Laser Sound Generation in a Weld Pool

Carlson, Nancy M.; Johnson, John A.

doi:10.1007/978-1-4613-0979-6_73

Cited by 3 publications

(1 citation statement)

References 11 publications

(12 reference statements)

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“…The 1 mm laser spot is delivered at a 20 Hz rate to the solidified top surface of the weld several inches behind the electrode using focusing optics mounted on the laser head [6,7]. The ultrasonic detector is an EMA T and amplifier designed and fabricated for PAWS at the National Institute of Standards and Technology in Boulder, Colorado [8].…”

Section: Introductionmentioning

confidence: 99%

Noncontacting Ultrasonic System for Concurrent Defect Detection in Solidified Weld Metal

Carlson

Johnson

Larsen

1993

Review of Progress in Quantitative Nondestructive Evaluation

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INTRODUCTIONIn-process ultrasonic sensing of welding allows detection of weld defects in real time. A noncontacting ultrasonic system is being developed to operate in a production environment. The principal components are a pulsed laser for ultrasound generation, an electromagnetic acoustic transducer (EMAT) for ultrasound reception, and a PC-based data acquisition system which determine the quality of the weld on a pass-by-pass basis. The laser/EMAT system interrogates the area in the weld volume where defects are most likely to occur [5]. This area of interest is identified by computer calculations on a pass-by-pass basis using weld planning information provided by the off-line programmer. The absence of a signal above the threshold level in the computer-calculated time interval indicates a disruption of the sound path by a defect. The ultrasonic sensor system then provides an input signal to the weld controller about the defect condition.The purpose of the ultrasonic sensor is to detect defects in the solidified weld metal on a pass-by-pass basis [2][3][4][5] for a multipass, pulsed gas metal arc welding (GMA W) process. The sensor is being developed under the Programmable Automated Welding System (PAWS) project. The purpose of the PAWS program is to demonstrate the integration of the latest welding technology into a single system. The PAWS system consists of a central control computer, an off-line programmer for planning, and eight different sensors. This paper discusses one of those sensors. The sensor system will be demonstrated on thick section (31.8 to 41.3 mm, 1.25 to 1.625 in.) steel weld samples.The ultrasound is generated by a short duration (11 ns) light pulse from an Nd:YAG laser with an exit beam power of 56 mJ/pulse. The 1 mm laser spot is delivered at a 20 Hz rate to the solidified top surface of the weld several inches behind the electrode using focusing optics mounted on the laser head [6,7]. The ultrasonic detector is an EMA T and amplifier designed and fabricated for PAWS at the National Institute of Standards and Technology in Boulder, Colorado [8]. The permanent magnet EMAT generates a magnetic field in the weld sample. The motion of electrons due to the sound generated by the laser pulse interacts with the magnetic field, changing an associated electrical field. This interaction is detected by a pickup coil. The signal is then evaluated as an ultrasonic A scan. The ultrasonic system includes the hardware and software necessary to monitor the condition of the solidified weld metal while receiving and sending information to a weld controller about the quality of the solidified weld bead. A first step in devising a noncontacting technique for sensing defect generation in the welding process is to develop a method for generating sound waves in the material. In this system, ultrasound is generated by a focused, 1 mm (0.039 in.) diameter laser spot from a pulsed Nd: Y AG laser operating at 1064 nm. The short duration, 11 ns, laser pulse has a peak intensity of 107 W/cm2 and generates high freq...

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Section: Introductionmentioning

confidence: 99%

Noncontacting Ultrasonic System for Concurrent Defect Detection in Solidified Weld Metal

Carlson

Johnson

Larsen

1993

Review of Progress in Quantitative Nondestructive Evaluation

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Laser-generated ultrasound: its properties, mechanisms and multifarious applications

Davies

Edwards

Taylor

et al. 1993

J. Phys. D: Appl. Phys.

334

154

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The laser generation d ultrasound in solids is reviewed with particular emphasis on the application of this unique ultrasonic source. Three regimes for the generation of ultrasound in solids using lasers in the visible near infrared wavelength region exist: thermoelastic, plasma and constrained surface source regimes. The mechanism for ultrasonic generation in each of these regimes is given. Recent experimental investigations into laser-generated unrasound are also described, including a description d a different mechanism for the generation of ultrasound in solids using a COn laser. Finally, the many applications of lasergenerated ultrasound are reviewed. These applications range from nondestructive testing to the determination of candle flame parameters. Possible future applications are also outlined.

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Laser Array/EMAT Ultrasonic Measurement of the Penetration Depth in a Liquid Weld Pool

Graham

Ume²,

Hopko

1998

Journal of Manufacturing Science and Engineering

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Ultrasonics has become widespread as a nondestructive testing technique. The most commonly used device for generation and reception of ultrasound are contacting piezo-electric transducers. Because these devices require physical coupling with the sample, test specimens must be stationary, and surfaces both cool and nonabrasive. Obviously, traditional contacting transducers cannot be used for real-time evaluation of certain manufacturing operations, such as weld quality control, where the test specimen could be in motion, and hot as well. This paper presents an evaluation of a noncontacting ultrasonic testing system consisting of a laser and fiber optic probe for generating ultrasound and an electromagnetic acoustic transducer for receiving the signals. This system has been applied to simulated liquid welds to demonstrate the feasibility of using similar equipment for real-time weld quality control. Weld penetration depth is investigated. [S1087-1357(00)70701-5]

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Laser Sound Generation in a Weld Pool

Cited by 3 publications

References 11 publications

Noncontacting Ultrasonic System for Concurrent Defect Detection in Solidified Weld Metal

Noncontacting Ultrasonic System for Concurrent Defect Detection in Solidified Weld Metal

Laser-generated ultrasound: its properties, mechanisms and multifarious applications

Laser Array/EMAT Ultrasonic Measurement of the Penetration Depth in a Liquid Weld Pool

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