The product design process runs from a written brief through concepts, detailed CAD, prototyping with a manufacturability review, and a handoff to whoever makes the part, and it loops back on itself more than that list suggests. Early decisions carry the most weight: engineering-change research finds that changes get more expensive and slower the later in development they arrive. The product design basics guide gives the wider overview, and this one goes stage by stage.
Why Does the Product Design Process Start With a Written Brief?
A brief answers a short list of questions: what the product has to do, who uses it and where, which loads, temperatures, and environments it faces, what the cost, size, weight, and regulatory limits are, and what counts as success. Write each answer so it can be checked. “Survives a one-meter drop onto concrete” can be tested, and “durable” cannot.
The brief becomes the benchmark for every later decision, so we would rather spend a day tightening a vague requirement than a month designing to it. It also gives the prototype rounds a test plan, since the Stanford guide recommends tracing each test back to the specification it checks. Expect the brief to change as prototypes teach you things, and revise it on purpose instead of letting it drift. Our guide to product design project structure shows how to separate a brief into functional, performance, and constraint requirements.
How Many Concepts Should You Explore Before Choosing One?
Stanford Biodesign’s prototyping guide describes a progression: hand-drawn sketches first, then a model in cardboard and tape, then CAD, then a printed part. The guide admits that this looks like more steps than necessary, and says the small steps go quickly while only experienced builders can tell which ones to skip without backtracking.
The same guide’s rule is that early builds stay cheap and incomplete, with time and money added only as the project earns them. We would want a few genuinely different directions on the table before choosing one, because a concept stage that produces a single real option has only confirmed the first idea, and accuracy matters little at this point.
What Happens in Detailed Design and CAD?
The chosen concept becomes CAD with defined geometry and tolerances plus a material, and how the model is built decides how easily it can change. The SOLIDWORKS reseller CATI shows the point with a plate and two holes. Dimension both holes from the left edge, and lengthening the plate from 100 to 200 mm leaves them stranded on the left. Dimension each from its nearest edge, and they follow the ends.
Driving dimensions, relations, and equations are what carry that intent. We would decide which dimensions drive the model before modeling anything, because a late rebuild lands when changes are still arriving and each one costs more.
Change control matters here too. A generic engineering change process has six steps, from raising the request to reviewing the result, and the assessment of risk and impact in the middle is what stops one fix from breaking something else.
Tolerances are the other half of the stage. Tightening a tolerance usually makes production costlier, according to Boeing research on tolerance stacks, so call them out where the function needs them and nowhere else. The same research describes the worst-case sum of a stack as a guaranteed bound, provided every part is inspected, and notes that it grows in step with the number of parts.
Prototyping Rounds and the DFM Review
Prototypes come in rounds, each answering one question, from looks-like models through works-like tests to something close enough to production to trust. Our piece on iterative design and prototyping covers how to run those rounds and when to stop.
A DFM (design for manufacturing) review then checks the design against the process that will make it. For molded parts that means uniform walls, since uneven ones cool unevenly and warp, draft on faces parallel to the mold opening, and moving tooling such as slides or lifters for any undercut.
Where stiffness is the goal, a rib beats a thicker wall on cost. Protolabs and Komaspec both give 40 to 60 percent of the adjoining wall as the base width for a rib, which makes 1.0 to 1.5 mm on a 2.5 mm wall.
Inside corners get a fillet of roughly half the wall thickness, because sharp corners concentrate stress. Weld lines form where flow fronts meet, such as behind holes, so keep them out of bosses and load paths, and run a mold-flow simulation of fill and warpage while the tool design can still change.
A printed prototype will not warn you about any of this. Print a part headed for molding and the printer never asks for draft, so build it in deliberately. The review pays for itself on molded or high-volume parts, where tooling is expensive. To pick a process, the fundamentals of product design guide compares what each one asks of the design.
What Belongs in a Manufacturing Handoff?
The handoff package is what lets someone else make the part without guessing. We would send the CAD files, drawings with tolerances and surface finish called out on every critical dimension, material specifications, and assembly notes for any step the drawing does not make obvious. We would also ask the maker to read the package before the order goes out, since a fresh reader finds the gaps the author cannot see.
Anything the package leaves out gets decided later by whoever is holding the part, and that decision is easy to make differently from one run to the next. When a drawing is silent, ISO 2768 fills the gap, and Protolabs applies class m to plastic parts. Class m allows a 60 mm dimension to vary by 0.3 mm either way. That is fine for a cover and wrong for a bearing seat.
Match the tolerance to the process as well, or the drawing promises what the process cannot deliver and the gap shows up at inspection. Protolabs’ published defaults are 0.5 mm for desktop FDM (fused deposition modeling) and 0.3 mm for SLA (stereolithography) or SLS (selective laser sintering) on small parts, so a feature drawn at 0.1 mm needs another route.
Kemperle’s design and engineering team works through this whole sequence, and because the same team runs CNC routing, 3D printing, molding, and casting, a DFM review can be checked against the processes that will make your part. Send the brief and the current CAD using the contact form, or ring 718-557-9578.
