Yong Chen of the Daniel J. Epstein Department of Industrial and Systems Engineering hopes to improve the current tools and processes -- and particularly, the software -- involved in in the growing field of digital manufacturing.
Chen: "People don't have experience, so they are hesitant. It will take time."
The solid freeform fabrication (SFF) processes developed for rapid prototyping, sometimes called "3D printing," have been widely adopted as a common practice in product development. However, to evolve these processes from prototype usage to direct product manufacturing purposes, significant advances in material, process and machine development are still required. Chen and his group are developing new SFF processes based on new technologies, such as digital micro-mirror device and inkjet printing.
"This field, which started developing about 20 years ago, currently involves a lot of new technology, which is why I am excited about the possibilities in this area,” he says.
Recently the Society of Manufacturing Engineers (SME) chose direct digital manufacturing, together with self-assembling nanotechnology, as one of the five “Innovations That Could Change the Way You Manufacture”.
A functional prototype based on Texas Instrument’s Digital Light Processing (DLP) technology has just been developed, which was funded by a research initiation award from the Society of Manufacturing Engineers. The process demonstrates significant cost and time benefits. Another research area of Chen' group is to investigate advanced computational techniques in process planning to improve the existing solid freeform fabrication processes such as Stereolithography (SLA) and Selective Laser Sintering (SLS).
“Different requirements in the manufacturing environment pose significant challenges, even though these processes have been widely adopted in rapid prototyping. For example, much better accuracy and surface finish, shorter building time and a higher degree of manufacturing automation are generally required for direct digital manufacturing,” said Chen. “Achieving theses requirements will require significant efforts, yet they are critical for a wider adoption of direct digital manufacturing in industries such as aerospace and the medical field.
Shapes within Shapes: new systems expand the boundries of manufacturing.
“The main reason for the SFF processes to be called a direct manufacturing process is because they can fabricate parts directly from CAD (computer aided design) models without part-specific tooling or fixtures. For the first time in history, we have a set of manufacturing processes that can cost-effectively fabricate truly complex 3-dimensional shapes in macro- and meso-scale levels,” said Chen.
“So if direct digital manufacturing is realized, the primary advantage is not its capability to reduce the manufacturing cost of the old design, but its capability to allow revolutionary new designs when complex geometry is no longer a limiting factor.”
But a major roadblock remains, Chen says: software.
“Unfortunately, existing CAD tools are inadequate for taking advantage of SFF’s unlimited geometric capabilities. They are developed for traditional manufacturing processes, in which there is a direct link between the complexity of a component and its cost. So the benefits of using DDM’s complex geometries for better design are still mainly untapped,” Chen says.
The challenge is therefore clear, the researcher continued. “To fully utilize the design freedom provided by DDM, it is crucial to develop new design methods and related CAD tools for product designers. Since this research field is so new, we do not yet know what capabilities should be included in the CAD tools for direct digital manufacturing.”
Supported by a USC Zumberge research initiation award, Chen has been testing various complex internal structure designs, both rigid and flexible, for better design performances. He believes the components with optimized rigid internal structures can minimize the weight of the final product while ensuring desired structural performance. This is attractive to the aerospace industry, in which reducing weight is a major design goal.
For a year, Chen has been testing his ideas with Solid Concepts, a company that supplies rapid prototyping, direct digital manufacturing, tooling and injection molding services to the aerospace industry.
“In the future, we may use complex shape design to achieve heterogeneous material properties, that is, material properties are different at different places and directions,” Chen says. “This may lead to a better design for applications such as customized cushions for debilitated patients.”
His team proposed the idea of performance-tailored mesostructures which can change or adapt their design performance based on 
given requirements. “Our goal is to develop a Computer-Aided Design (CAD) tool with the capability of specifying heterogeneous material properties in a product component, such that a designer can design the component with better performance," says the researcher, who came to USC in 2006. Chen now teaches manufacturing processes, computer-aided manufacturing and advanced computational design and manufacturing.
"A product designer can use our developed CAD system to generate CAD models with performance-tailored mesostructures. The generated CAD models can then be fabricated by a layer-based rapid manufacturing system," he continued. “Since direct digital manufacturing is new, people don’t have experience to use this new technology in their design and manufacturing. So they are hesitant.
"Like all new technologies, it will take time to find widespread use. People will gradually adopt it for its cost benefits. As far as the design performance is concerned, we don’t have a clear idea of what the technology can achieve. We know its capability, but no one knows what features are required for creating those designs that the technology is capable of creating,” says Chen.
With time, he hopes solutions for these problems will be discovered.
In May of next year, Chen plans to release a complex internal structure design software system. The effort is sponsored by a National Science Foundation (NSF) STTR award with Solid Concepts. If successful, Solid Concepts plans to add it to its software product, SolidView. Major aerospace companies such as Lockheed Martin and Northrop Grumman have showed interest and agreed to test the software.
