NSSCAS Design and Technology (8256) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Design fixation

A designer's tendency to stay anchored to an early idea and stop generating alternatives. It is reduced by deferring judgement, producing many concepts first and combining ideas from unrelated products.

Morphological analysis

A technique that lists each required function as a column and possible means as rows. Selecting one means from every column produces a new combined solution concept for evaluation.

Weighted decision matrix

A comparison tool where each concept is scored against criteria, each score multiplied by the criterion's importance weight, and the totals summed. The highest total justifies the chosen concept.

Design specification

A list of measurable requirements a product must meet, covering size, mass, performance, cost, finish, safety and lifetime. Each point must be testable so the final product can be evaluated against it.

Primary research

Data collected first-hand for the project, such as interviews, questionnaires, observation and user trials. It is specific to the target user but slower and smaller in sample than secondary research.

Constraint versus criterion

A constraint is a fixed limit that cannot be negotiated, such as budget, deadline or regulation. A criterion is a desirable quality ranked by importance and used to compare concepts.

Toughness

The ability of a material to absorb energy and deform plastically before fracturing. Tough materials resist impact and crack propagation, unlike hard but brittle materials such as glass.

Thermoplastic versus thermoset

Thermoplastics soften reversibly when heated and can be remoulded, for example acrylic and HDPE. Thermosets cross-link permanently and char rather than melt, for example epoxy resin.

Glass-reinforced plastic

A composite of glass fibres in a polyester or epoxy matrix. It gives high strength-to-weight ratio and complex moulded shapes, but is difficult to recycle and produces hazardous dust when cut.

Draft angle

A slight taper, typically one to two degrees, built into moulded parts so they release from the tool. Without it, vertical faces drag, scuff or stick during ejection from the mould.

Tolerance versus allowance

Tolerance is the permitted variation in a dimension during manufacture. Allowance is the intentional difference in size between mating parts, producing a clearance or interference fit.

Vacuum forming

A thermoplastic sheet is heated, drawn over a former and pulled against it by vacuum. Sharp corners and deep draws cause webbing and local thinning, so radii and draft are needed.

Jig

A device that holds the workpiece and guides the tool, usually a drill, so repeated operations are accurate without re-marking out. It gives interchangeability in batch production.

Third-angle projection

An orthographic layout where each view is placed on the side from which it is viewed, so the plan appears above the front elevation. The projection symbol shows a truncated cone.

Isometric drawing

A pictorial drawing on three axes at 30 degrees to the horizontal, with true lengths measured along the axes. It shows three faces in one view but no foreshortening.

Section view

A drawing that imagines the object cut away to reveal internal detail. Cut material is hatched at 45 degrees, and adjacent parts are hatched in opposing directions.

Life-cycle assessment

A structured evaluation of a product's environmental impact across raw material extraction, manufacture, distribution, use and end-of-life. It identifies which stage carries the greatest burden.

Design for disassembly

Designing products so parts can be separated for repair and recycling, using reversible fasteners and avoiding bonded dissimilar materials. It improves end-of-life material recovery and extends product life.

Hierarchy of control

The order of hazard control: eliminate, substitute, engineering controls, administrative controls, then personal protective equipment. PPE is the last resort because it protects only the wearer.

Planned obsolescence

Designing a product with a deliberately limited useful life or unrepairable construction so replacement is forced. It raises sales but wastes resources and raises ethical concerns.

Moment of a force

The turning effect of a force, calculated as force multiplied by the perpendicular distance from the pivot. Equilibrium requires the sum of moments about any point to be zero.

Stress and strain

Stress is force divided by cross-sectional area, in newtons per square millimetre. Strain is extension divided by original length and is dimensionless. Young's modulus is stress divided by strain.

Mechanical advantage

The load a machine can move divided by the effort applied. Efficiency is mechanical advantage divided by velocity ratio, expressed as a percentage and always below 100 in practice.

Buckling

Sudden sideways failure of a slender member under compression, occurring below the material's compressive strength. Risk rises with length and falls with greater second moment of area.

Closed-loop control

A system that measures output with a sensor, compares it with the set point, and corrects the error. A thermostat is an example; open-loop systems lack this feedback.

Gear ratio

The number of teeth on the driven gear divided by the number of teeth on the driving gear. It sets the change in speed and torque between the two shafts.

Manufacturing plan

An ordered list of operations needed to make a product, stating tools, jigs, settings, quality checks and time for each stage. It is evidence of planning before practical work begins.

Fair test

A test in which only one variable is changed while all others are held constant, with repeats averaged to reduce random error. It makes results comparable and defensible.

Risk assessment

A recorded evaluation of hazards in an activity, judging risk as likelihood multiplied by severity, then stating control measures and the residual risk after controls.

Anodising

An electrolytic process that thickens the natural oxide layer on aluminium, improving wear and corrosion resistance and allowing dye to be absorbed into the surface.

Galvanic corrosion

Corrosion caused when two dissimilar metals touch in the presence of an electrolyte, forming a small cell. The less noble metal corrodes, so the pair must be insulated.

Working drawing

A drawing containing all information needed to manufacture a part without verbal explanation: views, dimensions, tolerances, material, finish and scale, plus a title block.

Exploded view

An assembly drawing in which parts are drawn separated along their assembly axes, with numbered references to a parts list. It communicates build order and fastening.