AQA GCSE Engineering: Engineering manufacture, a complete overview of processes, joining, treatments, production and quality

What the engineering manufacture topic demands

Once a material is chosen, it must be shaped, joined, treated and checked. The engineering manufacture topic is about how products are actually made and how their quality is controlled. AQA tests both recall (naming and classifying processes) and application (choosing the right process for a material, shape and quantity, and calculating tolerances). This overview ties together the five dot-point pages in the topic.

Wasting and shaping processes

Processes split into two families. Wasting (subtractive) processes remove material: sawing, filing, drilling, turning on a lathe and milling. Shaping or forming processes move material into a new shape without cutting it away: casting (molten metal into a mould), injection moulding (molten thermoplastic forced into a mould), vacuum forming (a heated sheet sucked over a mould) and forging (hot metal hammered or pressed). The choice depends on the material, the shape and especially the quantity: a one-off bracket might be milled, but 100,000 caps are injection moulded because the cost per item is tiny once the mould exists.

Joining and assembly

Joining methods are permanent or temporary. Permanent joints cannot be undone without damage: welding (fusing metals), brazing and soldering (joining with a melted filler), adhesives and riveting. Temporary joints can be taken apart for maintenance: nuts and bolts, machine screws and self-tapping screws. The exam skill is choosing a method and justifying it by whether the joint must ever come apart, with the strength and sealing it needs.

Heat and surface treatments

Heat treatments change the whole metal's properties: hardening (quench) makes steel hard but brittle, tempering reduces that brittleness for toughness, annealing softens for working, and normalising relieves stress and refines grain. Surface treatments and finishes protect or improve the outside: galvanising (zinc), anodising (aluminium), painting and powder coating. A spring is hardened and tempered; a car body is galvanised then painted.

Production and quality

The four scales of production are one-off, batch, mass and continuous, and the quantity needed drives the choice of process, tooling, automation and cost per item. Quality control checks products meet the specification, using tolerance (the allowed variation, with upper and lower limits) and measuring tools (steel rule, vernier callipers, micrometer and go/no-go gauges) chosen to suit the required accuracy.

Check your knowledge

A mix of recall and application questions covering the engineering manufacture topic. Attempt them under timed conditions, then check against the solutions.

1. State the difference between a wasting and a shaping process. (2 marks)
2. Name a suitable process for making 100,000 identical plastic caps and justify it. (3 marks)
3. Give one permanent and one temporary joining method. (2 marks)
4. Explain why a chisel is hardened and then tempered. (3 marks)
5. Name the four scales of production. (4 marks)
6. A part is dimensioned $30 \pm 0.2$ mm. State the upper and lower limits and the tolerance. (3 marks)
7. Name a tool that quickly checks whether a part is within tolerance. (1 mark)