Modern Machine Shop

FEB 2018

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Page 39 of 147

ADDITIVE INSIGHTS MMS FEBRUARY 2018 38 Understanding Industrial 3D Printing Manufacturing for Design, Not the Other Way Around Good designers and engineers know how to design for manufacturing. Using their experience and guidelines for the various processes, they can design parts that are easy and cost-effective to machine, cast, forge or otherwise get into the shape they want. By some estimates, designers and engi- neers spend 30-50 percent of their time designing a shape to achieve the desired function and the rest of their time adapting that shape for the manufac- turing process that will be used to make it. While this is important, it is frustrating to think how much time is spent designing for manufacturing. Additive manufacturing changes that. With AM, we finally have manufacturing for design, because we can make nearly any shape we want with this technology. An AM system does not care, so to speak, whether it is making a solid block or a complex, organic shape; the computer just tells the laser or deposition head where to melt or deposit material in each layer. Yet, as we have discussed in the past, some shapes are easier to manufacture additively than others. For instance, overhanging features printed in metal often need support structures, thin walls can collapse or be damaged depending on their build orientation, and thick sections can tear themselves apart as residual stresses build up inside the part. While no AM equipment provider wants to admit it, these considerations do restrict what types of parts can be made easily with the TIMOTHY W. SIMPSON | COLUMNIST AM allows us to make any shape we want, without having to adapt the design for the manufacturing process. The distinction between oppor tunistic and restrictive DFAM was first introduced in the 2015 ar ticle "Assembly Based Methods to Suppor t Product Innovation in Design for Additive Manufac- turing: An Explorator y Case Study" published in the ASME Journal of Mechanical Design. technology. Fortunately, AM still allows ample opportunities to produce geometries that would be impossible to make with conventional processes. Its opportunistic versus restrictive nature exemplifies how design for additive manufacturing (DFAM) is both freeing and constraining at the same time. The extent to which designers think restrictively versus opportunistically depends on how AM is used. I generally think of three use cases: replicate with AM, adapt for AM and optimize for AM. Replicate with AM In this case, the geometry is given and cannot be modified, because the goal is to replicate an existing part exactly. One example is the link and fitting for a U.S. Navy helicopter that I discussed in the November issue ( ). Replicating with AM is often where organizations start, because they want to be able to make an "apples-to-apples" comparison between the AM part and its conventionally made counterpart. The only real benefit here is speed, because the part is being replicated exactly. It will not cost any less (in fact, it will likely cost a lot more, given the cost of material feedstock for AM systems), and it will not perform any better, or be lighter or stronger. In fact, because the part's geometry was designed

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