Concept Selection

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Concept Selection

• Product Design and DevelopmentChapter 7
• Karl T. Ulrich and Steven D. Eppinger

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Concept Development Process
Mission Statement
Development Plan
Identify Customer Needs
Establish Target Specifications
Generate Product Concepts
Select Product Concept(s)
Set Final Specifications
Plan Downstream Development
Test Product Concept(s)
Perform Economic Analysis
Benchmark Competitive Products
Build and Test Models and Prototypes
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Concept Development Funnel
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Concept Selection Process

• Prepare the Matrix
• Criteria
• Weightings
• Rate Concepts
• Scale ( 0) or (15)
• Compare to Reference Concept or Values
• Rank Concepts
• Sum Weighted Scores
• Combine and Improve
• Remove Bad Features
• Combine Good Qualities
• Select Best Concept
• May Be More than One
• Beware of Average Concepts
• Reflect on the Process
• Continuous Improvement

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Your text differentiates between concept
screening and concept scoring!

• Concept screening is used to narrow the number of
  concepts quickly and to improve concepts.
• Your text uses Pugh Concept Selection. We will
  use a modified technique used by IDEO.
• This technique is used when you dont have a lot
  of information about your design and you must
  make decisions.
• Concept scoring is used when increased resolution
  will better differentiate between concepts.
• Your text uses an unusual technique. We will use
  the technique introduced in freshmen design
  (except that you will use it better.)
• Concept scoring should be used when you have more
  information about your design.

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Example Concept Screening
Prepare the Matrix

• Concept screening works best with 20 or fewer
  criteria.
• Criteria should be based upon the PDS pay
  attention to customer needs.
• You may have to pick the most important criteria
  to obtain the desired limit.

• Criteria

Lightweight
Stable
Pinch Points
Maintenance
Range of Motion (legs)
Comfort
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Form the Matrix

• List the concepts
• Problem Definition
• 4 year old, handicapped child cannot support her
  body weight while learning to creep
• Options
• 1 - Catalog Device Modification
• 2 - Crane Suspension Device
• 3 - Cart Device

1 2 3
Lightweight
Stable
Pinch Points
Maintenance
Range of Motion (legs)
Comfort
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Clarify the concepts

• Catalog Device Modification A height adjustable
  crawler that provides upper body support, but
  doesnt keep legs from kicking out
• Crane Suspension Device Provides support of
  childs body using a spring suspended from a
  height adjustable support arm
• Cart Device Provides a seat that supports
  childs upper body. Also has a plate with bungee
  cords that limits forward and backward motion of
  the legs.

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• Run the Matrix
• Compare each option within each row.
• Indicate 1, -1, or 0
• This is a modification to the Pugh Concept
  Selection and allows the decision makers to
  automatically see the best available in each
• A description for the rationale behind each
  ranking should be included.

  Catalog Crane Cart
Lightweight 1 -1 1
Stable 0 -1 1
Pinch Points 1 -1 0
Maintenance 0 1 -1
Range of Motion (legs) 0 -1 1
Comfort -1 0 1
Totals 1 -3 3
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Attack negatives and enhance positives

• Can you combine portions of one design with
  another?
• Remember our functional analysis - is there a way
  to change one function and make the design better?

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3. Consider a material selection problem for a
refrigerated food preparation surface material
for use in an ice cream store. The surface will
be subsequently coated, but hand mixing of
ingredients on the surface is needed. Five
materials have been identified as possibilities
1020 Steel, 304 Stainless Steel, 5052 Aluminum,
Copper and Bronze. Use the modified concept
screening process discussed in class. To help you
in this process a table listing the material
properties for each criterion is given below.
Criteria Units Desired Direction 1020 Steel 304 SS 5052 AL Cu Bronze
Thickness (in.) less is better 0.107 0.107 0.407 0.205 0.205
Conductivity Btu-ft/(hroF-ft2) higher is better 27 9.4 80 200 109
Diffusivity ft2/hr higher is better 909 270 3749 6751 3809
Hardness Brinnell higher is better 111 95 47 2 1
Yield kips higher is better 30 110 13 40 37
Machinability 0-100 less is better 65 90 30 20 20
Thermal Mass Btu/oF lower is better 2.93 3.43 7.33 5.45 5.26
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Criteria Desired Direction 1020 Steel 304 SS 5052 Al Cu Bronze
Thickness less is better
Conductivity higher is better
Diffusivity higher is better
Hardness higher is better
Yield higher is better
Machinability less is better
Thermal Mass lower is better
Total
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Criteria Desired Direction 1020 Steel 304 SS 5052 Al Cu Bronze
Thickness less is better 1 1 -1 0 0
Conductivity higher is better -1 -1 0 1 0
Diffusivity higher is better -1 -1 0 1 0
Hardness higher is better 1 1 0 -1 -1
Yield higher is better 0 1 -1 0 0
Machinability less is better 0 -1 1 1 1
Thermal Mass lower is better 1 1 -1 0 0
Total 1 1 -2 1 0
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Weighted Decision Matrix

• Introduced in Freshman Design.
• Specify design criterion
• Enumerate alternatives
• Establish weightings
• Determine performance of each alternative for
  each criteria
• Score that performance as indicated by the data
  that you have.

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Available Data Controls Evaluation

• Some numeric and some quantitative use interval
  scales
• All numeric use ratio scales

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Lets return to our matrix for material
selection. We have actual numeric data for each
item. Lets see what we would decide if we use
ratio scales.
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Complete the Matrix Using Ratio Scales
Criteria Desired Direction 1020 Steel 304 SS 5052 Al Cu Bronze
Thickness less is better
Conductivity higher is better
Diffusivity higher is better
Hardness higher is better
Yield higher is better
Machinability less is better
Thermal Mass lower is better
Total
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Answers to the redo of material selection
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Evaluation Scheme for Interval Scales
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Example of Weighted Decision Matrix Using
Interval Scales Taken from Engineering Design by
Dieter and Schmidt

• A heavy steel crane hook, for use in supporting
  ladles filled with molten steel as they are
  transported through the steel mill, is being
  designed. Two crane hooks are needed for each
  ladle. These large, heavy components are usually
  made to order in the steel mill machine shop when
  one is damaged and needs to be replaced.
• Three concepts have been proposed
• Built up from flame-cut steel plates, welded
  together
• Built up from flame-cut steel plates, riveted
  together
• A monolithic cast-steel hook
• The first step is to identify the design criteria
  by which the concepts will be evaluated. The PDS
  is used and the design criteria are identified as
  material cost, manufacturing cost, time to
  produce a replacement hook if one fails,
  durability, reliability, and repairability.

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Determine Weighting Factor for Each Design
Criteria
Crane Hook 1.0
Cost 0.6
Quality in Service 0.4
Material Cost 0.3
Repairability 0.2
Durability 0.6
Time to produce 0.1
Manufacturing Cost 0.5
Reliability 0.3
Weight for Material Cost 0.3 0.6 0.18
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Results for Weighted Decision Matrix using
Interval Scales
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Remember

• The goal of concept selection is not to
• Select the best concept.
• The goal of concept selection is to
• Develop the best concept.
• So remember to combine and refine the concepts to
  develop better ones!

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Caveats

• Beware of the best "average" product.
• Perform concept selection for each different
  customer group and compare results.
• Check sensitivity of selection to the
  importance weightings and ratings.
• May want to use all of detailed requirements in
  final stages of selection.
• Note features which can be applied to other
  concepts.

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Individual Quiz Name____________________________
CM________________ Use the concept
screening method presented in class today to
evaluate which sport-utility vehicle designs
should be pursued. The ratings are given so that
you know the relative merits of each vehicle.
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