METHOD FOR PRODUCING A MATERIAL LAYER

Abstract

In a method for producing a material sheet, in particular a metallic material sheet, a green body containing solid-state particles is sintered at a sintering temperature by heating the green body during sintering at least partly using microwave energy in accordance with a defined temperature profile having a heating phase and an essentially isothermal hold phase. A temperature of the green body is ascertained contactlessly with a sensor, and a supply of heat energy is controlled as a function of the temperature of the green body. During the heating phase an average microwave power is supplied and during the hold phase another average microwave power is supplied which is less than the one average microwave power.

Claims

1-15. (canceled)

16. A method for producing a material sheet, in particular a metallic material sheet, said method comprising: sintering a green body containing solid-state particles at a sintering temperature by heating the green body during sintering at least partly using microwave energy in accordance with a defined temperature profile having a heating phase and an essentially isothermal hold phase; ascertaining contactlessly with a sensor a temperature of the green body; controlling a supply of heat energy as a function of the temperature of the green body; and supplying during the heating phase an average microwave power and during the hold phase another average microwave power which is less than the one average microwave power.

17. The method of claim 16, further comprising: debindering a binder contained in the green body at a debindering temperature before the green body is sintered at the sintering temperature, with the sintering temperature being higher than the debindering temperature; and heating the green body during debindering at least partly by using microwave energy in accordance with a defined temperature profile.

18. The method of claim 17, wherein the green body is debindered and/or sintered by hybrid heating.

19. The method of claim 17, wherein the green body is at least partly debindered in a reducing atmosphere.

20. The method of claim 16, wherein the green body is sintered at least partly in a vacuum.

21. The method of claim 17, wherein the temperature profile for the debindering comprises a heating phase in which an average microwave power is supplied, and an essentially isothermal hold phase in which another average microwave power is supplied which is less than the one average microwave power.

22. The method of claim 16, wherein the temperature profile includes a cooling phase which follows the hold phase, and further comprising controlling a temperature during the cooling phase through supply of microwave power.

23. The method of claim 17, further comprising producing the green body, prior to the debindering and sintering, by screenprinting a suspension comprising the binder and the solid-state particles.

24. The method of claim 23, wherein the binder is an organic binder.

25. The method of claim 16, further comprising disposing the green body on a support in a chamber of a hybrid oven designed as resonator for a microwave source.

26. The method of claim 25, further comprising supplying the microwave energy to the chamber through multiple hollow conductors at different positions.

27. A material sheet for a laminated stack of an electrical rotating machine, said material sheet being produced by a method as set forth in claim 16, said material sheet being composed of a metallic material and having a density of at least 85% of a corresponding metallurgically produced metallic material.

28. The material sheet of claim 27, wherein the density is 90%.

29. The material sheet of claim 27, configured as electrical sheet steel having a sheet thickness between 0.5 .Math.m and 500 .Math.m.

30. An electrical machine, comprising a laminated stack which includes a multitude of material sheets, each said material sheet being designed as set forth in claim 27.

31. A closed-loop control device, comprising means for performing a method as set forth in claim 16.

32. A computer program product for producing a material sheet, comprising a computer program embodied in a non-transitory computer readable medium, wherein the computer program, when loaded into a closed-loop control device and executed by a closed-loop control device, causes the closed-loop control device to perform a method as set forth in claim 16.

Description

[0039] The figures show:

[0040] FIG. 1 a schematic diagram of a production process for material sheets with a hybrid oven,

[0041] FIG. 2 an enlarged detail of a green body prior to debindering,

[0042] FIG. 3 a schematic diagram of a first configuration of a temperature profile for the debindering and sintering of a green body by means of hybrid heating,

[0043] FIG. 4 a schematic diagram of a second configuration of a temperature profile for the debindering and sintering of a green body by means of hybrid heating and

[0044] FIG. 5 a schematic diagram of a production process for material sheets with a microwave oven,

[0045] FIG. 6 a schematic diagram of a temperature profile for the sintering of a green body by means of microwave heating.

[0046] The working examples elucidated hereinafter are preferred embodiments of the invention. In the working examples, the described components of the embodiments each constitute individual features of the invention that should be considered independently, each of which also independently develop the invention and should thus also be regarded as part of the invention individually or in any combination other than that disclosed. Furthermore, the embodiments described can also be supplemented by further features of the invention that have already been described.

[0047] Identical reference numerals have the same meaning in the different figures.

[0048] FIG. 1 shows a schematic diagram of a production process for material sheets 2 having a hybrid oven 4, wherein the ready-sintered material sheets 2 each have an aspect ratio, i.e. a ratio of maximum length I to sheet thickness d, of at least 50:1, especially of 100:1. For example, the ready-sintered sheet thickness d is between 0.1 .Math.m and 1 mm, especially between 0.5 .Math.m and 500 .Math.m. In the hybrid oven 4, the material sheets 2 in the form of green bodies are debindered, and sintered immediately thereafter. The hybrid oven 4 is configured for debindering and sintering by means of hybrid heating. As well as microwave heating, hybrid heating additionally comprises conventional heating, for example via induction heating, resistance heating or gas heating. For example, the green bodies, prior to debindering and sintering, are produced by means of screenprinting from a suspension comprising at least one binder, especially an organic binder, and solid-state particles, and positioned on a carrier 6, the carrier 6 having been produced from a dielectric material, especially a ceramic such as aluminum oxide. The characteristics of the binder are such that it dissociates completely or virtually completely into gaseous constituents on heating. In particular, the material sheets 2 take the form of electrical steel sheets for an electrical machine, for example a motor or a generator, within the solid-state particles for an electrical steel sheet contain a soft magnetic material, for example iron, nickel, cobalt and/or alloys thereof.

[0049] The green bodies are disposed on the carrier 6 in a chamber 8 of the hybrid oven 4, wherein the chamber 8 takes the form of a resonator for a microwave source 10. The microwave source 10 especially takes the form of a magnetron and is connected by way of example to the chamber 8 via a hollow conductor 12. The microwave source 10 generates electromagnetic vibrations with a frequency range, for example, of 300 MHz to 300 GHz. In particular, electromagnetic vibrations are generated with frequencies within an ISM band (industrial, scientific and medical application band), for example at 915 MHz +/- 13 MHz, 2.45 GHz +/- 50 MHz or 5.8 GHz +/- 75 MHz. A maximum power of the microwave source 10 is chosen depending on the material, shape and number of the green bodies, and the size of the chamber 8. The microwave power can optionally be supplied via multiple hollow conductors 12 at different positions in order to achieve more homogeneous heating of the green bodies.

[0050] Furthermore, the hybrid oven 4 comprises a conventional heat source 14, which takes the form, for example, of an induction heat source, of a resistance heating source or of a gas-heated source. During the debindering and sintering, a temperature of at least one green body is monitored by means of a sensor 16, especially a contactless sensor 16. The sensor 16 takes the form, for example, of an infrared temperature sensor. Microwave source 10 and the conventional heat source 14 are actuated by a closed-loop control device 18 that controls the temperature of the at least one green body during the debindering and sintering with reference to a temperature profile. The temperature profile is recorded in a memory 20, for example in the form of a lookup table, in a setpoint device 22 and is compared with the temperature of the at least one green body for closed-loop control. The ascertained variance of the actual value from the target value is processed further in an open-loop control device 24 for actuation, especially separate actuation, of the microwave source 10 and the conventional heat source 14 for closed-loop control of the temperature. Optionally, the temperature ascertained by the sensor 16 is used together with a digital twin of the hybrid oven 4 for closed-loop temperature control. In addition, the closed-loop control device 18 controls a pressure and a gas composition in the chamber 8. The closed-loop control device 18 has a digital logic unit configured for the production process. The digital logic unit takes the form, for example, of a microprocessor, microcontroller, FPGA (field programmable gate array) or ASIC (application-specific integrated circuit).

[0051] FIG. 2 shows an enlarged detail of a green body 26 prior to debindering E, containing a suspension of solid-state particles 28 and a binder 30, especially an organic binder 30. The solid-state particles are in powder form and comprise particles of electrically and/or magnetically conductive material, especially metal particles. For example, the solid-state particles contain iron, nickel, cobalt and/or alloys thereof. The further configuration of the green body 26 in FIG. 2 corresponds to that in FIG. 1.

[0052] FIG. 3 shows a schematic diagram of a first configuration of a temperature profile 32 for the debindering E and sintering S of at least one green body by means of hybrid heating, showing a temperature profile 34 for the debindering E and sintering S by means of conventional heating by way of comparison. The temperature T is plotted qualitatively against time t. The total period tk of the temperature profile 34 for the conventional heating is, for example, 10 hours. The total period th of the temperature profile 32 for the hybrid heating is, for example, 33% shorter. The details that follow relate to the temperature profile 32 for the debindering E and sintering S by means of hybrid heating.

[0053] In addition, FIG. 2 shows an operation scheme 36 of the microwave source 10 for the debindering E and sintering S by means of hybrid heating as a function of time t in relation to the temperature profile 32, showing pulsed operation of the microwave source 10 with the aid of vertical dashes. The microwave source 10 takes the form, for example, of a magnetron, with closed-loop control of a power released by means of a duty cycle. The duty cycle or phase control factor is calculated from the ratio of pulse duration to period duration. Vertical dashes having a very small gap represent a high duty cycle, corresponding to a high average power at constant peak output. Continuous wave operation is also referred to as CW operation for short. The conventional heat source is operated parallel to the microwave source 10 during the debindering and sintering operation.

[0054] The at least one green body is heated up first to a debindering temperature Td and then to a sintering temperature Ts both in the case of hybrid heating and in the case of conventional heating. In the case of debindering E by means of hybrid heating, a heating phase Ae, for example in linear form, is followed by an essentially isothermal hold phase He. During the heating phase Ae, a first average microwave power P1 is supplied, wherein a second average microwave power P2 is supplied during the hold phase He and the second average microwave power P2 is less than the first average microwave power P1. During the debindering E, the binder, especially the organic binder, is driven out in a reducing atmosphere, so as to remove carbon atoms from the green body. Reducing atmosphere contains, for example, a hydrogen-nitrogen mixture or a hydrogen-noble gas mixture, especially a hydrogen-argon mixture, at a low pressure of less than 100 mbar. The nitrogen or the noble gas functions as purge gas. The debindering temperature Td here is, for example, 600 to 800° C.

[0055] The hold phase He of the debindering E is followed immediately by a heating phase As, for example in linear form, for the sintering S up to a sintering temperature Ts of, for example, 1200 to 1500° C. The heating phase As up to the sintering temperature Ts takes place at a low pressure, for example 20 mbar, with a reducing atmosphere being advisable in order that no carbonization takes place and any possible residual carbon is removed. The subsequent, essentially isothermal, hold phase Hs takes place in a vacuum. In the sintering operation S, during the heating phase As, a third average microwave power P3 is supplied, wherein a fourth average microwave power P4 is supplied during the hold phase Hs and the fourth average microwave power P4 is lower than the third average microwave power P3. Especially in the course of sintering S during the heating phase As, a maximum power of the microwave source 10 is supplied in order to shorten the heating phase. The hold phase Hs is followed by a cooling phase Cs, wherein the temperature during the cooling phase Cs is controlled by supply, especially variable supply, of microwave power P5, wherein the conventional heat source 14 is switched off during the cooling phase Cs.

[0056] The at least one material sheet 2 produced from a metallic material that has been sintered from the at least one green body, after the sintering S, has a density of at least 90% of the corresponding metallurgically produced material. For example, the at least one material sheet 2 has been produced from iron, i.e. from iron or and iron-base alloy, for example iron-cobalt or iron-silicon, and after the sintering S has a density of at least 6600 kg/m.sup.3.

[0057] FIG. 4 shows a schematic diagram of a second configuration of a temperature profile 32 for the debindering E and sintering S of at least one green body by means of hybrid heating, showing a temperature profile 34 for the debindering E and sintering S by means of conventional heating by way of comparison. During the debindering E, the green body is first heated in a vacuum in a cleaning heating phase Ar to a cleaning temperature Tr at the first average microwave power P1, with a cleaning temperature Tr of, for example, 100 to 300° C. During a cleaning hold phase Hr, solvents are evaporated, and a surface cleaning operation is conducted, before being followed by the heating phase Ae for the actual debindering E. The further configuration of the temperature profile 32 in FIG. 4 corresponds to that in FIG. 3.

[0058] FIG. 5 shows a schematic diagram of a production process for material sheets 2 with a microwave oven 38. The sintering operation is effected by means of microwave heating, which is provided by a microwave source 10 via a Hollow conductor 12. The further execution of the production process in FIG. 5 corresponds to that in FIG. 1.

[0059] FIG. 6 shows a schematic diagram of a temperature profile 40 for the sintering S of a green body by means of microwave heating, using a microwave oven 38 according to FIG. 5. The green body to be sintered here either does not include any binder, in which case a green body without binder comprises pressed solid-state particles, for example, or the green body includes solid-state particles with a readily volatile binder which is driven out directly, especially cracked, on sintering S in the heating phase As. Readily volatile binders are especially aromatic or aliphatic oils, for example mineral oil derivatives. The heating phase As is followed by a hold phase Hs, wherein the fourth average microwave power P4 supplied is lower than the fifth average microwave power P5 during the heating phase As. The hold phase Hs is followed by a cooling phase Cs, wherein the temperature during the cooling phase Cs is controlled by supply, especially variable supply, of microwave power P5. The further configuration of the temperature profile 40 in FIG. 6 corresponds to that in FIG. 3.

[0060] In summary, the invention relates to a process for producing a material sheet 2, especially a metallic material sheet 2. In order to achieve a higher speed of the production process and better cost position compared to the prior art, it is proposed that a green body 26 be provided, comprising solid-state particles 28, wherein the green body 26 is sintered at at least one sintering temperature Ts and wherein the green body 26 in the sintering operation S is heated at least partly by means of microwave energy.