MATSEC SEC Design and Technology cheat sheet

The iterative design cycle: identify the need, write a design brief, produce a specification, generate concepts, develop and model, test and evaluate, manufacture; evaluation feeds back into earlier stages.

A design brief states the problem and constraints in the client's terms; a specification converts it into measurable criteria (dimensions, cost ceiling, materials, safety standards, aesthetics) that can be tested.

Primary research collects new data (interviews, questionnaires, user observation, anthropometric measurement); secondary research uses existing sources (standards, market data, competitor products).

A design specification criterion must be verifiable: 'must weigh under 400 g' is a specification; 'must be light' is not.

Brainstorming rules: defer judgement, aim for quantity, build on others' ideas, encourage unusual ideas; screening then scores concepts against weighted specification criteria.

Evaluation types: formative (during development, informs changes) and summative (against the final specification); a fair test changes one variable at a time.

Ergonomic and anthropometric data (percentile 5th female to 95th male reach, grip, eye height) convert user needs into dimensions.

A design failure is analysed by root cause: function, material, manufacture, or user misuse; each points to a different corrective action.

Hardwoods come from broad-leaved trees (oak, ash, beech, mahogany); softwoods from conifers (pine, spruce, cedar); manufactured boards (MDF, plywood, chipboard) are dimensionally stable and cheap.

Ferrous metals contain iron (mild steel, cast iron, stainless steel); non-ferrous metals do not (aluminium, copper, brass, zinc); stainless steel resists corrosion because of its chromium content.

Thermoplastics soften repeatedly on heating (acrylic, HDPE, PVC, ABS) and are recyclable; thermosetting plastics char rather than melt (epoxy, polyester resin, melamine).

Material properties vocabulary: tensile strength, compressive strength, hardness, toughness, ductility, malleability, elasticity, thermal and electrical conductivity, density.

Density formula: density = mass / volume (kg/m3); comparing density explains weight differences between identical-volume parts.

Alloying changes properties: brass is copper plus zinc (harder, more corrosion resistant); solder is tin plus lead or silver (low melting point).

Composites combine two materials for properties neither has alone: GRP (glass-reinforced polyester) and carbon fibre give high strength-to-weight ratio.

Wood grain direction affects strength: a joint or bend is strongest parallel to the grain; cross-grain loads cause splitting.

Personal protective equipment: safety glasses for any cutting or drilling, dust masks for sanding and MDF, ear defenders above roughly 85 dB(A), apron or overalls, closed-toe shoes.

Tenon saw for accurate straight cuts and joints; coping saw for curves in thin stock; hacksaw (24-32 TPI) for metal; junior hacksaw for small pipe and bar.

Twist drills cut metal and plastics; brad-point bits cut wood cleanly; Forstner bits cut flat-bottomed holes; a countersink bit chamfers a screw head recess.

A bench drill needs the workpiece clamped, the chuck key removed, correct speed (slower for large bits and metals) and no gloves.

Files cut on the forward stroke only; cross-file for rough removal, draw-file for finishing; a file card cleans clogged teeth.

Marking out uses a steel rule, try square, marking gauge (parallel to an edge) and scriber for metal; always mark from a datum face.

Electrical safety rule: PAT-test portable equipment, use RCD protection, keep cables clear of cut lines, isolate before changing blades or bits.

Machine guards must remain in place; a band saw needs the blade guide set close to the work and a push stick for narrow stock.

Casting pours liquid material into a mould: sand casting for ferrous metals, die casting for high-volume non-ferrous parts, injection moulding for thermoplastics.

Moulding processes: vacuum forming for thin thermoplastic sheet, blow moulding for bottles, rotational moulding for hollow tanks, compression moulding for thermosets.

Joining methods: permanent (welding, brazing, soldering, riveting, adhesives) versus temporary (bolts, screws, knockdown fittings).

Wood joints: butt (weak, needs fixing), dowel, biscuit, mortise and tenon (strong, frame), dovetail (strong, drawers), halving and housing joints.

Scale of production: one-off, batch, mass, and continuous; unit cost falls with volume because setup costs are spread, but tooling investment rises.

CNC machines follow CAD-generated toolpaths; advantages are repeatability and complex geometry, disadvantages are setup cost and the need for skilled programming.

Quality control checks finished parts against tolerances (for example +/-0.2 mm); quality assurance builds checks into each stage of production.

Standard components (ISO metric screws, bearings, resistors) reduce cost and design time and simplify repair and replacement.

Third-angle orthographic projection: the plan sits above the front view and the end view to the side it is viewed from; first-angle places the plan below.

A drawing must show at least a front view plus sufficient other views, with hidden detail as dashed lines and centrelines as chain lines.

Scale is stated on the drawing: 1:1 full size, 1:2 half size, 2:1 double size; all dimensions are true size regardless of scale.

Isometric drawing uses 30-degree axes with vertical lines and full-length edges; oblique uses one face true shape with 45-degree receding lines.

Dimensioning rules: dimension lines outside the outline, arrowheads touching extension lines, no duplicate or scaled dimensions, units stated once.

Section views show internal detail; hatching at 45 degrees indicates cut material and adjacent parts are hatched in opposite directions.

CAD advantages: easy editing, layers, libraries of standard parts, 3D modelling for renders and simulations, direct export to CAM; disadvantages include licence cost and file compatibility.

A BSI/ISO title block carries drawing number, title, scale, projection symbol, material, tolerances, date and author.

Mechanical advantage = load / effort; velocity ratio = distance moved by effort / distance moved by load; efficiency = (work out / work in) x 100%.

Levers: class 1 fulcrum between load and effort; class 2 load between fulcrum and effort (wheelbarrow); class 3 effort between fulcrum and load (tweezers).

Moments: moment = force x perpendicular distance from pivot; a lever balances when clockwise moments equal anticlockwise moments.

Gear ratio = teeth on driven gear / teeth on driver gear; a larger driven gear reduces speed and increases torque.

Pulley and belt systems: a crossed belt reverses direction; a compound pulley reduces effort at the cost of pulling more rope.

Four-bar linkages convert rotary to oscillating motion; a crank and slider converts rotary to reciprocating motion (engine piston).

Structural forces: tension (pulling apart), compression (pushing together), shear, torsion and bending; triangulation prevents a frame from racking.

Open-loop control has no feedback (timer-based); closed-loop control uses a sensor and comparator to correct error (thermostat, light-activated switch).

Ohm's law: V = I x R; power: P = V x I = I squared x R; energy transferred = power x time (kWh when power is in kW and time in hours).

Series circuit: current is the same everywhere, voltages add; parallel circuit: voltage is the same across branches, currents add.

Resistor colour code order: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold and silver indicate tolerance.

Two equal resistors in parallel give half the value; in series they add; potential divider output Vout = Vin x R2 / (R1 + R2).

A diode allows current one way only; an LED needs a series resistor to limit current; a transistor or relay switches a larger load from a small signal.

Input components: LDR (light), thermistor (temperature), switch, microphone; output components: LED, buzzer, motor, solenoid, lamp.

Energy sources: renewable (solar, wind, hydro, tidal, biomass) versus non-renewable (coal, oil, gas, nuclear); a Sankey diagram shows energy transfers and losses.

Battery capacity in mAh divided by load current in mA gives approximate running time in hours; battery voltage drops as it discharges.

The six Rs: rethink, refuse, reduce, reuse, repair, recycle; designing for disassembly makes repair and material recovery possible.

Life cycle assessment covers raw material extraction, manufacture, distribution, use and disposal; the use phase often dominates energy impact for powered products.

Sustainable material choice: FSC-certified timber, recycled aluminium (about 95% less energy than primary), biodegradable polymers, avoiding mixed materials that cannot be separated.

Embodied energy is the total energy used to produce a material or product; aluminium and virgin plastics are high, timber and recycled glass lower.

Ergonomics matches products to human capability: grip diameter around 30-50 mm, seated work surface near elbow height, controls within the 5th-95th percentile reach envelope.

Inclusive design principles: equitable use, flexibility, simple and intuitive use, perceptible information, tolerance for error, low physical effort, size and space for approach.

Legislation affecting design: consumer product safety, CE/UKCA marking, WEEE for electronic waste, RoHS restricting hazardous substances, packaging waste rules.

Cultural and ethical factors include fair trade supply chains, local manufacture, obsolescence (planned versus functional) and accessibility for disabled users.