| This research presents a new mechanical micromachining technique that can be used to machine 2D or 3D microfeatures into many types of materials such as metals, semiconductor materials and glass. The microscopic cutting motion of the tool is based on orbital motion of a single-point tool tip that is made of a single crystal diamond. To generate the microscopic cutting motion, the tool tip is attached to the free end of a piezo tube while the other end is held stationary. Sinusoidal voltage signals are applied to the four electrodes (x+, x-, y+, y-) of the piezo tube to create cyclic bending that results in orbital motion of the attached tool tip. This allows various types of trajectories of the tool tip to be created that include circular, elliptical and tapered motion. Microfeatures can be created by combining the piezo tool, which produces the microscopic cutting motion, with a macroscopic motion module (any 3-axis stage such as a CNC machine tool), which is used to generate the feed motion. This research details the design and control of the tool and also reports on its dynamic behavior.A second aspect of this research is the development of a cutting force model capable of predicting the forces that occur between the tool tip and the work piece during orbital cutting. The force model is based on the determination of the contact area of a conical tool tip with a tip radius that is typically much larger than the uncut chip thickness. Experiments with aluminum alloy (AL 2024) were performed to obtain the specific cutting forces as well as the friction coefficients at these very small length scales. The model was validated by varying critical machining parameters such as depth of cut, orbital frequency as well as feed per orbit.Machining of brittle materials was performed on silicon, which is a very commonly used material in optical instruments as well as semiconductor-based products. Due to its high brittleness and low fracture toughness, it is rather difficult to machine with mechanical techniques. Owing to its tool radius, which is much larger than the uncut chip thickness, orbital micromachining produces relatively high hydrostatic pressure during cutting. This allows brittle materials to be cut in the ductile regime whereby material is removed without fracture, thereby producing very smooth surfaces. In reality, there are many machining parameters (orbital trajectory, tool geometry, etc.) that affect the machining result on silicon. This research presents experimental studies on single crystal silicon work pieces that demonstrated the feasibility of ductile regime machining for depths of cut less than 1 micron. |
