Materials Selection for Materials Selection for Engineering DesignEngineering Design

Materials SelectionMaterials Selection The designer of any product, other The designer of any product, other

than software must get involved with than software must get involved with material selection.material selection.

Only occasionally will the exact grade Only occasionally will the exact grade of material be specified by the of material be specified by the customer.customer.

Even then the designer must Even then the designer must understand the material to be able to understand the material to be able to design the product.design the product.

Decisions, decisions!Decisions, decisions!So many materials, so much information.So many materials, so much information.

How do we decide? How do we decide? How do we begin to choose?How do we begin to choose?

First we need to look at the function of First we need to look at the function of the product – product analysisthe product – product analysis

Product AnalysisProduct Analysis Just what it says – analyse the Just what it says – analyse the

product!product! What does it do?What does it do? How does it do it?How does it do it? Where does it do it?Where does it do it? Who uses it?Who uses it? What should it cost?What should it cost?

Case Study – a bikeCase Study – a bike What is the function of a bike – obvious?What is the function of a bike – obvious? How does the function depend on the How does the function depend on the

type of bike?type of bike? RacingRacing TouringTouring Mountain bikeMountain bike CommuterCommuter ChildsChilds

Case Study – a bike (2)Case Study – a bike (2) How is it made to be easily maintained?How is it made to be easily maintained? What should it look like (colours etc.)?What should it look like (colours etc.)? What should it cost?What should it cost? How has it been made comfortable to How has it been made comfortable to

ride?ride? How do the mechanical parts work and How do the mechanical parts work and

interact?interact?

Component or system?Component or system? 11stst problem is……. problem is…….

Is it one component or a system of Is it one component or a system of components working together?components working together?

A spanner is a component, a cordless A spanner is a component, a cordless screwdriver is a system.screwdriver is a system.

System AnalysisSystem Analysis When we analyse a system we need When we analyse a system we need

to break the system down into to break the system down into individual components and then individual components and then analyse each one.analyse each one.

Cordless screwdriverCordless screwdriver

System Analysis – the bikeSystem Analysis – the bikeThe bike breaks down (we hope not!) The bike breaks down (we hope not!)

into various parts:into various parts: FrameFrame ForksForks WheelsWheels SaddleSaddle Etc.Etc.

System Analysis – the bike System Analysis – the bike (2)(2)

We now need to look at the following We now need to look at the following for each part:for each part:

Requirements (mechanical, Requirements (mechanical, ergonomic, aesthetic etc.)ergonomic, aesthetic etc.)

FunctionFunction How many are going to be made?How many are going to be made? What manufacturing methods are we What manufacturing methods are we

going to use?going to use?

ManufacturingManufacturingOh No! Oh No! We have to actually make it!We have to actually make it!

This is a key question which has a This is a key question which has a massive influence on materials massive influence on materials selection.selection.

e.g. The frame, what materials could we e.g. The frame, what materials could we use?use?

Frame MaterialsFrame Materials Steel – Steel – Strong, stiff, heavy, but cheapStrong, stiff, heavy, but cheap Aluminium – Aluminium – weaker, lighter, more expensive than steelweaker, lighter, more expensive than steel Composite (CFRP) – Composite (CFRP) – strong, stiff, very light, but expensive to strong, stiff, very light, but expensive to

buy and to fabricatebuy and to fabricate

Bike FrameBike Frame

Frame Design DetailFrame Design Detail

What Properties?What Properties? Mechanical – Mechanical –

Strength, modulus etc.Strength, modulus etc. Physical – Physical –

Density, melting point.Density, melting point. Electrical – Electrical –

Conductivity, resistivity.Conductivity, resistivity. Aesthetic – Aesthetic –

Appearance, texture, colourAppearance, texture, colour Processability – Processability –

Ductility, mouldabilityDuctility, mouldability And last, but not least……….And last, but not least……….

Cost, cost, cost!Cost, cost, cost!

Where do I find the data?Where do I find the data? TextbooksTextbooks DatabooksDatabooks Manufacturer’s literatureManufacturer’s literature Internet SitesInternet Sites

TextbooksTextbooks Good for general informationGood for general information Some have tables of propertiesSome have tables of properties Not good for detailed specifications Not good for detailed specifications

and properties.and properties. A useful first point of callA useful first point of call

DatabooksDatabooks One of the quickest sources of One of the quickest sources of

detailed information.detailed information. Usually contain grades and Usually contain grades and

specifications as well as properties.specifications as well as properties. Small and perfectly formed – Small and perfectly formed –

pocketbookspocketbooks Easy to navigate aroundEasy to navigate around

Manufacturer’s literatureManufacturer’s literature Variable in quality and usefulness.Variable in quality and usefulness. Often only cover their products.Often only cover their products. Usually do not compare materials.Usually do not compare materials. Can be biased.Can be biased. Good for final selection before Good for final selection before

ordering.ordering.

Internet SitesInternet Sites Can be a real minefield.Can be a real minefield. Lots of poorly presented information.Lots of poorly presented information. Google searches bring up lots of Google searches bring up lots of

rubbish.rubbish. Hard to find technical information.Hard to find technical information. Best to use non-commercial sites.Best to use non-commercial sites.

Materials Selection ChartsMaterials Selection Charts

2323

Modulus - Density ChartModulus - Density Chart Modulus spans 5 orders of magnitudeModulus spans 5 orders of magnitude

0.01 GPa for foams to 1000 GPa for 0.01 GPa for foams to 1000 GPa for diamond diamond

The charts therefore use The charts therefore use logarithmiclogarithmic scales, where twice the distance scales, where twice the distance means means ten ten times.times.

This makes it possible to show the full This makes it possible to show the full range on one chart,range on one chart,

Materials Selection ChartsMaterials Selection Charts

Materials Selection ChartsMaterials Selection Charts Allow easy visualisation of propertiesAllow easy visualisation of properties Show lots of different materialsShow lots of different materials Can be ‘drilled down’ to specificsCan be ‘drilled down’ to specifics Show balances of properties Show balances of properties

e.g. strength v coste.g. strength v cost Ideal for a first ‘rough cut’ selectionIdeal for a first ‘rough cut’ selection

SummarySummary1.1. Think about the design from Think about the design from

ergonomic and functional viewpoint.ergonomic and functional viewpoint.2.2. Decide on the materials to be used.Decide on the materials to be used.3.3. Choose a suitable process that is also Choose a suitable process that is also

economiceconomicSteps 2 & 3 may be iterative. Don’t Steps 2 & 3 may be iterative. Don’t

forget the ……………forget the ……………

Bigger PictureBigger PictureIs the product Is the product performanceperformance driven or driven or cost cost driven?driven?This makes a huge This makes a huge difference when difference when choosing materials.choosing materials.

Manufacturing ProcessManufacturing ProcessAlthough we usually Although we usually choose materials first choose materials first sometimes it is the sometimes it is the shape and process shape and process which is the limiting which is the limiting factor.factor.

Case Study (2) Drink Case Study (2) Drink ContainerContainer

What are the What are the requirements?requirements?

Case Study (2) Drink Case Study (2) Drink ContainerContainer

Provide leak free environment for storing Provide leak free environment for storing liquid.liquid.

Comply with food standards & protect liquid Comply with food standards & protect liquid from health hazards.from health hazards.

For fizzy drinks, withstand pressure.For fizzy drinks, withstand pressure. Brand image & identityBrand image & identity Easy to openEasy to open Easy to store & transportEasy to store & transport Cheap for high volumesCheap for high volumes

Possible MaterialsPossible Materials SteelSteel AluminiumAluminium GlassGlass PlasticPlastic PaperPaper