Additive manufacturing, better known as 3D Printing, first started in the 1980s. Back then, it was a novelty concept reserved for advanced engineering research laboratories. In the 1990s, 3D printing made waves in the medical arena thanks to its ability to create custom medical devices. By the early 2000s, the open-source movement brought 3D printing into the homes of hobbyists and entrepreneurs During this time, people hailed it as the future of all manufacturing. It remains a promising technology, but subtractive manufacturing still offers many advantages over 3D printing.
Subtractive manufacturing techniques are those that remove material from a block to make a 3D part.
They are what we might call traditional manufacturing processes like milling, turning and even injection molding. Additive manufacturing processes, on the other hand, build up 3D parts by successively adding layers of material.
Although the cost for 3D printers continues to decrease, it’s still more expensive to 3D print many parts than it is to machine them. The printers themselves can be cost competitive, but the materials used in 3D printers are costly – especially if metals are involved.
Printing a part is a little bit like making pancakes – the first one usually gets tossed in the trash. This constitutes a waste of high-cost materials. Furthermore, 3D printers are more finicky and require frequent calibration and re-calibration when they’ve sat unused or when operators are swapping materials.
3D printed parts also require additional post-processing to achieve attractive surface finishes.
The additive component of the manufacturing process means pieces right out of a 3D printer have striations and stepped edges around radiuses. These surfaces require a subtractive manufacturing process to finish. Most subtractive manufacturing processes can produce finished surfaces.
Even if the striated surfaces of additive manufacturing is acceptable, 3D printer technology remains less reliable than subtractive manufacturing. High-reliability machines with good repeatability are expensive and require frequent maintenance while low-end devices typically cannot produce parts with consistent quality.
3D printing can be appealing for prototypes, but it is often limited to fit-and-feel prototypes. Because there are limited 3D printing materials available and the final mechanical properties are not always as good as those for machined parts, 3D-printed parts may not be robust or accurate enough for testing purposes. So, it sometimes makes sense to prototype with subtractive manufacturing processes and production materials instead.
Generally, subtractive manufacturing techniques are more familiar to designers.
Many designers even rely on certain functions that are common in CNC mills and lathes. For these folks, 3D printing can add cost for no discernible benefit. And with many machine shops capable of producing parts overnight using traditional techniques, the relative speed of 3D printing is rendered moot.
While additive manufacturing is attractive in some applications, good old milling, turning and molding are often better suited for the job at hand.