Week 4

For this week, we had recalled the concept of selecting materials by using COWS method. 

Recall what is COWS Method❗❗❗:

 

Criteria- Relevance

 

Options- All Feasible

 

Weighing- Contextualise 

 

Score- Assessment

How do we actually use the COWS Method?:

Criteria	Weightages	Options
		Idea #1		Idea #2		Idea #3
		Raw Score	Weighted Score	Raw Score	Weighted Score	Raw Score	Weighted Score
a.
b.
c.
d.
e.
Score

(Table 1: Example of COWS Decision Matrix)

Additionally, to find the weighted scores for the materials, we can calculate the scores by:

Weighted scores = Weightages X Raw Score (1-5)

To identify which options are the best, just simply evaluate and the highest scores for the ones are the most suitable that meet the criteria.

Task for Group 4: 

 

 

(Photo taken from Week 4 Material for Design.pptx) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Material requirements for the designs: 

For the teat of milk bottle: 

Function	To allow the baby to consume the milk from the top of the bottle safely.
Constraints	Low thermal conductivity.  Non-corrosive.  Low density.
Objectives	Ensure the baby to drink the milk safely.

 

For the cover of milk bottle: 

Function	To store the prepared milk for the baby to drink.
Constraints	Low thermal conductivity.  Food-safe.  High melting point.
Objectives	Ensure it is safe for the baby to consume the prepared milk.

 

Before we design both the teat and the cover of the milk bottle, we list down materials requirements for teat and cover of milk bottle: 

 

Material requirement for teat	Material requirement for cover
The material should not be able to conduct heat.	Withstand temperature of greater than 40C.
It needs to be non-corrosive.	Food safe.
High tensile strength.	Non-corrosive.
Low hardness.	Thermal insulator.
The teat should not break easily when force applied.	Excellent chemically compatible with milk. (Natural and formula)
High in ductility.
Low in density.

 

 

Select and evaluate candidate materials: 

 1. Properties and data for the materials selected: 

 

Materials for cover
Criteria	Borosilicate Glass	Polycarbonate	Polyethylene
Thermal conductivity(W/m.K)	1.1	1.08	0.28
Chemical compatibility with milk	Good	Good	Excellent
Corrosion resistant	Poor	Good	Excellent
Melting point/glass transition point(°C)	800	142	240
Density(g/cm3)	2.40	1.26	1.60

 

Materials for teat of the bottle
Criteria	Natural Rubber	Silicone
Thermal conductivity (W/m.K)	0.140	1.59
Chemical compatibility with milk	Good	Excellent
Corrosion resistant	Good	Excellent
Hardness	30 - 90	49.5
Ultimate Tensile Strength (MPa)	27.6	7.24
Density(g/cc)	0.930	1.24

 

2. COWS Method to choose the suitable material for teat and the cover of milk bottle: 

 

Materials for cover of milk bottle
Criteria	Weightage	Borosilicate Glass	Polycarbonate	Polyethylene
Thermal conductivity	20%	2	2	3
Chemical compatibility with milk	25%	3	3	3
Corrosion resistant	25%	2	2	3
Melting point	20%	3	2	3
Density	10%	2	3	2
Total	100%	245	235	290

 

Materials for teat of the bottle
Criteria	Weightage	Natural Rubber	Silicone
Thermal conductivity	10%	3	4
Chemical compatibility with milk	25%	3	4
Corrosion resistant	25%	3	4
Hardness	15%	3	4
Ultimate Tensile Strength	15%	3	4
Density	10%	3	4
Total	100%	300	400

 

Choose the most economical material: 

 

Materials for cover of milk bottle
Criteria	Weightage	Borosilicate Glass	Polycarbonate	Polyethylene
Cost of material	75%	4	3	4
Ease of handling/  manufacturing	25%	3	3	4
Total	100%	375	300	400

 

Materials for teat of milk bottle
Criteria	Weightage	Natural Rubber	Silicone   Rubber
Cost of material	75%	3	3
Ease of handling/  manufacturing	25%	3	4
Total	100%	300	325

 

Based on the table above, the most suitable material for the teat of the milk bottle is Silicone Rubber.  

For the cover of the milk bottle, the most suitable for the cover of the milk bottle is Polyethylene.

Reflection for Week 4:

Ambrose:

This week, our group will have to design the teat of the milk bottle and the cover of the milk bottle based on our prior knowledge such as COWS Method that we have learned in our first year. At first, I was struggled and could not start out with identifying the criteria and materials we were going to need. After several discussion with my fellow group mates, we worked together to make sure we produced a good quality work. Besides that, as group leader I had some difficulties in contacting some of the members in this group due to their inactivity in completing their work, but I am glad that we were able to complete and submit the task on time together.

Joshua:

Building off with the spiral curriculum, ICPD reintroduces the concepts of material of design that we learned in our first year. It was a good refresher activity on these skills that have become a bit rusty. We had a little trouble in selecting our materials since our research had some difficulty turning up something, but we persevered. I've always had a hard time fully using Mattweb because of the complexity in choices of materials and the great range of values and absence of some properties, a challenge that I once again had to face. But with some referral to my old lecture notes and activities I was able to complete it.

Yongjie:

Edmund:

For this week I have learnt about the categories of materials and when we discovered new materials through the videos. We were tasked to select materials for the teat and cover of a baby milk bottle and apply material selection by understanding the material requirements for the teat and cover of a baby milk bottle and apply COWS method to choose the most suitable material. We got to bond as a team through this assignment.