A pre-production prototype is the last prototype made before the mould tools are built, and unlike the prototypes before it, its job is to confirm the design rather than develop it. Produced in collaboration with the factory, it resolves the final production details, is often written into the manufacturing contract, and sets the boundary between design and tooling. This guide covers when it is needed, what gets refined, and why it protects the investment that follows.
A pre-production prototype is the last prototype made before the mould tools are built. It is the final milestone before a product moves into tooling, and it is quite different from the prototypes that come before it.
Up to this point, prototypes have been about developing and validating the design, from the early models that test rough ideas through to the standard Mark I that assesses the refined design in full. A more developed version of a Mark I, sometimes called a Mark 2, carries further design changes and improvements, but it still belongs to the same tier. The pre-production prototype is a different proposition. It isn't about developing the design further, but about confirming it, in collaboration with the factory, before committing to the expense of tooling.
What a pre-production prototype is
A pre-production prototype is usually produced in collaboration with the factory, so that all parties agree on the latest changes, updates and details of the product. In effect, it is the supplier saying, we understand your design as this, and we intend to manufacture something close to this prototype.
It's a final safety check, confirming everything is right before the point of no return. It is also where the supplier contributes to the design from their own perspective, adjusting details to allow for a smoother and more reliable manufacturing process. Because it pins down the design that will be made, it is commonly bound into the contract between client and manufacturer, tying down any loose ends, so that the responsibilities and limits of production are set clearly, and there are no surprises further down the line for either party.
This is what separates it from a factory sample, and the two shouldn't be confused. A factory sample is the first successful production result after tooling is complete. It is a sample of the final product itself, made in the specified materials. The pre-production prototype comes before tooling, whilst the factory sample comes after it.
When it is needed, and when it is not
A pre-production prototype isn't always necessary. Whether you need one depends on the complexity of the product, how successful the Mark 1 prototype was in ironing out any issues, and how resolved the design is.
Where it becomes unavoidable is on products with features such as low tolerances or interference fits, the snug fits where parts must meet precisely. In those cases, the supplier will include a pre-production prototype in their pricing even if you don't ask for one. They need you to have a prototype you can approve before they commit to tooling, and that prototype has to be as close as possible to what they intend to deliver. Suppliers use it to tie down anything left unresolved in the brief, so that liabilities and the boundaries of production are set properly before any mould is cut.
What gets refined at this stage
At the pre-production stage, you should expect optimisation rather than change. The supplier re-evaluates the design details one more time and raises any concerns, along with their solutions.
This tends to happen late in the day for a practical reason, as suppliers quote on a quick estimate in a short timeframe, and only engage properly with the detail of tooling design once the go-ahead is given. Their refinements often don't surface until this point.
Most of these refinements are production-led, and relate specifically to how the part leaves the mould. Suppliers comment on seam lines, joint lines and part details to help the tool operate more efficiently and to prevent deformation in the product. Deformation is a genuine risk, and not only during moulding. It can also occur as parts cool, or in transport, which makes it critical to address before production begins.
To give an example, one of our recent projects needed removable support bridges to preserve the form along the edge of a part. This wasn't flagged during the Mark 1 prototype build, but production analysis showed a high probability of deformation at that location, both during manufacture and in transport. A removable bridge support was added to the design, to be taken off once the product reached its final destination.
Some changes go beyond optimisation. Reducing component count or changing a material are dramatic changes, and they require testing before the project moves forward. Simplification is a normal part of design, particularly when a project is exceeding its retail price target, but it has to be done carefully and backed by proper analysis. A material change is much the same, since it can alter the characteristics of the product entirely. In both cases, re-prototyping is crucial to confirm the change works before committing.
Why the prototype doesn't need to be beautiful
A pre-production prototype doesn't need to look good, and it doesn't necessarily need to function fully. As with any prototype, it comes down to defining what the prototype is for, and what question it exists to answer. If the purpose is to confirm fit and manufacturability, there is no need to colour the parts or perfect the surface finish, unless the design depends on those things. A rough prototype is exactly the right tool here, because the questions at this stage are about fit, assembly and production, not appearance.
Assembly, and its effect on cost
This stage is also where a design can be improved for faster assembly, and that carries a real, if indirect, effect on the final cost. How long a product takes to assemble determines the labour requirements, and labour is included in the unit cost calculations. The faster and easier a product is to put together, the less it costs to make. Addressing this before tooling, rather than after, is what makes it worth doing at this stage. Of course, this is something to be considered at the very start of the project, and minimising part counts and assembly complexity should always be at the forefront of design development, but sometimes the factory is able to offer solutions that can reduce this further.
Making the leap into tooling
This is the handoff point to the factory and to tooling, and it comes with a clear condition. Before you cross it, the tolerances must be set and ready for the supplier, and there should be no outstanding design changes. Once the pre-production prototype is approved and the design is frozen, the project is ready to commit to moulds.
The significance of getting this right is easy to underestimate. One past project with an interference fit required six prototypes to achieve the perfect snug fit. That is the level of precision this stage exists to confirm, before the cost of tooling makes any further change expensive.
In summary
The pre-production prototype is the final check before manufacture. It is a collaboration with the factory that confirms the design, resolves the last production details, and sets the boundary between design and tooling. It isn't always needed, but where tolerances are tight and the stakes of tooling are high, it is what protects the investment that follows.
Once it is approved, the product is ready for tooling and factory samples, which is where manufacture begins. For the stage that follows, see our pillar on manufacturing a new product idea to production. For the technique detail behind the prototypes described here, see prototype manufacturing.
See it in practice: Dostea
