Assignment 4 : The Pugh Method

OBJECTIVES

·         Overcome negative features or shortcomings of design

·         Find different ideas to satisfy criteria

·         Exploring alternatives

INTRODUCTION

This method was invented by Stuart Pugh. The Pugh method also decision-matrix method,  Pugh Concept Selection is a quantitative technique used to rank the multi-dimensional alternatives of an option set. It is commonly used in engineering for making design decisions but can also be used to rank investment options, vendor options, product options or any other set of multidimensional entities.

The Pugh Method is a creative design idea or concept evaluation technique that uses criteria derived from the “voice of customer” in ad advantage-disadvantage matrix. Each concept is evaluated against a datum using a three way evaluation scheme which are:

·         + ; means substantially better

·         - ; means clearly worse (or flawled)

·         S ; means more or less the same

The method is associated with the QFD method and is a form of prioritization matrix. It is implemented by establishing an evaluation team and constructing the matrix which contains evaluation criteria versus alternative concepts. A baseline concept is selected and the other concepts are scored against the criteria relative to the baseline.

Pugh concept is parts of evaluation methods been used to decide mainly in design concept. This methods compare the design alternatives for redesign process. In easy word, it is a relative comparison technique. There are three series of absolute filters that must be passed by concept of design where will be included in the Pugh Concept. The series of absolute filters are listed below.

PROCESS / METHOD OF PUGH

Pugh Method can be done by below processes and it has two phases.

	PHASE I
Criteria	Develop list of evaluation criteria
Design Concept	Original design concept brainstormed
Evaluation matrix	Each design evaluated against datums, and add concepts
Analysis	Analyze each round, adjustment, and establish new datum, repeat.
	PHASE II
Better Design	Weak designs dropped, continue process, designs developed in more depth/detail, criteria refined
Superior Concept	Process converge on a strong consensus, team committed

Figure: Pugh Method Process

The steps in the Pugh concept selection method as given by Clausing are :

1.      Choose the criteria by which the concepts will be evaluated.

-          The QFD is the starting place to develop the criteria. The criteria will be based on the engineering characteristics which listed in the House of Quality. Other than engineering characteristics, there are also customer requirements that will be compared to the engineering requirement. Both of them will lead to the best decision making. Each team member need to be at list create 15 to 20 criteria but really to be based on QFD and functional analysis. Next , the list of criteria need to be combined, being discusses and prioritized.

2.      Formulate the decision matrix

-          The criteria next been entered into the matrix as the raw heading while the concepts into the column headings of  the matrix. It is important that concepts to be compared be the same level of abstraction.

3.      Clarify the design concepts

-          Common level of understanding resulted as a goal which brought the team member into it. A good team discussion regarding on the concepts is a creative experience. New ideas often come into view and used to improve concepts or entirely create new idea (concepts).

4.      Choose the datum concept

-          One concept is selected by the team as a datum for the first round which means the reference concept with all other concepts being compared. A poor choice of datum would cause all of the concepts to be positive. For a redesign, the datum is the existing design reduced to the same level of idea as the other concepts.

5.      Run the matrix

-          After completing the steps before, comparative evaluation will take its part. Each concept is compared to with the datum for each criterion. The first criterion is applied to each concept and so on. Three level of scale is used where better concept will be assigned (+), worse (-) and about the same (=).

-          The team discussion often arouse new ideas that lead to additional improved concepts. A major advantage of Pugh concept is it helps the team to develop better approaching into the types of features that strongly gratify the design requirements.

6.      Evaluate the ratings

-          Once the comparison matrix is completed, the sum of scales is determined. Few positive features in the concepts may be gems that that could be choose and apply in another concepts. Highly rated concepts verify their strengths are and what criteria they treat poorly. If most concepts get the same rating on a certain criterion, examine it to see whether it is stated clearly or not uniformly evaluated from concept to concept.

7.      Establish a new datum and rerun the matrix

-          The concept that received the highest rating in the first round usually been selected as a new datum. The lowest rating concept been eliminated. The use of a different datum will give a different perspective at each comparison that will help clarify relative strengths and weaknesses of the concepts.

8.      Examine the selected concept for improvement opportunities

-          Once the main concept is identified, each criterion that perform worse than reference concept been considered. New approaches emerge where negative scores can change to positive scores.

Selection method of Pugh can be explained briefly in the figure shown below.

Figure: Pugh Concept Selection Method

The method is very effective for comparing concepts that are not refined enough for direct comparison with engineering requirement. Basic table should be follow is shown below.

			Idea for Comparison (Step 2)
Criteria for comparison         (Step 1)		Weights	Generate Score (Step 3)
			Total (Step 4)

Below is the example of table which characterized concepts for both customer requirement and engineering concept that need to be compared.

			Engineering Characteristics
			Maintenance and testability provision	Strengthens of Material	Ergonomic Factor	Force to turning handle	Tendency to break
Customer Requirement	Performance	Light weight
		Attractive
		Design
		Safe
	Maintenance	Crack Resistant
		Scratch resistance
		Cost
		Ease of removing handle
		Ease of installing new handle

BENEFITS OF THE PUGH METHOD

The advantage of Pugh approach to decision making is that subjective opinions about one alternative versus another can be made more objective. Another advantage of this method is that sensitivity studies can be performed. An example of this might be to see how much your opinion would have to change in order for a lower ranked alternative to out rank a competing alternative.

Other benefits of Pugh Method are as follows :

1.      Discussions reveal arbitary criteria. Team members gain insight into the problem and clearly understand the criteria which become better defined.

2.      The discussion also leads to creative leaps between different concepts and idea synthesis, as flaws are attacked together and the team experiences synergy.

3.      The team develops consensus about the best solution.

4.      The resulting new concepts are better than the original ideas. No flaws are overlooked; engineering changes are eliminated and invulnerable products are developed that will succeed in the marketplace.

5.      The method results in cost savings:

·         Reduce cost in design process

·         Limit change later by better design

·         Invest effort early, benefits later

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