Modern Machine Shop

JAN 2018

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Page 39 of 163

ADDITIVE INSIGHTS MMS JANUARY 2018 38 Understanding Industrial 3D Printing Lightweighting with Lattices In the last two columns, we've explored two "speed plays" enabled by additive manufacturing (AM): direct part replacement and functional prototyping. In both cases, we also saw the related challenges of additively manufacturing parts that were not designed to be fabricated layer by layer. Namely, these challenges involved extensive post-processing to remove support structures and finish the parts so that they would be comparable to traditionally machined parts. We used the example of a piston crown to show how adapting a design for AM can help avoid some of the challenges. But if you had the freedom to design and develop a completely new geometry for additive manufacturing, could you improve part quality and performance, and reduce costs? I have mentioned techniques like topology optimization and conformal cooling before, but here I'd like to discuss lattice struc- tures, which AM can produce much more easily than conventional manufacturing. A lattice is made of repeated unit cells. There are countless options for the size and shape of such a cell, and for how it is repeated, and there are a lot of examples of lattice structures being used to provide internal support, reduce the amount of material or improve the strength-to- weight ratio of an AM component. Lattices can be uniform, meaning the exact same cell is repeated in all directions, or variable, meaning the size or spacing of the cells is different in different directions. Variable lattice structures are gaining traction in medical applications such as implants, as the variability of the cells enables such implants to better mimic our own bones. Bones are not solid, fully dense structures, so lattices can provide comparable strength-to-weight ratios and better osteointegration, resulting in quicker recovery and better performance. An added benefit of lattice structures is they can be additively manufactured faster, using less material and therefore requiring less build time TIMOTHY W. SIMPSON | COLUMNIST Instead of building components as a solid, building them as a network of unit cells may improve material utilization and performance. Building this oil and gas component additively using lat tice structures reduced its weight by 40 percent. Image provided by Imperial Machine and Tool Co. This cross section shows the component's "snaky" internal channels and the lat tice suppor t structure. than fully dense, solid components. This improved material utilization in some cases also allows use of better, more expensive materials. Case in point is the oil and gas component for downhole applications shown in Figure 1. This component pumps fluid up and down an oil well by means of "snaky" internal channels (see Figure 2). Traditionally, it is made by carefully machining internal channels into a solid block of metal. The internal shapes that can be machined and the Fig. 1 Fig. 2

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