System and method for laser deposition

Abstract

The present invention relates to laser deposition system. The laser deposition system comprises a laser module configured to generate a laser beam (120) having one or more recesses (130) in its intensity profile, an intensity of the laser beam (122) being lower in the recesses (130) than in the remainder of the laser beam (120), and each recess (130) being at least partly surrounded by the remainder of the laser beam (120); and a wire feeding module configured to feed one or more wires (110) through the one or more recesses (130) in the laser beam profile, for deposition onto a substrate..

Description

[0001] System and method for laser deposition

[0002] Technical Field

[0003] The present invention is concerned with laser deposition systems for use in additive manufacturing (AM). In particular, but not exclusively, the present invention is concerned with laser deposition systems for depositing a wire feedstock material by focused thermal energy from a laser’s light beam (i.e. laser beam).

[0004] Laser deposition systems, in the case of a metal wire feedstock also referred to as Laser Metal Deposition with wire (LMDw) systems, are used to build a work piece by melting a wire material (e.g. metal) using a laser beam thus providing a flow of the material from the wire to a melt pool created on a substrate or on a preceding deposited layer. The wire is typically fed into the path of the laser beam and the melt pool, for deposition onto the substrate.

[0005] LMDw systems provide improved material usage efficiency compared to subtractive manufacturing techniques. However, work pieces built using LMDw can suffer from defects, such as shape distortions, cracking, residual stresses, insufficient penetration, or lack of fusion. The systems disclosed herein are directed towards improving the quality of the built work piece and reducing the occurrence of such defects.

[0006] The systems herein allow making higher quality work pieces, thus allowing the use of AM in quality-sensitive fields such as the manufacture of aerospace components.

[0007] Summary of the Invention

[0008] Aspects of the invention are set out in the accompanying claims.

[0009] In accordance with some embodiments described herein, there is provided a laser deposition system comprising a laser module configured to generate a laser beam having one or more recesses in its intensity profile, an intensity of the laser beam being lower in the recesses than in the remainder of the laser beam, and each recess being at least partly surrounded by the remainder of the laser beam; and a wire feeding module configured to feed one or more wires through the one or more recesses in the laser beam profile, for deposition onto a substrate.

[0010] Upon vibration of the wire, each wire may at least partly move from the respective recess into the remainder of the laser beam. In examples, the intensity of the laser beam in the one or more recesses is substantially zero.

[0011] In examples, at least 50% of a perimeter of each recess is surrounded by the remainder of the laser beam.

[0012] In examples, each recess is wider than the respective wire such that a gap is provided between at least part of side portions of the recess and the wire.

[0013] In examples, the wire feeding module is configured to feed the one or more wires at an acute angle to the substrate.

[0014] In examples, each recess extends from an outer perimeter of the laser beam. Each recess may be partly surrounded by the remainder of the laser beam.

[0015] In examples, each recess extends towards a centre of the laser beam.

[0016] In examples, each recess terminates before the outer perimeter of the laser beam, and preferably at the centre of the laser beam

[0017] In examples, side portions of each recess are substantially aligned with a feeding direction of the respective wire.

[0018] In examples, each recess comprises an end portion, wherein the end portion is arranged perpendicular to the feeding direction of the respective wire.

[0019] In examples, a width of the recess decreases with increasing depth of the recess into the intensity profile of the laser beam.

[0020] In examples, each recess extends substantially along a line of symmetry of the laser beam profile.

[0021] In examples, the wire feeding module may be configured to feed the one or more wires substantially perpendicularly to the substrate.

[0022] In examples, each recess is fully surrounded by the remainder of the laser beam. In examples, the one or more recesses comprise one recess, wherein the recess is substantially concentric with the laser beam.

[0023] In examples, each recess is symmetrical about the feeding direction of the respective wire.

[0024] In examples, for at least part of the remainder of the laser beam, the intensity of the laser beam in the remainder of the laser beam increases with increasing distance from the recesses in the laser beam.

[0025] In examples, the system further comprises an electrical heating module configured to heat the one or more wires.

[0026] In examples, the electrical heating module is configured to heat the one or more wires using resistive heating.

[0027] In examples, the electrical heating module is configured to heat the one or more wires while they are being fed by the wire feeding module.

[0028] In examples, when arranged along its feeding direction, each of the one or more wires receives more energy from the electrical heating module than from the laser beam.

[0029] In examples, the one or more recesses comprise at least two recesses, the one or more wires comprise at least two wires; and the wire feeding module is configured to feed each wire through a respective recess in the laser beam profile.

[0030] In examples, each recess has a rectangular shape.

[0031] In examples, the laser beam has a circular outer perimeter.

[0032] In examples, the wire comprises a metal.

[0033] In examples, the wire has a first diameter, the laser beam has a second diameter, where the ratio between the second diameter and the first diameter is between 2:1 and 5:1 , for example between 3:1 and 4:1.

[0034] In examples, each recess and respective wire have matching shapes. In examples, the wire feeding module is configured to feed the one or more wires along respective feeding directions / axes; and the side portions of the one or more recesses extend in parallel to the feeding directions.

[0035] In examples, the laser beam has a horseshoe profile, with a rectangular recess in a top hat profile

[0036] In examples, the wire feeding module feeds the wire towards a centre of the laser beam profile on the substrate.

[0037] In examples, the laser module comprises beam shaping means for providing the one or more recesses in the profile of the laser beam.

[0038] In examples, Wherein the remainder of the laser beam has a Gaussian intensity profile. Alternatively, the remainder of the laser beam may have a substantially constant intensity.

[0039] In accordance with some embodiments described herein, there is provided a laser deposition method comprising: generating a laser beam having one or more recesses in its intensity profile, an intensity of the laser beam being lower in the recesses than in the remainder of the laser beam, and each recess being at least partly surrounded by the remainder of the laser beam; and feeding one or more wires through the one or more recesses in the laser beam profile to deposit the wires onto a substrate.

[0040] In examples, the substrate is a component of an aircraft.

[0041] Brief Description of the Drawings

[0042] One or more embodiments of the invention will now be described, by way of example only, and with reference to the following figures in which:

[0043] Figure 1 shows a schematic view of a laser deposition system;

[0044] Figure 2 shows a schematic view of an existing laser deposition system;

[0045] Figure 3a shows a schematic view of laser deposition in a stubbing transfer mode;

[0046] Figure 3b shows a schematic view of laser deposition in a dripping transfer mode;

[0047] Figure 4 shows a schematic perspective view of an example laser deposition system according to embodiments of the present disclosure;

[0048] Figure 5 shows a schematic top view of the laser deposition system of Figure 4; Figure 6 shows a graph of relative energy input to wire distance from laser beam centre for the laser deposition system of Figures 4 and 5, and existing laser deposition systems;

[0049] Figures 7A to L show schematic top views of example laser beam profiles according to embodiments of the present disclosure;

[0050] Figures 8A and 8B show schematic top views of further example laser beam profiles according to embodiments of the present disclosure;

[0051] Figure 9 shows a schematic top view of a yet further example laser deposition systems according to embodiments of the present disclosure, comprising an electrical heating module; and

[0052] Figure 10 shows a flow diagram of an example method according to embodiments of the present disclosure.

[0053] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[0054] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future. Detailed Description

[0055] An invention described herein relates to laser deposition systems and methods. A particular use for this invention may be in metal additive manufacturing; for instance, in the fields of automotive, space, aerospace, oil, and / or medical engineering. For example, the discussed arrangements may be used in the manufacture or repair of components for an aircraft, such as turbine blades. It will be appreciated that the invention may be used to manufacture a given component fully or in part, and that other techniques may be used in the making of the component.

[0056] Figure 1 shows a simple schematic view of a laser deposition system 100. The laser deposition system 100 is particularly applicable to the deposition of metal materials, such as steel (e.g. stainless steel), aluminium, cobalt, chromium, titanium, tungsten, nickel, niobium, or alloys, compounds (e.g. including resins, or plastics), or composites thereof. However, it will be appreciated that the laser deposition system 100 may alternatively be used to deposit wires (i.e. filaments) comprising other materials, such as ceramics (e.g. tungsten carbide, or alumina), or plastics. The laser deposition system 100 comprises a laser module 102, and a wire feeding module 104.

[0057] The laser module 102 generates a laser beam 120 for melting a wire 110 to deposit the wire onto a substrate 200, thereby making a work piece. The laser module 102 generates the laser beam 120 at a first axis 122. The laser beam 120 has an outer perimeter 124, and a diameter 126. The wavelength of the laser beam may be selected in dependence on the wire material being used; for instance, the wavelength of the laser beam may be selected to match the wire material’s absorption spectrum.

[0058] The wire feeding module 104 feeds a wire 110 towards the laser beam 120 and the substrate 200 for deposition onto the substrate 200. The wire 110 has an outer perimeter 114, and a diameter 116. The wire feeding module 104 feeds the wire at a second axis 112 which intersects the first axis 122. The wire feeding module 104 may comprise a guide and a tip. The wire 110 may be fed through the guide, and out of the tip onto the substrate 200 and / or existing work piece (e.g. when depositing multiple layers of material). The diameter 116 of the wire 110 is typically smaller than the diameter 126 of the laser beam 120. For example, the ratio between the laser diameter 126 and the wire diameter 116 may be between 2:1 and 5:1 , such as between 3:1 and 4:1. The heat from the laser beam 120 creates a melt pool (not shown) in the substrate 200. The wire 110 is melted, e.g. by the laser beam 120, allowing a flow of material from the wire to the melt pool created on the substrate 200. In the same way, one or more further layers of the wire material may be deposited on top of one another as required. The wire 110 may be continuously fed into the melt pool for deposition. The rate at which the wire is fed (i.e. the feeding rate) may depend on characteristics of the laser deposition system, such as the diameter 116 of the wire and / or the diameter 126 of the laser beam, or the power output by the laser beam 120. The feeding rate may for example be between 1 meter / minute and 10 meters / minute. The wire feeding module 104 and the laser module 102 may be moved along the substrate 200 to deposit various shapes of material.

[0059] It will be appreciated that the specific characteristics (e.g. dimensions, and laser power output) of the laser beam 120 and of the wire 110 may depend on the specific use case, such as the material being deposited, the substrate being used, and the desired deposition rate or thickness of deposited material. For example, the laser module 102 may have a power output of between 1 and 25 kW depending on these characteristics.

[0060] The material (e.g. metal) fed by the wire feeding module 104 may be transferred onto the substrate 200 via three different transfer modes: stubbing (i.e. plunging), smooth, or dripping (i.e. globular). The mode of transfer may impact the stability of the deposition, and the quality of the deposited layer. The mode of transfer may be dependent upon the amount of energy supplied to the wire 110 and the substrate (or preceding deposited layer), which itself may for example depend on the power and diameter of the laser beam 120, a surface profile of the substrate 200, the feeding rate of the wire 110, and a traverse speed of the laser deposition system 100. It will be appreciated that energy may be supplied to the wire by other means instead of, or in addition to, the laser beam module 102, for example via an electrical heating module as described later herein.

[0061] The dripping transfer mode occurs when the energy input to the wire material is too high (e.g. exceeding a predetermined threshold) and the wire 110 melts before reaching the melt pool. In the dripping transfer mode, surface tension forces between the molten wire and the melt pool are insufficiently strong to maintain a continuous link between the materials. As a result, the wire separates from the melt pool and transfers into the melt pool in a form of droplets. The dripping mode is characterized by an unstable transfer of wire material which is often deposited in the form of beads having an irregular shape and internal porosity. In turn, the stubbing transfer mode occurs when the energy input to the material is too low (e.g. below a predetermined threshold) and the wire 110 does not melt, or only partly melts, before entering the melt pool. In the stubbing mode, the wire 110 enters the melt pool in a solid or semi-solid state. As a result, as the wire 110 is fed towards the melt pool, the solid (or semisolid) may be in contact with the solid layer (e.g. substrate 200) below the melt pool causing vibrations and movement of the wire 110. This is undesirable as such vibrations may cause lack of fusion defects to be formed.

[0062] In the, preferred, smooth transfer mode, where the energy input to the wire 110 is lower than in the dripping mode and higher than in the stubbing mode, the wire melts in close proximity to the melt pool, thus providing a smooth and stable transfer of material from the wire 110 into the melt pool on the substrate 200 or a preceding deposited layer. Thus, a higher quality deposited material is provided with reduced occurrence of defects and more predictable morphology.

[0063] It is therefore desirable to maintain the smooth transfer mode throughout the deposition process in order to improve the quality of deposited layers. However, laser deposition systems often struggle to achieve this and suffer from unstable transfer in the dripping or stubbing modes, as further described below with reference to Figures 2 and 3.

[0064] Referring now to Figure 2, this shows a simple schematic view of the interaction of a wire 110’ with a laser beam 120’ during the stubbing transfer mode, from a top view looking down onto the substrate 200’. Figure 2 shows this interaction for a laser beam 120’ having a conventional Gaussian intensity profile, with a peak intensity at its centre which gradually decreases towards the outer diameter 124’ of the laser beam 120’. At the start of the deposition process, the tip of the wire 110a’ (for simplicity illustrated using its feeding / second axis) is arranged at the centre of the laser beam 120’ and thus receives a maximum energy input from the laser beam 120’. However, if this energy input is insufficient, e.g. as a result of an excessive feeding rate of the wire 110’ or deformation of the substrate 200’, the stubbing transfer mode may occur where the wire 110’ does not fully melt before reaching the melt pool and begins to vibrate. As a result, the wire may vibrate between positions 110b’; where the energy input to the wire 110’ is further reduced (due to the lower intensity of the laser beam 120’ at this position) thus further amplifying the vibrations of the wire to positions 110c’. The stubbing transfer mode may therefore be reinforced over time, leading to yet more unstable transfer of material from the wire 110’ over time. In some cases, the reinforced vibration of the wire 110’ may cause the wire to completely outside the laser beam 120’. Referring now to Figures 3a and 3b, these show simple schematics of the laser deposition system 100 for a substrate 200 that has undergone warpage (i.e. deformation). The substrate 200 may deform with respect to a reference (e.g. flat) plane, which may be referred to as warpage of the substrate 200. As a result of deformation, which may e.g. be caused by thermal distortion or local surface tension, the substrate 200 is not often not flat.

[0065] Warpage of the substrate can affect the energy input to the wire 110, and in practice is often a key cause for the occurrence of an unstable transfer mode of the wire material into the melt pool, as it makes it difficult to determine where the depositing surface is in relation to the wire. As shown in Figures 3a and 3b, such warpage of the substrate may result in insufficient energy being supplied to the wire 110 and thus stubbing (as shown in Figure 3a), or excessive energy being supplied to the wire 110 and thus dripping (as shown in Figure 3b). In Figure 3a, the substrate 200 is locally warped towards the laser beam 120. As a result, the wire 110 passes through the laser beam 120 for an insufficiently long time to melt and hits the substrate 200 in a solid state, thus leading to stubbing. In turn, in Figure 3b, the substrate 200 is locally warped away from the laser beam 120. As a result, the wire 110 passes through the laser beam 120 for a longer period of time such that the wire 110 melts before reaching the melt pool, thus leading to dripping and the wire transferring into the melt pool in the form of droplets 106.

[0066] The exact local profile of, and degree of warpage in, the substrate 200 can be difficult to control and determine in real-time as the laser deposition system is moved around the substrate. Accordingly, existing laser depositing systems typically struggle to control the exact arrangement of the wire 110 and laser beam 120 with respect to the substrate 200 and thus are often unable to maintain a smooth transfer mode during the deposition.

[0067] An existing approach for counteracting the above problems and maintaining a smooth transfer mode is to detect the occurrence of an unstable transfer mode (e.g. stubbing), and modify parameters of the laser deposition system (e.g. increase the laser power) to correct for this and return to the smooth mode. An example approach for detecting a stubbing transfer mode is to use image analysis. When stubbing occurs and the wire 110 is vibrating as a result of not enough energy being provided into the melt pool, the brightness of light emitted from the melt pool typically reduces, which can be detected using a camera. Upon detecting the reduction in brightness, the power of the laser may be increased to return to the smooth transfer mode. In a similar manner, scanning can be used to determine the position of the substrate (so as to account for its warpage). The parameters of the laser deposition system can then be adjusted based on the determined substrate position, e.g. the wire can be lowered or raised relative to the substrate, or the laser power may be adjusted. However, with existing image analysis techniques it can be difficult to accurately determine the exact position of the substrate (e.g. due to shiny substrate surfaces being used) and whether stubbing occurs as e.g. a similar reduction in brightness of the melt pool may be caused by factors other than stubbing, such as spattering, or hot air turbulence under the camera. There is therefore ongoing research to improve the image analysis techniques used for detecting unstable transfer modes and the determining the substrate position, in order to improve the quality of the deposited material.

[0068] Referring now to Figures 4 to 9, embodiments of the present disclosure aim to address the above-described challenges and provide improved control of the transfer mode of wire material to the melt pool while completely moving away from existing ‘reactive’ approaches based on detection techniques. In the laser deposition system 100 of the present disclosure, the laser module 102 generates a laser beam 120 having a recess 130 in its intensity profile 128, with the intensity of the laser beam being lower in the recess than in the remainder of the laser beam and with the recess 130 being at least partly surrounded by the remainder of the laser beam. The wire feeding module 104 then feeds a wire 110 through the recess 130 in the laser beam profile, for deposition onto the substrate 200. In this way, in its starting (i.e. natural) position, the wire 110 is fed towards the melt pool through the lower intensity recess in the laser beam 120 but is surrounded by higher intensity portions of the laser beam. As a result, if for any reason insufficient energy is supplied to the wire 110, e.g. as a result of warpage of the substrate as shown in Figure 3a, and stubbing and vibration of the wire occurs, the wire 110 moves into the higher intensity region of the laser beam 120 where it receives more energy and melts thus returning to a smooth transfer mode. The present approach therefore allows effectively counteracting stubbing, without increasing the risk of dripping, and so helps maintain a smooth transfer of wire material to the melt pool. This improved balance between stubbing and dripping contrasts with existing approaches where increasing the energy input (e.g. by increasing the laser beam power or decreasing the feeding rate of the wire) to reduce stubbing can increase the risk of dripping, while reducing the energy input (e.g. by decreasing the laser beam power or increasing the feeding rate of the wire) can increase the risk of stubbing.

[0069] In contrast to existing ‘reactive’ approaches that detect unstable transfer modes and react by adjusting process parameters, the present approach does not require such detection and allows ‘automatically’ self-correcting for the occurrence of stubbing. The present approach therefore allows maintaining a smooth transfer mode in a simpler and more efficient manner without requiring complex (and prone to error) detection techniques. By removing the need for stubbing detection, the present approach also allows correcting for stubbing faster as no latency is introduced by the detection step and instead upon stubbing the wire moves into the higher intensity remainder of the beam where it receives more energy thus correcting for stabbing and returning the wire to a smooth transfer mode.

[0070] By allowing effectively counteracting stubbing, the present approach allows otherwise configuring the laser deposition system 100 to reduce the risk of dripping (e.g. by lowering the laser beam power or increasing the wire feeding rate), as any resultant increase in stubbing can be counteracted against. Thus, the present approach can also allow improving the efficiency of the deposition process, e.g. by allowing reducing the power input and energy consumption, or by increasing the wire feeding rate and so increasing the speed of deposition.

[0071] In the same way, the present invention further advantageously allows increasing the operating window of the laser deposition system 100 with regards to the relative positioning of the wire 110, the laser beam 120, and the substrate 200, and improving the resilience of the laser deposition system 100 to warpage of the substrate 200. For example, the intersection point of the first axis 122 of the laser beam 120 and the second axis of the wire 110 may be moved closer to the assumed position of the substrate 120 (i.e. assuming no warpage of the substrate 120) to reduce dripping, while any resultant stubbing is counteracted by the present wire and beam arrangement. As a result, the present laser deposition system 100 has improved tolerance for substrate 200 deformation, and can provide smooth transfer of deposited material for a wider range of substrate deformations.

[0072] As used herein, the intensity of the laser beam 120 relates to the power per unit area delivered by the incident laser beam 120, e.g. to the substrate 200.

[0073] As used herein, the intensity profile of the laser beam 120 relates to a cross-sectional profile of the intensity of the laser beam 120 incident on the substrate 200. The intensity profile may have the same characteristics (e.g. shape) as an irradiance, power, or energy profile, of the laser beam 120 and these terms may be used interchangeably herein.

[0074] As used herein, the term “recess” as used in relation to the intensity profile of the laser beam 120 relates to a portion (i.e. region) of the intensity profile that has a lower intensity and hence may be referred to as a recess (i.e. aperture, hole, indent, indentation, and / or cut (out)) in the intensity profile. A wire receives less energy when inside the recess than when outside the recess in the laser beam. As the wire feeding module 104 feeds the wire 110 through the recess 130 in the laser beam 120, the recess is a region of the laser beam where energy is supplied to the wire in the wire’s natural position.

[0075] Referring to Figures 4 and 5, these show simple schematics of the laser beam 120 and wire 110 of a laser deposition system in accordance with an example of the present disclosure. Figure 4 shows a perspective view of the wire 110 and the laser beam 120; and Figure 5 shows a corresponding top view of the wire 110 and the laser beam 120.

[0076] The laser module (not shown) generates a laser beam 120 at the first axis 122. The laser beam 120 has an intensity profile 128 at incidence on the substrate 200. The intensity profile has a recess 130 in which the intensity of the laser beam is lower than in the remainder 144 of the laser beam. In other words, less energy is supplied to the substrate 200 in the recess 130 than in the remainder 144 of the laser beam.

[0077] The recess 130 is at least partly surrounded by the remainder 144 of the laser beam. For example, at least 50%, 60%, 70%, 80%, or 90% of the perimeter of the recess 130 may be surrounded by the remainder 144 of the laser beam. In some cases, the recess 130 may be fully surrounded by the remainder 144 of the laser beam. Increasing the extent to which the recess is surrounded by the remainder of the laser beam allows improving the counteraction of stubbing as it increases the likelihood that a given movement of the wire due to stubbing will result in the wire moving into the higher intensity remainder of the laser beam.

[0078] The laser module 102 may comprise means for shaping its beam (i.e. beam shaping means, or a beam shaping sub-module). For example, the laser module 102 may comprise one or more of: one or more lenses (e.g. aspheric or freeform lenses), one or more apertures (e.g. slits, or masks), mirrors, a laser beam integrator, conical surfaces, anamorphic prism pairs, spatial light modulators, holographic optical elements, and / or diffractive optical elements, appropriately arranged to shape the beam 120 into a desired shape and create a recess in the intensity profile of the laser beam. For instance, the recess may be provided in the laser beam using lens shaping, whereby convergence lens(es) are appropriately shaped to focus the laser beam into a desired shaped. Alternatively, or in addition, the recess may be provided using laser dithering by moving a smaller spot laser in a pattern at a fast speed to generate a larger laser beam 120 with a desired intensity profile. Alternatively, or in addition, an aperture in the shape of the recess 130 may be used to block part of the laser beam 120, thus providing a recess in the laser beam. In some cases, the laser module 102 may superimpose a plurality of lasers to generate the laser beam 120. The recess 130 may extend from the outer perimeter 124 of the laser beam 120, and into the laser beam 120. The recess has a width 142, and a depth 140 which defines the extent to which the recess 130 extends into the laser beam 130. The recess has side portions 132. As shown in Figures 4 and 5, the recess may further have an end portion 134 which connects the side portions 132, and which is the portion of the recess 130 furthest into the laser beam 120. The end portion 134 may be perpendicular to the side portions 132.

[0079] In alternative examples, the recess 130 may not have an end portion 134, e.g. the side portions 132 may be connected to one another (see e.g. triangular recesses 130 in Figure 7C), or the recess 130 may extend across the entire width of the laser beam 120 (i.e. between edges of the outer perimeter 124).

[0080] The wire feeding module (not shown) feeds the wire 110 at the second axis 112. It will be appreciated that the wire 110 is continuously fed, and so a given part of the wire moves along the second axis 112. As shown in Figures 4 and 5, the wire feeding module feeds the wire 110 through the recess 130 in the laser beam 120. In other words, the wire 110 is fed towards the melt pool in such a way that it passes through the recess 130 in the laser beam 120. The wire 110 has a tip 118. The wire 110 is typically fed such that the wire’s tip 118 is fed towards the centre (i.e. central axis) 125 of the laser beam 120.

[0081] In use, in its starting feeding arrangement (i.e. natural position), the wire 110 passes through the lower intensity recess portion 130 of the laser beam. This helps to prevent supplying excessive energy to the wire 110 and so helps avoiding the wire material being transferred via the dripping transfer mode. In the event that insufficient energy is supplied to the wire 110 and stubbing occurs, the wire 110 vibrates and moves away from its starting position and thus out of the recess 130 and into the remainder 144 of the laser beam 120. The intensity of the laser beam is higher in the remainder portion 144, and so in this ‘stubbing position’ the wire 110 is supplied with more energy which helps melt the wire 110 before it reaches the melt pool and reduce stubbing. In this way, the recess 130 and wire 110 arrangement allows counteracting stubbing and helps return the wire 110 to its starting position, thus improving control of the transfer mode of material onto the substrate 200 and helping maintain a smooth transfer mode.

[0082] The laser beam 120 may be profiled to exclude the area of wire 110 interaction. The recess 130 may be wider than the wire 110 such that a gap 136 is provided between at least part of the side portions 132 of the recess 130 and the wire 110. Providing the gap 136 between the wire 110 and the side portions 132 of the recess 130 helps avoid heating the outer part of the wire (which may lead to uneven heating of the wire 110 and dripping), and can provide tolerance for the wire 110 to not fall within the laser beam 120 in its natural position.

[0083] The gap 136 may be provided at least at the outer perimeter 124 of the laser beam; in other words, at least at the outer perimeter 124, the width 142 of the recess 130 may be greater than the diameter 116 of the wire 110. The gap 136 may be provided along part or all of the side portions 132 of the recess 130. For example, the gap 136 may be provided along at least 20%, 50%, or 80% of the recess depth 140 and / or of the length of the side portions 132. In the example shown in Figures 4 and 5, the gap 136 may extend along the entirety of the side portions 132 and of the recess depth 140. Alternatively, the gap 136 may extend along only part of the side portions 132, and the wire 110 may cross the side portions 132 part-way through the recess depth 140 (see e.g. Figure 7C).

[0084] The recess 130 may be symmetrical about the second axis 112 at which the wire 110 is fed. The gap 136 between the side portions 132 of the recess 130 and the wire 110 may be the same on each side of the wire 110, i.e. the gap 136 may be the same for each side portion 132 of the recess. A symmetrical recess 130 arrangement can provide more even heating of the wire 110 across its diameter / width 116, and so provide improved control over transfer of material from the wire 110 to the melt pool.

[0085] Vibration and movement of the wire 110 resulting from stubbing can be difficult to predict. For instance, the wire 110 may bend sideways about various different points along its length; e.g., the wire 110 may bend only very close to its tip 118 or further away from its tip 118, resulting in different positions of the wire 110 with respect to the laser beam 120.

[0086] As shown in Figure 5, to address this issue, the side portions 132 may be substantially aligned with the feeding direction of the wire 110, i.e. with the second axis 112. For example, the side portions 132 may extend in a direction less than 30 degrees, preferably 20 degrees, more preferably 10 degrees, yet more preferably 5 degrees from the feeding direction of the wire. This alignment between the side portions 132 and the second axis 112 allows providing a more consistent (in some cases, constant) width of the gap 136 (which gap may be positive or negative if the wire is wider than the recess) between the wire 110 and the side portions 132 along the entire length of the side portions 132 and the depth 140 of the recess 130. Aligning the side portions 132 of the recess 130 with the wire 110 and providing a constant gap 136 along the wire 110 length allows further reducing stabbing because it increases the probability that a given, and typically unpredictable, movement of the wire 110 (even if finer or about a different point along the wire) due to stubbing results in the wire 100 entering the higher intensity remainder 144 portion of the laser beam where more energy is supplied to the wire to return the deposition process to a smooth transfer mode.

[0087] As shown in Figure 5, the end portion 134 may be arranged perpendicular to the second / feeding axis 112 of the wire. This allows providing a more even energy input to the wire across the width 116 of the wire, and so further helps maintaining a smooth transfer of material during the deposition.

[0088] The width of the gap 136 may be a fraction of the width / diameter 116 of the wire 110. For example, the width of the gap 136 may be 1 / 5, 1 / 8, 1 / 10, or 1 / 20 of the diameter 116 of the wire 110. This can allow correcting for stubbing, while providing some tolerance for movement of the wire 110 relative to the laser beam 120, for example as the wire 110 and laser beam 120 are moved around the substrate 200 to deposit material across the substrate 200.

[0089] In alternative examples, the recess 130 may be narrower than the wire 110 such that in its normal position, the wire 110 is only partially within the recess 130 and partially in the higher intensity remainder of the laser beam. In other words, the width 142 of the recess 130 may be smaller than the wire diameter 116, and a ‘negative’ gap between the wire 110 and recess 130 may be provided. For example, the width 142 of the recess 130 may be 4 / 5, 7 / 8, 9 / 10, or 19 / 20 of the diameter 116 of the wire 110. This allows providing more energy from the laser beam to the wire in the wire’s natural position.

[0090] As noted above, the recess 130 may extend from the outer perimeter 124 (i.e. outer periphery) of the laser beam 120, and into the laser beam 120. The recess 130 may extend towards the centre 125 of the (intensity profile of the) laser beam 120. The recess 130 may terminate before the outer perimeter 124 (e.g. extend from one side of the outer perimeter and terminate before the opposite side of the outer perimeter). In some cases, the recess 130 may terminate at the centre 125 of the laser beam (i.e. at the first axis 122), e.g. the end portion 134 of the recess 130 may be aligned with a diameter of the laser beam profile as shown in Figure 5, or the side portions 132 of the recess 130 may meet at the centre 125 of the laser beam profile (see e.g. Figure 7C). The wire 110 is fed through the recess 130, so providing a recess 130 extending towards and / or terminating at the centre 125 (or before the end of the outer perimeter) of the laser beam profile allows feeding the wire tip 118 towards the centre 125 of the laser beam profile and so ensuring that the wire is more fully ‘surrounded’ by the remainder 144 of the laser beam 120. This allows further reducing stubbing as the wire 110 is more likely to remain within the remainder 144 of the laser beam 120 even in case of larger movement of the wire 110 due to stubbing, both side to side (i.e. perpendicular to the second axis 112) and back and forth (i.e. parallel to the second axis 112). For example, the wire 110 can move by a larger distance side to side and still end up in the remainder 144 of the laser beam 120 where it is provided with additional energy to melt the wire 110 and counteract stubbing.

[0091] In some cases, a Gaussian intensity profile may be provided for the remainder 144 of the laser beam, with a maximum beam intensity at the centre of the laser beam 125, together with the recess 130 extending towards and terminating at the centre 125 of the laser beam 120. In this recess and Gaussian profile arrangement, the laser beam 120 has a maximum intensity where the recess 130 terminates. This can allow the laser deposition system to more quickly respond to and counteract stubbing, as in the event of insufficient energy being supplied to the wire 110 and the wire 110 starting to vibrate and move out of the recess 130, the wire 110 enters the maximum intensity portion of the laser beam 120 where it is supplied with more energy thus melting the wire and retuning to a smooth transfer mode.

[0092] The recess 130 may extend into the laser beam 120 substantially along a line of symmetry of the laser beam profile 128. In other words, the depth 140 of the recess 130 may extend substantially along a line of symmetry of the laser beam profile 128. For example, the recess 130 may extend in a direction less than 30 degrees, preferably 20 degrees, more preferably 10 degrees, yet more preferably 5 degrees from a line of symmetry of the laser beam profile 128. For instance, for a circular laser beam 120, the recess may extend along a diameter of the laser beam 120. This recess 130 arrangement provides even areas of the remainder 144 of the laser beam 120 on either side of the recess 130, which can allow effectively counteracting stubbing independent of which direction the wire 110 moves in as a result of receiving insufficient energy.

[0093] As noted above, the recess 130 extends into the laser beam up to a depth 140. The recess depth 140 may be empirically determined depending on how much energy is to be supplied by the laser beam 120 to the wire 110 in the wire’s default / natural position (i.e. in the absence of stubbing). The lower the depth 140 of the recess 130, the more energy is supplied to the wire 110 in its natural position. The depth 140 of the recess may for example be between 20% and 80%, between 40% and 60%, or around 50% of the diameter of the laser beam profile 128.

[0094] For instance, in the example of Figures 4 and 5, the recess 130 extends to 50% of the diameter of the laser beam, and the depth 140 of the recess 130 is the same as the radius of the laser beam. In its natural position, the wire 110 is therefore fully within the lower-intensity recess 130 and outside of the higher-intensity remainder 144 of the laser beam 120, with less energy being supplied to the wire 110 by the laser beam 120 in the wire’s natural position. In such cases, to make up for the lower energy input from the laser beam 120 to the wire 110 in its natural position, energy may be supplied to the wire 110 via other means, such as via electrical heating as discussed in further detail with reference to Figure 8 below.

[0095] In other examples, the recess 130 may extend further or less into the laser beam profile 128 than 50% of the diameter of the laser beam 120. Reducing the depth 140 of the recess 130 below 50% of the laser beam diameter 126 increases the amount of energy that is supplied to the wire 110, and so can help prevent the occurrence of stabbing in the first place; however, at potentially increased risk of dripping.

[0096] Figures 4 and 5 illustrate a specific example of a laser beam 120. In this example, the laser beam 120 has a circular outer perimeter 124 (i.e. the laser beam 120 has a circular outer profile). The recess 130 has a rectangular shape with side portions 132 aligned with, and symmetrical about, the second axis 112, and an end portion 134 perpendicular to the second axis 112 and to the side portions 132. The recess 130 extends to and terminates at the centre 125 of the laser beam 120. The recess 130 has a width 142 of around 0.5mm. The intensity of the laser beam in the recess 130 is substantially zero, and the intensity of the laser beam in the remainder 144 of the laser beam is substantially constant. The laser beam profile of Figures 4 and 5 may for example be obtained by providing a recess 130 in a top hat laser profile 128. The intensity profile 128 of this example may be referred to as a ‘horseshoe’ profile. In order to provide sufficient energy to the wire 110 to melt it and deposit it onto the substrate 200, in this example the wire 110 is further heated using an electrical heating module as described in further detail below.

[0097] As noted above, the intensity of the laser beam 120 is lower in the recess 130 than in the remainder 144 of the laser beam. The intensity of the laser beam in the recess (11) may be less than the minimum (or average) intensity of the laser beam in the remainder 144 of the laser beam (I2). For example, the intensity 11 may be less than 50% of the minimum (or average) intensity I2, preferably less than 25%, more preferably less than 10%, yet more preferably less than 1 %, still more preferably less than 0.1 % of the minimum (or average) intensity I2. In some cases, the intensity of the laser beam 120 in the recess may be below 1 GW / m2, preferably below 1 MW / m2. In an example, the intensity of the laser beam 120 in the recess is substantially zero. The counteraction of stubbing may improve the lower the intensity of the laser beam in the recess, 11.

[0098] The intensity of the laser beam 120 in the recess 130 may be selected depending on how much energy the laser beam 120 is to provide to the wire 110 in the wire’s natural position. In examples using only energy provided by the laser beam 120 to melt the wire 110, the intensity of the laser beam in the recess 11 may be greater than in examples where other additional sources of energy (e.g. resistance heating) are used to melt the wire 110.

[0099] The remainder 144 of the laser beam 120 may for example have a Gaussian, or Top Hat intensity profile (i.e. approximately constant intensity).

[0100] Referring now to Figure 6, this shows a graph 600 of the relative power input on the wire 110 (y-axis) against distance of the wire 110 from the centre 125 of the laser beam 120 (x-axis) for different laser beam and wire arrangements. The relative power input is measured relative to the power input at the centre 125 of the laser beam 120 (i.e. centre of laser beam profile 128). For each of datasets 602, 604, 606, the wire 110 was fed at a wire feeding rate of 9 metres per minute. Datasets 602 and 604 relate to existing laser beam designs. Dataset 602 relates to a laser beam with a Gaussian intensity profile. Dataset 604 relates to a laser beam with a Top Hat intensity profile. In turn, dataset 606 relates to the laser beam 120 and wire 110 arrangement of Figures 4 and 5, in which the laser beam 120 has a Top Hat intensity profile with a rectangular recess 130.

[0101] As shown in Figure 6, with the Gaussian laser beam intensity profile of dataset 602, the relative power input on the wire 110 decreases with increasing distance of the wire 110 from the centre 125 of the laser beam 120. As described with reference to Figure 2, this can result in selfreinforcement of stubbing, where once the wire 110 starts vibrating and moves further away from the highest-intensity centre of the laser beam, the wire 110 receives even less energy which further reinforces stubbing.

[0102] With the Top Hat laser beam intensity profile of dataset 604, the relative power input on the wire 110 is remains approximately constant with increasing distance of the wire 110 from the centre 125 of the laser beam 120. If this constant energy input on the wire 110 is insufficient to melt the wire, stubbing can occur leading to defects in the deposited layer. While the stubbing is not reinforced as for a Gaussian intensity profile, the Top Hat intensity profile also does not provide any means for counteracting stubbing.

[0103] As shown in dataset 606, with the ‘horseshoe’ laser beam intensity profile of Figures 4 and 5, the energy / power input on the wire 110 is approximately constant within the recess 130, that is up to a distance of around 0.5mm from the centre 125 of the laser beam 120. This power input may for example be provided by electrically heating the wire 110. The power input on the wire 110 then increases with increasing distance of the wire 110 from centre 125 of the laser beam 120, once the wire 110 moves beyond the width of the recess 130 and into the higher- intensity remainder 144 of the laser beam 120. In the example of Figure 4 to 6, the power input gradually increases between around 0.5mm and 2.2mm which corresponds to the transition region of the Top Hat profile of the remainder 144 of the laser beam, and then plateaus once within the constant-intensity Top Hat section of the remainder 144 of the laser beam 120. In this way, even if the energy input to the wire 110 at the wire’s natural position at the centre 125 of the laser beam 120 is too low and the wire does not melt in time and enters the stubbing transfer mode (i.e. stubbing occurs), as the wire 110 moves away from the centre 125 of the laser beam 120 it receives more energy which promotes melting of the wire and counteracts stubbing, allowing the wire deposition to return to the smooth transfer mode.

[0104] The laser beam 120 may be shaped such that the intensity of the laser beam in the remainder 144 of the laser beam increases with increasing distance from the recess 130 (e.g. from side or end portions thereof) for at least part of the remainder of the laser beam. For example, the intensity of the laser beam may increase linearly, exponentially, or in steps with increasing distance from the recess 130 over part or all of the remainder of the laser beam. An example of a laser beam shaped in this way is shown in Figure 6, where for dataset 602, the relative power input gradually increases between around 0.5mm and 2.2mm which corresponds to the transition region of the Top Hat profile of the remainder 144 of the laser beam.

[0105] When insufficient energy is supplied to the wire 110, the wires enters the stubbing transfer mode and vibrates and moves away from its natural position. To counteract this, more energy is supplied to the wire as it enters the remainder 144 of the laser beam 120. However, if too much energy is supplied to the wire 110 to counteract stubbing, dripping may occur also resulting in defects. Having the intensity of the laser beam in the remainder 144 of the laser beam increase with increasing distance from the recess 130 helps balance these factors and maintain a smooth transfer mode of material from the wire to the substrate, while reducing stubbing and dripping. In this arrangement, the wire 110 is supplied with more energy the more it moves away from its natural position; thus, the amount of additional energy supplied to the wire increases with increasing stubbing, which allows counteracting stubbing at reduced risk of dripping as more energy is supplied to the wire only if it ‘stubs’ (i.e. moves) more indicating that it requires more energy to melt.

[0106] It will be appreciated that Figures 4 and 5 illustrate only one example laser beam profile 128. Further example laser beam profiles are shown in Figure 7. Figures 7A to 7L show simple schematics of laser beam intensity profiles 128 in accordance with embodiments of the present invention. Figures 7A to 7L each show a top view of the laser beam 120. In Figures 7A to 7L, the same reference numerals are used to denote the same parts of the laser beam 120 as in Figures 4 and 5. The wire is not shown in Figures 7A to 7L for simplicity; however, it will be appreciated that in use wires are fed through the recesses 130.

[0107] The laser beam outer diameter 124 may have any appropriate shape, such as circular, rectangular, or oval. Figures 4 and 5, and 7A to 7G show example laser beams 120 with a circular outer diameter 124. Figures 7H to 7L show example laser beams 120 with a rectangular outer diameter 124. Outer diameter 124 shapes having a similar radius (e.g. within 10% tolerance) in each direction can provide a similar laser beam 120 area around the wire 110 in each direction around the centre of the laser beam 125 and can reduce the risk of the wire 110 moving outside of the laser beam 120.

[0108] As noted above, the recess 130 in the laser beam profile 128 extends from the outer diameter 124 of the laser beam 120. For example, as shown in Figures 7I to 7L, for a laser beam 120 with a rectangular outer diameter 124, one or more recesses 130 may extend from a side of the laser beam profile 128 (as shown in Figures 7I, 7J, 7K), or from a corner of the laser beam profile 128 (as shown in Figure 7L).

[0109] Figures 7A to 7L also show various example recess 130 shapes. As shown in Figures 7A, 7B, 7J, 7K, and 7L, the recess 130 may comprise side portions 132 arranged in parallel to one another; such recesses 130 are also referred to as “rectangular” herein. The end portion 134 may be arranged perpendicular to the side portions 132 (see Figures 7J to L), at an oblique angle (i.e. at an angle other than 90 degrees) to the side portions 132, or the end portion 134 may be curved (see Figure 7A).

[0110] As shown in Figures 7C, 7D, 7E, 7H, and 7I, the recess 130 may comprise side portions 132 arranged at an oblique angle to one another; such recesses 130 are also referred to as “triangular” herein. As shown in Figures 7C, 7D, 7H, and 7I, the width of the recess 130 may decrease with increasing depth of the recess (i.e. the side portions 132 may be at an acute (i.e. less than 90 degrees) angle to the outer perimeter 124 of the laser beam). This can allow providing more even heating of the wire 110 during stubbing, as when the wire bends and moves away from its feeding axis, the wire diameter may be aligned (or be closer to being aligned) with side portions 132 of the recess thus providing more even heating across the wire diameter. The side portions 132 may be connected such that the recess 130 does not have an end portion; alternatively, an end portion may be provided that connects the side portions (e.g. thus providing a trapezium shaped recess). Alternatively, as shown in Figure 7E, the width of the recess 130 may increase with increasing depth of the recess (i.e. the side portions 132 may be at an obtuse angle to the outer perimeter 124 of the laser beam). The side portions 132 may be connected by an end portion 134.

[0111] As shown in Figure 7F, the recess 130 may be shaped as an arc. Similarly to the arrangement of e.g. Figure 7C, this can allow providing more even heating of the wire 110 during stubbing, as when the wire bends and moves away from its feeding axis, the wire diameter may be aligned (or be closer to being aligned) with the arc-shaped perimeter of the recess 130 thus providing more even heating across the wire diameter.

[0112] A further example recess 130 shape is shown in Figure 7G. The recess 130 of Figure 7G comprises side portions 132 arranged in parallel to one another, and an end portion 134 shaped as an arc connecting the side portions 132. The laser beam profile 128 of Figure 7G may for example be obtained by shaping a starting Doughnut profile laser beam 120 (thus providing the end portion 134) to make a rectangular recess in the laser beam (thus providing the side portions 132).

[0113] One or more recesses 130 may be provided in the laser beam profile 128. Figures 7A, 7C, 7E to 7G, 7I and 7J show example laser beam profiles 128 having a single recess 130. In turn, Figures 7B, 7D, 7K, and 7L show examples of laser beam profiles 128 comprising a plurality of recesses 130. For example, the laser beam profile 128 may comprise two recesses (see Figures 7D and 7L), or three recesses (see Figures 7B and 7K). The plurality of recesses 130 may be evenly distributed across the laser beam profile 128, e.g. the recesses 130 may be arranged at even angles around the outer diameter 124 of the laser beam 120. Each recess 130 may have the same, e.g. rectangular, shape. Alternatively, the recesses 130 may vary in shape or dimensions, e.g. the laser beam profile 128 may comprise two rectangular recesses of different depth, or a rectangular recess and a triangular recess.

[0114] The recesses 130 are provided so that wires 110 can be fed through them. For laser beams comprising multiple recesses 130, a respective wire 110 may be fed through each recess 130; or respective wires 110 may be fed through only a subset of the recesses 130. For example, for the laser beam of Figure 7D, a wire may be fed through only one of the recesses 130, or separate wires 110 may be fed through each of the two recesses 130. Simultaneously feeding multiple wires 110 towards the melt pool can allow increasing the rate of deposition.

[0115] It will be appreciated that further laser beam profile 128 shapes may be used beyond those shown in Figures 4, 5, and 7. For example, the laser beam profile 128 may comprise more than three recesses 130, a differently shaped outer diameter 124, or differently shaped recesses 130.

[0116] Figures 1 to 7 and 9 illustrate examples in which the wire feeding module 104 feeds the wire 110 into the path of the laser beam 120 at an acute angle to the substrate 200. In these examples, the recess 130 may extend from the outer perimeter 124 of the laser beam 120, and into the laser beam 120, as described elsewhere herein.

[0117] In alternative examples, the wire feeding module 104 may feed the wire 110 substantially perpendicularly (e.g. at between 85 and 95 degrees, or around 90 degrees) to the substrate 200. In these examples, the recess 130 may be separated from (i.e. not connected, or extending from) the outer perimeter 124 of the laser beam 120; in other words, the recess 130 may be a standalone recess.

[0118] The recess 130 may have any shape, such as circular, oval, triangular, rectangular, or hexagonal. The recess shape may match the shape of the wire diameter (e.g. both shapes being circular). Alternatively, the wire and the recess may have different shapes (e.g. the wire having a circular cross-section, and the recess being triangular).

[0119] The recess 130 may be arranged substantially at the centre 125 of the laser beam. In other words, the recess 130 may be substantially concentric with the laser beam. For example, the centre of recess 130 may be arranged within 20%, 10%, 5%, or 2% of the diameter of the laser beam from the laser beam centre 125.

[0120] Referring now to Figure 8, yet further example laser beam profiles are shown for examples where the wire 110 is fed substantially perpendicularly to the substrate 200. Figures 8A and 8B show simple schematics of laser beam intensity profiles 128 in accordance with embodiments of the present invention. As shown in Figures 8A and 8B, the respective recesses 130 may each comprise one or more side portions 132 but no end portion 134

[0121] In Figure 8A, the laser beam 120 has a circular outer diameter 124 and a circular recess 130, arranged away from the laser beam centre. The perimeter of the circular recess 130 may be considered a side portion 132 of the recess. In the example of Figure 8A, the wire 110 has a circular cross-section. The wire 110 is narrower than the recess 130 such that a gap is provided between the wire 110 and the remainder 144 of the laser beam. In Figure 8B, the laser beam 120 has a circular outer diameter 124 and a triangular recess 130, arranged at the laser beam centre 125. The three sides of the triangular recess 130 may be considered side portions 132 of the recess 130. In the example of Figure 8B, the wire 110 has a triangular cross-section. The wire is narrower than the recess 130 such that a gap is provided between the wire 110 and the remainder 144 of the laser beam.

[0122] It will be appreciated that, like the recess, the wire 110 may have various different shapes (e.g. cross-sectional shapes). The wire 110 cross sectional shape may match the shape of the recess 130. This can provide improved stubbing correction as finer movement of the wire during stubbing results in the wire moving into the remainder of the laser beam where it receives more energy thus counteracting stubbing. Alternatively, the shape of the recess and wire may differ; e.g. a circular cross-section wire may be used with a triangular recess.

[0123] Referring now to Figure 9, this shows a simple schematic view of a further example laser deposition system 900 in accordance with embodiments of the present disclosure. The laser deposition system 900 comprises the laser module 102 generating the laser beam 120, and the wire feeding module 104 feeding the wire 110; these modules 102, 104 may be configured in the same way as described with reference to Figures 1 to 7 above. In addition, the laser deposition system 900 comprises an electrical heating module 160.

[0124] The electrical heating module 160 converts electrical energy to thermal energy for heating of the wire 110. The electrical heating module 160 pre-heats the wire 110 before it reaches the laser beam 120. The electrical heating module 160 may heat the wire as it is being fed by the wire feeding module 104.

[0125] The electrical heating module 160 may heat the wire 110 via resistive heating. The electrical heating module 160 may comprise one an electrical power sources (not shown), and electrical wires 162, 164 connected to the electrical power source. The electrical power source builds a potential between the wires 162, 164, and supplies current to the first electrical wire 162. The electrical power source may for example supply a direct current (DC) to the electrical wire 162. The electrical power source may for example supply electricity at a current of between 50 and 180 A, and / or a power of between 500 and 5000 W. The first electrical wire 162 is electrically connected to the deposited wire 110 (e.g. via the nozzle of the wire feeding module 104). The second electrical wire 164 is electrically connected to a further contact point, such as a fixture for mounting the substrate 200. As current is passed through the wire 110, the wire 110 heats up due to its electrical resistance. Electrically heating the wire allows reducing the amount of energy that needs to be supplied by the laser beam 120, thus increasing the efficiency of the deposition process due to the higher efficiency of converting electrical energy to heat via electrical heating than via the user of a laser. Pre-heating the wire 110 before it reaches the laser beam 120 also increases the wire’s 110 absorptivity to the laser light. This further improves efficiency and allows the laser deposition system 900 to use a laser beam 120 with a lower power input to effectively counteract stubbing as described herein. Electrically heating the wire 110 also allows further decreasing the sensitivity of the laser deposition system 900 to the placement of the wire 110 with respect to the laser beam 120. Electrically heating the wire 110 can improve the quality and stability of deposited material, and reduce lack of fusion defects.

[0126] In some example, in its natural position, the wire 110 may be heated only, or primarily, using electrical heating by the electrical heating module 160; for example, where the intensity of the laser beam in the recess 130 is substantially zero and / or the wire 110 is fed such that it resides fully in the recess 130 in its natural position. In these examples, the laser beam 120 is used primarily to counteract stubbing, and in its natural position the wire 110 is melted mainly using electrical heating. For example, in its natural position, the energy input on the wire 110 may comprise at least 50%, 75%, 90%, or 95% electrical heating; and less than 50%, 25%, 10%, or 5% laser heating. This can provide improved efficiency due to greater use of electrical heating as opposed to laser heating.

[0127] Alternatively, in its natural position, the wire 110 may be heated using both electrical heating and via the laser beam 120. For example, the intensity of the laser beam 120 in the recess 130 may be non-zero, and / or the depth of the recess 130 may be lower such that the tip of the wire 110 extends beyond the recess 130.

[0128] In examples, instead of in addition to resistive heating, the electrical heating module 160 may heat the wire 110 via inductive and / or dielectric heating.

[0129] Referring now to Figure 10, a laser deposition method 1000 according to an example of the present disclosure is shown as a flow diagram. The method 1000 has three steps 1010, 1020, 1030, where step 1030 is optional.

[0130] In a first step 1010, a laser beam having one or more recesses in its intensity profile is generated, as described above. The intensity of the laser beam is lower (e.g. substantially zero) in the recesses than in the remainder of the laser beam. In a second, optional, step 1020, one or more wires are electrically heated prior to deposition. This allows further increasing the efficiency of the laser deposition method 1000. In some cases, when arranged along its feeding direction, each of the one or more wires may be within a respective recess in the laser beam, and be heated only via electrical heating. As noted above, the wires may for example be heated using resistive heating.

[0131] In a third step 1030, the one or more wires are fed through respective recesses in the laser beam profile, for deposition onto a substrate. This helps maintain a stable transfer of material from the wire to a melt pool on the substrate, as upon the occurrence of stubbing and movement of the wire, the wire moves into the higher-intensity remainder of the beam where it receives more energy thus returning to the smooth transfer mode. As noted above, each recess may be wider than the respective wire such that a gap is provided between at least part of the side portions of the recess and the wire. In some cases, steps 1020 and 1030 may be performed substantially simultaneously, where the one or more wires are electrically heated 1020 as they are being fed 1030 towards the substrate. Alternatively, the wires may be electrically heated 1020 before they are fed 1030 by the wire feeding module 104.

Claims

CLAIMS1. A laser deposition system comprising: a laser module configured to generate a laser beam having one or more recesses in its intensity profile, an intensity of the laser beam being lower in the recesses than in the remainder of the laser beam, and each recess being at least partly surrounded by the remainder of the laser beam; and a wire feeding module configured to feed one or more wires through the one or more recesses in the laser beam profile, for deposition onto a substrate.

2. The system of claim 1 , wherein the intensity of the laser beam in the one or more recesses is substantially zero.

3. The system of claim 1 or 2, wherein at least 50% of a perimeter of each recess is surrounded by the remainder of the laser beam.

4. The system of any preceding claim, wherein each recess is wider than the respective wire such that a gap is provided between at least part of side portions of the recess and the wire.

5. The system of any preceding claim, wherein each recess extends from an outer perimeter of the laser beam.

6. The system of claim 5, wherein each recess extends towards a centre of the laser beam.

7. The system of claim 5 or 6, wherein each recess terminates before the outer perimeter of the laser beam, and preferably at the centre of the laser beam8. The system of any of claims 5 to 7, wherein side portions of each recess are substantially aligned with a feeding direction of the respective wire.

9. The system of claim 8, wherein each recess comprises an end portion, wherein the end portion is arranged perpendicular to the feeding direction of the respective wire.

10. The system of any of claims 5 to 7, wherein a width of the recess decreases with increasing depth of the recess into the intensity profile of the laser beam.11 . The system of any of claims 5 to 9, wherein each recess extends substantially along a line of symmetry of the laser beam profile.

12. The system of any of claims 1 to 4, wherein each recess is fully surrounded by the remainder of the laser beam.

13. The system of claim 12, wherein the one or more recesses comprise one recess, wherein the recess is substantially concentric with the laser beam.

14. The system of any preceding claim, wherein each recess is symmetrical about the feeding direction of the respective wire.

15. The system of any preceding claim, wherein for at least part of the remainder of the laser beam, the intensity of the laser beam in the remainder of the laser beam increases with increasing distance from the recesses in the laser beam.

16. The system of any preceding claim, further comprising an electrical heating module configured to heat the one or more wires.

17. The system of claim 16, wherein the electrical heating module is configured to heat the one or more wires using resistive heating.

18. The system of claim 16 or 17, wherein the electrical heating module is configured to heat the one or more wires while they are being fed by the wire feeding module.

19. The system of any of claims 16 to 18, wherein, when arranged along its feeding direction, each of the one or more wires receives more energy from the electrical heating module than from the laser beam.

20. The system of any preceding claim, wherein the one or more recesses comprise at least two recesses; wherein the one or more wires comprise at least two wires; and wherein the wire feeding module is configured to feed each wire through a respective recess in the laser beam profile.21 . The system of any preceding claim, wherein each recess has a rectangular shape.

22. The system of any preceding claim, wherein the laser beam has a circular outer perimeter.

23. The system of any preceding claim, wherein the wire comprises a metal.

24. A laser deposition method comprising generating a laser beam having one or more recesses in its intensity profile, an intensity of the laser beam being lower in the recesses than in the remainder of the laser beam, and each recess being at least partly surrounded by the remainder of the laser beam; and feeding one or more wires through the one or more recesses in the laser beam profile to deposit the wires onto a substrate.

25. The method of claim 24, wherein the substrate is a component of an aircraft.

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