Transcript Concept Selection Product Design and Development Chapter 7 Karl T. Ulrich and Steven D.

Concept Selection
Product Design and Development
Chapter 7
Karl T. Ulrich and Steven D. Eppinger
Concept Development Process
Mission
Statement
Identify
Customer
Needs
Establish
Target
Specifications
Generate
Product
Concepts
Select
Product
Concept(s)
Test
Product
Concept(s)
Perform Economic Analysis
Benchmark Competitive Products
Build and Test Models and Prototypes
Set
Final
Specifications
Plan
Downstream
Development
Development
Plan
Concept Development Funnel
concept gener ation
concept screeni ng
concept scor ing
concept testi ng
Concept Selection Process
• Prepare the Matrix
– Criteria
– Weightings
• Rate Concepts
– Scale (+ – 0) or (1–5)
– 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
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 don’t 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.
Example: Concept Screening
Prepare the Matrix
• Concept screening works
• Criteria
best with 20 or fewer criteria.
• Criteria should be based
Lightweight
upon the PDS – pay
Stable
attention to customer needs.
Pinch Points
• You may have to pick the
Maintenance
most important criteria to
Range of Motion (legs)
obtain the desired limit.
Comfort
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
Lightweight
Stable
Pinch Points
Maintenance
Range of Motion (legs)
Comfort
2
3
Clarify the concepts
• Catalog Device Modification: A height adjustable crawler
that provides upper body support, but doesn’t keep legs
from “kicking out”
• Crane Suspension Device: Provides support of child’s
body using a spring suspended from a height adjustable
support arm
• Cart Device: Provides a seat that supports child’s upper
body. Also has a plate with bungee cords that limits
forward and backward motion of the legs.
•
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.
Lightweight
Stable
Pinch Points
Maintenance
Range of
Motion (legs)
Comfort
Totals
Catalog Crane Cart
1
-1
1
0
-1
1
1
-1
0
0
1
-1
0
-1
1
-1
0
-3
1
1
3
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?
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/(hroFft2)
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
Criteria
Desired
Direction
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
1020
Steel
304
SS
5052
Al
Cu
Bronze
Criteria
Desired
Direction
Thickness
less is
better
Conductivity
304
SS
5052
Al
Cu
1
1
-1
0
0
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
1
1
-2
1
0
Total
1020
Steel
Bronze
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.
Available Data Controls Evaluation
• Some numeric and some quantitative –
use interval scales
• All numeric = use ratio scales
Let’s return to our matrix for material selection. We
have actual numeric data for each item. Let’s see
what we would decide if we use ratio scales.
Complete the Matrix Using Ratio Scales
Criteria
Desired
Direction
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
1020
Steel
304
SS
5052
Al
Cu
Bronze
Answers to the redo of material selection
Evaluation Scheme for Interval Scales
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:
1. Built up from flame-cut steel plates, welded together
2. Built up from flame-cut steel plates, riveted together
3. 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.
Determine Weighting Factor for Each Design Criteria
Crane Hook = 1.0
Cost = 0.6
Material
Cost = 0.3
Quality in Service = 0.4
Repairability
= 0.2
Manufacturing
Cost = 0.5
Weight for Material Cost = 0.3* 0.6 = 0.18
Durability
= 0.6
Time to
produce = 0.1
Reliability
= 0.3
Results for Weighted Decision Matrix using Interval Scales
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!
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.
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.