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.