Sand casting and die casting were identified as potential processes for manufacturing a connector rod. Die casting has higher tooling and capital costs but can produce parts at a faster rate. For small batch sizes, the cost per part is dominated by fixed capital and tooling costs, making sand casting cheaper. However, as batch size increases, die casting becomes more economical due to its higher production rate reducing the impact of fixed costs per part. An analysis is needed to determine the optimal process based on the specific production volumes required.

1. The Design Core Market
Assessment
Specification
Concept
Design
Detail
Design
Manufacture
Sell
DETAIL
DESIGN
A vast subject.
We will concentrate on:
Materials Selection
Process Selection
Cost Breakdown

2. 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

3. Categories of Component
Shape SLENDERNESS
Ratio of section thickness to
the square root of section
area:
Similar to aspect ratio in 2-d
A
t
s =
COMPLEXITY
Relates 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






∆
=
L
L
nC 2log

4. 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.

5. 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
A
t
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 metals
cannot be chosen.
Define a search region that has
limits a factor of 2 on either side of the target
values.

6. Process for a Vacuum
Cleaner FanCOMPLEXITY
The micro-electronic fabrication methods
and sheet working processes for metals
are 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.

7. 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.

8. 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 and
T < 0.5 mm, define the search region
on the tolerance/roughness process
selection map.

9. 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.

10. 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?

11. Forming Ceramic Tap
ValvesSLENDERNESS
Process choice is often limited by
the capacity to make long, thin
sections (slenderness S of a
component), where
A
t
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.

12. 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.

13. 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.

14. Forming Ceramic Tap
Valves
The design constraints, R < ±0.1 µm and
T < 0.02 mm, define the search region
on 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.

15. 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.

16. 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.

17. Materials Costs
0.1
1
10
100
1020
steel
1040
steel
4140
steel
4340
steel
S304
stainless
steel
S316
stainless
steel
01
toolsteel
G
rey
castiron
2024
Alalloy
3003
or5005
Alalloy
6061
Alalloy
7075
Alalloy
70/30
brass
#110
C
u
alloy
Titanium
6-4
AZ63A
M
g
alloyABC
Polycarbonate
(PC
)
N
ylon
6/6
Polypropylene
(PP)
Polystyrene
(PS)
Alum
ina
ceram
ic
G
raphite
D
ouglas
Fir/Pine
O
ak
Fibreglass
G
raphite/epoxy
MATERIALSCOST($/kg)

18. Process Selection: Cost
Economic Criteria for Process Selection

19. 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
$/m2
h
$/yr
LoC
P
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.

20. Cost Modelling
[ ] [ ] 





+++++= se
c
c
Lotm CACP
Lt
C
C
n
C
n
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 C
n
C
n
mCC ,
11 

++=
Materials Dedicated cost/unit Gross overhead/unit
This reduces to:
o, Cost has 3 terms
Materials costs: independent of batch size and rate.
Dedicated capital investment (tooling, jigs, dies etc.): varies with the reciprocal of batch siz
Time dependent (operators, space, power etc.): varies with the reciprocal of batch rate.

21. 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
RelativeCostperComponent
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

22. Process Selection: Cost
107
106
105
104
103
103
102
102
10
101
1
ANNUAL PRODUCTION
UNITCOST
Injection
m
oulding
C
ontact m
oulding
Vacuum
form
ing
Blow
m
oulding

23. Fixed Costs Variable Costs Volume Total Unit Cost
Setup: Material:
570g of grey cast iron
$0.50 each
10
100
1000
$180.87
$18.87
$2.67
Tooling: $1.8k
8
impressions/pattern
no cores
Processing:
120 pcs/hr at $44/hr
Setup: Material:
2.6kg of grey cast iron
$2.30 each
10
100
1000
$243.77
$27.77
$6.17
Tooling: $2.4k
2
impressions/pattern
1 core
Processing:
30 pcs/hr at $44/hr
Setup: Material:
260g of yellow brass
$0.713 each
10
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 each
10
100
1000
$750.40
$120.40
$57.40
Tooling: $7k
3 cores
Processing:
1 pc/hr at $50/hrCASTINGS: Sand (top), Investment (bottom)

24. Fixed Costs Variable Costs Volume Total Unit Cost
Setup:
0.75hr at $60/hr
Material:
1.11kg of 6061 aluminium
$9 each
1
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 each
1
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 each
1
10
100
$646.00
$241.00
$200.50
Tooling:
Programming
2hr at $60/hr
Processing:
2.85hr/unit at $60/hr
Setup:
2hr at $60/hr
Material:
1.5kg of 6061 aluminium
$12 each
1
10
100
$612.00
$396.00
$374.40
Tooling:
Programming
2hr at $60/hr
Processing:
6hr/unit at $60/hr
CNC MACHINING

25. ASSEMBLY
Part Data Assembly Times
(s)
Assembly Cost
at $15/hr
No. Parts:
16
Slowest Part:
9.7
$0.52No. Unique Parts:
12
Fastest Part:
2.9
No. Fasteners:
0
Total:
125.7
No. Parts:
34
Slowest Part:
10.7
$0.78No. Unique Parts:
25
Fastest Part:
2.6
No. Fasteners:
5
Total:
186.5
No. Parts:
49
Slowest Part:
14.0
$1.11No. Unique Parts:
43
Fastest Part:
3.5
No. Fasteners:
5
Total:
266.0
No. Parts:*
56/17
Slowest Part:*
8.0/8.0
$1.73No. Unique Parts:*
44/12
Fastest Part:*
0.75/3.0
No. Fasteners:*
0
Total:*
277.0/138.0
*electronic/mechanical

26. Product Life Cycle
Development
Introductio
n to
market
Growth
Maturity
Decline
TIME
SALES

27. UNITCOST
No. CUMULATIVE UNITS PRODUCED
logUNITCOST
log No. UNITS PRODUCED
Cost Experience Curves

28. Pricinglog£
log TIME
Umbrella Pricing
log£
log TIME
Price pegged to manufacturing cost

29. The Design Core Market
Assessment
Specification
Concept
Design
Detail
Design
Manufacture
Sell
MANUFACTURE

30. The Design Core Market
Assessment
Specification
Concept
Design
Detail
Design
Manufacture
Sell
SELL