Assignment 4: Pugh Concept Selection Method

Problem 7.5

In the search for more environmentally friendly design, paper cups have replaced Styrofoam cups in most fast food restaurants. These cups are less effective insulation, and the paper cup often gets too hot for the hand. A design team is in search of a better disposable coffee cup. The design evaluated is: (a) a standard Styrofoam cup. (b) A rapid injection mold cup with a handle (c) a paper cup with a cardboard sleeve. (d) A paper cup with a pull out cup and, (e)a paper cup with a cellular wall. These design concepts are to be evaluated with the Styrofoam as the datum.

The engineering characteristics on which the cups are evaluated are:

1. Temperature in the hand

2. Temperature of the outside of the cup

3. Material environmental impact

4. Indenting force of cup wall

5. Porosity of cup wall

6. Manufacturing complicity

Answer:

Pugh concept selection for a fast-food coffee cup. We have substituted a paper cup with a cardboard sleeve for concept (e) in the problem statement, since it is a more current concept.

	DESIGN CONCEPTS
Design requirements	Regular paper cup	Styro- foam cup	Rigid injection molded with handle	Double-wall biodegradable plastic	Paper cup with fold- out handle	Paper cup with cardboard sleeve
Temperature in the hand		+	+	+	+	+
Material environ- mental impact	D	-	-	+	s	S
Indenting force of cup wall	A	+	+	+	s	S
Porosity of cup wall	T	+	+	+	s	S
Manufacturing complexity	U	+	-	-	-	S
Ease of stacking the cups	M	+	-	s	-	S
Ease of use by customer		s	+	s	-	+
Temperature loss of coffee over time		+	-	+	s	S
Overall cost		s	-	-	-	-
∑+		6	4	5	1	2
∑-		1	5	2	4	1
∑s		2	0	2	4	6

This problem illustrates that the Pugh chart is an excellent tool for quick comparison of alternative concepts. However, the numerical values should be used with caution. A rigid summation of pluses and minuses should never be done. Based on the analysis, it shows that the Styrofoam coffee cup is superior to the paper cup (DATUM) and to all other proposed concepts but its one negative outweighs all other considerations. Since Styrofoam does not degrade in a landfill it is banned in many jurisdictions and strongly frowned upon in others. All concepts are superior to a paper cup in providing better thermal insulation so that the cup is not too hot in the hand. However, they are all more expensive than either a paper or Styrofoam cup. The biodegradable plastic cup would be the best solution but it is the most expensive concept. The most widely adopted solution appears to be a paper cup with a cardboard sleeve. While it does not provide as much thermal protection as the two designs with handles, it is cost effective and acceptable to most people.

It is important to emphasize to them that the chief benefit to using the Pugh Chart is the insight to the problem to be gained from deep group discussion. Often concepts with many minuses have the kernel of a winning idea when combined with other concepts.