Modeling and application of plasma charge current in deep penetration laser welding

Zhang, Xudong; Chen, Wuzhu; Jiang, Ping; Guo, Jian; Tian, Zhiling

doi:10.1063/1.1570951

Cited by 17 publications

(7 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For instance, the inhomogeneous distribution of electron / ion density in the plasma cloud had been utilized to obtain signals characteristic for the welding process: In [22] the voltage drops between the work piece and the electrically insulated nozzle is taken as a sensor signal indicating various faults. A similar approach was presented in [23] where this potential was used to control the distance between nozzle and work piece. Basic studies such as, e.g.…”

Section: Laser Induced Plasma As Source For a Current In The Weld Poolmentioning

confidence: 94%

Laser-induced plasma as a source for an intensive current to produce electromagnetic forces in the weld pool

Ambrosy

Avilov

Berger

et al. 2006

XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers

View full text Add to dashboard Cite

Laser beam welding performed with a CO 2 laser by applying a magnetic field perpendicular to the welding direction influences the weld pool dynamics, which changes the seam properties significantly. From these results it was concluded [1] that an intensive current density must exist in the melt. In repeating those welding experiments with a Nd:YAG laser, however, no significant effects could be observed. To explain this discrepancy, detailed trials with both CO 2 and Nd:YAG lasers were carried out and led to an explanation which is presented in this paper.Looking at the welding process with radiation of 10.6 µm and 1.06 µm, the only significant difference is the presence of a laser-induced plasma plume above the workpiece in the case of the longer wavelength. Therefore, the investigations were concentrated on its possible role in establishing a current flow through the weld pool. This current was directly measured during the welding process (bead on plate): Two aluminum plates separated by an insulated gap of 0.85 mm were moved under the focused beam (3 kW; 5 m/min) and the signal was recorded as function of the gap's position. From these measurements were deduced values of current that amounted to approximately 0.3 A with CO 2 and more then one order of magnitude less with Nd:YAG lasers. BACKGROUNDIn recent years, several methods have been developed to modify the welding process in order to better meet requirements concerning process performance and stability. Among them a dynamic process stabilization [2], the use of so-called hybrid processes (combination of laser beam and arc-discharge techniques) [3,4], and the double-focus technique [5]. In addition to the last mentioned method, which already has found wide-spread applications in production [6], a further concept was investigated and is still being developed at the IFSW, i.e. a control of the weld pool dynamics and, hence, the seam properties by electromagnetic volume forces in the weld pool. Their positive effects regarding reduction of process pores [7], shaping the seam geometry [8], suppressing of humping [9], enhancing the mixing and element homogenization in the melt [10] and lifting up the melt pool [11] have been demonstrated by a variety of approaches using different sources and orientations of current density and magnetic field.The original idea was that, by applying a magnetic field B, a current density j will be induced in the weld pool and, by interaction of j r and B r , electromagnetic volume forces B j r r × would be produced within the melt directly affecting its momentum flux. Welding on the bead experiments performed with 7 kW power from a CO 2 -laser and magnetic field strength of typically 0.1 T showed drastic changes of bead appearance, seam cross-section and hot crack behavior compared to the results obtained without a magnetic field [9] (see Fig.1). Furthermore, with the magnetic field orientated perpendicular to the welding direction and laser beam axis, the characteristic features depended on the direction of B r . The interpretati...

show abstract

Section: Laser Induced Plasma As Source For a Current In The Weld Poolmentioning

confidence: 94%

Laser-induced plasma as a source for an intensive current to produce electromagnetic forces in the weld pool

Ambrosy

Avilov

Berger

et al. 2006

XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers

View full text Add to dashboard Cite

show abstract

“…It can explain both magnitude and sign of the experimentally observed potential difference during laser welding. The sheath effect has been proposed as mechanism for the potential difference observed between the workpiece and the nozzle in [3], but neglecting the fact that two sheaths form, one at the hot end and one at the cold end. However, since the sheath effect alone cannot explain the sign of the current observed in [5], we conclude that both effects are important and should be taken into account when calculating currents induced by a plasma cloud forming above a locally heated metal surface.…”

Section: Discussionmentioning

confidence: 99%

“…Another process induced by the plasma is the generation of electrical voltages and currents since the plasma contains free electrical charges. Such currents have been observed between workpiece and gas nozzle [3] and it has been shown that applying a magnetic field can control the plasma. An explanation of the observed current between workpiece and nozzle has also been put forward on the basis of sheath theory [3], neglecting however the effect that sheaths will form at both the hot and the cold side.…”

Section: Introductionmentioning

confidence: 99%

“…Such currents have been observed between workpiece and gas nozzle [3] and it has been shown that applying a magnetic field can control the plasma. An explanation of the observed current between workpiece and nozzle has also been put forward on the basis of sheath theory [3], neglecting however the effect that sheaths will form at both the hot and the cold side. Experiments using applied magnetic fields when no current was flowing between workpiece and nozzle have clearly shown that the welding seam quality can be influenced, pointing towards the generation of closed current loops within the workpiece and weld pool [4].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Electrical potential difference during laser welding

2014

View full text Add to dashboard Cite

Abstract:We present a new model for the generation of thermoelectric currents during laser welding, taking into account sheath effects at both contact points as well as the potential drop within the quasi-neutral plasma generated by the laser. We show that the model is in good agreement with experimentally measured electric potential difference between the hot and the cold part of the welded workpiece. In particular, all three elements of the model are needed to correctly reproduce the sign of the measured voltage difference. The mechanism proposed relies on the temperature dependence of the electron flux from the plasma to the workpiece and hence does not need thermoemission from the workpiece surface to explain the experimentally observed sign and magnitude of the potential drop.

show abstract

“…The laser-induced plasma above the workpiece surface diffuses towards the nozzle driven by the particle concentration gradient, so an electric potential is formed between the workpiece and the nozzle due to the large differences between the ion and electron diffusion velocities. Some experimental studies have measured the PCS signal variation with various welding conditions and the corresponding weld quality [18][19][20][21][22][23][24]. Li et al [19,20] described the mechanism of the PCS signal generation and developed an equation V p = 4.5kT e (where V p is the induced PCS voltage, k the Boltzmann constant and T the plasma temperature) to predict the voltage induced in the PCS.…”

Section: Introductionmentioning

confidence: 99%

Double closed-loop control of the focal point position in laser beam welding

Zhang

Chen

Jiang

et al. 2003

Meas. Sci. Technol.

View full text Add to dashboard Cite

Focal point position control is significant in deep penetration laser beam welding because it is apt to change during welding due to some fluctuating factors, such as the non-planar workpiece, welding distortion and thermal focusing. This work describes the design of a double closed-loop control of the focal point position for CO2 laser beam welding. A photodiode sensor (PS) and a plasma charge sensor (PCS) are simultaneously utilized to detect the optical emission and plasma charge current in welding. It is found that the PCS signal could be used to control the nozzle–workpiece distance based on the decrease of PCS signal intensity with increasing nozzle–workpiece distance. The PS signal could be used to control the focal point position by using PS signal variation with focal point position. Therefore, a system for double closed-loop controlling the focal point position has been set up, using the PCS signal to control the nozzle–workpiece distance and the PS signal to control the focal point position. The experimental results with a non-planar workpiece show that the double closed-loop control of the focal point position not only automatically follows the contours of the workpiece surface, but also controls the focal point position constant by compensating the effect of thermal focusing.

show abstract

Modeling and application of plasma charge current in deep penetration laser welding

Cited by 17 publications

References 7 publications

Laser-induced plasma as a source for an intensive current to produce electromagnetic forces in the weld pool

Laser-induced plasma as a source for an intensive current to produce electromagnetic forces in the weld pool

Electrical potential difference during laser welding

Double closed-loop control of the focal point position in laser beam welding

Contact Info

Product

Resources

About