Some believe that the future of 3D printing is in continuous composites, especially the continuous fiber ones, and many have come to believe that the future of extrusion (both thermal and pneumatic) is in robotic arms. Then there are those who see both of these futures as one. Some of them work on the hardware Stratasys and others, like Vynce Paradise, Vice President Manufacturing Engineering Solutions at Siemens PLM Software, work on implementation. We caught up with Mr. Paradise at last week’s TCT and he had quite a lot of interesting details to reveal on Stratasys’ plan to 3D print wing-size continuous composite parts through robotic arm thermal extrusion technology.
“The focus, in the teams that I have working for me, is in two different directions – Vince explained – one is the traditional fixed plain deposition. For example a powder bed would be always referred to as fixed space and most of the systems seen here are working on a fixed plain. My teams are also working on multi-access deposition, so we’re moving the printing – or the positing of the print head relative to the printer bed – on five, six or even seven axes. Generally this is done using a robot and on a machine tool, so typically it refers to metal printing. We print on a converted machine tool because that means we’ve got a chassis which is able to hold large metal components and move them very precisely. Because it’s a machine tool, it can move the component as it is being built in any position.”
3DPBD: Basically you’re talking about using DED or “powder fed” technology?
VP: Yes and now we’re doing both metal and thermoplastics. The main and difference is in the equipment, while the basic path technology has a lot of similarities and the software is a modified version of the software we’ve been using for years to drive subtractive machining. All we do is take the same software techniques and use them to drive the thermal extrusion head. The devil’s in the detail and exactly what the path is to look like is never the same as a subtractive path for many of reasons, but the basic skill sets and the mathematics are similar. I’m very interested in the machine knowing what the part looks like all the time in between operations because I want to know where I go next, whether I should come back with the next tool, and what materials are left. With subtractive technology I’m interested in avoiding collisions, so I need to know the shape of the metal as I’m subtracting material. In additive I have the reverse situation: I’m interested in the shape of the metal or the plastic as I add material because again I want to know where I come back to when I add more material.
3DPBD: Does working on a robotic arm extruder add a lot of complexity to the math?
VP: Really it’s quite different than the fixed plain, if you think about that, as I’m building this part I can rotate it and build up, rotate it and build up, I can point it at an angle in order to avoid adding support. In this process I don’t really need supports. In some cases a part’s features may be such that I can’t decompose and get them in the right orientation so I may have to build a support feature but it will simply be a kind of reinforcement, not starting from the base but from the part itself. I might put a little ledge under a part just to hold it while I’m building it then remove it.”
Davide: So the point of this is to try to give an FDM-like technology to the geometrical freedom of a powder bed type technology?
Man: With powder bed you’re still constrained by the size of the powder, so our goal is to go beyond that. SLS machines are expensive and heavy. If you put two powder bed machines together you don’t get a bigger part you just get two bigger machines. With the robots we could set them on a rail and drive them on multiple axes in order to build really large parts. If we could deposit thermoplastics – ideally with a continuous carbon fiber – we could build parts as large as airplane wings. I may use a robot on a large size gantry machine of the kind that already are working subtractively on airplane wings.
Davide: So you already have software that controls the robots, do an additive or not?
Man: (5:00) Historically… Siemens… We’ve been driving machine tools for years, I mean we’re one of the top players in that camp, so I have customers all over the world that use my software to do the machining in all sorts of industries
3DPBD: What are the challenges of running an additive robotic system on a software level?
VP: It may seem similar, since the parts look the same as subtractive parts, but it’s not. If I’m depositing and I stop putting material in, I’m still spushing powder out with a laser gun. With thermoplastics, it starts to build up so, for example, when I slow down on a corner because of the mechanics of the machine the material startts to build up. It sounds straightforward but you really have to calculate in the electronics or in the controller at a software level? If I’m extruding thermoplastics maybe I want a bead that gets wider as I go along; we never did that with metal so we would need new mathematics to do that”.
3DPBD: That’s a whole new set of calculations…
VP: “Yeah, I’ve got a team who’s been working on this for three years. Their day jobs were on complex five axis machining software; now they’re doing complex multi axis depositions for metals or for thermoplastics”
3DPBD: We’re journalists and we like to imagine things: I always thought that the future of FDM would multi-axes, but is it also multi-robot?
VP: It can be! So that’s where you would go next. Once you get these things done, and you’ve got the right control in place in the systems, you could have two robots. We have production cells at Siemens where you can have two robots which can both perform the same task or different tasks. If you deposit thermoplastics you can get quite a rough finish; so you can come use a more conventional software and a cutter on the side just to smooth it off.”
3DPBD: How concerned are you, from a software point of view, about the actual weight of the robot parts and the extruder being on the head of the robot?
VP: “Not at all, really. These machines, to me, they’re like paper printers, I’m used to massive gantries and cranes and big chunks of equipment so these things are relatively tiny and light.
3DPBD: Do you consider in this process also a pneumatic extrusion system or just thermal extrusion?
VP: On the extrusion system is where we partner we Stratasys. They just invented a new multi-stage extruder and the advantage is that they can control the deposition. That’s really important, so part of the control system is we’re controlling the rudder, the axes, we get the position right and record the position so that the part can simply can sit on the a table which itself can rotate with the robot. The control systems are getting more and more complicated and complex…. The important thing is to control them: to control the extrusion rate so that we control the robot and we can control the extruder’s movement.”
3DPBD: What kind of shapes would this process be used for that cannot be done today?
VP: “Ultimately we’re talking about huge parts. It could be the hood of a car, a turbine blade, fixtures, maybe up to five meters long. Even aircraft interiors.”
3DPBD: But is the goal is to have superior automatization of the process or new geometries?
VP: “Size: size is one of the big things we are going for”
3DPBD: Size through additive manufacturing….
VP: Think of an airplane fuselage part: you’ve got the cut out for a window and the wall, interestingly, is made of a composite form of plastic. In additive today this plastic is made of beads with very very short fibres inside of them. What we’re working towards is AM implementation of longer fibers and even continuous fibers.”
3DPBD: So you could do continuous fiber 3D printing through thermal extrusion?
VP: That’s the plan and that’s the goal!
3DPBD: That’s really interesting!
VP: “The problem with in plain additive manufacturing is that if I put carbon fiber in one plane I can strengthen that plane but not the entire structure in every direction. Now with multi axis I can keep the fibers together in any direction I like.”
3DPBD: So you’re in charge of the software to make this possible, who do you interface for the hardware in this case?
VP: “The robots are pretty standard, they’re Kuka robots but it could be any robot. Unlike the machine tool, that we’ve adapted from the metal DED technology, we haven’t really adapted the robot arm. We just fix it up and screw on the extrusion heads. The control system is from my colleagues at Siemens in motion control, which is a fantastic motion multi-axis controller used on fives axis machines, seven axis machines, robots. So we have Siemens in control of Siemens software, Kuka robots and then Stratasys for the extrusion head, the liquefier and the materials.”
Davide: Thank you, this was very interesting. It seems the industry is very interested at this time about composites and all the ways you can use composites materials in 3D printing, both short and long fiber but the long fibre is the most interesting, although it may take a while longer.
Man: There’s certainly more work to do.