22-Mec-B5 Product Design and Development · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, May 2013 — 07-Mec-B5, Product Design & Development. Three hours; open book; no calculator permitted. Question 1 is compulsory and carries 40 % of the paper; four of the remaining six questions are chosen, each worth 15 %, for 100 % in total, and only the first five questions appearing in the answer book are marked. Note 5 of the paper states that most questions require an essay answer or the use of tables, figures and charts, and that clarity and organisation of the answer carry marks; Note 1 invites the candidate to state any assumption made where a question is open to interpretation, and that licence is used several times below with each use flagged. All seven printed questions are worked here — 130 marks of material against the 100 marks a candidate would actually attempt — so that the set serves as a complete study resource.
Reference texts. Ulrich & Eppinger, Product Design and Development (McGraw-Hill) — the framework text for this exam code, and the source of the generic development process, the needs-to-metrics translation, concept screening and concept scoring used throughout; Dieter & Schmidt, Engineering Design (McGraw-Hill) for the specification, materials and process-selection material; Pahl & Beitz, Engineering Design: A Systematic Approach (Springer) for systematic concept generation and the function structure; Boothroyd, Dewhurst & Knight, Product Design for Manufacture and Assembly (CRC) for the design-for-assembly and design-for-manufacture rules; Ashby, Materials Selection in Mechanical Design (Butterworth-Heinemann) and Kalpakjian & Schmid, Manufacturing Engineering and Technology (Pearson) for the process-selection charts and cost models. Canadian context is taken from the Patent Act, Industrial Design Act, Trademarks Act and Copyright Act (Canadian Intellectual Property Office), from CSA standards (notably CSA B651 Accessible design for the built environment), from the Canada Consumer Product Safety Act, and from Engineers Canada / EGBC guidance on professional practice and on equity, diversity and inclusion in the profession.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
| Technique | Constraint 1 | Constraint 2 |
|---|---|---|
| Design for Manufacturing (and Assembly) | Process capability limits. Every feature must lie inside what the chosen process can achieve: minimum and uniform wall thickness, draft angles on moulded and cast surfaces, achievable tolerance and surface roughness, minimum bend radii, achievable weld access. A dimension toleranced tighter than the process capability forces a secondary operation or a scrap rate. | Tooling geometry and assembly access. Features must be formable and removable from the tool — no undercuts without side actions, a workable parting line — and the assembly sequence must permit tool and hand access, insertion along a single axis, and part count reduction through consolidation and standard fasteners. Tooling economics impose a further constraint: the design is committed to a minimum production volume over which the tool is amortised. |
| Design for the Environment | Material and substance restrictions. Restricted substances (lead, cadmium, hexavalent chromium, certain flame retardants and phthalates) are excluded; materials are restricted to families that can actually be recycled in the available Canadian systems, which in practice means avoiding painted, plated or glass-filled polymers, and avoiding dissimilar materials bonded together. | End-of-life and energy constraints. The product must be disassembled with common tools within a stated number of steps so that batteries and electronics can be separated as regulated waste; and in-use energy consumption must meet the applicable efficiency limits (the federal Energy Efficiency Regulations administered by Natural Resources Canada, and voluntary marks such as ENERGY STAR) which cap what the rest of the design may spend. |
| Universal Design | Anthropometric and force limits. The product must be operable across the design population, not at its mean: reach, grip span and clearance must suit approximately the fifth-percentile female to the ninety-fifth-percentile male, and operating forces must stay within a limit a person with reduced strength can apply — CSA B651 sets 22 N for door hardware — with no requirement for tight grasping, pinching or twisting of the wrist. | Perceptual and cognitive constraints. Essential information must be presented redundantly in more than one mode (visual, tactile and audible), with adequate luminance contrast and character size, never by colour alone; and the interface must tolerate error, so that a mistaken action is recoverable and hazardous actions are guarded. |
Design for manufacturing changes the architecture, not the detail. Its characteristic impact is part-count reduction: the Boothroyd–Dewhurst test asks of every part whether it must move relative to its neighbour, must be of a different material, or must be separable for assembly or service, and every part failing all three is a candidate for consolidation. On the bicycle trailer of question 1, a hitch arm fabricated from nine welded steel pieces with six fasteners becomes a single aluminium die-casting with two — the mass falls, the weld fixture and its inspection disappear, assembly time drops by roughly two thirds, and dimensional variation is set by one tool rather than by a weld sequence. The technique also imposes its own discipline on detail: ribs rather than thick sections in the moulded body, snap features aligned to a single insertion axis, self-locating chamfers so that the operator cannot assemble the part incorrectly, and standardised fasteners across the product so that the line needs one driver rather than four.
Design for the environment changes material and joint decisions. Its characteristic impact is on separability. A trailer body moulded in a single polypropylene family, with fabric of the same polymer family and mechanical fasteners instead of adhesive, can be separated at end of life and recycled; the same body painted, over-moulded with a soft-touch elastomer and bonded to an aluminium frame cannot. Applied to the kettle of question 4, the technique redirects effort from the housing to the use phase, because for a product that consumes electricity, the in-use energy dominates the life-cycle impact by an order of magnitude — which is why a life-cycle assessment is done before choosing where to spend the environmental effort, rather than assuming the answer is recycled content.
Universal design changes the user interface and often improves it for everyone. Its characteristic impact is the replacement of actions requiring fine motor control and strength with actions that do not: the lever door handle of question 7 instead of a round knob, since a lever can be operated with a closed fist, an elbow or a forearm; a tool-free quick-release wheel instead of a nut; a fill line on the kettle readable by touch as well as by sight; controls with high-contrast, large-character labelling. The same changes benefit the user carrying a child, wearing gloves in a Canadian February, or operating in poor light, which is the standard argument that universal design is not a special accommodation but a wider specification.
Design for manufacturing. Society gains a cheaper, more consistent, more repairable-by-replacement product, and manufacturers gain productivity that supports domestic production; against that, the same automation and part consolidation displaces assembly labour and tends to concentrate production where tooling capital is cheapest, which is a real cost borne by communities rather than by the balance sheet. Financially, the short-term effect is an increase: tooling capital, design time and the cost of process capability studies are all incurred before a unit is sold, and the tooling commits the company to a volume and a design freeze. In the long term the unit cost falls, scrap and rework fall, and warranty claims arising from assembly error fall — the payback is typically fast at consumer volumes and non-existent at low ones, which is precisely why process selection (question 7) is volume-driven.
Design for the environment. Society gains reduced landfill, lower emissions and less resource extraction, and the benefits are diffuse and long-dated while the costs are concentrated and immediate — the classic structure that makes regulation necessary. Financially, the short-term costs are material substitution premiums (recycled resins are not always cheaper), compliance testing and documentation, life-cycle assessment work, and occasionally a performance compromise. The long-term financial effects run the other way and are frequently underestimated: lower energy cost to the user (a purchase criterion in its own right), reduced extended-producer-responsibility fees under provincial stewardship regulations, avoided disposal and take-back cost, insulation from substance restrictions arriving in export markets, and reduced regulatory and reputational risk. For an energy-consuming product the user's operating saving usually dwarfs the manufacturer's added unit cost, which is what makes efficiency standards economically defensible.
Universal design. Society gains participation: a product usable by older adults and by people with disabilities keeps them independent, and in a country where a large and rising share of adults report a disability and the population is ageing, that is a public-cost question as well as an ethical one. The Accessible Canada Act and provincial accessibility legislation are steadily converting this from a preference into a requirement. Financially, short-term cost is added design and validation work — wider user testing, anthropometric analysis, sometimes a marginally more expensive component such as a lever mechanism in place of a knob. Long-term, the market widens (the accessible design is frequently preferred by users who have no disability at all), product liability and complaint exposure fall, and public and institutional procurement, which increasingly mandates accessibility, becomes available.
One observation ties the three together and is the reason all of them belong in the front end of the process rather than in a design review at the end. Roughly seventy to eighty per cent of a product's total lifetime cost — manufacturing, operating and disposal — is committed by decisions taken in the concept and architecture phases, while less than ten per cent of the development budget has been spent. All three techniques are therefore cheap when applied during concept selection, as additional criteria in the matrix of question 1, and expensive when applied afterwards, when the only remaining response is rework.
