General Motors got a lot of attention recently when they unveiled a 3D-printed seat bracket. With its weirdly organic shapes it looked like something that might have been grown rather than made, but it was in fact produced from stainless steel. GM noted that this one “printing” was 40% lighter and 20% stronger than the assembly it replaces. What’s of more interest to us is that it replaced eight separate pieces stamped and formed from sheet metal before being welded together. In other words, here’s additive manufacturing replacing fabrication. Should we be worried?
Spoiler alert: no. In fact additive manufacturing is becoming ever more interesting. We’ll explain why below.
Another Primer on Additive
Before diving into the impact of additive on fabrication we should all be “on the same page” as regards the technology. We’ve talked about 3D printing and additive manufacturing several times over the years, but it’s a fast-evolving subject. (Not to brag, but “Replacement or Complement? 3D printing vs. CNC machining,” is quite a good introduction to the topic.) So, here’s an update.
Additive is any way of making parts by adding or joining rather than cutting away, which is what machine shops do. By that definition you could argue that most fabrication is additive. What we’re interested in here though is that subset of additive where parts are built layer by layer and grain by grain. In other words, 3D printing.
Early 3D printers built plastics parts by depositing polymer only where it’s needed, somewhat like an inkjet printer but with a third “Z” axis for height. This polymer 3D printing is something growing numbers of companies are adopting, mostly as way of making prototypes you can touch and feel. They’re also very useful for verifying fit in assemblies.
In the last decade or so metal printing has begun to take off. This is what GM used to produce their seat bracket. Metal printing splits into two types: directed energy processes and powder bed processes.
Directed energy metal printing is similar to how polymer 3D printers work. A laser melts powder as it’s deposited to build up the shape required. Powder bed processes look more like screen printers used for tee-shirts and electronics: a layer of powder is spread over a surface, then a laser performs localized melting where the part is to be. Then another powder layer is deposited and the melting/solidification repeated.
Metal printing processes are particular about the materials and grain size used. Stainless, nickel alloys and titanium are among the more printable materials while carbon and mild steel are proving more of a challenge.
Why Use Additive?
The thing to remember about 3D printing is that it’s quite slow. Lasers are more powerful than ever and modern machines run faster than their predecessors, but it still takes minutes and hours to make a single piece. Then, those parts need finishing. This often means cutting away support structures and smoothing surfaces to remove the layering effect. To put it another way, the Star Trek replicator this ain’t!
Additive scores in two ways. First, it’s fast. If it seems we’re contradicting what we said in the paragraph above, well no, we’re not. The printing process is slow but it eliminates the need for tooling. Punches, dies, and even press brake tools can take days, weeks or even months to obtain, so printing saves all this time.
The second way in which additive scores is flexibility. When you build a part grain by grain you can make shapes that are impossible to produce any other way. Exhibit A for this: the GM seat bracket. (Quick detour: GM used something called “generative design” to design this bracket. It’s basically artificial intelligence optimizing for strength and weight and it leads to those weird organic designs that can only be made by 3D printing.)
Additive in Sheet Metal Fabrication
The fact is, additive is being used today but not as an alternative to cutting, bending and joining metal. Like we said before, it’s just too slow. Where it is being put to work is in fixturing and/or workholding and tooling. In other words, it’s helping speed up and improve conventional fabrication. Let’s take a closer look.
Additive for Workholding
We can start with press brake backgauge fingers. These go behind the bending tools where they create a stop for the operator to push the sheet against. When you’re bending simple rectangular shapes the fingers need be no more complex than metal blocks, but what about when the edges are curved or otherwise shaped?
Situations like those call for custom-made fingers, and those take time to procure. But if you can print the fingers in your own shop the saving could be days or even weeks. Looked at another way, having a 3D printer in the shop could let a fabricator quote shorter delivery times. Printed fingers like these were demonstrated at the FabTECH show late last year. No word on cost but we’re thinking if they were made in-house they might be cheaper than their metal equivalents.
Another application is robot end effectors, (grippers to you and us.) Robots are amazing tools, but their “hands’ need configuring for the part you want them to pick up. When you’re running an auto body plant you can take the time and spend the money to have these produced in steel, but fab shops need far more flexibility. So with a printer on site, just draw up what you need and print it.
Likewise, you could print fixtures to hold fabrications in particular orientations. This could be useful in welding but another area is inspection. Especially if a fabricator is blessed with a CMM, being able to locate parts consistently and cheaply could be a real boon.
Additive for tooling
Also demonstrated at FabTECH was 3D printed press brake tooling. Interestingly, like the backgauge fingers it was made in plastic rather than metal. Clearly, this kind of tooling isn’t going to withstand the rigors of serial production, but it’s ideal for prototype and low volume orders in relatively thin gauge material. Again, the main benefit is the leadtime saved compared to waiting for special tools to come in, but there could be a second benefit. As plastic tools don’t mark the sheet like metal can it may be possible to eliminate a polishing step.
Additive’s role in fabrication is emerging
The tools we use to make things have been evolving for thousands of years. Additive manufacturing is a leap forward compared to the old subtractive ways, but as with any advance, it takes time for engineers to figure out the best ways of using it.
With their 3D printed seat bracket GM showed it’s possible to re-engineer just about any part made today, taking out weight and increasing strength in the process. That’s exciting, but what brings us back to earth are the economics. Machine tools like punches and press brakes are fast and there’s no way additive can compete, perhaps ever. Yet despite that, it looks like additive has a role in manufacturing.
Additive won’t be making fabrications but it will be making tools that help us make parts. And by reducing leadtime, and perhaps saving money, additive will help fabricators meet the needs of their customers. That’s why additive is becoming ever more interesting.