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METALS - Processes - Coggle Diagram
METALS - Processes
Forming
Press forming - shapes sheet metal into 3D forms. often uses low carbon steel and aluminium. Common in mass production or large scale batch production due to cost of producing the dies. Dies are made from hardened steel, spark eroded and hand burnishes to give a high quality surface.
Spinning - a way of forming sheet metal giving radial symmetry. e.g objects like kettles and saucepans. Used in mass/ batch production
Cupping and deep drawings - used to form tube like shapes from sheet material. e.g fire extinguishers and aerosol cans are made in this way. deep drawing is when the depth of pressing exceeds the diameter.
corners of punch are rounded so metal stretches instead of shearing. high set-up costs of the hydraulic press and dies mean it is best suited to mass or continuous production
Forging/ Drop forging - Used to shape a hot metal. This is used when metal needs to be tough/ hard. objects such as spanners, pliers, etc. are made like this. Hot metal forced into shape under great pressure, therefore retaining the original grain structure. Suitable for mass production, however dies can be changed quickly to allow varied production.
Bending - press brake used for bending sheet/ plate of metal. stock material clamped between punch/ die. brake holds metal.
Rolling - reduce thickness of materials. makes structural steels like 'I beams'. Hot melt that's been heated above recrystallisation temperature. can result in surface carbon deposits. gives fine tolerance.
Sand Casting - used to form high melting point metals. carried out in foundries. its a slow/ labour intensive process. used for things such as engine blocks, post boxes, and used for one off/ batch production. Pattern used to make mould, complex solid/ hollow parts can be cast but need careful finishing.
Die Casting - used for metals with lower melting point e.g. aluminium, pewter, zinc. Tool steel used for reusable dies. used for mass production and gives a high quality finish. e.g gravity die casting/ high pressure die casting.
Investment casting - used to cast items with awkward shapes. uses brass, stainless steel and carbon steels. produces high quality products with excellent finish, repeatability is achieved because wax patterns are cast from a master mould
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Joining
MIG welding - (metal inert gas welding) is used to weld thin gauge metal such as aluminium and some steels. Heat is generated by electric arc. Workpiece must be clamped. e.g chimney frames, bike frames. Filler wire acts as an electrode which mlts in arc and fills the gap.
TIG welding - (tungsten inert gas welding) is used to weld stainless steel, aluminium and copper alloys. It's an electric arc welding process, however the tungsten electrode doesn't melt in the process, a filler material is added separately. Uses a gas shield (to stop oxidation) of argos and helium. This is a more controlled/ accurate weld.
Spot welding - welds sheet material together without filler material. Heat and pressure applied to area to be welded. Contacting metal surfaces joined by heat generated from resistance to electric current. Workpieces held together under pressure exerted by electrodes.
Oxy-acetylene - used to weld low carbon steel sheet, tube or plate. It mixes two high pressure gases (oxygen and acetylene) forming a very hot and intense flame (3500 degrees). Flame is adjusted by changing the gas mixture enabling flame cutting, welding or brazing.
Soft soldering - uses low melting point metals (solder) to join other metals together. Solder is a tin/lead alloy with low melting point. used in plumbing/ electronics.
Hard soldering - uses higher temperature. used to join precious metals like gold and silver. requires parent metal to be clean/ have no gap. Flux must be applied which stops metal oxidising.
Brazing - uses either oxy-acetylene flame or gas and compressed air brazing hearth. Needs a lower temperature than welding because the brazing rod melts at around 850 degrees, so joint isn't as strong. Can join dissimilar metals.
Rivets - semi-permanent joining method used to join sheet or plate metal. they are metal fasteners with a head at one end and a shaft/ tail at the other. Cold - formed rivets require access to both sides of material.
Pop rivets are quicker and easier but aren't as strong. they need a pop rivet gun. they're ideal when underside of joint is inaccessible. a form of pop rivets is used in aircraft production to join sheet aluminium to structural parts.
Screws - self tapping screws cut their own thread as they're screwed. Machine screws are a type of bolt with find threat. Used on motor and gear housings and many electric product casings. E.g cheesehead, round head, countersunk. Nuts and bolts are similar to machine screws. the nut is tightened at the other end by bolts.
castle/ nyloc nuts = don't work loose
wing nuts = loose work.
Wasting
Removal of material by cutting.
Milling machines - modern can cut on
many axis and work with CNC. some use
multi-tooled cutters to waste the workpiece.
Can be used to make holes, chamfers, slots,
joints and large flat surfaces,
Turning - metal is held with 3 or 4 jaw chuck in headstock whilst cutting tool is moved in axis. Centre lathes use single point cutting tools usually made from HSS or silicon carbide. Manual turning can produce bespoke/ one off items. CNC lathes can be used in mass/ batch. CNC lathes use multi-tool heads which change tools automatically for a given task
Flame cutting - uses oxyacetylene gas and a flame cutting torch to focus a flame up to 3500 degrees. Oxygen intensifies flame and forces molten metal out. used to cut low carbon/ alloy steel plate.
Plasma cutting - plasma is an ionised gas that's electrically conductive as high temps. generates a fast/ clean cut. can be as high as 28000 degrees. e.g cutting steel plate/ bespoke gates. process - manual or CNC arc sent through gas.
Metal laser cutters - high powered laser beam, directed through optics at workpiece on laser bed. laser melts metal/ compressed air. Very accurate because only fine laser.
Punching/ stamping - pierces a metal sheet. Blanking creates cut out parts for further processing/ recycles original punched sheet
Finishing
Ferrous metals rust over time. some non- ferrous metals corrode.
Cellulose and acrylic paint - give both colour and barrier from corrosion. must be degreased/ prepared. for cellulose more coats are needed. e.g bicycles and window frames/ car bodies
Electroplating/ galvanising - electroplating uses desired metal to coat a base metal. more aesthetic. negative electrode = must be plates. positive electrode = coating metal. Galvanising = coat iron/ steel with zinc, forming zinc carbonate which is tough and no corrosion.
Sealants and preservatives - block passage of air/ fluids through metal joints. prevent decay/ erosion. Applied through electrostatic boding. e.g machine beds to provide smooth frictionless surface.
Anodising, plating, coating and powder coating - used on aluminium to provide hard wearing corrosion resistant surface. aluminium is immersed in electrolyte bath and current passed. Plating is done using physical vapour deposition. powder coating is more hardwearing that paint.
Cathodic protection - sacrificial anodes used to control corrosion of surface. an easily corroded sacrificial metal bonded to surface which corrodes e.g fuel pipelines, boat hulls