Metallurgy

ENME221

Powder metallurgy

(PM)

PM

Producing parts from metallic powder

Pressing

compress powder into shape (punch and die)

Sintering

Below TM to bond particles (Heating)

PM Pros

near net shape, little waste, specified porosity, impregnated oil, high TM metals (tungsten) can only be shaped this way, dimension control, automation

PM Cons

high cost, hazard handling/storing powder, part geometry, density variation

Powder production

atomisation, chemical, electrolytic, mechanical

Gas automatization

molten metal through gas nozzle and spray (also into water)

PM Process

Mix powder together (homogenized), compact, sinter

blend

same chemical different size

Mixture

different material

Green strength

strength for handling

Compact

fill die with feeder, compress, eject. High pressure. Powder extrusion

Sinter

make particles form grain boundaries. Increase strength and hardness. 0.7-0.9 TM

Densification

repressing

Sizing

improve dimensional accuracy

Coining

imprinting pattern onto surface

Impregnation

oils into pores, polymer resins

Infiltration

molten metal (TM below TM of main material. Capillary action draws into pores. Uniform strength

Pure

iron, aluminium, copper, tungsten

Pre alloys

stainless steel, copper alloy, high speed steel

PM Design

Large quantities, Controlled porosity, Vertical sides, No threads, Unusual alloys, No side features, Vertical undercuts and holes, corner radii weakness, No under cuts/holes, Minimum diameter and wall thickness 1.5mm

Heat treating

Structural changes in mechanical properties

Heat treating Before shaping

Soften for forming

Heat treating After shaping

relieves strain hardening

Heat treating End

archives final strength and hardness

Annealing process

Heat, hold, slow cool

Hardness

ability to not break under load

Toughness

ability to bend without breaking

Annealing

Decrease hardness, increase ductility, increase toughness, relieves residual stresses

Martensite forming

Rapid cooling. Austenising, quenching (brine, water, oil, air). Temper to reduce brittleness

Mertensite

High strength, very brittle

Precipitation hardening

Particles on edge of crystal structure

Surface/case hardening process

Carburising, nitriding, carbon nitriding

Surface/case hardening

Only impacts outside shell/surface. Wear resistant

Carburising

Carbon diffused into steel by heating low carbon (900dc)

Nitriding

similar to carburising, lower temp, jigger hardness (600dc) (Al,Cr)

Carbonitriding

mix of carburising and nitriding

Surface/case hardening Method

fuel or electric furnace

Surface

flame, induction, high frequency alternating current, laser

Coasting and deposition Metal

painting, plating (except stainless steel and brass)

Coasting and deposition Why

corrosion, wear resistance, reduce friction, increase conductivity/resistance, appearance

Plaiting

Thin metallic layer on usually metallic substrate

Electroplating

Current through cathode work part, anode plate, in electrolyte solution (50micron)

Coating material

Normally steels

Coating - Galvanising

zinc

Coating - Nickel

corrosion resistant

Coating - Tin

less reactive

Coating - Copper

aesthetic, PCB

Coating - Chromium

wear resistant

Coating - Gold, silver, platinum

jewellery

Electroform

Like electroplating but thicker, patter removed (100 microns)

Hot dipping

Part dipped in molten metal. Basic clean, rinsing, pickling (acid), rinsing, flux (prevents oxide bond), molten bath

Conversion

Material chemically changes surface. Immersion or spraying

Conversion Why

corrosion, paint prep, wear resistance, lubrication holding, electrical resistance

Phosphate

turns to phosphate films

Chromate

transforms to chromate forms

Anodising

oxide coating by electrochemical reaction (dyes)

Physical vapor deposition (PVD)

Turns material to vapor, let condense into surface (over even)

Organic

Polymers and resins applied as liquid then hardened (brush, roll, spray, dip, flow)

Binders

strength, dies, solvents, additives. Liquid or powder

Drying

turns from liquid to solid

Curing

strengthens bonds

Porcelain enamelling

Ceramic coating powder, smooth, easy to clean, passive

Surface cleaning

Removes contaminants. Prepares for surface treating (hygiene, appearance, contaminant removal

Surface cleaning Steel

alkali

Surface cleaning Al

alkali or acidic

Surface cleaners

Alkaline, organic emulsion, solvent, acid, ultrasonic, chemical action, debur, surface finish, surface harden, blast, shot peening (little pellets)

Blast cleaning/sand blasting

Blast particle matter (air, centrifugal force)

Shot peening

Cast steel pellets blasts (cold work increases hardnesses)

Mass finishing

Bulk with abrasive stuff

Tumbling barrel

small parts, sand (change size for different finish)

Vibration

faster, visible

Media

control size and shape.