Localized Finishing of Freeform Geometries using Dynamic Magnetic Field-Manipulated Magneto-Viscoelastic Fluids

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Demand for biomedical prosthetic implants (e.g., total hip joints) is growing by 5 percent annually and this market is expected to exceed $35B by 2019. Local finishing of targeted regions of the surfaces of various joints is essential for their life assurance. The industry largely depends on laborious and expensive manual or chemical etching methods for localized finishing. This award supports fundamental research that can lead to new machine tools that use magnetic energy and abrasive-mixed magnetic "blob" (semisolid globule in a nonmagnetic fluid) for localized finishing of surfaces. These machine tools can be vital for affordable manufacturing of custom, functional free-form parts (e.g., durable, single piece prosthetic components). The focus of this research is on the effects of the composition of the magnetic fluid as well as the spatio-temporal variation of the external magnetic fields on the selectivity and material removal rates over 1-10 sq. cm area on freeform parts made of diamagnetic or weak paramagnetic materials. The first research objective is to establish quantitative relationships connecting the rheological properties of magnetic fluid blobs with their colloidal compositions and the spatio-temporal variation of external magnetic fields: This knowledge is essential to select magnetic field patterns that can create gradients conducive for optimal flow and selectivity of magnetic fluids, and make a blob exert appropriate down pressures. To achieve this objective, an experimental study will be conducted employing a specialized rheometer instrumented with array of magnets, Gauss meters, as well as force and vibration sensors. The rheometer provides a controlled means to estimate both the magneto-viscoelastic properties of the abrasive granular fluid (based on rubber elasticity theory) as well as the material removal rates for different fluid compositions and workpiece surfaces, and measure the induced magnetic field, forces, and the down pressure. The second objective is to establish a relationship between the localized magnetic field gradients induced over a magnetic blob and the applied spatio-temporal magnetic field: The resulting knowledge will provide guidance to realize sharp magnetic gradients at specified locations, and design magnetic enclosures capable of creating these patterns. To achieve this objective, a novel implicit viscoelastic modeling approach will be employed. This approach uses the property relationships gathered from the first objective to provide a computationally efficient means to capture the blob behaviors, including smooth transition from a magneto-elastic solid like response to that of a magneto-viscoelastic fluid.