Patent Description:
State of the art is reflected in welding wherein a material in a first plate is locally heated above the melting point and attached to a second plate. Heating can be performed in many ways such as laser welding.

Laser welding as a method for joining metal sheets by welding through one plate and into an underlying plate is nothing new and is used, for example, extensively in the automotive industry. Typical plate thickness in the automotive industry is in the order of <NUM>.

Reinforcement of structures by conventional welding methods is only possible by welding along the edges of the reinforcing elements, and a large number of reinforcement plates may be required to reinforce a given area. This can, for example, require positioning and welding of ten smaller plates compared to one larger plate being required when laser technology is applied.

From prior art one should refer to <CIT> which describes laser welding of two plates having a thickness of <NUM> - <NUM>, wherein the laser is moved in a pattern such as a band or stitching.

However, there has to be a gap between the plates during welding.

One should also refer to <CIT> which describes a method for laser welding of light metal bodies wherein one body is positioned to overlap the second body before welding the overlapping area using laser welding. The laser melts the first and the second body in a welding path in order to form a weld wherein the bodies can be thin plates having a thickness of <NUM> - <NUM>.

However, the welding has to be repeated in order to achieve sufficient strength.

Also one should refer to <CIT> which describes a method for laser welding of galvanised steel plates arranged to overlap, wherein the first plate has a thickness of <NUM> and the second has a thickness of <NUM>.

However also this requires a gap between the plates prior to welding.

Furthermore, one should refer to <CIT> which describes a method for welding of thin metal sheets in a manner similar to <CIT>.

However, one of the plates is provided with protrusions forming a gap when the plates are brought into contact with each other.

One should also refer to <CIT> which describes a method for joining at least two thin plates using laser through-welding, wherein the weld extends along protrusions provided in one plate, having a line form.

However, at least one of the plates have to be provided with protrusions and moreover a protective layer is applied to at least one of the plates.

Finally, one should refer to <CIT> which describes laser welding of plates having a thickness of <NUM>, wherein the plates are arranged to overlap and laser through-welding is used.

However, this solution requires welding from both sides, forming a weld penetrating both plates. It is also specified that the laser is moved in a circle.

Furthermore one should refer to <CIT> which relates to a method of laser welding a workpiece stack-up. The disclosed method includes directing a laser beam at a top surface of the workpiece stack-up to create a molten metal weld pool and, optionally, a keyhole, and further gyrating the laser beam to move a focal point of the laser beam along a helical path having a central helix axis oriented transverse to the top and bottom surfaces of the workpiece stack-up.

<CIT> relates to method of laser spot welding a workpiece stack-up(<NUM>) that includes at least two overlapping steel workpieces(<NUM>,<NUM>), at least one of which includes a surface coating(<NUM>), is disclosed.

Moreover, reference should be made to <CIT>, relating to prevention of surface bead shape roughening while removing gas of metallic vapour.

<CIT> relates to a manufacturing method of a laser lap weld joint.

<CIT> discloses according to its abstract, composite metal panels comprise two parallel plates <NUM>, <NUM> each laser-welded to an internally sandwiched corrugated stiffener plate.

<CIT> discloses according to its abstract, a <NUM>-<NUM> metal plate <NUM>, <NUM>, usually ferrous, is welded by a heavy-duty laser (<NUM>-<NUM> kw) which melts through the plate and into a support member below to give a unitary weld.

<CIT> discloses according to a translation of its abstract, a conductive member that includes: a first member made of <NUM> series aluminum alloy; a second member as to penetrate through the first member up to the inside of the second member in a portion where the first member and the second member are overlapped on each other.

<CIT> discloses according to its abstract, a body structure for rolling stock, where the body structure may include an outside sheathing of a side construction, and a plurality of reinforcement members joined to said outside sheathing interiorly of said outside sheathing.

<CIT> discloses according to a translation of its abstract, a side shield system that a shield gas is brought to face toward the welding part with the laser beam and to jet to the upper surface of steel plate by the prescribed angle is adopted.

<CIT> discloses according to its abstract, a method of laser welding a workpiece stack-up that includes at least two overlapping aluminum workpieces comprises advancing a laser beam relative to a plane of a top surface of the workpiece stack-up and along a spot weld travel pattern that includes one or more nonlinear inner weld paths and an outer peripheral weld path that surrounds the one or more nonlinear inner weld paths. Further, <CIT> discloses a laser welding method, wherein steel plates are welded together and generation of bubbles in the laser welding step is suppressed.

There is therefore a need for a method and a system to overcome the above-mentioned problems.

Therefore, a main objective of the present invention is to provide a method for combination of two or more preferably thick stacked metal plates by welding.

The objective is achieved according to the invention by a method for welding of thick plates as defined in the preamble of claim <NUM>, having the features of the characterising portion of claim <NUM>.

A number of non-exhaustive embodiments, variants or alternatives of the invention are defined by the dependent claims.

The present invention attains the above-described objective by a method for welding one or more thick plates into a welded assembly.

In a first aspect of the invention a method for welding a thick plate into a welded assembly is provided as defined in claim <NUM>.

In a second aspect of the invention a use of any of the above methods for strengthening an existing plate by welding in a second strengthening plate, is provided, wherein the second plate is a thick plate having a thickness greater than <NUM>.

In a non-claimed variation of the invention a welded assembly made using any of the above methods, is provided.

The present invention comprises a technological advantage over known systems and methods by use of thick plates, that is plates thicker than <NUM>.

The present invention provides several further advantageous effects:.

Importantly it makes it possible to weld in a continuous process without the use of microscopic beam patterns such as gyrations to melt a keyhole for letting gases escape.

The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an [exemplary] embodiment of the invention given with reference to the accompanying drawings.

The invention will be further described below in connection with exemplary embodiments which are schematically shown in the drawings, wherein:.

The following reference numbers and signs refer to the drawings:.

For example, an apparatus may be implemented, or a method may be practiced using any number of the aspects set forth herein. Nevertheless, the invention as such and the intended scope of protection is defined exclusively by the appended claims.

The invention will be further described in connection with exemplary embodiments which are schematically shown in the drawings, wherein <FIG> shows a strengthening plate overlaid a bulkhead plate, with intersecting welding lines.

Thin plate welding is well known, wherein plates are up to <NUM> thick. Many metals oxidise easily and the oxides release oxygen gas when the metal is heated and liquefied. This causes bubbles and welding defects that should be avoided.

In the context of this disclosure a thin plate is less than <NUM> thick, whereas a thick plate is at least <NUM> thick, typically <NUM> - <NUM> thick.

Welding is performed by heating metal until it is locally liquefied and bonds two or more bodies, typically plates. The inventor has realised that thick plates can be laser welded without formation of significant welding defects. Typically steel is suitable for this method of welding, but light metals with an insulating, protective oxide layer with a high melting point, such as aluminium and magnesium, are less suitable.

The embodiment of the method for forming a welded assembly <NUM> according to the invention shown in <FIG> comprises placing a first plate <NUM> in overlapping contact with a second plate <NUM>, wherein the plates are of materials that do not form unacceptable bubbling in the metal when heated.

The second plate <NUM> is of a thickness greater than <NUM>. The first plate can be thicker or thinner. Normally if the first plate is thinner one would want to weld from the opposite site. In some cases that can be impossible, for instance due to other obstructions on the inside. For strengthening the second plate is preferably thicker than <NUM>, in order to gain extra strength. More preferably the second plate is thicker than <NUM> in order to gain extra strength.

Next the plates are through welded using laser welding. The welding seams <NUM> can be a peripheral welding seam and interior welding seams <NUM>, <NUM> applied.

If deemed necessary, the operations described above, can be repeated with an additional plate welded to plate <NUM> from the other side.

More than one plate can also be welded from one side with additional plate(s) welded onto plate <NUM>. Further plates adds strength and using thick plates means fewer welding sequences have to be undertaken.

In a typical application of an embodiment of the method for forming a welded assembly <NUM> according to the invention the first plate <NUM> is a bulkhead plate of a ship or a tank. A second plate <NUM> for strengthening, repair and/or corrosion protection is brought in overlapping contact with the bulkhead plate. Next a laser is used to perform through welding between the plates, typically starting with an inner pattern. Typically a laser source with a power of <NUM> - <NUM> kW is used, which gives an effective welding speed of <NUM> - <NUM> / min. The laser beam is transferred from the source to the workpiece through an optical fibre.

<FIG> shows how horizontal <NUM> and vertical <NUM> welding seams are applied to the second plate <NUM> placed over the bulkhead plate <NUM>. It has been found that a pattern of perpendicular lines provides good strengthening when the plates are subjected to forces straining the plates. It is welded along the periphery <NUM>. These lines form a rectangular pattern.

Where necessary several plates will be required to cover the complete area, where strengthening is required. In such cases, the interface between adjoining plates will be butt welded and connected to the underlying plate in one laser welding operation.

<FIG> shows a cross section of <FIG> and shows how the welding seams penetrate the strengthening plate and into the bulkhead plate.

It has been found that welding of ferrous materials works well, including partially corroded steel. Also nickel, copper, and titanium have been found to work well.

A number of variations on the above can be envisaged. For instance the horizontal and vertical pattern of welding seams can be replaced by a closed geometric pattern enclosing a volume such as hexagon pattern, and circles, or open geometric pattern letting gas escape by not enclosing a volume such as spots, spirals, and meanders, and other patterns that substantially fill the contact area inside the periphery. The degree to which the area is covered is determined by the requirement for strength and time constraints.

<FIG> shows an embodiment of an open pattern in the form of a plurality of meanders. The meanders substantially cover the area defined by the second plate. The patterns can be unidirectional or in boustrophedonic order in order to save time.

<FIG> shows an embodiment of an open pattern in the form of a spiral, in this case a single spiral that substantially covers the area defined by the second plate. This pattern will weld the plates in a single movement.

<FIG> shows an embodiment of a closed pattern in the form of a plurality of circles, that together substantially cover the area defined by the second plate. In embodiments not shown the circles can be overlapping or concentric.

<FIG> shows an embodiment of a closed pattern in the form of a plurality of polygons, specifically pentagons.

<FIG> shows an embodiment where a third plate <NUM> is applied as an interposer between the first and the second plate. During welding the second and third plate are both welded through and into the first plate.

It is also possible to weld further plates (not shown) on top of existing plates <NUM>, <NUM> in subsequent welding. This is advantageous in cases where the single plates are too heavy to position comfortably. Instead a plurality of thinner plates are sequentially welded into a composite.

It is also within the scope of this invention to perform the above described processes on both sides of a plate such as a bulkhead plate, including sequential welding of a plurality of plates.

In a further variation the plate <NUM> can be subdivided into smaller plates that are still thick, wherein the plates are butt welded together. This is another useful way to overcome the problems involving heavy plates in an environment with many obstructions.

Claim 1:
A method for welding a thick plate (<NUM>, <NUM>) into a welded assembly (<NUM>), comprising the steps:
a) on a first plate (<NUM>) placing a second plate (<NUM>) having a periphery, in direct contact with the first plate (<NUM>),
wherein the first and second plates (<NUM>, <NUM>) are of materials that do not form unacceptable bubbling in the weld when heated and are metals that are selected from the group comprising ferrous materials, nickel alloys and copper alloys, and the group comprising titanium and zirconium, and
wherein the second plate is a thick plate having a thickness greater than <NUM>, and
b) through welding the second plate to the first plate,
wherein the through welding is performed using laser welding,
wherein the first and second plates are welded within and along the periphery of the second plate, and
wherein the first and second plates are welded within the periphery of the second plate using a pattern from the group comprising closed geometric patterns enclosing a volume such as rectangular pattern, hexagon pattern, and circles, and open geometric patterns such as spots, spirals, and meanders.