High-temperature joining furnace

Abstract

A high-temperature joining furnace is proposed which, in particular, is configured for diffusion welding of joining materials such as metals, plastics, ceramics and corresponding workpieces. The joining furnace comprises a heating chamber, a tool receptacle arranged in the heating chamber for receiving a workpiece to be processed in the joining furnace, a pressing device, arranged and configured to apply a pressing force to the workpiece, wherein the pressing device comprises a pressing plate for uniform application of the pressing force of the workpiece, and is characterized in that the press plate is equipped with a press plate heating device for heating the press plate and / or the workpiece.

Description

[0001] High-temperature joining furnace

[0002] Description

[0003] Field of the invention

[0004] The present invention relates to a high-temperature joining furnace, a method for diffusion welding and a heatable press plate.

[0005] Background and general description of the invention

[0006] It is generally known that metallic workpieces can be joined using diffusion bonding. For example, a metallic workpiece can be diffusion bonded if it is joined by a press at high temperature under pressure. The diffusion bonding process is a complex one, dependent on various influences, and even under identical process conditions, it does not necessarily lead to a comparable or at least satisfactory result.

[0007] During the joining process, for example, the deformation of the workpiece must be taken into account. For example, if the workpiece to be joined has cooling channels or other bores or openings inside, the pressing force exerted on the workpiece may vary locally, resulting in a different overall deformation compared to a solid body with identical dimensions. The history of the materials to be joined can also be important for the joining result; in particular, the grain size in the metal composite and the manufacturing process of the respective metal layers, for example, by rolling, can be relevant.Even if different materials for different workpieces should be considered fundamentally identical—that is, manufactured using the same manufacturing process and pretreated at the same temperatures, so that similar grain sizes can be assumed within the material—variances between materials must also be taken into account. This applies even if workpieces are provided or cut from the same piece of raw material. This can be further complicated for certain materials and / or material combinations.

[0008] A particular challenge in operating a diffusion welding system is achieving a uniform joining result across the component. In addition to the aforementioned considerations regarding the materials to be selected, various process parameters can also be reviewed to determine whether the process conditions can be further improved to further improve the uniform joining result across the component to be joined, or even to make it satisfactory in the first place. A further improved joining result can expand the application spectrum to include other materials that cannot be processed or can only be processed inadequately with existing systems. More complex structural shapes can be joined using materials that are already joinable. This can also help reduce production downtime.

[0009] Against this background, the invention has set itself the task of further homogenizing the joining result across a component to be joined. One partial aspect of the invention also sets out the task of being able to join new materials or more complex designs by means of diffusion welding, which could not previously be processed or could only be processed inadequately using this method. In particular, in a further partial aspect, the invention has set itself the task of enabling operation at lower temperatures in order to be able to join materials that would become too hot and therefore deform too severely using conventional joining methods. Another partial aspect of the invention sets out the task of further accelerating the process in order to reduce operating costs and increase component throughput. This problem is solved by the invention defined in the independent claims. Dependent claims set out further developments and preferred embodiments of the invention.

[0010] In a diffusion welding process, a workpiece or batch is deformed in a controlled manner. Any pores present in the joining material, recesses inside the workpiece, the number and size of the joining surfaces, and even the history of the joining material are all factors that can influence the process. When force is applied to the workpiece or batch using a press, the material contact at the joining surfaces is improved. This can create or precipitate inherent interdiffusion. Pressing therefore enlarges the contact surface in the area of ​​the joining surface(s). These processes differ from workpiece to workpiece, and the differences can be so significant that a first component can be joined sufficiently tightly, while a subsequent component, which is to be joined with identical parameters, only achieves insufficient strength or quality.On the other hand, under certain circumstances the shape of one component may be retained, while in the next, otherwise identical component with identical parameters, for example, deformation may occur in the area of ​​a cooling channel due to the pressing process.

[0011] According to the invention, a high-temperature joining furnace is provided, which is particularly designed for the diffusion welding of joining materials. Joining materials can be metals and include metallic workpieces. Metals can be any metal-containing materials or substances. For example, this includes metals such as iron, copper, aluminum, titanium, but also alloys such as stainless steel, tool steels, superalloys, bronze, tin, or others. Joining materials can also be non-metals or composite materials. Examples of non-metals include plastics or ceramics. Examples of composite materials include ceramic composites with aluminum or copper, or the like.

[0012] The high-temperature joining furnace can also be configured for force-assisted brazing or sintering of components. Overall, the high-temperature joining furnace is therefore configured for pressure-assisted material finishing, with or without filler material.

[0013] The high-temperature joining furnace includes a heating chamber. In the heating chamber, the workpiece, and usually also the furnace interior, are heated to the processing temperature.

[0014] A workpiece holder is arranged in the heating chamber for holding a workpiece to be processed in the joining furnace. Typically, the workpiece holder is located on the underside of the heating chamber. For example, the workpiece holder can comprise a plate, but also holders into which the workpieces to be joined are inserted. The workpiece holder can be part of a counter-pressing element or arranged on it. In other words, the workpiece holder can be a passive counterpart for a pressing device or can itself be subjected to a pressing force from underneath the workpiece holder, thus representing a counter-pressing element.

[0015] The joining furnace further comprises the pressing device, which is arranged and configured to apply a pressing force to the workpiece. For example, the pressing device is arranged such that an upper part, such as a press ram, presses against the workpiece from above, whereby the workpiece is pressed against the workpiece holder or the counter-pressing element. In other words, the workpiece is clamped between the upper part or press ram and the counter-pressing element or workpiece holder.

[0016] For this purpose, the upper part comprises a press plate, by means of which the pressing force can be evenly distributed and applied over a surface so that the workpiece is pressed evenly. Depending on the intended use or shape of the workpiece, the press plate can have a flat surface so that the workpiece can be evenly subjected to pressing force across the surface of the press plate. The press plate can also have recesses, projections, or steps in order to have or bring about a conformation of the press plate to a desired surface of the workpiece or workpieces. The press plate could therefore be generally described as a "pressing element." The term "press plate" will be used below, as this term appears to be common to those skilled in the art in light of the present description.

[0017] The press plate is equipped with a press plate heating device for heating the press plate and / or the workpiece. The press plate is, in particular, a pressure distribution plate, as it distributes the pressing force generated by the press device and applied to the workpiece across the surface of the workpiece. Using the press plate heating device, the press plate can be tempered or heated as evenly and homogeneously as possible across its surface. This also enables homogeneous heat dissipation across the press plate, so that the workpiece can also be heated evenly. In other words, the workpiece can now be heated conductively using the press plate heating device, which can potentially enable considerably faster heat transfer to the workpiece and, moreover, more even heat input across the surface of the workpiece.Furthermore, the use of the press plate heating device enables the use of materials that require a significantly lower processing temperature, at which radiant heat may not be able to transfer sufficient heat output into the workpiece, so that a uniform temperature distribution in the workpiece through radiant heat alone might not be possible at all. Thus, the press plate heating device according to the invention opens up the use of new materials as workpieces that were previously unavailable for diffusion welding.

[0018] The press plate heating device can preferably be integrated into the press plate, i.e., completely integrated if necessary. A heat supply can be connected or brought to the press plate from outside and supply the press plate heating device with heat. If the press plate heating device is integrated into the press plate, the most seamless, i.e., conductive, heat transfer to the press plate is improved.

[0019] The press plate can be a multi-part press plate. A multi-part press plate can comprise a workpiece-side layer and a press-side layer. The press plate heating device can preferably be arranged between the workpiece-side layer and the press-side layer of the press plate.

[0020] The joining furnace may include flexible connectors for connecting the press plate heating device to a power source. For example, the flexible connectors may comprise a metal strip material, such as a copper strip, which can absorb movement, shock, or vibration while maintaining electrical contact.

[0021] The press plate heating device provides conductive heat dissipation for the press plate, thus it is a conductive press plate heating device. In particular, the press plate heating device is electrically operable, so that it dissipates heat when it is supplied with electrical power from the energy source. Alternatively or additionally, the press plate heating device can be configured to permit fluid flow, so that it dissipates heat when it is supplied with a hot fluid from the energy source.

[0022] The press plate can be arranged so that it can be moved or moved. For example, the press plate is moved by one or more press rams, with the press ram(s) being set in motion by one or more press cylinders. When a pressing force is applied, the workpiece is successively deformed or joined.

[0023] The pressing device can also be arranged so that it presses onto the workpiece from below, for example by providing a movable workpiece holder and sliding the workpiece upwards on the workpiece holder, for example. In a further embodiment of the invention, a first and second pressing plate can be provided for applying force on both sides, for example an upper and a lower pressing plate or a left and a right pressing plate. To press the workpiece, a part that functions like a press ram is typically used, which can be subjected to a force from the outside, and a counter-pressing element that counteracts the pressing force. The workpiece is clamped between the press ram and the counter-pressing element, where it is joined or deformed.

[0024] The joining furnace can include a wall-mounted heating device or furnace heating device in the furnace chamber. The wall-mounted heating device can be designed to heat the workpiece by means of thermal radiation. Since a low pressure, i.e. the highest possible vacuum, is typically set in the furnace chamber, practically no convection takes place in the furnace chamber, so that a wall-mounted heating device can essentially transfer radiant power. The wall-mounted heating device can, if necessary, compensate for heat losses that result from the workpiece arranged in the furnace chamber continuously releasing a quantity of heat through radiant heat. The wall-mounted heating device can therefore be used in a supporting manner to further homogenize the temperature distribution in the workpiece. The furnace heating device can also be intended solely to release radiant heat into the furnace chamber.The two heating devices—that is, the press plate heating device and the furnace heating device—can complement each other in that the furnace heating device compensates for the heat being radiated away from the workpiece by radiating heat into the workpiece. This can prevent any cold spots that may occur on the workpiece, particularly at the side edges. Depending on the shape of the workpiece to be pressed and the requirements, the furnace heating device may not be necessary, however, since the press plate heating device is able to provide advantageously uniform heat output across the surface of the workpiece using conductive transfer.

[0025] A sensor device can be provided in the joining furnace, which provides at least one sensor signal. For example, the sensor device can detect the position or extended length of the press ram, or the position of the press plate. The sensor signal can be transmitted to or processed by a control device, which is configured to control at least the press device in response to the at least one sensor signal.

[0026] The sensor device of the joining furnace can record a process parameter. A process parameter can be the thickness of the workpiece, the position of a pressure ram or press ram of the pressing device. A process parameter can also be the applied pressing force, a hydraulic pressure, or a travel distance of the pressing device. A sensor signal can then be generated from the value base recorded by the sensor device, i.e., one of the aforementioned process parameters. Multiple sensor devices can be provided to simultaneously record various process parameters. A further sensor device can record one or more process parameters simultaneously with the first sensor device and thus generate at least one or more additional sensor signals. To control the joining process or the joining furnace, the one or more sensor signals can be processed so that, if necessary, different process parameters are taken into account in the control.

[0027] The pressing device can comprise a hydraulic device, whereby the pressing force is generated by building up hydraulic pressure. The pressing device can also comprise an electric spindle, which, for example, generates a feed through rotation and thereby applies the pressing force to the workpiece.

[0028] The joining furnace can include an input device for entering process parameter specifications. The input device can be, for example, a user-operated terminal. Process parameter specifications that can be stored before the start of the joining process include, for example, the desired process temperature, the process time, the material(s) of the workpiece, parameters or other data on the underlying material, and the number and / or size of the joining surface(s) of the workpiece.

[0029] For example, the workpiece can consist of a plurality of layers of different materials, i.e., at least two different materials stacked on top of each other, with each surface to be joined between two different materials being described as a joining surface. For a plate-like workpiece comprising, for example, 25 layers, 24 joining surfaces are arranged in the workpiece. Information about cavities in the workpiece can also be taken into account when specifying the process parameters.

[0030] The joining furnace may further comprise an output device, in particular for displaying or selecting process parameters and / or a control program. For example, information about the process step the joining furnace is currently in can be displayed on the output device.

[0031] The pressing device may comprise a pressing ram with which the pressing force is transmitted and / or it may comprise a pressing plate with which the pressing force is applied to the workpiece.

[0032] The pressing device can comprise a pressing cylinder. The pressing ram can be connected to the pressing cylinder, so that the pressing cylinder exerts the pressing force on the pressing ram and adjusts the pressing ram toward the workpiece. The pressing device can optionally comprise multiple pressing cylinders, in particular two, three, or four pressing cylinders.

[0033] It is preferable to use multiple press dies that act jointly on the workpiece, particularly via the press plate, which is subjected to pressing force by the two or more press dies as homogeneously or evenly distributed across the surface as possible. The multiple press dies can be arranged side by side, so that an array of press dies acts on the press plate. The goal is to distribute the pressing force as homogeneously as possible across the workpiece to be joined, because the pressing force required for joining could otherwise deform the press plate or the pressing element, so that the workpiece to be joined is not subjected to pressing force evenly.

[0034] The high-temperature joining furnace may comprise a housing. For example, the heating device, heating chamber, workpiece holder, and / or pressing device may be housed in the housing. The pressing device may be arranged on the housing by means of a press holder and / or supported on the housing. For example, the press holder is attached to the housing or rests against the housing, so that the press cylinder connected to the press holder can be supported against the housing of the high-temperature joining furnace.

[0035] For the purpose of supporting the pressing device on the housing, the housing may have a support or holding structure, such as a support frame or support cage. The support or holding structure may be a separate component from the housing or be formed integrally with the housing.

[0036] The support or holding structure and / or the press holder can be designed to be movable and / or deformable. When a pressing force is applied to the workpiece, the pressing device can support itself against the press holder and in the process shift and / or deform the press holder, for example by deforming the support or holding structure. In this case, a stored force can be absorbed between the press holder and the pressing device, in particular the press cylinder with press ram, similar to the preload of a spring, so that in particular when the pressing force is increased, the pressing effect on the workpiece can also be increased evenly or more gently. Due to the movable and / or deformable design of the press holder orthe support or holding structure, the pressing device can be prepared by preparing the pressing device in a starting position in which a pre-pressing force is already applied to the workpiece.

[0037] The joining furnace can be configured in such a way that the application of compressive force from the pressing device to the workpiece causes a lateral displacement and / or deformation of the press support. In other words, the application of compressive force to the press support, which acts as an abutment for the press, causes the lateral displacement and / or deformation of the press support. By absorbing compressive force in or near the press support, a spring effect is generated between the press support and the pressing device, or between the press support, the press cylinder, and the press ram.

[0038] The pressing device can be configured in such a way that a preload force can be built up between the pressing ram and the housing during a pressing process or when a pressing force is built up. The presence of a preload force in the pressing device allows for finer dosing and thus more precise detection and / or tracking of the ram position during the pressing process. Furthermore, the build-up of the preload force allows for more precise adjustment or dosing of pressure corrections or pressing force corrections.

[0039] For example, when subjected to a compressive force, the press mount can be displaced or deformed by more than 1 mm, in particular more than 3 mm, more particularly more than 5 mm, or even more than 10 mm. This can create a type of "spring accumulator," i.e., a preload force. Furthermore, the press mount can be displaced or deformed by less than 3 mm, preferably less than 6 mm, more preferably less than 12 mm, when subjected to a compressive force. Minimum and maximum specifications for the deflection can be combined as an interval, for example, more than 3 mm and less than 6 mm as "in the range between 3 and 6 mm."

[0040] The sensor device can be configured to detect the position of the pressure ram. The sensor device can also be configured to detect the pressing force applied to the workpiece.

[0041] The control device can be configured to determine the pressing force required for a joining process for the inserted workpiece by detecting and evaluating the sensor signal(s). Furthermore, the control device can automatically control the pressing device based on the determined required pressing force. In other words, the control device controls the pressing device taking into account the detected and evaluated sensor signals.

[0042] The control device can also, if necessary, regulate or control the heating device so that different temperatures can be maintained in the heating chamber at different times during the joining process.

[0043] The joining furnace may have a filling and removal opening. In one example, the filling and removal opening is connected to a safety circuit that detects the state of the opening.

[0044] The workpiece holder can advantageously serve as a counter-pressing element for the pressing device. The pressing device can thus press the workpiece against the workpiece holder, clamping the workpiece between the pressing device and the workpiece holder.

[0045] The control device can provide at least one selectable control program. The selectable control program can preselect basic parameters, for example, a typical compressive force that is frequently applicable for a specific material combination, or a minimum press stress with which the joining process can be initiated. The selectable control program can include a pretreatment program and / or a press execution program.

[0046] The control device is preferably configured to adapt a selected control program in response to at least one sensor signal, especially during the execution of the control program. The control program can be adapted in such a way that process parameters, such as in particular the pressing force, temperature, and / or travel distance of the pressing device, are changed or influenced during the joining process.

[0047] The at least one control program can be stored in a program memory of the high-temperature joining furnace. The control device can comprise a programmable logic controller.

[0048] The joining furnace is preferably designed to carry out joining processes, for example in the case of metals or metallic workpieces, at temperatures of 1200°C or lower, preferably 1000°C or lower, more preferably 950°C or lower. This means that the high-temperature joining furnace is capable of carrying out diffusion welding processes at lower temperatures than previously known for metals or metallic workpieces, and thus of subjecting new materials to diffusion welding that could not previously be processed using this process. At lower temperatures, on the one hand, the time required to introduce sufficient radiation energy into the workpiece to be processed is significantly longer; on the other hand, it may even be the case that the radiation and the radiation are balanced, or that a homogeneous temperature distribution could not be achieved inside the workpiece. These problems are solved with the press plate heating device presented here.The joining furnace can further be prepared to carry out joining processes at temperatures of 450 °C or higher, for example 500 °C or higher, preferably 550 °C or higher and more preferably 600 °C or higher.

[0049] The joining furnace can also be configured to perform joining processes, for example, in the case of non-metals such as plastics, ceramics, or corresponding workpieces, at temperatures of 350°C or lower, preferably 300°C or lower, more preferably 250°C or lower, or even 200°C or lower. This temperature range also opens up access to new materials for the diffusion bonding process. The joining furnace can also be configured to perform joining processes at temperatures of 80°C or higher, for example 100°C or higher, preferably 120°C or higher, and more preferably 140°C or higher.

[0050] The invention further describes a method for diffusion welding in a high-temperature joining furnace, in particular as described above. The method for diffusion welding comprises the steps of: filling the joining furnace with a workpiece; applying at least one press plate of a pressing device to the workpiece; heating the workpiece predominantly to a joining temperature by means of a press plate heating device; and pressing the workpiece with a pressing device to carry out, in particular, the diffusion welding process.

[0051] The method can be further developed by the step: during pressing, tempering or heating the press plate by means of the press plate heating device to homogenize the temperature distribution in the workpiece.

[0052] The method can further be implemented by the step of: detecting or determining the pressing force required for the joining process during the pressing process, in particular using an automatic control device such as a programmable logic controller (PLC); and controlling the pressing device in response to the detected or determined pressing force required for the joining process. For example, the required pressing force can be determined via the pressing path by means of distance measurement.

[0053] The method can be further developed by the step of repeatedly detecting or determining the pressing force required for the joining process, in particular at fixed time intervals, and adaptively controlling the pressing device in response to the repeatedly detected or determined pressing forces.

[0054] The method can also be further developed with the step of continuously monitoring the joining process by means of at least one sensor device, and continuously adapting the joining process upon detection of a deviation of a monitored value from a target value.

[0055] The method can also be further developed with the step of entering process parameter specifications, in particular by a user, before pressing the workpiece.

[0056] Furthermore, the step of taking into account the process parameter specifications when providing setpoints for automated process control can also represent a further development of the process.

[0057] The present description also describes a heatable press plate, in particular for a high-temperature joining furnace, as explained above. The press plate is designed to uniformly apply a pressing force to a workpiece placed in the high-temperature joining furnace. The press plate is characterized in that the press plate is equipped with an integrated press plate heating device for heating the press plate and / or the workpiece.

[0058] In an advantageous embodiment, the press plate heating device is integrated into the press plate, preferably completely integrated. The press plate can be a multi-part press plate, in particular comprising a workpiece-side layer and a press-side layer of the press plate. The press plate heating device can be arranged between the workpiece-side layer and the press-side layer. Each part of the press plate, i.e. in particular the workpiece-side layer, the press-side layer and, if applicable, the press plate heating device, can consist of the same base material but have different dopings. The press plate can comprise ceramic material. The workpiece-side layer and / or the press-side layer can comprise ceramic material or consist of ceramic material. Furthermore, the press plate heating device can comprise ceramic material or metal material or consist of ceramic material or metal material.

[0059] The ceramic material of the heatable press plate can comprise at least one of carbon fiber-reinforced graphite, carbon fiber-reinforced silicon carbide, titanium-zirconium-reinforced molybdenum, silicon carbide, or aluminum oxide fiber-reinforced oxide ceramic. The workpiece-side layer and / or the press-side layer can also be made of one of the aforementioned materials.

[0060] The press plate heating device of the heatable press plate may comprise or consist of at least one of tungsten, molybdenum, a nickel-based alloy such as Microfer, a non-oxide ceramic such as silicon carbide or graphite, or even carbon fiber reinforced carbon (CFG).

[0061] The press plate heating device can be plate-shaped. The press plate heating device can also be meander-shaped. The press plate heating device can have channels or tracks. The channels or tracks can be distributed evenly throughout the press plate such that the material of the press plate has a distance from one of the channels or tracks that is at most twice the width of the channels or tracks or less. Such a distribution of the channels or tracks in the press plate provides the most homogeneous heat distribution possible for the press plate.

[0062] The press plate heating device can be configured to be electrically operated, so that it releases heat when electrically supplied. Alternatively or additionally, the press plate heating device can be configured to allow fluid flow through it, so that it releases heat when exposed to a hot fluid.

[0063] The press plate heating device can preferably have two or more heating plates. The press plate heating device can also have a connecting piece for connecting two or more sub-areas, such as heating plates, wherein the connecting piece in particular comprises or consists of graphite.

[0064] The connecting piece can be designed to be reversibly deformable, so that it deforms under the application of a compressive force, in particular becomes wider, and improves or establishes the electrical contact between the sub-areas of the press plate heating device. In other words, the connecting piece is arranged in the press plate heating device such that, at the moment a compressive force is applied to the press plate, the electrical contact between the sub-areas of the press plate heating device is improved or even established for the first time by means of the connecting piece, thus improving the operational reliability of the press plate heating device.It is also important to consider that the compressive forces applied to the press plate are very high, and suitable materials are characterized by, on the one hand, their resistance to the given pressure and temperature conditions, and, on the other hand, the materials used are not reflected in the joining result. For example, materials of varying densities are often recognizable by the fact that they imprint themselves on the workpiece to be machined, like a stamp, and the arrangement of materials of varying densities, or at least of varying hardness, can be recognized in the finished workpiece. This should be avoided wherever possible. This can also be achieved with the press plate heating device presented here.

[0065] For precisely this purpose, the heatable press plate can further comprise a pressure equalization layer. The pressure equalization layer can be designed to cover the entire surface and, if necessary, be flexible or compressible. The pressure equalization layer can be arranged adjacent to the press plate heating device, for example, placed on the press plate heating device and, if necessary, completely covering the press plate heating devices. The pressure equalization layer can be a graphite foil. The pressure equalization layer enables further homogenization of the compressive force across the press plate, whereby local differences in the hardness or density of the materials used for the press plate heating device do not lead to a stamp-like imprint in the workpiece to be joined, or lead to a significantly lower degree of this.

[0066] The press-side layer and / or the workpiece-side layer can be designed as a tile carpet, in particular as a ceramic tile carpet. The use of small-scale components, such as in particular a tile carpet, can result in unevenness, for example edges of the heating device, being able to be compensated for and force being distributed across the tiles of the tile carpet and thus across the press plate. The press plate heating device can be arranged in a heating plane, i.e. in other words, the press plate heating device is limited to a vertical area in the press plate and is enclosed on both the top and bottom by press plate material. Ceramic tiles can be arranged between components of the press plate heating device.

[0067] In the following, the invention is explained in more detail using exemplary embodiments and with reference to the figures, wherein identical and similar elements are partly provided with the same reference numerals and the features of the various exemplary embodiments can be combined with one another.

[0068] Short description of the characters

[0069] It shows

[0070] Fig. 1 shows a first embodiment of a high-temperature joining furnace in a side sectional view with a workpiece inserted, Fig. 2 shows a further embodiment of a high-temperature joining furnace in a side sectional view, wherein the pressing device is applied to the workpiece or exerts a pressing force,

[0071] Fig. 3 Top view of a heating plate, a press plate heating device,

[0072] Fig. 4 Side sectional view of a heating plate,

[0073] Fig.5 Side view of a heating plate,

[0074] Fig. 6 perspective view of a continuous heating plate,

[0075] Fig. 7 perspective step-section view of a continuous heating plate,

[0076] Fig. 8 perspective partial sectional view of a press plate heating device with split heating plate,

[0077] Fig. 9 Side sectional view of the embodiment of Fig. 8,

[0078] Fig. 10 Top view of a split heating plate,

[0079] Fig. 11 Side view of a heating plate,

[0080] Fig. 12 Side view of a press plate with press plate heating device,

[0081] Fig. 13 Top view of a press plate with press plate heating device,

[0082] Fig. 14 perspective view of a press plate with press plate heating device,

[0083] Fig. 15 perspective partial sectional view of a press plate with press plate heating device,

[0084] Fig. 16 further perspective partial sectional view of a press plate with press plate heating device,

[0085] Fig. 17 perspective view of a flexible connector for a press plate heating device,

[0086] Fig. 18 Side view of a flexible connector,

[0087] Fig. 19 perspective partial sectional view of another embodiment of a press plate with press plate heating device with ceramic meander,

[0088] Fig. 20 perspective partial sectional view of another embodiment of a press plate with press plate heating device with ceramic tiles,

[0089] Fig. 21 is a perspective view of a high-temperature joining furnace,

[0090] Fig. 22 is another perspective view of a high-temperature joining furnace,

[0091] Fig. 23 a perspective view of a high-temperature joining furnace with peripheral attachments, Fig. 24 top view of a high-temperature joining furnace,

[0092] Fig. 25 perspective view of a high-temperature joining furnace, Fig. 26 a flow chart for a joining process.

[0093] Detailed description of the invention

[0094] Fig. 1 shows a first embodiment of a high-temperature joining furnace 1 with a heating chamber 15 arranged inside the housing 12, in which a workpiece 50 is arranged for a subsequent pressing process. The joining furnace 1 has a filling or removal opening 11 through which the workpiece 50 - or several workpieces 50 or a batch - can be introduced into the heating chamber 15 or removed from it. The workpiece 50 lies on the workpiece holder 34, which is arranged on the underside of the heating chamber 15. The workpiece holder 34 can be the counter-pressing element 38 or can be designed as a counter-pressing element 38 or can be arranged on the counter-pressing element 38. In the example in Figure 1, the workpiece 50 lies directly on the counter-pressing element 38, which simultaneously forms the workpiece holder 34. Depending on the design of the workpiece 50, the workpiece holder 34 can be placed on the counter-pressing element 38.

[0095] In this embodiment, the pressing device 20 is arranged on the top side of the housing 12 of the joining furnace 1 in order to be able to exert a pressing force from above onto the workpiece 50 and against the workpiece holder 34 or the counter-pressing element 38. A plurality of pressing rams 32—four pressing rams 32 in the example shown in Figure 1—are connected to a pressing cylinder 24. The pressing cylinder 24 is, for example, a hydraulic cylinder, wherein the pressing rams 32 are adjusted by the pressing cylinder 24 via the transfer piece 26 in the direction of the workpiece 50. A pressure distribution element 22 is arranged in the receiving area 6 of the housing 12 in order to distribute the pressing force of the pressing device 20 among the plurality of pressing rams 32.

[0096] Instead of the plurality of press rams 32, a single press ram 32 can also be used if necessary. By means of the plurality of press rams 32, e.g., 4, 8, or 12 press rams 32, the pressing force can be distributed more evenly across the pressing element 36. For example, by means of the plurality of press rams 32, an improved thermal seal of the heating chamber 15 can be achieved, since each press ram 32 requires only a comparatively small opening in the insulation 16 of the heating chamber 15, so that the energy losses from the heating chamber 15 can be lower. In addition, by means of the plurality of press rams 32, the thermal energy losses can be better equalized across the outer surface of the heating chamber 15 and an overall improved homogenization of the temperature distribution in the heating chamber 15 can be achieved.This also applies analogously to the counter-pressing rams 29 on the underside of the heating chamber 15, whereby the considerations of more homogeneous pressure distribution over the counter-pressing element 38 as well as lower and / or more uniform heat losses are taken into account.

[0097] A press force generator 28, in this example a hydraulic unit 28, supplies the press cylinder 24 with pressurized hydraulic fluid, causing it to detach from the press force generator 28 and engage the workpiece 50. For example, motor units 3 can generate the hydraulic pressure in the press force generator 28.

[0098] A first sensor device 4 is arranged on the top side, by means of which a displacement measurement of the press cylinder 24 takes place. The first sensor 4 accordingly detects the distance of the press cylinder 24 or the distance of the press ram 32 or the extension (the stroke) of the press cylinder 24 and provides a first sensor signal therefrom. A further sensor 5 can be arranged in the press force generator 28 and / or in the press cylinder 24, for example for measuring the hydraulic pressure in order to derive information about the applied press force and provide it as a sensor signal. The workpiece holder 34 is arranged within the heating device 14 to hold the workpiece 50 in the heating chamber 15.Also, to minimize the impact on the insulation 16 enclosing the heating chamber 15, the workpiece holder 34 is provided with a plurality of counter-pressing dies 29, which distribute the force as evenly as possible from the counter-pressing element 38, so that the counter-pressing element 38 is subjected to the least possible deformation. Since the counter-pressing dies 29 extend through the insulation 16, and the insulation 16 should be impacted as little as possible, a comparatively small penetration area can be created overall, and the counter-pressing dies 29 can be better thermally sealed.

[0099] Further underneath, a second sensor device 42 is arranged, which can, for example, detect the pressing force applied to the workpiece 50. Thus, the second sensor device 42 is, for example, a pressure sensor. A plurality of two or more pressure sensors can also be used as the second sensor device 42, for example, one in each area of ​​a counter-pressing ram 29, so that the pressure distribution acting on the counter-pressing element 38 can be detected and output as a sensor signal. Thus, it can be detected whether the pressure distribution on the workpiece or the batch 50 is as desired, i.e., for example, homogeneous across the workpiece or the batch 50.

[0100] In an alternative embodiment, a pressing force can be exerted on the workpiece or charge 50 from both sides. For example, the embodiment of Fig. 1 can be modified such that, instead of the (passive) subassembly, which in particular comprises counter-pressing punch 29 and counter-pressing element 38, a further pressing device 20' is arranged on the underside of the high-temperature joining furnace.

[0101] In this example, an automatic process control system 44 is arranged in the area of ​​the substructure 8 of the joining furnace 1. Input and output signals to the control system 44 are provided by means of the input device 48 and the output device 46, for example, a keyboard 48 and a screen 46, thus enabling manual control of the process flow or the input of process parameters.

[0102] In the high-temperature joining furnace 1 shown in Fig. 1, in which the upper-side press plate 36 has the press plate heating device 62 and the counter-pressing element 38 has the press plate heating device 64, the two press plate heating devices 62, 64 can be constructed similarly or identically in form and function, especially if both the press plate 36 and the counter-pressing element 38 are provided in the form of press plates. If both plates 36, 38 are equipped with a press plate heating device 62, 64, the heat distribution in the workpiece 50 can be further homogenized and, if necessary, the time required to heat the workpiece 50 can be further reduced.

[0103] Furthermore, Fig. 1 also shows the possibility of electrically contacting the press plate heating devices 62, 64 by means of contacting devices 100, wherein the current flow runs via the connecting element 112, the feedthrough 114 to the external contact 116. Further details of the contacting devices 100 can be found in Figures 17 and 18.

[0104] Referring to Fig. 2, the pressing device 20 is shown in an operating position, with the pressing plate 36 fully engaged with the workpiece 50 and a pressing force being applied to the workpiece 50. The pressing cylinder 24 or the transfer piece 26 is shown in the disengaged position. In this embodiment, the pressing rams 29 and 32 are each equipped with a pressure distribution piece 37, which is arranged at an angle between the pressing plate 36 and the respective pressing ram 32 and assists in transmitting the pressing force even more homogeneously to the pressing plate 36.

[0105] The pressing force applied by the pressing device 20 to the workpiece 50 can be detected by the pressure sensor(s) 42, which is transmitted as a sensor signal 170 to the control device 44. Otherwise, the embodiment of Fig. 2 corresponds to that shown and described with Fig. 1. Fig. 2 also shows the electrical contacting of the press plate heating devices 62, 64 by means of electrical contacting devices 100. Fig. 3 shows a first embodiment of a heating plate 62 for use in a high-temperature joining furnace 1. In the plan view shown, the press plate heating device 62 has a heating element cover layer 72 in which receptacles 68 for fastening means are provided. On both sides, a connection projection 66 projects laterally beyond the dimension of the cover layer 72, the connection projections 66 belonging to the heating element 74.

[0106] Fig. 4 shows a cross section of a press plate heating device 62, wherein the three-layer structure with heating element cover layer 72, heating element 74 and heating element bottom layer 76 can be seen.

[0107] Fig. 5 shows a side view of the press plate heating device 62, also showing the three layers 72, 74, 76 and the connection projection 66 of the heating element 74. The heating element 74 is enclosed laterally by lateral enclosures 72a, 76a, so that, with the exception of the connection projections 66, it is enclosed on all sides by the cover layer 72 and the base layer 76. The connection projections 66 serve to introduce the energy required for heating into the heating element 74. For example, an electrical contact can be established via the connection projections 66.

[0108] Referring to Fig. 6, a perspective view of a press plate heating device 62 is shown. For example, the heating device 62 shown in Fig. 6 may correspond to the heating device 62 shown in Figs. 3 to 5. The same reference numerals represent the same elements or components in all figures. Referring to Fig. 7, the embodiment of Fig. 6 is shown in a stepped section, wherein the three-layer structure comprising cover layer 72, heating element 74, and base layer 76 can be seen, as well as the enclosure of the heating element 74 by means of enclosures 72a, 76a.

[0109] With reference to Fig. 8, a further embodiment of a press plate heating device 62 is shown with a split heating plate 74. In other words, two heating plates 74 are provided, which are jointly encompassed by the cover layer 72 and the base layer 76. The heating elements 74 are in electrical contact with one another via the contact lips 67 and the connecting piece 78, so that an electrical current flow can be established from a first connection projection 66 via the first heating element 74, the contact lips 67 or the connecting piece 78, the second heating element 74a and the second connection projection 66a. Fig. 9 shows the heating element 62 of Fig. 8 in a cross-section, wherein the connecting piece 78 is visible. Figs. 10 and 11 show a single heating plate 74, in particular as a part of a split heating plate or heating plane, wherein the connection projection 66 and the contact lip 67 are visible.

[0110] There are several reasons for dividing the heating platens into several smaller heating plates 74, 74a, 74b, 74c instead of one continuous large heating platen. Firstly, it has been determined that a continuous large heating platen 74 is more prone to breakage during operation and may therefore fail sooner than when using several smaller heating plates 74, 74a, 74b, 74c. Furthermore, at the time of writing this application, any desired materials for producing the press plates 74, 74a, 74b, 74c cannot be produced in sizes corresponding to the full format of a current press platen 36. Finally, it has also been determined within the scope of the present invention that the use of smaller heating plates 74, 74a, 74b, 74c has the advantage of allowing for better selection for any material defects, and furthermore, any material defects (crack, chipping, grain mismatch, pore or cavity, etc.) can be identified more easily.) in the heating plate 74, 74a, 74b, 74c is less likely to cause breakage, since the bending moments (and deflections during operation) that occur are significantly smaller, and thus more material defects can be tolerated, which overall contributes to a reduction in manufacturing costs.

[0111] Referring to Fig. 12, a press plate heating device 62 is shown installed in a press plate 36, wherein the press plate comprises a press-side press plate element 71, a workpiece press plate element 77, and a press plate heating device 62 inserted between these two layers. These layers are connected to one another by means of the fastening means 80, for example, screwed.

[0112] Referring to Fig. 13, a plan view of a press plate 36 with press plate heating devices 62 is shown. The embodiment of Fig. 13 is reproduced in perspective in Fig. 14. The press plate heating device 62 is enclosed between the press-side press plate element 71 and the workpiece press plate element 77 and screwed together with screws 80. Referring to Fig. 15, the embodiment of Figs. 13 and 14 is shown in a stepped section, revealing the plurality of heating elements 74, 74a, 74b, 74c. The heating elements 74, 74a, 74b, 74c are electrically contacted with one another by means of connecting pieces 78. Fig. 16 shows the same press plate 36 once again in a further stepped section, revealing the four heating elements 74, 74a, 74b, 74c. The four heating elements 74 are arranged in a common heating element plane, ie next to each other.

[0113] Because they are arranged in the press plate 36, the heating elements are typically subject to movement during operation. Thus, the press plate 36 is positioned against the workpiece, and depending on the size of the workpiece, etc., the press plate 36 is in a different operating position during operation. To compensate for the different positions or movements of the heating elements 74, flexible contacting devices 100, as shown in Fig. 17, are provided, which can not only compensate for changes in position, but also compensate for movements such as impact movements or vibrations of the press plate or the press device 20. For this purpose, the contacting device 100 has a flexible compensating element 104, which dampens and decouples oscillations and vibrations. The contacting device 100 is attached to the heating element 74 with a heating element clamp 102, wherein the connection projection 66, 66a is clamped or enclosed.Screwing it tight to the connection projection 66 is also possible. On the top side, the contacting device 100 has a contact element 106, for example, for connecting a copper strip for further current conduction. In this embodiment, two contacting devices 100 are connected to a heating element 74 for supplying and dissipating current.

[0114] Fig. 18 shows the contacting device 100 in a sectional view, with the attachment to the connection projection 66 provided with further details, with the stud receptacle 108 and the stud 110 shown in cross section. In Fig. 18, a contacting device 100 is connected to two heating elements 74, although only one connection side is shown for better graphic clarity. Typically, a second contacting device 100 is used so that an electrical circuit or current flow can occur through the heating element(s) 74, 74a.

[0115] Referring to Fig. 19, a further embodiment of a heating device 62 is shown, wherein the heating element 74 is provided in the form of a ceramic meander. The heating element 74 could, for example, also be designed as a graphite, molybdenum, or CFC meander. The ceramic meander 74 is electrically conductive, so that a current flow can be realized from the first connection projection 66 through the ceramic meander 74 to the second connection projection 66a. The heating device 62 is enclosed in a press plate 36, wherein the press plate has the press plate elements 71, 77. The fastening means 80 are not explicitly shown in this embodiment for reasons of clarity. For example, the plates could be glued to one another; typically, a screw connection is advantageous due to the high operating temperature.

[0116] Referring to Fig. 20, yet another embodiment of the press plate heating element 62 is shown, wherein the heating element cover layer 72 and the heating element base layer 76 are designed as tiles. The heating element 74 is correspondingly embedded in the tiles 72, 76, 82. This provides the advantage that any unevenness or impacts that may be present are compensated for and are therefore less visible as restrictions in the workpiece 50.

[0117] 21 and 22, a high-temperature joining furnace 1 is shown, wherein an outer frame 7, 9, 10 is included for supporting the pressing device 20. The pressing cylinder 24 is mounted by the support frame element 10 so that the pressing force from the pressing device 20 can be transferred to the workpiece 50 arranged inside the high-temperature joining furnace 1 (see, for example, Figs. 1, 2). When the pressing force is applied, the total force is absorbed by the outer frame 7, 9, 10, which can bend in a direction away from the joining furnace 1 during operation. The bending of the outer frame 7, 9, 10 provides a dynamic bearing for the pressing device 20, so that a press abutment 18 is formed by the outer frame 7, 9, 10. In Fig. 23, a position sensor 5 is provided with which the positional displacement of the press abutment 18 can be detected.By means of the positional shift, a conclusion can also be drawn about the pressing force applied by the pressing device 20, and the information can be provided as a sensor signal.

[0118] Figures 23 to 25 show a further embodiment of a high-temperature joining furnace 1, which is now shown completed with additional add-on components. A vacuum generator 54, for example a turbomolecular pump, provides vacuum extraction so that the joining process in the high-temperature joining furnace 1 can be carried out in a vacuum, in particular a high vacuum or an ultra-high vacuum. The pressing force generator 28 is housed in a separate housing so that a larger unit can be accommodated there if necessary. An input and / or output device 48, 46 is housed in a user terminal 45, which includes the PLC 44 and input / output 48, 46.

[0119] Referring to Fig. 26, a flow diagram of a joining method 200 is shown. In a first step 210, the system is filled with a workpiece 50 or a batch of one or more workpieces. This is typically carried out by a user, but can also be automated. In a step 220, the system 1 is parameterized. Here, various specifications, such as in particular the materials and joining surfaces of the workpiece or batch 50, can be stored in the control device 44 using an input device 48. For example, the intended compression of the workpiece 50 or batch can also be entered in percent or distance, e.g., in millimeters. Temperature specifications, for example, can also be stored. The parameters entered in step 220 can be transmitted to a control device 44. The control device 44 can then generate a set of control parameters.After the filling opening 11 is closed, the joining furnace 1 is now ready for operation. Process phase 230 begins, e.g., with temperature parameters provided by the control device 44. Preparation of the press 20 then takes place. This may involve applying pre-pressure to the pressing device 20 so that the abutment 18 undergoes a displacement, deformation, or pre-tension, allowing the pressing device 20 to assume its initial position. During this time, or before or after, the workpiece 50 is heated in heating phase 230. During this process, the press plate heating device 62, 64 is heated, and the heat is evenly and conductively transferred to the workpiece 50.

[0120] The pressing process or joining process is then carried out in step 240; if necessary, this can be monitored and adjusted by the automatic process control 44. Sensors 4, 5, 42 can provide sensor signals, which are processed by the process control 44. The prepared control parameters can be checked or adjusted, if necessary, in response to the sensor signals provided by the sensors 4, 5, 42. If the control parameters need to be adjusted, the joining process 240 is continued in a modified form using the adjusted control parameters. This can be implemented as a control loop and carried out iteratively, for example, so that an improved parameter configuration can be set over the course of the joining process and an improved joining result can be achieved. In other words, in one example, a compression of the workpiece 50 by X% is specified.This occurs within a certain time, which can be calculated by the control system. An initial pressing force is applied, followed by step 240, the actual pressing process. During the execution of pressing process 240, it can be checked, if necessary, whether the required distance per unit of time has been reached and the pressing force can be adjusted if necessary.

[0121] For example, an increasing pressing pressure can be stored, which can be adaptively adjusted during the joining process 240. A maximum or desired deflection of the pressing cylinder 24 to a desired final value can also be stored in the set of original control parameters. During the review or adjustment of control parameters, it can also be determined whether the desired final value for the deflection of the pressing cylinder 24 and / or the deformation of the workpiece can be achieved without possibly exceeding a pressing pressure at which the workpiece or batch 50 could potentially be damaged or excessively deformed.

[0122] In a step 250, the workpiece or batch 50 may optionally be subjected to post-treatment. This may include further tempering, further heating, or cooling at a defined temperature constant. Following post-treatment 250, the workpiece or batch 50 has cooled sufficiently and can be removed from system 1 in step 260.

[0123] In the present description, a functional solution has been presented in a variety of examples, including features that can be individually combined with one another, showing how the homogeneity of the heat distribution in the workpiece 50 can be improved and / or the time required to heat the workpiece 50 can be reduced by integrating a heating device 62, 64 directly into the press plate 36, 38, particularly by means of conductive heat transfer. Furthermore, materials can now be processed by diffusion bonding that were previously inaccessible to this process due to the required low temperature ranges.

[0124] Conductive heating of the press platens 36, 38 by one or more heating elements 74, 74a, 74b, 74c, which may optionally be made of ceramic or another heating material, has proven advantageous for this purpose. The heater 62 is preferably an electrical resistance heater which is integrated in an electrically insulated manner. For support, a peripheral heater 14 can be provided in order to uniform the temperature at the edge and in the corners of the component 50. The supporting or peripheral heater can be moved vertically. The supporting heater can, if necessary, be divided into different temperature zones. Water-cooled pressure distribution plates 36, 38 can be used if necessary. A flexible heater connection 100 can, for example, be realized using copper strips 112.

[0125] One objective is to make the diffusion welding of large-format components (possibly larger than DIN A3 format) more efficient. Efficiency refers to both the energy consumption per welding cycle and the duration of a joining cycle. This can be achieved by heating the components to be joined via conduction heating—i.e., contact heating.

[0126] With the increasing degrees of design freedom due to additive manufacturing, there is also a desire to scale up the existing component volumes. While the build volumes of powder bed systems have also grown in recent years, systems with 500 x 280 x 850 mm are currently available. 3commercially available, but the build-up rates are still low, especially when it comes to massive components such as molds. An alternative additive build-up process can be material deposition with directed energy input (DED) using an arc and wire as filler material. High build-up rates in the range of several kilograms per hour are possible with this. A disadvantage, however, is the inadequate ability to produce internal channels. While these are feasible in principle, the shape and dimensional accuracy are currently only sufficient for cooling channels. Functions such as the distribution of plastic mass or heat exchanger structure cannot currently be implemented with this method. For this reason, diffusion welding is already being used for corresponding components.The size scale of diffusion welding systems with regard to the press plates currently available on the market is in the range of over one meter.

[0127] One objective of this description was to develop and establish design constraints for a heating concept for diffusion welding that homogenizes the heat input into the component and, if possible, achieves this through contact heating, i.e., heat conduction. Process temperatures of up to 900°C, for example, and the possibility of dynamic force application are targeted. Furthermore, the system is to be designed for use in high-vacuum furnace systems. Conductive heating avoids the lossy and emission-dependent heat transfer by radiation that occurs in a vacuum, making the energy input into the mostly plate-shaped joining parts considerably more efficient, homogeneous, and faster. The result is a heating system that enables a significant increase in energy efficiency in diffusion welding and significantly shortens cycle times.This will result in a significant cost reduction of the diffusion welding joining process and an increase in component quality, as well as increasing the competitiveness of the process.

[0128] Of particular importance is the heat control or heating of the components to be joined 50. Especially for non-ferrous metals, whose joining temperatures are below 1,000°C, the previously established heating by thermal radiation in a vacuum represents an inefficient process. Due to the low emissivity, only very low heating rates were possible, which has a negative impact on the cycle time and thus the costs of the process.The direct (conductive) component heating by heat conduction via the press plate 36, 38 accelerates the energy input into the component 50 and at the same time enables a more homogeneous temperature distribution, since the heat is introduced evenly over the largest surfaces of a plate-shaped component. While conventional heating takes place essentially via the outer edges, so that a gradient arises between the outer side and the component center due to the path length, which leads to quality differences in the composite formation if not adjusted by waiting (extending the cycle time).

[0129] The size of the press platen surface can advantageously be at least 300x500 mm or larger. The cyclic load capacity of system 1 is preferably 0.1 Hz or more, or even 0.5 Hz or more, or even 1 Hz or more. Operation in a fine or high vacuum at at least 10 5 mbar is advantageous. A transferable surface pressure of > 7 N / mm 2can be achieved on the system side. For example, by means of the press plates 36, 38, a surface pressure of at least 0.1 MPa can be achieved on the component 50, preferably of at least 0.5 MPa. For example, the surface pressure can be achieved up to a maximum of 50 MPa, optionally a maximum of 40 MPa. Alternatively or cumulatively, a force of 1 ton or more can be exerted on the component 50 by means of the press plates 36, 38; in this case, the system can even be used for force-assisted brazing (PAB). Preferably, a force of 5 tonnes or more can be exerted on the component 50 by means of the press plates 36, 38. If necessary, the force exerted on the component 50 by means of the press plates 36, 38 can be up to 5,000 tonnes, for example even up to 4,000 tonnes. Lower surface pressures of less than 0.1 MPa or force applications of less than 1 ton are not understood as pressing force or application of a pressing force within the meaning of this application.For example, wafer bonding processes, i.e., joining semiconductor circuit boards, are not press processes within the meaning of this application. Rather, the field of diffusion welding or force-applied soldering within the meaning of this application is subject to the aforementioned comparatively high pressure regime.

[0130] There are three key factors that are important for the diffusion welding process: the atmosphere in which the joining takes place, the type and method of force application, and the heating concept. If the component geometry is taken into account in addition to the process, the system concept, i.e. the design of the welding system, must also be considered. In principle, the components to be joined can be heated in a vacuum in a variety of ways: by means of thermal radiation, laser or electron beam, convection, direct resistance heating, induction, heat conduction, or a combination of individual variants. Beam-based processes (laser or electron beam) are particularly suitable for small, rotationally symmetrical parts, but have the disadvantage that an additional axis must be provided in the system (rotation axis for rotating the workpiece).A direct current application to the components to be joined leads to direct resistance heating, but here too, the component size is limited due to the electrical parameters. If the direct current is replaced by a pulsed current, larger currents can be implemented. This also results in sparkovers, comparable to plasma spark sintering. Due to the direct current flow through the components, only electrically conductive materials can be joined, whereby a homogeneous distribution of the electric field must be ensured, especially for large-format components. Induction heating is used much more frequently, especially historically. The heat is generated directly in the area of ​​the component surface, which heats the component quickly. Diffusion welding systems for mass production, among others.Valve disc seals, with production numbers of 3.1 million units per year, were already equipped with induction heating in the 1970s. The penetration depth can be adjusted using parameters such as frequency or current. However, the component-inductor distance or the shape of the inductor also influences the heat input and thus the temperature distribution within the component. A disadvantage is that for optimal heating, the inductor must be adapted to the component geometry, and not all materials can be heated inductively. However, induction heating is suitable, for example, for slim component geometries.

[0131] However, the current trend in component dimensions is toward solid, flat components with large dimensions in at least two spatial directions, e.g., plate heat exchangers or injection molds. Therefore, newer generations of diffusion welding systems are typically constructed according to the "oven principle." This means that a vacuum furnace system forms the basis for the welding system, into which a "pressing system" 20 must also be integrated. Heating occurs via thermal radiation, most commonly via resistance-heated elements. Infrared radiators can also be used for small parts. Since no convection occurs in a vacuum, heat transfer is limited solely to radiant heating between the heating element and the component. The key factor influencing radiant heating is the absorption coefficient of thermal radiation, which depends on the component surface condition.According to Kirchhoff's radiation law, which states that radiation absorption and emission correspond to each other at a given wavelength, often only the emissivity is given.

[0132] Molybdenum can be considered as a heating element material in air and in a vacuum. The oxide layer on the molybdenum dissolves in a vacuum, thus achieving a high emissivity in a vacuum, which is why the material is used for heaters. Furthermore, two typical material groups of the components to be joined are included: aluminum and steel. Purified steel has a comparatively high emissivity. This is temperature-dependent and increases with temperature. In comparison, the value for aluminum is significantly lower. Purified aluminum has very low values, whereas oxidized aluminum surfaces have a value that is only 2 to 3 times lower than that of steel. From a radiation technology perspective, oxidized surfaces are optimal with regard to the absorption of thermal radiation, but not from the perspective of diffusion welding, since oxide layers represent a diffusion barrier. Copper materials behave similarly to aluminum.This means that heating highly thermally conductive materials solely by radiation may be insufficient for the welding process. For materials with a low tendency to react with the environment, heat transfer can be enhanced by partial pressure in the working chamber (additional convection component) in addition to pure radiation heating. In aluminum and titanium alloys, impurities in the gas (including oxygen / nitrogen) lead to a reaction with the surface and the formation of layers, which in turn inhibit diffusion and can negatively affect the mechanical and technological properties.

[0133] Another disadvantage of the heating concepts described above is the temperature homogeneity within the component. Heat transfer always occurs via the component surface and is then conducted into the component interior by thermal conduction. Accordingly, a temperature gradient develops within the component 50 during heating, leading to uneven expansion and internal stresses. Depending on the thermal conductivity of the material to be joined, this must be counteracted by appropriately slow heating rates, also to avoid heat buildup and overheating of the component surface. In addition to the material, the aspect ratio of the component is of key importance. The concepts described above primarily incorporate heat input via the component's side surfaces. For plate-shaped components, this provides a maximum heat conduction path.However, such component geometries with low aspect ratios are currently in increasing demand (plate heat exchangers, tool inserts, etc.). The heat input via the base and top surfaces thus shortens the conduction path and allows for higher heating rates.

[0134] Press plates for diffusion welding systems fulfill the task of transferring the applied pressing force into the component and distributing this force as evenly as possible across the component or the joining surface. This results in a basic requirement for the mechanical properties of the plate 36, 38, such as a low modulus of elasticity and sufficient compressive and flexural strength. Due to use in a high-vacuum furnace system, these properties must be guaranteed across the entire range of application temperatures. Furthermore, the press plate material must be suitable for use in vacuum (high vapor pressure). In addition, the ideal press plate material has a low specific heat capacity, since from an energetic perspective, the press plates represent dead mass that must be heated and cooled again during the process. A further requirement is fatigue strength under dynamic load in the pressure threshold range.

[0135] In the field of metallic materials, titanium-zirconium-reinforced molybdenum (TZM) represents a good starting point and is used in many applications as a load-bearing element in the heating section of vacuum furnaces. In addition to its thermal and mechanical properties, its machining behavior is comparable to that of CrNi steels. Accordingly, TZM is also of interest for this description. The disadvantage of TZM is its comparatively high density of 10.2 g / cm³. 3 , the high thermal conductivity characteristic of metals and the high costs associated with production.

[0136] All-ceramic press plates offer the ideal press plate material due to their mechanical properties. For example, silicon carbide ceramics have a high elastic modulus of 350-450 GPa but also a compressive strength of over 2500 MPa, resulting in a very dimensionally stable material. A significant disadvantage of these ceramics is the high cost of processing them in the sintered state.

[0137] Steel materials such as heat-resistant steel 1.4828 are, in principle, conceivable as press plate materials. However, the exclusion criterion here is their low creep strength of less than 5 N / mm 2 at the desired operating temperature of 900°C.

[0138] An alternative to the aforementioned materials is ceramic-based fiber composites (CMC). Similar to carbon fiber reinforced plastics, carbon fibers or ceramic fibers are embedded in a ceramic matrix. This retains the outstanding properties of the ceramic, such as temperature resistance and compressive strength, while the fiber reinforcement increases the fracture toughness required for dynamic applications.

[0139] Carbon fiber reinforced graphite (CFC) can be used in diffusion welding systems with static force application. Due to its high thermal conductivity compared to the other fiber composites considered here, correspondingly more energy is extracted from the heating zone.

[0140] Carbon fiber reinforced silicon carbide is a composite material. This material has not previously been used in diffusion welding systems.

[0141] Aluminum oxide fiber-reinforced oxide ceramics exhibit a very low thermal conductivity of 0.4–2.7 W / mK and a relatively low modulus of elasticity (40 GPa), which would lead to excellent insulation and very good pressure distribution. However, the critical feature of this material is its low compressive strength of approximately 25 N / mm. 2 .

[0142] The general requirements for heater materials for the heating devices 62, 64 are essentially high electrical resistance, a high melting temperature that must significantly exceed the application temperature, and a low vapor pressure to minimize heater wear during vacuum operation. From a design perspective, a low thermal expansion coefficient is also desirable. Among metallic materials, molybdenum, along with tungsten, stands out as a heater material. With a melting temperature of 2623 °C, a specific electrical resistance in the range of 0.056-10-6 - 0.452-10-6 Ωm (20 - 1500 °C), and an expansion coefficient of 5.8-10-6 K-1, it is possible to achieve temperatures of up to 1600 °C with very high vacuum quality.

[0143] An alternative to this are nickel-based alloys, which have higher mechanical strength and toughness with comparable electrical resistance (e.g. Nicrofer® 0.103- 10-6 - 0.114 10-6 Qm (20 - 1000 °C). However, the range of applications is limited due to the lower melting temperature (1370-1425 °C) and the comparatively high expansion coefficient of 16.9-10-6 K-1 (1000 °C).

[0144] In addition to metallic materials, resistance heating can also be achieved using non-oxide ceramics such as SiC. These are now commercially available as hot plates for temperatures up to 1100 °C, allowing for a homogeneous temperature distribution. However, the high brittleness and sensitivity to bending stress are critical for the intended application.

[0145] Graphite is another alternative for heating furnace systems, with the advantages of its comparatively low material price and high electrical resistance. However, graphite is only suitable for use in high vacuums to a limited extent, as evaporating carbon can contaminate the parts being joined and cause material changes.

[0146] It will be apparent to those skilled in the art that the embodiments described above are to be understood as examples and that the invention is not limited to them, but can be varied in many ways without departing from the scope of the claims. Furthermore, it is clear that the features, regardless of whether they are disclosed in the description, the claims, the figures or otherwise, also individually define essential components of the invention, even if they are described together with other features. In all figures, the same reference numerals represent the same objects, so that descriptions of objects that may only be mentioned in one figure or at least not with regard to all figures can also be transferred to those figures with regard to which the object is not explicitly described in the description.

[0147]

[0148] 1 high-temperature joining furnace

[0149] 3 Motor unit

[0150] 4 first sensor device

[0151] 5 additional sensor devices

[0152] 6 Press receiving area of ​​the housing 12

[0153] 7 Support frame element (horizontal, bottom)

[0154] 8 Substructure

[0155] 9 Support frame element (vertical)

[0156] 10 Support frame element (horizontal, top)

[0157] 11 Filling and / or removal opening

[0158] 12 housings

[0159] 14 Oven heating device

[0160] 15 Heating chamber

[0161] 16 thermal insulation

[0162] 18 press abutments

[0163] 20 Pressing device

[0164] 22 Pressure distribution element

[0165] 24 press cylinders

[0166] 26 Transfer piece

[0167] 28 press force generators

[0168] 29 counter-press stamps

[0169] 32 press stamps

[0170] 34 Workpiece holder

[0171] 36 Press plate

[0172] 37 Pressure distribution piece

[0173] 38 Counter-pressing element

[0174] 42 second sensor device

[0175] 44 Programmable Logic Controller

[0176] 45 User terminal with PLC, input and output device

[0177] 46 Output device

[0178] 48 Input device

[0179] 50 workpieces

[0180] 54 Vacuum generator (vacuum pump)

[0181] 62 Press plate heating device in press plate

[0182] 64 Press plate heating device in workpiece holder

[0183] 66, 66a connection overhang, overhang collar

[0184] 67, 67a Contact lip

[0185] 68 Holder for fastening devices 71 Press-side press plate element

[0186] 72 Heating element cover layer

[0187] 72a Side enclosure of the heating element 74

[0188] 74, 74a, 74b, 74c heating element

[0189] 76 Heating element bottom layer

[0190] 76a Side enclosure of the heating element 74

[0191] 77 Workpiece press plate element

[0192] 78 connecting piece

[0193] 80 fasteners, screw

[0194] 82 tiles

[0195] 100 contacting device

[0196] 102 Heating element terminal

[0197] 104 Flexible compensation element

[0198] 106 Contact element

[0199] 108 Stud bolt holder

[0200] 110 studs

[0201] 112 Connecting element, e.g. copper tape

[0202] 114 Implementation

[0203] 116 External Contact

[0204] 200 joining processes

[0205] 210 Filling

[0206] 220 Parameterization

[0207] 230 Process phase

[0208] 240 pressing or joining step

[0209] 250 Follow-up treatment if necessary

[0210] 260 Unloading the system

Claims

High-temperature joining furnace (1), in particular equipped for diffusion welding of joining materials such as metals and metallic workpieces (50), comprising: a heating chamber (15), a workpiece fixture (34) arranged in the heating chamber for receiving a workpiece (50) to be processed in the joining furnace, a press device (20) arranged and equipped to apply a pressing force to the workpiece, wherein the press device comprises a press plate (36) for uniformly applying the pressing force to the workpiece, characterized in that the press plate is equipped with a press plate heating device (62) for heating the press plate and / or the workpiece.

2. Joining furnace (1) according to the preceding claim, wherein the press plate heating device (62) is integrated into the press plate (36), in particular is fully integrated, and / or wherein the press plate (36) is a multi-part press plate, wherein in particular the press plate comprises a workpiece-side element (77) and a press-side element (71), and / or wherein the press plate heating device (62) is arranged between a workpiece-side layer (77) and a press-side layer (71).

3. Joining furnace ( 1 ) according to one of the preceding claims, further comprising flexible connecting connectors (100) for connecting the press plate heating device (62) to an energy source.

4. Joining furnace ( 1 ) according to one of the preceding claims, wherein the press plate heating device (62) provides conductive heat output, i.e., is a conductive press plate heating device, and / or wherein the press plate heating device (62) is configured to be electrically operable, so that it emits heat when it is supplied with electrical power from the energy source, and / or wherein the press plate heating device (62) is configured to allow fluid flow, so that it emits heat when it is supplied with a hot fluid from the energy source.

5. Joining furnace (1) according to one of the preceding claims, wherein the pressing device (20) comprises a hydraulic device as a pressing force generator (28) and builds up the pressing force by means of a hydraulic pressure and / or wherein the pressing device (20) comprises an electric spindle, and / or wherein the pressing device (20) comprises a pressing cylinder (24), and / or wherein the pressing device (20) comprises several pressing rams (24), in particular two, three, four or more Pressing die. Joining furnace (1) according to one of the preceding claims, wherein the high-temperature joining furnace comprises an outer frame (7, 8, 10), and wherein the pressing device (20) is arranged on the outer frame and / or is supported on the outer frame, and / or wherein the outer frame (7, 8, 10) is designed to be movable and / or deformable. Joining furnace (1) according to one of the preceding claims, further comprising a press abutment (18) which is configured such that, by applying the pressing force by the press device (20) to the workpiece (50), a lateral displacement and / or deformation of the press abutment (18) takes place, and / or wherein the press device (20) is configured such that a preload force can be built up against a support frame element (10) during a pressing operation, and / or wherein the workpiece holder (34) serves as a counter-pressing element (38), and / or wherein the press device (20) presses the workpiece (50) against the workpiece holder (34).Joining furnace (1) according to one of the preceding claims, configured for carrying out joining processes, preferably of metal or metallic workpieces, at temperatures of 1200 °C or lower, preferably 1000 °C or lower, more preferably 950 °C or lower, and / or at temperatures of 450 °C or higher, preferably 500 °C or higher, more preferably 550 °C or higher, or also 600 °C or higher, and / or configured for carrying out joining processes, preferably of non-metals such as plastics, ceramics or corresponding workpieces, at temperatures of 350 °C or lower, preferably 300 °C or lower, more preferably 250 °C or lower, or also 200 °C or lower, and / or at temperatures of 80 °C or higher, for example 100 °C or higher, preferably 120 °C or higher and more preferably 140 °C or higher.Joining furnace (1) according to one of the preceding claims, further comprising a furnace heating device (14) for emitting radiant heat into the heating chamber (15). Method for diffusion welding in a high-temperature joining furnace (1), in particular according to one of the preceding claims, comprising the steps of: Filling the joining furnace with a workpiece (50), Applying at least one press plate (36) of a press device (20) to the workpiece, Heating the workpiece predominantly by means of a press plate heating device (62) to a joining temperature, Pressing the workpiece with a press device (20) to carry out the diffusion welding process.

11. Method according to the preceding claim, further comprising the step of tempering or heating the press plate (36) during pressing by means of the press plate heating device (62) to homogenize the temperature distribution in the workpiece (50).

12. Heatable press plate (36) for a high-temperature joining furnace (1), in particular according to one of the preceding claims, wherein the press plate is designed to uniformly apply a pressing force to a workpiece (50) placed in the high-temperature joining furnace, characterized in that the press plate is equipped with an integrated press plate heating device (62) for heating the press plate and / or the workpiece.

13. Heatable press plate (36) according to the preceding claim, wherein the press plate heating device (62) is integrated into the press plate, in particular is fully integrated, and / or wherein the press plate is a multi-part press plate, wherein in particular the press plate comprises a workpiece-side element (77) and a press-side element (71), and / or wherein the press plate heating device (62) is arranged between a workpiece-side layer (77) and a press-side layer (71).

14. Heatable press plate (36) according to one of the preceding claims with the multi-part press plate according to the preceding claim, wherein each part of the press plate consists of the same base material and has only different dopants.

15. Heatable press plate (36) according to any of the preceding claims, wherein the press plate comprises ceramic material, and / or wherein the workpiece-side layer (77) and / or the press-side layer (71) comprises or consists of ceramic material, and / or wherein the press plate heating device (62) comprises or consists of ceramic or metal material.

16. Heatable press plate (36) according to the preceding claim, wherein the ceramic material comprises at least one carbon fiber reinforced graphite, carbon fiber reinforced silicon carbide, titanium-zirconium reinforced molybdenum, silicon carbide or aluminum oxide fiber reinforced oxide ceramic, or the workpiece-side layer (77) and / or the press-side layer (71) consists of one of the aforementioned materials, and / or wherein the press plate heating device (62) comprises at least one tungsten, molybdenum, a nickel-based alloy such as Nicrofer®, a non-oxide ceramic such as silicon carbide or graphite, or a includes or consists of carbon fiber reinforced carbon.

17. Heatable press plate (36) according to one of the preceding claims, wherein the press plate heating device (62) is plate-shaped, and / or wherein the press plate heating device (62) is meander-shaped, and / or wherein the press plate heating device (62) has channels or webs and the channels or webs penetrate the press plate so uniformly that the material of the press plate has a distance to one of the channels or webs that is at most twice the width of the channels or webs or less.

18. Heatable press plate (36) according to one of the preceding claims, wherein the press plate heating device (62) is configured to be electrically operable, so that it emits heat when it is supplied with current, and / or wherein the press plate heating device (62) is configured to allow fluid flow through it, so that it emits heat when it is supplied with a hot fluid.

19. Heatable press plate (36) according to one of the preceding claims, wherein the press plate heating device (62) has at least two heating plates (74, 74a, 74b, 74c), and / or wherein the press plate heating device (62) has a connecting piece (78) for connecting two or more partial areas such as heating plates (74, 74a, 74b, 74c), wherein the connecting piece in particular comprises or consists of graphite.

20. Heatable press plate (36) according to the preceding claim, wherein the connecting piece (78) is designed to be reversibly deformable, so that it deforms under the application of a compressive force, in particular becoming wider, and improves or establishes the electrical contact between the partial areas (74, 74a, 74b, 74c) of the press plate heating device (62).

21. Heatable press plate (36) according to one of the preceding claims, further comprising a pressure equalization layer (104), wherein the pressure equalization layer is designed to cover the entire surface and is flexible or compressible, and / or wherein the pressure equalization layer is arranged adjacent to the press plate heating device (62), and / or wherein the pressure equalization layer is a graphite foil.

22. Heatable press plate (36) according to one of claims 13 to 21, wherein the press-side layer (71) is designed as a tile carpet, in particular a ceramic tile carpet, and / or wherein the press plate heating device (62) is arranged in a heating plane, and / or wherein ceramic tiles (82) are arranged between components of the press plate heating device (62).

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