Chapter 3 - Processes, techniques & specialist tools

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3.1 Heat Treatments

  • Hardening:
    • Medium & High Carbon steels are heated and then held at a certain temperature for a given time, then quenched in water, oil or saltwater baths
    • Process increases the hardness but also increases brittleness
  • Tempering
    • This reduces some excess hardness and brittleness from a hardened metal and increases the toughness and ductility
    • Metal is heated to below critical point for a given time then slowly air cooled
    • exact temp the metal is heated to will determine the amount of hardness removed
  • Annealing
    • The heating and slow cooling of work-hardened metal to make it easier to work, less brittle and more ductile
  • Normalising:
    • Used on low carbon steels to give the metal a uniform, fine-grained sturcture
    • Material is heated to about same temp as for hardening, quickly quenched then left to cool. Makes metal more ductile, with increased toughness
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3.1 Case Hardening

  • Case Hardening: 
    • Process hardens surface of steels which have <0.4 percent carbon content 
    • Produces outer surface which has improved hardness & resists indentation, while the inner core of the metal retains its original properties 
  • Case Hardening: Process:
    • Carburising: changes the chemical composition of the surface of low carbon steel so it can absorb more carbon to increase surface hardness
      • Steel is placed in ceramic box packed with carbon. Box is heated to approx. 930-950C, carbon atoms diffuse into the material's structure to build up the surface carbon content
      • Depth of carbon layer determined by the length of time the material is exposed to carbon
      • The longer the exposure, the thicker the carbon layer. The product is then heated to about 760C & then quenched
    • Quenching: Hot metal quenched in water to fast cool it and seal the hard surface case whilenot affecting inner core properties
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3.1 Alloying + Printing

  • Alloying:
    • Alloys are produced in either a furnace or in a casting process
    • The metals to be combined are melted together in specific quantities and then poured into bars or ingots to be used for future products 
  • Printing:
    • Flexography & offset lithography use a four-colour process: cyan, magenta, yellow and key (black) (CMYK)
    • The 4 colours are printed on top of each other in various quantities onto the material surface to create the print colour required
    • Colours must line up exactly to ensure a non blurry image
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3.1 Offset Lithography

  • Offest Lithography:
  • Process:
    • Versatile process capable of producing one colour [single roller], five colours [CYMK plus an additional metallic colour on a five-roller machine] and a ten feature machine [CYMK, metallic, varnishing, spot varnishing and duplex (both sides printed)] on a ten-roller machine
  • Uses:
    • Offset lithography is used for printing medium and long print runs of products such as books documents, magazines, posters and packaging
  • Advantages:
    • Consistently high-image quality
    • Higher volume print runs of 1000 or more
    • Long life of printing plates
  • Disadvantages:
    • Expensive set up and running cost for small quantities 
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3.1 Flexography

  • Process: 
    • Uses fast drying water-based inks
    • Ink transferred to the roller then transfered to the materila via pressure from the printing roller
  • Uses:
    • Newspapers, comics, catalogues, folding packaging cartons, labels, carrier bags and continuous pattern products such as wallpaper and gift wrap.
  • Advantages:
    • High print speed
    • Suited for long runs
    • Prints on a wide variety of substrate materials
    • Low cost of equipment and consumables; the least expensive printing process
    • low maintenance
  • Disadvantages:
    • Cost of the printing plates is relatively high, but last for millions of print runs
    • Time consuming to change for any alterations to the print content 
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3.1 Screen Printing

  • Process:
    • The screen has open areas for the ink to pass through
    • A different screen is required for each colour
  • Uses:
    • Used for small print runs of items such as posters, display boards and textile t-shirts
  • Advantages:
    • Minimal setup costs due to the use of basic screens & printing inks
  • Disadvantages:
    • A slow process with a reasonably high cost per product
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3.1 Gravure

  • Process:
    • Rotary printing process.
    • Image engraved or etched onto the rolling cyclinder
  • Uses: 
    • Used for high volume printing such as packaging, gift wrapping, wallpaper
  • Advantages:
    • Excellent print quality
    • High printing speed
    • Simple printing process
    • Can be used for CMYK printing 
  • Disadvantages:
    • Not economic for small print runs
    • Fine text lettering not as sharp as other processes
    • Expensive setup costs for making the cylinders
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Sand Casting

  • Sand Casting:
    • Split pattern is created. Half the pattern is placed in the moulding box (drag), with powder dusted over the pattern to help release it
    • Sand is pacted around the pattern and smoothed off
    • The drag is turned over and the cope, the runner and riser (Spruce pins) are put on top and the mould with the second half of the pattern is powder dusted
    • Sand is packed around the pattern, smoothed off and pouring basin created
    • The pattern, runner and riser are removed and channels and vents are put in to allow the metal to flow
    • The metal is poured into the hole left by the runner until it appears in the riser hole, it's the left to cool, the casting is removed and the waste is cut off
  • Used to make: railway carriage wheels, bollards, drain covers, vices,
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Investment casting

  • Step 1: tooling making: tooling or patterns are made normally using CNC
  • Step 2: wax injection and pattern assembly: Wax is then injected into the pattern to get a model with the same dimensions as the desired product
  • Step 3: Shell coating: The model is then dipped into a ceramic slurry and then while still wet, larger particles of cermaic coat the wet surface to build a thicker coat, this is then repeated until the shell thickness is appropriate 
  • Step 4: Dewax: The ceramic shell is put in a steam autoclave and rapidly heated so the wax is melted, then it gets fired (at approx 1000 degrees) to burn remove any more wax and to prepare it for casting 
  • Step 5: Casting or pouring: molten steel or aluminium is then poured into the mould and cooled under room temp
  • Step 6: Shell removing: Break ceramic shell & cut individual investment castings & remove excess metal through grinding
  • Step 7: Heat treatment + Shot/Sand Blasting
  • Step 8: Surface treatment + quality control
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Blow Moulding

  • Step 1: Heated plastic is extruded into hollow tube (parison)
  • Step 2: Mould closes and parison is gripped in place
  • Step 3: Compressed air blown into parison which inflates 
  • Step 4: Parison fills mould
  • Step 5: Product is trimmed and removed from mould
  • Stpe 6: Final product is ready for finishing
  • Has high initial tooling cost
  • Used for contniuous production
  • Used to make: Bottles 
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Injection moulding

  • Step 1: Plastic granules fed via hopper (funnel) into barrel and heated to a molten state
  • Step 2: Heated plastic fills barrel & archimedes screw pushes molten to mould while under even heating
  • Step 3: the screw then injects molten plastic at high pressure into the mould cavity
  • Step 4: Then the plastic product is allowed to cool and solidify before being ejected from the opened mould
  • Complex 3D shapes can be quickly and easily made
  • Fast industrial production method 
  • High initial tooling costs
  • Used for large scale mass or continuous production
  • Used to make: Electrical prouct casings {computers, TVs vacuum cleaners, calculators, etc}
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Rotational Moulding

  • Step 1: Moulding tool made normally from aluminium or steel
  • Step 2: Polymer powder placed in tool which is locked and loaded into oven
  • Step 3: Tool rotated on 2 axes, distributing polymer evenly
  • Step 4: Tool heated at a controlled rate and polymer sticks to the inside 
  • Step 5: As it's rotated simultaneously on 2 axes an even coating builds up
  • Step 6: Tool rotated for long enough to ensure product is properly formed with no air bubbles which could weaken its structure
  • Step 7: Tool cooled down using air jets, water mist or water spray
  • Step 8: Open the mould and remove the product
  • Produces seamless hollow components with a large wall thickness.
  • The mould is continuously rotated through heating and cooling stages.
  • Used in large-scale batch or mass production. 
  • Uses thermoplastic powder or granules.
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3.4 Adhesives

  • Adhesives are used to stick materials together.
  • Contact Adhesive:
    • Used for bonding large areas such as sheet materials
    • Can join same or different materials together i.e. wood sheet to wood sheet, metal sheet to wood sheet, metal sheet to polymer sheet, etc
    • The 2 surfaces are coated in contact adhesive and left for a few mins until the adhesive feels 'tacky'. On contact with other surface, adhesive is instant
  • Acrylic cement:
    • A clear liquid used to join polymers i.e. acrylic
    • Softens the surface of the polymers to be joined, allowing them to fuse together
  • Epoxy Resin:
    • A 2-part adhesive (resin & hardener) which is mixed together in equal parts 
    • Used to join diff materials together i.e. timber to metal, metal to polymer, polymer to timber.
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3.4 Adhesives

  • Polyvinyl acetate (PVA):
    • White liquid water-based adhesive used to join woods & wood composite materials
    • Not usually a waterproof adhesive 
    • Can be used to bond wood joints together for furniture & other wooden products
  • Hot melt glue:
    • Cylindrical solid stick of adhesive metled in a hot glue gun and applied
    • Can be used to join diff material i.e. papers, boards, plastics, metals & woods
    • Not a structurally strong adhesive, mostly used in model making & industrially by electronic device manufacturing to keep wires & circuit boards in place
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3.4 Adhesives

  • Cyanoacrylate (superglue):
    • Clear liquid used to join diff materials together such as plastic to metal
    • Fast acting adhesive which works best in the prescence of slight moisture 
    • Reacts with the moisture to create a very tight & instant bond 
    • Can instantly bond skin together so care required
    • Due to dangers of skin bonding, it's not used in some schools & colleges
  • Polystyrene cement:
    • clear gel consistency liquid used to join rigid polystyrene polymers
    • softens the surface of the polymers to be joined, allowing them to fuse together when the cement hardens
    • Adhesion isn't instant on contact, allowing parts to be positioned before the adhesive dries
    • Primarily used in model making assembly kits 
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3.4 Mechanical Joining

  • Screws - Features:
    • A clearance hole is drilled in the top part to be joined and a pilot hole is drilled into the botom part to be joined. This aids the screw to bite into the material to create the join.
    • Self tapping screws need a clearance hole but cuts its own thread to make the join
  • Screws - Uses:
    • For joining wood or metal to wood, or, wood to sheet polymer
    • Self tapping screws can be used to join thin sheet metal
  • Rivets - Features:
    • Riveting uses 2 pieces which are overlapped & drilled, then hammered over to join. Pop riveting uses a rivet gun (or riveting pliers) & a rivet & pin
  • Rivets - Uses:
    • Used to join thin sheet metal together
    • Pop rivets join thin sheet metal but are useful for where the underside of the joint is innaccessible
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3.4 Mechanical Joining

  • Uses off the shelf parts to create joins which make product disassembly easier
  • Nuts, bolts and washers - Features: 
    • The bolt sits in a clearance hole drilled through both parts to be joined
    • The bolt usually has a washer and then a nut on the threaded end to be tightened and create the join 
    • Washers spread the load aplied by the nut and prevent material damage from the nut being tightened
  • Nuts, bolts and washers - Uses:
    • Joins materials for disassembly or to allow access for repair
  • Press Joining - Features:
    • Material to be joined is placed in a machine & pressed between a punch & a die
    • Under pressure the metal deforms into an interlocked shape
    • Press  joining isn't as strong as riveting
  • Press Joining - Uses:
    • Joins thin ductil sheet metals together, more often used for bulk sheet metal applications.
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3.4 Heat Joining

  • Oxy-acetylene welding:
    • Uses a steel filler rod to create the weld 
    • Useful for repair jobs in remote locations where there's no electricity supply 
  • Uses: Used to weld mild steel sheet, tube or plate
  • Brazing (Hard soldering):
    • Uses a brass filler rod using either oxy-acetylene or a gas/compressed air brazing hearth
    • Suitable for one off production or small batch
    • Brazing Joins dissimilar metals i.e. mild steel sheet to aluminium or copper
  • Uses: Lower temperature than welding, so is suitable for joining thinner gauge mild steel tube or bar
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3.4 Heat Joining

  • MIG welding:
    • Uses an electrode wire with an inert gas i.e. Co2 or argon
    • Suitable for thin gauge metals, medium carbon steel or aluminium
  • Uses: Tubular products i.e. climbing frames, bike frames, vehicle exhausts
  • Soft soldering:
    • Generally joins copper or brass for light use applications
    • Uses a filler rod to flow between the metal surfaces to create the join 
    • Carried out in a brazing hearth or with a gas torch or a soldering iron for electronics
  • Uses: Lower temperature than brazing, used for joining copper piping in plumbing, jewellery, brass musical instruments, electrical components
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3.4 Jointing & knock down fitting

  • Comb/finger joint: Used for box construction, decorative edge joining
  • Housing joint: For framework construction, cabinets and shelving
  • Half lap joint: For simple frames or boxes
  • Dowel joint: For lightweight shelving or coner joining (bookcase or wardrobe)
  • Mortise and tenon joint: Frame constrcutions for tables, chairs
  • Knock down fittings allow products to be assembled and disassembled numerous times, without weakening the joint
  • Often used in flat-pack furnitureproducts which allows the user to build the product with minimal skill & without specialist tooling
  • Allows ease of transportation from store to home or when moving furniture to anoter loaction
  • Examples of knock down fittings: Corner blocks, CAM lock fittings, Barrel and screw, Cabinet hinges
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3.5 Paper and board finishing Process

  • Lamination:
    • Encapsulation: a desktop laminator and the seet of paper is encapsulated by a polymer pouch or film roll
    • Surface coating: liquid lamination (for signage) or film lamination (menu cards)
  • Embossing: 
    • Creates a raised design on the usrface of the paper or card to give a pleasing visual tactile effect 
    • Used for greeting cards, chocolate box lettering, letterheads
  • Foil Blocking: 
    • Heat & pressure applied to a metallic paper (foil) to create areas of depth and texture to add aesthetic impact
    • Used for greetings cards, letterheads, metallic cards
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3.5 Paper and board finishing Process

  • Varnishing:
    • clear ink used to enhance the colour and offer some protection against dirt, finger prints and water
    • UV varnishing: Provides a very smooth finish, usually high gloss or matt, & abrasion & chemical resistant. applied to a sheet via a set of rolers, then passed under UV light to cure
    • spot varnishing: Applied in specific areas or spots instead of the whole surface area
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3.2 Jigs and Fixtures (To be completed)

  • Jigs and fixtures are used in speeding up marking out & machining processes & also help to maintain repeated accuracy
  • A jig holds the work and guides a tool, eliminating the need to repeatedly mark out
  • Drilling jig csan be made to guide drill into correct position on material without marking out. - Allows less skilled workers to carry out task, makes task quicker and removes time for marking out 
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