Comparison of injection molding and 3D printing costs. It is assumed that the injection mold costs $5000 and the cost per part,
exclusive of mold-amortization, is 20¢. Total cost per molded part, including mold amortization declines with volume, while 3D-printed part cost is constant at an assumed 70¢.
GOING AFTER INJECTION MOLDING
According to Bentz, price isn’t the only reason to consider 3D printing. “Traditional manufacturing techniques,” he says, “require high up-front expenses for tooling and long-term, high-volume production of a component to amortize those initial expenses. But if there is a mistake in the product, or the market changes, so that the product must be modified, companies may lose the entire investment in molds and tooling. This high risk also makes entry into high-volume production challenging for small or new businesses.
“3D printing allows an idea to go from conception to manufacture quickly and much more affordably. There are no tooling costs or lead time. A company wishing to produce a product need only design it and then pay for the raw materials used to produce it. 3D printing puts physical products on equal footing with software products in production costs. Printing allows products to be produced at very low cost and constantly updated with no large capital expenditures.”
All that’s necessary is to email Slant 3D a design file, and it can be put into production with little delay. However, Slant 3D also offers design services help get new products ready for production. Slant can do design consultation to judge printability and works with clients to tweak existing designs for optimum printability.
“3D printing puts physical products on equal footing with software products in production costs. They can be constantly updated with no large capital expenditures.”
Bentz concedes that surface smoothness is one area in which injection molding has an advantage over most 3D printing. Because 3D printed parts are typically produced in a sequence of layers, they can be weaker in the Z-direction than injection molded parts.
However, Slant 3D has produced some structural parts. The key, Bentz notes, is that such parts must be designed specifically for 3D printing, not simply converted from an injection molded design. He adds that 3D printing has advantages for making so-called “impossible” parts. An example is the gear shafts shown in the photo above. They are built around a metal bearing, making the entire assembly effectively a single part.
Injection molded parts for this assembly would have to be designed to interlock and pull apart so that a bearing could be inserted. In this case, what is now manufactured as a single assembly would have to be split into the gear, toothed pulley, shaft, and metal bearing, all of which would be manufactured separately and then assembled together.
But since this part was 3D printed, the gear, pulley, and shaft were combined into a single part. During production, the build would pause to insert the metal bearing. Then the build would continue and the part would be built around the bearing.
3D printing reduced four parts to two. Manufacturing cost was dramatically reduced because there was no assembly and none of the tooling that would have been required for the three plastic parts combined with the bearing. Slant 3D is using this approach to develop a “fidget spinner” with an internal bearing.
Source: PT Plastics Technology