Patent Application
20230136257
The Invention relates to a laser cladding device, a method of operating such a device, and a component manufactured using such a device and/or such a method.
Laser cladding is a process for surface treatment (e.g. coating, repair) and additive manufacturing of components with wire or powder weld materials. Due to the greater robustness against adjustment errors in the process set up and the greater flexibility in the choice of materials, weld materials in powder form are predominantly used. The powder is introduced into a melt pool created by a laser beam on a surface of a component at a defined angle by means of a powder nozzle. During the interaction of laser radiation and powder particles above the melting bath, part of the laser radiation is absorbed by the powder. The non-absorbed part is (multiply) reflected or transmitted. The part of the radiation absorbed by the powder particles leads to a heating of the powder particles, the transmitted part of the radiation creates the melt pool. Depending on the degree of heating of the particles in the beam-substance interaction zone, the particles of the weld material are solid and/or partially or completely liquid before entering the melt pool.
If the component is now moved relative to the laser and the powder feed, the material of the melt pool moves out of the area of influence of the laser radiation and solidifies to form the layer. The prerequisite for the production of defect-free, melt-metallurgically bonded layers is to provide a process heat that is sufficient to initiate a temperature-time cycle that ensures melting of both the substrate and the weld material. Depending on the laser power and the setting of further process parameters (e.g. feed speed, track distance, beam diameter, material feed, etc.), a more or less pronounced mixing of weld material and component material takes place. The powder can be injected laterally or coaxially into the melt pool.
With the usual process control, feed rates, i.e. relative speeds of the component in relation to the laser beam, can typically be reached between 0.2 m/min and 2 m/min. In the process disclosed in DE 10 2011 100 456 84, the supplied material is already melted above the surface by means of an appropriately focused laser beam with high power, so that it already reaches the molten bath on the surface of the component in the molten state, which enables faster processing of the component by further increased feed rates in the range 2≥150 m/min. With the process according to DE 10 2011 100 456 B4, the area rate is now larger (thus the coating duration is smaller) than with conventional process control, but despite the larger area rate DE 10 2011 100 456 84 does not provide any approaches for increasing the cladding rate (cladded amount of powder per time unit).
Depending on the spatial extent of the melt pool, the materials are cladded in wider or less wide cladding tracks with a thickness that varies across the width of the cladding track. The cross-section of such a cladding track perpendicular to the feed direction in which the laser beam moves over the component is usually dome-shaped with a maximum layer thickness in the centre of the cladding track and a thickness decreasing towards zero towards the edges of the cladding track. When material is cladded over an area by laser cladding, the cladding tracks are cladded next to each other and may at least partially overlap. The resulting layer thickness of the material cladded as a layer varies over the individual cladding tracks. In addition, the movement of the molten bath and the adhering, only partially melted powder particles generally result in a high degree of surface roughness (compared to conventional manufacturing processes, e.g. turning, milling, grinding). If a flat layer of cladded material is desired as the end product, the cladded layer must be reworked.
This reworking is time-consuming. Depending on the waviness and roughness of the layer, a lot of cladded material may have to be removed again for smoothing. Especially in the case of hard layers or hard grains in composite layers, conventional smoothing causes a time-consuming reworking step, which may cause considerable mechanical wear on the smoothing agents and thus increase the tooling costs.
Particularly in the case of layer systems containing hard material particles, the cost share of the worn smoothing agents can amount to a considerable part of the value chain. It would therefore be desirable to make the finishing operation simple, reliable and less wear-intensive.
It is therefore a task of the invention to provide an effective laser cladding process that enables a simple, reliable and less wear-intensive reworking effort.
This task is solved by a device for laser cladding comprising a laser cladding unit with at least one laser cladding head arranged thereon, one or more material sources for supplying the laser cladding head with a material to be cladded, and a laser beam source for supplying the laser cladding head with laser light for carrying out the laser cladding, the device being configured for the application of layers of material from adjacent cladding tracks to a surface of a component in the form of at least a first layer of a material comprising structures protruding from the surface of the first layer and having a first hardness and a second layer cladded thereon of a material having a second hardness less than the first hardness, the application process being controlled in such a way that the second layer at least partially covers the structures protruding from the first layer.
Terminologically, the following should be explained:
First of all, 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 person skilled in the art that only “exactly one . . . ”, “exactly two . . . ”, etc. can be meant there.
The term “laser cladding” refers to all processes in which a material passing through a laser cladding head in the direction of the component to be processed, for example a material in powder form, is melted in a molten bath generated 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 cladding head in the direction of the component to be processed, and is thus cladded 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 in the form of a cladding track. If the cladding tracks are cladded next to each other or even at least partially overlapping, the component can be covered with material in the form of a layer of this material. The laser cladding 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 cladded, if necessary with an integrated, local shielding 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 cladding unit” means an element comprising the laser cladding head or heads. In this context, the laser cladding head or heads may, for example, be mounted on a support plate of the laser cladding unit. Preferably, the attachment may be such that, if there are multiple laser cladding heads, the laser cladding heads can move relative to each other. Furthermore, the laser cladding unit as a whole can be arranged spatially movable in the device, for example on an adjustment unit of the device. As an embodiment, the laser cladding unit may be arranged on a robot arm that can move the laser cladding unit spatially as desired by means of suitable traverse curves. The number of laser cladding heads here is at least one. Two, three, four, five or more laser cladding heads can therefore also be included in the laser cladding unit. How many laser cladding heads can be present in the device is generally a geometrical problem and is determined by the size of the laser cladding heads and the component to be processed.
The term “laser cladding head” means the unit which, by means of the laser beam passing through it, creates a laser cladding point on the surface of the component to be processed and which melts the material in the laser beam, also passing through it, on its way to the surface of the component so that it is welded to the component when it strikes the surface of the component. The term “laser cladding point” refers to the spatial location on the surface of the component where the molten material is cladded onto the surface by laser cladding. The laser cladding point can also be referred to as the melting area of the cladded material, where the material melted by laser light meets the surface of the component.
The cladded material can, for example, be provided in powder form for laser cladding. Here, any material suitable for laser cladding may be used as the material. For example, the material may comprise or consist of metals and/or metal-ceramic composite materials (so-called MMCs). The skilled person may select the materials suitable for the particular laser cladding process. Here, the material may be fed to the laser heads from a single conveyor unit. However, the device may also comprise a plurality of conveyor units, whereby the laser cladding heads may be supplied with different materials, so that the cladding tracks produced by different laser cladding heads may comprise the same or different materials, or the supply of material to one or more laser cladding heads may be changed or switched during laser cladding from one conveyor unit to another conveyor unit with a different material. Material layers are produced from material tracks cladded next to each other in an at least partially overlapping manner. How many material tracks arranged next to each other are needed to provide a surface of the component with a material layer depends, among other things, on the material width of the respective material track. The material width is determined by the details of the design of the laser cladding heads, such as material jet width, laser energy, extension of the laser focus and/or process speed.
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 cladding.
The term “on the surface of the component” refers to the current surface of the component at the time when the respective laser cladding point sweeps over the surface.
The surface of the component need not be the original surface of the component before laser cladding was started. The surface of the component can also be the surface of a cladding track that has already been cladded or of a layer of cladded material, since this is cladded to the previous surface after cladding and thus itself represents the surface of the component for subsequent cladding tracks.
The “protruding structures” are defined here as the texture of the surface that deviates from an ideal flat surface. The texture can be determined numerically in the form of a surface roughness. These structures may be partially within the first layer and protrude from the first layer with only a portion of their structure, the present invention considering only the portion of the structures that actually protrude from the first layer. The part of the structures that is already enveloped by the first layer is not of concern for reworking the cladded layers. Such protruding structures may, for example, be formed during the cladding of composite materials by a second material contained therein. In one embodiment, the first layer comprises a composite material comprising a matrix material having a third hardness lower than the first hardness, preferably the first layer comprises the composite material and the structures are at least partially embedded in the matrix material. Here, the composite material may be a metal-ceramic composite material containing grains forming the structures. For example, such grains are carbide grains. Such materials are characterised in particular by their high abrasion resistance and can be used, for example, as brake coatings. In this case, needles made of a carbide, nitride, oxide or similar material are formed on the surface of such a layer produced by laser cladding. The height of the needle can be up to half of the cladded layer, while the diameter of the needle is significantly smaller than its height.
In one embodiment, the material of the second layer is a metal or metal alloy. Layers of metal can be easily reworked in a defined manner. In a preferred embodiment, the material of the second layer is the matrix material of the first layer. This allows a good material bond to be created between the first and second layers, since the first layer differs from the second layer only in the presence of the structures protruding from the first layer.
By at least partially covering these protruding structures, the surface roughness is reduced compared to components with only one cladded first layer with such structures. In this case, the structures each have a highest point and, in a valley between adjacent structures, the adjacent structures each have a lowest point assigned to them, a distance between the highest and lowest points of the respective structure representing its height, and the second layer covering the structures protruding from the first layer at least up to 20%, preferably at least 40%, more preferably at least 60%, particularly preferably at least 80%, of the average height of all structures. In one embodiment, the second layer completely covers the structures protruding from the first layer. By the fact that the second layer consists of a material whose hardness is lower than that of the protruding structures, reworking of the component is facilitated or, in the case of only a small height of the structures effectively protruding from the second layer as well, unnecessary, since in this case the resulting surface roughness may already meet the requirements for the coated component as the product. With complete coverage of the structures protruding from the first layer, the surface roughness of the coated component corresponds to that of the surface of the second layer. Due to the fact that the second layer has a low hardness, the area of the second layer that protrudes above the structures can easily be removed by means of reworking, so that the structures do not determine the surface roughness of the coated component, but nevertheless have a significant influence on the strength of the overall layer consisting of the first and second layer. Components with a fully covering second layer can be used, for example, as or in drill heads to improve external wear protection. Components with a second layer that does not cover completely can be used, for example, as brake discs, as the friction provided by the structures and the second layer is sufficient. The terms “first layer” and “second layer” are not intended to imply that there cannot be other layers between the “first layer” and the surface of the component. For example, a “third layer” or other layers could be located between the first layer and the component.
The device may further comprise a control unit for controlling the laser cladding process and, if necessary, the rework, which may be any control unit suitable therefor, for example a processor or a computer unit on which an appropriate control program is installed and executed during the laser cladding and/or reworking.
The device according to the invention enables the execution of an effective laser cladding process, which enables a simple, reliable and less wear-intensive reworking effort.
In a further embodiment, the device further comprises a material removal unit which is provided for at least partially removing the structures of the first layer protruding from the second layer when the first layer is not completely covered, or for then partially removing the second layer when the structures of the first layer are completely covered by the second layer.
The term “material removal unit” refers to any form of removal unit with which material of a layer can be removed from this layer without completely detaching the layer from the underlying layers. The material removing process may be mechanical, thermal, chemical or other. In one embodiment, the material removal unit is a grinding unit, a milling unit or a laser melting or laser ablation unit. The material removal unit may be arranged separately from the laser cladding unit or connected to it or integrated in it.
In a further embodiment, the material removal unit is arranged on the laser cladding head downstream of the laser cladding head, as seen in the feed direction of the laser cladding head. This allows the material removing process to be carried out in the same work step as the laser cladding process. If necessary, the residual heat of the laser cladding process can be utilised.
In a further embodiment, the structures of the first layer protruding from the second layer are at least partially removed by being vaporised or melted by the material removal unit. In this case, the material removal unit can be designed as an optical unit that can direct a laser beam onto the surface of the second layer so that the structures of the first layer that still protrude from the second layer are thermally smoothed. For this purpose, it may comprise lenses, mirrors, light guides or other optical components, which may be cooled or subjected to shielding gas. This thermal smoothing is carried out, for example, by melting and subsequent melting to a smoother surface or vaporising the structures. In this case, the material removal unit smoothes the surface in that the smoothing process transforms at least some of the structures in such a way that they disappear as a result of the smoothing process or are at least reduced in size in the direction of a more ideal surface. Thus, the smoothing by the material removal unit reduces the surface roughness of the reworked surface of the second layer. The structures that are thermally preferentially affected by the laser beam are those that have the greatest share in the surface texture or surface roughness of the surface of the second layer to be reworked. During reworking, vaporising can always be carried out particularly effectively and precisely if the structures to be vaporised are narrow and high, so that the thermal conductivity of the structures is significantly lower compared to the layer of the cladded material as an extended body. In this case, the vaporising of the respective structure can take place partially or completely.
This is particularly important, for example, in the case of metal-ceramic composite materials with grains in the form of needles made of carbide, nitride, oxide or similar materials, where the diameter of the needle is significantly smaller than the height with which they still protrude from the second layer. Since the second layer already covers the structures at least partially, the part of the structures to be vaporised or melted is smaller than the height of the structures with which they protrude from the first layer. Due to the thin shape of the structures, the energy injected by the laser beam cannot flow quickly enough over the structure into the second layer, so that the residual needles are heated so much that they vaporise without heating the cladded second layer too much. A laser beam guided over the surface vaporises the remaining structures and smoothes the surface considerably. The laser beam smoothes the surface in a continuous process in which the structures are not detected separately, but rather, depending on their length, pass through the laser beam in a statistical process and are thus smoothed or vaporised. Preferably, the laser cladding head is used as the material removal unit, since the optical components and the light source are already present and the parameters of the laser beam and the beam guidance only need to be adapted to the material removing purpose.
In an alternative embodiment, when the first layer is completely covered by the second layer, the latter is removed over the entire surface by the material removal unit at least until the structures are reached. For this purpose, the material removal unit can be designed, for example, as a grinding, milling or other mechanical processing unit. Such material removal units can remove the second layer over a large area, depending on the design, so that the reworking step can be carried out effectively and with as little reworking time as possible.
In a further embodiment, the material removal unit is configured to stop the removing when at least the highest or some of the highest structures protruding from the surface of the first layer are reached by the material removal unit as a result of the removing process. Thus, the structures protruding from the first layer do not yet determine the surface roughness of the second layer and thus that of the coated component, but they nevertheless substantially influence the strength of the overall layer comprising the first and second layers, which substantially contributes to the durability of the overall layer package.
In a further embodiment, the material removal unit comprises a sensor which, during the removing process, detects a transition between the sole removal of the material with second hardness to an at least partial removal of the structures with first hardness. The sensor may use any suitable technology to distinguish, for example, between a softer material (second layer) and a harder material (said structures of the first layer), a change in surface structure, surface roughness and/or other differences in properties between the first and second layers. In a preferred embodiment, the sensor is configured to detect the changing mechanical, optical and/or acoustic properties of the material to be removed at the transition. For this purpose, the sensor may be a force sensor, a torque sensor, a rotation speed sensor, a surface roughness sensor, an optical, tactile, capacitive, inductive or acoustic sensor.
In a further embodiment, the device comprises a plurality of laser cladding heads for (quasi-) simultaneous cladding of material on a surface of the component, all of which are supplied in the device with the material to be cladded and with laser radiation for carrying out the laser cladding. The term “(quasi-) simultaneous cladding” refers to the process of laser cladding whereby separate cladding tracks are cladded on the surface per laser cladding head simultaneously (in advance or in succession) with other cladding tracks by means of other laser cladding heads. This (quasi-) simultaneous cladding takes place at the same time, but at different positions on the component, i.e. at different locations on the component. Thus, the material cladded to the surface per time unit increases proportionally with the number of laser cladding heads. The separate cladding tracks can be adjacent to each other or, if necessary, at least partially overlap. If necessary, the separate cladding tracks can also be cladded directly on top of each other. The (quasi-) simultaneous cladding of material by means of several laser cladding heads enables an even more effective laser cladding process with a higher cladding rate for a wide range of materials at a shorter process time for the component than would be possible with only one laser cladding head. 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 cladded layer and helps to avoid layer defects such as crack formation by means of a process-appropriate feed rate. For example, when processing brake discs by means of laser cladding, previously usual processing times of 3-15 minutes can be reduced to less than 1 minute. In another embodiment, each laser cladding head applies the cladding track generated by it at least partially overlapping the adjacent cladding tracks generated by the other laser cladding heads, so that the material is cladded over the surface.
In a further embodiment, the laser cladding points generate cladding tracks with a material width along the feed direction on the surface, in which a first offset of adjacent laser cladding points is between 10% and 90%, preferably between 40% and 60%, particularly preferably 50%, of the material width of the cladding track. The term “adjacent laser cladding points” refers to two laser cladding points which produce cladding tracks of material cladded to the surface of the component, which are adjacent to each other and which can, if necessary, at least partially overlap in order to produce an areal cladding of the material. Adjacent laser cladding points can be generated by adjacent laser cladding heads. Here, adjacent laser cladding points and/or laser cladding heads do not necessarily designate laser cladding points or laser cladding heads that have the smallest geometric distance from one another, but are or generate those laser cladding points that generate adjacent cladding tracks. Due to the at least first offset of the adjacent laser cladding points to each other, the preheating of the component can be controlled in a targeted manner, which simplifies the processing of difficult-to-weld alloys or, depending on the alloy, makes it possible in the first place. The at least first offset of a suitable size also reduces the amount of reworking required.
In another embodiment, the adjacent laser cladding points on the surface of the component have a second offset from each other in the feed direction. Through this second offset of the laser cladding points, the preheating of the component can also be controlled in a targeted manner, in particular in interaction with the first offset, which further simplifies the processing of difficult-to-weld alloys or, depending on the alloy, makes it possible in the first place. The second offset with a suitable size, especially in interaction with the first offset, also further reduces the amount of reworking required. In this case, the laser cladding head with the second offset to the adjacent cladding track can be used to remelt the neighbouring cladding track in addition to cladding its own cladding track.
In a further embodiment, the device is configured to be cladded at least a third layer between the component and the first layer.
The invention further relates to a method for operating a device according to the invention for laser cladding, having a laser cladding unit with at least one laser cladding head arranged thereon for cladding material in the form of one or more adjacent cladding tracks onto a surface of a component for producing material layers resulting therefrom, one or more material sources for supplying the laser cladding head with the material to be cladded, and a laser beam source for supplying the laser cladding head with laser light for carrying out the laser cladding, and a material removal unit for processing the cladded material, comprising the following steps:
With the method according to the invention, a laser cladding process is effectively carried out, which enables a simple, reliable and less wear-intensive reworking effort.
In one embodiment of the method, wherein the structures each have a highest point and, in a valley between adjacent structures, the adjacent structures each have a lowest point associated therewith, a distance between the highest and lowest points of the respective structure representing the height thereof, the application of the second layer is carried out until the second layer protrudes from the first layer and covers the structures at least up to 20%, preferably at least 30%, more preferably at least 40%, particularly preferably at least 50%, of the average height of all the structures; alternatively, the second layer also completely covering the structures protruding from the first layer. In the latter case, the layer thickness of the second layer may be greater than the height of the highest structure protruding from the first layer.
In a further embodiment, the method comprises the further step of:
In a further embodiment of the method, the removing of the structures is carried out by the material removal unit vaporising or melting the structures, preferably the laser cladding head is used as the material removal unit for this purpose, or the removing of the second layer is carried out by the material removal unit removing the second layer over the entire surface at least until the structures are reached.
In a further embodiment, the method comprises the further step of:
In a further embodiment, the method comprises the further step of detecting, by means of a sensor of the material removal unit, a transition in the removing process between the removing of the second hardness material alone to an at least partially removing of the first hardness structures. In a further embodiment, the sensor detects the changing mechanical, optical and/or acoustic properties of the material to be removed at the transition.
In a further embodiment, prior to cladding the first layer, the method comprises the further step of cladding a third layer or further layers onto the component, onto which the first layer is then cladded.
In a further embodiment of the method, the material removal unit moves over the surface of the component in a manner analogous to the laser cladding head.
In a further embodiment, the method comprises using a plurality of laser cladding heads in the device for cladding the material, all laser cladding heads in the device being supplied with the material to be cladded and with laser radiation for carrying out the laser cladding.
The invention further relates to a component having a surface onto which a first layer of a material comprising structures protruding from the surface of the first layer and having a first hardness is cladded by means of a device or process according to the invention, and wherein a second layer of a material having a second hardness less than the first hardness is cladded to the first layer, wherein the second layer at least partially covers the structures protruding from the first layer and a surface of the second layer or the structures, respectively, have been shaped after the cladding of the first and second layers such that the structures no longer protrude from the second layer. In this case, the material of the second layer may be a metal or a metal alloy. Here, the first layer may comprise a composite material having a matrix material with a third hardness less than the first hardness, preferably the first layer comprises the composite material where the structures are embedded in the matrix material. Here, the composite material may be a metal-ceramic composite material containing grains forming the structures, preferably the grains are carbide grains. Here, the material of the second layer may be the matrix material of the first layer. Here, a third layer may be cladded on the surface to which the first layer is cladded.
The embodiments listed above may be used individually or in any combination in deviation from the dependencies in the claims to each other for designing the devices or methods according to the invention.
These and other aspects of the invention are shown in detail in the figures as follows.
It is understood that the embodiment example explained above is only a first embodiment of the present invention. In this respect, the embodiment of the invention is not limited to this embodiment example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 106 823.9 | Mar 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2020/100787 | 9/9/2020 | WO |
