Rapid prototyping: 72-hour builds, one question at a time

A demo build is your first working unit: the one you show investors, hand to a pilot user or film for Kickstarter. It combines prototype boards, printed or machined housing parts and early firmware. It proves the idea works. It does not prove the product can be built in volume; EVT, DVT and PVT do that.

That difference matters when you plan. A demo build can carry known problems, as long as everyone knows they are there. Its job is to work on the day. The golden sample comes later, after DVT and PVT, and production is held to it. See what a golden sample is for the full difference.

Our engineers build demo units in the Shenzhen factory from reviewed files. The boards are assembled on the same SMT lines that later run production, and the SMT program, stencil and reflow profile carry into production, so the step to EVT does not start over with a new supplier.

For shape, fit and appearance, print it. SLA gives a fine surface for a model people will look at; SLS or MJF nylon gives a functional part for something that will be handled. For strength and stiffness, machine it from the real alloy. For enclosures, brackets and panels, fabricate it in sheet metal.

A machined prototype is made from the same wrought material as the production part and has none of the layer weakness a printed one has. A laser-cut and bent sheet metal part is close enough to the stamped version for fit and function checks. A printed housing arrives soonest when the question is whether the product looks and feels right.

Whether the production process will work. A printed housing tells you the shape is right. It says nothing about draft angles, gate positions or sink marks in the molded version. A machined bracket tells you the geometry carries the load; it says nothing about springback on a press brake or a stamping die.

That gap is what EVT, DVT and PVT exist to close, and why the portal records a project phase: concept, prototype, pilot or production. Treat a prototype as proof of the process and you find process problems after tooling. A DFM review during design closes part of the gap before the first part is cut.

Change one thing per iteration and decide in advance which result ends the loop. An iteration without an exit condition produces another iteration. When two designs both look plausible, build both at once: on every part route the quantity starts at one, and the setup costs more than the second part.

The free engineering review is the other lever. It comes before payment, and its findings arrive before you commit, so submitting a design for review spends an engineer's reading time instead of a build cycle.

When the demo build does what the product must do and the design questions are answered. EVT then proves the design works as drawn, on boards and parts built from frozen files. Moving earlier means EVT finds design problems; moving later means you pay for prototype parts that production will never use.

At that point the parts change route. Printed housings move toward molded ones, which is why the DFM review is repeated before tooling. Production molds are cut after DVT closes the design.