the design core market assessment specification concept design detail design manufacture sell detail...
Post on 20-Dec-2015
214 views
TRANSCRIPT
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.
Process for a Vacuum Cleaner Fan
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 for a Vacuum Cleaner Fan
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.
Meets all the design constraints.
Meets all the design constraints.
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.
Forming Ceramic Tap Valves
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.
Forming Ceramic Tap Valves
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
)
Process Selection: Cost
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
Process Selection: 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
Material:1.96kg of 6061 aluminium
$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
Material:1.5kg of 6061 aluminium
$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
$0.78No. Unique Parts:
25Fastest Part:
2.6
No. Fasteners:5
Total:186.5
No. Parts:49
Slowest Part:14.0
$1.11No. Unique Parts:
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
The Design Core Market Assessment
Specification
Concept Design
Detail Design
Manufacture
Sell
MANUFACTURE
The Design Core Market Assessment
Specification
Concept Design
Detail Design
Manufacture
Sell
SELL