Additive vs subtractive manufacturing throw down

Additive manufacturing has been deservedly billed as one of the cornerstones of the next industrial revolution. Yet more traditional core subtractive manufacturing processes are largely responsible for, oh, say the entirety of modern civilization for one. But which manufacturing technology will dominate the autonomous cars, hyperloops (not to be confused with the breakfast cereal), and plasma drives of the future? It’s high time to settle this once and for all. Don some safety glasses and roll out your CNC milling machines and your 3D printers into the alley. Things are going to get ugly.

Liberal Member of Parliament Justin Trudeau (L) and Conservative Senator Patrick Brazeau fight during their charity boxing match in Ottawa March 31, 2012.    REUTERS/Chris Wattie    (CANADA - Tags: SPORT BOXING POLITICS)

The case for additive

Additive manufacturing enters the fray with a strong uppercut. It’s as purely creative as a manufacturing process ever has been, enabling part builds literally from the bottom up, layer by layer, section by section, using just the right amount of material. Additive manufacturing removes many limits to innovative design, by removing long-held producibility barriers, the bane of neophyte engineers who naïvely assume that if they can model it, it can somehow be built.

Well now with AM, that euphoric design philosophy can actually become a thing, well at least within the capable precision of the 3D printer and available printable materials. And as the technology evolves, precision improves, more compatible materials are devised and finer microstructures can be embedded in parts, significantly reducing mass while maintaining strength and functionality. Conceivably, progress will eventually reach the molecular level, marking the birth of amazing, colossal materials featuring microscopic structures. Hey subtractive manufacturing, additive manufacturing blows its nose at you.

Subtractive’s response

Subtractive manufacturing, however, isn’t going to take it lying down. One of the larger criticisms with subtractive operations is that you always are removing a little (or a lot) of material from stock material, creating waste. Often overlooked, however, is that some spent material can be recovered and eventually recycled, reducing overall waste. Not to mention, additive processes aren’t immune to waste, either from temporary structure to support parts during a build, or finishing operations needed to smooth otherwise rough printed surfaces.

But what really sets subtracting manufacturing processes apart is most processes are comparatively faster and cheaper for the same level of precision, and available in a vastly wider range of possible materials and capable of superior surface finishes. Subtractive manufacturing will likely always have a cost and speed edge over additive manufacturing for a part that could be built using either process. That’s chiefly because it’s easier to destroy then create and technology will continue to drive costs down for both processes. Laugh while you can additive manufacturing, subtractive manufacturing farts in your general direction.

What if you need to use both?

What happens when you need the flexibility of additive manufacturing but the cost and speed advantages of subtractive manufacturing? Hybrids. This isn’t anything new or even profound, it’s the natural course of responsible engineering process optimizing design with cost and availability.

Take an aircraft seat track for example, a long cross section built from an extrusion process (which is technically additive) while any cutouts, pockets, mounting holes, or other features are added with a subtractive process as a secondary operation.

Another example: a classic composite sandwich panel (no, not that kind of sandwich) where an aluminum honeycomb core is created from folding and cutting aluminum sheets and then milled to shape (subtractive) while encased in a few sheets of thermosetting plastic (additive). Or maybe you flip that upside down and 3D print a honeycomb core and encase that in subtractive manufactured metal face sheets. See what the flexibility of multiple processes provides?

Noting these example reveals the larger lesson here and the winner of this brawl: the future much like the present is not solely additive or subtractive, it’s divided (see what I did there?). Printing one offs, it’s additive all the way – but when you have to make things at scale with finite budgets, subtractive matters. Now you might pine for the not-too-distant future where molecular additive manufacturing operates quickly and precisely, but even then, you’ll find that subtractive manufacturing will still have its place in cost optimization working in concert with future additive processes.

Fight’s over. Wipe the blood off your shirt and get back to work.


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