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TECHNICAL PAPERS

A Tool Path Modification Approach to Cutting Engagement Regulation for the Improvement of Machining Accuracy in 2D Milling With a Straight End Mill

[+] Author and Article Information
M. Sharif Uddin, Atsushi Matsubara

Department of Micro Engineering, Kyoto University, Sakyo-Ku, Kyoto 606-8501, Japan

Soichi Ibaraki1

Department of Micro Engineering, Kyoto University, Sakyo-Ku, Kyoto 606-8501, Japanibaraki@prec.kyoto-u.ac.jp

Susumu Nishida

 Manufacturing Technology Institute Inc., Ebisu 1-19-19, Shibuya-ku, Tokyo150-0013, Japannishida@mtii.jp

Yoshiaki Kakino

 Kakino Research Institute, Enpukuji-cho 324-1, Nakagyo-ku, Kyoto 604-8175, Japankakino@crux.ocn.ne.jp

1

Corresponding author.

J. Manuf. Sci. Eng 129(6), 1069-1079 (Mar 27, 2007) (11 pages) doi:10.1115/1.2752526 History: Received May 01, 2006; Revised March 27, 2007

In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Variation of cutting engagement angle with respect to different tool path geometry in 2D end milling (r=tool radius, αen=engagement angle, s=step-over distance (i.e., radial depth of cut)): (a) concave arc, (b) linear, and (c) convex arc

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Figure 2

Simplified illustration of path modification to regulate engagement angle by algorithm introduced by Stori and Wright (16)

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Figure 3

Concept of the algorithm for tool path modification to regulate cutting engagement angle

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Figure 4

Parallel offset of the tool center location, ok(i) by the distance r

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Figure 5

An illustrating example of tool path modification by the proposed algorithm

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Figure 6

An illustrative example where constant engagement over the finishing path is not geometrically possible: (a) finishing path with a square corner and (b) semi-finish surface for constant engagement

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Figure 7

Geometry of the core contour

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Figure 8

(a) Modified constant engagement (CE) tool path generated by the proposed algorithm (b) magnified view of the tool paths in the rectangular box

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Figure 9

Engagement angle profiles of an original contour parallel path and the modified CE tool path generated by the proposed algorithm on the finishing path

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Figure 10

Comparison of cutting force between contour parallel path and modified CE tool path

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Figure 11

Measured cutting force profiles along the semi-finishing path

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Figure 12

Machined surface profiles with respect to reference surface of core workpiece measured by the CMM: (a) contour parallel path (strategy 1) and (b) modified constant engagement (CE) tool path (strategy 2)

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Figure 13

Machined surface geometric error profiles with distance along reference surface of the core workpiece (the numbers on top of graphs correspond to the corner names, same as those indicated in Fig. 1)

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Figure 14

Mean surface geometric error profiles with respect to curvature radius of core workpiece (R(+): convex arc, R(−): concave arc; the numbers on top of graphs correspond to the corner names, same as those indicated in Fig. 1)

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Figure 15

Definition of feedrate at the cutting point and feedrate at tool the center in 2.5D contour milling: (a) concave arc milling and (b) convex arc milling

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Figure 16

(a) Modified semi-finishing tool path generated by the proposed algorithm with optimized cutting engagement angle and (b) magnified view of the tool paths in the rectangular box

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Figure 17

Comparison of cutting forces in finishing

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Figure 18

Profiles of measured and commanded feedrate in finishing under strategy 2 (feed-rate control)

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Figure 20

Machined surface trajectories with respect to the reference surface of core workpiece: (a) contour parallel path (strategy 1), (b) feed-rate control (strategy 2), and (c) feed-rate control with modified tool path (strategy 3)

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Figure 21

Machined surface geometric error profiles with distance along reference surface of core workpiece (the numbers on top of graphs correspond to the corner names, same as those indicated in Fig. 2)

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Figure 22

Mean surface geometric error profiles with respect to curvature radius of core workpiece (R(+): convex arc, R(−): concave arc; the numbers on top of graphs correspond to the corner names, same as those indicated in Fig. 2)

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