WO2023174484A1 - Method for reprocessing a coated workpiece - Google Patents

Abstract

The invention relates to a method for reprocessing a coated workpiece (1), comprising the following steps in the stated order: a) determining, by means of a processor (2) and using a measuring device (3), a quality of a form of a workpiece to be inspected (1); b) establishing, by means of a processor (2) by the use of a predefined form limit value (4) and on the basis of the determined form of the workpiece (1) to be inspected, whether the form has a sufficient level of quality, c) in the event of a level of quality established as sufficient in step b), determining, by means of a processor (2) on the basis of the form of the workpiece (1) to be inspected as determined in step a), a layer height (5) to be removed; d) removing the determined layer height (5) by means of a machining tool (6). With the method proposed here, a used workpiece can be economically reprocessed and thus can be reused.

Description

Method for reprocessing a coated workpiece

The invention relates to a method for reprocessing a coated workpiece, and to a machining center with such a method for reprocessing a coated workpiece.

It is a challenge to keep materials and effort as well as carbon dioxide emissions low. This goal is pursued with great effort in almost all branches of industrial production and is in demand by customers. An important step in this direction is to switch from complex and expensive solid material products to cost-effective materials and to provide them with a functional coating. For example, for brake discs, cast bodies with a stainless steel coating and embedded friction materials, such as carbides, are used. This coating can be applied, for example, using deposition welding or diffusion coating. However, such a component also has a limited service life, especially due to unavoidable abrasion, for example as a result of emergency braking, and the brake disc must then be replaced with a new one. The sustainability of this approach is physically limited.

The general aim is therefore to find a coating that has an increasingly longer service life. However, the limits of feasibility are encountered in view of permissible peak loads (albeit possibly rare) and increasing costs for materials.

Proceeding from this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art. The features according to the invention result from the independent claims, to which advantageous embodiments are shown in the dependent claims. The features of the claims can be combined in any technically sensible manner, for which the explanations from the following description and features from the figures, which include additional embodiments of the invention, can also be consulted. The invention relates to a method for reprocessing a coated workpiece, comprising the following steps in the order mentioned: a. using a processor and using a measuring device, determining a quality of a shape of a workpiece to be tested; b. based on the specific shape of the workpiece to be tested, using a predetermined shape limit value by means of a processor to determine whether the shape has sufficient quality. c. at one in step b. quality determined to be sufficient, based on the quality in step a. certain shape of the workpiece to be tested, using a processor to determine a layer height that is to be removed; d. using a processing tool, removing the specific layer height.

Ordinal numbers used in the preceding and following descriptions, unless explicitly stated to the contrary, only serve to clearly distinguish them and do not reflect the order or ranking of the designated components. An ordinal number greater than one does not mean that another such component must necessarily be present.

The reprocessing process proposed here proposes a completely new approach to the resource-saving production of a workpiece. While the recycling route, for example the re-melting of gray cast iron material, has been established, reuse and the associated reprocessing required for this have not yet been considered. This is understandable not only because of the effort involved and the costs to be feared, but also because the technologies that enable this are not yet widely known in the relevant specialist circles, let alone the associated possibilities. Nevertheless, the reprocessing of a workpiece offers enormous savings in terms of new material, energy use and costs can be neutral or even a saving can be achieved.

It should be noted that the steps listed may give the impression of a complex process, but they are significantly less complicated than recycling, especially since quality assurance is also necessary there is. It should also be noted that some steps can be carried out by hand, but are preferably integrated into a highly automated or even fully automated process.

During operation, unfavorable loads can occur on a workpiece, for example due to incorrect installation, excessive stress or not being removed in a timely manner. But a bad prerequisite is if the workpiece was on the edge of the permissible tolerances from the start and has now exceeded these tolerances as a result of (for example normal) loading and/or service life. A bad load may also mean insufficient (sufficient) use, for example pitting of rust due to a lack of abrasive load on the surfaces and/or a lack of oil use.

Such workpieces must be sorted out as early as possible in the reprocessing process. Sorting out does not necessarily mean sending it for recycling, but rather possibly requiring additional processing effort, i.e. sending it into a more complex process for reprocessing.

The quality of a mold here is, for example, a rust-degraded surface of the body of the workpiece, a distortion of the body (e.g. bowls from a brake disc) due to excessive thermal stress, a twisting of the body due to an excessive torque load, a corrugation of the surface, for example of locally very different thermal loads or an impact, concentricity, an impermissible deviation from roundness, axial runout, flatness and other possible deviations. It should be noted that it is not necessarily necessary to check all possible deviations, but only those that are relevant for the subsequent steps and can therefore affect the result of the reprocessing.

If the selected test steps for determining the quality of the shape of the workpiece to be tested is completed with a positive result, step b follows. It should be noted that exceeding specified values is also possible Tolerances are possible if these tolerances can be compensated for by post-processing. More details are explained below.

If the selected inspection steps for determining the quality of the shape of the workpiece to be inspected in step b. with a positive result (i.e. sufficient quality within a predetermined shape limit value), step c follows. The predetermined shape limit value for determining the quality of the workpiece is defined according to the type of possible deviation. A shape limit value generally includes a plurality of shape specifications, which may be independent of one another. It should be noted that it is also possible to exceed the tolerances specified for a new (i.e. not reprocessed) workpiece if these tolerances can be compensated for by post-processing. More details are explained below. The shape limit value is therefore not necessarily identical to the tolerance specifications for a new workpiece.

It should be noted that the workpiece has a coating and this coating is the defining property of the workpiece. If a shape deviation can be compensated for by means of a new coating, this is a permissible shape in one embodiment of the reprocessing method, i.e. the shape limit is adhered to and the quality is sufficient.

A particular advantage of the process is that it only removes as much of the existing coating as is necessary. For example, in the case of a coating that is subject to frictional wear, often only an upper layer of the coating is worn away or affected by the formation of grooves. In many applications it is then sufficient to replace this missing layer, although removal of an additional layer (which still exists and is determined to be intact) is generally necessary at least for a required safety factor.

For example, a one hundred percent test of the shape is not carried out, but rather a test at a number of measuring points and the quality is estimated from this. Preferably, the relevant surface is scanned completely and this additional effort is reflected in a significantly reduced amount of time, Production costs and/or material costs offset. It should be noted that even with a complete test, the entire tested surface is not necessarily examined, but rather a cloud of points is usually generated, with the distances between these points being so small that the estimate is sufficiently accurate and can therefore be considered a hundredth Percentage test can be viewed.

If the layer height (to be removed) in step c. is determined, it is then removed, for example by machining or (for very small amounts of material) by water jet removal or laser removal.

The workpiece prepared in this way can now be integrated into a process for new workpieces. The reprocessing is preferably completed by applying the required layers to form the desired coating on the same machine tool.

It should be noted that the layer height to be removed is not necessarily constant over the entire surface of the workpiece to be reprocessed. For example, a shape deviation is permitted up to the limits of the tolerance from the shape limit value, so that in some areas the layer height to be removed is greater than elsewhere.

It is further proposed in an advantageous embodiment of the method that e. using a processor and using a measuring device, determining a quantity and quality of a layer structure of a coating on a surface of a workpiece to be tested; f. at one in step e. Quantity and quality of the layer structure determined to be sufficient, based on that in step e. certain layer structure, using a processor to determine a layer height that is to be removed; and G. using a processor to determine, based on a predetermined removal limit value, whether the layer height is sufficiently low for necessary removal, with steps e. to g. before step d. are carried out, and / or wherein the steps in step c. and in step f. certain layer heights to be removed are accumulated and in a step g. based on a predetermined one Removal limit value determines whether the workpiece has sufficient quality.

While the checking of the shape of the workpiece to be reprocessed was described above, the analysis of the layer structure of the workpiece to be reprocessed is described here. It is considered advantageous to first check the shape and only then check the quantity and quality of the layer structure. This is because, for example, a distortion cannot be compensated for by an excessive new layer application and/or other deviations from the tolerated shape, for example a corrugation, can only be compensated uneconomically by means of a new layer structure. However, it should be noted that removing material from the base body (i.e. base material) can certainly be economical, with the excessively removed base material either being reprocessed with a coating according to a new coating to a final shape within the manufacturing tolerance for a new workpiece . Alternatively, an application with an additional layer is possible, for example from a welding filler material that is less expensive than the welding filler material of the regular (i.e. like a new workpiece) coating, preferably at least similar to the base material, in order to be able to meet the required shape tolerance.

The layer structure of the workpiece to be reprocessed is possible, for example, by means of a (destructive) sample, for example outside a functional area, preferably within a functional area. The affected area of the sample is closed again by applying material or can remain that way due to appropriate tolerances (e.g. the size) of the functional surface. Such a layer structure is analyzed, for example, by means of gas chromatographic analysis together with a gradual, for example layer-by-layer, and thus time-separated removal.

It should be noted that an analysis of the layer structure also involves testing the quality of the material, especially the remaining material, for example by means of X-ray testing to determine crack formation and/or embrittlement. It should also be noted that quantity primarily affects the amount and distribution of the coating to be reprocessed. In addition, the quantity of functional substances or functional particles, often referred to as doping, is often an important aspect. For example, in the case of a brake disc, the number of hard material particles that can be torn out of the embedding as a result of use is important. Even if the embedding layer is OK, it must then be removed and replaced because this is the only way new hard material particles can be embedded, for example when introduced into the melt. If the test of the layer structure and the resulting new layer height to be applied result in the existing hard material particles (possibly in sufficient quantities) being covered, i.e. enclosed, then this otherwise intact layer may still have to be removed in order to embed new hard material particles, which safely protrude beyond the level of the embedding material of the coating.

In step f. such a layer height to be removed is determined. As a rule, the lower the layer height to be removed, the lower the costs. Deviating from this, it may be more cost-effective to completely remove a specific layer with a specific property or a homogeneous composition and reapply it. For example, in the case of a brake disc with a two-layer structure of the coating with a binder layer and a hard material particle layer, it is advantageous to remove the entire hard material particle layer. In another example, it is advantageous to remove the entire coating and also a little of the base material of the workpiece in order to also remove a diffusion zone and/or to prevent measurement inaccuracies or manufacturing inaccuracies during removal. This removal of base material is preferably kept so low that the coating does not have to have a greater (new) layer height than a layer height for a new workpiece, while still maintaining the tolerances for a shape limit value. With such a procedure, unevenness and/or undulations in the workpiece are preferably compensated for and/or a defined roughness is created for optimal material application. If it turns out that the necessary removal is too great for economical reprocessing, the workpiece is sent to scrap, for example for a recycling process.

In one embodiment, the steps mentioned here are e. to g. after step d. executed. This has the advantage that the shape is already determined and only the remaining coating needs to be analyzed.

The steps mentioned here are preferred: e. to g. before step d. executed. This has the advantage that the deviations from the shape limit and the properties of the layer structure are first considered (in accumulation) before further (possibly unnecessary) effort is applied to a potential scrap workpiece. A removal limit value is therefore set, in which both the quality of the shape (shape limit value) and the quantity and quality of the layer structure are taken into account, and the (overall) quality is determined exclusively in compliance with the removal limit value and a decision is made on subsequent processing based on this.

Accumulation here does not mean a pure addition of the determined values of the layer height to be removed, but rather an overlap at least in some areas when the connections are taken into account.

It should be noted that the layer height to be removed is not necessarily constant over the entire surface of the workpiece to be reprocessed. For example, a quantity of the layer structure is permitted up to the limits of the tolerance from, for example, the shape limit, so that in some areas the layer height to be removed is greater than elsewhere. Furthermore, for example, a shape deviation is permitted up to the limits of the tolerance from the shape limit value, so that in some areas the layer height to be removed is greater in comparison to the other due to the shape or due to the quality of the layer structure.

It is further proposed in an advantageous embodiment of the method that in a step h. using a coating tool new coating at least on the one in step d. treated and to be coated surface of the workpiece is applied.

Here, as already mentioned above, it is suggested that the workpiece be provided with a new coating (preferably in the same machining center). In an advantageous embodiment of the method, the new coating is identical to a coating for a new workpiece. This is advantageous in a complex approval process in which a deviation of the layer structure from that of an approved new layer structure outside of a permissible manufacturing tolerance would require a new approval.

In another embodiment, the layer structure may be individually adapted to the workpiece to be reprocessed, with approval of the coating being subject to wide limits and/or not being necessary. If necessary, logging the respective layer structure is sufficient. This protocol is, for example, linked to a serial number or made available for individual workpieces in an integrated memory chip (for example designed as RFID [radio-frequency identification] or NFC [near field communication]).

It is further proposed in an advantageous embodiment of the method that the layer structure is tested non-destructively, preferably using at least one of the following methods:

- Eddy current testing;

- X-ray examination; and

- Surface scan together with an associated coating certificate.

In this advantageous embodiment, the (old) layer structure is tested non-destructively. A common method that can be used for this is eddy current testing, which is based on the magnetic resistance and/or the alignment of the magnetic field lines. For example, an increased number of cracks or an enlargement of (possibly desired) cracks can be easily checked. Also is the number of Hard material particles can therefore be determined stochastically. Another common procedure is X-ray testing, in which, among other things, cracks and inclusions as well as differences in material density can be visualized.

A very cost-effective procedure is a surface scan. Here, the property of the (old) surface is recorded, for example in the resolution range of a usual roughness measurement, namely as a height profile. In an advantageous embodiment, a reflection property and thus a conclusion about the type of material is also recorded.

The surface scan is particularly preferably used together with a coating certificate, although this is also advantageous in the aforementioned and other test methods for determining the layer structure. The information in the coating certificate from the once new coating that is now to be replaced or reprocessed preferably includes not only the (theoretical or probable) layer structure, but preferably the level of detail of the old layer structure, carried out at approximately the same resolution as the surface scan, before the workpiece is put into operation. The new measurement allows conclusions to be drawn about events that cannot otherwise be determined from the outside (i.e. non-destructively). If there is any doubt about the quality, the committee can then follow suit or a destructive test can be carried out. On the other hand, in the case of a largely intact surface, on which only a (remaining) layer height has been reduced by abrasion compared to the new condition, no further test than a surface scan may be necessary. In an advantageous embodiment, this test is therefore preceded by further potentially subsequent (possibly also non-destructive) tests.

It should be noted that in one embodiment the surface of the workpiece to be reprocessed is formed from the solid material, i.e. the functional surface is formed by the body of the workpiece, for example from a stainless steel cast body, which has preferably been prepared as a functional surface by means of machining. Here too, an (old) layer structure can be checked, for example corrosion progression and/or crack formation. In one embodiment, at least a worn portion of the layer structure removed and the workpiece made usable again by means of a subsequently applied (new and in this case for the first time) coating.

It is further proposed in an advantageous embodiment of the method that the layer structure is destructively tested, preferably with material removal, using at least one of the following methods:

- microscopic sectional image;

- Mass spectrometry and/or gas chromatography, preferably laser-induced plasma spectroscopy; and

- gradual surface removal together with a chemical analysis, with the material being preferably removed from outside a functional area.

In this advantageous embodiment, the (old) layer structure is destructively tested. As already mentioned above, in one embodiment, a sample is taken in the area of the functional surface, with which a meaningful sample (material removal) can be taken for the effects on the (old) coating or (old) solid material surface over the course of its life. Alternatively or additionally, a sample is taken outside of a functional surface, so that no impairment is to be expected if the layer is removed less than the entire (existing) layer structure. However, it should be pointed out again that if material is removed appropriately in the area of the functional surface, there does not necessarily have to be an impairment of the function, either although it is then left as is or by the material removed being replenished or at least covered (for example against corrosion).

The material removal can be analyzed using common methods, for example using a microscopic sectional image, whereby the layer structure is clearly visible. Alternatively or additionally, mass spectrometry, gas chromatography, particularly preferably laser-induced plasma spectroscopy [LIBS] can be carried out. The respective procedure is scheduled based on availability and an expert decision on the significance. A similar process in which lower costs and/or other The focus can be on chemical analysis, whereby a layer structure can be analyzed using staggered (i.e. stepwise) surface removal.

It should be noted that one or more destructive analysis(s) of the layer structure can also be carried out in combination with one or more non-destructive analysis(s).

It is further proposed in an advantageous embodiment of the method that if based on the results of step b. and/or step g. If it is determined that a layer height that is too high for a predetermined use needs to be removed, one of the following decisions is made:

- declare the workpiece in question as scrap;

- remove the specific layer height and prepare it for: i. another use for which the workpiece is still suitable; or ii. Building up the excessively removed layer, preferably using additive manufacturing.

For an overall cost-effective reprocessing process, it may be advantageous if a layer height to be removed that is determined to be too large leads to scrap, for example for recycling the material of the workpiece. In an overall calculation, however, it is sometimes advantageous in terms of costs if a layer height that is initially too large to be removed still leads to the workpiece being reprocessed. This is the result, for example, if an analysis has already been carried out, which reduces the effort for later quality assurance. This is the case if the coating for reprocessing does not require further testing of the shape of the workpiece because thermal distortion or other consequences of the coating beyond a permissible tolerance can be excluded. It is also the case when, due to the type of processing center or the infrastructure in which the reprocessing process is integrated, the short distances and processing times enable otherwise uneconomical (re)coating. This is also the case if there is a minimum amount of reprocessed workpieces (e.g contractually) must be guaranteed or excessive waste is associated with (e.g. financial and/or legal) disadvantages.

In the example of a brake disc, for example, a brake disc must be designed with a specific (axial) thickness, for example not because of thermal load, but because of the installation situation. At the same time, the brake disc with a smaller thickness (as a result of reprocessing) can be reused for a different installation situation and/or reusable together with an adjustment to the installation situation. This means that the only thing that needs to be reduced is the service life for the second use of the brake disc. Alternatively or additionally, the second-use brake disc can be used in a smaller (lighter) and/or slower vehicle in which a thinner brake disc can or should be used, i.e. a larger layer height to be removed is permissible. Such connections have, for example, already been considered when preparing for initial use or have been taken into account as an option when designing a new generation of vehicles. It should be noted that the method proposed here is primarily intended to reprocess the workpiece for the same use. At the same time, reprocessing for another, for example similar, purpose is also a goal of the method proposed here. In one embodiment, for a workpiece that is discarded in this step, the remains of the (old) coating (made of a material that is generally of higher quality or at least processed differently) are removed beforehand and sent separately for reuse.

Alternatively or additionally, part of the base material is rebuilt, for example using additive manufacturing such as deposition welding. If the functional coating, i.e. the actual coating on a new workpiece or reprocessed workpiece corresponding to the new condition, is also built up additively, the effort is not cost-relevant due to the existing tools and infrastructure, with preference being given to rebuilding a part of the base material in comparison to that Functional coating cheaper welding filler material is used. It is further proposed in an advantageous embodiment of the method that a coating of a surface of a workpiece to be tested is completely removed, with base material preferably also being removed.

The advantage of this embodiment of the reprocessing method is that the quantity and quality of the (old) coating does not necessarily have to be determined. This can be advantageous for high cycle times and/or low measurement effort (possibly cost-relevant). It also opens up the possibility of applying a new type of coating, which, for example, meets higher environmental standards, has a longer service life and/or causes reduced abrasion (fine dust) under the same load. An adaptation to a different counterpart or other lubricants is also possible, for example in the case of a brake disc the friction lining of a brake pad or in the case of a piston a different oil with, for example, a different viscosity.

In one embodiment, base material is also removed, preferably as little as possible being removed so that a desired thickness tolerance can be maintained without additional layers of welding filler material. Particularly preferably, a (for example standardized) coating approved for coating a new workpiece is applied to the workpiece to be reprocessed, from which base material has been removed. One advantage of removing base material is that the old coating is safely removed even within tolerances and an ideally prepared surface can be created for coating.

It is further proposed in an advantageous embodiment of the method that a depth of removal penetrating into the base material of the workpiece is a maximum of 10 pm to 200 pm.

In this embodiment, base material is removed, with minimal

10 pm [ten micrometers] to a maximum of 200 pm, preferably a minimum of 20 pm to a maximum

100 pm, particularly preferably around 50 pm, is removed so little that one desired thickness tolerance can be maintained without additional layers of welding filler material. Particularly preferably, a (for example standardized) coating approved for coating a new workpiece is applied to the workpiece to be reprocessed, from which base material has been removed. One advantage of removing base material is that the old coating is safely removed even within tolerances and an ideally prepared surface can be created for coating.

In one embodiment, the workpiece to be reprocessed does not have any coating in advance, but rather the surface of the solid material is designed as a functional surface. Here too, it is worth reprocessing with a coating that preferably differs from the solid material. In some cases, the new coating to be applied and the base material will be compatible in such a way that only a few layers and particularly preferably a homogeneous coating can be applied. With the advantageous values stated above (but not necessarily to be used in such a case), a worn surface can be safely removed from a sufficiently large number of workpieces that are potentially to be reprocessed and at the same time the new coating to be applied can be achieved within the framework of a cost approach and/or a (preferably standardized) Thickness of an approved coating.

It is further proposed in an advantageous embodiment of the method that for step e. a material, preferably as a running ring, is removed, preferably turned, from the outer edge of a surface of the workpiece to be tested.

The outer edge may be outside of a (at least new) functional surface and therefore does not need to be reapplied. In another case, a completely new layer structure can be created with little effort in terms of costs, processing time and material and/or risk. In addition, the outer edge is easily accessible for removal, for example by turning off a rotary workpiece. It should be noted that in one embodiment the removed material is analyzed (e.g gas chromatography) and/or an optical inspection (for example a micrograph) of the adjacent material is carried out.

A circumferential ring provides information about the state of wear of the (old) coating or solid material surface over a number of sections. This allows a sufficiently precise statement to be made about the necessary extent of reprocessing.

It is further proposed in an advantageous embodiment of the method that a workpiece after step h. the desired properties of the workpiece as a new part are met.

According to a further aspect, a machining center for reprocessing a coated workpiece is proposed, having at least the following components:

- a measuring device;

- an editing tool; and

- a processor, wherein the processing center is set up to carry out a method according to an embodiment according to the above description.

The processing center proposed here is a compact device which, with short distances and (at least for this purpose) complete infrastructure, enables reprocessing according to an embodiment of the method described here in a particularly cost-effective manner. The measuring device is set up for at least one of the aforementioned measuring methods in order to determine the surface and/or the layer structure of the workpiece to be reprocessed. For example, the measuring device includes laser optics and/or a chemical-physical analysis unit, such as a gas chromatograph.

The processing tool comprises at least one tool by means of which material can be removed, for example by cutting or vaporizing using a laser. In an advantageous embodiment, using the same processing tool, If necessary, a new coating can be applied to the respective workpiece using a different tool. The processing tool also includes a tool chuck in order to fix the workpiece and, if necessary, also to move it in the analysis process and/or coating process. It should be noted that the processing tool and also the measuring device are not necessarily a compact unit, but in one embodiment comprise a plurality of subunits that may be spatially and/or control-technically separate from one another. In one embodiment, the processing tool comprises a turning tool and laser optics, for example for extremely high-speed laser deposition welding [EHLA],

The processor is set up to control at least one component, preferably a plurality of components of the machining center. For example, the processor is part of a control device for controlling, and preferably also regulating, at least one of the processes that can be carried out using the processing center. In one embodiment, the processor or the control device is integrated into the processing center. In one embodiment, the processor or the control device is docked to the processing center, for example as an edge device, and is set up for communication directly or indirectly with the actuators and sensors of the processing center. In one embodiment, the processor is arranged outside the processing center and is part of the cloud for communication with a control device integrated there or docked thereto as well as with the cloud or as a computer.

The invention described above is explained in detail below against the relevant technical background with reference to the associated drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, although it should be noted that the drawings are not true to size and are not suitable for defining size relationships. It is presented in

Fig. 1: a flowchart of a method for reprocessing a coated workpiece; Fig. 2: a machining center with a workpiece;

Fig. 3: a workpiece in a worn condition;

Fig. 4: the workpiece according to Fig. 3 with the coating partially removed; and Fig. 5: the workpiece according to Fig. 3 and Fig. 4 with newly applied coating.

1 shows a flowchart of a method for reprocessing a coated workpiece 1. In one step a. The method determines the quality and shape of a workpiece 1 using a processor 2 and a measuring device 3. The quality of a mold here is, for example, a rust-degraded surface 9 of the body of the workpiece 1, a distortion of the body (e.g. bowls from a brake disc) due to excessive thermal load, a twist of the body due to an excessive torque load, and/or others possible deviations.

In step b. is based on step a. determined whether a predetermined shape limit value 4 is met, i.e. whether it has sufficient quality. The shape limit value 4 is stored in a memory 18.

If in step b. If sufficient quality has been determined, step c. A layer height 5 to be removed is determined by means of the processor 2. The layer height 5 to be removed is determined in such a way that (from an economic point of view, at least on average) only as much of the existing coating 8 is removed as is necessary individually or according to predetermined empirically determined requirements. For example, in the case of a coating 8 that is subject to frictional wear, often only an upper layer of the coating 8 is removed or affected by the formation of grooves. In many applications it is then sufficient to replace this missing layer, although removal of an additional layer (which still exists and is determined to be intact) is generally necessary at least for a required safety factor.

In the embodiment shown, step c. Steps. and step f. executed. In this embodiment, preferably using the captured shape from step b., by means of the processor 2 using the Measuring device 3 determines a quantity and quality of a layer structure 7 of the coating 8 of the surface 9 of the workpiece 1. For example, a distortion cannot be compensated for by an excessive new layer application and/or other deviations from the tolerated shape, for example excessive corrugation, can only be compensated uneconomically by means of a new layer structure 7.

In step f. based on the data in step e. determined quality and quantity of the (old) layer structure 7 determines a layer height 5 to be removed. As a rule, the lower the layer height 5 to be removed, the lower the costs. Deviating from this, it may be more cost-effective to completely remove a specific layer with a specific property or a homogeneous composition and reapply it.

For example, in the case of a brake disc with a two-layer structure of the coating 8 with a binder layer 19 and a hard material particle layer (functional layer 20), it is advantageous to remove the entire hard material particle layer.

It should be noted that both in step c. as well as in step e. until step f. a layer height 5 to be removed is determined. In this preferred exemplary embodiment of the method for reprocessing a coated workpiece 1, the respective specific layer height 5 to be removed is accumulated, with step c. and the steps e. to f. run in parallel in this exemplary embodiment. Accumulation here does not mean addition, but rather an at least partial overlap when considering the connections. For example, a shape deviation is permitted up to the limits of the tolerance from the shape limit value 4, so that in some areas the layer height 5 to be removed is greater in comparison to the other due to the shape or due to the quality of the layer structure 7.

In a subsequent step g. a predetermined removal limit value 10 is used to determine whether the workpiece 1 has sufficient quality. This has the advantage that the deviations from the shape limit value 4 and the properties of the layer structure 7 are first considered (in accumulation) before further (possibly unnecessary) effort is required for a potential Reject workpiece is applied. A removal limit value 10 is therefore set, in which both the quality of the shape (shape limit value 4) and the quantity and quality of the layer structure 7 are taken into account, and the (overall) quality is determined exclusively in compliance with the removal limit value 10 and based on this subsequent processing decided.

If the workpiece 1 or the shape and/or the layer structure 7 of the workpiece 1 has an insufficient (overall) quality in accumulation, the workpiece 1 is declared as scrap in the process for reprocessing in this exemplary embodiment of the process or sub-step i follows . or substep ii..

If the workpiece 1 (for example, was designed as a brake disc for a motor vehicle, but) no longer meets the shape limit value 4 for use (as a brake disc for a motor vehicle), the (rejected) workpiece 1 is, for example, sent for melting down, preferably after Beforehand, the remains of the (old) coating 8 (made of a material that is generally of higher quality or at least processed differently) are removed and reused separately.

If the workpiece 1 (for example, was designed as a brake disc for a motor vehicle, but) no longer meets the shape limit value 4 for an equivalent use (as a brake disc for a motor vehicle), then in sub-step i. The (rejected) workpiece 1 is prepared, for example, for a different purpose (for example a smaller, lighter and/or slower motor vehicle) because there are lower demands on the workpiece 1.

If the workpiece 1 (for example, was designed as a brake disc for a motor vehicle, but) no longer meets the shape limit value 4 for an equivalent use (as a brake disc for a motor vehicle), then in sub-step ii. as a counterproposal to sub-step i. decided that in step d. too much is removed. So it will be in sub-step ii. following step d. a layer thickness of base material 13 of the workpiece 1 that is too large for dimensional accuracy in conjunction with a (for example approved) tested coating 8 removed. The base material 13 that has been removed in excess is then removed in step h. applied again, for example by means of a thicker (possibly different type) coating 8 and/or by means of a filling layer.

If the workpiece 1 (for example, was designed as a brake disc for a motor vehicle and) meets the shape limit value 4 for equivalent use as a brake disc for a motor vehicle, then step d is carried out immediately. executed. No filling layer or thicker coating 8 is then applied here.

In step d. The layer height to be removed is 5, which is in step c. or step f. was determined, removed. The workpiece 1 prepared in this way can now be integrated into a process for new workpieces 1 or is processed in a subsequent step h. (re)processed.

In a final step h. A new coating 8 is applied using a coating tool 11 of the machining center 17, at least on the surface in step d. treated and to be coated surface 9 of the workpiece 1 is applied. In an advantageous embodiment of the method, the new coating 8 is identical to a coating 8 for a new workpiece 1. Following on from substep ii. the new coating 8 comprises a greater layer thickness and/or a further filling layer.

In Fig. 2 a machining center 17 with a workpiece 1 is shown in a schematic spatial view. The workpiece 1 here is purely optionally a rotary workpiece 1, which can be rotated about an axis of rotation 21 during reprocessing, and is rotated in a direction of rotation 22, for example, fixed by means of a chuck during the process. For example, the workpiece 1 is a brake disc.

The workpiece 1 comprises a base material 13, which is set up, for example, as a thermal and mechanical support for a surface 9 serving as a functional surface 12. In this exemplary embodiment, the base material 13 is with a coating 8 having a plurality of layers Mistake. An (intermediate) layer of the coating 8 is, for example, a binder layer 19 and the second (outer) layer forms the functional surface 12. Hard material particles 23, for example, are embedded within the (outer) layer (see FIG. 3).

The machining center 17 shown here is set up to carry out a reprocessing process from measuring to recoating. A measuring device 3 is provided to record the quality of the shape of the workpiece 1 (step a.). Here, from the measuring device 3, a laser optics 24 with a movable mirror 25 for generating a surface scan and a gas chromatograph 26 (for example for high performance liquid chromatography [HPLC]) are shown purely by way of example. All components of the measuring device 3 are preferably set up on both sides for measuring all relevant surfaces 9. Furthermore (purely optional) to determine the layer structure 7 in step e. a chip-removing machining tool 6 (here designed as a turning tool) is provided, for example by removing a ring 15 of material on the outer edge 16 of the workpiece 1 by machining and using the measuring device 3 to determine the layer structure 7 of the coating 8 of the workpiece 1. This allows a micrograph to be made on the cut edge in question or the composition of the individual layers to be chemically or physically determined by means of gradual removal at the appropriate resolution. The elements of the measuring device 3 mentioned are purely exemplary. The specific data of the layer structure 7 or the shape of the workpiece 1 are transmitted to a control device 27, which comprises a processor 2 and a memory 18, of the measuring device 3.

The processor 2 is set up to carry out at least part of the method for reprocessing a coated workpiece 1. For example, before step d. a layer height 5 to be removed is determined by the processor 2 and in step d. This layer height 5 to be removed is removed by means of the processing tool 6 (compare FIG. 4), so that, for example, the functional surface 12 and one underneath are arranged Binder layer 19, and preferably a small proportion of the base material 13 is removed.

In the embodiment of the machining center 17 shown, a (re)application of a coating 8 can also be carried out using a coating tool 11, for example a laser with a powder nozzle for a welding filler material (step h.). The coating 8 is applied to the workpiece 1, for example, using extreme high-speed laser deposition welding [EHLA],

In Fig. 3 a workpiece 1 is shown in a worn state in a schematic sectional view. In the exemplary embodiment of a workpiece 1 shown here, for example a brake disc, a layer structure 7 of the coating 8 is provided, in which, as shown, a binder layer 19 is arranged adjacently above the base material 13 and a functional layer 20 is arranged adjacently above it. The binder layer 19 is intended for the mechanical connection between the base material 13 of the workpiece 1 and the functional layer 20. It should be noted that this configuration of the layer structure 7 is a frequently used one, but a larger number of different layers 19, 20 or even a single (then functional) layer 20 is also possible.

In the embodiment shown, the functional layer 20 comprises hard material particles 23, with some defects 28 being visible where hard material particles 23 have been torn out. Furthermore, in comparison to the following FIG. 5 it can be seen that the thickness of the functional layer 20 is significantly reduced.

Furthermore, it can be seen that the workpiece 1 is bowled overall or in the area of the surface 9 to be tested, i.e. a central depression is formed in the (old) base area 29 compared to the outer edges shown (left and right) as shown. In this example, however, this deviation from the ideal is still within the shape limit value 4, which is shown here with a dash-colon line. This shape limit value is preferably 4 (at least in this constellation) is congruent with the removal limit value 10, i.e. the maximum layer height 5 that can be removed economically and/or permissibly. It should be noted that the shape limit value 4 does not necessarily have to correspond to an ideal straight line, for example because other mechanical requirements are placed on the functional surface 12 in some areas .

It should be noted that, on the one hand, the illustration is purely schematic and, on the other hand, in no way describes the wear conditions conclusively. Rather, grooves, cracks and broken-off material, as well as corrosively decomposed areas of the coating, are common phenomena. With regard to the shape, corrugations and axial runout errors and others should be mentioned.

4 shows the workpiece 1 according to FIG. 3 with the coating 8 partially removed. Please refer to the previous description for the components shown. Here, a minimum layer height 5 to be removed is determined, which includes a depth 14 of removal of base material 13 in order to remove the coating 8 just completely. If necessary, a little more than this is removed, for example a safety factor of 2 pm [two micrometers]. In this example it can be seen that the removal limit 10 is not fully utilized, but a new base area 30 is formed above it. It is therefore possible to apply a thinner (new) coating 8. In one embodiment, the binder layer 19 is completely or sufficiently intact. The layer height 5 to be removed is then set just so that the binder layer 19 (as far as the shape deviation allows) remains complete or at least a portion remains, preferably at least so much that no base material 13 has to be removed. For some applications, for example, it is advantageous to replace at least part of the binder layer 19 because a new coating 8 has different requirements and/or better properties than the old binder layer 19.

In Fig. 5 the workpiece 1 according to Fig. 3 and Fig. 4 is shown with newly applied coating 8. Please refer to the previous description for the components shown. In the process according to FIG. 4, a new base area 30 has been created. The old base area 29 is shown in dashed lines in comparison. Furthermore, for better orientation, the dimensions for the removed layer height 5 and the depth 14 of the removed base material 13 are shown. In one embodiment, the new binder layer 19 is equal to the removed old binder layer 19 in terms of thickness and/or metallurgical composition. In one embodiment, the new functional layer 20 is the same as the old removed functional layer 20 in terms of thickness, metallurgical composition and/or additives (here shown the hard material particles 23). In this example, the new functional layer 20 is, as is probably the most common case, thicker than the removed old functional layer 20. With the method proposed here, a used workpiece can be reprocessed in a cost-sensitive manner and can therefore be reused.

Reference character list

Workpiece Processor Measuring device Form limit Layer height to be removed Processing tool Layer structure Coating Surface to be tested

Removal limit coating tool functional surface

Basic material

Depth of a removal of base material removed ring for testing outer edge

Machining center storage

Binder layer functional layer rotation axis direction of rotation hard material particles laser optics movable mirror

Gas chromatograph control device defective area old base area new base area

Claims

Patent claims 1 . Method for reprocessing a coated workpiece (1), comprising the following steps in the order mentioned: a. using a processor (2) and using a measuring device (3), determining a quality of a shape of a workpiece (1) to be tested; b. based on the specific shape of the workpiece (1) to be tested, using a predetermined shape limit value (4) to determine by means of a processor (2) whether the shape has sufficient quality. c. at one in step b. quality determined to be sufficient, based on the quality in step a. certain shape of the workpiece (1) to be tested, determining by means of a processor (2) a layer height (5) which is to be removed; d. using a processing tool (6), removing the specific layer height (5). 2. The method according to claim 1, further comprising the following steps: e. using a processor (2) and using a measuring device (3), determining a quantity and quality of a layer structure (7) of a coating (8) of a surface (9) of a workpiece (1) to be tested; f. at one in step e. Quantity and quality of the layer structure (7) determined to be sufficient, based on that in step e. certain layer structure (7), by means of a processor (2) determining a layer height (5) which is to be removed; and G. based on a predetermined removal limit value (10) using a processor (2) to determine whether the layer height (5) is sufficiently low for necessary removal, wherein steps e. to g. before step d. are carried out, and / or wherein the steps in step c. and in step f. certain layer heights (5) to be removed are accumulated and in a step g. based on a predetermined removal limit (10), it is determined whether the workpiece (1) has sufficient quality. 3. The method according to claim 1 or claim 2, wherein in step h. a new one using a coating tool (11). Coating (8) at least on the one in step d. treated and to be coated surface (9) of the workpiece (1) is applied. Method according to one of the preceding claims, wherein the layer structure (7) is tested non-destructively, preferably by means of at least one of the following methods: - Eddy current testing; - X-ray examination; and - Surface scan together with an associated coating certificate. Method according to one of the preceding claims, wherein the layer structure (7) is destructively tested, preferably with material removal, using at least one of the following methods: - microscopic sectional image; - Mass spectrometry and/or gas chromatography, preferably laser-induced plasma spectroscopy; and - gradual surface removal together with a chemical analysis, with the material being preferably removed outside a functional surface (12). Method according to one of the preceding claims, wherein if based on the results of step b. and/or step g. If it is determined that a layer height (5) that is too high for a predetermined use needs to be removed, one of the following decisions is made: - declare the workpiece (1) in question as scrap; - remove the specific layer height (5) and prepare it for: i. another use for which the workpiece (1) is then still suitable; or ii. Building up the excessively removed layer, preferably using additive manufacturing. 7. The method according to any one of the preceding claims, wherein a coating (8) of a surface (9) to be tested of a workpiece (1) is completely removed, with base material (13) preferably also being removed. 8. The method according to any one of the preceding claims, wherein a depth (14) of a removal penetrating into the base material (13) of the workpiece (1) is a maximum of 10 pm to 200 pm. 9. The method according to any one of the preceding claims, wherein for step e. a material, preferably as a circumferential ring (15), is removed, preferably turned, from the outer edge (16) of a surface (9) of the workpiece (1) to be tested. 10. Machining center (17) for reprocessing a coated workpiece (1), comprising at least the following components: - a measuring device (3); - a processing tool (6); and - a processor (2), the processing center (17) being set up to carry out a method according to one of the preceding claims.