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Special Section Papers

Radial Throw in Micromilling: A Simulation-Based Study to Analyze the Effects on Surface Quality and Uncut Chip Thickness

[+] Author and Article Information
Sudhanshu Nahata

Department of Mechanical Engineering,
Carnegie Mellon University,
5000 Forbes Avenue,
Pittsburgh, PA 15213
e-mail: snahata@andrew.cmu.edu

Recep Onler

Department of Mechanical Engineering,
Carnegie Mellon University,
5000 Forbes Avenue,
Pittsburgh, PA 15213
e-mail: ronler@andrew.cmu.edu

O. Burak Ozdoganlar

Department of Mechanical Engineering;
Department of Material Science and
Engineering;
Department of Biomedical Engineering,
Carnegie Mellon University,
5000 Forbes Avenue,
Pittsburgh, PA 15213
e-mail: ozdoganlar@cmu.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO-AND NANO-MANUFACTURING. Manuscript received November 12, 2018; final manuscript received March 10, 2019; published online April 11, 2019. Assoc. Editor: Lawrence Kulinsky.

J. Micro Nano-Manuf 7(1), 010907 (Apr 11, 2019) (8 pages) Paper No: JMNM-18-1053; doi: 10.1115/1.4043176 History: Received November 12, 2018; Revised March 10, 2019

This paper presents a simulation study toward analyzing the effect of radial throw in micromilling on quality metrics and on the deviation in tool-tip trajectory from its prescribed pattern. Both the surface location error (SLE) and the sidewall (peripheral) surface roughness are analyzed. The deviation in tool-tip trajectory is evaluated considering the flute-to-flute variations in the uncut chip thickness and changes in the tooth spacing angle. Radial throw indicates the instantaneous radial location of the tool axis, thereby capturing all salient features of tool-tip trajectory deviations, such as the general elliptical form of the radial motions. This is in contrast to the concept of run-out, which is a scalar quantity (total indicator reading) indicating the total displacement or change in the radial throw measured from a perfect cylindrical surface for one complete rotation of the axis. As such, measurement and analysis of radial throw is essential to understanding micromachining processes. In our previous work, we described an experimental approach for accurate determination of radial throw when using ultra-high-speed micromachining spindles. In this work, we present a simulation-based study to relate radial throw parameters and form to SLE, sidewall surface roughness, flute-to-flute variations of uncut chip thickness, and changes in tooth spacing angle for a two fluted micro-endmill. As expected, our study concludes that the magnitude, orientation, and form of radial throw all significantly affect the studied quality metrics, tooth spacing angle, and the flute-to-flute chip thickness variations. Specifically, the presence of radial throw with an elliptical form induces up to 50% variation in SLE, up to 20% variation in sidewall surface roughness, up to 60% variation in tooth spacing angle deviations, and up to 50% variation in flute-to-flute chip thickness. As such, the presented simulation approach can be used to assess the direct (kinematic) effects of the radial throw parameters on the quality metrics and chip thickness variations.

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References

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Figures

Grahic Jump Location
Fig. 1

Description of radial throw magnitude ρz(θ) and radial throw orientation ηz(θ). The one-per-rev component of radialthrow with its general elliptical trajectory is shown. The radial throw magnitude is significantly exaggerated with respect to the micro-endmill diameter for illustration purposes.

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Fig. 2

The trochoidal tool-tip trajectory in the presence of radial throw ρ, and the parameters for calculation of the associated output metrics

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Fig. 3

Description of various forms (trajectories) of radial throw discussed in the text (a) circular and (b) elliptical. θia is the inclination angle of the ellipse with respect to the feed direction.

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Fig. 4

SLE (in μm) for (a) varying radial throw magnitude and orientation for circular radial throw and (b) varying radial throw orientation and ellipse inclination angle for elliptical (fixed elliptical ratio) radial throw

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Fig. 5

Peripheral surface roughness for ((a) and (b)) up-milling and ((c) and (d)) down-milling cases. (a) and (c) are for a circular trajectory with varying radial throw magnitude and orientation, and (b) and (d) are for an elliptical (fixed elliptical ratio) trajectory with varying radial throw orientation and ellipse inclination angle. The Ra is in μm.

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Fig. 6

Uncut chip thickness variations for a circular radial throw trajectory at a fixed radial throw magnitude of 2.5 μm and at varying radial throw orientations. A two-fluted tool is considered. Each radial throw orientation is listed on the right column, and the cutting edges #1 and #2 are represented by solid and dotted lines, respectively. Note that the ideal case (in the absence of radial throw) would be similar to the 90 deg radial throw orientation case (the readers are referred to the web version of the paper for clear interpretation).

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Fig. 7

Uncut chip thickness variation for an elliptical trajectory fixed at a semimajor and a semiminor axis of 3 μm and 2 μm, respectively. The ellipse inclination angle is varied for radial throw orientations of (a) 0 deg and (b) 90 deg. Each ellipse inclination angle is listed on the right column, and the cutting edges #1 and #2 are represented by solid and dotted lines, respectively (the readers are referred to the web version of the paper for clear interpretation).

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Fig. 8

(a) The description of deviation in the tooth-spacing angle Δθp for (b) varying magnitude and orientation of radial throw for a circular trajectory, and (c) varying radial throw orientation and ellipse inclination angle for an elliptical ratio of 1.5 (from Table 1) The unit is deg

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Fig. 9

(a) A change in radial throw orientation with change in axial position (indicated by z) arising from the helical flutes and (b) the effect of a finite depth of cut results in a variable magnitude (effect of tool-tilt) and variable orientation of radial throw (effect of helix angle), highlighted by red circles (the readers are referred to the web version of the paper for clear interpretation)

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Fig. 10

(a) An example 3D surface generated by a 254 μm, two fluted micro-endmill (30 deg helix angle) at a feed of 25 μm/flute and depth-of-cut of 700 μm, (b) up-milling, and (c) down-milling. ((d) and (e)) The cusps also translate laterally (in x) with z (indicated by nonvertical arrows) because of the finite helix angle of the cutting tool. Note that the scales are different along different axes. A circular form of radial throw was assumed with a constant magnitude of 15 μm and an orientation of 0 deg at the tool-tip.

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Fig. 11

The variation in channel width and radial throw orientation with depth of cut for the example case presented in Fig. 10. The prescribed width is 254 μm.

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