Week 4

 COWS... Moo?

COWS is a helpful decision-making framework in which a score basis is used and many different attributes of the decision being made are used. In our case for this week's activity, it helped us to select the most appropriate material for the lid and the inner walls of a thermal flask.

In essence, it is an acronym that stands for:

• Criteria
• Options
• Weightage
• Score

This is a framework that helps with decision-making by helping us organise the information we have on the items being deliberated.

In the context of material selection, the Criteria section helped us to list down the attributes of the materials that make them suitable for use in the area needed. In other cases, this can be used to list down what requirements are needed of an idea for brainstorming.

The Options section was where we listed down the materials that we have found to meet the requirements and would like to deliberate on further.

In the Weightage section, we gave each desirable attribute listed in the Criteria section a weightage, which is a measure of how much that specific attribute will affect our decision making. For example, in the thermal flask's inner wall, we had high melting point and low specific heat capacity for two of our four criteria. Since we felt that needing more energy to raise its temperature is more important than having a high melting point (since we were only using hot water in the flask), we gave low specific heat capacity a 30% weightage whereas we gave high melting point of 20%. This way, the specific heat capacity of the material will have a larger impact on the comparison of that material to the others.

The Score section is where the bulk of our decision-making takes place. For this section, our group decided to first collect and collate relevant data (i.e. data related to the criteria). We gave a score by comparing the material's specific value for that criterion with one another and give a score accordingly. An example of this is shown below.

All in all, the COWS decision matrix is a really useful tool as not only can we organise the data and information we need to make a decision but also make the decision-making process more streamlined and systematic. We did not have to fuss over just comparing the materials based on research on the application but rather through how its properties make it the most suitable for use.

For this week, we had an activity where, as we mentioned above, we needed to suggest materials to use for the lid and the inner wall of a thermal flask. We applied the COWS decision matrix and we have come to the suggestions of grade 316 stainless steel for the inner wall of the flask and phenolic resin for the cap. 

Here is an example of the scoring for the decision-making process:

Score:

Ranking: 1 (worst) to 3 (best)

Material Property	Stainless Steel-316	Ceramic, Al2O3	Glass
	Data
Melting Point (°C)	1385	2054	1000
Thermal Conductivity (W/m.°C)	16.2	30	1.5
Specific heat capacity (J/kg.°C)	0.5	0.85	0.79
Corrosion resistance (Rating – Cole Parmer, Water)	A-Excellent	A-Excellent	A-Excellent

Material Property	Scores
	Stainless Steel-316		Ceramic, Al2O3		Glass
	Points	Score	Points	Score	Points	Score
Melting Point	3	60	3	60	2	40
Thermal Conductivity	2	50	2	50	3	75
Specific heat capacity	3	90	2	60	2	60
Corrosion resistance	3	75	3	75	3	75
Total score	-	275	-	245	-	250

As stainless steel-316 had the highest score, that was the material that we chose to postulate.

Economic Consideration

Aside from being suitable for use, we also had to consider the economic viability of using that material for the thermal flask.

In our case, we wanted the material to be cheap to incur low procurement costs as well as having good machineability to reduce costs incurred by manufacturing as it would be easier to mould, cut or be used in any other processes needed in manufacturing. We also applied the COWS decision matrix for the economical viability, as shown here:

Criteria and weightage for selection:

• Material cost (60%)
• Machinability (40%)

Criteria	Scores
	Stainless Steel-316		Ceramic, Al2O3		Glass
	Points	Score	Points	Score	Points	Score
Cost	2	120	3	180	1	60
Machineability	3	120	3	120	2	80
Total score	-	240	-	300	-	140

Given that stainless steel-316 had the highest score and has the second highest score in the economic viability COWS matrix (and not very far off the highest-scoring material, Alumina), we consider it as the best material to use for the inner walls of the flask.

We applied the same decision matrix for the cover of the thermal flask as well. That concludes our activity for week 4 :D poggers!!!