Jeremiah A. Couey

Nanometer-Level Comparison of Three Spindle Error Motion Separation Techniques

This work demonstrates the state of the art capabilities of three error separation techniques for nanometer-level measurement of precision spindles and rotationally-symmetric artifacts. Donaldson reversal is compared to a multi-probe and a multi-step technique using a series of measurements carried out on a precision aerostatic spindle with a lapped spherical artifact. The results indicate that subnanometer features in both spindle error motion and artifact form are reliably resolved by all three techniques. Furthermore, the numerical error values agree to better than one nanometer. The paper discusses several issues that must be considered when planning spindle or artifact measurements at the nanometer level.

Predicting surface figure in diamond turned calcium fluoride using in-process force measurement

Single crystal calcium fluoride (CaF2) shows significant variation in material properties as a function of crystallographic orientation. The surfaces generated by material removal processes such as diamond turning are influenced by this anisotropy and consequently show periodic undulations aligned with the crystal structure. This article explores the relationship between surface figure and cutting forces measured during the diamond turning of single crystal calcium fluoride. The cutting forces, when mapped to the physical geometry of CaF2 plano (flat) optics, show good correlation with surface figure measured by interferometry. A model is presented to predict the surface figure error from the experimentally measured normal component of the cutting force. The model also shows how the surface figure obtained under various machining parameters may be extrapolated from force measurements made during a single diamond turning operation.

In-process force monitoring for precision grinding semiconductor silicon wafers

Forces generated during precision wafer grinding are small and present challenges for accurate and reliable process monitoring. In this work, these challenges are met by incorporating noncontact displacement sensors into an aerostatic spindle that is calibrated to measure grinding forces from the relative motion between the spindle rotor and stator. This arrangement allows the calculation of grinding forces without introducing compliance into the structural loop of the grinding machine. Aerostatic spindles are used in precision wafer grinding requiring high stiffness and very low error motions (5-25 nm). Several experiments evaluate this force sensing approach in detecting workpiece contact, process monitoring with small depths of cut, and detecting workpiece defects. The results indicate that force measurements offer good performance for monitoring precision wafer grinding since this approach provides excellent contact sensitivity, high signal resolution, and has sufficient bandwidth to detect events occurring within a single revolution of the grinding wheel.

THE ROLE OF CUTTER ECCENTRICITY ON SURFACE FINISH AND MILLING FORCES

In this paper, the role of milling cutter eccentricity, commonly referred to as runout, is explored to determine its effects on surface topography and milling forces. This work is motivated by the observation that commercially-available cutter bodies often exhibit variation in the teeth/insert radial locations as a result of manufacturing issues. Consequently, the chip load on individual cutting teeth varies periodically, which can lead to premature failure of the cutting edges. Additionally, this chip load variation increases the roughness of machined surfaces. This research isolates the effect of runout on cutting forces and the machined surface finish in a series of experiments completed on a precision milling machine with 0.1 μm positioning repeatability and 0.02 μm spindle error motion. The runout is varied in a controlled fashion and results compared between experiment and a comprehensive time-domain simulation.Copyright

The role of crystallographic orientation on the forces generated in ultra-precision grinding of anisotropic materials such as monocrystalline silicon

Monitoring forces when grinding crystalline materials is advantageous for optimising process conditions, improving process control and producing high quality parts. Yet, this is challenging in precision applications where aerostatic spindles and small depths of cut are common. This work presents a system of measuring grinding forces in precision applications. Several experiments demonstrate the performance in monitoring diamond wheel dressing, detecting workpiece contact and process monitoring. The system appears promise for monitoring precision wafer.

A comparison of force and acoustic emission sensors in monitoring precision cylindrical grinding

Aerostatic spindles are used in precision grinding applications requiring high stiffness and very low error motions (5 to 25 nm). Forces generated during precision grinding are small and present challenges for accurate and reliable process monitoring. These challenges are met by incorporating non-contact displacement sensors into an aerostatic spindle that are calibrated to measure grinding forces from rotor motion. Four experiments compare this force-sensing approach to acoustic emission (AE) in detecting workpiece contact, process monitoring with small depths of cut, detecting workpiece defects, and evaluating abrasive wheel wear/loading. Results indicate that force measurements are preferable to acoustic emission in precision grinding since the force sensor offers improved contact sensitivity, higher resolution, and is capable of detecting events occurring within a single revolution of the grinding wheel.

Analysis and performance of a parallel axis flatness measuring instrument

This article describes the design, analysis, and performance of a flatness inspection instrument to measure workpieces with up to 1mm departure from flatness. The instrument uses two air bearing spindles arranged with parallel axes to simultaneously rotate a workpiece and slowly pass a capacitance probe over the spinning surface. Capacitance probes offer user-selectable sensitivity to provide multiple combinations of measurement range and resolution. In tests with a high sensitivity probe, the instrument demonstrated measurement repeatability of 25nm on a ∅75mm workpiece. This article presents a complete homogeneous transformation matrix analysis of the propagation of errors into the measurement as well as sample measurements on diamond turned workpieces.