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Material Processes

Introduction

  • Manufacturing processes are categorized into:

    • Forming: Includes wasting and deforming.

    • Redistribution: Includes casting and moulding.

    • Addition: Includes additive processes and fabrication.

  • Examples:

    • Wasting/Deforming: Cutting, drilling, bending.

    • Casting/Moulding: Die casting, injection moulding, extrusion.

    • Additive/Fabrication: Welding, joining, 3D printing.


Redistribution

  • Material is moved around to shape it into a product.

  • Two methods:

    • Deforming: Changing shape without changing the material's state (remains solid).

    • Reforming: Changing the material's state (e.g., solid to liquid and back to solid).

Deforming
  • Changing the shape of a material without altering its state (remains solid).

  • May involve heat and/or pressure.

  • Wood:

    • Generally not suitable for deforming due to its natural state and strength.

    • Exceptions: Steam bending, kerfing, laminating.

  • Thermoplastic Polymers:

    • Soften at relatively low temperatures, making them easy to deform.

  • Metals:

    • Relatively easy to deform with heat and pressure.

Deforming Wood
  • Typically, wood is joined rather than deformed.

  • Steam Bending:

    • Wood is bombarded with steam until flexible, then bent into shape.

    • Held in place while water content is slowly removed.

    • Traditionally used for Windsor chairs.

  • Kerfing:

    • Grooves are cut into the wood to facilitate bending.

    • Technically a wasting process.

    • Used for guitar and violin shells.

  • Laminating:

    • Thin sheets of wood (veneers) are glued together and placed in a mould.

    • Retains the mould's shape once the glue sets.

    • Used to make skateboards.

Deforming Metal
  • Metal is well-suited to deformation with pressure and heat.

    • Bending and Folding:

      • Can be done cold or hot.

      • Sheet metal can be folded like plastic but needs high-pressure machinery.

    • Spinning:

      • A disc of metal is rotated at high speed and formed into a symmetrical part.

      • No material removal; the metal is moulded over an existing shape.

      • Applications: rocket nose cones, cookware, gas cylinders, musical instrument bells, waste receptacles.

    • Sinking:

      • Flat sheet metal is formed into a non-flat object by hammering.

      • Stretches and thins the metal, risking failure if sunk too far.

      • Used in jewelry and plate armour manufacture.

    • Punching:

      • A punch press forces a tool (punch) through the workpiece to create a hole via shearing.

      • A scrap slug is deposited into a die.

      • Cost-effective for creating holes in sheet metal in medium to high production volumes.

      • Blanking:

        • A shaped punch creates multiple usable parts from a sheet of material.

    • Blanking and Piercing:

      • Shearing processes using a punch and die. Tooling and processes are the same, but terminology differs.

        • Blanking: punched out piece is used.

        • Piercing: punched out piece is scrap.

      • Parts manufactured with both techniques are termed 'pierce and blank'.

      • Piercing can also be called punching.

    • Forging:

      • Shaping metal using localized compressive forces.

      • Classified by temperature: cold, warm, or hot forging.

      • Forged parts range from less than a kilogram to 580 metric tons.

      • Usually requires further processing.

    • Drop Forging:

      • A hammer is raised and dropped onto the workpiece to deform it according to the die shape.

      • Two types: open-die and closed-die drop forging.

    • Drawing:

      • Uses tensile forces to stretch metal.

      • Two types: sheet metal drawing and wire, bar, and tube drawing.

        • Sheet metal drawing: plastic deformation over a curved axis.

        • Wire, bar, and tube drawing: stock is drawn through a die to reduce diameter and increase length.

      • Usually done at room temperature (cold working), but can be done at elevated temperatures (hot working).

    • Deep Drawing:

      • Sheet metal forming process where a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch.

      • Sheet metal is drawn into a die.

      • 'Deep drawing' when the depth exceeds the diameter; achieved by redrawing through a series of dies.

      • Used to make aluminium drink cans.

    • Press Forming:

      • Sheet metal process using a die inside a press.

      • High pressure (3000+ tons) is applied to form the material to match the die shape.

      • Used for white product cases (fridges) and car body parts.

Deforming Polymers
  • Polymers are commonly formed due to their ease of softening and solidifying at low temperatures.

    • Line Bending:

      • A small area of plastic sheet is heated to allow folding or bending around a former.

    • Vacuum Forming:

      • A heated plastic sheet is draped over a former, and a vacuum removes air below.

      • Gravity forces the plastic onto the former.

      • Used for hollow 'shell-like' items like yoghurt pots, baths, and moulds.

    • Vacuum Forming Mould Characteristics:

      • Sides should slope outwards (draft angle) for easy removal.

      • No sharp edges (radius edge) to prevent thinning.

      • Air holes to avoid trapped air.

      • Sufficient space between peaks to avoid webbing.

    • Thermoforming:

      • Similar to vacuum forming but uses an outer mould for greater detail, lettering, and sharp edges.

    • Blow Moulding:

      • Forms hollow plastic parts.

      • Plastic is melted and formed into a parison (tube-like piece with a hole).

      • The parison is clamped into a mould, and air is blown into it.

      • The plastic expands to match the mould, cools, hardens, and is ejected.


Reforming

  • Changing the shape of a material by changing its state (solid to liquid to solid).

Reforming Wood
  • Wood isn't typically reformed, but:

    • In a pulped state, it can be mixed with resin to make MDF.

    • Paper and board are sourced from wood and can be shaped when reformed into egg boxes.

Reforming Polymers
  • Commonly formed due to the ease of transitioning between liquid and solid states at low temperatures.

Reforming Metals
  • Commonly reformed as they are originally processed in a liquid state.

    • Sand Casting:

      • Uses sand as the mould material.

      • Over 70% of metal castings are produced this way.

      • Sand is mixed with a bonding agent (clay) and moistened.

      • The mixture is compacted around models to create mould cavities.

      • A slow process because the sand mould must be broken up to remove the cooled metal object.

    • Die Casting:

      • Molten metal is forced under high pressure into a mould cavity.

      • Mould cavity is created using hardened tool steel dies.

      • Most die castings are made from non-ferrous metals (Zinc, Copper, Aluminium, Magnesium, Lead, Pewter, and Tin-based alloys).

      • Uses hot- or cold-chamber machines depending on the metal.

      • High capital costs limit the process to high-volume production.

      • Simple, four-step manufacturing process keeps incremental cost per item low.

      • Suited for large quantities of small to medium-sized castings.

      • Characterized by good surface finish and dimensional consistency.

    • Gravity Die Casting:

      • Uses gravity to force molten material into the mould.

    • Pressure Die Casting:

      • A ram forces molten metal into the former using a hot or cold chamber.

      • The additional pressure ensures greater accuracy and detail.

    • Industrial Die Casting:

      • Uses multi-slide die castings; traditional die casting only uses two halves, limiting shape complexity.

      • Four or more slides enable complex 3D shapes.

    • Lost Wax Casting:

      • A metal object (often Pewter, Silver, Gold, Brass, or Bronze) is cast from an original wax sculpture.

      • Intricate works can be achieved.

      • The mould is destroyed to remove the cast item.

      • In modern industrial use, the process is called investment casting.

    • Extrusion:

      • Creates objects of a fixed cross-sectional profile.

      • Material is pushed or drawn through a die of the desired cross-section (hot or cold).

      • Commonly extruded materials include metals, polymers, ceramics, concrete, play dough, and foodstuffs.

Reforming Polymers
  • Commonly reformed due to their ease of transitioning between liquid and solid states at relatively low temperatures.

    • Injection Moulding:

      • Material is injected into a mould cavity, where it cools and hardens.

      • Can be performed with metals, glasses, elastomers, confectionary, and most commonly thermoplastic polymers.

      • Moulds are made from steel or aluminium and precision-machined.

      • Widely used for manufacturing parts, from small components to car body panels.

    • Rotational Moulding:

      • A heated hollow mould is filled with a charge of material and slowly rotated.

      • The softened material disperses and sticks to the walls.

      • Continuous rotation during heating and cooling maintains even thickness and avoids deformation.

      • Shapes can be hollow with thick walls.

    • Compression Moulding:

      • A preheated moulding material (thermosetting polymer such as Urea Formaldehyde) is placed in an open, heated mould cavity.

      • The mould is closed with a top force, and pressure is applied.

      • Heat and pressure are maintained until the material has cured.

      • Used for complex, high-strength fiberglass reinforcements.

      • One of the lowest cost moulding methods with relatively little material waste.

    • Resin and GRP Moulding:

      • Not strictly a reforming process, but involves using a liquid polymer (Resin) that cures and sets hard.

      • Combined with glass strips (GRP) to reinforce the resin.

    • 3D Printing:

      • An additive process that builds a 3D shape by adding layers of plastic.

      • The molten plastic makes it essentially a reformation process, but it's considered additive.

      • Can print metal, food, and body parts.

Summary

  • Redistribution involves moving material to shape it, either by deforming or reforming.

  • Reforming is mainly used with metal and plastics.

  • Wood can be reformed into MDF, Chipboard and Maplex but can be deformed by steam bending or laminating.

  • Most complex plastic components are made by moulding.

  • Plastic bottles are commonly made by deforming.

  • Terms are not rigid; 3D printing is additive but involves melting the polymer filament, potentially considered reforming.


Fabrication Processes

  • Joining like or unlike materials (additive process, opposite of wasting).

  • Wood and metal are often fabricated; plastic is more commonly formed or moulded.

  • Two main types:

    • Temporary (T): can be dismantled.

    • Permanent (P): fuses materials together.

Fabrication in Wood
  • Commonly used method.

  • Typically permanent if nails or glue are used, otherwise, they can be dismantled.

  • Many types of wood joints; can combine different types for reinforcement.

  • Wood joints fall into two categories: frame joints and box joints.

  • Frame Joints

    • Corner halving

    • Cross halving

    • Dowel joint

    • Mitred bridle

    • Dovetail halving

    • Bridle joint

    • Tee Halving

  • Box Joints

    • Dovetail nailing

    • Dovetail Plywood

    • Housing Joints

    • Veneer keys

    • Mitre joint

    • Butt joint

Wood Glues
  • Wood (porous) joins with resin, polymer, and water-based adhesives.

    • PVA (Polyvinyl Acetate): Most common; requires clamping while setting (hours).

    • Cascamite: Resin-based powder (mix with water); ideal for laminating/veneering.

    • Gorilla Glue: Strong adhesive; requires wetting surfaces before clamping; expands like foam for a strong joint.

Fabrication in Metal
  • Versatile material (hot or cold); fabrication is common.

  • No common metal joints; fused/welded or joined using screws, rivets, and bolts.

    • Crimping (P):

      • Joins thin sheets using folded edges pressed together by rollers.

      • Can be reinforced by welding.

    • Soldering (P):

      • Joins metal items by melting solder (Tin and Lead alloy) into the joint.

      • The solder has a lower melting point (180^{\circ}C) than the adjoining metal.

      • Suitable for intricate work (circuit boards).

    • Silver Soldering (P):

      • Joins precious metals (Gold, Silver, Brass, and Copper).

      • Solder is classified as easy, medium, or hard, based on melting temperature (not strength).

      • Extra - easy solder
        56% Silver, Meltsat1, 618 degrees C

      • Extra - hard solder
        80% Silver, Meltsat1, 740 degrees C

      • Small pieces of solder wire are placed onto the metal before heating.

      • Flux is used to keep the metal and solder clean.

      • The joint is stronger than the base metal, requiring perfectly flush pieces because silver solder cannot fill gaps.

    • Brazing (P):

      • Joins metal by heating a filler metal above its melting point and distributing it between close-fitting parts.

      • Protected by a flux; used for decorative work as the soft (Brass) brazing rod is easier to file to shape.

    • Welding (P):

      • Joins materials (metals) by melting the workpieces and adding a filler material to form a weld pool for a strong joint.

      • Several types are used, depending on the job and material.

        • Gas Welding (P):

          • Uses Oxygen and Acetylene gases; filler material is like brazing but at a higher temperature.

          • The metal is heated until white hot, then welding rod is added.

          • Slower but yields a neater finish; inexpensive equipment without an electrical supply.

        • Arc Welding (P):

          • Uses an electric arc between an electrode and the base material.

          • The welding region is protected by shielding gas, vapor, or slag.

          • Important for steel structures and vehicles.

        • MIG Welding (P):

          • Metal Inert Gas (MIG) or Metal Active Gas (MAG) welding.

          • Uses a consumable wire electrode and shielding gas (usually Carbon Dioxide) to weld steel.

        • TIG Welding (P):

          • Tungsten Inert Gas (TIG) welding.

          • Uses a non-consumable tungsten electrode. Shielding by an inert gas such as Argon, and a filler metal is normally used.

          • Typically used to weld thin sections of Stainless Steel and non-ferrous metals (Aluminium, Magnesium, and Copper alloys).

          • Greater control over the weld; stronger, higher quality welds. This is a skilled process which is difficult to master, and furthermore, it is significantly slower than most other welding techniques.

        • Spot Welding (P):

          • Joins contacting metal surfaces using heat from resistance to electric current.

          • Shaped copper alloy electrodes concentrate welding current into a small ‘spot’, simultaneously clamping the metal sheet together.

Metal Glues
  • Metal must be meticulously cleaned since its non-porous and difficult to manage using adhesives, however, Epoxy Resin may be used.

    • This adhesive is stronger than a welded joint.

    • Domestic version is commonly sold in hardware stores and is known by the brand name Araldite. 2-part glue with resin and hardener is needed.


Fabrication in Polymers
  • Polymers can be welded (P) using a heat gun or plastic welding or glued together with Tensol Cement or Polystyrene Cement (lightly melts surfaces).

Fixtures and Fittings
  • Nails (P)

    • Reinforce joints or quickly join wood.

    • Not for metal; likely to crack plastic.

    • Different shapes/sizes.

  • Screws (T)

    • Pass through one material, screw into another; act as a clamp.

    • Wood screws vs. self-tapping screws (metal/plastic).

    • Countersunk, dome, and pan heads;

  • Nuts and Bolts (T)

    • Join materials by passing through holes, clamping them.

    • Washers protect surfaces.

    • Different lengths/gauges/styles (glass/concrete).

  • Rivets (P)

    • Clamp materials like nuts/bolts; require drilling/boring for removal classified as permanent.

    • Traditionally Iron (heated red hot).

    • Now Aluminium pop rivets.

  • Hinges (T&P)

    • Allow parts to hinge or swing.

    • Attach through gluing/welding (permanent) or screws/bolts (temporary).

  • Knock Down (KD) Fittings (T)

    • Modern invention for flat pack furniture (temporary fixing).

  • Other Adhesives (P)

    • Araldite for gluing unlike materials.

    • Contact adhesive for laminates to wood.

  • Multi-Purpose Adhesives (T)

    • Araldite, Gorilla Glue, Bostick and UHU, Superglues, Copydex (fabrics/paper).

Adhesive Compatibility
  • A chart to match adhesives to material combinations including paper, plastic, and wood.

Summary of Processes
  • A table summarizing: Wood, Metal, Plastic, Paper, Glass, Fabric.

    • Material vs process/techie

    • Wasting, Redistribution, Fabrication.

Summary of the Unit

  • Fabrication joins materials permanently or temporarily.

  • Methods vary for like or unlike materials.

  • Fabrication joins parts unless moulded/cut into shape.

  • Wood and metal use fabrication; plastic easily moulded.

  • Furniture uses flat pack fittings (KD fittings).

  • Welding and brazing permanently join metal.


Wasting Processes

  • The object or component is shaped by material removal (subtractive).

  • Can be wasteful; some materials (metals, polymers) are recyclable, but wood waste isn't always usable.

  • Processes presented in the order of waste produced (guideline only).

Lathes
  • Used for wood, metal, polymers, styrofoam.

  • Wood lathe (wood) or centre lathe (metal/polymers): the material rotates.

  • A cutting tool shapes the material by moving left to right and towards the centre.

  • CNC versions allow greater speed and accuracy.

Chiseling and Carving
  • Only suitable for wood (cold chisel on sheet metal).

  • Flat chisels - used to remove wood for making joints.

  • Gouging chisels can be used for carving.

Milling
  • For metal and plastic.

  • Uses rotary cutters to remove material.

  • Traditional milling moved in three axes manually; CNC machining is now computer controlled.

Die Cutting, Creasing, and Folding
  • For paper and board.

  • Products like fold-flat cardboard packaging are made from a flat sheet and are cut and creased with a die.

Routering
  • For wood and plastic.

  • Rotary cutters remove material but for softer materials such as wood, foam, and some metals.

  • CNC-operated or handheld form:

    • Plunge router (profile on the edge or cut shapes).

    • Table-mounted (user feeds the material into the cutter).

Planing
  • For wood.

  • Shaving away at the wood with a sharp blade mounted into the plane's body.

Cutting
  • Wood saws (hand saws).

  • Metal saws.

Drilling
  • For wood, metal, and plastic.

  • Holes in materials generally made by using a drill and a dril bit.

  • Different materials call for different types of drill bits and different speeds.

  • Metal should be slow and wood fast with plastic somewhere in between.

Filing
  • Used to apply a final shape to a product or to remove imperfections.

Abrasives
  • Products that affect the surface finish of a material.

  • On wood use glass/sandpaper to remove the rough surface and leave the wood smooth.

  • Wood, particularly after varnish or lacquer has been applied, receive a final smooth finish by using wire wool.

  • On metal you use emery cloth and/or silicon carbide (wet and dry) paper.

  • Many polymers used, such as Acrylic, are self finishing so do not need abrasives other than for cut edges.

  • File to shape, sand to finish= affect the surface finish and feel of the material rather than shaping it.

Summary of the Unit

  • Wasting is a subtractive process.

  • Because of the nature of wood, it is commonly shaped through wasting techniques.

  • Metal and plastic can exist in a molten state.

  • Wasting techniques are often the least environmentally friendly due to the amount of waste material.

  • There are a range of tools and processes that can be used to shape an object by removing material.

  • There are various abrasives used to affect the surface finish of materials.