How are commercial products actually shaped in quantity, and which process suits which product?
Processes used in the commercial manufacture of products: the appropriate uses and features of moulding, casting, forging, forming and digital processes, and the issues that influence the selection of a process.
An SQA Advanced Higher Design and Manufacture answer on the processes used in commercial manufacture, covering the uses and features of injection, blow, compression, rotational and gas-assisted moulding, die casting, drop forging, press forming, thermoforming, 3D printing, laser cutting and CNC machining, and how a process is selected.
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What this key area is asking
The SQA wants you to know the commercial processes used to shape products, their appropriate uses and features, and the issues that influence process selection. Advanced Higher expects a wide range of industrial processes, including several moulding variants and the digital processes. You must match a process to the product, material and scale of production, and know the features that identify each.
Moulding polymers
- Injection moulding, plus two-shot (two materials in one part) and gas-assisted (gas core reduces material and sink marks) variants.
- Over-moulding: a second material is moulded onto an existing part, such as a soft elastomer grip over a rigid handle.
- Blow moulding: injection or extrusion blow moulding inflates a heated tube against a mould to make hollow parts such as bottles.
- Compression moulding: a thermoset charge is squeezed in a heated mould and cures permanently, suiting handles and electrical parts.
- Rotational moulding: powder is tumbled in a heated rotating mould to coat the walls, making large hollow parts (tanks, kayaks); the inner surface is typically grainy.
- Thermoforming and press forming: a heated sheet is formed over or into a mould (thermoforming for packaging and trays; press forming for sheet metal panels).
Shaping metals
- Die casting: molten metal is forced into a reusable steel mould. Gravity die casting pours under gravity; high-pressure die casting injects under pressure for thin, detailed parts at high volume (zinc and aluminium parts).
- Drop forging: heated metal is hammered between shaped dies, aligning the grain to give a strong part (spanners, crankshafts).
Both have high tooling cost, so they suit batch and mass production where the tool cost is spread over many parts.
Digital processes
- 3D printing: builds a part layer by layer directly from a CAD model with no tooling, so it suits one-offs, prototypes and complex shapes; cost per part stays high, so it does not suit mass production.
- Laser cutting: a laser cuts or engraves flat sheet quickly and accurately from a digital file, suiting one-off to batch work.
- CNC machining: a computer-controlled cutter removes material from a block to a CAD model, giving accurate parts in metal, plastic or wood, from one-off to batch.
The digital processes need little or no tooling, so they win where volume is low and change is frequent.
Selecting a process
The issues that influence the choice include: the material and whether the process can shape it; the form (hollow, sheet, solid, complex); the surface finish and tolerance needed; the scale of production; and the tooling cost weighed against cost per part. The same product can use different processes at different volumes, so always tie the process to the scale.
Where this fits in the course
Processes sit at the centre of the Manufacture area: a process must suit the material and the designing-for-manufacture features of the part, and the choice is tied to the scale of production. Identifying processes is also central to product analysis.
Try this
Q1. Describe the main stages of injection moulding. [4 marks]
- Cue. Granules melted; screw injects melt under pressure into a closed steel mould; part cools and solidifies; mould opens and ejector pins remove the part.
Q2. Explain which process suits a large hollow water tank and why. [3 marks]
- Cue. Rotational moulding, because powder tumbled in a heated rotating mould coats the walls to make a large, seamless hollow part.
Q3. Explain why drop forging produces a strong metal part. [3 marks]
- Cue. Hammering heated metal between dies aligns the grain flow with the shape, giving greater strength than casting or machining.
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 Advanced Higher6 marksDescribe the injection moulding process and explain why it suits the high-volume manufacture of a plastic casing.Show worked answer →
Worth about 6 marks, so the marker wants the process described in stages
and a reasoned link to high volume.
The process. Thermoplastic granules are heated to a melt, then an
Archimedean screw injects the melt under high pressure into a closed steel
mould; the part cools and solidifies, the mould opens and ejector pins
push the part out.
Features. The mould has draft angles, cooling channels and ejector pins,
and the part shows a split line and ejector marks.
Why high volume. The steel mould is very expensive but, once made, parts
are produced fast and identically with little labour, so the high tooling
cost is spread over millions of units, giving a very low cost per item.
Conclude. A strong answer states that injection moulding only makes sense
at mass-production volume, linking the process to the scale, which is what
the marker rewards.
SQA Advanced Higher4 marksExplain why 3D printing is well suited to making a one-off prototype but not to mass production.Show worked answer →
Worth about 4 marks. The markers want the strengths for prototyping and
the limits for mass production, both reasoned.
Suited to prototypes. 3D printing builds a part directly from a CAD model
with no tooling, so a one-off or complex shape can be made quickly and
cheaply and changed between prints, which is ideal for prototyping.
Not suited to mass production. Each part is built slowly layer by layer, so
the cost per part stays high and does not fall with volume, unlike
injection moulding where tooling cost is spread over many parts.
Conclude. A strong answer notes that 3D printing wins where volume is low
and change is frequent, while moulding wins at high volume, so the choice
depends on the scale of production.
Related dot points
- Materials used in the commercial manufacture of products: the properties and uses of thermoplastics, thermosetting plastics, elastomers, bio-based plastics, ferrous and non-ferrous metals and alloys, timbers, boards and composites, and the issues that influence material selection.
An SQA Advanced Higher Design and Manufacture answer on the materials used in commercial manufacture, covering the properties and uses of thermoplastics, thermosetting plastics, elastomers, bio-based plastics, ferrous and non-ferrous metals and alloys, timbers, boards and composites, and the issues that influence selection.
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