Models to determine the process parameters required to sculpt desired micro-feature topographies on flat and curved surfaces using abrasive jet technology

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Jets of small abrasive particles propelled by air or water have been used for many years to modify the topography of engineered surfaces. One of the most important applications of abrasive jet technology (AJT) is as a low cost and rapid micro-fabrication platform for microfluidics, micro-electomechanical systems (MEMS), and opto electronics components. The proposed research will focus on two AJT's for this purpose: air driven abrasive jet micro-machining (AJM) and abrasive waterjet micro-machining (AWJM). The advantages of these technologies are many, but perhaps the most important are that they can machine without creating a heat affected zone, and that they have a unique directional etch capability that most competing technologies do not. For example, traditional isotropic wet etching of channels results in a single basic U-shaped micro-channel cross-section. The directional etch capability of AJT, however, allows the sculpting of many different shapes by changing the process parameters (e.g. jet scan speed and inclination angle, particle size, etc). The proposed research will exploit this unique capability, allowing the technology to be used in the manufacture of novel devices. We have previously developed "surface evolution" models for the AJM of a wide variety of materials that can predict the development of machined topography on an initially flat surface for various combinations of process parameters. The next generation of microfluidic and MEMS devices, however, will require micro-machining 3D (i.e. non-planar) components, an area that has not yet been explored for AJM, despite its great potential. Similarly, there is currently no surface evolution model to predict machined topography using AWJM, a newer process that is fundamentally different than AJM because of abrasive slurry backflow effects and the lack of a mask. Through an exclusive agreement with an industrial partner, we have an AWJM setup with a unique micro-nozzle that will allow us to do ground-breaking research in this area. A complicating factor for AJT is the tendency for particles to embed into the surface and thus affect the surface quality, erosion rate, roughness, etc. Currently, no model exists for predicting what particle and process parameters control the extent of this embedding when machining metals using AJT. The initial portion of the proposed research will focus on addressing these important shortcomings in the modeling of AJT processes. Surface evolution models are important because they can predict machined topography as a function of input process parameters; however, there are currently no techniques to solve the inverse problem, i.e. predicting the process parameters necessary for sculpting particular desired topographies. The final portion of the proposed research will tackle this important problem that would allow the sculpting of particular desired feature shapes using AJT. In other words, we will develop methodologies that allow the inputs (the process parameters) to the surface evolution equation to be determined from a desired solution of the equation at some future time (the desired cross sectional profile). The problem is challenging because the surface evolution partial differential equation is nonlinear and cannot be solved in closed form. Initially, optimization routines will be used to determine the set of parameters that comes closest to a desired topography. Later, novel techniques for sculpting surfaces of desired shapes using combinations of inclined and perpendicular incidence nozzles will developed. These techniques will open up a host of new device design opportunities for the design of 3D MEMS and microfluidics devices, and thus support Canada's growing micro-technology sector.