Notes · Design and TechnologyUK · A-Levels

Forming, redistribution, addition processes and finishes

This chapter explains how materials are turned into products: by forming (reshaping), by redistribution (melting and casting or moulding), by wasting (cutting away) and by addition (joining and fabricating), and how surfaces are treated and finished. For each process it sets out how it works, the scale of production it suits, and how a designer chooses it against the product, material and quantity required.

5 sections~19 min reading time3 competenciesLevel Standard 4 · Advanced 1

T·0444 / 18

Exam profile

AO4 · Explain forming, redistribution, wasting, addition and finishing processes and the use of jigs and fixturesAO3 · Analyse and evaluate the most appropriate process and finish for a product, material and scale of productionAO2 · Select and use processes and finishes accurately when making a prototype

Operators:explaindescribecompareanalyseevaluatejustifyselect

basic level

AS-Level expects the main processes described and matched to a product, with the reasons for finishing.

higher level

The full A-Level expects the stages of a process such as injection moulding explained, and the process and finish justified against material, scale of production and cost.

Depth

Text

Contents · 5 sections

Forming, redistribution, addition processes and finishes

Forming and shaping processes#

StandardAQA 7552 3.1.4DfE GCE D&T - forming processes

Vacuum forming

Fig. 1Vacuum forming: a thermoplastic sheet is heated until soft, then the air beneath it is evacuated so atmospheric pressure pushes the sheet down onto the mould, taking its shape - a cheap process for shallow, open forms in modest volumes.

Forming (or deforming) processes reshape a material without adding or removing much of it, usually by making it soft or fluid enough to take a new shape and then setting it. For thermoplastics this exploits their softening on heating: vacuum forming pulls a heated sheet onto a mould by evacuating the air beneath it (packaging trays, baths, casings); line bending softens a strip along a line and folds it (acrylic display stands); blow moulding inflates a hot tube against a mould to make hollow items (bottles); rotational moulding tumbles powder in a heated hollow mould for large hollow parts (water tanks, cones); and extrusion pushes molten polymer through a die to make continuous sections (pipes, curtain track).

Metals are formed by deforming while solid or by redistributing when molten. Cold and hot forming - bending, pressing, forging, drawing and rolling - reshape solid metal using its malleability and ductility; deep drawing presses sheet into cups and cans. Casting redistributes molten metal into a mould: sand casting is cheap and suits one-offs and low volumes of large parts (engine blocks, bench ends), while die casting forces molten metal into a reusable steel mould at high pressure for fast, accurate, high-volume production (toys, fittings, housings).

Choosing a forming process depends above all on the material, the shape (solid, hollow, flat, continuous) and the scale of production. Vacuum forming suits shallow, open shapes in modest volumes because the mould is cheap; injection and die casting suit complex parts in high volumes because the expensive tooling is spread over many units; extrusion suits any product that is a constant cross-section. Matching the shape and quantity to the process is a recurring exam demand.

Every process leaves its signature on the design. Moulded parts need draft angles so they release from the mould and even wall thicknesses to cool without sinking; vacuum-formed parts must avoid deep, narrow shapes that thin and tear; cast parts need generous radii. A designer therefore designs for the chosen process, not just for appearance - a theme developed in the design-for-manufacture chapter.

Worked example

Matching a process to shape and scale

A company will make 200,000 identical hollow plastic bottles a year and, separately, a one-off transparent acrylic display stand. Recommend a forming process for each and justify by shape and scale.

Analyse the bottle
It is a hollow, thin-walled item made in very high volume - blow moulding inflates a hot polymer tube against a mould to make hollow shapes quickly, and the expensive mould is spread over 200,000 units, so the unit cost is low.
Analyse the display stand
It is a one-off flat-and-folded transparent piece - line bending softens the acrylic along a line so it can be folded to shape, needing only simple equipment, which suits a single item where tooling cost must be near zero.
Justify by shape and scale
Blow moulding matches a hollow product at high volume where tooling cost is amortised; line bending matches a one-off flat-and-folded acrylic piece where cheap, flexible processing is essential.

Result: Blow moulding for the high-volume hollow bottle (hollow shape, tooling spread over many units) and line bending for the one-off acrylic stand (simple, cheap forming of a folded transparent part) - each process chosen by shape and scale.

Typical mistakes

Confusing vacuum forming (a sheet drawn onto a mould) with injection or blow moulding (molten polymer forced into or inflated within a mould).
Ignoring the scale of production - proposing an expensive-tooling process such as injection moulding for a one-off, or vacuum forming for millions of complex parts.

Active revision

A designer must choose a process for a new hollow plastic watering can to be made in large volumes. Recommend a process, justify it by shape and scale, and name one design feature the process requires.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for design and technology (Department for Education) · AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Redistribution, wasting and addition#

StandardAQA 7552 3.1.4DfE GCE D&T - process families

Families of manufacturing process

Fig. 2The families of process: wasting removes material, forming reshapes it, redistribution melts and re-moulds it, and addition joins pieces. The family predicts the waste, tooling cost and scale a process suits.

It helps to see all manufacturing as belonging to a few families defined by what happens to the material. Wasting (subtractive) processes remove material to reveal the shape - sawing, drilling, turning, milling, routing and laser cutting. They are versatile and accurate and need no expensive moulds, so they suit one-offs and low volumes and are the basis of most workshop and CNC work; their drawback is the waste (offcuts, swarf) they generate and the time each part takes.

Redistribution processes melt or soften the material and reshape it in a mould - casting metals and moulding polymers. Because the material is redistributed rather than cut away there is little waste, and once the mould exists identical parts can be made quickly, so redistribution suits high volumes. The catch is the cost and lead time of the mould or die, which only pays back over a large quantity - the reason injection moulding and die casting belong to mass production, not one-offs.

Addition processes build a product by joining pieces together - fabrication and assembly using adhesives, mechanical fixings and heat joining, and, increasingly, additive manufacture (3D printing) that builds a part layer by layer. Addition lets complex products be made from simpler components and different materials combined, and additive manufacture in particular makes one-off complex geometries possible without tooling. The trade-off is the time and reliability of the joints and, for 3D printing, slower build speeds unsuited to mass volumes.

Recognising the family a process belongs to guides the designer to the right choice for a quantity. A single bespoke bracket is best wasted from stock or 3D printed; a million identical caps are best redistributed by injection moulding; a piece of furniture is an addition of fabricated parts. The families also carry different waste, cost and flexibility profiles, so classifying the process is the first step to justifying it against scale, cost and sustainability.

Worked example

Choosing a process family by scale

A start-up needs one prototype phone stand now and, if it sells, 100,000 units a year. Recommend a process family for each stage and justify the change.

The prototype (quantity one)
Use wasting or additive manufacture - 3D print or CNC-cut the stand from stock. There is no tooling cost, changes are easy, and only one part is needed, so speed and flexibility matter more than unit cost.
Mass production (100,000 a year)
Switch to redistribution - injection moulding. The steel mould is expensive but is spread over 100,000 units, so unit cost falls dramatically, cycle times are seconds, and every part is identical.
Justify the change
Additive suits the one-off because tooling would never pay back; redistribution suits mass production because the high tooling cost is amortised and the low unit cost and speed dominate - the right family depends on the quantity.

Result: 3D print or CNC the single prototype (no tooling, flexible), then move to injection moulding for 100,000 units (tooling cost amortised, low unit cost) - the process family follows the scale of production.

Typical mistakes

Muddling redistribution (melting and re-moulding, little waste, high tooling cost) with wasting (cutting away, more waste, no mould).
Ignoring waste and tooling cost when comparing processes for a given scale of production.

Active revision

For each of a bespoke trophy, a run of 50 school badges and a million bottle caps, name the process family you would use and justify it by scale, waste and tooling cost.

Active recall

Recall the key points — then reveal.

Sources: AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Injection moulding and mass polymer processes#

AdvancedAQA 7552 3.1.4DfE GCE D&T - injection moulding

The injection moulding process

Fig. 3Injection moulding: granules are melted by the heated barrel and screw, injected at high pressure into a cooled steel mould, held while they cool and solidify, and ejected - a cycle of seconds once the costly mould exists.

Injection moulding is the dominant process for mass-producing thermoplastic components, and understanding its stages is a common exam requirement. Polymer granules are fed from a hopper into a heated barrel, where a rotating Archimedean screw both moves the polymer forward and shears and melts it. The screw then rams the molten polymer at high pressure through a nozzle and sprue into a closed, cooled steel mould. The polymer fills the mould cavity, is held under pressure, cools and solidifies to the mould's shape, and the mould opens so ejector pins push the finished part out; the cycle then repeats.

The process is defined by a high tooling cost and a very low unit cost. The steel mould is expensive and slow to make, so injection moulding is uneconomic for small quantities; but once the mould exists, parts are produced in seconds with little waste, so over hundreds of thousands or millions of units the cost per part becomes tiny. This economic profile is exactly why injection moulding belongs to mass and continuous production and why the break-even quantity is a key decision.

Designing for injection moulding shapes the product. Walls must be of roughly even thickness so the part cools evenly without sink marks and warping; draft angles (a slight taper) let the part release from the mould; ribs and bosses stiffen and locate without thick sections; and sharp internal corners are radiused to avoid stress concentrations and ease flow. A part designed without these features may not mould reliably, so the designer works within the process's rules.

Related high-volume polymer processes share the same logic. Blow moulding makes hollow parts (bottles) by inflating a hot tube; extrusion makes continuous constant-section products (pipe, film, track); and rotational moulding makes large hollow parts. All trade high tooling or equipment cost for very low unit cost at volume, so the designer's task is to match the product's geometry and quantity to the process and to design the part so it can actually be made by it.

Worked example

Explaining and applying injection moulding

A firm will injection-mould a polypropylene lunchbox in high volume. Describe the process stages and explain two features the design must include so it moulds reliably.

State the process stages
Granules from the hopper are melted by the heated barrel and rotating screw; the screw rams the melt at high pressure into a closed, cooled steel mould; the polymer fills the cavity, is held and cooled until solid; the mould opens and ejector pins push out the box; the cycle repeats in seconds.
First design feature
Even wall thickness - so the box cools uniformly and does not warp or show sink marks; thick sections would cool slowly and distort.
Second design feature
Draft angles on the sides - a slight taper so the box releases cleanly from the mould; a straight-sided box would jam. Radiused internal corners would also aid polymer flow and reduce stress.

Result: The lunchbox is moulded by melting granules and ramming them into a cooled mould, cooling and ejecting; to mould reliably it needs even wall thickness (no warping or sink marks) and draft angles (clean release) - the design is shaped by the process.

Typical mistakes

Describing injection moulding as pouring molten plastic in - it is rammed under high pressure by a screw into a closed, cooled mould.
Proposing injection moulding for low volumes, ignoring that the expensive mould only pays back over a very large quantity.

Active revision

Describe, in order, the stages of injection moulding a polypropylene bottle cap, and explain two design features the cap must have to be moulded successfully.

Active recall

Recall the key points — then reveal.

Sources: AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Joining: adhesives, fixings and jigs#

StandardAQA 7552 3.1.4DfE GCE D&T - joining and jigs

Products are assembled by addition, and joints are classified as permanent or temporary. Permanent joints cannot be undone without damage - adhesives, welding, brazing, soldering, riveting and integral moulded features; temporary joints can be dismantled for maintenance, repair or flat-pack assembly - screws, nuts and bolts, and knock-down (KD) fittings. The choice matters for the whole life of the product: a permanent joint is strong and cheap but frustrates repair and recycling, while a temporary joint supports maintenance and disassembly at some cost in parts and strength.

Adhesives bond by chemical or mechanical grip and each suits particular materials. PVA glues timber and card; epoxy resin bonds most materials strongly, including dissimilar ones; contact adhesive bonds laminates and rubber over large areas; solvent cement welds thermoplastics such as acrylic by softening and fusing them; and hot-melt glue gives quick temporary bonds. The right adhesive depends on the materials being joined, the strength and gap-filling needed, the working time, and the service environment.

Mechanical and heat joining offer strength and, often, the option of dismantling. Screws, nuts and bolts and rivets fix metals and rigid materials, with bolts and screws removable and rivets permanent; knock-down fittings (cam locks, corner blocks) let flat-pack furniture be assembled and dismantled by the customer. Heat joining - welding (fusing metals), brazing and soldering (joining with a lower-melting-point filler) - gives strong permanent metal joints. The designer selects the method by the materials, the strength required and whether the joint must ever come apart.

Jigs, fixtures and formers are the tools that make joining and shaping accurate and repeatable, especially in batch and volume production. A jig guides a tool (for example a drilling jig that positions holes identically on every part); a fixture holds the work securely in the same position each time; a former or template gives a consistent shape (a bending former, a router template). They remove the variation of marking out each part by hand, speeding production and guaranteeing that parts are interchangeable - essential for quality and assembly.

Worked example

Selecting joints and a jig

A company batch-produces a flat-pack wooden desk. Recommend how the panels should be joined and explain how production accuracy is guaranteed.

Choose the joint type
Use temporary knock-down fittings (cam locks and dowels) so the customer can assemble and later dismantle the desk for moving or recycling, while the fittings still pull the joints tight enough to feel solid.
Justify against the need
Permanent glued joints would be stronger and cheaper but would prevent flat-pack shipping and later disassembly, so the temporary fittings better serve a flat-pack product's whole life.
Ensure repeatable accuracy
A drilling jig positions the fitting holes identically on every panel, so the parts are interchangeable and line up during assembly in every desk - removing the variation of marking out each panel by hand.

Result: Knock-down fittings and dowels give a solid but dismantlable flat-pack desk, and a drilling jig guarantees the holes align on every unit - the joint supports the product's life and the jig supports repeatable batch production.

Typical mistakes

Choosing an adhesive without regard to the materials - for example using PVA (a wood glue) on metal or polymer, where it will not bond.
Confusing a jig (guides the tool) with a fixture (holds the work), or ignoring their role in making parts repeatable.

Active revision

A flat-pack desk must be assembled and later dismantled by the customer, yet feel solid in use. Recommend joining methods and explain how a jig would ensure the holes line up in every desk produced.

Active recall

Recall the key points — then reveal.

Sources: AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Surface finishes and treatments#

StandardAQA 7552 3.1.4AQA 7552 3.3.9DfE GCE D&T - finishes

Surface finishes by material

Fig. 4Finishes are chosen to protect and to decorate: metals are painted, powder-coated, galvanised or anodised against corrosion; timbers are varnished, oiled, waxed or veneered; many polymers are self-coloured and need no finish.

A finish is applied to a surface for two broad reasons: to protect the material and to improve its appearance (and sometimes to change a functional property such as grip, hygiene or electrical insulation). Timber must usually be finished to resist moisture and wear; most metals must be finished to resist corrosion; many self-coloured polymers need no finish at all, which is one of their advantages. Identifying why a finish is needed - protection, aesthetics or function - is the first step to choosing one.

Metals are finished mainly to prevent corrosion and to decorate. Painting and powder coating (electrostatically applied powder cured into a tough film) protect and colour steel; galvanising coats steel with zinc for outdoor corrosion resistance (galvanised fencing, car bodies); anodising thickens and dyes aluminium's oxide layer for a hard, coloured, corrosion-resistant surface (phone bodies, drink bottles); electroplating deposits a thin metal layer (chrome, nickel) for appearance and protection; and dip-coating covers with a plastic film for grip and protection (tool handles).

Timber finishes protect against moisture and wear while showing or colouring the grain. Varnish and lacquer give a hard protective film; oils (Danish, teak, linseed) soak in to give a natural, easily-repaired finish; waxes give a soft sheen; paint protects and colours opaquely; and stains and preservatives colour and protect, especially outdoors. Veneering and laminating apply a thin decorative or protective surface layer - a real-wood veneer or a plastic laminate - over a cheaper substrate, common on manufactured boards.

Choosing a finish weighs the protection and appearance required against cost, durability, the service environment and, increasingly, environmental impact. An outdoor steel gate needs galvanising or powder coating for years of weather resistance; an indoor oak table might be oiled for a natural, repairable finish; an aluminium phone body is anodised for a hard, coloured, wear-resistant surface. The finish is part of the design, not an afterthought, and must be specified with the same care as the material and process.

Worked example

Specifying finishes for a product

A park bench has a steel frame (outdoors, must resist rust for years) and slats that could be oak or self-coloured recycled polymer. Recommend a finish for the frame and comment on the slats.

Finish the steel frame
Outdoors the steel must be protected from corrosion for years, so galvanise it (a zinc coating) or powder-coat it (a tough cured film that also colours it); both give durable, low-maintenance weather protection.
Consider the oak slats
If oak is used it must be oiled or treated to resist moisture and wear and repaired periodically; a naturally durable timber and a maintainable oil finish suit an outdoor seat.
Note the self-finished option
Recycled polymer slats are self-coloured and weatherproof and need no finish at all, saving a process and maintenance - an advantage of polymers that the designer can exploit here.

Result: Galvanise or powder-coat the steel frame for durable outdoor corrosion resistance and colour; oil the oak slats (and maintain them), or choose self-coloured recycled polymer slats that need no finish - each choice matched to material, environment and maintenance.

Typical mistakes

Applying a metal finish to timber or vice versa (for example 'anodising' wood) - finishes are material-specific.
Treating finishing as optional decoration and forgetting its protective and functional purpose, especially corrosion resistance on metals.

Active revision

An outdoor aluminium bench frame and an indoor oak seat are to be finished. Recommend a finish for each, justify it by protection, appearance and environment, and note one that needs no finish.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for design and technology (Department for Education) · AQA A-level Design and Technology: Product Design (7552) specification (AQA)

References & sources

Sources

Department for Education

GCE AS and A level subject content for design and technology

AQA

AQA A-level Design and Technology: Product Design (7552) specification

Forming, redistribution, addition processes and finishes

5 sections~19 min reading time3 competenciesLevel Standard 4 · Advanced 1

Forming, redistribution, addition processes and finishes

Key points

Matching a process to shape and scale

Key points

Choosing a process family by scale

Key points

Explaining and applying injection moulding

Key points

Selecting joints and a jig

Key points

Specifying finishes for a product

Sources

Forming, redistribution, addition processes and finishes

Key points

Matching a process to shape and scale

Key points

Choosing a process family by scale

Key points

Explaining and applying injection moulding

Key points

Selecting joints and a jig

Key points

Specifying finishes for a product

Sources