The company, Desktop Metal, has raised nearly $100 million from leading venture capital firms and the venture units of such companies as General Electric, BMW, and Alphabet. The founders include four prominent MIT professors, including the head of the school's department of materials science and Emanuel Sachs, who filed one of the original patents on 3-D printing in 1989.

Though it is possible to 3-D-print metals, doing so is difficult and pricey. Advanced manufacturing companies such as GE are using very expensive machines with specialized high-power lasers to make a few high-value parts. But printing metals is limited to companies with millions to spend on the equipment, facilities to power the lasers, and highly trained technicians to run it all.

Desktop Metal will have the tough task of converting manufacturers away from production methods that are at the heart of their businesses. But the very existence of this large, established market is what makes the prospect so intriguing. Making metal parts, says Fulop, "is a trillion-dollar industry." And even if 3-D printing wins only a small portion of it, he adds, it could still represent a multibillion-dollar opportunity.