3rd June 2013 by Bob Yancey
Additive Layer Manufacturing (ALM) has been around for some time. I got involved with this industry almost 20 years ago when it was called Rapid Prototyping and then 3D Printing and now ALM. ALM builds structures layer by layer which is different than traditional manufacturing methods which either starts with a shape and machines away the excess or uses tooling to form a part to net shape. Some ALM processes rely on lasers to cure or solidify the material and others deposit the material through tiny nozzles but all methods build up a part in thin layers.
It has been a great technology for creating prototypes but has had little application in making production parts. New methods and new materials have emerged more recently that may be able to make ALM more relevant to production applications. A good article appeared recently in Technology Review that discusses some of the current and future applications of the technology. Altair recently had an ALM panel at our European Altair Technology Conference where leaders from the industry discussed the technology and its applications.
When I joined Altair in 1999, given my involvement in the Rapid Prototyping industry, I immediately saw a connection with OptiStruct. At the rapid prototyping trade shows, rapid prototyping service bureaus would often have give-away items produced on their equipment that could not have been manufactured in any other way. Items like a ball inside a cage or a staircase inside a little castle were cool little trinkets that demonstrated what you could do with the technology. Since you are building the part layer by layer, you could include intricate internal details inside a closed structure.
With the topology optimization technology that forms the basis of OptiStruct, the optimal structure is often one with an internal structure enclosed in an outer shell. Since topology optimization was inspired by looking at structures in nature and trying to understand the mathematics behind these designs, it produces organic looking structures that have material only where it is needed. For any structure that has to carry bending loads, we know that it is best to have material on the outside. If you want to minimize mass, that means we want little material near the axis of the bending load. Nature uses this principle and we see this most evidently in the structure of bones which have a solid outer layer and a porous inside.
Due to the limitations of current manufacturing methods, Altair has put in many manufacturing constraints in OptiStruct to produce designs that can be made with current manufacturing methods. This produces designs that can be machined, cast, molded, or forged but they are no longer optimal designs from a purely structural performance standpoint. ALM changes this as now we don’t have any manufacturing constraints to limit us so we can create truly optimized designs. ALM really opens the applications of OptiStruct.
Topology optimization technology is based on finite element analysis (FEA) so OptiStruct was designed in a traditional FEA user environment. It became another user profile in HyperMesh and we added optimization set-up dialogs in the interface so the user can put all of the specific FEA information into the solver deck to solve the problem and produce results. For an FEA user familiar with HyperMesh, learning how to run OptiStruct is a relatively simple process. It can take some time to understand the best set-up for a particular type of problem but learning how to navigate the interface is pretty intuitive for the experienced HyperMesh user.
Several years ago, Altair recognized the challenge that FEA engineers are often not that involved in the design of the structure. They definitely analyze the structure and provide feedback on sizing, areas of concern, potential failure modes, and choice of materials but they usually do not originate the design. Industrial designers and design engineers develop the initial concepts, the styling, and the function of the part, and they are generally not familiar with FEA methods so it makes it difficult for them to use OptiStruct. Altair’s solution to this is solidThinking Inspire™ which is easy to learn and works with existing CAD tools to help design engineers use topology optimization to design structural parts right the first time. This puts the technology in the hands of the people that create the designs and gives them a mathematical engine to produce optimized designs.
Now with ALM, the design engineer or the FEA analyst can create optimized designs that can be manufactured without the traditional constraints that have existed with traditional fabrication methods. Since nature produces optimal designs and we look to nature for inspiration, ALM coupled with topology optimization can open the way to truly create shapes that are optimized for the function on which they are called to perform.
In looking to the future, ALM has the possibility to grade the material properties in the structure just as we see in nature. For example, bones are not composed of a single outer layer and then a porous center but the material transitions in structure and material properties throughout. ALM holds the promise of eventually engineering the structure molecule by molecule so that the optimal amount of material and the optimal material properties exist throughout the structure. For example, if one could vary the alloy composition such that you had high stiffness where stiffness is needed and more ductility where controlled deformation is needed, you could create integrated structures without traditional bond or weld lines that would be optimized for function and performance. This may be off into the future, but we see how technology continues to march forward and initial applications of this concept may not be too far off. There is active research on-going to simply vary material properties by varying process parameters so that is starting to be available now. As this continues to develop, be assured that Altair will provide the design technology that will help us make the most of ALM.