Metals: Treating, joining, forming and finishing

Essentially everything about metals exc. types and uses

Work hardening

Working a metal when it is cold, distorting its internal structure and making it harder.

Annealing

Reversing the stress from work hardening to prevent brittleness, involving heating and soaking the metal at a high temperature

Soaking

The process of maintaining a metal at a specific temperature to grow its internal crystals

Quenching

Plunging a metal into water or oil to rapidly cool it, sealing and hardening the surface and causing internal stress.

Hardening

The process of changing the carbon distribution in steel, by heating and quenching it, making it harder and stronger

Tempering

A follow-up process to hardening, done to steel to reduce its brittleness whilst maintaining its toughness and hardness, by heating and quenching the hardened steel.

Normalising

Increasing the toughness and hardness of a metal by heating, soaking, then cooling the metal in air.

Case hardening

The process of carburising and quenching low carbon steel to harden its surface but maintain its internal properties

Carburising

Heating steel to 950^oC in a carbon-packed ceramic box, forcing carbon atoms into its external structure and creating a layer of carbon around the steel

Adhesive, mechanical, thermal

The 3 categories of metal joints

Epoxy resin

Very strong adhesive, fills space between metal, 2 components

UV hardening glue

Strong bond adhesive, readily available superglue

Contact adhesive

Adhesive able to join metals and non-metals, hazardous fumes so requires ventilation

Bolts

Mechanical joining method, removeable, quick, cheap, easy and can join different materials and thicknesses

Self tapping screws

Mechanical joining method, removeable, only 1 side access needed, usable for thin metal only

Machine screws

Mechanical joining method, removeable, can join different materials and thicknesses, specialist machinery required to cut threaded holes

Self-secured joints

Mechanical joining method, manufacturing a part so it its self-joining when produced, strong permanent joint, no additional parts needed, specialist machinery needed

Rivets

Mechanical joining method, fastening sheets of metal by deforming the ends of a metal shaft either side of the fastened metals, very strong joint but requires specialist equipment and access to both sides

Pop rivets

Mechanical joining method similar to rivets, except only 1 side access is needed, forming a strong joint but less strong than a regular rivet

Soldering

Thermal joining method, joining two metals with a filler rod of low melting temperature solder, typically used for electronics

Brazing

Thermal joining method, similar process to soldering but at a higher temperature, used to join copper and steel

Oxy-acetylene welding

Fusion welding method, using a high temperature oxy-acetylene flame to melt parent materials

Arc welding

Thermal joining method, creating and electric current across gap between parent steel and filler rod to melt and join materials

MIG welding

Type of electric arc welding using metal inert gas around filler rod to prevent oxidisation, suitable for medium carbon steel or aluminium.

TIG welding

Type of electric arc welding, using tungsten inert gas around filler rod to prevent oxidisation, suitable for stainless steel and non-ferrous metals

Spot welding

Thermal joining method using pressure and temperature to melt and fuse parent metals in a specific spot, using electric currents to heat parent metals.

Milling

The wasting process of moving a ‘bed’ of metal around a cutting head to produce the desired shape.

Turning

The wasting process of cutting a metal piece whilst rotating at a high speed on a lathe.

Plasma cutting

The wasting method of using a high temperature plasma beam to cut through thick sheet metal in a fine cut.

Blanking

The use of a die cutter to cut component nets or larger parts from a sheet of metal.

Piercing

The use of a punch to cut out small holes for joins or assembly from metal components.

Forging

Bending, drawing down, punching and drifting, twisting and scrolling

Bending

The forging method of bending a metal when heated to achieve a sharper bend.

Drawing down

The forging method of stretching and hammering a metal whilst hot to reduce its thickness and increasing its length.

Punching

The forging method of using a spiked tool to create a hole in the hot metal.

Drifting

The forging method of hammering into an existing hole in a hot metal to increase its diameter.

Twisting

The forging method of twisting a metal piece whilst hot using a clamp and twisting wrench to rotate the piece around its own centre.

Scrolling

The forging method of rolling a metal along its length using scrolling tongs to create a spiral.

Drop forging

The process of manufacturing large batches of worked metal products, creating the rough shape via a machine then refining its shape with drop forging dies.

Cold forming

Rolling, drawing, bending, pressing, cupping, deep drawing, spinning

Rolling

The cold forming method of extruding sheet metal between 2 large rollers to decrease its thickness.

Drawing

The cold forming method of forcing metal bar or tubing through dies of gradually decreasing diameter to reduce the materials thickness.

Bending

The cold forming method of using a corresponding die and punch to bend a sheet of metal into a desired form.

Pressing

The cold forming method of using a corresponding die and blank to form a desired shape, often with multiple bends and unique forms.

Cupping

The cold forming method used specifically to form shallow cups in sheet metal, done by holding the sheet metal in place to prevent wrinkling.

Deep drawing

The cold forming method of using a punch of gradually increasing diameter when cupping a metal sheet in order to increase the height of the cupped metal.

Spinning

The cold forming method of creating hollow metal object by pressuring a sheet of metal against a rotating former with a roller.

Sand, gravity die, pressure die, investment

4 types of metal casting

Sand casting

The casting method of pressing a former into tightly packed sand to create a mould of the desired piece, then casting into the sand

Gravity die casting

The casting method of casting into a metal mould to create a repeatable shape.

Pressure die casting

The casting method of using a metal mould and hydraulic ram to force the molten metal into the mould.

Investment casting

The casting method of creating a wax version of the desired shape, coating it in a layer of clay, then firing it in the kiln, burning the wax and leaving a clay mould of the desired product to be metal cast.

Natural barrier

A protective layer around a metal which forms naturally when exposed to air to prevent it from oxidising and corroding

Applied barriers

Painting, varnishing, sealing, preseratives, powder coating, dip coating, galvanising, electroplating, anodising, cathodic protection

Painting

The finishing method of covering the primed metal in a layer of colourful and/or textured paint.

Varnishing

The finishing method of brushing or spraying on a protective, clear coating onto the metal.

Sealing

The finishing method of applying a polymer-based coating to the metal to prevent corrosion and tarnishing.

Preservatives

The finishing method of using a metal preservatives to provide them atmospheric protection and prevent condensation

Powder coating

The finishing method of applying a coating of powder to a statically charged metal piece, then baking the piece so the powder metls and forms a tough, hard skin around the product.

Dip coating

The finishing method of dipping the metal product into liquid polymer to create an even layer of protective polymer coating.

Galvanising

The finishing method of coating a metal in a layer of zinc to protect it against corrosion or oxidisation.

Electroplating

The finishing method of using electrolysis to coat a metal part.

Anodising

The finishing method of creating a protective layer on a metal by a process similar to electrolysis, with the product being coated acting as the positive anode.

Cathodic protection

The finishing method similar to electroplating, with the product being coated acting as the negative cathode, using a more actively corroding metal as a sacrifical anode.