A4.1 — Manufacturing techniques (HL)

Key concepts

Designing a great prototype is only half the battle. A product must be manufactured — converted from a digital model or single prototype into hundreds, thousands, or millions of units, consistently, economically, and at a quality the user can rely on. Every design decision has manufacturing implications.

Classifying manufacturing processes

Processes fall into four categories:

• Forming — material is shaped without removing or adding it. Includes casting, forging, extrusion, moulding, vacuum forming, pressing.
• Cutting / subtractive — material is removed. Includes turning, milling, drilling, laser cutting, punching.
• Joining — separate pieces are combined. Includes welding, brazing, soldering, adhesives, mechanical fasteners, riveting.
• Additive — material is built up layer by layer. Includes 3D printing processes (FDM, SLA, SLS).

Forming is typically most efficient for large volumes. Additive is most flexible for small volumes and complex shapes. Most real products combine several processes — a laptop might use die-cast housing, CNC-milled ports, and laser-welded hinges.

Forming processes

• Injection moulding — molten thermoplastic forced into a steel mould. Extremely fast (seconds per part), precise, repeatable. High tool cost (moulds cost £10,000+) so only economical at large volumes. Almost every plastic product in your home is injection moulded.
• Extrusion — material forced through a shaped die to produce continuous profiles. Aluminium window frames, plastic tubing, pasta.
• Die casting — molten metal (usually aluminium or zinc alloy) forced into a mould under pressure. Good for complex metal shapes in volume.
• Vacuum forming — heated thermoplastic sheet drawn over a mould by vacuum. Lower tooling cost than injection moulding; good for larger, simpler parts (packaging, yoghurt pots).
• Blow moulding — air inflates molten polymer inside a mould, creating hollow bodies (bottles, containers).
• Forging — metal shaped by hammering or pressing. Produces strong aligned grain structure (spanners, engine crankshafts).

Cutting / subtractive processes

• Turning — workpiece rotates, cutter removes material to create cylindrical parts (shafts, bolts). Done on a lathe.
• Milling — rotating cutter moves across a stationary workpiece to produce prismatic shapes. Manual or CNC.
• Drilling — creates round holes.
• Laser cutting — high-power laser vaporises material along a programmed path. Fast and precise on flat sheet.
• Waterjet cutting — abrasive water stream cuts through almost any material with no heat-affected zone.

Joining processes

• Welding — melts parent material to fuse pieces together. Arc, MIG, TIG, spot, laser welding.
• Brazing and soldering — joins with a lower-melting-point filler without melting parent metal.
• Adhesives — chemical bonds; fast, clean, distribute load, but can be harder to disassemble.
• Mechanical fasteners — bolts, screws, rivets, clips. Easy assembly, often easier disassembly (supports repair).

Additive vs subtractive

Additive (3D printing) builds parts layer by layer, ideal for: - Complex internal geometries - Low-volume / custom parts - Rapid iteration (no tooling) - Lightweighting through lattice structures

Subtractive removes material, ideal for: - Tight tolerances - Real engineering materials - Good surface finish - Medium volumes

Design decisions around process directly affect cost, volume, lead time, and environmental impact.

Finishing processes

Finishing is the fifth category of manufacturing process, alongside additive, subtractive, forming and joining — and the one students most often forget, because it happens last and adds no shape. Its job is to protect and enhance the surface, which drives durability, ease of maintenance and ultimately product life.

• Anodizing — thickens the natural oxide layer on aluminium electrolytically, giving a hard, corrosion-resistant surface that can be dyed. Used on laptop bodies, bike components, cookware.
• Electro-plating — deposits a thin metal layer (chrome, nickel, gold) by electrolysis, for corrosion resistance, conductivity or appearance.
• Galvanizing — coats steel in zinc. The zinc corrodes sacrificially in place of the steel, so a scratch does not start rust. Used on outdoor structures and fasteners.
• Powder-coating — an electrostatically applied polymer powder, cured by heat into a tough, thick barrier against moisture and UV. Used on garden furniture, appliance panels, bike frames.
• Polishing — mechanical smoothing that raises reflectivity, reduces friction, and removes the surface defects where corrosion and cracks begin.
• Sealants and natural finishes — oils, waxes and silicones that penetrate or coat porous materials such as timber, resisting moisture while leaving the material visible.

Finishes are chosen against four criteria at once: aesthetics, protection, durability and longevity, and ease of maintenance. They frequently conflict. A high-polish finish looks superb and shows every fingerprint; a textured powder-coat hides marks but cannot be locally repaired. Natural materials add a further consideration — an oiled timber surface must be re-oiled periodically, moving maintenance from the factory to the owner.

5D additive manufacturing goes further again. Where conventional 3D printing builds flat layers along a fixed vertical axis, a 5D machine rotates both the extruder head and the print bed, printing along five axes. Layers can therefore be laid down as curved surfaces that follow the shape of the part rather than slicing across it.

The payoff is strength. Flat-layered parts are weakest at the bond between layers, so a load across those layers splits them. Curved layers follow the stress path instead, producing components reported as substantially stronger than the equivalent 3D print, with less need for support material. That matters where a part must be complex and long-lasting: biomedical implants and prosthetics shaped to a patient, automotive components under vibration and load, and aerospace parts where every gram removed must not cost strength.

CNC and CAM

Computer Numerical Control (CNC) — machine tools driven by programmed paths. Reliable, repeatable, minimal operator skill needed per-part.

Computer Aided Manufacturing (CAM) — software that converts a CAD model into machine instructions (G-code). Bridges design and production.

Tolerances and quality control

Tolerance is the permitted variation in a dimension — e.g. "10 ± 0.1 mm". Tight tolerances are expensive; loose tolerances risk fit and function problems. Good designers specify only what is needed.

Quality control verifies parts meet specification. Methods include go/no-go gauges, coordinate measuring machines (CMM), vision systems, and statistical process control (SPC).

Process selection

Select manufacturing based on:

• Material — not every process works for every material
• Volume — injection moulding for millions, 3D printing for dozens
• Geometry — undercuts, thin walls, internal channels constrain choice
• Tolerance and finish — required precision
• Cost — tooling cost spread over production run

Case studies

Apple MacBook unibody — single aluminium billet CNC-milled into a complete housing. Rejects the traditional assemble-from-parts approach. Enabled by Apple's willingness to pay higher per-part cost for superior structural rigidity and aesthetic quality.

LEGO brick — injection moulded ABS to tolerances of ±2 microns. Hundreds of moulds running simultaneously produce billions of bricks annually, yet any brick from 1958 still clicks perfectly with a modern one. Process precision enables brand equity.

Airbus A350 wing — CFRP laid up over male moulds, cured in autoclave. Manufacturing process as important as design: fibre orientation, layup sequence, and cure cycle all affect performance.

Adidas 4D midsole — 3D-printed resin lattice structure tuned zone by zone for cushioning. Impossible to produce by traditional moulding. Demonstrates additive enabling designs subtractive cannot achieve.

Glossary

• Finishing — processes that protect and enhance a surface, increasing durability and product life.
• Anodizing — electrolytic thickening of aluminium's oxide layer for hardness and corrosion resistance.
• Galvanizing — zinc coating on steel that corrodes sacrificially in place of the steel.
• Powder-coating — electrostatically applied polymer powder cured into a tough protective layer.
• 5D printing — additive manufacturing rotating the extruder head and bed to print on five axes, giving curved layers and greater strength.
• Forming — shaping material without adding or removing it.
• Subtractive manufacturing — removing material to form a part.
• Additive manufacturing — building a part layer by layer.
• Injection moulding — forcing molten thermoplastic into a closed mould.
• Extrusion — forcing material through a die to produce a continuous profile.
• Vacuum forming — drawing heated sheet over a mould by vacuum.
• CNC — Computer Numerical Control machining.
• CAM — Computer Aided Manufacturing software.
• Tolerance — permitted variation in a specified dimension.
• Quality control (QC) — measurement and verification that parts meet specification.
• Tooling — the moulds, dies, jigs, or fixtures required for a manufacturing process.

Check your understanding

1. Distinguish between forming, subtractive, and additive manufacturing with an example of each.

Forming shapes material without adding or removing it — e.g. injection moulding a plastic bottle cap. Subtractive removes material — e.g. CNC milling an aluminium phone case. Additive builds material up layer by layer — e.g. FDM 3D printing a prototype enclosure. Each has distinct strengths around geometry, volume, tolerance, and waste.

2. Explain why injection moulding is only economical at high volumes.

Injection moulding requires a steel mould (tool) costing £10,000+ per part. The mould lasts for hundreds of thousands or millions of cycles. Per-part cost is very low once the tool is paid off, but producing 100 parts with this process would charge £100 per part for tooling alone. Low-volume alternatives (3D printing, vacuum forming) skip the expensive tool. Break-even volume is typically 10,000+ parts.

3. Describe two factors a designer must consider when selecting a manufacturing process.

Volume: injection moulding, die casting, and stamping amortise expensive tooling over large runs; 3D printing, laser cutting, and CNC require no product-specific tooling and suit low volumes. Geometry: some processes cannot produce undercuts, thin walls, or complex internal features — for example, injection moulding needs draft angles for parts to release, while additive manufacturing can produce internal channels no subtractive process could reach.

4. Why are design-for-manufacture considerations best introduced early rather than late in the design process?

A design that ignores manufacturing constraints risks being unmakeable at production volumes — requiring expensive redesign near launch. Introducing DFM early lets designers select geometry, tolerances, and materials compatible with the intended process from the start, reducing cost, lead time, and scrap. Apple, for example, chooses materials and processes in parallel with industrial design; late-stage retrofitting of manufacturing would compromise their precise tolerances.