22-Mec-B5 Product Design and Development · May 2015

Question 4 of 7: The four components of a complete product design

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

Notes on this paper

National Exams, May 2015 — 07-Mec-B5 Product Design and Development. Three hours. Open book; no calculator is permitted. Question 1 must be completed and is worth 40 marks; four of the six remaining questions are chosen, each worth 15 marks, for 100 marks in total. Only the first five questions as they appear in the answer book are marked. The paper states that most questions require an answer in essay format or the use of tables, figures and charts, and that clarity and organisation of the answer are important.

The paper prints 40 + 6 × 15 = 130 marks and a candidate attempts 40 + 4 × 15 = 100 of them. All seven questions are answered below, because this set is a study resource rather than an examination script. The marking scheme printed on the last source page splits Question 1 as 6 / 9 / 9 / 6 / 4 / 6 and gives the part weights for each 15-mark question, and the answers here are proportioned to that split. Because no calculator is allowed, every calculation is arranged so that it can be carried out on paper in one or two lines.

Reference texts for this subject

K. T. Ulrich and S. D. Eppinger, Product Design and Development — the framework text for this exam code: identifying customer needs, target specifications, concept generation, concept selection by Pugh screening and weighted scoring, design for manufacturing, and product development economics.
G. E. Dieter and L. C. Schmidt, Engineering Design — problem definition, decision matrices, design for the environment and life-cycle assessment, standards and codes, and the four components of a complete design.
G. Pahl and W. Beitz, Engineering Design: A Systematic Approach — the systematic conceptual / embodiment / detail sequence and function structures.
G. Boothroyd, P. Dewhurst and W. Knight, Product Design for Manufacture and Assembly — part-count reduction, handling and insertion time, and the design-for-assembly index used in Question 6.
M. F. Ashby, Materials Selection in Mechanical Design — translate, screen, rank and seek supporting information; the property charts and material indices used in Question 7.
S. Kalpakjian and S. R. Schmid, Manufacturing Engineering and Technology — process selection, process capability, tooling cost and economic batch size.
I. Gibson, D. Rosen and B. Stucker, Additive Manufacturing Technologies — process families and design for additive manufacturing, for Question 2.
W. Preiser and K. Smith (eds.), Universal Design Handbook, and the seven Principles of Universal Design (Centre for Universal Design, North Carolina State University, 1997) — the framework Question 1 asks for.
Canadian context: CSA B125.3, Plumbing fittings; CSA B651, Accessible design for the built environment; the National Plumbing Code of Canada; the Accessible Canada Act framework; CSA Group, Standards Council of Canada and Health Canada under the Canada Consumer Product Safety Act.

Check: the exam gives no data of its own — every question asks the candidate to bring a product, a set of numbers and a method. All quantities used below (operating torques, embodied energies, machine rates, process sigmas, material properties) are stated explicitly as design assumptions drawn from the reference texts and from Canadian standards, and each answer is written so that the method stands whatever numbers a marker would prefer.

Question 4: The four components of a complete product design (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.

Part A — The four components (6 marks)

A design is not complete until four things have been decided, and a decision on any one of them is provisional until the other three are consistent with it. Following Dieter and Schmidt, the four components are function, form, material and manufacturing process; cost is not a fifth component but the currency in which all four are traded.

Function is what the product must do, expressed independently of how it does it. It is captured as a function structure — the transformation of energy, material and signal from input to output — and then as a set of measurable engineering specifications with marginal and ideal values. Function is the only one of the four the customer actually buys; the other three exist to deliver it. A complete statement of function includes the secondary and undesired functions too: a toaster must brown bread, but it must also not start a fire, not burn a hand, and not fall off a counter when the lever is pushed.

Form is the physical embodiment: architecture (how functions are allocated to physical elements, and whether that allocation is modular or integral), configuration, geometry, dimensions, tolerances and surface condition, together with the industrial-design qualities of proportion, texture and colour. Form is where function becomes an object, and it is the component with the most degrees of freedom — which is why it is the one most often frozen too early for aesthetic reasons.

Material is the substance each element is made from, specified not merely by name but by the properties that matter to the function: modulus, strength, toughness, density, thermal and electrical behaviour, corrosion resistance, cost per kilogram, and increasingly embodied energy and recyclability. Material selection is a translation problem — function and geometry constraints become a material index, as Question 7 develops.

Manufacturing process is how the form is imposed on the material and how the elements are joined: the primary shaping route, secondary operations, joining, finishing, inspection, and the assembly sequence. It carries its own constraints — achievable tolerance and finish, minimum wall thickness, draft, batch size economics, tooling lead time and capital.

Part B — How the components interact (6 marks)

The four are coupled pairwise, and the couplings run in both directions, which is why a serial design process fails. Function constrains form, but form also reveals function: a chosen architecture creates interfaces, and interfaces create functions nobody specified — sealing, alignment, thermal expansion, tolerance stack-up. Function constrains material through the material index, but the material available constrains the function that can be promised; a specification written without knowing what materials exist is a wish. Material and process are the most tightly coupled pair of all: a material is only useful if a process can shape it, and every process has a material family it belongs to. Choosing die casting chooses zinc, aluminium or magnesium; choosing a thermoset chooses compression or transfer moulding and forecloses recycling. Process constrains form through draft angles, minimum radii, parting lines, undercuts and achievable tolerance, and form constrains process by dictating the size of the machine and the number of operations. And every one of them prices into cost, which is the shared constraint through which the couplings are ultimately resolved.

Because the couplings are two-way, the design process is iterative rather than sequential: a decision is made on one component, propagated to the other three, and revised if any of them cannot absorb it. The practical management of this is the design freeze discipline — the recognition that early decisions are cheap to change and late ones are not. Roughly 70–80 % of a product’s eventual cost is committed during concept and system-level design, when only a small fraction of it has been spent, so the four components must be brought into consistency before that commitment hardens. A worked instance from this paper makes the coupling concrete: the faucet lever of Question 1 has a function (12 N operating force), which fixes a form (a 100 mm blade with a specified sweep), which suits a material (die-cast zinc for a chrome-plated finish, or moulded acetal), which selects a process (die casting with a draft on the blade and a machined stem bore), which feeds back on form because the blade must now carry draft and a parting line — and back on function, because the plated finish must not become slippery when wet.

Part C — Advantages and disadvantages of establishing them concurrently (3 marks)

Advantages. Concurrent engineering shortens development time, because material and process work proceeds in parallel with form rather than after it, and tooling can be ordered against a design that manufacturing has already accepted. It reduces expensive late change: manufacturing, materials and service engineers present at concept stage catch the unmouldable undercut and the unobtainable tolerance while the drawing is still cheap. It produces better designs, not merely faster ones, because a design negotiated across four components finds compromises a serial hand-off never sees — part consolidation, for instance, is only visible to someone thinking about form and process at once. And it builds shared ownership, so that manufacturing does not receive a design it had no part in and is not committed to.

Disadvantages. Concurrency means working from information that is not yet firm, so downstream work is done against a moving target and some of it is wasted; tooling started early against a design that then changes is expensive rework. It demands far more coordination — cross-functional teams, co-located or well-supported by shared data, with disciplined configuration management, all of which costs overhead a small firm may not have. It raises the risk of premature commitment: freezing an architecture early to let manufacturing start can lock out a better concept that had not yet been explored. And it needs a mature product-data infrastructure and a culture in which a manufacturing engineer can overrule an industrial designer, which many organisations do not have. The sensible position is that concurrency is right for the decisions that are genuinely coupled and expensive to reverse, and that some detail work is better left serial.

Topic. The four components of a complete design (function, form, material, process) and concurrent engineering.

Key relations. The material–process–form–function coupling diagram of Ashby; the cost-commitment curve, on which roughly 70–80 % of life-cycle cost is committed in the first 20 % of spend; Pahl and Beitz’s conceptual / embodiment / detail sequence, in which each phase resolves the four components at a finer grain.

Why this works. Treating design as four coupled components rather than as a sequence of hand-offs explains most real product failures. A part that cannot be moulded, a material that cannot meet the specification, an assembly that cannot be automated — each is a case of one component being fixed without consulting another. The framework also explains why concurrency pays: the cost of resolving a coupling rises by roughly an order of magnitude at each phase boundary it crosses, so resolving all four together while they are still cheap is not a scheduling trick but a cost decision.

Common pitfall. Listing the four components and stopping there. The marks in parts B and C are for the couplings and for an honest account of concurrency’s costs; an answer that presents concurrent engineering as free is as incomplete as one that presents it as impossible.

Source. Dieter & Schmidt, Engineering Design, ch. 1 and ch. 8–11 (the design process, embodiment, materials and process selection, concurrent engineering); Pahl & Beitz, Engineering Design: A Systematic Approach, ch. 4–7; Ulrich & Eppinger, ch. 2 (Development Processes) and ch. 9 (Product Architecture).

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