Begell House Inc.
High Temperature Material Processes: An International Quarterly of High-Technology Plasma Processes
HTM
1093-3611
4
2
2000
Short pulse high intensity laser machining
10
10.1615/HighTempMatProc.v4.i2.10
Xiangli
Chen
General Electric Corporate Research and Development P.O. Box 8, Schenectady, NY 12301, USA
Recent developments in the study of drilling and cutting performance of metals, ceramics, and composites are reviewed. Machined quality comparisons are made using a high brightness Nd:YAG laser and an ultrafast Ti:sapphire laser, with pulse widths ranging from 100 ns to 100 fs. Significant quality improvements are achieved over that of conventional Nd:YAG lasers at about 1 ms pulse width. It is shown that the shortening of pulse length and the subsequent increase in beam intensity result in much thinner recast layers and heat affected zones (HAZ), less microcracking or delamination of materials, and much better geometry stability. Both the Nd:YAG fundamental 1064 nm and the second harmonic wavelength of 532 nm are tested, showing substantial additional advantage for the shorter wavelength.
Thermal and dimensional characteristics of vapor-plasma plume and layer deposition in laser-aided rapid manufacturing
40
10.1615/HighTempMatProc.v4.i2.20
Franz-Josef
Kahlen
School of Optics and Center for Research and Education in Optics and Lasers, Department of Mechanical, Materials and Aerospace Engineering, The University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816-2700
Aravinda
Kar
School of Optics and Center for Research and Education in Optics and Lasers, Department of Mechanical, Materials and Aerospace Engineering, The University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816-2700
Three-dimensional structures of copper, Ti-6Al-4V, aluminum, and stainless steel 304 were fabricated by melting the powders of these materials with a CO2 laser beam. A vapor-plasma plume is generated at the top of the melt layer. The emission spectra of the plume were recorded using an optical multichannel analyzer, and the plume temperatures are determined to be in the range of 4920 K to 6720 K. A one-dimensional model is developed to calculate the plume temperature, process parameters and melt pool characteristics. The model accounts for the transmission of the laser beam through the plume, energy transfer in the molten phase and the Stefan conditions at the solid-liquid and liquid-vapor interfaces. The surface temperature at the molten surface is found to exceed the normal boiling temperature causing the pressure to be higher than one atmospheric pressure. The calculated plume temperatures are in good agreement with the values obtained from the spectral data. Also, the model predictions for remelt layer depth, deposition height and plasma height compare well with experimental data.
Conductive Losses Experienced during CO2 Laser Cutting
12
10.1615/HighTempMatProc.v4.i2.30
J.
Powell
Laser Expertise Ltd., Harrimans Lane, Dunkirk, Nottingham NG7 2TR, UK; and Division of Materials Processing, Lulea University of Technology, SE-97187 Lulea, Sweden
A.
Ivarson
Lulea University of Technology, SE-971 87 Lulea; and Atlas Copco Rock Drills AB, SE-701 91 Orebro, Sweden
L.
Ohlsson
Lulea University of Technology, SE-971 87 Lulea, Sweden
C.
Magnusson
Division of Materials Processing, Lulea University of Technology, SE-97187Lulea, Sweden
This paper begins by describing laser cutting in terms of a single energy balance. Analysis of this energy balance reveals that the efficiency of laser cutting decreases as the material thickness is increased. This point is demonstrated by the following experimental programme which investigates thermal losses by conduction from the cut zone. It is also shown that the magnitude of these conductive losses can exceed the laser output power if a laser-oxygen jet is used to cut steels.
The Effect of Process Speed on Energy Redistribution in Deep Penetration CO2 Laser Welding
14
10.1615/HighTempMatProc.v4.i2.40
C.
Lampa
The Swedish Institute of Production Engineering Research, Argongatan 30, SE-43153 Molndal, Sweden
A.F.H.
Kaplan
Department of Non-Conventional Processing, Forming and Laser Technology, Vienna University of Technology, Arsenal Objekt 207, A-1030 Vienna, Austria
J.
Powell
Laser Expertise Ltd., Harrimans Lane, Dunkirk, Nottingham NG7 2TR, UK; and Division of Materials Processing, Lulea University of Technology, SE-97187 Lulea, Sweden
C.
Magnusson
Division of Materials Processing, Lulea University of Technology, SE-97187Lulea, Sweden
This work discusses energy absorption mechanisms in CO2 laser welding and how they are affected by changes in the process speed. Two main energy absorption processes govern the welding interaction:
Fresnel absorption at the keyhole walls.
Absorption by the partially ionised metal vapour (or plasma) in the keyhole (laser energy absorbed in this way is re-radiated or conducted to the keyhole walls).
A theoretical model of these absorption mechanisms has been developed and shown to agree closely with experimental results. Fresnel absorption has been identified as being dominant over plasma absorption and becomes even more influential as welding speeds are increased.
Interactive Effects of Reactivity and Melt Flow in Laser Machining
26
10.1615/HighTempMatProc.v4.i2.50
Kai
Chen
Department of Mechanical Engineering, Columbia University, New York, NY 10027
Y. Lawrence
Yao
Department of Mechanical Engineering, Columbia University, 220 SW Mudd Building New York, NY 10027
A numerical model is developed to study the oxidation effects in oxygen-assisted laser cutting of mild steel. Coupled oxygen concentration and energy balance equations are solved by a control-volume based computational scheme while the velocity field is obtained by analytical boundary theory. Theoretical explanation on striation formation is given based on an instability analysis of the molten front. The striation frequency and depth are predicted. The steady-state simulation results include the temperature and oxygen concentration profiles at the cut front, the effects of impurity gas on the cutting speed, reaction energy, conduction loss, and heat affected zone. The dynamic simulation shows the oscillation of the molten temperature that is related to striations. The striation frequency and depth are experimentally validated.
Dimensional characteristics and mechanical properties of laser-formed parts
38
10.1615/HighTempMatProc.v4.i2.60
Wenchuan
Li
Department of Mechanical Engineering, Columbia University, New York, NY 10027
Jiangcheng
Bao
Department of Mechanical Engineering, Columbia University, New York, NY 10027
Y. Lawrence
Yao
Department of Mechanical Engineering, Columbia University, 220 SW Mudd Building New York, NY 10027
Recent developments in the study of the laser bending process are reviewed and presented to obtain new perspectives along the lines of dimensional characteristics and mechanical properties of the formed parts. Both numerical and experimental results are described and compared. The dimensional characteristics examined include bending angle variation and bending edge curving. The mechanical properties examined include residual stress, hardness and microstructural change.
Multiple-Beam Materials Processing
18
10.1615/HighTempMatProc.v4.i2.70
Elijah
Kannatey-Asibu, Jr.
Professor, Department of Mechanical Engineering and Applied Mechanics, The University of Michigan, Ann Arbor, MI 48109-2125
Multiple-beam processing is a relatively new field that has the potential to enhance the capabilities of high intensity laser and electron beam processes. This paper presents a review of work done in this area to date. It focuses on multiple-beam welding, where it has been most extensively applied. The multiple-beam laser preheating and postheating concept is first presented and analyzed. This is followed by multiple-beam flow control, which has thus far been applied mainly to electron beam welding. Arc-augmented laser welding is then outlined, and finally, other applications involving laser machining and cladding.