|
|
This is only a preview of the paper
Click here to register and get the full text.
Existing members click here to login
|
|
|
Laser Assisted Oxygen Cutting
W. ... uk
It has been nearly 33 years since the first laser cut was produced at The Welding Institute, Cambridge, UK. It is quite remarkable that laser cutting as we know it today has changed very little since these first trials. The developments that have taken place relate to greater process understanding, improved laser sources, enhanced beam handling systems and process refinements. Much effort has been placed in improving the efficiency of the process such that thicker sections can be cut with moderate laser powers. Yet for all of these developments laser cutting has seen little movement in maximum section limits that can be cut. ... While it is true that the market is small for steel sections above 15mm it is apparent that some industries such as offshore, marine, construction and heavy engineering would benefit greatly from a laser process capable of cutting sections much greater than 15mm. This paper presents results obtained from a study of a new thick section laser cutting process capable of cutting sections up to 50mm thick in the first instance with power levels less than 2kW whilst maintaining excellent cut quality. The work presents initial results of cutting steel up to 50mm thick and examines the process using theoretical and experimental analysis.
Introduction
In gas assisted laser cutting mild and carbon steels, a high power laser is used to melt the required metal volume that is then blown away by an assist gas jet. Most often oxygen is used to contribute energy to the process, enhancing process speeds and cut depths in ferrous metals through the release of exothermic energy from the combustion of iron. ... While sections up to 15mm represent the majority of those cut by laser there are applications that require sections greater than 15mm. ... In the limit above 25mm thick conventional laser cutting is severely restricted. The authors have been engaged in a range of studies aimed at developing a thick section laser cutting process. ... A number of solutions have been determined and this paper presents one of those solutions, namely the Laser assisted oxygen process or Lasox as it will be referred to hereafter.
Conventional laser cutting has to operate at high cutting speeds and low gas pressure to minimise side burning. This effect is due to workpiece overheating leading to side burning as the oxygen gas jet reacts with the surrounding material outside the cutting zone [O’Neill, 1992]. Side burning occurs in all oxygen laser cutting processes and is represented in the stable form by the striation pattern on the cut walls. At low cutting speeds, energy from the process conducts away from the interaction point and elevates the local temperature of the metal far away from the laser beam. ...
Thick section plates are generally cut with a much reduced oxygen pressure (< 1bar) compared to thin sections (>1 bar). The reduced gas pressure minimises the likelihood of side burning although, as most laser operators know, side burning often occurs randomly. ... In the conventional sense it is possible to cut sections up to 25mm thick with laser powers of around 3kW. The process window in this case is largely determined by the M2 value of the laser beam, oxygen gas pressure and nozzle diameter. ...
Basic Principles
The ability of oxygen to react violently with steel is evident when observing the oxygen assisted laser cutting process. ... Assuming that all of the metal removed from a thick section is ignited to form FeO (this is not an unreasonable assumption as the debris from a thick section laser cutting process is composed of oxide scale rather than re-solidified iron) the calculated power generated by the combustion process is given in Table. ... 1 one can see that tens of kilowatts are available to the cutting process when the iron completely reacts with oxygen. ... In order to generate this power one must deliver sufficient oxygen to the kerf. This can only be achieved at high pressures that, as we know, cause problems in thick section cutting due to side burning. The Lasox technique applied here relies on the laser beam heating the surface of the steel to the ignition point across the whole area of gas jet impingement. In this case the laser power requirements are much reduced and the dynamics of the gas jet control the process result.
Approximate Word count = 3520
Approximate Pages = 14.1
(250 words per page double spaced)
|
|
|
|
|
|