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23-Mechatronics-B8 Product Design and Development · December 2019

Question 6 of 7: Design for Manufacturing and Design for Assembly

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams, 16-Mex-B8, Product Design and Development — December 2019, 3 hours, open-book examination (Casio or Sharp approved calculator only). Question 1 (40 marks) is mandatory; candidates choose 4 of the remaining 6 questions (15 marks each, only the first five questions as they appear in the answer book are marked, for a total of 100%). This is an essay/design-methodology paper with no numerical calculations. All seven questions are answered below for completeness.

Reference texts: Ulrich, Eppinger & Yang, Product Design and Development, 7th ed. (generic product-development process, concept generation and selection, Design for Manufacturing and Assembly, intellectual-property strategy); Government of Canada, Canadian Intellectual Property Office (CIPO), A Guide to Patents (Patent Act novelty/ utility/non-obviousness requirements, first-to-file rule, maintenance fees); Transport Canada, Motor Vehicle Safety Act and Canada Motor Vehicle Safety Standards (CMVSS).

The wording of Question 1 parts A, D and E is assumed from the sub-part labels. Question 1 is an open-ended design-process question (the paper states that following a defined design process matters more than the actual design), so it is answered as: pick a team; state objectives; propose competing solutions; select the best; write specifications. Question 5 parts B and C are answered from their stems, which are clear. Question 7's sub-parts are taken to be the text printed under Question 6 part C; see the check note on Question 7 for the reasoning.

Question 6: Design for Manufacturing and Design for Assembly (15 marks)

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.

A. How DFM and DFA together lower product cost

Design for Manufacturing (DFM) reduces the cost of making each individual part — by selecting materials and processes suited to the required volume, and by relaxing tolerances and geometry to whatever the chosen process can hold economically. Design for Assembly (DFA) reduces the cost of putting those parts together — chiefly by minimizing part count and making the remaining parts self-locating and easy to handle and orient. Applied together, the two compound: a part-count reduction driven by DFA (combining several parts into one moulded or cast piece) is simultaneously a DFM win, because it removes an entire manufacturing and inventory step for the eliminated parts, not just an assembly step — which is why DFM and DFA are normally run as one combined review rather than two separate exercises.

B. Three design improvements that satisfy both DFM and DFA

(1) Snap-fit joints replacing threaded fasteners: fewer discrete parts (no screws, washers) and no fastening tooling or torque-control step, satisfying DFA directly, while also eliminating a manufacturing step (drilling/tapping for the fastener) — a DFM win. (2) Consolidating several stamped sheet-metal brackets into a single injection-moulded part: reduces part count and the joining operations (welding/riveting) between them, cutting both assembly labour (DFA) and the number of separate manufacturing processes and tooling sets (DFM). (3) Standardizing fastener sizes and types across the whole product line: reduces tool- changeover time and inventory complexity on the shop floor (DFM) while also reducing the number of distinct tools an assembler must use and the chance of a wrong-fastener assembly error (DFA).

C. A strategy for consistently achieving DFM/DFA in-house

Because the facility manufactures its own products, DFM/DFA guidance can and should be tied directly to that facility's actual process capabilities rather than generic rules of thumb. A sustainable strategy: publish design guidelines/checklists calibrated to the plant's own equipment and achievable tolerances; require a manufacturing engineer to sit on every design review from the concept stage onward, not just at a late "manufacturing sign-off" gate; track quantitative DFM/DFA metrics (estimated assembly time, part count, tooling cost) at each review so improvement is measurable rather than subjective; and maintain a direct, short feedback loop from the shop floor back into design (e.g. co-located production and design engineers, or a standing defect/assembly- difficulty review) so that recurring manufacturing pain points are captured as design-guideline updates rather than being silently absorbed by production every time.