Patent Application
20230001507
The invention relates to an apparatus for laser-deposition welding with multiple laser-deposition welding heads and to a method for operating such an apparatus.
Laser-deposition welding is a method for surface treatment (e.g. coating, repair) and additive manufacturing of components with filler materials in wire or powder form. Due to greater resilience to adjustment errors in the process setup and greater flexibility in material selection, filler materials in powder form are predominantly used. The powder is introduced, by means of a powder nozzle at a defined angle, into a molten pool created by a laser beam on a surface of a component. During the interaction between laser radiation and powder particles above the molten pool, a portion of the laser radiation is absorbed by the powder. The non-absorbed portion is reflected or transmitted (several times). The portion of radiation absorbed by the powder particles causes the powder particles to heat up, and the transmitted portion of radiation creates the molten pool. Depending on the degree to which the particles are heated in the zone of beam-substance interaction, the particles of the filler material are solid and/or partially or completely liquid before they enter the molten pool.
If the component is then moved relative to the laser and the powder feed, the material of the molten pool moves out of the area of influence of the laser radiation and solidifies to form a layer. The prerequisite for producing defect-free layers bonded by melt metallurgy is to provide a process heat that is sufficient to initiate a temperature-time cycle that ensures that both the substrate and the filler material are melted. The filler material and component material are therefore mixed to a greater or lesser extent depending on the laser power and the setting of other process parameters (e.g. feed rate, track distance, beam diameter, material feed, etc.). The powder can be injected laterally or coaxially into the melt pool. With the customary process control, it is possible to achieve feed rates, that is relative speeds of the component in relation to the laser beam, of typically between 0.2 m/min and 2 m/min. In the method disclosed in DE 10 2011 100 456 B4, the supplied material is already melted above the surface by means of an appropriately focused laser beam with high power, such that it reaches the molten pool on the surface of the component already in the molten state, which enables faster processing of the component through further increased feed rates in the range of ≥150 m/min. In the method according to DE 10 2011 100 456 84, the area coverage rate is now higher (and thus the coating time is shorter) than in the conventional procedure, but the high cooling rates due to the increased feed rate favour the formation of cracks (stress cracks due to the shrinkage stresses). As a result, many alloys, in particular difficult-to-weld alloys mainly for wear protection, can no longer be processed. Despite providing a larger area coverage rate, DE 10 2011 100 456 84 does not offer any approaches for increasing the deposition rate (amount of powder deposited per unit of time).
By applying preheating to the component, the tendency to crack can in principle be reduced and the deposition rate increased. EP 0 190 378 A1 discloses that faster processing of the component can be achieved by subjecting the entire component to additional thorough preheating in a furnace before the treatment described above. The preheating temperature of the furnace heating is up to 600° C. This allows the material to be deposited at a feed rate of up to 5.4 m/min. EP 1 285 719 A1 discloses a modified preheating method that allows significantly higher feed rates to be achieved while simultaneously avoiding cracks in the layer or substrate material. In this method, the workpiece is inductively heated during laser-deposition welding. The use of inductive preheating restricts its use to components with a suitable geometry. DE102011100456 84. It would be desirable to avoid time-consuming preheating procedures or additionally required components such as inductive heaters.
It would therefore be desirable to have an effective laser-deposition welding process available that enables a higher deposition rate for a wide range of materials with less process time for the component.
It is therefore an object of the invention to provide an effective laser-deposition welding process that enables a higher deposition rate for a wide range of materials with less process time for the component.
This object is achieved by an apparatus for laser-deposition welding having a laser-deposition welding unit with multiple laser welding heads arranged thereon for (quasi-)simultaneous depositing of material onto a surface of a component and having one or more conveying units for supplying the laser-deposition welding heads with the material to be deposited and having one or more laser beam sources for supplying the laser-deposition welding heads with laser radiation for carrying out the laser-deposition welding.
With regard to terminology, the following should be explained:
First, it should be expressly pointed out that, in the context of the present patent application, indefinite articles and numerical indications such as “one”, “two”, etc. are generally to be understood as “at least” indications, i.e. as “at least one . . . ”, “at least two . . . ”, etc., unless it expressly follows from the respective context or it is obvious or technically imperative for the skilled person that only “exactly one . . . ”, “exactly two . . . ”, etc. can be meant in this case.
The term “laser-deposition welding” refers to all methods in which a material passing through a laser-deposition welding head in the direction of the component to be processed, for example a material in powder form, is melted, in a molten pool created by the laser beam on the surface of the component, by means of a laser beam which is also guided through the material by the laser-deposition welding head in the direction of the component to be processed, and is thus deposited onto the surface of the component which has also been melted by the laser beam. The subsequently solidified material remains there as material welded to the surface. The laser-deposition welding head comprises, for example, an optical system for the laser beam and a powder feed nozzle including an adjustment unit for the material to be deposited, optionally with an integrated, local protective gas supply. The laser beam can also be guided in such a way that the material is already melted in the laser beam, for example by a laser beam that has a focal point above the surface of the component.
The term “laser-deposition welding unit” means a component comprising the laser-deposition welding heads. In this respect, the laser-deposition welding heads can, for example, be attached to a carrier plate of the laser-deposition welding unit. Preferably, the attachment can be designed in such a way that the laser-deposition welding heads can move relative to one another. In addition, the laser-deposition welding unit as a whole can be arranged so as to be spatially movable in the apparatus, for example on an adjustment unit of the apparatus. As an embodiment, the laser-deposition welding unit can be arranged on a robot arm that can move the laser-deposition welding unit spatially as desired by means of suitable traversing curves. The number of laser-deposition welding heads is at least two in this case. It is therefore also possible for three, four, five or more laser-deposition welding heads to be included in the laser-deposition welding unit. The number of laser-deposition welding heads that can be present in the apparatus is usually a geometrical problem and is determined by the size of the laser-deposition welding heads and the component to be processed.
The term “laser-deposition welding head” refers to the unit which, by means of the laser beam passing through it, creates a laser welding spot on the surface of the component to be processed and which melts the material in the laser beam, which material also passes through said unit on its path to the surface of the component such that it is welded to the component upon impact with the surface of the latter.
The material deposited can, for example, be provided in powder form for laser-deposition welding. The material may be any material suitable for laser-deposition welding. For example, the material may comprise or consist of metals and/or metal-ceramic composites (so-called MMCs). The skilled person can select the materials suitable for the respective laser-deposition welding process. In this case, the material can be fed to the laser heads from a single conveying unit. However, the apparatus can also comprise several conveying units, whereby the laser-deposition welding heads can be supplied with different materials, such that the deposition welding tracks produced by different laser-deposition welding heads can comprise the same or different materials, or the material feed to one or more laser-deposition welding heads can, during laser-deposition welding, be changed or switched from one conveying unit to another conveying unit with a different material.
The laser radiation is provided by means of one or more laser beam sources. The skilled person can select suitable laser beam sources for laser-deposition welding.
The term “(quasi-)simultaneous deposition” refers to the process of laser-deposition welding, whereby, for each laser-deposition welding head, separate deposition welding tracks are deposited onto the surface at the same time as (preceding or following) other deposition welding tracks by means of other laser-deposition welding heads. This (quasi-)simultaneous deposition takes place at the same time, but at other positions on the component, i.e. at different locations on the component. Thus, the material deposited onto the surface per unit of time increases proportionally with the number of laser-deposition welding heads. The separate deposition welding tracks can adjoin or, optionally, at least partially overlap one another. Optionally, the separate deposition welding tracks can also be deposited directly on top of one another. For example, the apparatus according to the invention can be used to reduce previously common processing times of 3-15 minutes to less than 1 minute when processing brake discs by means of laser-deposition welding.
Through the (quasi-)simultaneous deposition of material by means of multiple laser-deposition welding heads, the apparatus according to the invention thus enables an effective laser-deposition welding process, which enables a higher deposition rate for a wide range of materials with a shorter process time for the component than would be possible with only one laser welding head. In order to achieve a shorter process time, the feed rate does not need to be increased compared to known methods, which improves the quality of the deposited layer and helps to avoid layer defects such as the formation of cracks by means of a feed rate appropriate to the process.
In one embodiment, the laser-deposition welding heads each produce a laser welding spot on the surface of the component, and adjacent laser welding spots have a first offset from one another perpendicular to a feed direction of the laser welding spots on the surface of the component. The expression “on the surface of the component” refers to the current surface of the component at the time when the respective laser welding spot sweeps over the surface. The surface of the component need not be the original surface of the component before laser-deposition welding begins. The surface of the component can also be the surface of a deposition welding track that has already been deposited or of a layer of deposited material, as this is welded to the previous surface after being deposited and thus in itself constitutes the surface of the component for subsequent deposition welding tracks. The term “laser welding spot” refers to the spatial location on the surface of the component where the molten material is deposited onto the surface by means of laser-deposition welding. The laser welding spot can also be referred to as the melting area of the deposited material, where the material melted by laser radiation meets the surface of the component. The term “adjacent laser welding spots” refers to two laser welding spots which produce deposition welding tracks of material applied to the surface of the component, and which can adjoin and optionally overlap one another at least partially to produce an areal deposition of the material. Adjacent laser-deposition welding spots can be produced by adjacent laser-deposition welding heads. In this case, adjacent laser welding spots and/or laser-deposition welding heads do not necessarily refer to laser welding spots or laser-deposition welding heads that have the smallest geometric distance from one another, but are or produce those laser welding spots that create adjoining deposition welding tracks. Due to the at least first offset of the adjacent laser welding spots from one another, the preheating of the component can be controlled in a targeted manner, which makes it easier or, depending on the alloy, even possible to process difficult-to-weld alloys. The at least first offset of a suitable size also reduces the amount of post-processing required. In a further embodiment, the laser welding spots produce deposition welding tracks for the aforementioned purpose with a material width along the feed direction on the surface, in which welding tracks the first offset of adjacent laser welding spots is between 10% and 90%, preferably between 40% and 60%, most preferably 50%, of the material width of the deposition welding track.
In a further embodiment, the adjacent laser welding spots on the surface of the component have a second offset from one another in the feed direction. Due to this second offset of the laser welding points, the preheating of the component can also be controlled in a targeted manner, in particular in conjunction with the first offset, which makes it easier or, depending on the alloy, even possible to process difficult-to-weld alloys. The second offset of suitable size, in particular in conjunction with the first offset, also further reduces the amount of post-processing required.
In one embodiment, the second offset is set in such a way that temperature profiles induced by the laser welding spots on the surface overlap to such an extent that the material in an overlap region of adjacent deposition welding tracks still has a residual heat that is usable/admissible for the process. In this case, the laser welding head with the second offset from the adjacent deposition welding track can be used not only to deposit its own deposition welding track, but also to remelt the deposition welding track deposited adjacent.
In one embodiment, the apparatus is configured, after an areal deposition of the material as a preceding layer onto the surface of the component, to guide the laser-deposition welding heads in such a way that a further areal deposition of the material as a subsequent layer onto the preceding layer is carried out in order to deposit the material as a multilayer system. This makes it easy to produce multilayer systems. These multilayer systems can consist of the same or different materials. Multilayer systems can be used to produce layers with a greater layer thickness than would be possible with a single-layer system, or to deposit multiple different functional layers through a common process. In this case, the deposition process for the subsequent layer can be used to remelt the most recently deposited layer in order to modify its properties as desired. Using the apparatus according to the invention, layer thicknesses of 0.3 mm to 3.0 mm per layer can typically be deposited. If greater layer thicknesses are desired, these can be achieved by depositing multiple layers of the same material on top of one another. The same applies to layers of different materials.
In a further embodiment, the deposition welding tracks of the subsequent layer are deposited onto the preceding layer with a third offset perpendicular to the feed direction relative to the underlying deposition welding tracks of the preceding layer. This means, for example, that the contours of the individual layers can overlap in such a way that the surface of the multilayer system has an undulation lower than the undulations of the respective individual layers, which reduces the intensity of any necessary post-processing steps such as sanding and smoothing.
In a further embodiment, the deposited layers have a varying layer thickness, with a smaller layer thickness and a larger layer thickness, wherein the third offset of the deposition welding tracks of superimposed layers is set in such a way that the larger layer thicknesses of the subsequent layer are arranged above the smaller layer thicknesses of the preceding layer. This means that the surface of the multilayer system can be provided with a very small contour or a very small surface unevenness or roughness. This makes post-processing steps such as grinding to smooth the surface of the deposited material in the multilayer system less time-consuming or, where applicable, even obsolete.
In a further embodiment, the apparatus is configured to supply, by suitable control of the conveying units, the laser-deposition welding heads with different materials for deposition onto the surface of the component. As a result, adjacent deposition welding tracks from different laser welding heads can consist of different materials, and different layers in a multilayer system can be made from different materials.
In a further embodiment, the control for this purpose is carried out in such a way that layers of a multilayer system consist of different materials, with first layers of a first material and second layers of a second material. This means that if components are processed using laser-deposition welding, for example, a first layer of a first material and a second layer of a second material can be deposited onto the first layer. In this case, the second layer can be, for example, an anti-corrosion layer made of a corrosion-resistant material to protect the properties of the first layer. In another example, the second layer could also be an abrasion layer, for example for brake discs. In this instance, to increase the layer thickness, the preceding first and second layers may themselves each be a multilayer system made of layers of the same material in each case.
In a further embodiment, the laser-deposition welding unit is, in order to perform a movement relative to the surface of the component, arranged in the apparatus so as to be movable, preferably by means of a movement unit. This allows components to be flexibly processed by area by guiding the laser-deposition welding unit over a surface, for example on a rotating surface or along a rotating shaft.
In a further embodiment, the laser-deposition welding heads are, in order to perform a movement relative to one another, arranged in the apparatus so as to be movable, preferably by means of a laser-deposition welding head movement unit. This allows the individual deposition welding tracks to be precisely guided relative to one another and across the surface of the component to be processed.
In a further embodiment, the apparatus comprises a control unit designed to suitably control at least the movements of the laser-deposition welding unit and/or of the laser-deposition welding heads and/or the conveying units and/or of the laser beam sources in order to carry out the laser-deposition welding, for which purpose the control unit is suitably connected to these components. The control unit may be a software-based machine controller on which an appropriate control program is installed and executed accordingly to control the process.
The invention further relates to a method for operating an apparatus for laser-deposition welding according to the invention, having a laser-deposition welding unit with multiple laser-deposition welding heads arranged thereon, comprising the step of (quasi-)simultaneously depositing material onto a surface of a component. Through the (quasi-)simultaneous deposition of material by means of multiple laser-deposition welding heads, the method provides an effective laser-deposition welding process which enables a higher deposition rate for a wide range of materials with a shorter process time for the component than would be possible with only one laser welding head, in order to achieve a shorter process time, the feed rate does not need to be increased compared to known methods, which improves the quality of the deposited layer and helps to avoid layer defects such as the formation of cracks by means of a feed rate appropriate to the process.
In one embodiment of the method, the laser-deposition welding heads each produce a laser welding spot on the surface of the component, wherein the method comprises the further step of moving adjacent laser welding spots with a first offset from one another perpendicular to a feed direction of the laser welding spots on the surface of the component.
In a further embodiment, the method comprises the further step of moving adjacent laser welding spots on the surface of the component with a second offset from one another in the feed direction.
In a further embodiment, the method comprises the further step of controlling at least the movements of the laser-deposition welding unit and/or of the laser-deposition welding heads and/or of the conveying units and/or of the laser beam sources in order to carry out the laser-deposition welding by means of a control unit suitably connected to these components.
In a further embodiment, the method comprises the further step of depositing a multilayer system onto the surface of the component by suitably guiding the laser-deposition welding heads of the apparatus, in which, after an areal deposition of the material as a preceding layer onto the surface of the component, a further areal deposition of the material as a subsequent layer onto the preceding layer takes place.
In a further embodiment of the method, wherein the deposited layers of the multilayer system have a varying layer thickness with a smaller layer thickness and a larger layer thickness, said method comprises the further step of setting a third offset perpendicular to the feed direction between deposition welding tracks of the subsequent layer and underlying deposition welding tracks of the preceding layer such that the larger layer thicknesses of the subsequent layer are arranged above the smaller layer thicknesses of the preceding layer.
In a further embodiment, the method comprises the further step of controlling the conveying units for the laser-deposition welding heads in such a way that the layers of the multilayer system consist of different materials, with first layers of a first material and second layers of a second material.
In a further embodiment of the method, wherein the component, preferably a brake disc, comprises a circular surface having a rotation axis onto which the material is deposited, said method comprises the further steps of
Through the movement of the laser-deposition welding heads in combination with the rotating component, the material is deposited onto the entire area of the component. The speed of the individual movements for the component and laser-deposition welding heads determines, inter alia, the extent to which the adjacent deposition welding tracks overlap one another.
In a further embodiment of the method, wherein the component, preferably a shaft, comprises a rotationally symmetrical surface having a rotation axis onto which the material is deposited, said method comprises the further steps of
Through the movement of the laser-deposition welding heads in combination with the rotating component, the material is also deposited onto the entire area of the component for this component geometry. The speed of the individual movements for the component and laser-deposition welding heads determines, inter alia, the extent to which the adjacent deposition welding tracks overlap one another.
The embodiments listed above can be used individually or in any combination deviating from the references in the claims relative to one another in order to design apparatuses or methods according to the invention.
These and other aspects of the invention are shown in detail in the figures as follows.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 132 191.3 | Nov 2019 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2020/100961 | 11/10/2020 | WO |
