Material for design (MFD)
For material for design (MFD), our group was asked to find material to make a razor. To do that we first identify the parts and stated the function. After that we used COWS matrix to find the best material. This isn’t the first time using COWS matrix in fact it was in one of my blogs also.
A disposable safety razor can be divided into two parts:
1. Blade;
2. Body/Handle;
Step 1. List the material requirements for the design (Blade)
To be an efficient safety razor, the blade must be able to cut stems of hair easily to prevent friction burns. The handle must be durable enough to withstand the force applied by the user onto the surface which requires shaving.
Function: To shave off hair on the human skin, usually on the chin, armpits or genitals.
Constraints: High Strength, low thermal conductivity, good corrosive resistance
Objectives: Maximize sharpness.
Criteria | Weightage | Reason it was chosen |
Low thermal conductivity | 20 | The razor will normally be put in the toilet basin and it will be exposed to the steam coming from the showers. The razor must not heat up quickly. This will cause the user to experience discomfort as the temperature might be hot on their skin. |
High young's modulus | 40 | This has the highest weightage as it is important that the razor be stiff enough so that it does not bend while being in use. |
Corrosive resistance | 10 | Razor will most likely be placed in the toilet where it will be exposed to moisture. Hence, it must be corrosive resistant to water. |
Cost | 20 | The raw material of the blade should not be too expensive to ensure that the consumer would not have to buy it at a higher price. |
Ease of manufacturing | 10 | The material should be easy to manufacture as it will have to be mass produced. Also with easier manufacturing, the manufacturing cost will go down. |
Step 2. Select and evaluate candidate materials (Blade)
Based on description above, metals have been shortlisted as the possible materials. And out of so many metals, three possible metals/alloys have been selected as candidates: Stainless steel, cast irons, copper
COWS Matrix for blade
|
| Options |
Criteria | Weightage | Stainless steel 304 | Cast iron | Copper |
Low thermal conductivity, λ | 20% | λ = 50.2 W/m.K Score: 3 3 x 20% = 60% | λ = 79.5 W/m.K Score: 2 2 x 20% = 40% | λ = 385 W/m.K Score: 1 1 x 20% = 20% |
High young's modulus | 40% | 193 MPa Excellent Score: 3 3 x 40% = 120% | 66 MPa Poor Score: 1 1 x 40% = 40% | 130 MPa Good Score: 2 2 x 40% = 80% |
Corrosive resistance | 10% | Very good Score: 2 2 x 10% = 20% | Poor Score: 1 1 x 10% = 10% | Excellent Score: 3 3 x 10% = 30% |
Cost | 20% | Expensive Score: 1 1 x 20% = 20% | Cheap Score: 2 2 x 20% = 40% | Cheapest Score: 3 3 x 20% = 60% |
Ease of manufacturing | 10% | Poor Score: 2 2 x 10% = 20% | Good Score: 3 3 x 10% = 30% | Very Poor Score: 1 1 x 10% = 10% |
Total | 100% | 240% | 160% | 200% |
The Material chosen is stainless steel 304.
Step 1. List the material requirements for the design (handle)
To be an efficient safety handle, the handle must be durable enough to withstand the force applied by the user onto the surface which requires shaving.
Function: To provide a handle for the user to grip on to.
Constraints: High tensile Strength, Low density, Good corrosion resistant, High Young modulus
Objectives: Provide the user a place to hold the razor without cutting themself.
Criteria | Weightage | Reason it was chosen |
Density | 20 | The body of the razor must be light. |
High tensile strength | 25 | This is important as the body must not break when the consumer is using it. |
Young's modulus | 30 | It has the highest weightage as the handle must not bend under stress from the user during usage. If it bends, the user will experience discomfort when they use it. |
Corrosion resistance | 25 | Razor will most likely be placed in the toilet where it will be exposed to moisture. Hence, it must be corrosive resistant to water. |
Step 2. Select and evaluate candidate materials (handle)
Based on the description above, plastic has been shortlisted as the possible material. And out of the plastics, these possible materials have been selected as candidates: silicone, polypropylene and polyurethane.
COWS Matrix for body/handle
|
| Options |
Criteria | Weightage | Silicone | Polypropylene | Polyurethane |
Density | 20% | ρ = 1.42 g/cc Score: 2 2 x 20% = 40% | ρ = 1.92 g/cc Score: 1 1 x 20 % = 20% | ρ = 1.12 g/cc Score: 3 3 x 20% = 60% |
tensile strength | 25% | 7.24 MPa Score: 1 1 x 25% = 25% | 29.2 MPa Score: 3 3 x 25% = 75% | 23.4 MPa Score: 2 2 x 25% = 50%
|
Young modulus | 30% | 1.52 GPa Score: 2 2 x 30% = 60%
| 1.68 GPa Score: 3 3 x 30% = 90%
| 0.147 GPa Score: 1 1 x 30% = 30%
|
Corrosion resistant | 25% | Good Score: 2 2 x 25% = 50%
| Excellent Score: 3 3 x 25% = 75%
| Excellent Score: 3 3 x 25% = 75%
|
Total | 100% | 175% | 260% | 215%
|
The two highest scoring materials are polypropylene and polyurethane.
We choose not to combine the cost of material and ease of manufacturing into 1 table for the handle as it will be too much of a factor for one table.
Step 3: Choose the most economical material
Criteria | Weightage | Options |
Polypropylene | Polyurethane |
Cost of material | 70% | $0.27 Score: 2 2 x 70% = 140%
| $8.19 Score: 1 1x 70% = 70%
|
Ease of manufacturing | 30% | Excellent Score: 2 2 x 30% = 60%
| Good Score:1 1x 30% = 30%
|
Total | 100% | 200% | 100% |
Based on this, the selected material is polypropylene.
Design for Material (DFM)
For design for material, we were asked to find a material that interest us and discuss how the material can be used to replace another material and how it can be used to enhance functionality of an existing product.
We chose the shape memory alloy.
Name of material | Shape Memory Alloy |
Chemical Name | Ni-Ti alloy |
General Description | Shape memory alloys can remember their original shape and when exposed to stimuli will regain their original shape even after bending, twisting or deforming. |
General Properties | – Shape altering – Available in a range of forms, shapes and products – Corrosion resistant – Bio-compatible |
Opportunities | Unlike plastics, metals, and traditional alloys, shape-memory alloys are both strong and flexible, easy to sterilize, and corrosion-resistant too. Being lightweight, tough, and capable of operating at high temperatures, they’re also widely used in aerospace components in such things as space rockets and space probes. Shape-memory alloys (SMAs) have been used in the manufacture of orthodontic wires due to their shape memory properties, super-elasticity, high ductility, and resistance to corrosion. SMAs have greater strength and lower modulus of elasticity when compared with stainless steel alloys. |
Discuss among the group how this material can be used as a direct replacement to a material in an existing product without any significant changes in the design. Shape memory alloy can replace plastics when designing a frame for spectacles. The benefit of using shape memory alloy is that it is much more flexible than plastic and since spectacles are one of the things that accompany us daily. It is much more likely that they will be damaged. By using the shape memory alloy, even if those spectacles frames are damaged, as long as it's not broken into pieces, the spectacle will go back to its original shape. |
Discuss among the group how this material can be used to enhance the functionality of an existing product through some changes in the design.
The material can be used to make the body of a car. The benefit is that it can return to its original shape when force is applied. We can design it to be thicker so it can provide the same toughness as the metal usually used.
The change of design is that we can change the coating of the car since the shape memory alloys are more corrosion resistant and don't rust as easily as other metals. As the car is exposed to moisture and oxygen when travelling on the road. Body of cars that are usually made of iron, aluminum, copper and steel are coated with polymer paint to prevent corrosion and rusting of the metal. Now, since we are replacing it with the shape memory alloy, there is no need for the coating of polymer paint.
Without the coating, all the cars will have the same colours however, we can modify it with decal stickers. And since the decal stickers can be removed easily the user can modify the design of the car whenever they want.
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It might seem that MFD and DFM are similar because they sound about the same just that the material and design words are switched. In fact, they are the opposite of each other. In MFD, we are looking for a material that suits the design, while in DFM we are looking at changing a design to suit a material.
We also learn about sustainable design. We were asked to modify our product to be more environmentally sustainable.
Our idea is to use recycled plastic for the upper layer of our product. Since the upper layer of our product is only required to be structurally stable while being able to contain the grater and the fan. Instead of just using normal plastic to make the first layer, we can use recycled plastic. Our design can also be disassembled into first and second layer, thus the material we choose could be cleaned easily and can be reused. This is a product that is supposed to last for a period of time.
Here is a sketch to show what I meant:
References
Matweb, no date. Online Materials Information Resource - MatWeb [online]. Available from: <https://www.matweb.com/> [Accessed 14 July 2022].
Daniel, J, F, et al., 2011. Understanding the Shape-Memory Alloys Used in Orthodontics [online]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3185255/#:~:text=Nickel%2Dtitanium%20(NiTi)%20shape,compared%20with%20stainless%20steel%20alloys [Accessed 14 July 2022].
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