Additive’s idiosyncrasies — producing functional parts
Yet how does the engineer who is seeking this kind of design optimisation—that is, this kind of improvement through subtraction—actually know what material to subtract and what form ultimately matches the load paths in the part? Most design engineers have not had to face these questions, because they work with constraints so common to manufacturing that we don’t even think of them as constraints. That is, designers are usually required to begin with a solid block or semi-net-shape form, machining away material to obtain external features. Elaborate forms are beyond consideration because machining can’t produce them. Take this limitation away, and the resulting freedom is actually too vast for an unassisted engineer to know what form to select.
That is why additive demands a different approach to design, Dickman says. Software tools operating at a higher level than traditional CAD are employed to begin with boundary conditions defining the part’s function and available space. These tools then calculate an efficient geometric form for those conditions through iterative mathematical analysis.
Most machine shops have never heard of these software tools, but they do exist, and CIMP-3D has grown accustomed to them. One choice at the high end, Dickman says, is Altair Optistruct. This software’s geometric calculations are sophisticated enough that the software might need to be left running all night to perform a topology optimisation for a particular form. Less capable but easier-to-use optimisation tools include Solid-Thinking Inspire, he says.
One of the problems with the false picture of additive manufacturing literally “printing” a ready-to-use part is that this picture overlooks the amount of physical support the part is liable to require while being built. In metal additive manufacturing, support structures help transfer heat away from the part as new additive layers are added and also help hold the part’s shape as it forms. A typical step in the design of a part produced additively is designing its support structures.
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