ME251 Exam 3

Mer

# of monomer units used to make a polymer chain

Thermosets

- no melting temp - pour/form into shape, then initiate chemical reaction to solidify (add heat, mix two parts, etc) - setting time: time to remain in mold -much stronger and more rigid than thermoplastics - greater dimensional stability - lower ductility - poorer impact properties

Deformation Processes

-"plasticity": exploit the ability of engineering materials to flow as a solid without deterioration of properties pros: -no need to handle molten metal or deal with solidification problems -often very low waste cons: -required forces can be very high -machinery and tooling are often expensive

What are some of the disadvantages of cold working/formimg processes (compared to hot working/forming)?

-Cold working requires heavier and more powerful equipment -Cold working requires higher forces -Final products of cold working have lower ductility

Methods to Prevent Gas Porosity

-Prevent the gas from dissolving in the liquid: -melting in a vacuum or covered with flux -melting in environment with low solubility gases -minimize turbulence Gas Flushing: -passing inert gases or reactive gases through the liquid metal

Processing of Rubber and Elastomers

-Products produced by: injection molding, compression and transfer molding, extrusion, and calendering (sheet products)

Additional Effects of Cold Working

-annealing heat treatments may be required -allows additional cold working and deformation >>> intermediate anneal resets cold work back to zero, strength goes down and %EL goes up -cold working often produces an anisotropic structure

Filters

-can be used in gating systems to trap foreign material -removes contaminants -decreases liquid flow rate (not necessarily good)

Molten Metal Problems

-chemical reactions can occur between molten metal and its surroundings -metal oxides created due to reactions between oxygen and the molten metal -ladles attempt to preserve the metal and only use good metal in the mold -when remelted, metal absorbs gas in atmosphere. After pouring, metal solidifies and gas becomes less soluble, forms pores in solid metal

Isothermal Forming

-deformation occur under constant temperatutre -dies, tooling, and work piece are heated, -eliminates cracking -inert atmospheres may be required -expensive **use when material properties are very temperature dependent

Gating Systems

-delivers the molten metal to the moldcavity; proper design minimizes turbulence -wells designed to catch the first metal; first metal has lowest quality due to slag and porosity

Grain Growth and Structure

-direction, rate, and type of grain growth is determined by direction and rate of heat removal Three distinct regions or zones: 1. Chill Zone: rapid nucleation at cold walls of the mold (part right on the surface, small spherical grains) Fastest cooling region > highest strength region*** 2. Columnar Zone: rapid growth perpendicular tot he casting surface, long and thin, highly directional (anisotropic) (big long grains in the middle) Lowest strength region*** 3. Equiaxed Zone: crystals in the interior of the casting, spherical, randomly oriented crystals (small crystals in the very middle) intermediate properties

Type 2: Particulate Composites

-discrete particles of one material in a matrix of another material -concrete and asphalt -tungsten carbide -grinding/cutting wheels -typically isotropic (behaves the same in every direction)

Thermoplastic vs Thermosetting Elastomers

-elastomers can be made as either thermoplastic or setting polymers -cross-linking process is required to produce thermosetting elastomers -cross-linking helps reduce Viscous Deformation, but decreases Elastic Deformation, makes the material a little stiffer

Polymer Coatings

-enhance appearance and corrosion resistance -used on electrical cords/metals

Engineering Plastics

-enhanced impact and stress resistance -polyamides, polyacetals, polyketones, etc.

Design Factors Related to Finishing

-finish and appearance of plastics is important to customers -parting lines result in flash -place at corners or edges if possible -flat areas should be avoided -flash can be shaved off, but shows the inside of the plastic, doesn't look pleasing

Luders Bands (Stretcher Strains)

-form when material is stretched to an amount less than the yield point run-out

Structure from Hot Working

-grain size not uniform -plastic material flow -forming gives stronger parts than casting because grains bend and flow with the geometry, which makes the material stronger **grains parallel to features >> more fracture resistant

Prediction of Solidification Time

-heat removal is related to the surface area and voume of casting *Chvorinov's Rule: ts = B(V/A)^n where n=1.5-2.0 -B is the mold constant -V is the volume of the casting -A is the surface area of the casting

Blow Molding

-hollow shaped products and containers 1. heated parison placed in mold 2 .mold closes 3. air forces the plastic against the cavity walls 2. mold opens and part is removed

Plastics as Adhesives

-hot melt glues -two part epoxies

Foamed Plastics

-incorporate gases in their structure -cushioning, flotation devices, insulation, disposable food trays

Surface Deterioration

-lubricants used to reduce friction and wear, also can serve as a coolant, thermal barrier and/or flame retardant -surface wear is related to friction -wear of the work piece is okay (makes the surface shiny) -wear of the tooling is not okay (loses tolerances, has a negative impact on surface finish, eaves scuffs and scars, cam impact response to fatigue, **tooling is expensive, don't want to have to replace it)

General Material Parameters

-material being deformed must be well characterized *Important Parameters* -yield strength or resistance for deformation -conditions at different temperatures -formability limits (%EL needs to be large) -reactivity (consider oxidation possibility at high temps) -speed of deformation and its effects

Recycling of Plastics

-materials must be sported based on resin type, fillers, and color -packaging is one of the largest usage for plastics (PET, HDPE, PE, PS) -only some plastics are recyclable: thermoplastics almost always recyclable because we can melt them down and reform them again (loses a little quality each time) thermosets cannot be recycled, but can be reused or repurposed

Molten Metal Fluidity

-metal should flow into all regions of the mold cavity and then solidify *fluidity is the inverse of viscosity -determines: minimum section thickness, maximum length of a thin section, fineness of detail, ability to fill mold extremities

Casting Plastic vs Casting Metal

-metal: much higher temps, risks oxidation, have to choose mold with high temp compatibility, stronger adhesion between mold and material, done at lower pressure -there temps make it necessary to use different geometry and materials when making molds ti be used with metal * casting metal: high temp low pressure * casting plastic: low temp high pressure

Sand Casting

-molds made out of sand 1. Starts with a pattern (typically cut in two halves) looks like what the final product ill look like 2. put pattern into "flasks" (boxes) (top is the cope bottom is the drag) 3. add sand and binder 4. after solidification, assemble mold, and add pouring cup (hole in the top half of the sand mold that allows us to pour the metal in) 5. pour metal into mold cavity (through pouring cup) pouring cup leaves some access metal 6. break part out of mold 7. cut off access material if needed

The Solidification Process

-molten material cools to solidify into the final shape. Critical step for the final quality of the product. (determines material properties) Two Stages: Nucleation and Growth (both determine grain structure) -casting defects occur during solidification: gas porosity, oxidation reactions, thermal expansion/contraction

Compression Molding

-more complex than casting -plastic placed in an open cavity -heat and pressure applied -pressure maintained until material is set -a little more commonly used in thermosets but can also be used for thermoplastics -really inexpensive (slightly more than casting) -good surface finish and tolerances -best for a small number of parts (maybe a few hundred)

Transfer Molding

-more complex than compression molding -material heated separately and then forced into mold-reduces turbulance and uneven material flow -can be used will both types of plastics -more expensive -easier to automate, better for larger number of parts (maybe a few thousand) -makes it possible to make more complex geometry

Fabrication of Plastics

-most methods will be some form of molding/casting Specific methods used for fabrication depends on: -size, shape, and quantity -type of the polymer

Fabrication of Composite Materials

-most processes are slow and require considerable amounts of labor Particulate Composites -processed by introducing particles into a liquid melt or slurry OR powder metallurgy methods Laminar Composites -processed by forming bond between distinct layers of different ,aterials Fiber Reinforced Composites -processed by embedding fiber in a matrix -attention to alignment and spacing necessary to produce desired final properties

3. Ceramics

-naturally derived ceramics have been in use for a long tie -engineered ceramics have superior properties and are used in many high tech applications Typical Properties -high operating temperatures -high melting point -good creep resistance -low thermal expansion, low thermal conductivity -hard and brittle -high compression strength and low tensile strength

4. Composite Materials

-nonuniform solid consisting of two or more different materials -mechanically or metallurgy bonded together (they retain their identity i.e. structure and properties) Compostie properties depend on: -properties of individual components -relative amounts -size, shape, and distribution -orientation (anisotropic: behaves differently in different directions) -degree of bonding

Additional Plastics

-oriented plastics -engineering plastics -plastics as adhesives -foamed plastics -polymer coatings

Inserts

-plastic isn't great for everything we need to make so we use inserts and mold around them -incorporated to enhance performance Ex: threaded inserts, mounting surfaces, electrical terminals

Fabrication of Crystalline Ceramics

-processed in the solid state: dry or isostatic pressing -clay products are ceramics blended with water and additives -plastic forming: wet pressing, extrusion, or injection molding -casting processes: slip or tape casting

Oriented Plastics

-processing aligns the molecules in parallel, up to 50% increase in TS -when heated, molecules tend to revert back to their original orientation

Risers and Riser Design

-risers are reservoirs of liquid metal that feed extra metal to the mold to compensate for shrikage *open vs blind type Blind riser: contained completely within the mold, cannot be seen from outside of the mold Open riser: you can see the metal from the outside Dead: material flows through mold cavity before getting to riser (top riser) Live: material flows through riser on its way to the mold cavity (side riser)

Forming Operations

-rolling -tube spinning -forging (smashing material into final shape) -swaging or kneading -extrusion -deep drawing (shaping) -shear spinning -wire and tube drawing -stretching -straight bnding -contoured flanging (convex or concave) **when an annealing process occurs in between other shaping processes, it is called an intermediate anneal

Foam Molding

-similar to reaction injection molding -mixes either thermoplastic or thermoset with a foaming agent -releases gas when heated during molding (chemical reaction) -open or closed cell -rigid or flexible foams created

Casting

-simplest of the shape-forming processes -can be used with thermoplastics or thermosets -thermoplastics must be cooled to retain solid shape -thermosets must complete crosslinking to retain shape -simplest, most straight forward fabrication -not great to scale

Metal Properties and Cold Working

-stress strain curves are useful in predicting results ~Key Properties~ -magnitude of the yield-point stress (determines how much force is needed to cause permanent deofmation) -extent of plastic strain region from yield stress to fracture (determines how much we can deform the material before it breaks) (delta x) -spring back should also be considered when selecting a material

2. Elastomers

-subset of plastics/polymers that can experience large amounts of elastic deformation and still return to original shape -temporary deformation caused by uncoiling/recoiling of polymer chains called "Elastic Deformation" -permanent deformation caused by sliding of polymer chains with respect to one another called "Viscous Deformation"

Type 3: Fiber Reinforced Composites

-thin fibers of one material embedded in a matrix (most advanced) -fibers can be discrete or spun into ropes or fabric -wood and bamboo are natural examples -fibers of nylon, rayon, Kevlar, steel. glass, graphite, whiskers, or ceramic (very strong) **can offer very high strength to weight ratio** -anisotropic due to of orientation of fibers

Friction in Deformation Processes

-up to 50% of force required in deformation processes goes towards overcoming friction -high forces/pressures are required to deform a material -friction: resistance to sliding contact between two surfaces -for elastic loads, friction is proportional to the applied pressure -at high pressures, friction is proportional to the strength of the weaker material and the contact area

Extrusion

-used for long products with uniform cross section -material fed into hopper, melted, and then compressed through die -material cooled by air or water spraying (or bath)

Fabrication Techniques for Glasses

-viscous masses may be used instead of molten glass -processes siilar to compression molding -processes similar to blow molding are used to make bottles and containers

Nucleation

-when it first starts to go from liquid to solid -"undercooling" is the difference between the melting point and the temp of nucleation. -each nucleation event produces a grain -"inoculation" or "grain refinement" is the introducing of solid particles to promote nucleation **more grains and smaller grains >> better mechanical properties

Temperature Concerns

-work piece temperature often the most important of the process variables -typically an increase in temp is related to: -decrease in strength -increase in ducitlity -decrease in rate of strain hardening As temp increases >> material becomes easier to deform

Shape Producing Processes

1. Casting 2. Material Removal 3. Additive Processes 4. Consolidation Processes 5. Deformation Processes

Properties of Plastic Determined By:

1. Chain length 2. Properties of included monomers 3. Degree of crosslinking

Fabrication of Fiber Reinforced Composites

1. Filament Winding 2. Pultrusion Process (extrusion with a pulling force) 3. Lamination (produces sheets or rolls) **4. Molding Processes: -spray molding -hand lay-up -vacuum bag molding process -pressure bag molding -compression molding -resin-transfer molding -injection molding -parts may be cured in autoclave (system with high temp and high pressure)

4 Major Nonmetallic Materials

1. Polymers/Plastics 2. Elastomers 3. Ceramics 4. Composites

Special Ceramics

1. Refractory Materials: good mechanical and chemical properties at high temps, can be made from a number of base materials (silca, alumina, zirconia, carbon, graphite, etc) 2. Amorphous Materials: *glass* soft and moldable when hot, easily shaped,excellent corrosion resistance 3. Cermets: combinations of metals and ceramics, crucibles, nozzles, aircraft brakes 4. Cements: plaster of Paris, sand casting, Portland cement

2 Categories of Polymers

1. Thermoplastic: can melt and solidify repeatedly, due to long polymer chains with no cross-linking 2. Thermosetting: irreversible chemical reaction, can't remelt them

Dipping (for Elastomers only)

1. metal master form is dripped into liquid and then dried -additional dips, if required to achieve desired thickness -electrostatic charge any accelerate the process (static electricity makes elastomer stick to the mold better) 2. material is vulcanized and removed from orm **done with only elastomers because pther plastics are too hard to remove from mold

Casting Process

6 steps 1. create mold cavity (single use or multi use) 2. melt material (possible oxidation) 3. pour material (possible slag, air pockets) 4, solidify material 5. remove mold 6. finishing and inspection (secondary operations included)

Ceramics Applications

Abrasives: -grinding applications -diamond and cubic born nitride are superabrasives Electrical and Magnetic Applications: -resistors, heating elements, insulators -piezoresistive materials (adding force generates electrical current) Coatings: -enamels, porcelains, glazes

Warm Forming

Advantages compared to Cold Working: -reduced loads on the tooling an equipment -increased material ductility -possible reduction in the number of anneals -expanded range of materials and geometries Advantages compared to Hot Working -less scaling an decarburization -better dimensional precision and smoother surfaces than hot working -less energy required -finish machining reduced -finer structure with strain hardening often eliminates heat treatments

Plastics vs Metals

Advantages of plastic: -cheaper, especially for high volume -easier to build complex geometry (can reduce number of total components and assembly operations) -very easy to reuse manufacturing scrap -reduced finishing costs -lower weight Advantages of metal: -can be cheaper for low volume -far superior mechanical properties: impact resistance, strength, rigidity, etc. -better high temp performance -resistance to flames, acids, and solvents ** metals substantially stronger and stiffer, ductility varies

Practical Concerns with Composites

COST Defects: (hard to detect these issues, inside the material) -delamination voids -missing layers -contamination -fiber breakage -improperly cured resin Areas of Application (low weight needs) -aerospace -sporting equipment -automobiles -boat hulls -pipes

the ________ composites are capable of withstanding the highest temperatures.

Carbon-carbon

_______ are ceramic materials that harden via chemical reaction instead of requiring a heat-based processing step.

Cements

Open vs Closed Cell Foam

Closed: air pockets are contained, no link from one side of the material to the other (water tight and air tight) Open: gas pockets merge together, path from one side of material to the other, not air or water tight

Hot vs Cold Working

Compared to hot working, cold working requires less heating, produces a better surface finish, and offers superior dimensional control, better reproducibility, improved strength, directional properties, and reduced contamination problems.

Fabrication of Plastics, Ceramics, and Composites vs Fabrication of Metals

Compared to metals: -products are used closer to design limits -lower "factors of safety" especially for plastic parts -conversion of raw material to final part in a single operation (most metals require multiple fabrication steps) -large complex shapes can be formed in a single part

The difference between thermosetting and thermoplastic polymers is the presence or absence of ________ between the polymer chains. Thermosetting polymers have ________, which makes it impossible to remelt these polymers once they have been solidified.

Cross links

Which of the following is the main advantage of deformation processes compared to other metal manufacturing processes?

Deformation processes produce very little waste material

General Properties of Plastics

Desirable: light weight, corrosion resistance, electrical resistance, low thermal conductivity, optical properties, formability, surface finish, low cost (compared to metals), low energy content Undesirable: poor strength, low impact strength, poor dimensional stability, heat sensitivity, UV sensitivity, low stiffness ** good physical properties, poor mechanical properties**

Elastic vs Viscous Deformation

Elastic deformation in elastomers is caused by temporary uncoiling of polymer chains in response to an applied force. When the force is released, the chains will recoil and the polymer will return to its original shape. Viscous deformation is a permanent effect caused by sliding of polymer chains in response to an applied force; when the force is released, this deformation remains. Crosslinking can help reduce or eliminate the permanent effects of viscous deformation.

Designing Parts for Fabrication

Keep in mind: -adequate fillets between adjacent sections (make openings slanted so fluid fills the whole mold) -uniform wall thickness **plastic has very high coefficient of thermal expansion (how much a material changes as far as geometry is concerned when it heats or cools) (plastic expands and contracts a lot!) Thicker sections expand or contract more than thinner sections >> make uniform thickness throughout -appropriate dimensional tolerances (be realistic)

Advanced Fiber Reinforced Composites

Polymer M Matrix Composites: -sports equipment, light weight, low temp aerospace applications Metal Matrix Composites (MMC) -nonflammable, do not absorb water or gases, corrosion resistance, used up yo 2300 F Ceramic Matrix Composites (CMC) -high temp strength, stiffness, and environmental stability, used up to 2700 F Carob Carbon Composites -high temp applications, used up to 3600 F

Synthetic Nonmetallic Materials

Polymer: PVC, Acrylic Elastomer: Polyurethane Ceramic: Aerospace Tiles Composite: Kevlar

Naturally Occuring

Polymer: Proteins, DNA Elastomers: Rubber Ceramics: Clay, Diamond Composites: Wood, Bamboo

Pros & Cons of Deformation Processes at Different Temps

Process classification based on working temperature and material being formed: 1. T < 30% of melting temp >>> "Cold Forming/Working": plastic deformation below the re-crystallization temperature 2. T > 60% of melting temp >>> "Hot Forming": plastic deformation above the re-crystallization temp 3. 30% < T < 60% >>> "Warm Working": plastic deformation under conditions of transition

Typical Elastomer Properties and Applications

Properties: -good flexibitlity -good electrical insulation -typically very good corrosion and chemical resistance -poor performance at high temperatures -good damping Applications: -shock absorption, noise and vibration control vehicle tires -sealing, waterproofing -safety gloves -electrical insulation

Green State

correct shape, low strength

________ can be used to produce relatively thin elastomeric products with uniform wall thickness, such as boots, gloves, or balloons.

dipping

Fabrication of Laminar Composites

face sheet adhesive honey comb adhesive face sheet --add heat and pressure >> fabricated sandwich panel

Fibers vs Matrix

fibers: strong, stiff, and brittle matrix: low strength, compliant, ductile, helps distribute forces

When crystalline ceramics are processed, the first step is typically to press moist aggregates or powder into the correct shape. At this point, the ceramic is the correct shape but has to mechanical strength; the ceramic is referred to as being in its _______ state. The second step is to use heat or chemicals to bond the material together, which provides the actual strength.

green

Fluidity

how easily the liquid metal will pour **determined by superheat

Superheat

how much hotter a metal is when you pour it than the solidification temperature -increasing superheat increases fluidity but also breaks down the mold more

Factors of Safety

how much more force a particular design can withstand before failure

_________ molding is used to produce more plastic products than any other process.

injection

A metal that is ideal for metal forming (deformation) processing would have:

low strength, high ductility and low springback

Stress Concentrations

places in a part where the local stress is very high because of the local geometry

________ is the material property that describes the ability of a solid to flow (plastically deform) without deterioration of its properties.

plasticity

Which of the following are common undesirable properties of plastics?

poor high temperature performance poor mechanical properties

Cold Working

pros: -no heating required -good surface finish -superior dimensional control and reproducibility -strain hardening improves strength, fatigue, and wear properties -directional properties can be imparted cons: -higher forces required; requires heavier and more powerful equipment -ductility of material is lower -surfaces must be clean and scale free -strain hardening may require intermediate anneals to restore ductility

Hot Working

pros: -recrystallization eliminates the effects of strain hardening -shape can be drastically altered without fear of fracture -achieve deformation without using excessively high forces -temp promotes diffusion to improve homogeneity cons: -undesirable reactions between metal and surroundings (steel oxidizes at high temps) -tolerances are poorer -structure may be non uniform -non uniform temps can cause residual stresses

Basic Plastic Terminology

~plastics composed of simple basic units called "monomers" ~monomers chemically linked to together to form long chains called "polymers" ** process of linking monomers to form polymers called "polymerization"

1. Plastics/Polymers

- large molecules (larger than metals) composed of smaller molecules - made from natural or synthetic resins and compounds - can be molded, extruded, cast, or used for coatings - very versatile materials - vast majority of costumer products have at least one plastic component in them

Casting Metal Advantages

(compared to other fabrication processes) -complex shapes -parts can have hollow sections or cavities -very large parts -use to form parts from metals that are difficult to machine like high strength materials -Types of metal casting processes: -different mold materials (sand, ceramics, other metals) -different pouring methods (gravity, pressure, vacuum)

Injection Molding

**most widely used process for production of thermoplastic parts -only for thermoplastics -highly automated -material fed into hopper -material is heated/melted in the barrel -fluid injected through sprues and runners into mold *only useful for very large number of parts

Rotational Molding

**works for thermoplastic material that needs to be hollow with thick walls -mold filled with specific amount of material -mold rotated simultaneously about two axes -even distribution across mold walls

Vulcanization

*cross linking process -uses sulfur to cross link rubber "vulcanized rubber"

Additive Agents in Plastics

*mixed into plastic before melting (thermoplastic) or before cross-linking (thermosets) process -increase strength, toughness or ductility (plasticizer for ductility) -decrease weight -increase dimensional stability -reduce flammibility -increase resistance to chemicals *can also add "fillers" like wood flour or cloth fibers -increases fluidity of plastic -reduce adhesion strength to mold -add or modify color

Thermoforming

*only for thermoplastics -sheet of material heated and placed over mold -vacuum, pressure, or mechanical tool forms material into mold -imparts shape and texture to product Example: clam shell packaging

Reaction Injection Molding

*used for thermosets -two or more liquid reactants mixed together -mixture flows into mold -chemical reaction solidifies material ** lower processing temperature and pressure than injection molding since material is a thermoset not thermoplastic

Thermoplastics

- contains molecules of different lengths - do not have an exact melting temp * shorter chains have a lower melting temp, longer chains have a higher melting temp - easy to form above the melting temp - > poured and cast, injection molding, extruding, etc. To form: heat >> form to shape >> cool to retain shape

Type 1 Composites: Laminar or Layered

Examples (Structural) -plywood -surface coatings -safety glass -corrugated cardboard -laminate flooring or counter tops -composite honeycomb panels Nonstructural Example: "bimetallic strips" two materials with different coefficients of thermal expansion (one expands more at high temps than the other)

Which of the following are properties usually associated with ceramic materials?

Excellent high temperature performance High compression strength Good thermal insulation (low thermal conductivity)

Filament winding and pultrusion are manufacturing techniques used for processing which type of materials?

Fiber-reinforced composites

Cooling Curves

For an alloy, the plateau region in the middle is slightly sloped, and this is the "freezing range" -solidification for alloy takes place over multiple temps where as a single metal solidifies at a single temp

Mold Geometry

Gating system: made up of runner, sprue, and pouring cup, allow material tom flow from outside of mold into the mold cavity. Cope and Drag: top and bottom Riser: only in metal casting, essentially a reservoir for extra metal, fills up until solidification and then has extra material ready for when metal contracts in the mold cavity

Which of the following is an advantage of isothermal forming?

Isothermal forming typically eliminates cracks in the final product

Bimetalic strips are an example of a ________ composite material; they are most often used to measure ___________

Laminar Temperature

Anisoptropic Materials

Laminar composites and fiber reinforced composites

Solidification Shrinkage

Material contracts in 3 stages: 1. contraction of liquid 2. solidification shrinkage 3. solid metal contraction

Sand Cast vs Permanent Mold vs Die Cast

Sand Cast: slowest cooling rate (lowest strength) Die Cast: fastest cooling rate (highest strength) **Faster cooling rates > smaller grain structure > better mechanical properties (higher strength)

Cold vs Hot Working Usage

Smaller number of parts and smaller deformation >> use cold working Large number of parts and large deformations >> use hot working

Which of the following are advantages of using thermoplastic polymers instead of thermosetting polymers?

Thermoplastic polymers are more typically more ductile than thermosetting polymers Thermoplastic polymers are more easily recycled than thermosetting polymers

Which of the following are typical production shapes that could be produced by the extrusion of plastics?

Tubes, Wires, Pipes *not variable cross sections

Patterns

Two basic categories for casting processes: expendable mold processes and permanent mold processes ~Depending on process, patterns can be made form wood, metal, foam, plastic, etc -patterns are generally larger than final part dimensions, to allow for: -material contraction -draft -finishing operations

Processing of Ceramics

Two distinct classes of processing ceramics: . glasses -manufactured by means of molten material via viscous flow 2. crystalline ceramics -manufactured by pressing moist aggregates or powder into shape -material bonded together to from high strength final state by chemical reaction or heat ("sintering")

The ____________ fabrication method can be used with thermoplastics or glass to form thin-walled, hollow-shaped products and containers. The process uses a pre-formed tube of material (parison), heats it to soften the material, and injects high pressure air into the parison to force the material against the mold walls.

blow molding

In general, an increase in temperature brings about:

a *decrease* in material strength, an *increase* in ductility, and a *decrease* in the rate of strain hardening - all effects that would tend to promote ease of deformation.