Solid Freeform Fabrication - Milwaukee School of Engineering

What is Solid Freeform Fabrication?

FDM Machine Solid Freeform Fabrication (SFF) is an important developing technology that enables the fabrication of custom objects with novel properties directly from computer data. The basic operation of any SFF system consists of slicing a 3-D computer model into thin cross sections, translating the result into 2-D position information, and using this data to control the placement of solid material. This process is repeated for each cross section and the object is built up one layer at a time. Solid Freeform Fabrication has historically been associated with manufacturing environments, where it is used for the rapid production of visual models, low-run tooling, and functional objects. The impact of SFF goes far beyond these applications, however; the additive nature of SFF techniques offers great promise for producing objects with unique material combinations and geometries which could not be attained by traditional manufacturing methods. Because of this, Solid Freeform Fabrication is seeing increased use in fields as diverse as biomedical engineering, electronics, aerospace, architecture, and archeology.

Solid Freeform Fabrication Equipment at MSOE

Milwaukee School of Engineering is the only university in the world to have equipment representing all four major rapid prototyping technologies available for student researchers. Other research facilities include extensive computer and software systems, vacuum systems, materials processing equipment, a full machine shop, and specialty research apparatus developed for specific projects.

Stereolithography (SLA)

Stereolithography uses a UV laser to create successive cross-sections of a three-dimensional object within a vat of liquid photopolymer. The cross-sections build layers typically of 0.004 inches or 0.006 inches. A platform is placed on top of the vat filled with the polymer (an epoxy resin). Just before the build begins, the platform is moved to a point just below the surface of the resin. As the UV laser (a Helium-Cadmium laser) traces the layer in the polymer, the resin begins to cure; thus, solidifying the part to be manufactured. Once the cross-section has been traced with the laser, the platform drops down again and the same procedure takes place until the object is fully constructed. The parts that are built using the stereolithography machine are durable, but fragile. These parts must be handled with extreme care. The dimensions of these parts are very accurate, only varying at times by 0.002 to 0.005 inches. The SLA machine is also highly accurate with building parts containing complex geometries and intricate details.

Laminated Object Manufacturing (LOM)

Laminated Object Manufacturing uses a carbon-dioxide laser to create successive cross-sections of a three-dimensional object from layers of paper with a polyethylene coating on the backside. A sheet of paper is laminated to the previous layer by a roller which provides heat and pressure. The carbon-dioxide laser then etches the outline of the cross-sectional pattern into the top layer of paper. The laser then proceeds to create hatch marks, or cubes that surround the pattern. The cubes behave as supports for the part to ensure that no shifting or movement takes place during the entire build. When the build is completed, the part must be "decubed" to removing the supports. Often times the supports can be removed from simple shaking the part; other times it is necessary to use a chisel to pry the cubes away from the part. When all of the cubes have been removed, the unfinished part is sanded down and a lacquer is used to seal the part. The LOM is very useful in manufacturing large parts quickly.

Fused Deposition Modeling (FDM)

Fused Deposition Modeling creates successive cross-sections of a three-dimensional object from deposited beads of ABS plastic or investment casting wax. Similar to a hot glue gun, the FDM heats plastic to a temperature just below its melting point, then extrudes the plastic through a small nozzle. As the nozzle moves in both the x- and y-axis across a foundation, it deposits beads of material. Once the material is forced through the tip, the plastic becomes hard again and fuses with the previously deposited layer. In this way each cross-sectional pattern is laid down until the object is completed. The FDM had the advantage of utilizing ABS plastic (a tough, durable material) and building parts in a variety of colors. The envelope build space for the Stratasys FDM-1650 is 10"x10"x10".

Selective Laser Sintering (SLS)

The Selective Laser Sintering process creates solid three-dimensional objects, layer-by-layer, from plastic, metal, or ceramic powders that are "sintered" or fused using CO2 laser energy. The inherent materials versatility of SLS technology allows a broad range of advanced rapid prototyping and manufacturing applications to be addressed. A number of plastic-based powders are used to produce functional models directly in the SLS process. These models can be used for advanced testing in an environment similar to that intended for the final product. The tooling and patterns are built from a variety of plastic, metal, and ceramic-based powders.

Rapid Prototyping of Complex Composites for Biomedical Applications

"You will learn a ton, not just about RP but also about yourself. The experiences you have will force you to think about things in a new way. You meet a lot of new people, and a lot about other technologies. This was awesome!"

--Becky Zick, Milwaukee School of Engineering

The impact of the program on student participants can best be illustrated by an example from a previous REU project. Becky was a Junior-level Biomechanical Engineering Major. She had no previous research experience, and limited computer use and independent project background. Becky was teamed with an advisor who is a professor in Biomedical Engineering at MSOE. The problem presented was to create a mechanically-accurate model of a vertebra. Background information was available detailing previous attempts to use SFF in aerospace applications to create complex composites, and previous work using medical imaging to produce the surface geometry for SFF models. Solving the problem required library research, discussions with her advisor, and phone/e-mail correspondence with radiologists at the Medical College of Wisconsin. Becky ultimately developed a method to use existing software to identify not only external geometry, but to create CAD files that differentiated between dense and spongy bone. Again accessing a knowledge base of previous REU laboratory books and with the assistance of mechanical engineers involved in a tooling project, she modified existing techniques to ultimately create a vertebra model that was produced with two chambers.

Her experience under the REU Program ended at this stage, but Becky continued this work with her advisor and with the Veteran's Hospital of Milwaukee to fill each chamber of the model with different composite materials that more accurately represents the mechanical properties of each bone type. She ultimately was the co-author on a number of papers, and presented her work at national conferences. The topics she learned from her experience include the scientific method, anatomy, physiology of bone, biomaterials, composites, medical imaging, use of specialized software (3 types), technical communication, specialized manufacturing, and Solid Freeform Fabrication.

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