The Design Core Market Assessment Specification Concept Design Detail Design Manufacture Sell DETAIL...

The Design Core Market Assessment

Specification

Concept Design

Detail Design

Manufacture

Sell

DETAILDESIGN

A vast subject. We will concentrate on:

Materials Selection

Process Selection

Cost Breakdown

Systematic Process Selection

Subset of Processes

Supporting Information: handbooks, suppliers data sheets, databases, WWW(Search “family history” of candidates)

All Processes

Screening: apply attribute limits (eliminate processes that cannot do the job)

Ranking: order by relative cost (find processes that can do the job economically)

Prime Candidates

Local Conditions(does the choice match local needs, expertise etc.?)

Final Process Choice

Categories of Component ShapeSLENDERNESS

Ratio of section thickness to the square root of section area:

Similar to aspect ratio in 2-dAt

s

COMPLEXITYRelates to the number of specified dimensions of the component and the precision required:

But life is more complicated, e.g. spheres have low complexity, but are difficult to make compared with cylinders of higher complexity. We should also consider other attributes such as symmetry.

L

LnC 2log

Process for a Vacuum Cleaner Fan

Constraint Value

Materials -Nylon

-Al alloys

Complexity

Minimum section

Surface area

Volume

Weight

Mean precision

Roughness

Process

Tm = 550 - 573 K, H = 150 - 270 MPa

ρ = 1080 kg/m3

Tm = 860 - 933 K, H = 150 - 1500 MPa

ρ = 2700 kg/m3

2 - 3

1.5 - 6 mm

0.01 - 0.04 m2

1.5x10-5 - 2.4x10-4 m3

0.03 - 0.5 kg

0.5 mm

<1 µm

Net shape preferred

Fans for vacuum cleaners are designed to be cheap, quiet and efficient. Nylon and Al alloys have been identified as candidate materials.

Net shape processing is preferred for low cost.

Complexity is classified as 3-D solid.

Process for a Vacuum Cleaner FanSLENDERNESS

Process choice is often limited by the capacity to make long, thin sections (slenderness S of a component), where

At

S

The fan can be shaped in a large number of ways including die-casting for Al alloys and injection moulding for polymers.

The hot working processes for metalscannot be chosen.

Define a search region that has limits a factor of 2 on either side of the target values.

Process for a Vacuum Cleaner FanCOMPLEXITY

The micro-electronic fabrication methods and sheet working processes for metalsare eliminated.

The search region falls in a regime in which many alternative processes are possible.

Hence, in this case, we learn nothing new.

Define a search region that has limits on either side of the target values.

Process for a Vacuum Cleaner FanHARDNESS / MELTING POINT

In this case almost all processes for polymers and metals are viable.

Only electron beam casting is eliminated.

Hence, in this case, we again learn nothing new.

Define search regions that have limits on either side of the target values.


A significant number of processes are eliminated.A number of polymer moulding processes, including injection moulding are acceptable.Machining from solid meets the specifications, but is not net-shape.Many casting processes are eliminated, but pressure die-casting, squeeze casting and investment casting are acceptable.

SURFACE ROUGHNESS

In the designer’s view, it is the surface finish is the discriminating requirement. It (and the geometry) determines the fan’s pumping efficiency of and influences the noise it makes.

The design constraints, R < 1 µm andT < 0.5 mm, define the search regionon the tolerance/roughness process selection map.


Process Comment

Nylon and Al-alloys

Machine from solid

Electro-form

Al-alloy only

Cold deformation

Investment casting

Pressure die casting

Squeeze casting

Nylon only

Injection moulding

Resin transfer moulding

Expensive, not a net-shape process.

Slow, and thus expensive.

Cold forging meets the design constraints.

Accurate, but slow.

Meets all the design constraints.




N.B. The charts can only narrow the choice. There are other considerations of course: capital investment, batch size and rate, supply, local skills etc.

A cost analysis is now required to establish the best choice.

Forming Ceramic Tap Valves

Constraint Value

Material -Zirconia

Complexity

Minimum section

Surface area

Volume

Weight

Mean precision

Roughness

Tm = 2820 K, H = 15000 MPa

ρ = 3000 kg/m3

1 - 2

5 mm

10-3 m2

1.5x10-6 m3

4.5x10-3 kg

0.02 mm

<0.11 µm

Vitreous alumina is commonly used in hot eater valves, but it may not be the best due to thermal shock. The materials selection procedure offered Zirconia as a possible alternative. How should the valve discs be shaped?

Forming Ceramic Tap ValvesSLENDERNESS

Process choice is often limited by the capacity to make long, thin sections (slenderness S of a component), where

At

S

The ceramic discs are not particularly slender. Some metal forming and polymer moulding processes are eliminated, but we would not expect to use those processes for ceramics in any case.

Hence, we do not learn much.

Define a search region that has limits a factor of 2 on either side of the target values.

Forming Ceramic Tap ValvesCOMPLEXITY

The micro-electronic fabrication methods and ceramic moulding processes are eliminated.

Powder routes, machining and molecular methods are viable alternatives based on complexity.

Define a search region that has limits on either side of the target values.

Forming Ceramic Tap ValvesHARDNESS / MELTING POINT

High melting point and hardness are restrictive.

Machining is now eliminated.

Electron beam casting, electroforming, and CVD and evaporation methods are possibilities.

Powder routes emerge as the practical alternative, but can these methods adhere to the tolerance and surface finish required?

Define search regions that have limits on either side of the target values.


The design constraints, R < 0.1 µm andT < 0.02 mm, define the search regionon the tolerance/roughness process selection map.

Powder routes are now eliminated as they cannot give the required tolerance and surface finish.Mechanical polishing is possible.

SURFACE ROUGHNESS

The surface of the discs must be flat and smooth to ensure a good seal between the mating faces.


Process Comment

Powder methods

CVD and evaporation methods

Electron beam casting

Electro-forming

Machining

Capable of shaping the disc, but not desired precision.

No CVD route available. Other gas-phase methods possible for thin sections.

Difficult with a non-conductor.

Not practical for an oxide.

Material too hard, but polishing is possible.

No single process is ideal for producing the ceramic valve discs from zirconia.A combination of processes emerges. Powder methods can be used to form the discs. The mating faces could then be polished to the desired tolerance and surface finish.

Process Selection: Cost

Three rules for minimizing cost

1. Keep things standard: It is cheaper to buy a standard part than make it in house. If nobody makes the part you want, then design it to be made from standard stock materials, and use as few of them as possible.

2. Keep things simple: If a part requires machining then it will need to be clamped. Keep it simple so that the number of times it has to be re-jigged is minimized. If a part requires casting the minimize re-entrant angles which require complicated and expensive dies.

3. Do not over-specify performance: Higher performance increases cost. Higher strength alloys are more heavily alloyed with expensive elements. Higher strength materials require more energy to form. Increased tolerance leads to higher machining or finishing costs.

Materials Costs

0.1

1

10

100

1020

ste

el

1040

ste

el

4140

ste

el

4340

ste

el

S304

stain

less

steel

S316

stain

less

steel

01 to

ol ste

el

Gre

y ca

st iro

n

2024

Al a

lloy

3003

or 5

005 A

l allo

y

6061

Al a

lloy

7075

Al a

lloy

70/3

0 br

ass

#110

Cu a

lloy

Titani

um 6

-4

AZ63A M

g al

loy

ABC

Polyc

arbo

nate

(PC)

Nylon

6/6

Polyp

ropy

lene

(PP)

Polys

tyrene

(PS)

Alum

ina

cera

mic

Gra

phite

Douglas

Fir/

PineOak

Fibre

glas

s

Gra

phite

/epo

xy

MA

TE

RIA

LS

CO

ST

($

/kg

)


Economic Criteria for Process Selection

Cost Modelling

Resource Symbol Unit

Materials:

Capital:

Time:

Energy:

Space:

Information:

inc. consumables

cost of equipment

cost of tooling

basic overhead rate

power

cost of energy

area

cost of space

R&D, royalty payments

Cm

Cc

Ct

Ce

A

Ci

$/kg

$

$

$/hr

kW

$/kWh

m2

$/m2h

$/yr

LoCP

sC

The producing a component consumes resources (see below).

All processes consume these resources to some extent and thus a resource based approach is useful at the broad level we are dealing with.

Cost Modelling

se

c

cLotm CACP

LtC

Cn

Cn

mCC 11

Cost:

where m is the mass of material used, n is the batch size (no. units), is the batch rate (no. units per hour), tc is the capital write-off time, and L is the capital load factor (the fraction of time over which the equipment is used productively)

n

Materials Tooling Time Capital Energy Space

grossLtm Cn

Cn

mCC ,

11

Materials Dedicated cost/unit Gross overhead/unit

This reduces to:

So, Cost has 3 terms1. Materials costs: independent of batch size and rate.2. Dedicated capital investment (tooling, jigs, dies etc.): varies with the reciprocal of batch size.3. Time dependent (operators, space, power etc.): varies with the reciprocal of batch rate.

Cost Modelling: A Cast Connector Rod

Cost parameter Sand Casting

Die Casting

Material, mCm

Basic overhead, CLo(h-1)

Capital write-off time, tc (yrs)

Dedicated tool cost, Ct

Capital cost, Cc

Batch rate, n (h-1)

1

20

5

210

10000

5

1

20

5

16 000

300 000

200

0.1

1

10

100

1000

10000

1 10 100 1000 10000 100000 1E+06

Number of Components

Rel

ativ

e C

ost

per

Co

mp

on

ent

Die Casting

Sand Casting

Material Cost

Labour (sand)Labour(die)

.

.

The materials and process selection processes have identified the sand casting and die casting processes for a connector rod. Which process is economical?

The cost of both processes is dominated by capital and tooling costs for small batch sizes; and dominated by materials and labour costs for large batch sizes.

For very large batch sizes the cost of die casting is dominated by material costs. For batch sizes < 4000, sand casting is most economical.

For batch sizes > 4000, die casting is most economical.

All costs are normalized to the material cost


107106105104103

103

102

102

10

1011

ANNUAL PRODUCTION

UN

IT C

OS

T

Injection moulding

Contact moulding

Vacuum form

ing

Blow moulding

Fixed Costs Variable Costs Volume Total Unit Cost

Setup: Material:570g of grey cast iron

$0.50 each10

100

1000

$180.87

$18.87

$2.67

Tooling: $1.8k8

impressions/patternno cores

Processing:

120 pcs/hr at $44/hr

Setup: Material:2.6kg of grey cast iron

$2.30 each10

100

1000

$243.77

$27.77

$6.17

Tooling: $2.4k2

impressions/pattern1 core

Processing:

30 pcs/hr at $44/hr

Setup: Material:260g of yellow brass

$0.713 each10

100

1000

$163.21

$28.21

$14.71

Tooling: $1.5k

no cores

Processing:

4 pcs/hr at $50/hr

Setup: Material:180g of 712 aluminium

$0.395 each10

100

1000

$750.40

$120.40

$57.40

Tooling: $7k

3 cores

Processing:

1 pc/hr at $50/hrCASTINGS: Sand (top), Investment (bottom)

Fixed Costs Variable Costs Volume Total Unit Cost

Setup:

0.75hr at $60/hr

Material:1.11kg of 6061 aluminium

$9 each1

10

100

$75.00

$21.00

$15.50

Tooling:Programming

0.25hr at $60/hr

Processing:

6min/unit at $60/hr

Setup:

1.75hr at $60/hr


$16 each1

10

100

$386.00

$102.50

$74.15

Tooling:Prog’g 1hr at $60/hr

Fixtures: $150

Processing:

55min/unit at £60/hr

Setup:

5.5hr at $60/hr

Material:4.6kg ultra-high Mw PE

$25 each1

10

100

$646.00

$241.00

$200.50

Tooling:Programming2hr at $60/hr

Processing:

2.85hr/unit at $60/hr

Setup:

2hr at $60/hr


$12 each1

10

100

$612.00

$396.00

$374.40

Tooling:Programming2hr at $60/hr

Processing:

6hr/unit at $60/hr

CNC MACHINING

ASSEMBLY

Part Data Assembly Times(s)

Assembly Costat $15/hr

No. Parts:16

Slowest Part:9.7

$0.52No. Unique Parts:

12Fastest Part:

2.9

No. Fasteners:0

Total:125.7

No. Parts:34

Slowest Part:10.7


25Fastest Part:

2.6

No. Fasteners:5

Total:186.5

No. Parts:49

Slowest Part:14.0


43Fastest Part:

3.5

No. Fasteners:5

Total:266.0

No. Parts:*56/17

Slowest Part:*8.0/8.0

$1.73No. Unique Parts:*

44/12Fastest Part:*

0.75/3.0

No. Fasteners:*0

Total:*277.0/138.0

*electronic/mechanical

Product Life Cycle

Development

Introduction to market

Growth

Maturity

Decline

TIME

SALES

UN

IT C

OS

T

No. CUMULATIVE UNITS PRODUCEDlo

g U

NIT

CO

ST

log No. UNITS PRODUCED

Cost Experience Curves

Pricinglo

g £

log TIME

Umbrella Pricing

log

£log TIME

Price pegged to manufacturing cost


Specification

Concept Design

Detail Design

Manufacture

Sell

MANUFACTURE


Specification

Concept Design

Detail Design

Manufacture

Sell

SELL

The Design Core Market Assessment Specification Concept Design Detail Design Manufacture Sell DETAIL...

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