) 399-7510


DFMA References


7. Introduction to Design for (Cost Effective) Assembly and

Manufacturing David Steinstra, Rose-Hulman, 2015

Documents

Design for Manufacturing and Assembly - cbinet.com for... · Design for Manufacturing and Assembly ... DFA Analysis Worksheet ... Functional Analysis / Redesign Opportunity