From functional prototype to mass production: what still has to happen

Every few weeks someone sends us a video of a prototype that works. The mechanism moves, the light comes on, the app connects. The question that follows is always the same: how long until we can make a thousand of these?

The honest answer is that a working prototype proves the idea. It does not prove the product. Between the two sit a dozen jobs that are invisible until they are missed. This is the list we walk through with every client at that moment.

1. Decide what "done" means

Before any engineering, write down the specification the production unit has to meet: target unit cost at a given volume, weight, size, the standards it must pass, the environments it must survive, the life it must last. A prototype rarely has this written down, because it only had to work once. Production parts have to work every time, and the specification is how you prove it.

2. Pick the manufacturing process per part

A 3D-printed housing becomes an injection-moulded one. A machined bracket becomes a stamped one. A hand-soldered board becomes a panelised one. Each switch changes the geometry: draft angles, wall thickness, ribs, radii, parting lines. We make this decision part by part, from cost, volume, finish and the suppliers we expect to use, before touching the CAD.

3. Redraw the CAD for the process

This is the step people underestimate most. Production CAD is not the prototype CAD cleaned up. It is rebuilt around the chosen process: uniform walls so the part does not sink or warp, draft so it leaves the tool, ribs instead of thick sections, fillets instead of sharp corners, and features that let two halves of a housing locate and seal. For the Xenolidar G6, the cast aluminium housing was designed as two halves with the sealing surfaces, heat path and connector panel built into the casting itself, rather than added as separate parts.

4. Tolerance the assembly

Prototypes are adjusted by hand until they fit. Production parts come from different tools, suppliers and batches and have to fit without adjustment. That means a tolerance stack-up for every critical interface: lens to housing, button to aperture, battery to compartment. We put GD&T on the drawings where it matters and leave it off where it does not, because every tight tolerance is a cost.

5. Design for assembly

How many parts, how many screws, how many orientations, how many hands. A product assembled in a workshop by the person who designed it can be assembled in any order. A product assembled on a line by someone who has never seen the drawing cannot. We reduce part count, make parts self-locating, make wrong assembly impossible where we can, and write the assembly sequence before the tools are cut.

6. Choose materials that exist at volume

The resin in a prototype is often whatever the printer had loaded. Production materials are chosen for the process, the environment, certification, colour matching across batches and, above all, availability from the supplier you will actually use. A beautiful specialty polymer with a twelve-week lead time is a production risk, not a design choice.

7. Build pre-production prototypes from the real process

Before tooling, we build what we can from the production process: machined aluminium parts, cast urethane in silicone moulds, sheet-metal samples, and pre-production circuit boards. These prototypes test the design decisions above, not the idea. The G6 went through a machined hard model and several aluminium prototypes before the first casting.

8. Test against the specification

Drop, vibration, thermal cycling, ingress, load, cycle life, electromagnetic compatibility if there are electronics, and the standards your market requires. Testing finds the problems that are cheap to fix now and expensive to fix after tooling. Every test result goes into the design history, which becomes the evidence file for certification.

9. Produce the documentation a supplier can quote from

A factory cannot quote from a 3D file alone. The production package contains: 3D models, 2D drawings with tolerances, a bill of materials with approved materials and suppliers, surface finish and colour specifications, assembly drawings and sequence, test requirements and acceptance criteria. If a supplier can misread it, they will, in good faith, and you will find out at the first article inspection.

10. Select and qualify suppliers

Request quotations from several candidates per process, compare more than the price: tooling cost and ownership, minimum order quantity, lead time, quality system, who you will be talking to when something goes wrong. Visit if you can. We run this from Leuven for European suppliers and from our Shanghai office for Asian ones, which lets us compare both honestly for the same product.

11. Run a pilot batch and inspect it

The first parts out of a new tool are never perfect. A pilot batch of tens to a few hundred units lets you measure, assemble, test and fix tool and process issues before the volume order. We define the inspection criteria in advance so the discussion with the supplier is about measurements, not opinions.

12. Plan the ramp-up

Packaging, labelling, serial numbers, firmware loading, incoming inspection, logistics, spare parts. None of it is glamorous and all of it has to exist before the first pallet leaves the factory. We stay involved through this stage because the product is not finished until it ships, and because the first production problems are usually design problems in disguise.

What this means for your plan

If you have a functional prototype, you are roughly halfway through the development effort and have spent well under half of the money, because tooling, certification and the pilot batch are still ahead. The good news: the twelve steps above are predictable. They can be scoped, costed and scheduled, which is exactly what a DFM review at this stage produces.