Custom Product Design and Engineering
Core concepts
Custom design engineering translates a customer requirement into a manufacturable specification. Candidates must understand the design workflow: requirements capture, concept selection, detailed design, design for manufacturing and assembly (DFMA), prototyping, and design transfer. Key ideas include functional requirements versus design parameters, tolerance stack-up, standardization of components, and design review gates.
What to know cold
- DFM/DFA: reduce part count, simplify fixturing, standardize fasteners, design for the chosen process.
- Tolerance stack-up: worst-case (arithmetic sum) versus statistical (root-sum-square) methods.
- GD&T basics: datum reference frames, position tolerance, and material condition modifiers.
- Configuration control: revision discipline, change orders, and traceability from requirement to drawing.
Traps in questions
A frequent trap is treating a customer wish as a verified requirement without a measurable acceptance criterion. Another is confusing worst-case and statistical stack-up results. Questions may also probe whether a design change requires re-validation; the safe answer is yes when form, fit, or function is affected. Watch for items that look like DFM improvements but actually shift cost elsewhere.
Rule of thumb
Write every requirement so it can be tested: subject, condition, and measurable limit. For stack-up, use worst-case when safety or fit is critical and statistical when many independent dimensions combine and some risk of out-of-spec is acceptable.
Worked example
Four dimensions each ±0.10 mm stack in a critical gap. Worst-case total variation is 0.40 mm; RSS gives about 0.20 mm. If the gap allows only 0.25 mm, worst-case analysis fails but statistical passes - the choice must be justified by risk, not convenience.