Rapid Prototyping Methods Compared
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A prototype exists to answer a question: whether the part fits, whether it works, whether people like it, and whether it can be made at volume. The best method is the cheapest one that answers the question well enough. Production-quality methods used too early waste money, and rough methods used too late hide the problems you most need to find.
Looks-like and works-like prototypes
Early on, it often pays to split the job. A looks-like prototype shows the shape, color and finish, and may be hollow or have no working parts; it's for design reviews, user feedback and photos. A works-like prototype proves the function: mechanisms, loads, heat and electronics, even if it looks rough. The two come together as the design matures.
From concept to production: the stages
- Concept models test size, shape and feel. Foam, cardboard and quick 3D prints are fine.
- Engineering prototypes prove the design works. Electronics companies call these builds EVT (engineering validation test). Parts are usually 3D printed or machined, in small numbers.
- Design validation (DVT) builds use production-intent materials and processes, often from prototype or bridge tooling, so the design can be tested for reliability and certification.
- Production validation (PVT) is the first run off production tooling, on the production line, at the planned rate.
The terms come from electronics, but the stages apply to almost any product.
3D printing
The fastest route to a first part, with no tooling. FDM is good for fit checks, resin printing for appearance models and small detailed parts, nylon powder (SLS and MJF) for functional plastic parts, and metal printing for complex metal parts. The limits: printed plastics behave differently from molded ones, parts can be weaker between layers, and surfaces need finishing to look like production parts. See the seven categories of 3D printing and 3D printed prototypes by development stage.
CNC machining
Machining makes prototypes from the real production metals and plastics, with real strength and tight tolerances. It's the default for metal parts and for any prototype that has to behave like the final part under load or heat. Complex shapes cost more, and some features, like sharp inside corners, can't be machined at all. See CNC machining processes.
Vacuum casting
A master pattern, often a resin print, is used to make a silicone mold. Polyurethane resin is then cast into the mold under vacuum, so it fills fine detail without bubbles. Each silicone mold typically yields around 20 parts, and resins are available that mimic ABS, polycarbonate, clear plastics and rubber in a range of hardnesses. Vacuum casting suits batches of 10 to 50 parts that need to look and feel like molded parts, such as samples for users and trade shows.
Rapid and bridge tooling
Aluminum injection molds, or steel molds of simple construction, mold the actual production plastic for hundreds to thousands of parts. That proves the part can be molded, settles questions about draft, gate location and shrink, and supplies parts for testing and early sales while the production tool is built. See what tooling is and aluminum vs steel injection molds.
Sheet metal and fabricated prototypes
Laser-cut and press-brake bent parts need no hard tooling, so sheet metal prototypes are quick and inexpensive, and the same process often carries on into low-volume production. When the production part will be stamped, prototypes are usually laser cut and formed, and the design is then adjusted for the die. See metal fabrication processes.
Composite prototypes
When the final part will be carbon fiber, prototype it in carbon fiber, so you test the real weight, stiffness and finish. Prototypes can be laid up by hand or in prepreg on 3D printed, tooling board or machined molds before committing to matched production molds. See prototyping a carbon fiber part without a production mold and composite manufacturing processes.
Side by side
| Method | Typical quantities | Materials | Best for | Speed |
|---|---|---|---|---|
| FDM printing | 1 to 20 | Thermoplastics | Fit and form checks | Fastest |
| Resin printing (SLA, DLP) | 1 to 20 | Photopolymer resins | Appearance and detail | Fast |
| Nylon powder (SLS, MJF) | 1 to a few hundred | Nylon, TPU | Functional plastic parts | Fast |
| CNC machining | 1 to a few hundred | Metals, plastics | Production material and tolerances | Fast to moderate |
| Vacuum casting | 10 to 50 | Polyurethane resins | Production-like look and feel | Moderate |
| Rapid tooling | Hundreds to thousands | Production plastics | Production material and process | Slower |
| Sheet metal | 1 to thousands | Steel, stainless steel, aluminum | Brackets, enclosures, frames | Fast to moderate |
| Composite layup | 1 to 20 | Carbon and glass fiber | Real weight and stiffness | Moderate |
Getting more from each round
- Write down the question each prototype has to answer before choosing a method.
- Change as few things as possible between rounds, so you know what made the difference.
- Use the production material whenever strength, heat or wear is being tested.
- Keep CAD revisions under control and label every part with its revision.
- Design for the production process early: draft for molding, inside radii for machining, even wall thickness. See injection molding design rules and CNC design features that add cost.
We make prototypes by CNC machining, 3D printing and composite layup, and carry the same files into production tooling. See prototyping.
Related reading
- 3D printed prototypes by development stage
- The seven categories of 3D printing
- Prototyping a carbon fiber part without a production mold
- Tooling: molds, dies, jigs and fixtures
- What to include in a quote request
Terms are defined in the glossary, and every guide is listed in the knowledge base.