Magdi Naim Azer

Predictive Modeling for Glass-Side Laser Scribing of Thin Film Photovoltaic Cells

Laser scribing of multilayer thin films is an important process for producing integrated serial interconnection of minimodules, used to reduce photocurrent and resistance losses in a large-area solar cell. Quality of such scribing contributes to the overall quality and efficiency of the solar cell and therefore predictive capabilities of the process are essential. Limited numerical work has been performed in predicting the thin film laser removal processes. In this study, a sequentially-coupled multilayer thermal and mechanical finite element model is developed to analyze the laser-induced spatio-temporal temperature and thermal stress responsible for SnO2:F film removal. A plasma expansion induced pressure model is also investigated to simulate the non-thermal film removal of CdTe due to the micro-explosion process. Corresponding experiments on SnO2:F films on glass substrates by 1064nm ns laser irradiation show a similar removal process to that predicted in the simulation. Differences between the model and experimental results are discussed and future model refinements are proposed. Both simulation and experimental results from glass-side laser scribing show clean film removal with minimum thermal effects indicating minimal changes to material electrical properties.

Formation of 238U16O and 238U18O observed by time-resolved emission spectroscopy subsequent to laser ablation

We have measured vibronic emission spectra of an oxide of uranium formed after laser ablation of the metal in gaseous oxygen. Specifically, we have measured the time-dependent relative intensity of a band located at approximately 593.6 nm in 16O2. This band grew in intensity relative to neighboring atomic features as a function time in an oxygen environment but was relatively invariant with time in argon. In addition, we have measured the spectral shift of this band in an 18O2 atmosphere. Based on this shift, and by comparison with earlier results obtained from free-jet expansion and laser excitation, we can confirm that the oxide in question is UO, consistent with recent reports based on laser ablation in 16O2 only.We have measured vibronic emission spectra of an oxide of uranium formed after laser ablation of the metal in gaseous oxygen. Specifically, we have measured the time-dependent relative intensity of a band located at approximately 593.6 nm in 16O2. This band grew in intensity relative to neighboring atomic features as a function time in an oxygen environment but was relatively invariant with time in argon. In addition, we have measured the spectral shift of this band in an 18O2 atmosphere. Based on this shift, and by comparison with earlier results obtained from free-jet expansion and laser excitation, we can confirm that the oxide in question is UO, consistent with recent reports based on laser ablation in 16O2 only.

Large diameter and thin wall laser tube bending

Large diameter and thin wall tube bending is challenging for mechanical methods. Although laser tube bending has been used for <2” diameter tubes, larger diameter laser tube bending is not thoroughly studied yet. This paper reports the challenges and our progress in large diameter laser tube bending. Special issues such as cooling, surface non-uniformity, beam shape and cross section deformation were investigated in comparison with small diameter tube bending.Large diameter and thin wall tube bending is challenging for mechanical methods. Although laser tube bending has been used for <2” diameter tubes, larger diameter laser tube bending is not thoroughly studied yet. This paper reports the challenges and our progress in large diameter laser tube bending. Special issues such as cooling, surface non-uniformity, beam shape and cross section deformation were investigated in comparison with small diameter tube bending.

Investigation on toolpath geometries for surface quality improvement in laser net shape manufacturing

Laser net shape manufacturing (LNSM) builds parts by successively cladding layers of powder on a substrate. The accuracy of deposition and the quality of the clad surface are highly dependent on the process parameters used in the deposition. A key process parameter is the NC toolpath used to drive the deposition nozzle. The NC toolpath is composed of the geometric path of the nozzle head and the parameters used to control the motion of the nozzle. This paper investigates the effect of deposition geometries and process parameters on the surface quality of the clad artifact. Prominent surface defects in the clad part are identified. Additionally, toolpath strategies are proposed to address these defects and improve the surface quality. The scope of the discussion is limited to hollow parts with no internal features.Laser net shape manufacturing (LNSM) builds parts by successively cladding layers of powder on a substrate. The accuracy of deposition and the quality of the clad surface are highly dependent on the process parameters used in the deposition. A key process parameter is the NC toolpath used to drive the deposition nozzle. The NC toolpath is composed of the geometric path of the nozzle head and the parameters used to control the motion of the nozzle. This paper investigates the effect of deposition geometries and process parameters on the surface quality of the clad artifact. Prominent surface defects in the clad part are identified. Additionally, toolpath strategies are proposed to address these defects and improve the surface quality. The scope of the discussion is limited to hollow parts with no internal features.

Laser shock peening plasma diagnostics sensors for real time process monitoring

A system for monitoring a laser shock event includes a detector (20,74,110) connected to a controller (14). The controller (14) includes an input configured to receive a signal from the detector (20,74,110) that is indicative of an emission (36,75,128) associated with a laser shock event at a workpiece (26,56,120). A processor (16,76,140) is connected to the input and is configured to determine a cause of an unacceptable peen event from the signal associated with the emission (36,75,128).

Laser near net shape manufacturing for nickel alloy parts with complex structure

To fabricate near net-shape nickel alloy turbine blade airfoil with complex internal structure, process of laser net shape manufacturing (LNSM) is studied in two aspects. One is steady process analysis to establish transfer functions between dimension and process parameters. Another one is dynamic process analysis focusing on decreasing defects in the region of special geometry features. Two solutions, path planning with process parameters optimization and vision based closed loop control are implemented to keep the process stable in those areas. Both solutions are applied successfully in nickel alloy turbine blade airfoil deposition with LNSM system. Geometric inspection shows good dimensional accuracy and surface quality can be achieved with this technology.To fabricate near net-shape nickel alloy turbine blade airfoil with complex internal structure, process of laser net shape manufacturing (LNSM) is studied in two aspects. One is steady process analysis to establish transfer functions between dimension and process parameters. Another one is dynamic process analysis focusing on decreasing defects in the region of special geometry features. Two solutions, path planning with process parameters optimization and vision based closed loop control are implemented to keep the process stable in those areas. Both solutions are applied successfully in nickel alloy turbine blade airfoil deposition with LNSM system. Geometric inspection shows good dimensional accuracy and surface quality can be achieved with this technology.

Laser net shape manufacturing of metallic materials with CO 2 and fiber laser

Laser net shape manufacturing of metallic materials has been carried out with CO2 and fiber lasers. The effect of the processing parameters, such as laser power, scanning velocity, and spot size on the impact of final deposition result was investigated. A comparison study of the as-deposited materials with the use of the two lasers was also conducted. It was found that the alignment of powder stream and laser beam is a critical element of ensuring high quality of deposition.Laser net shape manufacturing of metallic materials has been carried out with CO2 and fiber lasers. The effect of the processing parameters, such as laser power, scanning velocity, and spot size on the impact of final deposition result was investigated. A comparison study of the as-deposited materials with the use of the two lasers was also conducted. It was found that the alignment of powder stream and laser beam is a critical element of ensuring high quality of deposition.

Development of transfer functions for controlling fabrication of components by laser net shape deposition (LNSM)

Although laser cladding was developed thirty years ago, it has only been in the last ten years that research groups and companies have begun to exploit this technology to produce fully dense, near-net shape components with metals through techniques such as Direct Metal Deposition (DMD), Directed Light Fabrication (DLF), Laser Consolidation (LC), or Laser Engineered Net Shape (LENS). In order to produce components with fine features, it is necessary to provide proper thermal management of the weld pool during deposition. This is achieved by two means. First, proper choice of process parameters must be made to generate uniform deposits. Second, external sensor and control strategies must be employed to insure that the weld pool size is stable during the course of deposition. In this paper, the process for developing the transfer functions for laser net shape manufacturing (LNSM) is discussed. Finally, the strategy for how these transfer functions can be combined with sensors to control deposition is outlined.Although laser cladding was developed thirty years ago, it has only been in the last ten years that research groups and companies have begun to exploit this technology to produce fully dense, near-net shape components with metals through techniques such as Direct Metal Deposition (DMD), Directed Light Fabrication (DLF), Laser Consolidation (LC), or Laser Engineered Net Shape (LENS). In order to produce components with fine features, it is necessary to provide proper thermal management of the weld pool during deposition. This is achieved by two means. First, proper choice of process parameters must be made to generate uniform deposits. Second, external sensor and control strategies must be employed to insure that the weld pool size is stable during the course of deposition. In this paper, the process for developing the transfer functions for laser net shape manufacturing (LNSM) is discussed. Finally, the strategy for how these transfer functions can be combined with sensors to control deposition is outlined.

Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. Using emission spectroscopy acquired after ablation of a SrZrO3 target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO2 are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an 18O2 environment by observing the in-growth of Zr18O in the emission spectra relative to Zr16O, which was formed by reaction of Zr with 16O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Using a simple temperature-dependent reaction model, we have illustrated that the formation sequence of these oxides subsequent to ablation is predictable to first order.

Method for controlling a laser additive process using intrinsic illumination

One form of additive manufacturing is to use a laser to generate a melt pool from powdered metal that is sprayed from a nozzle. The laser net-shape machining system builds the part a layer at a time by following a predetermined path. However, because the path may need to take many turns, maintaining a constant melt pool may not be easy. A straight section may require one speed and power while a sharp bend would over melt the metal at the same settings. This paper describes a process monitoring method that uses the intrinsic IR radiation from the melt pool along with a process model configured to establish target values for the parameters associated with the manufacture or repair. This model is based upon known properties of the metal being used as well as the properties of the laser beam. An adaptive control technique is then employed to control process parameters of the machining system based upon the real-time weld pool measurement. Since the system uses the heat radiant from the melt pool, other previously deposited metal does not confuse the system as only the melted material is seen by the camera.