Monitoring and Adaptive Control of Laser Processes

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

Three dimensional(3D) displacements, which can be translated further into 3D strain, are key parameters for design, manufacturing and quality control. Using different optical setups, phase-shift methods, and algorithms, several different 3D electronic speckle pattern interferometry(ESPI) systems for displacement and strain measurements have been achieved and commercialized. This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement. After an overview of the fundamentals of ESPI theory, temporal phase-shift, and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI system, which is suited well for static measurement, and by the spatial phase-shift ESPI system, which is particularly useful for dynamic measurement, are discussed. For each method, the basic theory, a brief derivation and different optical layouts are presented. The state of art application, potential and limitation of the ESPI systems are shown and demonstrated.

Review of electronic speckle pattern interferometry (ESPI) for three dimensional displacement measurement

A laser weld monitoring system capable of assessing a weld quality of welding using a pulsed laser is provided. The system includes at least one sensor capable of capturing a weld characteristic of welding using said pulsed laser. The weld characteristic has multiple attributes. The system also includes data acquisition and processing equipment adapted for storing and analyzing the weld characteristic. A user first performs multiple welds to capture at least one weld characteristic for each weld. The user then determines the weld quality of each weld, and runs at least one of a library of algorithms associated with the attributes on said at least one weld characteristic for each weld to generate a single value output for the associated attribute. The user selects an attribute indicative of the weld quality by correlating the single value outputs of said at least one algorithm with the weld qualities of the welds.

Laser weld monitor

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

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

We developed a highly efficient diode side-pumped Nd:YAG ceramic laser with a diffusive reflector as an optical pump cavity A maximum output power of 2116W was obtained with an optical -to- optical conversion efficiency of 487% This corresponds to the highest conversion efficiency in the side-pumped ceramic rod Thermal effects of the Nd:YAG ceramic rod were analyzed in detail through the measurements of laser output powers and beam profiles near the critically unstable region A M-2 beam quality factor of 187 was obtained at the maximum laser output power (c) 2006 Elsevier Ltd All rights reserved

Highly efficient diode side-pumped Nd:YAG ceramic laser with 210W output power

We have developed a laser isotope separation technology for the production of the 168Yb and 176Yb isotopes 168Yb is very useful for the generation of a non destructive testing source, 169Yb 176Yb can be used to produce 177Lu which is known to be a promising radioisotope for a medical application For these applications, the abundances of 168Yb and 176Yb isotopes should be enriched to more than 15% and 97%, respectively Our developed system consists of three dye lasers pumped by a diode-pumped solid-state laser, a Yb evaporator, and a photo-ion extractor Up to now, we could enrich 168Yb to more than 31% with a productivity of 05 mg/h Also, we succeeded in enriching 176Yb to more than 97% with a productivity of 27 mg/h

Cheol-Jung Kim

Papers

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

A center detection algorithm for Shack–Hartmann wavefront sensor

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

Highly efficient diode side-pumped Nd:YAG ceramic laser with 210W output power

Stable Isotope Production of 168Yb and 176Yb for Industrial and Medical Applications