Dynamic Behaviors of Plasma Reflection during Keyhole Arc Welding

Transcription

1 Dynamic Behaviors of Plasma Reflection during Keyhole Arc Welding YuMing Zhang and Yi Ma Welding Research laboratory Center for Robotics and Manufacturing Systems and Department of Electrical and Computer Engineering College of Engineering University of Kentucky

2 Keyhole Double-Sided Arc Welding Work PAW Electrode Current, Arc, Plasma Jet and Keyhole PAW Torch Power Supply Arc GTAW Torch Arc: through the thickness Why? through-thickness current Importance: continuous energy compensation! Energy Compensation: in any existing arc welding process? No! Why Not in Keyhole PAW? No current through the keyhole! Plasma Jet does not imply current flow!

3 Keyhole Double-Sided Arc Welding System

4 Keyhole Double-Sided Arc Welding: 3/8 inch Plate

5 Keyhole Plasma Arc Welding

6 Keyhole Process Control Objective: Minimize weld pool size and heat input Solution: Controlled pulse keyhole process

7 Sensor

8 Sensor

9 Keyhole State and Plasma Reflection

10 High Speed Imaging System Power Supply MeteorII Dig Frame Grabber Installed in PC PC system CA-D6-0256W

11 Reflection Arc Angle Detector

12 4.5 mm Thick Plate

13 4.5 mm Thick Plate fully penetrated reflection arc angle curve point mean Oscillating Amplitude box 0-20 non-penetrated keyhole

14 6.5 mm Thick Plate

15 6.5 mm Thick Plate 00 fully penetrated 80 reflection arc angle curve points mean 20 Oscillating Amplitude box 0-20 non-penetrated keyhole

16 Keyhole Development State Stable Non-Penetrated Keyhole Period Unstable Transition Period Stable Penetrated Keyhole Period

17 Stochastic System Stochastic System 2 2 ) ( z z z z H T j T j T j T j e e e e H 2 2 ) ( ARMA System (Input: white noise; Output: reflection angle) Frequency Response

18 Summary: Keyhole Development States First, after the current is switched to the peak current, the plasma is reflected with a small but varying angle. During this period, the development or variation of the geometry of the non-penetrated keyhole is relatively stable. The process is in the stable non-penetrated keyhole state. Second, when the keyhole is first fully penetrated or is ready to be fully penetrated, the development of the geometry of the keyhole will become relatively rapid and unstable. During this period, the reflection condition varies and the angle of the reflected plasma varies or oscillates at a relatively high speed and amplitude; the keyhole may or may not have been fully penetrated and the condition for maintaining a fully penetrated keyhole is not completely established yet. Hence, this state is referred to as the transition. Third, after the weld pool size is sufficient, the condition for maintaining a stable keyhole will be firmly established and the geometry of the keyhole will then reach a steady-state shape. As a result, the reflected plasma maintains a constant angle. The process enters into another stable state, the stable keyhole state. Because part of the plasma exits through the keyhole, the amount of the reflected plasma will be reduced. The reflected plasma will be cooled by the shielding gas faster. As a result, the reflected plasma appears lower and closer to the weld pool surface.

19 Acknowledgement National Science Foundation: Grant DMI National Shipbuilding Research Program Center for Robotics and Manufacturing Systems