Research Papers

Thermal and Structural Deformations During Diamond Turning of Rotationally Symmetric Structured Surfaces

[+] Author and Article Information
Stefan Rakuff

2 Barclay Street, Clifton Park, NY 12065

Paul Beaudet

 Paul Beaudet & Associates, Inc., 4604 Greenbriar Court, Boulder, CO 80303

J. Manuf. Sci. Eng 130(4), 041004 (Jul 08, 2008) (9 pages) doi:10.1115/1.2951929 History: Received January 10, 2007; Revised April 14, 2008; Published July 08, 2008

Diamond turning of microstructures on the surface of large cylindrical workpieces has become important with advances made in roll-to-roll manufacturing processes of optical films, drag reduction films, microfluidic devices, and organic electronic components. Micromachined cylindrical workpieces are used as production masters in various printing, embossing, and coating processes. The microstructures machined in this study were 18μm in height and had a pitch of 35μm. These dimensions required control of the location of the single crystal diamond cutting tool that was used for machining to submicrometer levels. The significant error sources identified in the machining process were thermal effects and deflections of the structural loop of the diamond turning machine (DTM) that led to registration errors of the cutting tool between consecutive passes. Environmental temperature variation errors (ETVEs) were measured and modeled as a function of long-term ambient temperature fluctuations. Also studied was the mechanical compliance of the structural loop of the DTM. The height adjustable tool stack and aerostatic spindle were identified as the most compliant components. The cutting forces for radius and V-shaped diamond cutting tools at various depths of cut were measured using the known compliance of the aerostatic bearing to predict workpiece deflections.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Side view of microstructured cylindrical workpiece

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Figure 2

Single crystal V-shaped single crystal diamond tool mounted in tool holder

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Figure 3

4500× (a) and 20,000× (b) SEM photos of the tip of the single crystal diamond tool showing the high quality cutting edges and tool tip

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Figure 4

View of the V-shaped cutting tool during a machining pass

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Figure 5

Microscopic images of prismatic microstructures with defects (a) in the form of burrs and chatter along the prism flanks and near defect free (b). Valleys are dark and peaks are bright.

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Figure 6

10,000× SEM photo of a nickel electroform showing the valley between two prisms

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Figure 7

Partial disengagement of the cutting tool and defects between prisms caused by a tool positioning error between consecutive passes

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Figure 8

Thermal and elastic errors affecting the structural loop of the diamond turning process leading to nonrepeatability of the cutting tool position

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Figure 9

Capacitance sensor mounted on the tool post in the radial (Δx) and axial (Δz) directions to measure ETVE. Nozzles were operated to determine the effect of cutting fluid on workpiece expansion.

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Figure 10

YSI surface thermistors (Model 6500-0081) used for thermal measurements

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Figure 11

Mounting of the thermistors in air (a) and on the part surface (b)

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Figure 12

Long-term drift test over 22h showing a maximum ETVE of 1.6μm in the axial direction

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Figure 13

Long-term drift test over 25h showing axial and radial ETVEs of 1.6μm in the axial direction

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Figure 14

Radial (Δx) and axial (Δz) displacements at free end of workpiece during simulated machining run at 100rpm

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Figure 15

Ambient temperature step of 4°C and measured temperature of part

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Figure 16

Measured and theoretical axial displacement responses to 4°C temperature step

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Figure 17

Measurement of overall loop compliance with force gage and LVDT indicator

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Figure 18

Stiffness measurement of tool height adjuster and cutting tool

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Figure 19

Compliance measurement of solid riser block and tool shank

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Figure 20

Measurement of radial spindle compliance due to tilt loading as a function of overhang d

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Figure 21

Measurement of workpiece deflections during machining in the horizontal (Δx), vertical (Δy) and axial (Δz) directions using capacitance sensors

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Figure 22

Horizontal (Δx), vertical (Δy), and axial (Δz) displacements during setup and first pass caused by thermal effects, spindle startups, and cutting forces

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Figure 23

Horizontal (Δx), vertical (Δy), and axial (Δz) displacements during second and third pass

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Figure 24

Top view radius tool and workpiece interface

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Figure 25

Top view of V-shaped cutting tool and workpiece interface




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