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Special Section: Micromanufacturing

Model-Based Pulse Frequency Control for Micro-EDM Milling Using Real-Time Discharge Pulse Monitoring

[+] Author and Article Information
Jae Won Jung, Sang Jo Lee

School of Mechanical Engineering, Yonsei University, 134 Shinchon, Seodaemun, Seoul 120-749, Korea

Young Hun Jeong1

School of Mechanical Engineering, Yonsei University, 134 Shinchon, Seodaemun, Seoul 120-749, Korea

Byung-Kwon Min2

School of Mechanical Engineering, Yonsei University, 134 Shinchon, Seodaemun, Seoul 120-749, Koreabkmin@yonsei.ac.kr

1

Currently with Korea Polytechnic University.

2

Corresponding author.

J. Manuf. Sci. Eng 130(3), 031106 (May 06, 2008) (11 pages) doi:10.1115/1.2917305 History: Received April 16, 2007; Revised January 19, 2008; Published May 06, 2008

Because electrode wear in microelectrical discharge machining significantly deteriorates the machining accuracy, the electrode wear must be compensated in process to improve the geometric accuracy of the product. Therefore, there has been a substantial amount of research on electrode wear and the compensation for EDM processes. In this study, a novel control method for a micro-EDM process using discharge pulse counting is proposed. The method is based on the proportional relationship between the removed workpiece volume and the number of discharge pulses. A model-based control was designed using the relationship between the pulse frequency and gap distance, and implemented in an actual micro-EDM system. Experimental results demonstrated that the developed method makes two- and three-dimensional micro-EDM milling processes fast and accurate without complex path planning to compensate electrode wear.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of experiment setup

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Figure 2

Schematic of discharge pulse counting: (a) gap voltage; (b) counting pulse; (c) number of discharge pulses (NP); (Vref=120V)

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Figure 3

Captured wave form of attenuated gap voltage and comparator output

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Figure 4

Averaged number of discharge pulses curve with various initial gap distances

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Figure 5

Pulse frequency profile when electrode is fixed at initial gap distance of 0.1μm

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Figure 6

Approximated relationship between pulse frequency and gap distance

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Figure 7

Schematic block diagram of EDM milling process control

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Figure 8

Schematic block diagram of model-based control for EDM milling

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Figure 9

Schematic detailed drawing of EDM milling process control

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Figure 10

Longitudinal cross section profiles of machined grooves by model-based EDM milling process control (machining direction: left to right): (a) result when ṄPd=2kHz; (b) result when ṄPd=8kHz

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Figure 11

Controlled motion of Z-axis stage during EDM milling using model-based process control

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Figure 12

Comparison of longitudinal cross section profile of machined groove by model-based EDM milling process control and that by without gap control (six layer milling)

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Figure 13

Profiles of moving averaged pulse frequency with various reference commands: (a) result when ṄPd=2kHz (KC=1.0); (b) result when ṄPd=8kHz (KC=20)

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Figure 14

Experimental results about relationship between desired pulse frequency and machined depth

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Figure 15

Machining paths for square pocket (500×500μm2)

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Figure 16

Cross sectional profiles of machined pockets with model-based control and without control

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Figure 17

Tool paths for microchannel machining (A→B→A)

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Figure 18

Machined microchannel measured by optical scanning interferometer: (a) Machined microchannel; (b) cross sectional profile of 1–2 direction; (c) cross sectional profile of 3–4 direction

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Figure 19

SEM image of machined microchannel

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Figure 20

Tool paths for square and circular pockets: (a) square pocket; (b) circular pocket

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Figure 21

SEM image of shallow pockets: (a) square pocket; (b) circular pocket

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Figure 22

SEM image of a square pillar (250×250×300μm3) in the square cavity

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Figure 23

SEM image of a pyramid (600×600×300μm3) in the square cavity

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Figure 24

SEM image of a hemisphere (0̸600μm) in the circular cavity

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