Which processes shape plastics, metals and timbers into products, and how does a designer choose the right one?
Manufacturing processes for shaping materials: moulding and forming processes for polymers, casting and forming processes for metals, and cutting, shaping and joining for timbers, and matching a process to the material, form and scale of production.
An SQA Higher Design and Manufacture answer on manufacturing processes, covering moulding and forming of polymers (injection moulding, vacuum forming, blow moulding), casting and forming of metals, and shaping and joining of timbers, and how a designer matches a process to the material, the form and the scale of production.
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What this key area is asking
The SQA wants you to know the main manufacturing processes that shape the three material groups, to describe how the key ones work, and to explain why a process suits a given material, form and scale of production. The question paper often asks you to describe a process (especially injection moulding or vacuum forming) and to justify why it suits a product, for 4 to 6 marks.
Processes for polymers
- Injection moulding
- Thermoplastic granules are heated and melted in a barrel by a rotating screw, then injected under high pressure into a closed steel mould; the part cools, the mould opens and ejects it, and the cycle repeats. It makes complex, accurate parts in one step and is fast and automated, so it is ideal for mass production, but the steel mould is expensive, so it is only economic at high volume.
- Vacuum forming
- A thermoplastic sheet is clamped, heated until soft, and drawn down over a mould by sucking out the air beneath it; it cools to the mould shape. It makes thin-walled, shallow shapes (trays, packaging, casings) with cheap wood or resin moulds, suiting lower volumes and prototypes, but only open, fairly simple shapes.
- Blow moulding
- A tube of molten thermoplastic is inflated with air inside a mould so it takes the mould's shape, making hollow products such as bottles and containers quickly and cheaply in volume.
Processes for metals
Casting makes complex shapes (engine parts, fittings) by filling a mould with molten metal. Forming reshapes solid metal: pressing and deep-drawing make car panels and cans, forging makes strong tools and spanners. Machining removes metal to make precise parts and is flexible but slower and wasteful, so it suits small numbers or finishing.
Processes for timbers
Timber is shaped by cutting and shaping (sawing to size, planing flat, routing profiles, turning round work on a lathe) and joining (frame and box joints such as mortise-and-tenon and dovetail, plus knock-down fittings, glues, screws and nails). Manufactured boards are cut and routed cleanly, often on CNC machines, which suits batch production of identical panels.
Matching the process to material, form and scale
The right process depends on three things together:
- Material - most plastic moulding needs a thermoplastic; casting needs a metal with a suitable melting point; timber processes suit wood and boards.
- Form - injection moulding suits complex solid parts, vacuum forming suits thin shallow shapes, blow moulding suits hollow shapes.
- Scale of production - high-tooling-cost processes (injection moulding, die casting, pressing) are economic only at high volume; cheap-tooling processes (vacuum forming, sand casting, hand jointing) suit one-offs and low volumes.
Where this fits in the course
Manufacturing processes are central to the Materials and Manufacture area and link directly to the material groups and to scales of production. The question paper asks you to describe and justify processes, and your design assignment must explain how your outcome would be manufactured. Knowing the stages of the key processes and matching them to material, form and scale earns marks in both.
Try this
Q1. Describe the main stages of injection moulding. [4 marks]
- Cue. Granules melted in a heated barrel by a screw, injected under pressure into a closed steel mould, cooled and solidified, mould opens and ejects the part, cycle repeats.
Q2. Explain why vacuum forming is chosen over injection moulding for a low-volume packaging tray. [4 marks]
- Cue. Cheap wood/resin moulds and a simple set-up make it economic at low volume; it suits thin, shallow open shapes.
Q3. Explain why casting is used to make a complex metal component such as a vice body. [3 marks]
- Cue. Molten metal fills a mould to form a complex shape in one piece, which would be hard and wasteful to machine from solid.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher6 marksExplain why injection moulding is suited to the mass production of a plastic product, and describe the main stages of the process.Show worked answer →
Worth about 6 marks, so the marker wants the process described in stages
plus reasons it suits mass production. The mark scheme rewards both the
sequence and the link to high-volume manufacture.
The stages. Thermoplastic granules are fed into a hopper, then heated and
melted in a heated barrel as a rotating screw moves them forward; the
molten plastic is injected under high pressure into a closed steel mould;
it cools and solidifies to the mould shape; the mould opens and the part
is ejected, and the cycle repeats.
Why it suits mass production. Once the expensive steel mould is made, each
cycle is fast and largely automated, so thousands of identical, accurate
parts are produced quickly at low cost per item, spreading the high tooling
cost over a large run.
Complex shapes in one step. Detailed, complex parts are formed in a single
operation with a good finish, reducing assembly. A strong answer notes the
high tooling cost means injection moulding is only economic at high volume,
which is exactly mass production.
SQA Higher4 marksExplain why vacuum forming is a suitable process for making a thin-walled tray or packaging insert.Show worked answer →
Worth about 4 marks. The markers want the suitability linked to the
process and the product.
Suits thin sheet and shallow shapes. Vacuum forming heats a thermoplastic
sheet until soft and pulls it down over a mould by removing the air
beneath, so it forms shallow, thin-walled shapes such as trays and inserts
well.
Cheaper tooling than injection moulding. The mould (former) can be made
from wood or resin rather than expensive steel, so set-up cost is lower,
which suits lower volumes and prototypes.
A strong answer adds that the process is quick and the moulds are cheap, so
it is economic for packaging and short runs, though it only makes open,
relatively simple shapes, not complex enclosed parts.
Related dot points
- Polymers used in product design: thermoplastics and thermosetting plastics, their key properties (formability, strength, toughness, durability, finish, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on polymers, covering thermoplastics and thermosetting plastics, their key properties such as formability, toughness and durability, common examples and uses, and how a designer matches a polymer to the demands of a product.
- Metals used in product design: ferrous and non-ferrous metals and alloys, their key properties (strength, hardness, ductility, malleability, conductivity, corrosion resistance, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on metals, covering ferrous and non-ferrous metals and alloys, their key properties such as strength, ductility, conductivity and corrosion resistance, and how a designer matches a metal to the demands of a product.
- Timbers used in product design: natural hardwoods and softwoods and manufactured boards, their key properties (strength, hardness, durability, workability, finish, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on timbers, covering natural hardwoods and softwoods and manufactured boards, their key properties such as strength, durability, workability and cost, and how a designer matches a timber to the demands of a product.
- Scales of production and manufacturing systems: one-off (job), batch and mass or continuous production, and the systems that support them - standardisation, tolerance, jigs and templates, and CAD/CAM.
An SQA Higher Design and Manufacture answer on scales of production and manufacturing systems, covering one-off, batch and mass or continuous production, when each is used, and the systems that keep products consistent such as standardisation, tolerance, jigs and templates, and CAD/CAM.