Additive Manufacturing

SEP 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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SEPTEMBER 2018 Additive Manufacturing FEATURE / Metal Additive Manufacturing 30 cutting strategies, which 3DEO refers to as its "Intelligent Lay- ering" strategies. Parts can be cut after every layer for the best tolerances, or after multiple layers to save time. For 2.5D parts or features, up to 10 layers can build up before machining, sav- ing time. The machine can also cut at depths of less than a full layer's thickness to create intralayer features and enable finer tolerances than the printer could alone. Or, it can cut across multiple layers in a three-dimensional tool path to eliminate stair stepping and improve the finish. Once the print is complete, the entire block of material is removed from the printer. Parts are freed from the cake using the "super puncher," a device fitted with custom tooling that forces the parts to break out through the bottom of the powder cake. Excess material is removed manually, and then the parts are sintered in a standard MIM furnace that accommodates as many as 5,000 pieces at a time, in 10 to 15 trays. Facing the Competition 3DEO doesn't see other metal AM processes as its competition. Rather, it is competing with CNC machining, with investment casting and with MIM—and currently thriving on complex geometries that would be difficult or time-consuming to make with these methods. Part of 3DEO's advantage comes from its pursuit of a "balanced line," McGough says. A MIM line can become unbalanced because the furnace can be a bottleneck. MIM parts require a debinding step and then a 24-hour sintering cycle, which means a furnace can only sinter one batch per day. But because 3DEO's parts have low binder content, they can go straight into the furnace, no debinding required. And, a sintering cycle for these parts takes only 12 hours, essentially doubling production volume over MIM. The sintered parts are more than 99 percent dense, with properties that are actually closer to wrought material than MIM parts, the company says. Part quality is another advantage. The company's printers are capable of holding one thousandth of an inch in resolution, and raw parts out of the furnace have surface roughness ranging from 100 to 120 microinches Ra. "The closer you are to near-net shape in the printing process, the lower the cost," McGough explains, that is if the cost for a metal part comes from achieving near-net shape (through 3D printing, casting, etc.) and then machining it to final dimensions. For example, the company currently manufactures a few hun- dred gear parts per month that previously cost $30 to $40 apiece to machine. The 3D-printed gear still requires post machining, but 3DEO's process enables including starter hole in the near-net shape, which saves time in finishing and helps locate the hole correctly, reducing scrap and overall cost. This isn't to say that 3DEO would always win work away from these more established processes, especially on simpler designs. But it currently thrives on small to medium volumes—applica- tions in which the quantity of parts requires a prohibitively high number of change-overs for milling or EDM, or where MIM tooling would be too costly to justify the batch size. For example, 3DEO recently won a job producing 2,400 pieces per month of a part that was previously CNC machined, with a tight hole location tolerance. When order quantities increased to this new level, the machine shop declined to ramp up production because the change-over between each piece would make the job too time consuming. 3DEO was able to make the part using the original design, competing only on the strength of its process. Toward Repeatability at Scale For now, the company relies on 100 percent inspection of its production parts. The goal, however, is to get away from the need to inspect every part by more tightly controlling the pro- cess overall. Once the process is dialed in this way, the company says it can scale up accordingly. With this end in mind, 3DEO is embarking on a detailed process mapping exercise, with the goal of understanding pro- cess ranges and variations, and then keeping each print within predictability zones. For instance, 3DEO has found that the bed temperature has a direct influence on the quality of the part, and therefore should be held consistent within the bed and across all the printers. The ability to monitor and adjust bed temperature will be one more way of ensuring part quality. Long-term, automation is the objective. The bones of closed- loop control are already in place, with an overhead camera inside each printer that takes a 4K-resolution image of every layer. One day the machine control will use these images to detect errors in the layer and instruct the printer to lay down more material or perform additional machining to correct it. 3DEO will eventually utilize a central server to communicate with all its printers, with monitoring software to provide alerts and real-time control. Tracking machine to machine, part to part and layer to layer is a step toward machine learning for more repeatable production. Other advancement will include adding more machines— the current facility could support as many as 50 printers—and bringing postprocessing capabilities in-house. There's also potential to sell the "pods" as self-contained systems in the fu- ture, but 3DEO is in no rush to get there. Instead the focus for now is fast-tracking its services to customers by finessing the process, adding new materials and pursuing certifications. For 3DEO, these efforts represent its ongoing pursuit of repeatabil- ity, which is ultimately the enabler of production. "Getting the part right three times is trivial," Petros says. "Getting it right three thousand times, or three hundred thou- sand times, is the goal."

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