Method for cleaning a sintered component

Abstract

The invention relates to a method for cleaning a sintered component (1), at least comprising the following steps: a) arranging the sintered component (1) in a heating device (2); b) operating the heating device (2) and heating only a first partial region (3) of the sintered component (1) to a predetermined first temperature (4) which is required to drive contaminants out of the sintered component (1).

Description

[0001] Method for cleaning a sintered component

[0002] The invention relates to a method for cleaning a sintered component (hereinafter also referred to as a sintered part). A sintered component is produced, in particular, from a powdered material by pressing it into a green compact and subsequently by sintering it into a solid workpiece (sintered component). Such sintered parts can be post-processed by re-pressing (calibration) to achieve higher dimensional accuracy. Alternatively or additionally, the calibrated sintered parts are mechanically machined, e.g., by a machining process or by grinding.

[0003] In particular, a sintered component is heat-treated, e.g. by generating certain material properties, e.g. a certain hardness, ductility, etc.

[0004] In particular, sintered components are mechanically post-processed using cooling lubricants, calibrated with the aid of lubricating oils, or heat-treated, especially hardened, using a liquid quenching medium. These media (i.e., cooling media, lubricating media, quenching media, but also washing media, preservatives, etc.) can adhere to sintered components, especially those exhibiting (residual) porosity, or penetrate / be absorbed into the pores, thus impairing weldability. The porosity of the sintered component material, which causes such media to remain on the component, leads in particular to very irregular, porous weld seams.

[0005] Thermal cleaning refers to the heat treatment of sintered components at a temperature that is (just) above the boiling or decomposition temperature of the liquid media present in the porosity of the sintered component. It is known that the cleaning result can be improved by applying negative pressure (e.g., by heating the sintered component in a vacuum chamber).

[0006] Thermal de-oiling of hollow bodies is known from DE 44 15 093 Al.

[0007] The object of the present invention is to at least partially solve the problems cited with reference to the prior art. In particular, a method for cleaning a sintered component is to be proposed, which ensures cost-effective yet effective cleaning. The method is intended to guarantee, in particular, a high degree of dimensional accuracy of the sintered component.

[0008] A method with the features according to claim 1 contributes to solving these problems. Advantageous further developments are the subject of the dependent claims. The features listed individually in the claims can be combined in a technologically meaningful way and can be supplemented by explanatory facts from the description and / or details from the figures, thereby showing further embodiments of the invention.

[0009] A method for cleaning a sintered component is proposed, comprising at least the following steps: a) arranging the sintered component in a heating device; b) heating only a first sub-area of ​​the sintered component with the heating device to a predetermined first temperature at which impurities are driven out of the sintered component.

[0010] The above (non-exhaustive) division of the procedural steps into a) and b) is primarily intended for differentiation purposes and does not impose any sequence or dependency. The frequency of the procedural steps may also vary. It is also possible that procedural steps may overlap, at least partially. In particular, steps a) and b) are carried out in the order listed.

[0011] The sintered component is manufactured, in particular, from a powdered material by pressing it into a green compact and subsequently by sintering it into a solid workpiece (sintered component). Before step a), the sintered component can be post-processed by re-pressing (calibration) to achieve higher dimensional accuracy. Alternatively or additionally, the calibrated sintered component can be machined before step a), e.g., by a machining process or by grinding.

[0012] In particular, the sintered component contains impurities. Impurities are defined here specifically as liquid and / or gaseous materials or media that are not a deliberately chosen component of the sintered component's material composition, but are used only as (temporarily present) process aids during the manufacturing of the sintered component (e.g., for producing the green body, producing the sintered component, calibrating, machining, heat treatment (excluding the cleaning described here), or washing).

[0013] In step a), the sintered component can be arranged, at least partially, within or relative to a heating device. The arrangement is specifically designed to ensure a high-energy and uniform heat supply to the first section of the sintered component (while, if necessary, significantly reducing or even blocking the heat supply to the subsequent sections). The heating device can include an (integrated) heating chamber in which (only) the first section of the sintered component can be used. In step b), the heating device is activated and operated so that the (immediate) heating of the first section of the sintered component to the predetermined initial temperature is achieved. This initial temperature is predetermined such that, upon reaching it, impurities are driven out of the sintered component, primarily from the first section.Just as a precautionary measure, it should be noted that the term "contaminants" does not require that various materials be expelled.

[0014] In particular, impurities are considered to be materials that hinder further processing of the sintered component later (i.e., after step b)), e.g., impair the weldability of the sintered component.

[0015] In particular, the sintered component is mechanically post-processed, for example, using cooling lubricants, calibrated with the aid of lubricating oils, or heat-treated, especially hardened, using a liquid quenching medium. These media (i.e., cooling media, lubricating media, quenching media, but also washing media, preservatives, etc.) can adhere to sintered components, especially those exhibiting residual porosity, and thus impair weldability. Such media are referred to here as contaminants.

[0016] In particular, the impurities are driven out of the sintered component to a depth of no more than three millimeters, more particularly no more than two millimeters, preferably no more than 1.5 millimeters, or even only one (1) millimeter. The depth extends from a surface of the sintered component into the material of the sintered component and denotes the smallest distance from the respective surface of the sintered component. In particular, the impurities are driven out of the sintered component to a depth of at least one (1) millimeter, more particularly at least 1.5 millimeters, preferably at least two millimeters, or even at least three millimeters.

[0017] "Driven out" means in particular that after step b) the impurities are reduced to such an extent that, for example, weldability is (significantly) improved.

[0018] "Expelled" means, in particular, that the impurities present before step b) up to the specified depth have been noticeably reduced.

[0019] The amount of impurities on the sintered component (before and after step b)) can be determined, in particular, through laboratory tests. Accordingly, preliminary investigations can be used to determine process parameters for step b) that allow the desired degree of ejection to be achieved reproducibly.

[0020] In particular, the first temperature in step b) is maintained for a period of at most three seconds, preferably at most one second, and most preferably at most 0.5 seconds or less.

[0021] In particular, the first sub-area heated to the first temperature comprises at most 20%, preferably at most 5%, most preferably at most 2% of the material volume of the sintered component.

[0022] In particular, the first temperature is between 100 degrees Celsius and 400 degrees Celsius, preferably more than 220 degrees Celsius or even more than 250 degrees Celsius, preferably less than 340 degrees Celsius or even less than 330 degrees Celsius. In particular, the sintered component, at least in the first section, preferably the entire sintered component, has a density value below a full density and a porosity of at least 2%, preferably at least 2.5% or even at least 3%, and in particular at most 12% or at most 10%.

[0023] In particular, prior to step a), the sintered component is subjected to heat treatment in step aO), at least in a second sub-area that differs from the first sub-area, or possibly the entire sintered component, wherein, as part of the heat treatment, at least the second sub-area (or the entire sintered component) is heated to a predetermined second temperature that is higher than the first temperature.

[0024] In particular, the sintered component is hardened during heat treatment, at least in the second sub-area, or possibly the entire sintered component.

[0025] In particular, the first temperature is at most 50% of the value of the second temperature. In particular, the second temperature is at least 200% of the value of the first temperature.

[0026] In particular, a process called tempering can also be carried out as part of the heat treatment, for example to make a hardened structure of a steel material more ductile. Tempering can also be limited to the second section or encompass the entire sintered component.

[0027] In particular, the specified (first and second) temperatures apply to sintered components made of a steel material.

[0028] In particular, the sintered component is inductively heated by the heating device. Inductive heating can be carried out in a targeted and localized manner, so that only the first section is heated to the predetermined initial temperature.

[0029] In particular, the sintered component is moved relative to the heating device during step b). Preferably, the sintered component rotates about an axis of rotation.

[0030] In particular, the first sub-area extends rotationally symmetrically around an axis of rotation of the sintered component.

[0031] In particular, the sintered component undergoes several rotations during the period of step b), in particular at least 5, preferably at least 10, and especially preferably at least 20. In particular, this allows the heat input into the sintered component or the first sub-area to be evened out.

[0032] The proposed method is based in particular on the understanding that in certain applications, a complete and comprehensive cleaning of a sintered component is not necessarily required or even possible, because, for example, hardened areas of the sintered component cannot be heated to the decomposition temperature of a contaminant to be removed without compromising quality. In such cases, the required martensitic microstructure would revert to pearlite / ferrite / cementite, and the required hardness could no longer be achieved. Therefore, drying temperatures below the tempering temperature would have to be used, which, however, are generally insufficient to, for example, drive off or decompose lubricating oils.

[0033] Instead of cleaning or degreasing an entire sintered component, the cleaning process is limited to the volume area relevant to the specific application (the first sub-area). Heat is therefore only introduced into this first sub-area, and this heat is designed to be as minimal as possible while still being sufficient to achieve the desired cleaning effect.

[0034] The temperature level reached at the first temperature results in the transformation or expulsion of foreign substances / contaminants from the pore structure of the sintered component. The first temperature is selected primarily depending on the media or contaminants to be expelled.

[0035] The heating phase of the heating device is particularly short to limit the temperature increase of the sintered component to the first sub-area to be cleaned.

[0036] The proposed method describes the local heating of a sintered component. Specifically, an area of ​​the sintered component that is to be subsequently welded is heated to a first temperature at which liquid foreign substances (e.g., oils and water-based process media) or impurities evaporate or decompose.

[0037] The first temperature is maintained only briefly (i.e., only for the described period), and therefore only above the relevant de-oiling temperature, in order to, for example, avoid tempering effects in a previously hardened sintered component and / or to minimize the diffusion tendency of the remaining impurities in the sintered component.

[0038] In particular, the short and reduced heat input during step b) allows for the maintenance or further assurance of high dimensional accuracy of the sintered component. The first section cleaned by step b) extends to a depth within the sintered component sufficient for welding, especially laser welding.

[0039] The time interval between the described (thermal) cleaning and subsequent welding of the sintered component can be several weeks in particular, without impairing weldability due to internal diffusion of the component.

[0040] Furthermore, a sintered component is proposed, manufactured by the described process, with at least a first sub-area that has a lower concentration of impurities compared to other areas (e.g., a second sub-area or a third sub-area) of the sintered component.

[0041] A second sub-section of the sintered component was subjected to heat treatment, particularly prior to step a) in step aO), wherein, as part of the heat treatment, at least the second sub-section (or the entire sintered component) is heated to a predetermined second temperature that is higher than the first temperature. A third sub-section may have been designed or pretreated in the same way as the first sub-section, in the same way as the second sub-section, or differently from the aforementioned sub-sections.

[0042] In particular, a weld seam is provided (because the sintered component is manufactured for a corresponding application) or arranged in the first sub-section. The weld seam is specifically produced by a laser welding process or is itself a laser weld seam.

[0043] In particular, a system is proposed, comprising at least a heating device and a sintered component, wherein the heating device can selectively heat only a specific section (i.e., not the entire sintered component). Specifically, the system is equipped, designed, and configured to carry out the described process and / or to produce the described sintered component.

[0044] In particular, at least one data processing system is provided or included in the plant, which has means that are suitable for carrying out the procedure, are configured or programmed, or that execute the procedure.

[0045] In particular, the plant or heating device includes a data processing system, e.g. a control unit, which has means for carrying out the steps of the procedure and / or has means that are suitably equipped, configured or programmed to carry out the steps of the procedure or that carry out the procedure.

[0046] The means include, for example, a processor and a memory in which instructions to be executed by the processor are stored, as well as data lines or transmission devices that enable the transmission of instructions, measured values ​​(e.g. temperature of the sintered component in certain areas), data or the like between the aforementioned elements.

[0047] The "means" may include, in particular, one or more of the following components: control(s), microcontroller, data storage, data connection, display devices (such as a display), counter or timer, at least one other sensor, a power source, etc.

[0048] Furthermore, a computer program is proposed, comprising commands which, when executed by a computer, cause the computer to perform the described procedure or the steps of the described procedure.

[0049] Furthermore, a computer-readable storage medium is proposed, comprising instructions which, when executed by a computer, cause it to perform the described procedure or the steps of the described procedure.

[0050] The explanations regarding the process are particularly applicable to the sintered component, the plant, the data processing system and / or the computer-implemented process (i.e., the computer program and the computer-readable storage medium) and vice versa.

[0051] The use of indefinite articles (“a”, “an”, “one”, and “ones”), particularly in the patent claims and the description reproducing them, is to be understood as such and not as a numeral. Accordingly, terms or components introduced by these articles are to be understood as occurring at least once and, in particular, may also occur multiple times.

[0052] It should be noted as a precaution that the numerical terms used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific embodiment described. Insofar as a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory. The invention and the technical context are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited.In particular, unless explicitly stated otherwise, it is also possible to extract aspects of the facts illustrated in the figures and combine them with other components and findings from the present description. It should be noted in particular that the figures, and especially the depicted proportions, are only schematic. They show:

[0053] Fig. 1: a heating device and a sintered component in a side view in

[0054] Cut;

[0055] Fig. 2: a system with a sintered component; and

[0056] Fig. 3: the sintered component according to Fig. 2.

[0057] Fig. 1 shows a heating device 2 and a sintered component 1 in a side view in section. Fig. 2 shows a system 11 with a sintered component 1. Fig. 3 shows the sintered component 1 according to Fig. 2. Figs. 1 to 3 are described together below. In Figs. 2 and 3, temperature diagrams are shown that illustrate the temperatures reached in certain areas of the sintered component 1 during step b).

[0058] The sintered component 1 shown in Figures 2 and 3 is a stator of a camshaft adjuster for a motor vehicle, used for variable valve timing of the vehicle's internal combustion engine. The first section 3, which is selectively heated and thus cleaned, later serves as the basis for a weld 10, through which the sintered component is metallurgically joined to another component. The system 11 comprises a heating device 2 and a sintered component 1, wherein only a first section 3 (i.e., not the entire sintered component 1) can be selectively inductively heated by the heating device 2. The system 11, or rather the heating device 2, includes a data processing system 12, e.g., a control unit, which has means for executing the steps of the described process.

[0059] The sintered component 1 according to Fig. 1 has a first sub-area 3 which has a lower concentration of impurities compared to other areas (a second sub-area 7 or a third sub-area 9) of the sintered component 1.

[0060] A second sub-section 7 of the sintered component 1 was subjected to heat treatment prior to step a) in a step aO), wherein, within the scope of the heat treatment, only the second sub-section 7 is heated to a predetermined second temperature 8, which is higher than the first temperature 4. A third sub-section 9, like the first sub-section 3, has not been subjected to any prior heat treatment.

[0061] In the first sub-area 3, a weld seam 10 is provided (because the sintered component 1 is manufactured for a corresponding application) or arranged.

[0062] In the method for cleaning the sintered component 1, step a) comprises arranging the sintered component 1 in a heating device 2. Step b) comprises operating the heating device 2 and heating only a first partial area 3 of the sintered component 1 to a predetermined first temperature 4, which is required to drive off impurities from the sintered component 1.

[0063] In step b), the impurities are driven out of the sintered component 1 to a depth 5. Depth 5 extends from a surface of the sintered component 1 into the material of the sintered component 1 and denotes the smallest distance from the respective surface of the sintered component 1 (see Fig. 1). The first temperature 4 is maintained for only a short period of time in step b).

[0064] The first sub-area 3, heated to the first temperature 4, comprises at most 10% (here approx. 2%) of a material volume 6 of the sintered component 1 (see Fig. 1).

[0065] The sintered component 1 can, prior to step a), be subjected to heat treatment in a step aO), at least in a second sub-area 7 that differs from the first sub-area 3, or optionally the entire sintered component 1, wherein, as part of the heat treatment, at least the second sub-area 7 (or the entire sintered component 1) is heated to a predetermined second temperature 8 that is higher than the first temperature 4 (see Fig. 1).

[0066] The sintered component 1 is inductively heated by the heating device 2. Inductive heating can be carried out in a targeted and locally or spatially limited manner, so that only the first sub-area 3 is heated to the predetermined first temperature 4.

[0067] During step b), the sintered component 1 is moved relative to the heating device 2. The sintered component 1 rotates about an axis of rotation 13 (see Figs. 2 and 3). The first section 3 extends rotationally symmetrically around the axis of rotation 13 of the sintered component 1.

[0068] The proposed method utilizes the understanding that in certain applications, a complete and comprehensive cleaning of a sintered component 1 is not necessarily required or even possible, because, for example, hardened areas of the sintered component 1 cannot be heated to the decomposition temperature of a contaminant to be removed without compromising quality. In such cases, the required martensitic microstructure would revert to pearlite / ferrite / cementite, and the required hardness could no longer be achieved. Therefore, drying temperatures below the tempering temperature would have to be used, which, however, are generally insufficient to, for example, drive off or decompose lubricating oils.

[0069] Instead of cleaning or degreasing an entire sintered component 1, the cleaning process is limited to the volume area relevant to the application (first sub-area 3). Heat input therefore only occurs in this first sub-area 3, and this heat is designed to be as low as possible while still being sufficient to achieve the desired cleaning effect.

[0070] The temperature level reached at the first temperature 4 results in the transformation or expulsion of foreign substances / impurities from the pore structure of the sintered component 1. The first temperature 4 is selected depending on the media or impurities to be expelled.

[0071] The heating phase of the heating device 1 is sufficiently short to limit the temperature increase of the sintered component 1 to the first sub-area 3 to be cleaned.

[0072] The proposed method describes the local heating of a sintered component 1. In particular, a first sub-area 3 of the sintered component 1, which is to be welded subsequently, is heated to a first temperature 4 at which liquid foreign substances (e.g., oils and water-based process media) or impurities evaporate or decompose.

[0073] The first temperature 4 is only maintained briefly (i.e., only for the described period), in particular above the relevant de-oiling temperature, in order to, for example, avoid tempering effects in a previously hardened sintered component 1 (e.g., in the second sub-area 7) and / or to minimize the diffusion tendency of the remaining impurities in the sintered component 1.

[0074] The first sub-area 3 cleaned by step b) extends to a depth 5 of the sintered component 1, which covers a material depth sufficient for welding, in particular for laser welding.

[0075] Reference symbol list

[0076] 1 sintered component

[0077] 2 Heating device 3 First sub-area

[0078] 4 first temperature

[0079] 5 Depth

[0080] 6 Material volume

[0081] 7 second sub-area 8 second temperature

[0082] 9 third sub-area

[0083] 10 weld seam

[0084] 11 Annex

[0085] 12 System 13 Axis of rotation

Claims

Patent claims 1. Method for cleaning a sintered component (1), comprising at least the following steps: a) arranging the sintered component (1) in a heating device (2); b) heating only a first partial area (3) of the sintered component (1) with the heating device (2) to a predetermined first temperature (4) at which impurities are driven out of the sintered component (1).

2. Method according to claim 1, wherein the impurities are driven out of the sintered component (1) to a depth (5) of at most three millimeters.

3. Method according to one of the preceding claims, wherein the first temperature (4) in step b) is maintained for a period of at most three seconds.

4. Method according to one of the preceding claims, wherein the first partial area (3) heated to the first temperature (4) comprises at most 20% of a material volume (6) of the sintered component (1).

5. Method according to one of the preceding claims, wherein the first temperature (4) is between 100 degrees Celsius and 400 degrees Celsius.

6. Method according to one of the preceding claims, wherein the sintered component (1) has at least in the first sub-area (3) a density value below full density and a porosity of at least 2%.

7. Method according to one of the preceding claims, wherein the sintered component (1) is subjected to heat treatment in at least a second sub-area (7) that differs from the first sub-area (3) prior to step a), wherein, as part of the heat treatment, at least the second sub-area (7) is heated to a predetermined second temperature (8) which is higher than the first temperature (4).

8. Method according to claim 7, wherein the sintered component (1) is hardened as part of the heat treatment.

9. Method according to one of the preceding claims, wherein the sintered component (1) is inductively heated by the heating device (2).

10. Method according to one of the preceding claims, wherein the sintered component (1) is moved relative to the heating device (2) during step b).

11. Sintered component (1) produced by a method according to one of the preceding claims, comprising at least a first sub-area (3) which has a lower concentration of impurities compared to other areas (7, 9) of the sintered component (1).

12. Sintered component (1) according to claim 12, wherein a weld seam (10) is arranged in the first sub-area (3).

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