Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/02—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a press ; Diffusion bonding
  • B23K20/023—Thermo-compression bonding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/02—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a press ; Diffusion bonding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/26—Auxiliary equipment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
  • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
  • B29C65/18—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools
  • B29C65/24—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools characterised by the means for heating the tool
  • B29C65/26—Hot fluid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
  • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
  • B29C65/18—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools
  • B29C65/24—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools characterised by the means for heating the tool
  • B29C65/30—Electrical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/02—Dies; Inserts therefor; Mounting thereof; Moulds
  • B30B15/026—Mounting of dies, platens or press rams
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/06—Platens or press rams
  • B30B15/062—Press plates
  • B30B15/064—Press plates with heating or cooling means
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/20—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater
  • H05B3/22—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater non-flexible

Definitions

• the present invention relates to a high-temperature joining furnace, a method for diffusion welding and a heatable press plate.
• a metal workpiece can be diffusion welded if it is joined under pressure by a press at high temperature.
• the process of diffusion welding is a complex process that depends on various influences and does not necessarily lead to a comparable or at least satisfactory result, even under the same process conditions.
• the deformation of the workpiece must be taken into account.
• the workpiece to be joined has cooling channels or other bores or openings in its interior, the pressing force exerted on the workpiece can deviate locally, so that overall a different deformation results in comparison to a solid body whose dimensions are identical.
• the history of the materials to be joined can also be important with regard to the joining result; in particular, the grain sizes 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 basically be described as identical, i.e. manufactured using the same manufacturing process, pretreated to the same temperatures, so that similar grain sizes in the material should be assumed, differences between materials must also be taken into account. This also applies when workpieces are prepared or cut from the same piece of raw material. This can be even more difficult for certain materials and/or combinations of materials.
• a particular challenge when operating a diffusion welding system is to obtain a uniform joining result across the component.
• various process parameters can also be checked to see whether the process conditions can be further improved in order to further improve the uniform joining result across the component to be joined, or even to make them satisfactorily available in the first place.
• a further improved joining result can expand the range of applications for other materials that cannot be processed or can only be processed inadequately with the existing systems. More complicated construction shapes can be joined using materials that are already joinable. This can also help reduce manufacturing downtime.
• the invention has set itself the task of further homogenizing the joining result over a component to be joined.
• the task is also to be able to join new materials or more complex designs using diffusion welding, which previously could not be processed or only insufficiently processed using this process.
• 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 in conventional joining processes and would therefore deform too much.
• the task is to further accelerate the process flow in order to reduce operating costs and increase the component throughput.
• a workpiece or batch is deformed in a controlled manner. Possibly existing pores in the joining material, recesses inside the workpiece, the number and size of the joining surfaces and also the history of the joining material are variables that can influence the process flow.
• force is applied to the workpiece or batch by a press, the material contact on the joining surfaces is improved. In this way, an inherent interdiffusion can be created or brought about.
• pressing the contact surface is enlarged in the area of the joining surface(s).
• 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 or 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 composite with aluminum or copper or the like.
• the high-temperature joining furnace can also be prepared for power-assisted soldering or sintering of components. Overall, the high-temperature joining furnace is therefore prepared for material refinement subjected to pressure force with or without additional material.
• the high-temperature joining furnace includes a heating room.
• the workpiece and usually also the interior of the furnace, is heated to the processing temperature.
• a workpiece holder is arranged in the heating room to hold a workpiece to be processed in the joining furnace.
• the workpiece holder is arranged on the underside of the heating chamber.
• the workpiece holder can include a plate, but also holders into which the workpieces to be joined are to be inserted.
• the workpiece holder can be part of a counter-pressing element or can be arranged on it.
• the workpiece holder can be a passive counterpart for a pressing device or can itself be subjected to a pressing force from the underside of the workpiece holder and thus represent a counter-pressing element.
• the joining furnace further comprises the pressing device, which is arranged and prepared to apply a pressing force to the workpiece.
• the pressing device is arranged in such a way that an upper part, such as a press stamp, presses against the workpiece from above, with the workpiece being pressed against the workpiece holder or against the counter-pressing element. In other words, the workpiece is clamped between the upper part or press ram and counter-pressing element or workpiece holder.
• the upper part includes a press plate, by means of which the pressing force can be distributed and applied evenly over a surface, so that the workpiece is pressed evenly.
• the press plate can have a flat surface so that the workpiece can be subjected to a uniform pressing force across the surface of the press plate.
• the press plate can also have recesses, projections or steps in order to allow the press plate to be formed onto a desired surface of the workpiece or workpieces to exhibit or effect.
• the press plate could therefore be generally described as a “press element”.
• the term “press plate” is used herein because this term appears common to those skilled in the art in the light of the present description.
• 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, since it distributes the pressing force generated by the pressing device and applied to the workpiece over the surface of the workpiece.
• the press plate heating device By means of the press plate heating device, the press plate can be heated or heated as evenly and homogeneously as possible across its surface. This also enables homogeneous heat release via the press plate, so that the workpiece can also be heated evenly.
• the workpiece can now be heated conductively by means of the press plate heating device, which may enable a significantly faster heat transfer into the workpiece and, moreover, a more uniform heat input over the surface of the workpiece.
• 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 transport sufficient heat output into the workpiece, so that a uniform temperature distribution in the workpiece may not be possible using radiant heat alone.
• the press plate heating device according to the invention thus opens up the use of new materials as workpieces that were previously not available for diffusion welding.
• the press plate heating device can preferably be integrated into the press plate, i.e., if necessary, be completely integrated.
• a heat supply can be brought to or connected 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 into the press plate is improved.
• the press plate can be a multi-part press plate.
• a workpiece-side layer and a press-side layer can be included; the press plate heating device can preferably be arranged between the workpiece-side layer and the press-side layer of the press plate.
• the joining oven can have flexible connection connectors for connecting the press plate heating device to an energy source.
• the flexible terminal connectors may comprise a metal strip material, such as a copper strip, which can compensate for movements, shocks or vibrations while maintaining electrical contact.
• the press plate heating device provides a conductive heat release for the press plate, so it is a conductive press plate heating device.
• the press plate heating device is designed to be electrically operable, so that it emits heat when it is supplied with electrical power from the energy source.
• the press plate heating device can be designed to allow fluid to flow through it, so that it emits heat when a hot fluid is applied to it from the energy source.
• the press plate can be arranged to be movable or movable, for example the press plate is displaced by one or more press rams, the press ram(s) being set in motion by one or more press cylinders.
• the press plate is displaced by one or more press rams, the press ram(s) being set in motion by one or more press cylinders.
• 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 moving the workpiece upwards on the workpiece holder, for example.
• a first and second press plate can be provided for application of force on both sides, for example an upper and a lower press plate or a left and a right press plate.
• a part that functions like a press punch 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 punch and the counter-pressing element and is joined or deformed there.
• the joining furnace can include a wall-side heating device or furnace heating device in the furnace chamber.
• the wall-side 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, there is practically no convection in the furnace chamber, so that a wall-side heating device can essentially transmit radiant power.
• the wall-side 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-side heating device can therefore be used to provide support in order to further homogenize the temperature distribution in the workpiece.
• the oven heating device can also be provided solely to emit radiant heat into the oven space.
• the two heating devices - that is, the press plate heating device and the oven heating device - can complement each other in that the oven heating device compensates for the radiation of heat away from the workpiece by radiating radiant heat into the workpiece. In this case, any cold spots that may occur on the workpiece can be avoided, particularly on the side edges.
• the oven heating device may, however, be unnecessary, since the press plate heating device is able to provide an advantageously uniform heat output across the surface of the workpiece in a conductive manner.
• a sensor device can be provided in the joining furnace, which provides at least one sensor signal.
• 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 transferred to or processed by a control device, which is set up to control at least the pressing device in response to the at least one sensor signal.
• the sensor device of the joining furnace can detect a process parameter.
• a process parameter can be the thickness of the workpiece, the position of a pressure stamp or press ram of the pressing device.
• a process parameter can also be the applied pressing force, a hydraulic pressure or a distance of the pressing device.
• a sensor signal can subsequently be generated from the value base recorded by the sensor device, i.e. one of the process parameters mentioned.
• Several sensor devices can be provided in order to simultaneously record different process parameters.
• a further sensor device can detect one or more process parameters at the same time as the first sensor device and thus generate at least one or more further sensor signals. To control the joining process or the joining oven, the one or more sensor signals can be processed, so that different process parameters may be taken into account in the control.
• the pressing device can comprise a hydraulic device, wherein the pressing force is built up by building up hydraulic pressure.
• the pressing device can also include an electrospindle, which generates a feed, for example through rotation, and thereby applies the pressing force to the workpiece.
• the joining furnace can include an input device for entering process parameter specifications.
• the input device can be, for example, a user-operable terminal.
• Process parameter specifications that can be stored before the joining process begins include, for example, the desired process temperature, the process time, the materials of the workpiece, parameters or further data on the underlying material and the number and/or amounts of the joining surface or joining surfaces of the workpiece.
• the workpiece can consist of a plurality of layers of different materials, for example at least two different materials, which are stacked on top of each other, with each surface to be joined between two different materials being described as a joining surface.
• a plate-like workpiece which, for example, comprises 25 layers, 24 joining surfaces are arranged in the workpiece.
• Information about cavities in the workpiece can also be taken into account when specifying process parameters.
• the joining oven can further comprise an output device, in particular for displaying or selecting process parameters and/or a control program. For example, information about which process step the joining oven is currently in can be output on the output device.
• the pressing device can comprise a press stamp with which the pressing force is transmitted, and/or it can comprise a press plate with which the pressing force is applied to the workpiece.
• the pressing device can comprise a pressing cylinder.
• the press ram can be connected to the press cylinder, so that the press cylinder acts on the press ram with the pressing force and sets the press ram in the direction of the workpiece.
• the pressing device can optionally comprise several pressing cylinders, in particular 2, 3 or 4 pressing cylinders.
• press stamps which act together on the workpiece, in particular via the press plate, which is subjected to pressing force by the two or more press stamps as homogeneously or evenly distributed over the surface as possible.
• the multiple press punches can be arranged next to one another so that an array of press punches acts on the press plate.
• the aim is to distribute the pressing force as homogeneously as possible on the workpiece to be joined, because the pressing force that is necessary for joining can otherwise deform the press plate or the pressing element, so that the workpiece to be joined is not subjected to pressing force evenly.
• the high-temperature joining furnace may include a housing.
• heating device, heating chamber, workpiece holder and/or pressing device can be accommodated in the housing.
• the pressing device can be arranged on the housing by means of a press holder and/or can be supported on the housing.
• the press holder is attached to the housing or lies 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.
• the housing can have a support or holding structure such as a support frame or support cage.
• the support or holding structure can be a component separate from the housing, or can be formed integrally with the housing.
• the support or holding structure and/or the press holder can be designed to be movable and/or deformable.
• the pressing device can counter-support itself against the press holder and thereby shift and/or deform the press holder, for example by deforming the supporting or holding structure.
• a storage 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 the pressing effect on the workpiece can be increased evenly or more gently, particularly when the pressing force is increased.
• the pressing device Due to the movable and/or deformable design of the press holder or the support or holding structure, the pressing device can be prepared, in which the pressing device is prepared into a starting position in which a pre-pressing force is already applied to the workpiece.
• the joining furnace can be prepared in such a way that a lateral displacement and/or deformation of the press holder takes place by applying the pressure force to the workpiece by the pressing device.
• applying the compressive force to the press holder which acts as an abutment for the press, produces the lateral displacement and/or deformation of the press holder.
• a spring effect is created between the press holder and the pressing device or between the press holder, press cylinder and press ram.
• the pressing device can be prepared in such a way that a preload force can be built up between the pressing punch and the housing during a pressing process or when a pressing force is built up.
• a preload force can be built up between the pressing punch and the housing during a pressing process or when a pressing force is built up.
• the presence of one Preloading force in the pressing device allows finer dosing and thus more precise detection and/or tracking of the stamp position during the pressing process. Furthermore, building up the preload force allows pressure corrections or pressing force corrections to be set or metered more precisely.
• the press holder can be displaced or deformed by more than 1 mm when a compressive force is applied, in particular more than 3 mm, more particularly more than 5 mm, or even more than 10 mm.
• a type of “spring accumulator” can be formed here, i.e. a preload force.
• the press holder can also be displaced or deformed by less than 3 mm, preferably less than 6 mm, more preferably less than 12 mm when a compressive force is applied; Minimum and maximum deflection specifications can be combined as an interval, for example more than 3 mm and less than 6 mm as “in the range between 3 to 6 mm”.
• the sensor device can be prepared to detect the position of the pressure stamp.
• the sensor device can also be designed to detect the pressing force applied to the workpiece.
• the control device can be set up to determine a pressing force required for the inserted workpiece for a joining process 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 or evaluated sensor signals.
• the control device can optionally also regulate or control the heating device, so that different temperatures can be maintained in the heating chamber at different times during the joining process.
• the joining oven can have a filling and removal opening.
• the filling and removal opening is connected to a safety circuit that detects the state of the opening.
• the workpiece holder can advantageously serve as a counter-pressing element for the pressing device.
• the pressing device can therefore press the workpiece against the workpiece holder, so that the workpiece is clamped between the pressing device and the workpiece holder.
• 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 often applicable for a specific material combination, or a minimum pressing tension with which the joining process can begin.
• the selectable control program may include a pretreatment program and/or a press execution program.
• the control devices are preferably designed 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 distance of the pressing device, are changed or influenced during the joining process.
• the at least one control program can be stored in a program memory of the high-temperature joining furnace.
• the control device can include a programmable logic controller.
• the joining furnace is preferably prepared 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 able to carry out diffusion welding processes at lower temperatures than previously known for metals or metallic workpieces and thus to introduce new materials into diffusion welding that previously could not be processed using this process.
• the time required to introduce enough radiation energy into the workpiece to be processed is, on the one hand, but on the other hand, it may even be that irradiation and radiation are in balance or that a homogeneous temperature distribution could not be achieved inside the workpiece.
• the joining oven can also 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.
• the joining furnace can also be prepared to carry out 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 at 200 °C or lower. This temperature range also opens up access to new materials for the diffusion welding process.
• the joining oven can also be prepared to carry out 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.
• the invention further describes a method for diffusion welding in a high-temperature joining furnace, in particular as described above.
• the diffusion welding process includes the steps: 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 using a press plate heating device; Pressing the workpiece with a pressing device for carrying out in particular the diffusion welding process.
• 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.
• the method can be formed by the step: during pressing, detecting or determining the pressing force required for the joining process, in particular with an automatic control device such as a programmable logic controller (PLC); and controlling the pressing device in response to the recorded or determined pressing force required for the joining process.
• PLC programmable logic controller
• the required pressing force can be determined over the pressing path by measuring the distance.
• the method can further 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.
• 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 adjusting the joining process when a deviation of a monitored value from a target value is detected.
• the method can also be further developed with the step of entering process parameter specifications, in particular by a user, before pressing the workpiece.
• step of taking the process parameter specifications into account when providing target values for automated process control can also represent a further development of the method.
• the present description also describes a heatable press plate, in particular for a high-temperature joining oven, as explained above.
• the press plate is prepared for uniformly applying 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.
• 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, press-side layer and possibly press plate heating device, can consist of the same base material but have different dopings from one another.
• the press plate may include ceramic material.
• the workpiece-side layer and/or the press-side layer can comprise ceramic material or consist of ceramic material.
• the press plate heating device can comprise ceramic material or metal material or consist of ceramic material or metal material.
• the ceramic material of the heatable press plate may 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 and/or the press-side layer can also consist of one of the aforementioned materials.
• the press plate heating device of the heatable press plate can 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 carbon fiber reinforced carbon (CFG).
• tungsten molybdenum
• a nickel-based alloy such as Microfer
• a non-oxide ceramic such as silicon carbide or graphite
• the press plate heating device can be plate-shaped.
• the press plate heating device can also be designed in a meandering shape.
• the press plate heater may have channels or tracks.
• the channels or tracks can pass through the press plate so evenly that the material of the press plate has a maximum distance from one of the channels or tracks that corresponds to 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 possible heat distribution for the press plate.
• the press plate heating device can be designed to be electrically operable so that it emits heat when it is supplied with electricity. Alternatively or cumulatively, the press plate heating device can be designed to allow fluid to flow through it, so that it emits heat when it is exposed to a hot fluid.
• 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 partial areas, such as heating plates, the connecting piece in particular comprising or consisting of graphite.
• the connecting piece can be designed to be reversibly deformable, so that it deforms when a compressive force is applied, in particular becomes wider, and improves or establishes the electrical contact between the partial areas of the press plate heating device.
• the connecting piece is arranged in the press plate heating device in such a way that at the moment when a compressive force is applied to the press plate, the electrical contact between the partial areas of the press plate heating device is improved or even established by means of the connecting piece and thus the operational safety of the press plate heating device is improved.
• the compressive forces applied to the press plate are very large and suitable materials are characterized, on the one hand, by the fact that they hold up under the given conditions of pressure and temperature and, on the other hand, the materials used are not reflected in the joining result.
• materials of different densities can often be recognized by the fact that they are imprinted on the workpiece to be machined, like a stamp, and the arrangement of material of different densities or at least material of different hardness can be recognized in the finished workpiece. This should be prevented if possible. This can also be achieved with the press plate heating device presented here.
• the heatable press plate can also include a pressure equalization layer.
• the pressure compensation layer can be designed over the entire surface and, if necessary, be designed to be flexible or compressible.
• the pressure compensation layer can be arranged adjacent to the press plate heating device, that is, for example, placed on the press plate heating device and, if necessary, completely cover the press plate heating devices.
• the pressure equalization layer can be a graphite foil. The pressure equalization layer enables further homogenization Compressive force over 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 impression in the workpiece to be joined, or to a much lesser extent.
• the press-side layer and/or the workpiece-side layer can be designed as a tiled carpet, in particular as a ceramic tiled carpet.
• the use of small-scale components, such as in particular a tiled carpet can mean that unevenness, for example edges of the heating device, can be compensated for and force can be distributed over the tiles of the tiled carpet and thus over 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 surrounded by press plate material on the bottom and top. Ceramic tiles can be arranged between components of the press plate heating device.
• FIG. 1 shows a first embodiment of a high-temperature joining furnace in a side sectional view with an inserted workpiece
• FIG. 4 side sectional view of a heating plate
• FIG.5 side view of a heating plate
• FIG. 6 perspective view of a continuous heating plate
• FIG. 7 shows a perspective, step-sectional view of a continuous heating plate
• FIG. 8 shows a perspective partial sectional view of a press plate heating device with a divided heating plate
• Fig. 10 view of a divided heating plate
• FIG. 11 side view of a heating plate
• FIG. 13 top view of a press plate with press plate heating device
• Fig. 18 side view of a flexible connector
• FIG. 19 shows a perspective partial sectional view of a further embodiment of a press plate with a press plate heating device with a ceramic meander
• FIG. 20 is a partial perspective sectional view of a further embodiment of a press plate with a press plate heating device with ceramic tiles,
• 21 is a perspective view of a high-temperature joining furnace
• FIG. 23 is a perspective view of a high-temperature joining furnace with peripheral attachments, Fig. 24 top view of a high-temperature joining furnace,
• Fig. 25 is a perspective view of a high-temperature joining furnace
• Fig. 26 is a flow chart for a joining process.
• 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 later 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 of Figure 1, the workpiece 50 rests 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 placed on the counter-pressing element 38.
• the pressing device 20 is arranged on the top of the housing 12 of the joining furnace 1 in order to be able to develop a pressing force from above onto the workpiece 50 and against the workpiece holder 34 or the counter-pressing element 38.
• a plurality of press rams 32 - four press rams 32 in the example shown in FIG. 1 - are connected to a press cylinder 24.
• the press cylinder 24 is, for example, a hydraulic cylinder, with the press rams 32 being positioned by the press cylinder 24 via the transmission 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 to the plurality of press rams 32.
• a single press ram 32 can also be used if necessary.
• the plurality of press stamps 32 e.g. B. 4, 8 or 12 press stamps 32
• the pressing force can be distributed evenly on the pressing element 36.
• an improved thermal seal of the heating chamber 15 can also be achieved, since each press ram 32 only requires 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.
• the thermal energy losses can be better equalized across the outer surface of the heating chamber 15 and, overall, an improved homogenization of the temperature distribution in the heating chamber 15 can be achieved.
• This also applies analogously to the counter-press stamps 29 on the underside of the heating chamber 15, taking into account the considerations of the more homogeneous pressure distribution over the counter-press element 38 as well as the lower and/or more uniform heat losses.
• a press force generator 28 in this example a hydraulic unit 28, applies pressurized hydraulic fluid to the press cylinder 24, so that it switches off or disengages from the press force generator 28 and places it on the workpiece 50.
• motor units 3 can generate the hydraulic pressure in the press force generator 28.
• a first sensor device 4 is arranged on the top side, by means of which the distance of the press cylinder 24 is measured.
• the first sensor 4 therefore 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 pressing force generator 28 and/or in the pressing cylinder 24, for example for measuring the hydraulic pressure, in order to derive information about the applied pressing force and to provide it as a sensor signal.
• the workpiece holder 34 is arranged within the heating device 14 in order to accommodate the workpiece 50 in the heating space 15.
• the workpiece holder 34 is provided with a plurality of counter-pressing punches 29, which distribute the force distribution as evenly as possible from the counter-pressing element 38, so that the counter-pressing element 38 is exposed to the least possible deformation. Since the counter-pressing punches 29 pass through the insulation 16 and the insulation 16 should be affected as little as possible, a comparatively small breakthrough area can be caused overall and the counter-pressing punches 29 can be better thermally sealed.
• a second sensor device 42 is arranged further underside, which can, for example, detect the pressing force applied to the workpiece 50.
• 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 case in the area of a counter-press stamp 29, so that the pressure distribution acting on the counter-press element 38 can be detected and output as a sensor signal. It can thus be determined whether the pressure distribution on the workpiece or the batch 50 takes place in the desired manner, for example homogeneously across the workpiece or the batch 50.
• a pressing force can be exerted on the workpiece or batch 50 from both sides.
• the embodiment of FIG. 1 can be modified in such a way that instead of the (passive) subassembly, which in particular includes counter-pressing punch 29 and counter-pressing element 38, a further pressing device 20' can be arranged on the underside of the high-temperature joining furnace.
• an automatic process control 44 is arranged in the area of the substructure 8 of the joining furnace 1.
• the input device 48 and the output device 46 for example keyboard 48 and screen 46, inputs and outputs to the control device 44 and thus manual influence on the process flow or input of process parameters are made possible.
• the two press plate heating devices 62, 64 can be similar or be constructed identically, especially if both press plate 36 and counter-press 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 up the workpiece 50 can be further reduced.
• FIG. 1 also shows the possibility of electrically contacting the press plate heating devices 62, 64 by means of contacting devices 100, the course of the current flow running 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.
• the pressing device 20 is shown in an operating position, with the pressing plate 36 being fully engaged on the workpiece 50 and a pressing force being applied to the workpiece 50.
• the press cylinder 24 or the transfer piece 26 is shown in the disengaged position.
• the press rams 29 and 32 are each equipped with a pressure distribution piece 37, which are arranged at the angle between the press plate 36 and the respective press ram 32 and help transfer the pressing force to the press plate 36 even more homogeneously.
• 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.
• the press plate heating device 62 has a heating element cover layer 72, in which receptacles 68 are provided for fasteners.
• a connection projection 66 protrudes beyond the dimension of the cover layer 72, the connection projections 66 being associated with the heating element 74.
• Fig. 4 shows a cross section of a press plate heating device 62, whereby the three-layer structure with heating element cover layer 72, heating element 74 and heating element bottom layer 76 can be seen.
• Fig. 5 shows a side view of the press plate heating device 62, whereby the three layers 72, 74, 76 and the connection projection 66 of the heating element 74 can also be seen.
• the heating element 74 is laterally surrounded by lateral enclosures 72a, 76a, so that it is surrounded on all sides by the cover layer 72 and the bottom layer 76, with the exception of the connection projections 66.
• the connection projections 66 serve to introduce the energy required for heating into the heating element 74. For example, electrical contact can be established by means of the connection projections 66.
• FIG. 6 a perspective view of a press plate heater 62 is shown.
• the heating device 62 shown in FIG. 6 can correspond to the heating device 62 shown in FIGS. 3 to 5.
• the same reference numbers stand for the same elements or components in all figures.
• Fig. 7 the embodiment of Fig. 6 is shown in a step section, whereby the three-layer structure of cover layer 72, heating element 74 and bottom layer 76 can be seen, as well as the enclosure of the heating element 74 by means of the enclosures 72a, 76a.
• a further embodiment of a press plate heating device 62 is shown with a divided heating plate 74.
• two heating plates 74 are provided, which are jointly encompassed by the cover layer 72 and the bottom 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 from a first connection projection 66 via the first heating element 74, the contact clips 67 or the connecting piece 78, the second heating element 74a and the second connection projection 66a, an electrical one Current flow can be established.
• 9 shows the heating element 62 of FIG. 8 in a cross section, with the connecting piece 78 being visible.
• 10 and 11 show a single heating plate 74, in particular as a section of a divided heating plate or heating level, with the connection projection 66 and the contact lip 67 being visible.
• the use of smaller heating plates 74, 74a, 74b, 74c has the advantage that it is easier to select for any material defects that may be present, and moreover any material defects that may be present (cracks, chips, faulty grains, pores or cavity, etc.) in the heating plate 74, 74a, 74b, 74c leads less to a break, since the bending moments that occur (and deflections during operation) are significantly smaller, and therefore more material defects can be tolerated, which leads to an overall cost reduction contributes to the production.
• a press plate heater 62 installed in a press plate 36 is shown, the press plate having a press-side press plate element 71, a workpiece press plate element 77 and a press plate heater 62 inserted between these two layers. These layers are connected to one another by means of the fastening means 80, for example screwed.
• FIG. 13 a top view of a press plate 36 with press plate heating devices 62 is shown.
• the embodiment of FIG. 13 is shown in a perspective view 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 with screws 80.
• FIG. 15 the embodiment of Figs. 13 and 14 is shown in a step 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 again in a further stepped section, so that the four heating elements 74, 74a, 74b, 74c become apparent.
• the four heating elements 74 are arranged in a common heating element plane, ie lying next to each other.
• the heating elements since they are arranged in the press plate 36, are typically subject to movement during operation. So the press plate 36 is placed on the workpiece and depending on the size of the workpiece etc. the press plate 36 is in operation at a different position of use.
• flexible contacting devices 100 are provided, as shown in FIG.
• the contacting device 100 has a flexible compensation 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, with the connection projection 66, 66a being clamped or enclosed. It is also possible to screw it tight to the connection projection 66.
• the contacting device 100 On the top side, the contacting device 100 has a contact element 106, for example in order to connect a copper strip there for further current conduction.
• two contacting devices 100 are connected to a heating element 74 for supplying and discharging power.
• FIG. 18 shows the contacting device 100 in a sectional view, the attachment to the connection projection 66 being provided with further details, the stud bolt receptacle 108 and the stud bolt 110 being shown in cross section.
• a contacting device 100 is connected to two heating elements 74, with only one connection side being shown for better graphic visibility.
• a second contacting device 100 is used so that a circuit or current flow can take place through the heating element(s) 74, 74a.
• a further embodiment of a heating device 62 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 from the first connection projection 66 through the ceramic meander 74 to the second connection projection 66a can be realized.
• the heating device 62 is enclosed in a press plate 36, the press plate having 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 together; screwing would typically be advantageous due to the high operating temperature.
• 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 bottom layer 76 are designed as tiles.
• the heating element 74 is accordingly embedded in the tiles 72, 76, 82. This has the advantage that any unevenness or bumps that may be present are compensated for and are therefore less visible as a restriction in the workpiece 50.
• a high-temperature joining furnace 1 is shown, wherein an outer frame 7, 9, 10 is included to support the pressing device 20.
• the pressing cylinder 24 is supported by the support frame element 10, so that the pressing force is transmitted by the pressing device 20 the workpiece 50 arranged inside the high-temperature joining furnace 1 (see, for example, FIGS. 1, 2) can be delivered.
• 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.
• a position sensor 5 is provided, with which the positional shift 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.
• FIGS 23 to 25 show a further embodiment of a high-temperature joining furnace 1, which is now shown complete with further attachments.
• a vacuum generator 54 for example a turbomolecular pump, provides a vacuum suction so that the joining process in the high-temperature joining furnace 1 can be carried out in the range of a vacuum, in particular a high vacuum or an ultra-high vacuum.
• the press 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 outsourced to a user terminal 45, which includes the PLC 44 and input/output 48, 46.
• a flowchart of a joining method 200 is shown.
• 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 done automatically.
• the system 1 is parameterized.
• various specifications such as in particular the materials and joining surfaces of the workpiece or the batch 50, can be stored in the control device 44 using an input device 48.
• the intended compression of the workpiece 50 or the batch can also be entered in percent or distance, for example in millimeters.
• temperature specifications can also be stored.
• the parameters entered in step 220 can be transmitted to a control device 44.
• the controller 44 can then generate a set of control parameters.
• the process phase 230 begins, for example with temperature parameters provided by the control device 44.
• the press 20 is then prepared. This can include applying pre-pressure to the pressing device 20 so that the abutment 18 experiences a displacement or deformation or prestress and thus a starting position of the pressing device 20 can be assumed.
• the workpiece 50 is heated in the heating phase 230.
• the press plate heating device 62, 64 is heated and the heat is evenly given off to the workpiece 50 in a conductive manner.
• the pressing process or the 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, if necessary, provide sensor signals which are processed by the process control 44.
• the prepared control parameters can, if necessary, be checked or adjusted in response to the sensor signals provided by the sensors 4, 5, 42. If the control parameters are adjusted, the joining method 240 is continued in a modified manner with the adjusted control parameters. This can be implemented as a control loop and can be carried out iteratively, for example, so that an improved parameter configuration can be set in 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.
• step 240 This happens in a certain time, which can be calculated by the control.
• a pressing force is initially applied and the actual pressing process takes place in step 240. While the pressing process 240 is being carried out, it may be possible to check whether the corresponding distance per unit of time has been reached and, if necessary, change the pressing force.
• an increasing pressing pressure can be stored, which can be adjusted adaptively in the course of the joining process 240.
• a maximum or desired deflection of the press cylinder 24 to a desired final value can also already be stored in the set of original control parameters. While checking or adjusting control parameters, it can also be determined whether the desired final value for the deflection of the press cylinder 24 and/or the deformation of the workpiece can be achieved without possibly exceeding a pressing pressure with which the workpiece or the batch 50 could possibly experience damage or excessive deformation.
• a post-treatment of the workpiece or the batch 50 can optionally follow. This can be further tempering, further heating or cooling with a defined temperature constant. Following the aftertreatment 250, the workpiece or the batch 50 has cooled down sufficiently and can be removed from the system 1 in step 260.
• a functional solution could be presented in a large number of examples, which also contain features that can be individually combined with one another, as to how the homogeneity of the heat distribution in the press plate 36, 38 can be achieved by integrating a heating device 62, 64 directly into the press plate 36, 38, in particular by means of conductive heat transfer Workpiece 50 can be improved and/or the time period for heating the workpiece 50 can be reduced.
• materials can now be processed using diffusion welding that were previously not open to this process due to the low temperature ranges required.
• the heater 62 is preferably an electrical resistance heater that is integrated in an electrically insulated manner.
• a peripheral heater 14 can be provided to even out the temperature at the edge and in the corners of the component 50.
• the support or peripheral heating can be moved vertically. If necessary, the support heater can be divided into different temperature zones. If necessary, water-cooled pressure distribution plates 36, 38 can be used.
• a flexible heater connection 100 can be realized, for example, using copper strips 112.
• Efficiency refers, on the one hand, to the energy consumption per welding cycle and also to the duration of a joining cycle. This can be achieved by heating the components to be joined via conduction - i.e. contact heating.
• One aim of the present description was the development and elaboration of design boundary conditions for a heating concept for diffusion welding, which homogenizes the heat input into the component and, if possible, realizes it through contact heating, i.e. heat conduction.
• the aim is to achieve process temperatures of up to 900°C, for example, and the possibility of dynamic force application.
• the system should be designed for use in high vacuum furnace systems. Conductive heating avoids the lossy and emissivity-dependent heat transfer through radiation that occurs in a vacuum, which means that the energy input into the mostly plate-shaped parts to be joined are considerably more efficient, more homogeneous and quicker.
• the result is a heating system that enables a significant increase in energy efficiency during diffusion welding and significantly shortened cycle times. This results in a significant reduction in the cost of the diffusion welding joining process and an increase in component quality, as well as increasing the competitiveness of the process.
• the heat conduction or heating of the components 50 to be joined is of particular importance. Particularly 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 levels were only very Low heating speeds are possible, which has a negative impact on the cycle time and thus the costs of the process.
• the direct (conductive) heating of the component 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 areas of a plate-shaped component, while conventional heating essentially over the outer edges takes place, so that due to the path length, a gradient arises between the outside and the component center, which, if not adjusted by waiting (extending the cycle time), leads to quality differences in the composite formation.
• the size of the press plate area can advantageously be at least 300x500 mm or larger.
• the cyclic load capacity of the 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 > 7 N/mm 2 can be achieved on the system side.
• a surface pressure of at least 0.1 MPa, preferably of at least 0.5 MPa can be achieved on the component 50 by means of the pressure plates 36, 38.
• the surface pressure can be achieved up to a maximum of 50 MPa, if necessary a maximum of 40 MPa.
• a force of 1 ton or more can be exerted on the component 50 by means of the press plates 36, 38, then the system can even be used for power-assisted soldering (PAB).
• PAB power-assisted soldering
• a force of 5 tons or more can be exerted on the component 50 by means of the press plates 36, 38.
• the force exerted on the component 50 by means of the press plates 36, 38 can be up to 5,000 tons, for example up to 4,000 tons.
• 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.
• processes for wafer bonding, i.e. joining semiconductor boards are not pressing processes within the meaning of this application. Rather, the field of diffusion welding or force-applied soldering in the sense of the present application is subject to the aforementioned comparatively high pressure regime.
• Heating the components to be joined in a vacuum can in principle be done in a variety of ways, by heating using thermal radiation, laser or electron beam, convection, direct resistance heating, induction, heat conduction (conduction) or the combination of individual variants.
• the beam-based methods laser or electron beam
• the beam-based methods are particularly suitable for rotationally symmetrical small parts, but have the disadvantage that an additional axis must be provided in the system (rotation axis for rotating the workpiece).
• 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 variables. If the direct current is replaced by a pulsed current curve, larger currents can be implemented. Spark flashovers also occur, 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 electrical field must be ensured, especially in large-format components. Induction heating is used much more frequently, especially historically. The heat is generated directly in the area of the component surface generated, causing the component to heat up quickly. Diffusion welding systems for mass production, including for valve disk sealing rings with production figures of 3.1 million pieces per year, were already equipped with induction heating in the 1970s.
• the penetration depth can be adjusted using setting parameters such as frequency or current.
• the component-inductor distance or the shape of the inductor also influence the heat input and thus the temperature distribution in the component.
• the disadvantage here 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 example, for slim component geometries.
• Molybdenum can be considered as a heating element material in air and in vacuum.
• the oxide layer on the molybdenum is dissolved in a vacuum and thus a high emissivity is achieved in a vacuum, which is why the material is used for heaters.
• two typical material groups of the components to be joined are included, aluminum and steel.
• Cleaned steel has a comparatively high level of emissivity. This is temperature dependent and increases with temperature. In comparison, the value for aluminum is significantly lower.
• Cleaned aluminum has very low values, whereas oxidized aluminum surfaces only have a value 2 to 3 times lower than steel. From a radiation technology perspective, oxidized surfaces are optimal in terms of absorbing thermal radiation, but from a diffusion welding perspective this is not the case because oxide layers represent a diffusion barrier.
• Copper materials behave similarly to aluminum.
• heating the highly thermally conductive materials via radiation alone may be insufficient.
• heat transfer can be increased by means of partial pressure in the working chamber (additional convection component).
• impurities contained in the gas including oxygen / nitrogen
• Another disadvantageous aspect of the heating concepts described above is the temperature homogeneity in the component. Basically, heat transfer always takes place via the component surface and is conducted from there to the interior of the component by heat conduction. Accordingly, a temperature gradient forms in the component 50 during heating, which leads to uneven expansion and internal stresses. Depending on the thermal conductivity of the material to be joined, this circumstance must be countered by appropriately slow heating rates, also in order to avoid heat build-up and overheating of the component surface. In addition to the material, the aspect ratio of the component is of great importance.
• the concepts described above implement the heat input predominantly via the component side surfaces. This means a maximum heat conduction path for plate-shaped components. However, such component geometries with low aspect ratios are currently in increasing demand (Plate heat exchangers, tool inserts, etc.). The introduction of heat via the ground and top surface thus shortens the conduction path and thus allows higher heating rates.
• Press plates for diffusion welding systems fulfill the task of introducing the applied pressing force into the component and distributing this force as homogeneously as possible over the component or the joining surface. This initially 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 bending strength. Due to the use in a high vacuum furnace system, these properties must be guaranteed over the entire range of application temperatures. Furthermore, the press plate material must be suitable for use in a vacuum (high vapor pressure). In addition, the ideal press plate material has a low specific heat capacity, since from an energetic point of view the press plates represent dead mass that has to be heated up and cooled down again during the process. Another requirement is the fatigue strength under dynamic loads in the pressure threshold range.
• titanium-zirconium-reinforced molybdenum represents a good starting point and is used in many areas as a load-bearing element in the heating area of vacuum furnace systems.
• the behavior during machining which is comparable to that of CrNi steels, is also advantageous. Accordingly, TZM is also interesting for the present description.
• the disadvantages of TZM are the comparatively high density of 10.2 g/cm 3 , the high thermal conductivity characteristic of metals and the high manufacturing costs.
• All-ceramic press plates are the ideal press plate material made from a mechanical layer.
• silicon carbide ceramic has a high modulus of elasticity of 350 - 450 GPa but also a compressive strength of over 2500 MPa, which results in a very dimensionally stable material.
• the main disadvantage of ceramics is the high cost of processing them in the sintered state.
• Steel materials such as heat-resistant steel 1.4828 are in principle conceivable as pressed plate materials.
• the exclusion criterion here is the low creep strength of less than 5 N/mm 2 at the desired operating temperature of 900°C.
• CMC ceramic-based fiber composite materials
• carbon fibers or ceramic fibers are embedded in a ceramic matrix. This means that the outstanding properties of the ceramic, such as temperature resistance and pressure resistance, are retained, but the fiber reinforcement increases the fracture toughness required for dynamic use.
• Carbon fiber reinforced graphite can be used in diffusion welding systems with static force application. Due to the high thermal conductivity compared to the other fiber composite materials considered here, more energy is removed from the heating zone.
• Carbon fiber-reinforced silicon carbide is a composite material. This material has not yet been used in diffusion welding systems.
• Alumina fiber-reinforced oxide ceramics have a very low thermal conductivity of 0.4-2.7 W/mK and a relatively small modulus of elasticity (40 GPa), which would lead to excellent insulation and very good pressure distribution.
• this material is its low compressive strength of approx. 25 N/mm 2 .
• heater materials for the heating device 62, 64 are essentially a high electrical resistance, a high melting temperature, which must significantly exceed the application temperature, and a low vapor pressure in order to minimize heater wear in vacuum operation. From a design perspective, a low thermal expansion coefficient should still be aimed for. In the area of metallic materials, alongside tungsten, molybdenum 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 sqm (20 - 1500 °C) and an expansion coefficient of 5.8-10-6 K-1, it is possible to reach temperatures of up to 1600 °C with very high vacuum quality realize.
• 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).
• Graphite is another alternative for heating furnace systems; the advantage here is the comparatively low material price and high electrical resistance.
• graphites are only suitable to a limited extent for use in high vacuum, as evaporating carbon can contaminate the parts to be joined and cause material changes.

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