Chapter 9Chapter 9Material SelectionMaterial Selection

EIN 3390 Manufacturing ProcessesEIN 3390 Manufacturing ProcessesSpring, 2011 Spring, 2011

9.1 Introduction9.1 IntroductionThe goal of manufacturing is to create

products and components that perform properly

Due to advances in materials science, there is a wide array of available materials◦The increase in the number of choices has often led

to improper or poor materials selection◦Sometimes, a more expensive alloy is chosen when a

cheaper alloy would have been sufficientDesign engineers have the responsibility of

proper materials selection

IntroductionIntroductionMaterial selection processes should be

constantly reevaluatedMaterials selection concerns are always

changing◦Environmental pollution◦Recycling◦Energy ◦Health or safety constraints◦Geopolitical issues

IntroductionIntroduction

Materials in many products have changed over the years

Figure 9-2 a) (Left) A traditional two-wheel bicycle frame (1970s vintage) made from joined segments of metal tubing,

b) (Right) a top-of-the-line (Tour de France or triathlon-type) bicycle with one-piece frame, made from fiber-reinforced polymer-matrix composite. (Courtesy of Trek Bicycle Corporation, Waterloo, WI.)

9.2 Material Selection and 9.2 Material Selection and Manufacturing ProcessesManufacturing Processes

Material and manufacturing processes are extremely interdependent

Change in a material will likely cause a change in the manufacturing process needed

A successful product has gone through both proper material selection and processing selection

Figure 9-4 Schematic showing the interrelation among material, properties, processing, and performance.

Example of Material Changes in a Vacuum CleanerExample of Material Changes in a Vacuum Cleaner

Materials for parts of VacuumMaterials for parts of Vacuum

9.3 The Design Process9.3 The Design ProcessDesign is the first stage in manufacturing

processes◦What it is◦What properties must it possess◦What material◦How to make it◦How many to make◦What conditions will it see during use

Steps for DesignSteps for Design

1. Conceptual◦Several concepts may be considered

2. Functional◦Workable designs are developed◦Detailed plan for manufacturing◦Prototyping

3. Production◦Full production◦Production speeds and quantities

9.4 Procedures for Material 9.4 Procedures for Material SelectionSelectionGeneral sequence of product design

◦design→material selection→process selection→production→evaluation→redesign

Case-history method◦Evaluates what has been done in the past

Modification of an existing product◦Evaluates the current product and manufacturing

techniques◦Changes or improves upon features of the existing

productDevelopment of a new product

◦Follows the full sequence of product design above

Geometric ConsiderationsGeometric ConsiderationsRelative sizeShape complexitySpecified dimensionsPrecisionComponent interactionSurface-finishesTolerances

◦Tolerances due to environmental or usage concernsMinor changes to improve manufacture or

performance

Mechanical PropertiesMechanical Properties

Static strengthBrittle fracturePlastic deformationAllowable bend, stretch, twist, or

compressImpact loadingsVibrations or cyclic loadingsWear resistanceOperating temperatures

Example: Cantilever Beam DesignExample: Cantilever Beam Design

design: equal strength

design: equal cross section

Parabola curve

Physical Properties (Electrical, Physical Properties (Electrical, Magnetic, Thermal, and Optical)Magnetic, Thermal, and Optical)Electrical requirements

◦Conductivity, resistivityMagnetic Thermal conductivityThermal expansionOptical requirementsWeightAppearance (color, texture, feel)

Environmental ConsiderationsEnvironmental ConsiderationsOperating temperaturesCorrosionErosionLifetimeFatigueExpected level of maintenanceDisassemblyRepairabilityRecyclability

Manufacturing ConcernsManufacturing Concerns

QuantityRateLevel of qualityQuality control and inspectionAssembly concernsSection thicknessStandard sizes and shapesLiability if product failure occursEnd-of-use disposal

Proper Materials SelectionProper Materials SelectionAll factors and service conditions must be

metAbsolute requirements

◦No compromise possibleRelative requirements

◦Compromises can be made◦Good, better, best are all acceptable

9.5 Additional Factors to Consider9.5 Additional Factors to ConsiderHandbook data is valuable in determining

materialsNote the conditions under which values for

materials were obtainedCost is often one of the biggest additional factors

◦Often, compromises between material properties and cost must be made

Material availabilityAre there any possible misuses on the part of the

consumer?Have there been failures for similar products?Material’s usage historyMaterial standardization

9.6 Consideration of the 9.6 Consideration of the Manufacturing ProcessManufacturing ProcessOverall attractiveness

◦Physical properties◦Mechanical properties◦Formability

Economical concernsAll processes are not compatible with all

materials

9.7 Ultimate Objective9.7 Ultimate Objective

Develop a combination of material and processes that is the best solution

Material or manufacturing selection normally imposes restrictions or limitations on the other

Economics, environment, energy, efficiency, recycling, inspection, and serviceability are important deciding factors

Decision ModelsDecision Models

Figure 9-5 Sequential flow chart showing activities leading to the production of a part or product.

Figure 9-6 Alternative flow chart showing parallel selection of material and process.

CompatibilityCompatibilityFigure 9-7 Compatibility chart of materials and processes. Selection of a material may restrict possible processes. Selection of a process may restrict possible materials.

9.8 Materials Substitution9.8 Materials Substitution

Care should be taken so that all requirements are still met

The total picture should be considered so that any possible compromises can be determined◦Aluminum sheets have replaced steel for

weight reduction, but vibration problems require special design considerations

Material SubstitutionsMaterial Substitutions

Material SubstitutionsMaterial SubstitutionsCauses of product failure

◦Failure to know and use the best materials information

◦Failure to account for all reasonable material uses

◦Use of materials with insufficient data◦Inadequate quality control◦Material selection made by unqualified people

9.10 Aids to Material Selection9.10 Aids to Material SelectionThere is an enormous amount of resources

available for materials selectionMetals Handbook, published by ASM

InternationalASM Metals Reference BookHandbooks are available for specific classes of

materialsAmerican Metal Market provides material costsMaterials Selection in Mechanical Design by M.

F. AshbyComputer software

Selection of a Material with Rating ChartSelection of a Material with Rating Chart

Example: Selection of a Material:Example: Selection of a Material:

Solution:Solution:• Finding “Go-No-Go” property: weldability

• - S: satisfactory• - U: unsatisfactory

• Calculating: R = Material Rating Number, and r = rating factor.

Relative rating number = rating number x weighting factor

• rating number of material’s property: excellent = 5, good = 3, fair = 2.

• weighted factor for material’s property: • - Stiffness : 1• - Stability: 4• - Fatigue: 5• - Tensile strength: 4

Solution (cont.)Solution (cont.)

Weldability Stiffness Stability Fatigue Tensile Strength

R r R/r

Go-No-Goscreening

(1) (4) (5) (4)

X

Y

Z

Rating chart for selecting material

Solution (cont.)Solution (cont.)

Weldability Stiffness Stability Fatigue Tensile Strength

R r R/r

Go-No-Goscreening

(1) (4) (5) (4)

X S 3x1 3x4 2x5 3x4 37 14 2.64

Y U 3x1 5x4 3x5 5x4 58 14 4.14

Z S 3x1 3x4 5x5 2x4 48 14 3.43

Rating chart for selecting material

Solution (cont.)Solution (cont.)

Weldability Stiffness Stability Fatigue Tensile Strength

R r R/r

Go-No-Goscreening

(1) (4) (5) (4)

X S 3x1 3x4 2x5 3x4 37 14 2.64

Y U 3x1 5x4 3x5 5x4 58 14 4.14

Z S 3x1 3x4 5x5 2x4 48 14 3.43

Rating chart for selecting material

Concusion:Concusion:

Based on the chart below, material Y has the highest rating number. However, because it does not have satisfactory weldability and this is an "absolute" requirement, it should not be selected. Material Z should be used.

SummarySummaryProper materials selection is vital to a

product’s successThe design engineer is responsible for

materials selectionMaterials and process selection go hand-

in-handData should be used to validate materials

selection

Homework:Homework:

Review questions: 7, 9, 12, 17

Due Date: 1/18/2011