Additive Manufacturing

AUG 2015

Modern Machine Shop and MoldMaking Technology present ADDITIVE MANUFACTURING, a quarterly supplement reporting on the use of additive processes to manufacture functional parts. More at additivemanufacturinginsight.com.

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10 — AM Supplement F E A T U R E Precision Without Deposition By Peter Zelinski 3 D printers building functional parts in plastic share a characteristic in common. Chicago- area inventor Robert Swartz would argue that they share a limitation in common. That is, these machines require material to be forced through a head, and from there layered onto the part. The head, and the need to apply material this way, affects what materials can be used and therefore constrains the range of material properties that can be achieved. Swartz has a different idea. His company, Impossible Objects, was founded to develop a process he calls "composites-based additive manufacturing," or CBAM. In this process, thermoplastic material is used, but it is not applied through a moving head. The process recently manufactured a carbon fber component for an un- manned aircraft that successfully replaced a part prone to breaking when the aircraft landed. CBAM builds carbon fber parts by stacking sheets of the material. It can also build parts out of Kevlar, or any engineered material obtainable in sheets. Each successive sheet gets a fuid ap- plied to it in a precise profle generated from the cross-sectional layer of the CAD model. Only this step involves a digitally controlled moving head. The fuid, a noncritical ingredient, temporarily holds in place a thermoplastic, which is applied onto the wet silhouette in a powder. Successive sheets with plastic powder adhering to the part profles in this way are stacked until the layers are complete. The entire stack is heated so the plastic melts between layers, and mechanically compressed to bond the sheets and plastic together. Then, after the part solidifes, the unbonded sheet material around it is removed by bead blasting. The result, says Swartz, is a workpiece that is up to 10 times stronger than what plastic 3D printing can achieve—produced without any precision-controlled deposition or cutting in order to apply or shape the material. The process is currently being applied manually. Impossible Objects is functioning as a service bu- reau today, supplying functional CBAM parts to end users. But the ultimate aim is to produce a commer- cial, sheet-fed CBAM machine, says company CEO Lawrence Kaplan. It's too early to announce when that machine will be available, he says, but the proj- ect is actively underway. In addition, components for automating the process will be introduced into the current service business as they are developed. Yet even for now, the manual process—in which employees place sheets by hand on a gantry ma- chine that applies the fuid, and manually dust these sheets with powder—is not as ponderous as it might sound. A batch of several 3D-printed parts covering the area of an 18-inch square of sheet material could be produced through this manual process in 6 to 8 Here is a selection of parts made from the composites-based additive manufacturing process. Just above the little gear, the part with two parallel legs is a production part currently fying on unmanned aircraft. Is it possible to 3D print with carbon fber fabric? It is, except that "printing" is not the right word. This additive process builds parts by stacking the carbon fber sheets. The result is composite parts that don't need tooling—but are strong enough that they could be used as tooling.

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