The two processes are similar — they both primarily produce parts and
components from plastic, and they are both capable of high degrees of geometric
complexity. However, there are important differences as well.
One of the more appealing aspects of 3D printing is the absence of steep
initial costs. Because of its need for specially tooled dies, the creation of
which is an expensive process, injection molding requires considerable initial
costs. Though imposing at first, these startup costs are amortized over the
lifespan of the die and the production run — in large volume injection molding
projects, the startup costs are amortized over more individual parts, leading to
a relatively low per-part cost.
Aside from its benefit in terms of initial costs, 3D printing has a number of
limitations that the technology has yet to surmount, especially when compared to
injection molding. There are still technical and software issues that cause
costly and time consuming misprints; 3D printers are still quite rare, the
printing process is notably slower than injection molding, and the produced
parts are restricted in size.
Even 3D printing companies acknowledge these drawbacks. ODM WORK, a injection
molding design manufacturer, conducted a study and found 3D printing mold to be cost
effective only for very low volume runs of very small parts.