Stuff i keep forgetting mech2305

What are the properties of a cast iron?

Low melting temperatures, more brittle, harder than steel, good for complex shapes

Features of grey cast iron

Graphite flakes in ferrite/pearlite matrix. Brittle, low strength

Features of ductile (nodular) iron.

Mg or Ce added to make graphite spherical. Higher strength but moderate ductility.

Features of white cast iron

Adding carbide formers, high hardness and wear resistant but brittle.

Features of compacted graphite

Intermediate between flakes and nodules. Better properties than grey cast iron but not as good as ductile iron.

What is grinding in machining?

Uses abrasive particles to remove a very small amount of metals. very smooth surface finish

Describe the differences between continuous, discontinuous, and serrated chips.

Continuous chip = smooth, long, ductile materials. Discontinuous chip = broken segments, brittle materials. Serrated chips = segmented due to shear instability.

Difference between rake face vs flank face

The rake face is where the chip flows whereas the flank face rubs against the surface causing wear.

Machining: water jet cutting

High-pressure water and abrasives. Cuts almost everything, no heat damage, thick materials. However, less accurate for thick parts, slow for hard materials

Machining: wire EDM

Uses electrical sparks to erode material. Extremely precise, no cutting force, great for hard materials. Slow, only works on conductive materials

Machining: laser cutting

Melts material and removes it with gas. Fast, no contact, complex shapes. Surface finish issues, fumes, and oxidisation.

What are the key characteristics of SMF

Versatile in shape and processing, applied stress must exceed yield strength to cause plastic deformation, performed at room temperature, and springback, sheet exhibits anisotropic behaviour.

What are the signs of rolling?

Flattened elongated grains, strong texture along rolling direction

What are the signs of forging?

Curved grain flow lines following shape,

What are the signs of PM?

Rounded residual pores and uniformly distributed porosity

Signs of thread rolling?

Grain flow lines follow thread profile

Signs of thread cutting?

Grain flow is interrupted, threads machined from stock

Manufacturing ceramics: Powder processing

Blend powder, press powder to create a green part, remove the binder by heat, sinter to improve the properties, and finally apply secondary operations

Manufacturing ceramics: Clay products

Rocks/clay is crushed into powder, water is added, extruded, cut to size, dried, and fired in kiln.

Manufacturing ceramics: Slip casting

Make clay slurry, pour into mould, solid clay forms on mould walls, liquid is removed, the green part is removed, dried and sintered. Used for complex shapes and smooth surfaces

Define a carbon fibre-reinforced polymer

Lay fibre cloth in mould, infuse with resin, apply a vacuum, remove the trapped air, and cure in an autoclave. Use of a pre-preg which pre-impregnates fibre with resin.

What is joining used for?

Parts that cannot be created all at once.

Define fusion welding.

Melts base metals together by heat, requires shielding gas, filler mold.

TIG (GTAW)

Non-consumable tungsten electrode, inert gas shield. Best for quality and thin sheets

MIG (GNAW)

Consumable wire electrode, inert gas shield, and continuous wire feed. The fastest and automated.

Stick (SMAW)

Consumable flux-coated electrode. Best for portability and outdoors.

Flux Cored

Tubular wire filled with flux. Best for thick plates, heavy fabrication.

SAW

Arc hidden beneath granular flux. Best for mass production

PAW

Plasma jet from tungsten electrode. Precision TIG

EBW

Electron beam in vaccum. Best quality welds, but most expensive

LBW

Laser beam melts material. Fastest precision welding, but expensive

Resistance welding

Heat generated by electrical resistance. Best for metal sheet spot welding

Common weld defects

Porosity, slag inclusions, cracking, lamellar tearing

Hot working vs Cold working

Hot working: Above Trec, lower forces, better ductility, poor finish, lower accuracy, no strain hardening. Cold working: Below Trec, higher forces, higher strength, excellent finish, higher accuracy, strain hardening occurs.

Open-die vs closed-die forging

Open die: simple dies, low tooling cost, large parts, poor accuracy, and low production. Closed die: sharpened dies, high tooling costs, small/medium parts, good accuracy, and high production.

Hot rolling vs Cold rolling

Hot rolling: Large reductions, lower force, rough surface, lower accuracy. Cold rolling: better finish, higher strength, smooth surface, high accuracy.

Direct extrusion vs indirect extrusion vs hydrostatic extrusion

Direct extrusion: material flows with ram, the simplest. In indirect extrusion, material is forced in, lower force. Hydrostatic force: pressure transmitted through fluid, almost frictionless.

What are mechanical surface treatments?

Delays cracking by inducing compressive stresses at the surface to counteract tensile loads. Use when you want better fatigue life.

Mechanical: Shot peening

Steel/ceramic/glass shot at surface. Best for fatigue life improvement. Used for gears and springs and under cylic loading.

Mechanical: Laser shot peening

High energy laser pulse creates shock waves. Produces the deepest compressive stresses. Best for aerospace.

Mechanical: Water jet peening

High-pressure water against surface. Best for surface finish, no contamination. Used in nuclear components

Mechanical: Ultrasonic peening

High-frequency vibrating pins strike the surface. Good for welded structures.

Mechanical: Shock hardening

Creates plastic deformation and work hardening. Best for wear-critical surfaces.

When do we use thermal surface treatment techniques?

Improves surface hardness.

Thermal: Flame hardening

Oxy-fuel heats surface above austenising temperature. Cheapest. Best used for gears, rails, shafts.

Thermal: Induction hardening

Electromagnetic induction heats the surface. Most common, fast process. Used for gears, crankshafts.

Thermal: Laser Beam Hardening

Laser heats the surface. Used in aerospace parts, the most precise.

Thermal: Electron beam hardening

Electrons heat the surface. Aerospace applications, highest precision.

When do we use thermochemical or coatings?

To improve corrosion resistance, wear resistance, appearance.

Thermochemical: Ion Plating

Best for strong adhesion. Used in cutting tools

Thermochemical: Electroplating

Electric current deposits metal onto surface. Best for being cheap, used in jewellery.

Thermochemical: Electroless plating

Chemical reduction deposits metal without electricity. Used for complex geometries, electronic components. Best for uniform thickness.

Thermochemical: Brush Plating

Electroplating performed locally with a brush electrode. Best for repair work.

Thermochemical: Anodising

Protects aluminium with oxide. Used for aluminium products, electronics, aerospace. Best for aluminium protection.

Thermochemical: Galvanising

Steel coated with zinc. used for structural steel, best for steel.

Thermochemical: Hard-facing

Best for wear resistance, used for mining equipment.

Thermochemical: Thermal spraying

Molten particles are sprayed into the surface. Used for turbine coatings, best for thick coatings.

Thermochemical: Cold spraying

Powder particles below melting temperature. Used in aerospace repairs. Best for no heat damage.

Thermochemical: Vapour deposition

Material deposited atom-by-atom. Very expensive and best for hard, thin coatings.

What materials are used in AM?

Polymers, metals, and ceramics.

SLA

UV laser cures liquid resin. Choose for excellent surface finish, high accuracy for detailed prototypes.

DLP

Entire layer cured at once using projected light. Choose when you need the quality of SLA but faster production speeds.

Material Jetting.

Inkjet-like droplets cured by UV light. Choose when you want multi colour or multi material parts with exceptional surface finishes.

Binder jetting.

Binder glues powder particles together. Choose when you want large, complex parts that must be produced quickly without supports.

Material Extrusion (FDM)

Melted filament extruded through nozzle. Choose when you want low cost and ease of use are more important than accuracy and surface finish.

Sheet Lamination

Layers formed by bonded sheets. Use when producing large, low-cost prototypes with simple geometry

SLS (Selective laser sintering)

Laser sinters polymer powder. Choose when you have strong polymer parts with complex geometries are required.

SLM (Selective laser melting)

Laser fully melts the metal powder. Choose when you have a high-strength, high-density metal components and need excellent acccuracy.

EB-PBF (Electron beam powder bed fusion)

Electron beam melts metal powder in vaccum. Choose when manufacturing titanium components.

Laser DED.

Laser melts incoming powder/wire during deposition. Choose when repairing an expensive metal component or adding materials to existing part.

Electron beam DED

Electron beam melts incoming material. Use when producing large titanium structures with high deposition rates.

WAAM

Welding arc melts continously fed wire. Choose when manufacturing large metal components quickly and economically.