FIELD OF THE INVENTION
The present invention generally relates to a hybrid laser arc welding technique in
which laser beam welding and arc welding simultaneously occur in the same weld
pool. More particularly, the invention relates to a hybrid laser arc welding process for
welding of stainless steel capacitor box for power generator to improve weld quality.
BACKGROUND OF THE INVENTION
Low-heat input welding processes, and particularly high-energy beam welding
processes such as laser beam and electron beam welding (LBW and EBW,
respectively) is known, and operated over a narrow range of welding conditions to
produce crack-free weld joints in a wide variety of materials, including but not
limited to alloys used in turbo machinery. An advantage of high-energy beam welding
processes is that the high energy density of the focussed laser or electron beam is
able to produce deep narrow welds of minimal weld metal volume, enabling formation
of butt welds that add little additional weight and cause less component
distortion in comparison to other known welding techniques, such as arc welding
processes. Additional advantages particularly associated with laser beam welding
include the ability to be performed without a vacuum chamber or radiation shield
usually required for electron beam welding. Consequently, the laser beam welding is
proved to be a lower cost and more productive welding process as compared to the
electron beam welding.
Though filler materials are used for certain specific applications and welding
conditions, the laser beam and electron beam welding processes are typically
performed autogenously (no additional filler metal added). A high-energy beam is
focused on the surface to be welded, for example, and interface (weld seam) between
two components to be welded. During welding, the surface is sufficiently heated to
vaporize a portion of the metal, creating a cavity ("keyhole") that is subsequently
filled by the molten material surrounding the cavity. A relatively recent advancement
in the laser beam welding technique is the development of high powered solid-state
lasers, which as defined herein involves power levels of greater than four kilowatts
and especially ten kilowatts or more. Particular examples are solid-state lasers that
use ytterbium oxide (YD2O3) in disc form (Yb: YAG disc lasers) or as an internal
coating in a fiber (Yb fiber lasers). These lasers substantially increase efficiencies and
power levels, for example, from approximately four kilowatts to over twenty kilowatts.
Hybrid laser arc welding (HLAW), also known as laser-hybrid welding, is a process
that combines laser beam and arc welding techniques, such that both welding
processes simultaneously occur in the same weld pool. The laser beam is typically
oriented perpendicular to the surfaces to be welded, while the electric arc and filler
metal of the arc welding process (for example, gas metal arc welding (GMAW, also
known as metal inert gas (MIG) welding) or gas tungsten arc welding (GTAW, also
known as tungsten inert gas (TIG) welding) are typically positioned behind and angled
forward toward the focal point of the laser beam on the weld joint surfaces. This
position of the arc welding process is known as a "forehand" technique. The benefit
of the HLAW process is the ability to increase the depth of weld penetration and/or
increase productivity by increasing the welding process travel speed, for example, by
as much as four times faster than conventional arc welding processes.
Even though laser beam welding is known to have various benefits noted above, the
deep penetrating laser beam welding techniques are known to be prone to a
phenomenon of trapped porosity. This propensity of forming trapped porosity, can be
attributed to the low heat input associated with the laser beam welding compared to
typical fusion arc processes. As a result, the weld pool produced by the laser beam
welding tends to freeze very quickly, trapping gas-metal reaction products generated
during the welding process. Though the inclusion of an arc process in HLAW
processes helps to reduce porosity in shallow welds, for example, weld depths of less
than one-half inch (about one centimeter), however, the porosity resulting from
trapped gas bubbles is an issue when attempting to achieve greater weld depths.
Reducing or eliminating the porosity in deep laser welds would be particularly
advantageous from the standpoint of achieving longer lives for components subjected
to cyclic operations. One commercial example is the fabrication of wind turbine
towers. Currently the use of welding processes that utilize a laser beam welding
technique is discouraged for such applications, because of the propensity for large
amounts of fine-sized internal porosity found in deep weldments produced by the
laser beam welding. The presence of porosity can significantly reduce the fatigue life
of a weld joint vis-a-vis that of a structure that contains the weld joint. Consequently,
other welding techniques such as submerged arc welding (SAW) processes are more
typically employed in the fabrication of structures subjected to cyclic operations, such
as wind turbine towers. However, when used to weld large thick sections required in
the construction of wind turbine towers, a significant drawback of the SAW process is
the low productivity, for example, resulting from the necessity to perform multiple
passes at relatively low speeds, for example, about twenty to forty inches (about 50
to 100 cm) per minute. Though preheating the components just prior to welding
might achieve a lower cooling rate to allow gas bubbles to escape the weld pool, in
practice a component may require heating to nearly three-quarters of its melting
temperature, which is both expensive and can have deleterious effects on the base
material properties of the component. Following a laser beam welding with a second
laser beam welding treatment to release the gas bubbles has also proved to be
ineffective since the weld pool produced by the second treatment also tends to freeze
too quickly to allow gas bubbles to float free of the weld pool.
US 6844521 describes an apparatus, in particular a laser hybrid welding head for a
laser hybrid welding process, in which a laser or laser optics or an optical focusing
unit and elements of a welding torch for an arc welding process and/or a feed device
for a welding wire as well as a device for generating a cross jet connected by at least
an incoming line and an outgoing line to a compressed air supply system, are
mounted on at least one mounting element. The incoming line and the outgoing line
carrying compressed air for the cross jet are disposed between the two components,
in particular the laser and laser optics or the optical focusing unit and the elements of
the welding torch or feed device for the welding wire.
US 6469277 talks about a hybrid welding from a combination of laser beam welding
with gas-shielded welding by electric arc uses at least two electrodes are used. The
electrodes can be flooded by a common shielding gas curtain or separately or in
groups. The hybrid welding increases the possibility of influencing the welding
process and especially provides improved possibilities for automation.
US 6683268 teaches a process for manufacturing a welded pipe from a metal strip
having two longitudinal edges approximately parallel to each other, which are brought
together so as to come approximately into contact with each other and thus form an
unwelded pre-tube, the pre-tube then being welded in order to join the edges
together. The two edges are welded together to obtain a welded metal pipe by using,
approximately simultaneously, at least one laser beam and at least one electric arc,
that is to say using a hybrid arc/laser, preferably plasma/laser, welding process.
US 6603092 discloses a Hybrid welding process and apparatus for welding metal
workpieces, such as tailored blanks, by using a laser beam and an electric arc,
preferably a plasma arc, in which process, after a welded joint has been produced,
the laser beam is sent and/or deflected into radiation absorption means, such as an
absorption cavity, allowing the radiation of said beam to be absorbed. The beam
continues to be deflected during the welding stop phase after producing one welded
joint and before starting to weld a second welded joint. The process and the
apparatus of this invention are particularly suitable for the mass production of
workpieces for the motor vehicle industry, such as tailored blanks that can be used to
manufacture, for example, motor-vehicle body components, or for the mass
production of pipes.
US 20070251927 provides a method for welding coated sheet metal, which comprises
at least one laser and at least one shielded arc unit and a rod feeding device for a
welding rod. The aim of this invention is to provide a method or a device of the
aforementioned kind which allows for reducing or completely avoiding inclusions such
as are e.g. caused by the evaporation of the coating of the metal sheet.
To summarize the prior art, the known inventions in Laser/Laser Hybrid welding are
primary related to the construction and working of the Laser/Laser Hybrid welding
principle. Thus, the prior art fail to teach or suggest a method/ process for welding of
stainless steel capacitor boxes, in particular for welding generators.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a hybrid laser arc welding
method/process for welding of Stainless steel capacitor box on power generator.
Another object of the invention is to propose a hybrid laser welding process for
welding of Stainless steel capacitor box on power generator, which improves the weld
quality.
A further object of the invention is to propose a hybrid laser welding process for
welding of Stainless steel capacitor box on power generator, which reduces the
welding cycle time and improve the productivity.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides a method of welding together at least two
parts of a capacitor box on a welding generator which comprises the steps of placing
the at least two parts of the capacitor box to be welded along a line adjacent to each
other, and forming a weld along the line using a laser/laser hybrid arc welding,
wherein the laser hybrid arc with the adjacently located components fixed in a single
plane, allows, simultaneous production of a fillet/butt on edges of the capacitor box
panel, thereby reducing the stress concentration. The method can therefore be
used to weld capacitor box solely from one side of the box, while still producing a
full penetration weld, i.e. a weld that penetrates to the opposite side of the joint. This
in turn reduces welding time and distortion. Distortion is also reduced because the
laser/laser hybrid welding imparts less heat to the parts to form a weld. According to
to the disclosed hybrid laser arc welding technique, the laser beam, welding and arc
welding simultaneously occur, and in that the laser beam that precedes the hybrid
laser arc, further utilizes a second laser beam welding to increase the weld depth and
to eliminate the porosity and gas pockets in the resulting weld joints.
Accordingly, the invention enables making butt welding/fillet welding of stainless steel
plates/sheets, using laser arc as the source. Thus, multi-layer welding can be
achieved for all sizes of higher thickness material. The filler wire of different sizes can
be welded by the laser hybrid welding, including a combination of filler materials.
WE CLAIM:
1. A hybrid laser arc welding process for welding of stainless steel capacitor box
on the welding generator to improve weld quality, comprising the steps of:
- locating at least two parts of the capacitor box along a line in a single plane
adjacent to each other;
- forming a weld along the line by implementing a laser beam/hybrid laser arc
welding to produce fillet/butt joints on edges of the capacitor panel;
characterized in that the laser beam, welding and arc welding simultaneously
occur, and in that the laser beam that precedes the hybrid laser arc, further
utilizes a second laser beam welding to increase the weld depth and to
eliminate the porosity and gas pockets in the resulting weld joints.
2. The process as claimed in claim 1, wherein said at least two parts is welded
solely from one side of the capacitor box with full penetration weld.
3. The process as claimed in claim 1, wherein the simultaneous production of fillet/
butt joint on the edges of the capacitor box reduces stress-concentration.
4. The process as claimed in any of the preceding claims, wherein the distortion of
the weld is eliminated due to lesser heat being imparted by the laser/laser hybrid
welding.