Methods for the thermal processing of machining areas on surfaces of workpieces, semi-finished products or powder beds

Abstract

In this case, an energy beam with a base power P is used. Basis directed at the surface and its focal spot moved two-dimensionally along a predetermined starting contour within the processing area so that the focal spot is moved from a position P at each time xi,yi to a subsequent position P xi+1,yi+1 , which are at a given distance Δl i to the previous position P xi,yi is arranged, moved, and there are predefinable holding times Δt Basis The temperature at the surface of the processing area is measured with spatial resolution and fed to an electronic evaluation and control unit. Subsequently, depending on the spatially resolved temperatures, a control is implemented such that a predefined initial contour to be followed is modified accordingly, taking the spatially resolved temperatures into account, and / or the predefined distances Δl are adjusted. i+xbetween the individual positions P, which were driven on one after the other xi+x,yi+x and / or the holding times Δt i+x at the individual positions P xi,yi , are adjusted. This is repeated until a predetermined, locally defined temperature distribution is achieved in the processing area.

Description

[0001] The invention relates to a method for thermally processing processing areas on the surfaces of workpieces, semi-finished products, or powder beds using a deflectable energy beam. The thermal processing can be a primary forming, reshaping, joining, coating, or a process for influencing material properties.

[0002] A laser or electron beam, for example, can be used as an energy beam (EB), with which locally defined thermal energy can be introduced into the workpiece surface, leading to the heating of the surface in the respective specified surface area of ​​a workpiece. Since the impact zone of the EB projected onto the processing area (hereinafter the focal spot size) is technically limited, the energy input (E) can be distributed over the surface of the processing area in a time interval (Δt) by means of a (highly dynamic) deflection (scanning) of the EB. The deflection movement of the focal spot of the EB can, on the one hand, occur continuously at the speed v. On the other hand, a time-defined holding at specified positions is possible (holding time = Δt). The time interval for the jump (Δt Sprung) between the individual positions at which no further movement of the focal spot occurs during a holding time Δt, should be significantly smaller than the holding time at one position. (Δt Sprung « Δt Punkt ). If this condition is met, the speed along a linear movement of the focal spot is v=l / (N∗ΔtPoint)

[0003] For both variants of the deflection movement, the ES can be moved along various geometric shapes to follow specific contours. These can be traversed in a static position, preferably linearly, or even flatly. Depending on the technology, this movement of the ES's focal spot can be achieved using magnetic fields (electron beam), mechanical axes, or mirrors (laser beam), etc. The arrangement of these positions at which the movement of a focal spot is stopped is almost arbitrary within the technological scanning limits, enabling the heating of a wide variety of contours.

[0004] For an energy beam of constant power P, v or Δt = const. results in a constant energy input within the contour, i.e., each position is subjected to the same energy. The resulting temperature distribution is influenced by many variables, e.g., different heat dissipation conditions, varying geometry, etc., and therefore cannot be defined and / or reproducibly adjusted. Therefore, local control of the energy input is desirable. The present invention enables the adjustment of any two-dimensional temperature distribution within the limits of physical laws without the use of additional heat sources apart from the energy beam. For this purpose, the power of the energy beam and the holding time Δt at the positions, hence the scanning speed v, can be controlled during the machining process. Control of the contour to be traversed (e.g.,Adding / removing positions is also possible.

[0005] Previously, influence was exerted by repeatedly scanning a treatment area with defined cooling intervals, a control of the beam power based on the measured surface temperature of a pyrometer (measurement at two wavelengths) averaged over a limited measuring area within the scanned treatment area with constant contour and constant hold time (Δt) or scan speed (measurement area of ​​the pyrometer < scanned area), a control from a previous position with adjusted hold time at defined positions of the scanned area based on a numerical simulation, a temperature-related adjustment of the energy distribution on a linear scan path (one-dimensional, oscillating mirror optics with adjustment of the oscillation function (adjustment of the continuous speed v)).

[0006] In this case, a desired predetermined temperature distribution on the surface of a processing area can only be achieved inadequately and with increased effort.

[0007] It is therefore an object of the invention to provide possibilities for thermal processing of tools with which a predetermined temperature distribution can be achieved within a processing area on a workpiece surface, wherein the heating is to be achieved with a single deflectable energy beam.

[0008] According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims.

[0009] In the process for thermal processing of machining areas on workpiece surfaces, in which an energy beam with a base power P Basisis directed onto the surface, its focal spot is moved two-dimensionally along a given initial contour within the processing area in such a way that the focal spot is moved from a position P xi,yi to a subsequent position P xi+1,y+1 , which are at a given distance Δl i to the previous position P xi,yi is arranged, is moved. The respective initial contour can be specified, for example, based on empirical values ​​or simulation calculations.

[0010] At the respective positions P xi,yi the focal spot is held for a predefined base hold time Δt Basis This continues until the specified initial contour has been traversed with the focal spot.

[0011] The temperature on the surface of the processing area is measured with spatial resolution, and the respective spatially resolved temperature measurements are fed to an electronic evaluation and control unit. The appropriately designed electronic evaluation and control unit then carries out a control depending on the spatially resolved temperatures so that During control, the specified initial contour to be followed is changed according to the spatially resolved temperature measured values ​​and / or the specified distances Δl i+x between the individual positions P traveled one after the other xi+1,yi+1 and / or the holding times Δt i+x at the individual positions P xi,yi adjusted and this is repeated until a predetermined locally defined temperature distribution in the processing area has been achieved.

[0012] In addition, at least one of the following control options can be changed depending on the spatially resolved temperature measurement signals. This can be the power P i with which the energy beam is operated, the power density in the focal spot, the speed v i with which the focal spot from position P xi,yi to a subsequent position P xi+1,yi+1 is moved and / or the pulse frequency, pulse length and pulse duration of a pulsed energy beam.

[0013] Where i = 1 to N can be selected and N in particular a number of complete descents of contours until a predetermined target temperature distribution within a respective machining area of ​​a workpiece has been achieved, by which a certain heating with possible subsequent cooling should be achieved,

[0014] An outer contour or contour can be understood as the path or feed direction of the focal spot of the energy beam along the respective surface during a single traverse. A respective initial contour can be specified before machining begins, and subsequent contours can then be controlled. The focal spot will then travel different paths when traversing a contour as a result of the control.

[0015] A given initial contour can, for example, be spiral, meandering, circular, circular ring-shaped with changing radii, a row and column arrangement of positions P x,y but can also be selected completely arbitrarily or randomly. This contour can then be changed as a result of the control by moving the focal spot to other positions P xi,yithan those selected for the initial contour. When contours are repeatedly traversed in a controlled manner, the contour geometry can also be changed. It may also be the case that with each traversal of a contour, the respective contour can be adapted to the currently measured temperature distribution within the respective processing area, so that the individual contours used in the process differ from one another during at least some traversals of the contour's focal spot.

[0016] As is already practiced elsewhere, a relative movement of the focal spot of the energy beam and the respective surface can be achieved by two-dimensional movement of a workpiece, semi-finished product or powder bed and / or by a correspondingly controlled or regulated deflection of the energy beam with which the impact position of the focal spot on the respective surface can be influenced.

[0017] Accordingly, the distances Δl i of positions P x,y at which the focal spot movement is stopped, which are approached one after the other and / or the respective holding times Δt i during a stop. If larger distances Δl i selected, a smaller energy input per area occurs. For longer holding times Δt i can store more energy and thus in the area of ​​the respective position P xi,yi a greater temperature increase can be achieved.

[0018] The speed v of the feed movement can also be controlled depending on the temperature.

[0019] If no continuously operated ES is used, the pulse duration and / or the pulse pause length can also be controlled depending on the spatially resolved measured temperatures.

[0020] Likewise, the power of the respective ES, as well as the power density at the focal spot, can be controlled. By adjusting the power density, the respective size of the focal spot area can be adjusted as needed by adjusting the focus accordingly. This also allows for changes in the geometry of a focal spot resulting from larger deflection angles at which the ES impinges on a surface to be taken into account.

[0021] This makes it possible to traverse an unchanged initial contour or a subsequently traversed contour with the respective focal spot multiple times before an adjustment to a changed temperature distribution on the surface of the respective processing area is required and carried out. This can be done without having to change any of the control options mentioned above, which would be necessary for multiple traversals, before actual adjustment of at least one of the additional parameters mentioned is carried out.

[0022] Initially, an initial contour is specified. The distances Δl between the positions P xiyi not be significantly larger than the diameter of the energy beam focal spot. The relative energy input (E relativ ) at each position is determined based on a preselected base residence time (Δt Basis ), the current residence time Δt iat the respective individual position (for N points i = 1 ... M, a preselected base beam power (P Basis ) and the current beam power (P) according to equation 2. Erelative=(P∗Δti) / (Pbasis∗Δtbasis) For an initial contour, Δt i = Δt Basis and P = P Basis

[0023] The input variables can be sent to an actuator and to a control system of the energy beam ES. The ES projects the output contour onto the surface of the processing area (this can also be one or more parts of a larger total area) and scans it repeatedly (initially with the output power P Basis). The projection of the contour onto the surface of the processing area is referred to below as the heating field. The temperature distribution established in the heating field is the controlled variable for the associated control loop of the electronic evaluation and control system. The radiation emitted by the component surface can be received by a measuring element as spatially resolved measurement signals. A thermal camera capable of measuring in the infrared range can be used as a sensor for this purpose. Measurement in a different wavelength range is also conceivable.

[0024] The temperatures should be recorded at at least 50, preferably at least 100 and most preferably at least 10,000 positions simultaneously and taken into account in the control system.

[0025] The digitized measurement signals can be used to determine a two-dimensional actual temperature distribution. The number of pixels of the temperature measurements measured by the thermal camera and the positional distances of the respective contours can be adjusted in advance so that the xy coordinates of the contour positions match those of a respective pixel. The actual temperature distribution thus determined is compared with a specified target temperature distribution. For each position P xi,yi The difference between the determined actual temperature and the respective target temperature is calculated. This results in a matrix with the target-actual deviations for each pixel of the measured temperature distribution. These deviations form the basis for a control process, which can be implemented, for example, with a PID controller (proportional-integral-derivative controller). On the one hand, Δt ifor each position with an individual control curve. On the other hand, the control of P* Δt i to compensate for temperature differences within a traced contour, while P for each position P xi,yi is identical and therefore only proportionally regulates the amount of energy input. Consequently, there is no need for temporal synchronization between the current beam position and the beam power. Controlling the beam power using another non-contact measuring method in a separate control loop or based on a section of the actual temperature distribution is also conceivable.

[0026] Based on the differences, a contour is created with individually adjusted holding times for each position P xi,yi. and an adjusted beam power can be maintained or set. Both are fed back to the actuator, the energy beam. Scanning then takes place along a new contour to be followed, with the power adjusted if necessary. A further run of the control loop then begins until the specified target temperature distribution within the processing area is reached.

[0027] It should be noted that the energy beam repeatedly scans the surface throughout the entire control cycle, tracing the contours of its focal spot. The number of scan cycles completed with an individual contour and beam power also depends on the control or scanning frequency. This control method can be applied both to a statically held processing area and to relative movement between the heating field and the processing area.

[0028] During the processing / heating process, the specified starting surface, the processing / heating area, the specified temperature distribution and / or the parameters of the electronic control and evaluation unit can also be modified.

[0029] During processing, the spatially recorded temperatures and associated parameters used for the controlled processing can be transferred to a memory, and an electronic evaluation unit can be used to determine and make available control strategies for future, at least similar, processing operations. Using stored values ​​and the resulting control strategies, subsequent identical or similar processing operations can be carried out, allowing the control to be improved over time.

[0030] Essentially, the invention enables the control of a 2D temperature distribution at definable coordinates using an energy beam in a closed control loop. The main advantage over the prior art is that • the solution to this problem by means of a single energy beam, without additional heating devices, combined with the fact that • the control is carried out, among other things, by means of the relative energy input at definable positions of the heating field: ie the control of the 2D temperature distribution does not require any direct temporal synchronization between beam power and beam movement, since the localization of the energy input is inherent to a control variable and • each coordinate in the heating field can be controlled with an individual control process. • Furthermore, the resolution of the subdivision of the treatment area is high due to the use of an energy beam with a small focal spot diameter.

[0031] The invention can be used for • preheating, sintering and fusion in additive manufacturing / coating processes, • surface hardening or remelting of moving or static components with a wide variety of geometries, • further local heat treatments (e.g. annealing) on ​​almost any surface contour, for joining technologies (e.g. maintaining the temperature during soldering or pre- or post-heating during welding).

Claims

[1] Process for the thermal processing of processing areas on surfaces of workpieces, semi-finished products or powder beds, in which an energy beam with a base power P Basis directed at the surface and its focal spot is moved two-dimensionally along a given initial contour within the processing area in such a way that the focal spot is moved from a position P xi,yi to a subsequent position P xi+1,yi+1 , which are at a given distance Δl i to the previous position P xi,yi is arranged, moves and at the respective positions P xi,yi over a preset holding time Δt Basis is not moved any further and This is carried out until the specified initial contour has been traversed with the focal spot and the temperature on the surface of the processing area is measured spatially resolved and fed to an electronic evaluation and control unit and subsequently, with the appropriately designed electronic evaluation and control unit, a control is carried out depending on the spatially resolved recorded temperatures in such a way that a predetermined initial contour which is to be traversed is changed accordingly into adapted contours which take into account the spatially resolved recorded temperatures and / or the specified distances Δl i+x between the individual positions P xi+x,yi+x and / or the holding times Δt i+x at the individual positions P xi,yi , be adjusted and this is repeated until a predetermined locally defined temperature distribution in the processing area has been achieved. [2] Method according to claim 1, characterized by that in addition to changing the initial contour, at least one of the following control options is changed during thermal processing depending on the spatially resolved temperatures in the processing area and for this purpose the power P i with which the energy beam is powered, the power density in the focal spot, the speed v i with which the focal spot from position P xi,yi to a subsequent position P xi+1yi+1 is moved and / or the pulse frequency, the pulse duration and the pulse pause duration of a pulsed energy beam is / are regulated. [3] Method according to one of the preceding claims, characterized bythat a predefined initial contour is spiral, meandering, circular, circular ring-shaped with changing radii, a row and column arrangement of positions P xi,yi but is also chosen completely arbitrarily or randomly. [4] Method according to one of the preceding claims, characterized by that during the temporal processing / heating process a modification of the specified starting surface, the processing / heating area, the specified temperature distribution and / or the parameters of the electronic control and evaluation unit is carried out. [5] Method according to one of the preceding claims, characterized bythat during processing, the spatially resolved temperatures and associated parameters with which the controlled processing is carried out are transferred to a memory and, by means of an electronic evaluation unit, control strategies for future and at least similar processing operations are determined and made available.