Real-time structured light profilometry: a review

Monitoring and Adaptive Control of Laser Processes

Quality assessment methods and techniques for laser welding have been developed both in- and post-process. This paper summarizes and presents relevant studies being classified according to the technology implemented (vision, camera, acoustic emissions, ultrasonic testing (UT), eddy current technique (ECT)) for the quality inspection. Furthermore, the current review aims to map the existing modeling approaches used to correlating measured weld characteristics and defects with the process parameters. Research gaps and implications of the quality assessment in laser welding are also described, and a future outlook of the research in the particular field is provided.

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Quality assessment in laser welding: a critical review

According to one embodiment of the invention, a system for fabricating a part includes a computer operable to control the fabrication of a three-dimensional part using a solid CAD model, a deposition station operable to deposit successive two-dimensional layers of material to fabricate the three-dimensional part, and a machining station operable to remove at least a portion of one or more of the deposited two-dimensional layers of material. The deposition station includes a substrate on which to fabricate the three-dimensional part, a welding-based deposition system having a welding torch, a laser-based deposition system having a laser head, a plasma powder cladding system having a plasma torch, and a multi-axis robot operable to, when directed by the computer, utilize one of the welding-based deposition system, laser-based deposition system, and plasma powder cladding system to deposit any of the two-dimensional layers of material. The machining station includes a multi-axis milling machine and an automatic tool changer. The milling machine is operable to, when directed by the computer, select from a plurality of machining tools associated with the automatic tool changer for use in the milling machine.

System and method for fabricating or repairing a part

The invention features a centralized control architecture for a closely-coupled plasma arc system, in which the “intelligence” of the system is integrated into a single controller. The closely-coupled plasma arc system includes a power source, an automatic process controller and a torch-height controller, where each of these components individually has a closed-loop dynamic relationship with the controller.

Centralized control architecture for a plasma arc system

A method and apparatus for real-time weld process monitoring are provided for a pulsed laser welding. The thermal radiation from a weld pool is measured at several spectral bands through an aperture with single-element detectors after splitting the spectral bands with dichromatic mirrors and beam splitters. The distal end of an optical fiber for laser delivery can be used as an aperture and each spectral band signal is measured with a single-element detector. Due to the chromatic aberration of an imaging optics, the field of view from a single-element detector through the aperture is varied by the wavelength of spectral band. The weld pool size contributing to the spectral band signal varies by the wavelength of the spectral band. The transmittance profile of each spectral band also depends on the focus shift of imaging optics. By processing the measured spectral band signals, the size of a weld pool, the power variation on a workpiece and the focus shift of imaging optics can be monitored simultaneously. Furthermore, the weld pool sizes at predetermined positions in time are correlated to the weld depth and the weld defect such as a weld gap for weld quality assurance.

Method and apparatus for real-time weld process monitoring in a pulsed laser welding

A modified center position detection algorithm of the spot image for the Shack–Hartmann wavefront sensor was experimentally investigated. The modified center of weight algorithm uses some power from the gray level intensity of the spot images instead of the gray level intensity itself. From the experiments, the repeatability and accuracy of the center position detection of the spot images which used the algorithm were improved when compared with those using the conventional center of weight algorithm. Applications of the algorithm to the measurement of the displacement of the spot images of the Shack–Hartmann wavefront sensor and the experimental results of the closed-loop wavefront correction are described in this paper.

A center detection algorithm for Shack–Hartmann wavefront sensor

A study on the 3-D measurement by using digital projection moiré method

In a laser welding, a laser beam is focused on a workpiece by a focusing lens or lenses. The focusing lens or lenses image an aperture liming the size of the laser beam on the workpiece and the size of focused laser beam is the image size of the aperture on the workpiece at the wavelength of the laser. A weld pool is generated by the interaction of the focused laser beam and the workpiece. Due to the thermal conduction of the workpiece, the size of the weld pool is generally not the same as the size of the focused laser beam and varies with the power of the laser or with the focus shift of the focusing lens or lenses. The weld pool radiates a thermal radiation. An apparatus and method is disclosed wherein the thermal radiation is measured back through the focusing lens or lenses and through the aperture limiting the size of the laser beam or any other aperture limiting a size of the thermal radiation to be measured in at least three spectral bands with single element detectors. Due to the chromatic aberration of the focusing lens or lenses, the transmittance of each spectral band of the thermal radiation varies with the size variation and with the focus position of a weld pool and the spectral band signals measured with single-element detectors vary if the size and/or the focus position of a weld pool varies. Algorithm to monitor the size variation and/or the focus position of a weld pool is disclosed wherein the size variation of a weld pool is monitored independently from the focus shift of the focusing lens or lenses and the focus position of a weld pool is monitored independently from the power variation of the laser.

Method and apparatus for monitoring the size variation and the focus shift of a weld pool in laser welding

The measuring resolution and speed for wavefront are important to improve the performance of an adaptive optics system. In this paper, we propose a fast measuring technique with high resolution in the Shack–Hartmann wavefront sensor. The proposed measuring technique of wavefront combines the conventional center of mass algorithm with an estimated weighting factor. The estimated weighting factor is a real value anticipating the real center of mass in a wavefront spot image. This estimated weighting factor can be calculated at the initialization step of an adaptive optics system. We designed a robust adaptive optics system with this proposed measuring algorithm. The measuring accuracy and speed are investigated by using the proposed algorithm compared with the conventional center of mass algorithm in experiments.

Sung-Hoon Baik

Papers

Method and apparatus for real-time weld process monitoring in a pulsed laser welding

A center detection algorithm for Shack–Hartmann wavefront sensor

A study on the 3-D measurement by using digital projection moiré method

Method and apparatus for monitoring the size variation and the focus shift of a weld pool in laser welding

A study on a fast measuring technique of wavefront using a Shack Hartmann sensor