| This work focuses on characterizing and manufacturing porous metal scaffolds for bone ingrowth. First, the formability of a conventional scaffold, Trabecular Metal (TM), is studied. Manufactured using chemical vapor deposition (CVD) on top of a carbon foam substrate, TM has a regular matrix of interconnected pores, high strength, and high porosity. Conventional processing has involved machining the desired parts from bulk TM disks using milling or electrical discharge machining (EDM). EDM is time consuming, and since many desired part geometries have thin cross-sections, both EDM and milling are costly and wasteful. For these reasons, plastic deformation through stamping is thought of as a viable alternative to machining, but a better knowledge of the forming properties of TM is needed. As such, a forming-limit diagram for TM is obtained using 1.65 mm thick sheets. To overcome difficulties associated with inscribing circles to measure the surface strains of a porous material, CCD cameras are employed to monitor the strain state evolutions. In addition, lubricants are not used due to the cleanliness requirements for orthopedic implants.; The elastic recovery of Trabecular Metal after forming is also examined. Experimentally, bending about a single axis using a wiping die is studied by observing cracking and measuring springback. Die radius and clearance strongly affect the springback properties of TM, while punch speed, embossing, die radius, and clearance all influence cracking. Depending on the various die radius and clearance combinations, springback factor ranges from 0.70-0.91. To study the effect of the foam microstructure, bending also is examined numerically using a horizontal hexagonal mesh. As the hexagonal cells are elongated along the sheet length, elastic springback decreases. At zero clearance, the numerical results are slightly higher than the experimental ones. However, larger differences at higher clearances result from an imprecise characterization of the post-yield properties of tantalum.; Along with the characterization of the formability of Trabecular Metal, a novel method for ingrowth scaffold fabrication is developed. This layered manufacturing approach involves several steps. First, thin layers are machined to have a desired microstructure. The layers are then treated, stacked, and bonded together. The result is an ingrowth scaffold with many material and microstructural possibilities.; To examine the feasibility of using a layered approach to generate an ingrowth scaffold, metal prototypes are created. Layer geometries are derived from a bovine tibia sample to generate a biomimetic microstructure. Using laser machining, these microstructures are cut into titanium foil. The laser cut layers are then treated by a chemical etching process to remove any slag and remaining slugs. Then, the layers are stacked and joined together by diffusion bonding. The final result is the fabrication of three metal ingrowth scaffold prototypes and the validation of the manufacturing process. |
