The Design Core

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The Design Core
Market Assessment
Specification
DETAIL DESIGN A vast subject. We will
concentrate on Materials Selection Process
Selection Cost Breakdown
Concept Design
Detail Design
Manufacture
Sell
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Systematic Process Selection
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Categories of Component Shape
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Process for a Vacuum Cleaner Fan
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.
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Process for a Vacuum Cleaner Fan
SLENDERNESS
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Process for a Vacuum Cleaner Fan
COMPLEXITY
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Process for a Vacuum Cleaner Fan
HARDNESS / MELTING POINT
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Process for a Vacuum Cleaner Fan
SURFACE ROUGHNESS
In the designers view, it is the surface finish
is the discriminating requirement. It (and the
geometry) determines the fans pumping efficiency
of and influences the noise it makes.
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Process for a Vacuum Cleaner Fan
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.
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Forming Ceramic Tap Valves
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?
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Forming Ceramic Tap Valves
SLENDERNESS
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Forming Ceramic Tap Valves
COMPLEXITY
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Forming Ceramic Tap Valves
HARDNESS / MELTING POINT
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Forming Ceramic Tap Valves
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Forming Ceramic Tap Valves
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.
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Process Selection Cost

• Three rules for minimizing cost
• 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.
• 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.
• 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.

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Materials Costs
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Process Selection Cost
Economic Criteria for Process Selection
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Cost Modelling
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.
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Cost Modelling

• So, 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 size.
• Time dependent (operators, space, power etc.)
  varies with the reciprocal of batch rate.

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Cost Modelling A Cast Connector Rod
The materials and process selection processes
have identified the sand casting and die casting
processes for a connector rod. Which process is
economical?
.
.
All costs are normalized to the material cost
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 lt 4000, sand casting is most
economical. For batch sizes gt 4000, die casting
is most economical.
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Process Selection Cost
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CASTINGS Sand (top), Investment (bottom)
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CNC MACHINING
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ASSEMBLY
electronic/mechanical
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Product Life Cycle
SALES
Maturity
Decline
Growth
Introduction to market
Development
TIME
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Cost Experience Curves
UNIT COST
No. CUMULATIVE UNITS PRODUCED
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Pricing
log
log TIME
Umbrella Pricing
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The Design Core
Market Assessment
Specification
Concept Design
MANUFACTURE
Detail Design
Manufacture
Sell
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The Design Core
Market Assessment
Specification
Concept Design
SELL
Detail Design
Manufacture
Sell