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

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

Concept Development Funnel

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 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

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 Lightweight Stable Pinch Points Maintenance Range of Motion (legs) Comfort 1 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. CatalogCraneCart Lightweight11 Stable01 Pinch Points10 Maintenance01 Range of Motion (legs)01 Comfort01 Totals1-33

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. CriteriaUnitsDesired Direction 1020 Steel 304 SS 5052 AL CuBronze Thickness(in.)less is better ConductivityBtu-ft/(hr o F- ft 2 ) higher is better Diffusivityft 2 /hrhigher is better HardnessBrinnellhigher is better Yieldkipshigher is better Machinability[0-100]less is better Thermal Mass Btu/ o Flower is better

CriteriaDesired Direction 1020 Steel 304 SS 5052 Al CuBronze Thicknessless is better Conductivityhigher is better Diffusivityhigher is better Hardnesshigher is better Yieldhigher is better Machinabilityless is better Thermal Mass lower is better Total

CriteriaDesired Direction 1020 Steel 304 SS 5052 Al CuBronze Thicknessless is better 1100 Conductivityhigher is better 010 Diffusivityhigher is better 010 Hardnesshigher is better 110 Yieldhigher is better 0100 Machinabilityless is better 0111 Thermal Mass lower is better 1100 Total

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.

CriteriaDesired Direction 1020 Steel 304 SS 5052 Al CuBronze Thicknessless is better Conductivityhigher is better Diffusivityhigher is better Hardnesshigher is better Yieldhigher is better Machinabilityless is better Thermal Mass lower is better Total Complete the Matrix Using Ratio Scales

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 = 0.6Quality in Service = 0.4 Material Cost = 0.3 Manufacturing Cost = 0.5 Repairability = 0.2 Durability = 0.6 Reliability = 0.3 Time to produce = 0.1 Weight for Material Cost = 0.3* 0.6 = 0.18

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.