Additive’s idiosyncrasies — producing functional parts

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One organisation that helps companies with ascending that learning curve is the Center for Innovative Materials Processing through Direct Digital Deposition, or CIMP-3D, at Pennsylvania State University. The faculty and researchers in this facility work with companies interested in additive manufacturing to explore processes such as direct metal laser sintering (DMLS), electron beam additive manufacturing and laser metal deposition. For all of these technologies, the value CIMP-3D offers is that it can help companies move more quickly through the trial-and-error period with additive manufacturing by guiding them in investigating the variables to obtain an additive process that is ready for their own particular, proprietary ongoing production.

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What are these variables? I recently had a chance to speak about this with Timothy W. Simpson, Ph.D., professor of mechanical and industrial engineering and a co-director of the center, as well as CIMP-3D R&D engineer Corey Dickman. Some of the variables in an additive process involve the adjustable parameters of a particular additive manufacturing machine. The user of a DMLS machine, for example, might alter the laser power and beam diameter for different jobs and different alloys. But other considerations are more universal to the nature of additive manufacturing. Just as CNC machining has inputs affecting success (such as cutter selection, feed rate and the rigidity of the workholding), additive manufacturing has comparable inputs that affect its success – inputs that the user of additive manufacturing learns to apply over time. Describing these inputs is helpful for developing a more realistic picture of what it’s like to apply additive manufacturing in production. Here, then, are some of the factors that the user of additive manufacturing learns to consider:

1. Topology

To say that additive manufacturing permits complex parts does not go far enough, says Dickman. It does indeed permit this – growing a part in digital layers means that intricate structures for reduced weight are easy to create. However, the fuller truth is that additive manufacturing actually prefers this complexity. Tailoring the form of a part to match only the load that part has to carry and the service it has to perform results in an additive build that uses less material, requires fewer supports while the part is growing and is less prone to the accumulation of residual stresses.

The search continues: graphite or copper – which to choose?

The figure on the right shows an example. Penn State graduate student Jessica Menold submitted this entry in a GE-sponsored contest to redesign an aircraft bracket. Her design, if produced in metal, would be 88 percent lighter than the bracket that had previously been in use, while still meeting the design requirements for this part.

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