Marshall Gordon Jones

Laser Forming of Varying Thickness Plate—Part I: Process Analysis

Laser forming (LF) is a non-traditional forming process that does not require hard tooling or external forces and, hence, may dramatically increase process flexibility and reduce the cost of forming. While extensive progress has been made in analyzing and predicting the deformation given a set of process parameters, few attempts have been made to determine the laser scanning paths and laser heat conditions given a desired shape. This paper presents a strain-based strategy for laser forming process design for thin plates with varying thickness, which is utilized in determining the scanning paths and the proper heating conditions. For varying thickness plates, both the in-plane membrane strain and the bending strain need to be accounted for in process design. Compared with uniform thickness plate, the required bending strain varies with not only the shape curvature but also with the plate thickness. The scanning paths are determined by considering the different weight of bending strain and in-plane strain. A thickness-dependent database is established by LF finite element analysis simulation, and the heating conditions are determined by matching the ratio of bending strain to in-plane strain between the required values and the laser forming values found in the database. The approach is validated by numerical simulation and experiments using several typical shapes.

Direct Laser Sintering of Metals

The use of a directed laser bealn source to selectively sinter multiple layers of binderless metal powder for the purposes of rapid prototyping is described. The work in this paper is restricted to -325 mesh iron powder, which was sintered using a C\V 50 W Nd:YAG laser to approximately 3.5% density. A subsequent post-treatlnent was perfornled to achieve a fully dense saulple. It is envisioned that such a system can be used to manufacture functional metallic prototypes directly from CAD without part-specific tooling.

Effects of Scanning Schemes on Laser Tube Bending

Four laser scanning schemes for tube bending, including point-source circumferential scanning, pulsed line-source axial procession, and line-source axial scanning without and with water cooling are investigated in numerical simulation. The coupled thermomechanical model established using the finite element method is validated and applied to predict the bending deformation and help better understand bending mechanisms under different schemes. The influence of important parameters such as beam coverage, scanning velocity and cooling offset on the deformation is investigated in detail. Parametric studies are carried out to determine proper processing windows at which the largest bending can be obtained. The deformation characteristics, including the wall thickness variation and the cross-section distortion produced by different scanning schemes are analyzed, along with the processing efficiency. DOI: 10.1115/1.2113047

Laser forming: Industrial applications

Laser forming is currently a laboratory technique that is beginning to see industrial applications. In this paper, we discuss practical concerns and review the progress of laser forming at GE Global Research. Two applications, 3D shape tuning and precision tube bending, are presented. Topics include considerations for industrial applications, methods for qualifying a process window, materials characterization, path planning, and system integration.Laser forming is currently a laboratory technique that is beginning to see industrial applications. In this paper, we discuss practical concerns and review the progress of laser forming at GE Global Research. Two applications, 3D shape tuning and precision tube bending, are presented. Topics include considerations for industrial applications, methods for qualifying a process window, materials characterization, path planning, and system integration.

Laser hot-wire welding for minimizing defects

The objective of laser hot-wire welding is to provide a low heat input procedure which could minimize defects in crack sensitive supper alloys and increase over all deposition rates in cladding operations. Another potential benefit of laser hot-wire welding is that thermal distortion effect are greatly reduced. A continuous wave (CW) neodymium (Nd): yttrium-aluminum-garnet (YAG) operating in the kilowatt regime was used to successfully weld similar and dissimilar crack sensitive supper alloys. Results will include welding data that addresses joints with gaps greater than 0.5 mm.The objective of laser hot-wire welding is to provide a low heat input procedure which could minimize defects in crack sensitive supper alloys and increase over all deposition rates in cladding operations. Another potential benefit of laser hot-wire welding is that thermal distortion effect are greatly reduced. A continuous wave (CW) neodymium (Nd): yttrium-aluminum-garnet (YAG) operating in the kilowatt regime was used to successfully weld similar and dissimilar crack sensitive supper alloys. Results will include welding data that addresses joints with gaps greater than 0.5 mm.

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.

Effects of scanning schemes on laser tube bending

Four laser scanning schemes for tube bending, including point-source circumferential scanning, pulsed line-source axial procession, line-source axial scanning without and with water cooling are investigated in numerical simulation. The coupled thermo-mechanical model established using the finite element method is validated and applied to predict the bending deformation and help better understand bending mechanisms under different schemes. The influence of important parameters such as beam coverage, scanning velocity and cooling offset on the deformation is investigated in detail. Parametric studies are carried out to determine proper processing windows at which the largest bending can be obtained. The deformation characteristics, including the wall thickness variation and the cross-section distortion produced by different scanning schemes are analysed, along with the processing efficiency.Four laser scanning schemes for tube bending, including point-source circumferential scanning, pulsed line-source axial procession, line-source axial scanning without and with water cooling are investigated in numerical simulation. The coupled thermo-mechanical model established using the finite element method is validated and applied to predict the bending deformation and help better understand bending mechanisms under different schemes. The influence of important parameters such as beam coverage, scanning velocity and cooling offset on the deformation is investigated in detail. Parametric studies are carried out to determine proper processing windows at which the largest bending can be obtained. The deformation characteristics, including the wall thickness variation and the cross-section distortion produced by different scanning schemes are analysed, along with the processing efficiency.

Flexible beam delivery for material processing laser power through a fiber optic cable

A neodymium: yttrium-aluminum-garnet (Nd:YAG) laser used in a pulsed mode is coupled to and passed through a single quartz fiber optic cable at peak power levels required for laser material processing. This flexible fiber permits laser cutting, drilling, and welding of metals with a robot. Metals in excess of 2 mm (0.080 inches) thick have been laser cut.A neodymium: yttrium-aluminum-garnet (Nd:YAG) laser used in a pulsed mode is coupled to and passed through a single quartz fiber optic cable at peak power levels required for laser material processing. This flexible fiber permits laser cutting, drilling, and welding of metals with a robot. Metals in excess of 2 mm (0.080 inches) thick have been laser cut.

Experimental Evaluation and Finite Element Analysis of Laser Welded Copper-Copper And Copper-Aluminum Joints

The effect of temperature as a function of time in laser welding of similar and/or dissimilar materials was evaluated experimentally and by finite element analysis. Three cases = copper-copper, copper-aluminum, and aluminum-aluminum welded joints - were analyzed by simulation. There were four tests evaluations: tensile strength, relative impact strength, resistance versus temperature variation, and an electron microprobe analysis. Good tensile strength and low electrical resistance results were obtained for welding ETP copper with a neodymium (Nd)-glass laser. Copper-aluminum conductors responded with good tensile and impact strengths to laser welding.

Interlaminar Toughening of GFRP—Part II: Characterization and Numerical Simulation of Curing Kinetics

Various methods of toughening the bonding between the interleaf and laminate glass fiber reinforced polymer (GFRP) have been developed due to the increasing applications in industries. A polystyrene (PS) additive modified epoxy is used to improve the diffusion and precipitation region between polysulfone (PSU) interleaf and epoxy due to its influence on the curing kinetics without changing glass transition temperature and viscosity of the curing epoxy. The temperature-dependent diffusivities of epoxy, amine hardener, and PSU are determined by using attenuated total reflection–Fourier transfer infrared spectroscopy (ATR–FTIR) through monitoring the changing absorbance of their characteristic peaks. Effects of PS additive on diffusivity in the epoxy system are investigated by comparing the diffusivity between nonmodified and PS modified epoxy. The consumption rate of the epoxide group in the curing epoxy reveals the curing reaction rate, and the influence of PS additive on the curing kinetics is also studied by determining the degree of curing with time. A diffusivity model coupled with curing kinetics is applied to simulate the diffusion and precipitation process between PSU and curing epoxy. The effect of geometry factor is considered to simulate the diffusion and precipitation process with and without the existence of fibers. The simulation results show the diffusion and precipitation depths which match those observed in the experiments. [DOI: 10.1115/1.4036127]