By Brad Cleveland, Protomold

Related links: Plastic Prototyping | CNC Milling | 3D Printing

Comparative Cost

With vast amounts of revenue riding on virtually any new product brought to market, the cost of prototyping is not likely to be anyone’s first consideration in directing the development process. Still, cost matters; just ask your CFO.

Of course, the biggest cost you could possibly incur is that of bringing a poorly conceived or badly executed product to market. It could exceed everything you’ve spent on development, production, and marketing, not to mention lasting damage to your company’s reputation and position in the market. Another significant cost is the delay incurred by having to backtrack if problems are caught late in the development process due to inadequate prototyping. The costs we’re addressing here, however, are the simple, up-front costs of various prototyping methods.

The graph at the right represents the relative costs of the three prototyping options: Cut (e.g. CNC milling), Mold (e.g. rapid injection molding) and Build (e.g. 3D printing). The greatest disparity comes with the very first prototype: 3D printing is somewhat less expensive than CNC machining, and rapid injection molding, due to the cost of mold milling, is significantly more costly than either of the other two. The exact trajectory of each of the trend lines will, of course, depend on the material being used and the complexity of the part.

Because it has low fixed costs, the total cost of 3D printing starts low and climbs at a steady rate. The last copy costs the same as the first with no economies of scale.

Like 3D printing, CNC machining also has low fixed costs and total cost rises at a steady rate. Typically the cost of each machined part will be somewhat higher than that of a similar part produced by an additive process.

The cost of rapid injection molding is relatively high for the first 25 parts but climbs far less steeply than the cost of CNC or 3D printing.

Clearly, the relative cost per part will depend largely on the total number of parts required, and this will affect the way each method is used. For example, in the earliest phase of development, when the likelihood of change is great and parts are being made in small quantities, RP may be the ideal method. In the early phases of functional testing, when material properties are critical, developers might switch to CNC machining despite the somewhat higher cost per part. And finally, when a lot of parts are needed for extensive laboratory or market testing, rapid injection molding will be the most cost-effective alternative. And, of course, rapid injection molding is a very affordable approach for moderate-volume production or for bridge tooling while steel molds are being made.