Despite its great potential, additive manufacturing has the current drawback of requiring secondary operations to complete a part. A methodology dubbed “AIMS” is attempting to overcome this challenge via an integrated and hybrid, i.e., additive plus subtractive (read: machining), approach.
“Art-to-part” is a term best coined to mean the realization of an idea from conceptualization through to physical manifestation. In manufacturing, the term tends to be centered on step-function improvements of how one moves from computer-aided design (CAD) to manufacturing code (e.g., computer-aided manufacturing, or CAM, tools for generating CNC-like code), all but neglecting multi-process capabilities.
Additive manufacturing (AM) has a unique feature in its design space that better enables complex part features that otherwise could not be affordably or actually manufactured, but it comes with a post-processing cost. This cost has diminished, if not eliminated, some business cases for additive-manufactured products. An option to realize art-to-part with additive manufacturing may be found in synthesizing the best attributes of both additive (e.g., design complexity) and subtractive (e.g., accuracy) manufacturing techniques into a singular hybrid approach. If one were to develop such a capability, then maybe the proverbial “make button” could be closer to reality than we currently suppose.
The somewhat historically limited definition of art-to-part is now being challenged by the researchers at North Carolina State University (NCSU) from a couple of perspectives: 1) converging multi-process capabilities into a singular hybrid solution and 2) enabling the make button with digital manufacturing. While hybrid equipment does exist today, there are still limitations, especially in the metals regime, where support structures and some part features are inaccessible in the additive build orientation. This still requires separate subsequent setup and fixture efforts to complete the part.
NCSU has called its hybrid manufacturing system “AIMS,” or Additive Integrated with subtractive Manufacturing System. Where NCSU has differentiated the AIMS approach is upstream, during the design process. Using seminal work by Pennsylvania State University that was further developed at Iowa State University[1], the research team at NCSU has taken a fully automated subtractive rapid prototyping process (CNC-RP) and incorporated key enabling attributes. In areas of a product that require high dimensional accuracy, high fatigue properties, or mating surfaces, preferential machining processes are required. Other machining processes are also required for support structure removal that is common in many additive manufacturing part designs.
Professor Ola Harrysson describes the new developments: “A new software system will be developed which takes inputs of 1) the desired part file, 2) important features which will require post-build machining, and 3) the material type (to determine machinability index and corresponding machining strategy) and returns outputs of 1) the desired part to be made via an additive process, including the necessary machining allowance, 2) optimized sacrificial support fixtures, and 3) the necessary NC (numerical control) code generated for [the machining process], along with requisite tooling choices and fixture offset information. The architecture will be developed in a modular basis to include future improvements such as adding other processes to meet closer part tolerances (i.e., grinding or polishing for further surface refinements) and automatically generated machining to remove some or all of the sacrificial supports created via AM.”
AIMS may also accommodate related American Society of Mechanical Engineers (ASME) Y14.5 datum schemas to Additive Manufacturing File (AMF) and “.stl” file formats, which is a non-trivial task[2] and requires further investigation to implement.
The AIMS solution addresses a critical issue affecting the adoption of additive manufacturing methodologies: creating a system that will be able to produce a mechanical product to final geometric specification. To date, almost all functional additive manufactured parts have required secondary processing that, in many cases, can more than double the cost of the final part.
A hybrid manufacturing system that leverages both additive and subtractive processing can better enable mechanical parts to be “digitally manufactured” in order to meet the necessary final geometric accuracy required of a part. AIMS exploits digital design optimization capabilities by better realizing the art-to-part process upstream in a more cohesive and synchronized means.
This program, along with other complementary projects (funded through the National Science Foundation), is being developed through America Makes, which was known as the National Additive Manufacturing Innovation Institute.
[1] Frank 2004, Frank 2006, Li 2006, Li 2007, Boonsuk 2009, Petrzelka 2010, Li 2012
[2] NCSU describes that additive processes and the AMF format are made up from triangles, so they are either featureless or triangle-based facets, meaning that even the simplest of specifications, like hole features, will require analyzing and characterizing of several surfaces. These surfaces would also vary with AM build direction.
Tim Shinbara is the technical director of AMT – The Association For Manufacturing Technology. Based in McLean, Va., AMT represents and promotes U.S.-based manufacturing technology and its members – those who design, build, sell, and service the continuously evolving technology that lies at the heart of manufacturing. For more, visit AMT’s website at www.amtonline.org.
