High temperature bonding furnace

Abstract

A high temperature bonding furnace designed for diffusion bonding to bond materials, such as metals, plastics, ceramics, and corresponding workpieces, is presented, the bonding furnace comprising a heating chamber, a workpiece holder disposed within the heating chamber for receiving the workpiece to be processed within the bonding furnace, a pressing device disposed and adapted to apply a pressing force to the workpiece, wherein the pressing device comprises a pressing plate for uniformly applying the pressing force to the workpiece, the pressing plate comprising a pressing plate heating device for heating the pressing plate or the workpiece or both.

Description

[Technical field]

[0001] The present invention relates to a high temperature bonding furnace, a process of diffusion bonding and a heatable press plate. [Background technology]

[0002] It is generally known that metal workpieces can be joined by diffusion bonding, for example by pressing at high temperatures. The diffusion bonding process is a complex procedure that depends on many different influences, and the same process conditions do not always lead to equivalent, or at least satisfactory, results.

[0003] During the joining process, for example, deformations of the workpieces must be taken into account. For example, if the workpieces to be joined have cooling channels or other holes or openings inside, the pressing force applied to the workpieces will be locally offset, resulting in a globally different deformation compared to an individual of identical dimensions. The history of the materials to be joined may also be important with respect to the result of the joining, in particular the grain size of the metal composite and the manufacturing process of the respective metal layers, for example by rolling. Even if the different materials of the different workpieces are essentially described as being identical, i.e. manufactured using the same manufacturing process, pre-treated at the same temperature, and one must assume that the grain size in the materials is similar, the scattering width between the materials must also be taken into account. This applies even when the workpieces are provided or cut from the same raw material piece, which can be made more difficult with certain materials and / or material combinations.

[0004] A particular challenge in the operation of diffusion bonding systems is to achieve a uniform bonding result across the entire component. In addition to the aforementioned considerations regarding the material selected, the parameters of the various processes can also be checked to see if the process conditions can be further improved to further improve the uniform bonding result across the components being bonded, or to allow satisfactory utilization in the first place. Further improvement of the bonding result can be extended to other materials that cannot be processed or can only be processed poorly with existing systems. Even more complex structural shapes can be bonded using materials that are already bonded. This can also help reduce production downtime.

[0005] Against this background, the invention sets itself the task of further homogenizing the joining result over the components to be joined. In one aspect of the invention, it is also a task to be able to join new materials or more complex designs by means of diffusion bonding that could not previously be processed using this method or could only be processed poorly. In yet another aspect, the invention sets itself the task of enabling lower temperature operation in order to be able to join materials that get too hot and thus deformed too much in conventional joining processes. In yet another aspect of the invention, the task is to further accelerate the process sequence in order to reduce the operating costs and increase the throughput of components.

[0006] This problem is solved by the invention as defined in the independent claims. The dependent claims provide further embodiments and provide preferred embodiments of the invention.

[0007] In diffusion bonding processes, the workpieces or batches are deformed in a controlled way. Pores in the joining material, indentations on the inside of the workpieces, the number and size of the joining surfaces as well as the history of the joining materials are variables that can affect the sequence of the process. The pressing applies a force to the workpieces or batches, improving the contact of the materials at the joining surfaces. In this way, an inherent internal diffusion can be created or introduced. The pressing is used to increase the contact surface in the area of ​​the joining surfaces. As these processes vary from workpiece to workpiece, the differences can be so great that the first component can be joined with sufficient strength, while the next component, joined with the same parameters, may have insufficient strength or quality. On the other hand, the shape of one component may be maintained, while the same component with otherwise the same parameters may experience deformations in the area of ​​the cooling channels, for example, due to the pressing process.

[0008] According to the present invention, for example, a high temperature bonding furnace is provided that is prepared for diffusion bonding of bonding materials. The bonding materials can be metals and can include metal workpieces. The metals can be any metal-containing material or substance. For example, this includes metals such as iron, copper, aluminum, titanium, but also alloys such as stainless steel, tool steel, superalloys, bronze, tin, etc. The bonding materials can also be non-metallic or composite materials. Examples of non-metallic materials include plastics or ceramics. Examples of composite materials include ceramic composites with aluminum or copper, etc.

[0009] The high-temperature bonding furnace can also be prepared for power-assisted soldering or sintering of components. Overall, the high-temperature bonding furnace is therefore prepared for producing materials under pressure, with or without additional materials.

[0010] High temperature bonding furnaces include a heating chamber in which the workpieces, and usually also the interior of the furnace, are heated to a processing temperature.

[0011] A workpiece holder is placed in the heating chamber and holds the workpieces to be processed in the joining furnace. Typically, the workpiece holder is located below the heating chamber. For example, the workpiece holder can include a plate, but also a holder into which the workpieces to be joined are inserted. The workpiece holder can be part of or located on a counter-pressing element. In other words, the workpiece holder can be a passive counterpart of the pressing device, or it can itself be a counter-pressing element, receiving a pressing force from the underside of the workpiece holder.

[0012] The joining furnace also includes a pressing device arranged and designed to apply a pressing force to the workpieces. For example, the pressing device is arranged such that an upper part, such as a press punch, presses against the workpieces from above, so that the workpieces are pressed against a workpiece holder or a counter-pressing element. In other words, the workpieces are clamped between the upper part or press punch and the counter-pressing element or workpiece holder.

[0013] The upper part contains a press plate for this purpose, by which the pressing force is evenly distributed and applied to the surface, and the workpiece is pressed evenly. Depending on the application or shape of the workpiece, the press plate can have a flat surface, which allows a uniform pressing force to be applied to the workpiece via the surface of the press plate. In order to mold the press plate to the desired surface of the workpiece(s), the press plate can also have recesses, protrusions or steps. Thus, the press plate can be generally described as a "press element". In the following, the term "press plate" is used, which is obviously common to the skilled person in the light of the present description.

[0014] The press plate comprises a press plate heating device for heating the press plate or the workpiece or both. For example, the press plate is a pressure distribution plate for distributing the pressing force generated by the press device and applied to the workpiece over the entire surface of the workpiece. The press plate heating device allows the press plate to be conditioned or heated evenly and homogeneously over its entire surface. This also allows for uniform heat dissipation over the entire press plate so that the workpiece can also be heated evenly. In other words, the workpiece can be heat-conducted by the press plate heating device, allowing for a much faster heat transfer to the workpiece and a uniform heat input over the entire surface of the workpiece. Furthermore, the use of the press plate heating device allows for the use of materials that require a much lower processing temperature, for which sufficient heat output may not be transferred to the workpiece by thermal radiation, such that thermal radiation alone does not allow for a uniform heat distribution in the workpiece. The press plate heating device according to the invention therefore allows for the use of new materials as workpieces that were previously not amenable to diffusion bonding.

[0015] The press plate heater can preferably be integrated, i.e. completely integrated, with the press plate. In this case, a heat source can be introduced or connected to the press plate from the outside and supply heat to the press plate heater. If the press plate heater is integrated with the press plate, the heat transfer to the press plate is as seamless as possible, i.e. conductive.

[0016] The press plate may be a multi-part press plate that may include a workpiece side layer and a press side layer, and the press plate heater may preferably be disposed between the workpiece side layer and the press side layer of the press plate.

[0017] The bonding furnace can have a flexible connector for connecting the press plate heater to an energy source. For example, the flexible connector can include a metal strip material, such as a copper strip, that can counteract movement, shock, and vibration while maintaining an electrical connection.

[0018] The press heater provides conductive heat output to the press plate, i.e., it is a conductive press plate heater. For example, the press plate heater is designed to be electrically operable to emit heat when supplied with electrical power from an energy source. Alternatively or additionally, the press plate heater may be designed to allow hot fluid to pass through it to emit heat when supplied with hot fluid by an energy source.

[0019] The press plate may be movable, for example moved by one or more press punches, which in turn are actuated by one or more press cylinders. When a pressing force is applied, the workpieces are deformed or joined one to the other.

[0020] The pressing device may be configured to press the workpiece from below, for example by providing a movable workpiece holder and moving the workpiece upwards on the workpiece holder. In further embodiments of the invention, first and second press plates may be provided for applying forces on both sides, for example on the upper and lower sides of the press plate or on the left and right sides of the press plate.

[0021] To press the workpieces, a part that acts like a press punch, which can apply force from the outside, and a counter-press element that opposes the pressing force are usually used. The workpieces are clamped between the press punch and the counter-press element, where they are joined or formed.

[0022] The joining furnace may include a sidewall heating device or a furnace heating device in the furnace chamber. The sidewall heating device may be designed to heat the workpiece by thermal radiation. Since a low pressure, i.e. the highest possible vacuum, is usually set in the furnace chamber, there is practically no convection in the furnace chamber, and the wall heating device may transfer substantially radiant power. The sidewall heating device may compensate for the heat loss resulting from the workpiece placed in the furnace chamber continuously emitting a quantity of heat through thermal radiation. The sidewall heating device is therefore used to support a further homogenization of the temperature distribution in the workpiece. The furnace heating device may also be provided solely for emitting radiant heat into the furnace chamber. The two heating devices, i.e. the press plate heating device and the furnace heating device, may complement each other in that the furnace heating device compensates for the radiation of heat from the workpiece by emitting radiant heat to the workpiece. In this way, cold spots that may occur on the workpiece, especially at the edge of the side, may be avoided. However, depending on the design and requirements of the workpiece being pressed, a furnace heater may not be necessary since the press plate heater can provide uniform heat output across the entire surface of the workpiece through conductive transfer.

[0023] A sensor device may be provided in the joining furnace for providing at least one sensor signal. For example, the sensor device may detect the position or extension length of a press punch or the position of a press plate. The sensor signal is transferred to or processed by a control device designed to control at least the press device in response to the at least one sensor signal.

[0024] The sensor device of the joining furnace can detect a process parameter. The process parameter can be the thickness of the workpiece, the position of the pressure ram or the press ram of the pressing device. The process parameter can be the applied pressing force, the hydraulic pressure or the travel distance by the pressing device. A sensor signal is then generated based on the values ​​recorded by the sensor device, i.e. from one of the aforementioned process parameters. In order to simultaneously record different process parameters, several sensor devices are provided. The further sensor device can detect one or more process parameters simultaneously with the first sensor device and thus generate at least one or more further sensor signals. The one or more sensor signals can be processed for controlling the joining process or the joining furnace, so that the different process parameters can be taken into account in the control.

[0025] The press may include a hydraulic device to increase the hydraulic pressure and thereby the pressing force. The hydraulic device may also include an electric spindle, for example, which rotates to generate the feed and apply the pressing force to the workpiece.

[0026] The bonding furnace may include an input device for inputting process parameter settings. The input device may be, for example, a user operation terminal. Process parameter characteristics that may be stored before the start of the bonding process are, for example, a desired process temperature, a process time, the material(s) of the workpieces, parameters of the underlying material or other data, and the number or amount of bonding surfaces of the workpieces, or both.

[0027] For example, a workpiece may be constructed from a plurality of layers of different materials, e.g., at least two different materials stacked on top of each other, with each surface of the two different materials that is joined being described as a joining surface. Thus, for example, in the case of a planar workpiece that includes 25 layers, 24 joining surfaces are disposed on the workpiece. Information regarding cavities within the workpiece may also be taken into account as a processing parameter characteristic.

[0028] The bonding furnace may also include an output device, for example, for displaying or selecting process parameters or control programs or both. For example, information about which process stage the bonding furnace is currently in may be displayed on the output device.

[0029] The press apparatus may include a press punch through which a pressing force is transmitted, or may include a press platen that applies a pressing force to the workpiece, or may include both.

[0030] The press device may include a press cylinder. The press punch may be connected to the press cylinder such that the press cylinder exerts a pressing force on the press punch and adjusts the press punch in the direction of the workpiece. The press device may include several press cylinders, for example, 2, 3 or 4 press cylinders.

[0031] It is preferable to use several press punches which act together with the workpieces, for example via a press plate, in order to distribute the pressing force of two or more press punches as evenly or uniformly as possible over the entire surface. Several press punches can be arranged next to each other so that an array of press punches acts on the press plate. The aim here is to distribute the pressing force as evenly as possible on the workpieces to be joined, otherwise the pressing force would not be applied evenly on the workpieces to be joined and the pressing force required for joining could cause deformation of the press plate or the press elements.

[0032] The high temperature bonding furnace can include a housing. For example, the heating device, the heating chamber, the workpiece holder, and / or the press device can be housed within the housing. The press device can be disposed on the housing via a press mount, or can be supported on the housing, or both. For example, the press mount can be attached to the housing or supported by the housing such that a press cylinder connected with the press mount can support against the housing of the high temperature bonding furnace.

[0033] For the purpose of supporting the press device on the housing, a support or retaining structure, such as a support frame or cage, may be provided. The support or retaining structure may be a separate component of the housing or an integral component of the housing.

[0034] The support or holding structure and / or the press mount can be designed to be movable and / or deformable. For example, the press device supports itself against the press mount when a pressing force is applied to the workpiece, thereby moving and / or deforming the press mount, for example by deforming the support or holding structure. Here, the accumulated forces are absorbed between the press mount and the press device, for example in a press cylinder with a press punch, similar to the pretension of a spring, allowing for an even or more gradual increase in the pressing effect on the workpiece, for example when the pressing force is increased. The movable and / or deformable design of the press mount or the support or holding structure can be used to prepare the press device, which is prepared in an initial position where a preliminary pressing force is already applied to the workpiece.

[0035] The joining furnace can be set up in such a way that the application of a compressive force to the workpieces by the press device results in a lateral displacement and / or deformation of the press mount. In other words, the application of a compressive force to the press mount, which acts as the abutment of the press, causes a lateral displacement and / or deformation of the press mount. Due to the absorption of the compressive force in or in the area of ​​the press mount, a spring effect is created between the press mount and the press device or between the press mount, the press cylinder and the press punch.

[0036] The press can be prepared so that a pretension can be built up between the press punch and the housing during the pressing process or when the pressing force is built up. The presence of the pretension in the press allows for more precise injection and therefore more accurate detection and / or tracking of the punch position during the pressing process. Furthermore, the build-up of the pretension allows for more accurate setting or measurement of the pressure compensation or pressing force compensation.

[0037] For example, the press mount can be displaced or deformed by 1 mm or more, e.g., 3 mm or more, more specifically, 5 mm or more, or even 10 mm or more, when a compressive force is applied. This can form a kind of "spring mechanism", i.e., a preload force. The press mount can also be displaced or deformed by 3 mm or less, preferably 6 mm or less, more preferably 12 mm or less, when a compressive force is applied, and the minimum and maximum deflection values ​​can be combined as an interval, e.g., 3 mm or more and 6 mm or less, as a "3-6 mm range."

[0038] The sensor device can be designed to detect the position of a press punch. The sensor device can also be designed to detect the pressing force applied to the workpiece.

[0039] The control device can be set to determine a pressing force required for the inserted workpiece for the joining process by recording 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 recorded or evaluated sensor signal.

[0040] If desired, the controller can also regulate or control the heating device so that different temperatures can be maintained within the heating chamber at different times during the bonding process.

[0041] The bonding furnace may include a loading and unloading opening, hi one example, the loading and unloading opening is connected to a safety circuit that detects an open condition.

[0042] The workpiece holder can advantageously function as a counter-pressing element of the pressing device, which can thus press the workpiece against the workpiece holder, such that the workpiece is clamped between the pressing device and the workpiece holder.

[0043] The control device can provide at least one selectable control program. The selectable control program can preselect basic parameters such as, for example, a typical pressing force that is often applied in a particular material combination or a minimum press tension at which the joining process can begin. The selectable control program can include a pre-processing program or a press run program or both.

[0044] The control device is preferably designed to adapt the selected control program in response to at least one sensor signal, in particular during execution of the control program. The control program can be adapted so that processing parameters, such as the pressing force, temperature or path of the pressing device or a combination thereof, are changed or influenced during the processing process.

[0045] At least one control program can be stored in a program memory of the high temperature bonding furnace. The control device can include a programmable logic controller.

[0046] The joining furnace is preferably designed to carry out the joining process at temperatures below 1200°C, preferably below 1000°C, more preferably below 950°C, for example in the case of metal or metallic workpieces. This means that the high temperature joining furnace can carry out the diffusion joining process of metal or metallic workpieces at temperatures lower than previously known, and therefore new materials can be introduced to the diffusion bond that could not be processed in this way before. At low temperatures, the time required to introduce sufficient radiant energy into the workpiece to be treated can be very long, which may result in an unbalanced irradiation and radiation or a homogeneous temperature distribution inside the workpiece. These problems are solved with the press plate heating device herein. The joining furnace may be designed to carry out the joining process at temperatures above 450°C, for example above 500°C, preferably above 550°C, more preferably above 600°C.

[0047] The joining furnace may also be arranged to carry out the joining process at temperatures below 350°C, preferably below 300°C, more preferably below 250°C or below 200°C, for example in the case of non-metallic, such as plastic, ceramic or corresponding workpieces. This temperature range also allows access to new materials for the diffusion bonding process. The joining furnace may also be designed to carry out the joining process at temperatures above 80°C, for example above 100°C, preferably above 120°C, more preferably above 140°C.

[0048] The present invention describes a method for diffusion bonding in a high temperature bonding furnace, such as that described above, which includes the steps of filling the bonding furnace with workpieces, applying at least one press plate of a pressing device to the workpieces, primarily heating the workpieces to a bonding temperature by a press plate heating device, and pressing the workpieces in the pressing device to perform, for example, a diffusion bonding process.

[0049] The method can be further developed by the step of quenching or heating the press plate by a press plate heater during pressing to equalize the temperature distribution in the workpiece.

[0050] Further, the method can be formed by detecting or determining, using an automatic control device, such as a programmable logic controller (PLC), a pressing force required for the joining process during pressing, 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 a pressing path by measuring the distance.

[0051] The method may also be further developed by a step of repeatedly detecting or determining the pressing force required for the joining process, for example at fixed time intervals, and adaptively controlling the press device in response to the repeatedly detected or determined pressing force.

[0052] The method may also be further developed by the steps of continuously monitoring the bonding process by means of at least one sensor device and continuously adjusting the bonding process when a deviation of a monitored value from a target value is detected.

[0053] The method may further be developed with the step of inputting process parameter characteristics, for example by a user, prior to pressing of the workpiece.

[0054] Additionally, taking process parameter characteristics into account when setting target values ​​for the automatic process control may also represent a further development of the method.

[0055] The present specification also describes a heatable press plate for a high temperature bonding furnace, such as those described above. The press plate is designed for uniform application of a pressing force to a workpiece placed in the high temperature bonding furnace. The press plate is characterized in that the press plate comprises an integral press plate heating device for heating the press plate or the workpiece or both.

[0056] In an advantageous embodiment, the press plate heater is incorporated, preferably fully integrated, into the press plate. The press plate can be a multi-piece press plate, for example including a workpiece side layer and a press side layer of the press plate. The press plate heater can be disposed between the workpiece side layer and the press side layer.

[0057] Each part of the press plate, i.e. for example the workpiece side layer, the press side layer and possibly the press plate heater, can be made of the same basic material but with different doping. The press plate can include a ceramic material. The workpiece side layer or the press side layer or both can include or consist of a ceramic material. Furthermore, the press plate heater can also include or consist of a ceramic or metallic material.

[0058] The ceramic material of the heatable press plate can include 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 or the press side layer, or both, can also be constructed from one of the aforementioned materials.

[0059] The press plate heater of the heatable press plate can also include or consist of one of tungsten, molybdenum, a nickel-based alloy such as Microfer, a non-oxide ceramic such as silicon carbide or graphite, or carbon fiber reinforced carbon (CFC).

[0060] The press plate heater can be plate-shaped. The press plate heater can also be serpentine-shaped. The press plate heater can have channels or tracks. The channels or tracks can run uniformly through the press plate, with the material of the press plate having a distance from one of the channels or tracks that is no more than a maximum of two times the width of the channel or track. Such a distribution of channels or tracks in the press plate provides the press plate with the most uniform heat distribution possible.

[0061] The press plate heater can be electrically operated so as to release heat when supplied with electrical current. Alternatively or additionally, the press plate heater can be designed to allow hot fluid to flow through it so as to release heat when supplied with hot fluid.

[0062] The press plate heater can preferably comprise two or more heating plates. The press plate heater can also have a connecting part for connecting two or more sub-areas such as heating plates, the connecting part for example comprising or consisting of graphite.

[0063] The connecting parts can be designed to be reversibly deformable in the event of the application of a compressive force, for example to become wider, and in such a way that the electrical contact between the sections of the press plate heater is improved or established from the start by the connecting parts in the press plate heater. In other words, the connecting parts are arranged in the press plate heater in such a way that at the moment when the compressive force is applied to the press plate, the electrical contact between the sections of the press plate heater is improved or established from the start by the connecting parts, thus improving the safety of the operation of the press plate heater. It should also be taken into account that the compressive forces applied to the press plate are very high, characterized on the one hand by the fact that suitable materials withstand the given conditions of pressure and temperature, and on the other hand that the materials used do not leave any traces in the joining result. For example, materials with different densities are often recognized by the fact that they are processed and imprinted like a stamp on the workpiece to be processed, and the arrangement of materials with different densities or at least materials with different hardness can be recognized in the finished workpiece. This should be prevented as much as possible. This can also be achieved with the press plate heater described herein.

[0064] The heatable press plate can also include a pressure-equalizing layer in this very embodiment. The pressure-equalizing layer can be designed to cover the entire surface and can be flexible or compressible. The pressure-equalizing layer can be arranged adjacent to the press plate heater, for example arranged on the press plate heater, and in some cases completely covering the press plate heater. The pressure-equalizing layer can be a graphite foil. The pressure-equalizing layer further allows for an equalization of the compression force across the press plate, so that local differences in the hardness or density of the material used in the press plate heater do not leave, or leave only very little, stamp-like marks on the workpieces to be joined.

[0065] The press side layer or the workpiece side layer or both can be designed as carpet tiles, for example as ceramic carpet tiles. The use of small components, for example carpet tiles, makes it possible to compensate for irregularities, for example edges of the heating device, and to distribute forces via the tiles of the carpet tiles and thus via the press plate. The press plate heating device can be arranged on the heating surface, i.e. in other words it is limited to the vertical area of ​​the press plate and is surrounded by the press plate material both below and above. Ceramic tiles can be arranged between the components of the press plate heating device. [Brief description of the drawings]

[0066] In the following, the invention will be described in more detail with reference to embodiments and with reference to the drawings, in which identical and similar elements are partly provided with the same reference signs and in which the features of the various embodiments can be combined with one another.

[0067] [Figure 1] FIG. 2 is a side cross-sectional view of a first embodiment of a high temperature bonding furnace with a workpiece inserted therein; [Diagram 2] 13 is a side cross-sectional view of a further embodiment of a high temperature bonding furnace in which a pressing device is applied or exerts a pressing force on the workpiece. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. 2 is a partial cross-sectional perspective view of a press plate heating device having a divided heating plate. [Figure 9] FIG. 9 is a side cross-sectional view of the embodiment of FIG. 8. [Figure 10] Diagram of a split heating plate. [Figure 11] FIG. [Figure 12]FIG. 2 is a side view of a press plate having a press plate heater. [Figure 13] FIG. 2 is a diagram of a press plate having a press plate heater. [Figure 14] FIG. 2 is a perspective view of a press plate having a press plate heater. [Figure 15] FIG. 2 is a partial cross-sectional perspective view of a press plate having a press plate heater; [Figure 16] FIG. 2 is a further partial perspective cross-sectional view of a press plate having a press plate heater; [Figure 17] A perspective view of the flexible connector of the press plate heating device. [Figure 18] Side view of the flexible connector. [Figure 19] 13 is a partial cross-sectional perspective view of a further embodiment of a press plate having a press plate heater with a ceramic serpentine; FIG. [Figure 20] 13 is a partial cross-sectional perspective view of a further embodiment of a press plate having a press plate heater comprising ceramic tiles; FIG. [Figure 21] FIG. [Figure 22] FIG. [Diagram 23] FIG. 2 is a perspective view of a high temperature bonding furnace with peripheral equipment. [Figure 24] Top view of the high-temperature bonding furnace. [Diagram 25] FIG. [Figure 26] 13 is a flowchart of a joining process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] FIG. 1 shows a first embodiment of a high-temperature joining furnace 1 with a heating chamber 15 arranged inside a housing 12, in which a workpiece 50 is arranged for a subsequent pressing process. The joining furnace 1 has a loading or unloading opening 11 through which a workpiece 50 or several workpieces 50 or a batch can be inserted into or removed from the heating chamber 15. The workpiece 50 is placed on a workpiece holder 34 arranged on the underside of the heating chamber 15. The workpiece holder 34 can be a counter-pressing element 38 or can be designed as a counter-pressing element 38 or can be arranged on a counter-pressing element 38. In the example of FIG. 1, the workpiece 50 is placed directly on the counter-pressing element 38, which also forms the workpiece holder 34. Depending on the design of the workpiece 50, the workpiece holder 34 can be arranged on the counter-pressing element 38.

[0069] In this embodiment, the pressing device 20 is arranged on the upper side of the housing 12 of the joining furnace 1 in order to be able to generate a pressing force from above on the workpiece 50 and against the workpiece holder 34 or the counter-pressing element 38. A number of pressing punches 32 - four pressing punches 32 in the example of FIG. 1 - are connected to a pressing cylinder 24. The pressing cylinder 24 is, for example, a hydraulic cylinder, and the pressing punches 32 are set in the direction of the workpiece 50 by the pressing cylinder 24 via a transmission part 26. 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 to the number of pressing punches 32.

[0070] Instead of multiple press plungers 32, a single press plunger 32 can also be used if necessary. With multiple press punches 32, for example 4, 8 or 12 press punches 32, the pressing force can on the one hand be distributed more evenly (more uniformly) across the press element 36. With the help of multiple press plungers 32, for example an improved thermal sealing of the heating chamber 15 can also be achieved, since each press plunger 32 requires only a relatively small opening in the insulation 16 of the heating chamber 15, resulting in lower energy losses from the heating chamber 15. In addition, by using multiple press plungers 32, the thermal energy losses can also be more uniform through the outer surface of the heating chamber 15, and an overall uniformity of the temperature distribution of the heating chamber 15 can be achieved. This also applies to the counter press plunger 29 below the heating chamber 15, taking into account the considerations of a more uniform pressure distribution across the counter press element 38 and lower and / or more uniform heat losses.

[0071] A compression force generator 28, in this example a hydraulic unit 28, supplies compressed hydraulic fluid to the press cylinder 24 such that the fluid is released or withdrawn by the compression force generator 28 and applied to the workpiece 50. For example, the motor unit 3 can generate hydraulic pressure in the compression force generator 28.

[0072] The first sensor device 4 is arranged on the upper side and serves to measure the path of the press cylinder 24. The first sensor device 4 thus detects the distance of the press cylinder 24 or the distance of the press plunger 32 or the extension (stroke) of the press cylinder 24 and provides therefrom a first sensor signal. A further sensor 5 can be arranged in the compression force generator 28 or in the press cylinder 24 or both, for example to measure the hydraulic pressure, in order to obtain information about the applied compression force and provide it as a sensor signal.

[0073] The workpiece holder 34 is arranged in the heating device 14 to accommodate the workpiece 50 in the heating chamber 15. In order to minimize damage to the insulation 16 accommodating the heating chamber 15, the workpiece holder 34 is provided with a number of counter press punches 29 which distribute the force from the counter press element 38 as evenly as possible, so as to minimize deformation of the counter press punch 38. Since the counter press punch 29 passes through the insulation 16 and damage to the insulation 16 should be minimized as much as possible, a relatively small penetration area is generated throughout or the counter press punch 29 can be thermally sealed better.

[0074] A second sensor device 42 is also arranged underneath and can detect, for example, the pressing force applied to the workpiece 50. For example, the second sensor device 42 is a pressure sensor. Two or more pressure sensors can also be used as the second sensor device 42, for example one each in the area of ​​the counter-press punch 29, so that the pressure distribution at which the counter-press element 38 operates is detected and output as a sensor signal. In this way, it can be detected whether the pressure distribution on the workpiece or charge 50 occurs in the desired way, for example uniformly over the entire workpiece or charge 50.

[0075] In alternative embodiments, the pressing force can be applied from both sides to the workpiece or charge 50. For example, the embodiment of Fig. 1 can be modified such that instead of the (passive) subassembly including, for example, the counter-press punch 29 and the counter-press element 38, a further pressing device 20' is arranged below the high-temperature bonding furnace.

[0076] In this example, the automatic process control 44 is arranged in the area of ​​the substructure 8 of the joining furnace 1. Input devices 48 and output devices 46, such as a keyboard 48 and a screen 46, allow input and output to the control device 44 and thus manual influence over the input of process sequences or process parameters.

[0077] In the proposed joining furnace 1 shown in Fig. 1, in which the upper press plate 36 is equipped with a press plate heater 62 and the counter-press element 38 is equipped with a press plate heater 64, the two press plate heaters 62, 64 can be of similar or identical design with respect to shape and function, in particular if both the press plate 36 and the counter-press element 38 are provided in the form of press plates. If both plates 36, 38 are equipped with press plate heaters 62, 64, the heat distribution in the workpiece 50 can be made more uniform and, if necessary, the time required to heat the workpiece 50 can be further reduced.

[0078] 1 also shows the possibility of electrical connection of the press plate heaters 62, 64 by means of a connection device 100, thereby showing the course of electrical current flow via a connection element 112, a feedthrough 114 to an external contact 116. Further details of the connection device 100 can be found in FIGS.

[0079] 2, the press apparatus 20 is shown in an operating position with the press plate 36 fully engaged against the workpiece 50 and a pressing force being applied to the workpiece 50. The press cylinder 24 or transmission element 26 is shown in a disengaged position. In this embodiment, the press plungers 29 and 32 each include a pressure distribution element 37 disposed at an angle between the press plate 36 and each press plunger 32 to assist in a more even transfer of the pressing force to the press plate 36.

[0080] The pressing force applied by the press device 20 to the workpiece 50 can be detected by the pressure sensor(s) 42, which is transmitted to the controller 44 as a sensor signal 170. Otherwise, the embodiment of Figure 2 corresponds to the embodiment shown and described in Figure 1. Figure 2 also shows the electrical connection of the press plate heaters 62, 64 by the electrical connection device 100.

[0081] 3 shows a first embodiment of a heating plate 62 for use in a high-temperature bonding furnace 1. In the plan view shown, the press plate heater 62 has a heating element cover layer 72, in which receptacles 68 are provided for fastening means. Connecting projections 66 project laterally on both sides beyond the dimensions of the cover layer 72, the connecting projections 66 being associated with heating elements 74.

[0082] FIG. 4 shows a cross-sectional view of press plate heater 62, showing the three layer construction of heating element top layer 72, heating element 74 and heating element bottom layer 76.

[0083] 5 shows a side view of the press plate heater 62, in which the three layers 72, 74, 76 and the connecting projections 66 of the heating element 74 can also be seen. The heating element 74 is laterally surrounded by side housings 72a, 76a, such that the heating element 74 is surrounded on all sides by the top layer 72 and the bottom layer 76, except for the connecting projections 66. The connecting projections 66 serve to introduce the energy required for heating to the heating element 74. For example, an electrical connection can be established by the connecting projections 66.

[0084] Referring to Figure 6, a perspective view of a press plate heating apparatus 62 is shown. For example, the heating apparatus 62 shown in Figure 6 may correspond to the heating apparatus 62 shown in Figures 3-5. In all figures, the same reference numbers represent the same elements or components. Referring to Figure 7, the embodiment of Figure 6 is shown in a stepped section, showing a three-layer structure including a top layer 72, a heating element 74 and a bottom layer 76, with enclosures 72a, 76a for the heating element 74.

[0085] With reference to FIG. 8, a further embodiment of the press plate heating device 62 is shown, which comprises a split heating plate 74. In other words, two heating plates 74 are provided, integrally surrounded by a top layer 72 and a bottom layer 76. The heating elements 74 are electrically connected with the other via the contact lip 67 and the connecting part 78, and a current flow can be established from the first connecting protrusion 66 via the first heating element 74, the connecting lip 67 or the connecting part 78, the second heating element 74a and the second connecting protrusion 66a. FIG. 9 shows a cross-sectional view of the heating element 62 of FIG. 8, the connecting part 78 being visible. FIG. 10 and FIG. 11 show a single heating plate 74, for example as a split heating plate or heating plate, the connecting protrusion 66 and the contact lip 67 being visible.

[0086] The division into several smaller heating plates 74, 74a, 74b, 74c instead of one continuous large heating plate can have several reasons. On the one hand, it has been found that one continuous large heating plate 74 is more likely to break during operation and therefore may fail sooner than using several smaller heating plates 74, 74a, 74b, 74c. Furthermore, any desired material for manufacturing the press plates 74, 74a, 74b, 74c cannot be manufactured in a size that corresponds to the full size of the current press plates 36 at the time of preparation of this application. Finally, it has also been established in the context of the present invention that the use of smaller heating plates 74, 74a, 74b, 74c has the advantage that any material defects present in the heating plates 74, 74a, 74b, 74c (cracks, spalling, inappropriate grain size, holes or cavities, etc.) can be easily selected and, furthermore, that any material defects present in the heating plates 74, 74a, 74b, 74c can be detected. Furthermore, any material defects present in the heating plates 74, 74a, 74b, 74c (such as cracks, delaminations, improper grain size, holes or cavities, etc.) are less likely to result in failure because the bending moment (and deflection during operation) that occurs is much smaller, and therefore more material defects can be tolerated, contributing to an overall reduction in manufacturing costs.

[0087] 12, the press plate heater 62 is shown mounted on the press plate 36, which comprises a press-side press plate element 71, a workpiece press plate element 77 and the press plate heater 62 inserted between these two layers, which are connected to each other by fastening means 80, for example by screws.

[0088] With reference to FIG. 13, a top view of the press plate 36 with the press plate heater 62 is shown. The embodiment of FIG. 13 is shown in a perspective view in FIG. 14. The press plate heater 62 is sealed between the press-side press plate element 71 and the workpiece press plate element 77 and is screwed by screws 80. With reference to FIG. 15, the embodiment of FIGS. 13 and 14 is shown in a stepped section, where a number of heating elements 74, 74a, 74b, 74c are represented. The heating elements 74, 74a, 74b, 74c are electrically connected to each other by a connecting piece 78. FIG. 16 shows the same press plate 36 again in a further stepped section, so that four heating elements 74, 74a, 74b, 74c are represented. The four heating elements 74 are arranged in a common heating element plane, i.e. next to each other.

[0089] As the heating elements are arranged in the press plate 36, they are usually prone to movement during operation. The press plate 36 is therefore arranged relative to the workpiece, and depending on the size of the workpiece etc., the press plate 36 has different insertion positions during operation. In order to compensate for different positions or movements of the heating elements 74, a flexible connection device 100 is provided, as shown in FIG. 17, which can not only compensate for the changes in position, but also for movements, such as shock movements or vibration movements, of the press plate or the press device 20. For this purpose, the connection device 100 has a flexible compensation element 104 which damps and isolates oscillations and vibrations. The connection device 100 is attached to the heating element 74 with a heating element clamp 102, where the connection lugs 66, 66a are clamped or sealed. It is also possible to screw into the connection lugs 66. The upper part of the connection device 100 has a connection element 106, which is connected, for example, with a copper strip for further current conduction. In this embodiment, the two connection devices 100 are connected with the heating element 74 for supplying and removing the current.

[0090] Fig. 18 shows a cross-sectional view of the connection device 100, providing further details of the attachment to the connection lug 66, with the stud bolt receptacle 108 and the stud bolt 110 shown in cross-section. In Fig. 18, the connection device 100 is connected to two heating elements 74, with only one connection side shown for better visibility. A second connection device 100 is typically used to create a current circuit or flow through the heating elements 74, 74a.

[0091] With reference to FIG. 19, a further embodiment of the heating device 62 is shown, in which the heating element 74 is provided in the form of a serpentine ceramic. The heating element 74 can also be provided, for example, as a serpentine graphite, molybdenum or CFC. The ceramic serpentine 74 allows for a current to flow from the first connecting lug 66 through the ceramic serpentine 74 to the second connecting lug 66a. The heating device 62 is sealed to the press plate 36, which has press plate elements 71, 77. The fastening means 80 are not explicitly shown in this embodiment for reasons of clarity. For example, the plates can be glued, but due to the high operating temperatures, screwing is usually advantageous.

[0092] 20, a further embodiment of the press plate heater 62 is shown in which the heating element top layer 72 and heating element bottom layer 76 are provided as tiles. The heating elements 74 are thus embedded in the tiles 72, 76, 82. This has the advantage that irregularities and seams are evened out and therefore less noticeable as limitations on the workpiece 50.

[0093] With reference to Fig. 21 and Fig. 22, a high-temperature joining furnace 1 is shown, in which an outer frame 7, 9, 10 is included to support a pressing device 20. A pressing cylinder 24 is supported by the support frame element 10 so that a pressing force can be transferred from the pressing device 20 arranged in the high-temperature joining furnace 1 to a workpiece 50 (see, for example, Fig. 1, Fig. 2). When a pressing force is applied, the entire force is absorbed by the outer frame 7, 9, 10, which can be bent in a direction away from the joining furnace 1 during operation. By bending the outer frame 7, 9, 10, a dynamic bearing of the pressing device 20 is provided, and a pressing bearing 18 is formed by the outer frame 7, 9, 10. In Fig. 23, a position sensor 5 is provided, which can detect a positional displacement of the pressing bearing 18. The positional displacement is used to draw conclusions about the pressing force applied by the pressing device 20, which information is provided as a sensor signal.

[0094] 23 to 25 show further embodiments of the high temperature bonding furnace 1, now shown with further attachments. A vacuum generator 54, e.g. a turbomolecular pump, provides a vacuum suction system so that the bonding process in the high temperature bonding furnace 1 is performed in vacuum, e.g. high or ultra-high vacuum. The pressing force generator 28 is provided in a separate housing to accommodate larger units if required. The input devices 48 or output devices 46 or both are outsourced to a user terminal 45 including a PLC 44 and inputs / outputs 48, 46.

[0095] With reference to FIG. 26, a flow diagram of the joining process 200 is shown. In a first step 210, the system fills the workpiece 50 or a batch of one or more workpieces. This is usually performed by a user, but may also be done automatically. In step 220, the system 1 is parameterized and various characteristics, such as the material and joining surface of the workpiece or batch 50, can be stored in the control device 44 using the input device 48. For example, the intended compression of the workpiece 50 or batch may be input as a percentage or as a distance, for example in millimeters. For example, temperature characteristics may be stored. The parameters entered in step 220 are transmitted to the control device 44. The control device 44 can then generate a set of control parameters. After closing the filling opening 11, the joining furnace 1 is ready for operation. The process phase 230 starts with, for example, temperature parameters provided by the control device 44. The press 20 is then prepared. This may include applying a preload to the press device 20 so that the receiving part 18 is displaced or deformed or preloaded, thus allowing the press device 20 to assume an initial position. During, before or after this process, the workpiece 50 is heated in a heating phase 230, in which the press plate heaters 62, 64 are heated and heat is transferred uniformly to the workpiece 50 by conduction.

[0096] The pressing or joining process is then performed in step 240, which may be monitored and adjusted by the process control 44, if necessary. The sensors 4, 5, 42 may provide sensor signals that are processed by the process control 44. The prepared control parameters may be checked and adjusted in response to the sensor signals provided by the sensors 4, 5, 42. Once the control parameters are adjusted, the joining process 240 continues in a modified form with the adjusted control parameters. This may be implemented as a control loop, for example, performed iteratively, such that improved parameter configurations may be set in the course of the joining process to achieve improved joining results. In other words, in one example, a compression of X% of the workpiece 50 is specified. This occurs within a certain time that may be calculated by the control system. An initial pressing force is applied and the actual pressing process begins in step 240. During the pressing process 240, it may be checked whether a corresponding distance per unit time has been reached and the pressing force may be changed if necessary.

[0097] Here, for example, increasing pressing forces can be stored and adaptively adjusted during the joining process 240. The maximum or desired deflection of the press cylinder 24 up to the desired final value can also be already stored in the original set of control parameters. During a check or adjustment of the control parameters, it can also be determined whether the desired final value of the deflection of the press cylinder 24 or the deformation of the workpiece or both can be achieved without exceeding a pressing pressure that could cause the workpiece or batch 50 to be damaged or subjected to excessive deformation.

[0098] In step 250, the workpiece or batch 50 may undergo further processing, which may be further tempering, further heating, and cooling at a defined temperature coefficient. After post-processing 250, the workpiece or batch 50 may be sufficiently cooled and removed from the system 1 in step 260.

[0099] Thus, in many examples, functional solutions, including features that can be combined individually with others, are presented herein, where the solution is a method for improving the uniformity of the heat distribution in the workpiece 50, for example by conduction of heat transfer, and / or reducing the time required to heat the workpiece 50, by integrating the heating devices 62, 64 directly with the press plates 36, 38. In addition, materials that were previously inapplicable to this method due to the low temperature range required can now be processed by diffusion bonding.

[0100] Conductive heating of the press plate by one or more heating elements 74, 74a, 74b, 74c, which may consist of ceramic or other heating materials, proves advantageous for this purpose. The heater 62 is preferably an electrical resistance heater integrated in an electrically insulating manner. A peripheral heater 14 can be provided to homogenize the temperature at the edges and corners of the component 50. The support or peripheral heating can be moved vertically. The support heater can be divided into different temperature zones if necessary. Water-cooled pressure distribution plates 36, 38 can be used if necessary. The flexible heating connection device 100 can be realized, for example, by copper strips 112.

[0101] One of the objectives is to make the diffusion bonding of large components (which can be larger than DIN A3 format) more efficient. Efficiency refers to the energy consumption per bonding cycle and the duration of the bonding cycle. This is achieved by heating the components to be joined via conduction, i.e. contact heating.

[0102] As additive manufacturing increases design freedom, there is also a demand for parts with larger volumes than traditional sizes. However, the manufacturing volumes of powder bed systems have also increased in recent years, reaching 500 x 280 x 850 mm. 3Although systems for this are now commercially available, the production rates are still low, especially for larger components such as moulds. An alternative additive manufacturing process is directed energy deposition (DED) using electric arcs and wires as filler material. High build-up rates in the range of several kilograms per hour are possible. However, the drawback here is the insufficient possibility of manufacturing internal channels. Although feasible in principle, at present dimensional accuracy and dimensional stability are only valid for cooling channels at best. Features such as distribution of plastic mass or heat exchanger structures are not currently feasible. Therefore, diffusion bonding is already used today for such components. The size scaling of diffusion bonding systems on press plates, available on the market in recent years, is in the range of more than one meter.

[0103] One objective of this document is the development and elaboration of design boundary conditions for a heating concept for diffusion bonding, which is to homogenize the heat input to the components and, if possible, to achieve it via contact heating, i.e. thermal conduction. The aim is to achieve process temperatures, for example up to 900 °C, as well as the application of dynamic forces. Furthermore, the system is designed for use in high-vacuum furnaces. Conduction heating prevents radiation losses and emission-dependent heat transfer that occur in vacuum, which makes the energy input to the mainly plate-shaped joining parts significantly more efficient, homogenized and faster. The result is a heating system with significantly improved energy efficiency during diffusion bonding and significantly shorter cycle times. This significantly reduces the costs of the diffusion bonding process, improves the quality of the components and increases the competitiveness of the process.

[0104] Of particular importance is the thermal conduction or heating of the components 50 to be joined. Conventional heating by thermal radiation in a vacuum is an inefficient process, especially for non-ferrous metals with joining temperatures below 1000°C. Due to the low emissivity, only very low heating rates are possible, which negatively affects the cycle time and therefore the cost of the process. Direct (conductive) heating of the components by thermal conduction through the press plates 36, 38 accelerates the energy input to the component 50 and at the same time allows a more uniform temperature distribution, since the heat is introduced uniformly over the large surface of the plate-like component, while conventional heating is essentially performed through the outer edge, which results in gradients between the outside and the center of the component due to the path length, which, if not equalized by waiting (longer cycle times), make a difference in the quality of the composite formation.

[0105] Advantageously, the size of the press plate surface is at least 300×500 mm. The cycle load capacity of the system 1 is preferably at least 0.1 Hz, or at least 0.5 Hz, or at least 1 Hz. -5 Operation in good or high vacuum of 7 N / mm is advantageous. 2A transferable surface pressure of at least 0.1 MPa, preferably at least 0.5 MPa, can be achieved on the component 50 using the press plates 36, 38. For example, a surface pressure of up to 50 MPa, possibly even up to 40 MPa, can be achieved. Alternatively or additionally, a force of 1 ton or more can be applied to the component 50 by the press plates 36, 38, in which case the system can also be used for power-assisted brazing (PAB). If required, a force of 5 tons or more can be applied to the component 50 by the press plates 36, 38. If required, the force applied to the component 50 by the press plates 36, 38 can be up to 5000 tons, for example up to 4000. The application of a low surface pressure of 0.1 MPa or less or a force of 1 ton or less is not to be understood as a compressive force or application of a compressive force for the purposes of this application. For example, the process of wafer bonding, i.e. bonding of semiconductor substrates, is not a pressing process in the sense of this application. Rather, the field of diffusion bonding or force soldering within the meaning of the present application falls into the aforementioned field of relatively high pressures.

[0106] For the diffusion bonding process on the system side, three main factors are important: the atmosphere in which the joining takes place, the method of applying the force and the heating concept. If in addition to the process the geometry of the components is also taken into account, then the concept of the system, i.e. the design of the welding system, must also be taken into account. In principle, the components to be joined in a vacuum can be heated in various ways: thermal radiation, laser or electron beam, convection, direct resistance heating, induction, thermal conduction (conduction) or a combination of the variants here. 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 (axis of rotation for rotating the workpieces). If a direct current is passed through the components to be joined, then a direct resistance heating occurs, but due to electrical variables the size of the components is also limited here. If the direct current is replaced by a pulsed current flow, this can be converted to a higher current. In this case sparkovers occur, which are comparable to plasma discharge sintering. Due to the direct current passing through the components, only electrically conducting materials can be joined, so a homogeneous electric field must be guaranteed, especially for large components. Induction heating has been used very frequently, especially historically. Here, heat is generated directly in the area of ​​the component surface, heating the component rapidly. Diffusion bonding systems for mass production, e.g. for valve disks and seal rings with an annual production volume of 3.1 million pieces, were already equipped with induction heating in the 1970s. The penetration depth can be adjusted via setting parameters such as frequency or current. However, the distance between the component and the inductor or the inductor's shape also influences the heat input and therefore the temperature distribution in the component. A disadvantage is that the inductor has to be adapted to the component geometry for optimal heating and not all materials can be heated inductively. Induction heating is still suitable for slim component geometries, for example.

[0107] However, the current trend regarding component dimensions is towards solid flat components with large dimensions in at least two spatial directions, e.g. plate heat exchangers or injection mouldings. For this reason, the latest generation of diffusion bonding systems are usually designed according to the "furnace principle". This forms the basis for welding systems, where the vacuum furnace system must also be integrated into the "press system" 20. Heating is most often done via thermal radiation, via resistive heating elements. Infrared radiators can also be used for small parts. Due to the absence of convection in a vacuum, heat transfer is limited to radiative heating between the heating element and the component. The main influencing factor of radiative heating is the degree of absorption of thermal radiation, which depends on the condition of the component surface. Often only the emissivity is specified, according to Kirchhoff's radiation law, which states that radiation absorption and emission at a given wavelength correspond to each other.

[0108] Molybdenum can be considered as a heating element material in air and in vacuum. This material is used for heaters because the oxide layer on molybdenum melts in vacuum and therefore achieves a high degree of emissivity in vacuum. Furthermore, two typical material groups of components to be joined include aluminum and steel. Refined steel has a relatively high emissivity. It is temperature dependent and increases with temperature. In contrast, the value of aluminum is significantly lower. Cleaned aluminum has a very low value, but an oxidized aluminum surface is only 2-3 times lower than steel. From the point of view of irradiation technology, an oxidized surface is optimal in terms of absorbing thermal radiation, but not optimal from the point of view of diffusion bonding, since the oxide layer acts as a diffusion barrier. Copper materials behave similarly to aluminum. This means that heating of high temperature conductive materials by radiation alone may be insufficient for the welding process. In the case of materials that are less reactive with the environment, in addition to the pure thermal radiation, the heat transfer due to the partial pressure in the work chamber (additional convection component) increases. In the case of aluminium and titanium alloys, impurities present in the gas (e.g. oxygen / nitrogen) can cause reactions with the surface and the formation of layers which have diffusion-hindering effects and adversely affect the mechanical-technical properties.

[0109] Another drawback of the aforementioned temperature concept is the temperature uniformity within the component. As a rule, heat is always transferred via the component surface and from there to the interior of the component by thermal conduction. Thus, a temperature gradient forms within the component 50 during heating, which leads to uneven expansion and internal stresses. Depending on the thermal conductivity of the materials to be joined, this situation must be addressed by slowing down the heating rate accordingly, also to avoid heat build-up and overheating of the component surface. In addition to the material, the aspect ratio of the component also plays an important role here. The aforementioned concept realizes heat input mainly via the side surfaces of the component. This means that the heat conduction paths for plate-shaped components are the largest. However, such component shapes with low aspect ratios are currently in increasing demand (plate heat exchangers, mold inserts, etc.). Thus, heat input via the base and top surface shortens the conduction paths and increases the heating rate.

[0110] The press plate in a diffusion bonding system serves to introduce the pressing force into the component and distribute this force as uniformly as possible over the entire component or joining surface. This first of all places basic requirements on the mechanical properties of the plate, such as a low modulus of elasticity and sufficient compressive and bending strength. For use in high vacuum furnace systems, these properties must be guaranteed over the entire range of application temperatures. Furthermore, the press plate material must be suitable for use in vacuum (high steam pressure). In addition, an ideal press plate material must have a low specific heat capacity, since the press plate corresponds to a dead mass from the energy point of view and must be heated and cooled during the process. Another requirement is the fatigue strength under dynamic loads within the pressure threshold range.

[0111] In the field of metallic materials, titanium-zirconium-molybdenum (TZM) is a good starting point and is used in many areas, for example as a load-bearing element in the heating area of ​​vacuum furnace systems. In addition to its thermal and mechanical properties, its behavior during processing is comparable to that of CrNi steels. TZM is therefore also the subject of this specification. The disadvantage of TZM is its low modulus of 10.2 g / cm 3 These include its relatively high density, the high thermal conductivity inherent to metals, and the high associated costs of manufacturing.

[0112] All-ceramic press plates are ideal press plate materials from a mechanical point of view. For example, silicon carbide ceramics have a high elastic modulus of 350-450 GPa, but also a compressive strength of more than 2500 MPa and are dimensionally stable materials. The main disadvantage of ceramics is the high cost of processing in the sintered state.

[0113] Steel materials such as heat-resistant steel 1.4828 are considered as press plate materials. However, at the desired service temperature of 900°C, it has a strength of 5 N / mm 2 Since the creep rupture strength is low at or below this level, it is an exclusion criterion.

[0114] An alternative to the aforementioned are ceramic-based fiber composites (CMCs). Similar to carbon fiber reinforced plastics, carbon or ceramic fibers are embedded in a ceramic matrix. This preserves the excellent properties of ceramics, such as heat resistance and compressive strength, but the fiber reinforcement increases the fracture toughness required for dynamic use.

[0115] Carbon fiber reinforced graphite (CFC) can be used in statically loaded diffusion bonding systems, where more energy is extracted from the heated zone due to its high thermal conductivity compared to the other fiber composites considered here.

[0116] Carbon fiber reinforced silicon carbide is a composite material. This material has not yet been used in a diffusion bonded system.

[0117] Aluminum oxide fiber reinforced oxide ceramics have a very low thermal conductivity of 0.4-2.7 W / mK and a relatively low elastic modulus (40 GPa), which gives them excellent thermal insulation and very good pressure dispersion. However, they have a compressive strength of about 25 N / mm 2 The major problem with this material is that it has a low

[0118] The general requirements for the heating material of the heating devices 62, 64 are essentially high electrical resistivity, a high melting temperature which must be significantly above the application temperature, and a low vapor pressure to minimize heater wear in vacuum operation. From a design point of view, a low coefficient of thermal expansion is also desirable. In the field of metallic materials, molybdenum stands out alongside tungsten as a heater material. It has a melting point of 2623°C and a specific electrical resistivity of 0.056·10 -6 ~0.452 10 -6 Ωm (20~1500℃), expansion coefficient 5.8·10 -6 K -1 This allows temperatures of up to 1600°C to be achieved in ultra-high vacuum.

[0119] Alternatively, a material with equivalent electrical resistance (e.g. Nicrofer® 0.103·10 -6 ~0.114 10 -6 There are nickel-based alloys that have high mechanical strength and toughness while retaining a low melting point (1370-1425°C) of 16.9·10 -6 K -1 Its applications are limited due to its relatively high expansion coefficient (1000°C).

[0120] In addition to metallic materials, it is also possible to realize resistive heating using non-oxide ceramics such as SiC. Currently, these are commercially available as hotplates for temperatures up to 1000 °C and allow the achievement of a homogeneous temperature distribution. However, for the planned applications, their high brittleness and sensitivity to bending stresses are major problems.

[0121] Graphite is another alternative for furnace systems, where the relatively low material price and high electrical resistance are advantages. However, graphite has only a limited use in high vacuum, since the evaporating carbon can contaminate the parts to be joined and cause material changes that make it unsuitable.

[0122] It is clear to those skilled in the art that the above embodiments are illustrative and that the invention is not limited thereto, but can be modified in many ways without departing from the scope of protection of the claims. Moreover, it is also clear that features individually define essential components of the invention, even when described together with other features, regardless of whether they are described in the description, claims, figures or otherwise. In all figures, the same reference signs represent the same objects, and therefore the description of an object that is only mentioned in one figure or at least not mentioned in all figures can also be transferred to those figures in which the object is not explicitly described in the description. [Explanation of symbols]

[0123] 1...High temperature bonding furnace, 3. Motor unit, 4...first sensor device, 5...further sensor devices, 6…Press mount area of ​​housing 12, 7...Support frame elements (horizontal, bottom), 8...Substructure, 9…Support frame element (vertical), 10...Support frame element (horizontal, upper surface), 11...filling and / or unloading opening, 12…Housing, 14...Furnace heating device, 15...heating chamber, 16…Insulation material, 18...Press receiving part, 20...Press device, 22...Pressure dispersion element, 24…Press cylinder, 26...Transmission parts, 28…Pushing force generator 29…Counter Press Punch, 32…Press punch, 34…Workpiece holder, 36…press plate, 37...Pressure dispersion parts, 38…Counter-press element 42...second sensor device, 44…Programmable logic controller, 45...PLC, user terminal including input and output, 46...output device, 48...input device, 50…workpiece, 54...Vacuum generator (vacuum pump), 62...press plate heating device in the press plate, 64…Press plate heating device in the workpiece holder, 66, 66a…connection protrusion, projection color, 67, 67a…connecting lip, 68... Fastener holder, 71...press side press plate element, 72...Heating element upper layer, 72a...side enclosure for heating element 74; 74, 74a, 74b, 74c...heating element, 76...Heating element bottom layer, 76a...side enclosure for heating element 74; 77...Workpiece press plate element, 78…connecting parts, 80…Fasteners, screws, 82…tile, 100...connection device, 102...heating element clamp, 104... Flexible compensation element, 106...connecting element, 108…Stud bolt holder, 110…Stud bolt, 112...connection elements, e.g. copper strips; 114…Implementation, 116…External contact, 200...Joining process, 210…filling, 220...parameterization, 230... Processing phase, 240…pressing or joining step, 250…Post-processing if necessary, 260…System unload

Claims

1. A heating chamber (15); a workpiece holder (34) disposed within the heating chamber for holding a workpiece to be processed in the bonding furnace; A press apparatus (20) arranged and arranged to apply a pressing force to a workpiece, comprising a press plate (36) for applying a uniform pressing force to said workpiece, said press plate being provided with a press plate heating device (62) for heating said press plate or said workpiece or both. A high temperature joining furnace (1) for diffusion bonding of joining materials, such as metals and metal workpieces, comprising:

2. The press plate heater (62) may be integral, e.g., fully integrated, with the press plate (36) and / or The press plate (36) is a multi-part press plate, for example the press plate comprises a workpiece side element (77) and a press side element (71), and / or The press plate heater (62) is disposed between the workpiece side layer (77) and the press side layer (71). The joining furnace according to claim 1.

3. and a flexible connector (100) for connecting the press plate heater (62) to an energy source. The joining furnace according to claim 1 or 2.

4. the press plate heater (62) provides conductive heat output, i.e. is a conductive press plate heater; and / or the press plate heater (62) is arranged to be electrically operated to emit heat when powered by the energy source; and / or the press plate heater (62) is arranged to flow with hot fluid so as to release heat when supplied with hot fluid from the energy source; The joining furnace according to any one of claims 1 to 3.

5. The press device (20) is and / or comprising a hydraulic device as a pressing force generator (28) for building up the pressing force by building up a hydraulic pressure. The pressing device (20) includes an electric spindle and / or The pressing device (20) includes a pressing cylinder and / or The press device (20) is a press punch (24) including a plurality of press punches, in particular two, three, four or more; The joining furnace according to any one of claims 1 to 4.

6. The high temperature bonding furnace includes an outer frame (7, 8, 10); and the pressing device (20) is disposed on and / or supported by the outer frame; and / or said outer frame (7, 8, 10) is designed to be movable or deformable or both; The joining furnace according to any one of claims 1 to 5.

7. and / or a press bearing (18) arranged such that a lateral displacement or deformation or both of said press bearing (18) is caused by the application of a compressive force to the workpiece (50) by the pressing device (20); said pressing device (20) being configured so that a prestress force can be built up in the support frame element (10) during the pressing operation; said workpiece holder (34) being operated as a counter-press element (38); and / or a pressing device (20) for pressing the workpiece (50) against the workpiece holder (34); The joining furnace according to any one of claims 1 to 6.

8. and / or arranged to carry out the process of joining preferably metal or metallic workpieces at a temperature of the metal workpieces of 1200° C. or less, preferably 1000° C. or less, more preferably 950° C. or less, and / or at a temperature of 450° C. or more, preferably 500° C. or more, more preferably 550° C. or more, or 600° C. or more; Provided for carrying out a process for joining preferably plastic, ceramic or corresponding workpieces or the like at a temperature of 350° C. or less, preferably 300° C. or less, more preferably 250° C. or less or 200° C. or less, and / or 80° C. or more, for example 100° C. or more, preferably 120° C. or more, more preferably 140° C. or more, The joining furnace according to any one of claims 1 to 7.

9. and a furnace heating device (14) for emitting radiant heat into the heating chamber (15). The joining furnace according to any one of claims 1 to 8.

10. For example, a method for diffusion bonding in a high-temperature bonding furnace according to any one of claims 1 to 9, Loading a workpiece (50) into the bonding furnace; applying at least one press plate (36) of a press apparatus (20) to the workpiece; heating a majority of the workpieces to a joining temperature by a press plate heater (62); pressing the workpieces in a press (20) to perform the diffusion bonding process; A method comprising:

11. quenching or heating the press plate (36) by a press plate heater (62) during pressing to homogenize the temperature distribution within the workpiece (50). The method of claim 10 further comprising:

12. For example, a heatable press plate (36) for a high-temperature joining furnace according to any one of claims 1 to 9, the press plate is prepared for uniform application of a pressing force to a workpiece (50) disposed within the high temperature bonding furnace; the press plate is characterized in that it includes an integrated press plate heater (62) for heating the press plate or the workpiece or both; Heatable press plate.

13. the press plate heater (62) is integral, e.g., fully integrated, with the press plate; and / or The press plate is a multi-part press plate, so that for example the press plate comprises a workpiece side element (77) and a press side element (71), and / or The press plate heater (62) is disposed between the workpiece side layer (77) and the press side layer (71).

13. The heatable press plate of claim 12.

14. 14. The multi-piece press plate of claim 13, wherein each portion of the press plate is made of the same base material, only with a different doping than the others.

14. A heatable press plate according to claim 12 or 13.

15. the press plate comprises a ceramic material; and / or the workpiece side layer (77) or the press side layer (71) or both comprise or consist of a ceramic material; and / or The press plate heater (62) comprises or consists of a ceramic or metal material; A heatable press plate according to any one of claims 12 to 14.

16. the ceramic material comprises 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; and / or the press side layer (71) is made of the aforementioned material; The press plate heating device (62) is comprising or consisting of at least one of tungsten, molybdenum, a nickel-based alloy such as Nicrofer®, a non-oxide ceramic such as silicon carbide or graphite, or carbon fiber reinforced carbon; 16. The heatable press plate of claim 15.

17. the press plate heater (62) is of plate-like design and / or the press plate heater (62) is of serpentine design; and / or The press plate heater (62) comprises a channel or track; the channels or tracks pass uniformly through the press plate, and the press plate material is from one of the channels or tracks a distance corresponding to no more than twice the width of the channel or track; A heatable press plate according to any one of claims 12 to 16.

18. the press plate heater (62) being electrically operatively arranged to emit heat when an electric current is passed therethrough; and / or The press plate heater (62) is arranged to allow liquid flow so as to release heat when hot fluid is supplied. A heatable press plate according to any one of claims 12 to 17.

19. said press plate heating device (62) comprising at least two heating plates (74, 74a, 74b, 74c); and / or The press plate heating device (62) comprises a connecting part (78) for connecting two or more partial areas such as heating plates (74, 74a, 74b, 74c), the connecting part comprising, for example, graphite or consisting of graphite. A heatable press plate according to any one of claims 12 to 18.

20. the connecting piece (78) is designed to be reversibly deformable and, when a compressive force is applied, deforms, e.g. widens, improving or establishing an electrical connection between the sub-areas (74, 74a, 74b, 74c) of the press plate heating device (62); 20. The heatable press plate of claim 19.

21. further comprising a pressure equalization layer (104); The pressure equalization layer is designed to be all over the surface, arranged to be flexible or compressible, and / or said pressure levelling layer being disposed adjacent to a press plate heating means (62); and / or The pressure equalization layer is a graphite foil. A heatable press plate according to any one of claims 12 to 20.

22. The press side layer (71) is formed as a carpet tile, for example a ceramic carpet tile, and / or The press plate heater (62) is arranged on a heating surface and / or Ceramic tiles (82) are disposed between the components of the press plate heater (62). A heatable press plate according to any one of claims 13 to 21.

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