But engineers know that making spindly parts is not how lightweighting works. The spindly parts paraded before them, the result of topology optimization, will never hold up in design review – much less in real life. A more realistic approach would be to use lighter material, carefully reduce volume and maybe make it hollow. Like a round tube that is perfect in tension. Or monocoque. If you hollow a part, you can’t make it so thin that the walls collapse. So, you fill the void with something, anything… structural foam, perhaps, or a cellular structure. A honeycomb would work if it was a flat shape, like a floor panel, but your part is not like that. You need a cellular structure that can conform to a shape, that can vary according to a loads or restraints. Where have I seen that? Was it a dream?
It's not a dream for orthopedic surgeons, zoologists, naturalists… or any others who have studied bones where the irregular cell structure you were dreaming of can be found. The head of a femur, for example, is smooth and solid on the outside and remains solid for a few millimeters into the bone but gives way to microscopic cells at first then cells large enough to see in the middle. An engineer seeing a section of a femur for the first time will have these thoughts in quick succession: 1) God is an engineer and 2) why can’t my design software do this?
CAD software vendors and most generative design vendors, too, give lots of reasons why design software cannot do what Nature (or God, if you prefer) has done for so long and done so well. CAD software, almost all of them, built on standard geometry kernels, cannot handle the fractal-like detail of cells and lattices. There are simply too many faces for the software to generate and display. It’s a capacity problem.
But one company, nTopology, has found a way to handle the complexity. They have their own geometry kernel. They don’t rely on Parasolid, ACIS or one of the other B-rep (boundary rep) geometry kernels.
nTopology, arguably the most advanced generative design software, just increased its lead with its latest release with its “3rd generation” of lattices.
nTopology now creates lattices with speed – lots of it. The company says that in one benchmark a lattice that took 45 to 60 seconds was rebuilt in 1-2 seconds. Lattices are created ten to one hundred times faster, they say. For a model with as many elements as lattice patterns create, speed to create and display all of them comes from harnessing the power of the graphical processing units, or GPUs, found in most workstations.
Indeed, the improvements in lattice generation are most intriguing. nTopology looks like it can lightweight a part like nothing else on the strength of its lattices. We requested a demo to see the new latticing for ourselves.
Todd McDevitt, nTopology head of product development, was kind enough to accommodate us. Todd, a mechanical engineer (PhD, University of Michigan) has worked at Ansys and MSC. He knows his way around simulation, the hidden engine of nTopology.
Todd took us through lightweighting a part with nTopology 3.0 starting with the construction of a unit cell. nTopology allows you to design the elemental geometry, which when repeated along 3 axes, will fill up a volume. Volumes can be rectangular, cylindrical or spherical. nTopology worked for almost two years to create a library of 37 elements. Previously, nTopology had 25 elements.
The volume can be set up in nTopology or can be imported CAD geometry. We will see this as we fill the sole of a shoe. Wait for it.
You might be wondering if the ability to design a lattice structure is a big deal. CAD programs, which have only recently started offering lattices, offer only a few simple element shapes and do so reluctantly. The number of geometric shapes a lattice structure produces can overwhelm a CAD programs. Your part, hollowed out and filled with a lattice structure, will make your CAD program grind to a halt.
In our demo, we see a few volumes filled with the microstructure. We’ve seen this before. We’re starting to fidget.
Then the shoe drops. Literally. It's the sole of a shoe, imported from a CAD program. It’s going to get filled in with a dense cell structure for the heel, because there is where the highest impact forces will be in a running shoe. Forces will be less under the ball of the foot and denser yet everywhere else. Different distinct volumes, each with a different cell structure. We’ve seen that movie.
But here Todd throws in a twist. The regions under each part of the foot are not distinct. The density of the microstructure varies gradually between low pressure and high-pressure areas.
And the best part? The pressure is read in from a simulation (Ansys?). We see red areas under at the heel and where the ball of the foot would go. nTopology has reacted to the pressure map and created (what looks like) the right size of microstructure. Automatically. Todd calls this field-driven design. (Soon to come is field driven optimization, where the size of the local infrastructure not only looks right, it is confirmed.) The whole of the sole is filled with (what looks like) the right density for the specific varying loads and itself varies seamlessly and gradually between high- and low-density regions. There are no distinct sub-volumes, each with a specific uniform lattice pattern. They get bigger and smaller from one area to another gradually. Where have we seen that? Oh, yeah: Nature.
Field-driven generation of lattices is the key improvement for nTopology. Every other generative design will have you apply forces one at a time, which can be a laborious process.
Being able to do something similar to what Nature does naturally should be a wakeup call for design software. Under the spell of conventional solid modeling, we have accepted shapes that are straighter, smoother and rounder than any naturally occurring shape. All our machined parts were solid because our stock material was solid and hollowing it out was more machining, so more time and money. We have become designers whose designs are dictated by our design tools and stock material.
While all the time, the optimum design was under your nose. About 3 ft under. About the distance from your nose to the top of a femur.
Find out more about nTopology's new latticing capability here.