Solid Freeform Fabrication Process Research Articles

Modeling and designing functionally graded material components for fabrication with local composition control

Solid Freeform Fabrication (SFF) processes have demonstrated the ability to produce parts with locally controlled composition. In the limit, processes, such as three dimensional (3D) Printing can create parts with composition control on a length scale of 100 μm. To exploit this potential, new methods to model, exchange, and process parts with Local Composition Control need to be developed. An approach to modeling a part's geometry, topology, and composition is presented. This approach is based on subdividing the solid model into sub-regions and associating analytic composition blending functions with each region. These blending functions define the composition throughout the model as mixtures of the primary materials avialable to the SFF machine. Design tools based upon distance functions are also introduced, such as the specification of composition as a function of the distance from the surface of a part. Finally, the role of design rules restricting maximum and minimum concentrations is discussed.

Design by Composition for Layered Manufacturing*

Three dimensional rapid prototyping processes, also called layered manufacturing or solid freeform fabrication (SFF), promise designers the ability to automatically fabricate complex shapes. SFF processes were invented with the assumption that designers would submit complete part models for automated planning and manufacturing. This planning process is normally based on some form of “decomposition,” for example, slicing into layers. Especially for newer, more complex SFF processes, there are several disadvantages to this approach, primarily that decomposition is difficult and does not reliably produce good process plans. Furthermore, it is hard for the designer to get feedback on the manufacturability of his design, and today’s decomposition systems are not fully automated. This paper presents an alternative approach, “design by composition,” where users build designs from “primitives” that include high-level manufacturing plans. When the user combines two primitives with a Boolean operation, software will automatically generate a manufacturing plan for the new design from the plans for the source primitives. In contrast to the decomposition method, design by composition offers several benefits to designers, primarily access to manufacturability feedback during design-time, a greater degree of automation, the ability to create designs with embedded components (such as sensors, electronic circuits, bearings, and shafts), and enhanced control over manufacturing plans. These advantages make design by composition a more attractive approach to SFF processing, especially for designers who are new to these processes. [S1050-0472(00)01701-3]

Rapid Tooling Die Cast Inserts Using Shape Deposition Manufacturing

Solid Freeform Fabrication (SFF) platforms such as stereolithography have successfully created rapid tooling injection molding inserts to produce plastic parts. However, the rapid tooling of viable aluminum die casting inserts presents more challenges because of the high pressures and temperatures associated with aluminum die casting. The objective of this research was to optimize the Shape Deposition Manufacturing (SDM) process to produce die cast inserts. SDM is a SFF process which can produce fully dense metal structures with Computer Numerical Control (CNC) accuracy. SDM laser-based metal deposition of tool steel powder was optimized for material properties by a Taguchi based design of experiment utilizing the process parameters of laser power, laser scanning rate, and powder feed rate. An insert was created using the optimized settings and run in a 600 ton die cast machine. The insert was used in the “as deposited” condition without any heat treatments. Over 150 aluminum pieces wsre produced without any signs of insert wear or fatigue.

Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing

Polylactic acid (PLA) is a bioresorbable polymer that is used in a number of clinical situations. Complex shapes of PLA are commonly machined for bone fixation and reconstruction. Solid free form fabrication methods, such as 3D printing, can produce complex-shaped articles directly from a CAD model. This study reports on the mechanical properties of 3D-printed PLLA parts. 3D printing is a solid free-form fabrication process which produces components by ink-jet printing a binder into sequential powder layers. Test bars were fabricated from low and high molecular weight PLA powders with chloroform used as a binder. The binder printed per unit line length of the powder was varied to analyze the effects of printing conditions on mechanical and physical properties of the PLA bars. Furthermore, cold isostatic pressing was performed after printing to improve the mechanical properties of the printed bars. The maximum measured tensile strength for the low molecular weight PLLA (53 000) is 17.40 ± 0.71 MPa and for high molecular weight PLLA (312 000) is 15.94 ± 1.50 MPa.