Rapid tooling

Rapid tooling (also called prototype tooling or, for aluminum and silicone tools, soft tooling) is the umbrella term for methods that produce molds or tools quickly and with low investment for prototype and short production runs. Instead of a hardened steel production mold, which takes weeks to months to build, a simpler tool is made, usually in days to a few weeks. The goal is to get parts in the production material and process, or something close to it, such as moldings in the actual plastic, sooner and at lower cost.

There are two main groups of methods. Indirect rapid tooling starts from a master pattern (3D-printed or machined) from which a mold is cast, most often a silicone mold for vacuum casting polyurethane resins. Direct rapid tooling makes the mold or its cavity inserts directly: milled from aluminum alloys or pre-hardened steel, 3D printed from high-temperature photopolymers, or built by metal 3D printing, which also allows conformal cooling channels that follow the shape of the part.

Tool life differs by orders of magnitude. A silicone mold usually lasts about 15 to 25 castings. A printed polymer insert handles tens, occasionally hundreds, of shots depending on the plastic and geometry. An aluminum mold typically produces thousands to tens of thousands of parts, whereas hardened steel production molds are designed for hundreds of thousands to millions of cycles.

The lower cost comes from simplification: the mold is usually single-cavity, undercuts are formed by hand-loaded inserts instead of automatic slides, cooling is simpler, and cavity inserts are often mounted in a universal master frame. The same principle works outside injection molding too, for example in 3D-printed molds for thermoforming, forming tools for short runs of sheet metal parts, or printed sand molds and cores for foundries.

Rapid tooling pays off when you need tens to thousands of parts in production material before the production mold is ready, or when the total volume will never justify an expensive production mold. Typical uses are parts in the real plastic for functional and certification testing, pilot production, first market deliveries (so-called bridge tooling, which covers the time until the production mold arrives), low-volume products and spare parts.

Compared with 3D printing, you get the properties and surface of a genuine molded part; compared with a production mold, a lower investment and a shorter lead time. Calculate the break-even point between 3D printing, rapid tooling and a production mold for each specific part, because it depends on its size, complexity, material and quantity.

A part from a prototype mold is not necessarily identical to one from the production mold. Different cooling, gating and mold stiffness change shrinkage, warpage, residual stress and surface appearance, so dimensional and strength results cannot simply be carried over to production. If the parts are to serve as a basis for series production, design them from the start to injection molding rules (draft angles, uniform walls, a suitable gate location) and review them with the toolmaker.

In the quote, check the guaranteed number of cycles, whether sampling and modifications are included, how undercuts are handled (hand-loaded inserts lengthen the cycle and raise the part price), which plastics the mold can take (glass-fiber-filled plastics wear out an aluminum mold quickly) and who owns the mold. Expect a major design change to mean a new insert.