Method, apparatus and computer program product for monitoring electrolyte condition

Abstract

A method and a device for monitoring an electrolyte state during the plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3) are described, in which at least one property of an electrolyte that is stored, circulated and / or applied to the surface (2) of the workpiece (3) is recorded. The described technical solution is characterized in that the strength of an electric current passed through the electrolyte is measured and a charge is determined, and that a state indicator is determined on the basis of the determined charge by means of a transformation function, wherein the state indicator takes into account a limit value, if the limit value is exceeded, a plasma electrolytically processed workpiece does not meet at least one predetermined quality criterion.

Description

[0001] The invention relates to a method, a device, and a computer program for monitoring the electrolyte state during the plasma electrolytic processing of an electrically conductive surface of a workpiece. In this process, at least one property of an electrolyte that is stored, circulated, and / or applied to the surface of the workpiece is detected, and based on this, a statement is made about the state of the electrolyte.

[0002] For workpieces made of metal alloys, the desired surface properties are not typically achieved in the primary manufacturing step, necessitating subsequent finishing or refining. This includes, for example, polishing, cleaning, sterilizing, texturing, and coating the surface, as well as deburring and rounding workpiece edges. Processes that modify surface properties through material removal are of particular economic and technological importance.

[0003] Metal surfaces are typically finished using machining processes with geometrically undefined cutting edges, such as grinding or mechanical polishing, which achieve low roughness and high gloss. These processes always require the surface to be accessible to a tool, usually a rotating one, making the machining of narrow, concave contours and internal surfaces virtually impossible. Furthermore, the process principle always necessitates precise alignment of the tool's relative position to the surface being machined. Changes to the target contour, for example, due to varying or customized workpieces, require complex adjustments to the NC program in automated processes, significantly limiting flexibility. If these adjustments are made manually, comparatively long machining times can be expected for complex components.

[0004] For this reason, electrochemical material removal processes, such as electropolishing and electrochemical machining, which are characterized by force-free material removal, are often used. In electrochemical metalworking, workpieces are processed by anodic dissolution of the metal on the surface. These processes are used in various areas of mechanical engineering, such as aerospace engineering, automotive engineering, toolmaking, medical and microsystems technology, and energy plant engineering. Almost all metals can be processed in this way, and unlike machining, the process is not negatively affected by high strength or hardness. Therefore, electrochemical processing is particularly interesting for high-alloy materials such as nickel-based alloys, titanium alloys, or hardened materials.

[0005] Plasma electrolytic processing of electrically conductive surfaces represents a specific advancement in the known methods for the electrochemical treatment of metallic workpieces. Plasma electrolytic processing methods are processes by which the properties of a workpiece surface that is at least temporarily in contact with an electrolyte are altered by applying an electrical voltage. This alteration is enabled, promoted, or influenced by the near-surface formation of a plasma. While plasma electrolytic oxidation, among other things, serves to produce wear-resistant surface layers, particularly on light metals, plasma electrolytic polishing modifies the surface layer by material removal.

[0006] In contrast to electropolishing, this is done using aqueous salt solutions instead of highly concentrated acids as the electrolyte, with the workpiece typically being immersed in such an electrolyte bath and anodically contacted.

[0007] This method allows for the rapid production of exceptionally smooth and glossy surfaces without the need for form-specific tools. Furthermore, there is no need to pretreat the workpiece or remove any oils or lubricants present on the surface. Depending on the material being processed, plasma electrolytic machining can also create a workpiece surface with reduced corrosion resistance. The process is therefore suitable not only for reducing surface roughness but also for deburring, creating a glossy finish, passivating, cleaning, sterilizing, and smoothing the surface profile.

[0008] In general, two different technical designs for the plasma electrolytic processing of workpieces are known. For example, DE 10 2006 016 368 B4 describes a system with an immersion bath into which a workpiece is immersed for processing. The described system is suitable for cleaning and polishing electrically conductive workpiece surfaces and includes an electrolyte container, a workpiece holder, and a power supply to provide the voltage required for plasma electrolytic processing. Furthermore, a control system is provided for monitoring and adjusting the required current, which adjusts the current depending on the speed at which the workpiece is immersed in the electrolyte container.

[0009] German patent DE 20 2016 100 50 U1 discloses the locally limited plasma electrolytic processing of a workpiece using systems that have nozzles for applying the electrolyte to the workpiece area to be processed. This plasma electrolytic processing method, known as jet plasma polishing, is based on the use of an electrolyte jet instead of an electrolyte bath, with the electrolyte nozzle, which directs an electrolyte jet onto the workpiece, simultaneously forming the cathode. Material removal occurs only at the point where the electrolyte jet strikes the surface of the workpiece. This limits the maximum required current and allows the processing to be focused on selected areas.

[0010] A system for implementing the previously described process is known from WO 2024 / 003401 A1. The essential feature of the system for the plasma electrolytic processing of workpieces described in this document is that a plurality of nozzles are provided for emitting electrolyte jets in order to process a material surface with differently shaped and / or oriented electrolyte jets. In this way, even comparatively complex component geometries can be plasma electrolytically processed, produced, or polished.

[0011] In plasma electrolytic processing systems for workpieces, the condition and quality of the electrolytes used are of crucial importance. This is especially true in systems where an electrolyte is applied to the workpiece via multiple nozzles. This is because, unlike the more common electrolyte bath systems, these types of systems are either automated or integrated into largely automated production processes, such as those used for manufacturing aluminum profiles, deep-drawn components, or extruded profiles in the automotive industry. In these processes, the workpieces are automatically clamped, processed, and then removed from the system.Such system integration is generally associated with significantly higher levels of contamination on individual workpieces, for example from cooling lubricants or scale, which places a heavy burden on the electrolyte. Previously, the impact on the electrolyte was not to this extent, because on the one hand, the degree of integration of individual processes was lower, and on the other hand, when using electrolyte baths, the influence of the aforementioned contaminants is so small that it can be almost ignored, especially since contaminant particles usually sink to the bottom of the electrolyte bath and components are generally machined in a pre-cleaned state.In contrast, systems with multiple nozzles for electrolyte dispensing, often integrated into automated manufacturing processes, contamination and dirt particles are circulated with the electrolyte. This creates the risk of nozzles becoming clogged or damaged, and / or the contaminants in the electrolyte negatively impacting workpiece processing. Without reliable monitoring of the electrolyte's properties, the economical use of such systems is hardly conceivable. Therefore, monitoring the condition of the electrolyte in use is particularly important, and reliable results are essential.

[0012] In known systems, the condition of an electrolyte is monitored by measuring its pH value and electrical conductivity, both of which must be kept within permissible limits. While these parameters represent important properties of an electrolyte, they do not provide a truly reliable indication of its condition, particularly its deterioration during processing. Furthermore, the electrolyte is consumed during use as erosion products accumulate and active reagents decrease. Until now, the responsibility for the proper condition of the electrolyte lay solely with the system operator, who, based on the aforementioned measurements and a visual inspection, decided whether the electrolyte could still be used or needed to be replaced or reprocessed.This regularly requires considerable experience from the machine operator, meaning that the efficiency and cost-effectiveness of a plasma electrolytic processing of workpieces depend heavily on the personnel available to operate the system. This is particularly true for the aforementioned beam-based plasma polishing systems. These systems enable particularly efficient and uniform material removal, but they are sensitive to changing process parameters, materials, and electrolyte composition, depending on the materials being processed and the electrolytes used. The choice of material being processed, in particular, has a significant impact on the aging or changes in the state of the electrolyte during the processing.

[0013] Based on known systems for monitoring the properties of an electrolyte used for plasma polishing, and the problems described above, the invention aims to provide a monitoring system that allows for the most accurate possible statements about the quality, current state, and, above all, the suitability of the electrolyte for processing workpieces, taking into account existing quality requirements. This includes considering factors such as electrolyte contamination and enabling a reliable and relatively simple assessment of which workpieces can still be processed with the respective electrolyte.The described method for determining the state of an electrolyte used in workpiece processing should also make it possible to consider the material type, the shape of the workpiece, and / or the design of the workpiece clamping during processing. The primary objective of the invention is therefore to provide information about the state of the electrolyte used in each plasma electrolytic processing operation based on acquired sensor data, and thus to generate a forecast for the planned processing, in particular the number of workpieces still to be produced, taking into account predefined quality parameters. Furthermore, the described technical solution should be relatively easy to integrate into existing systems and ensure a reliable, automated process for the plasma electrolytic processing of workpieces.

[0014] The problem described above is solved by a method according to claim 1. Likewise, this problem is solved by a monitoring and / or control unit according to claim 15 and by a computer program product implemented according to claim 16. Advantageous embodiments of the invention are the subject of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

[0015] The invention relates to a method for monitoring the electrolyte state during the plasma electrolytic processing of an electrically conductive surface of a workpiece, in which at least one property of an electrolyte is detected that is stored, circulated, and / or applied to the surface of the workpiece. The method according to the invention is characterized in that the magnitude of a current passed through the electrolyte is measured and the electrical charge introduced into the electrolyte is determined, that a state indicator is determined based on the determined electrical charge using a transformation function, and that a limit value is specified for the state indicator, upon reaching or exceeding this limit value, a plasma electrolytically processed workpiece fails to meet at least one predetermined quality criterion.Preferably, this allows information to be output and / or a signal to be generated, at least when the limit value is reached, indicating the state of the electrolyte. In this context, it is conceivable that a signal is generated when the limit value is reached or exceeded, in order to control an output unit, such as a screen or display, to output the information, and / or to control at least one device based on the signal in such a way that the plasma electrolytic processing is automatically interrupted, at least temporarily.

[0016] For the purposes of this invention, reaching and / or exceeding a limit value means conforming to, or exceeding and / or falling below, a predetermined, stored, or otherwise determined limit value. The essential aspect of the invention is that, based on a measured current, the electrical charge introduced into the electrolyte during the plasma electrolytic processing of at least one workpiece is determined. This charge corresponds to the product of the current flowing through the electrolyte and the duration of the respective measurement period. A state indicator is then determined from this result using a transformation function.The state indicator determined in this way provides quantifiable information about the state of the electrolyte, which ultimately forms the basis for deciding whether a currently manufactured and / or a workpiece to be processed in the future meets a quality criterion, without the need for additional measures influencing the state of the electrolyte, such as reprocessing or replacement. The inventive method, based on the determination of a state dictator using a transformation function, allows the state, and in particular any deterioration, of the electrolyte used to be advantageously quantified.In this process, the electrical charge introduced into the electrolyte is converted into a state indicator using a transformation function, whereby the transformation function is implemented depending on the system components present that influence the properties of the electrolyte, for example those intended for the removal of erosion products from the electrolyte system.

[0017] With regard to determining a suitable transformation function, it is generally conceivable that this is determined experimentally and / or at least partially using mathematical methods. In a particular embodiment of the invention, it is provided that the transformation function is based on a finite mathematical series of products, wherein an electric charge introduced into the electrolyte, in particular a relative charge, i.e., the quotient of introduced charge and volume of the provided electrolyte, forms at least a part of at least one summand of the finite series.

[0018] Furthermore, it is conceivable to take into account, at least partially, the following factors when determining the individual summands of the mathematical series: the time elapsed since the electrolyte was prepared, the time span during which the electrolyte assumes or exceeds a specific temperature, a temperature profile or at least a temperature assumed by the electrolyte in the past, the amount of water added, at least one property of the added water and / or the nature of any measures taken in the meantime to prepare the electrolyte.

[0019] According to a particularly preferred embodiment of the invention, the state indicator Z is determined using the transformation function specified below: Z = A * RLM + B * P 1 + C * P 2 , where: RLM: Amount of charge introduced into the electrolyte; A: Factor that takes into account the design of the plasma polishing system, e.g., the properties of the filters used; P1: First process parameter; B: Factor that takes into account the influence on the first process parameter; P2: At least one second process parameter; C: Factor that takes into account the influence on at least one second process parameter

[0020] When determining the appropriate transformation function, virtually any number of state parameters, properties of the system used, and / or properties of the electrolyte employed can be taken into account. According to a further development, it is conceivable, for example, to consider characteristics of current peaks that indicate a higher degree of electrolyte aging, and / or feedback from the system operator, when determining the state indicator.

[0021] During the machining process, the current condition indicator is compared to a limit value determined experimentally and / or computationally. As long as the condition indicator does not exceed the limit value, the workpieces machined up to that point meet the required quality criterion. However, if the currently determined condition indicator exceeds the limit value, a workpiece being machined at that point will no longer meet the quality criterion after machining is complete. It is therefore advantageous to stop a machining process shortly before reaching the limit value, especially by automatically interrupting it. It is essential that the defined limit value is always specific to the material being machined, the workpiece geometry, and / or the electrolyte used.It is therefore conceivable that a situation exists in which workpieces made of one material can no longer be machined because the limit value of the condition indicator has already been reached, while workpieces made of another material can still be machined while adhering to the quality requirements, since the condition indicator still assumes a value below the limit value.

[0022] According to a particular embodiment, the chemical composition of the electrolyte, for example the capacity of the electrolyte to absorb metal ions, the corrosion susceptibility of the material to be processed, the geometry of the workpiece to be processed, such as flow separation edges or cavities, the desired surface quality and / or the time profile of the polishing current are taken into account when determining the limit value.

[0023] According to a preferred training program, the previously described influencing factors are classified into different quality requirement levels, for example: Q1: Difficult-to-machine materials, complex flow conditions in the electrolyte; Q2: Standard materials to machine, workpieces with non-complex geometries, normal flow conditions; Q3: Simple workpiece geometries, low surface requirements

[0024] Furthermore, it is advantageously conceivable that, to increase the accuracy of assessing the state of an electrolyte, additional operating parameters and / or measured properties of the electrolyte are taken into account. It is conceivable that, to assess the state of an electrolyte, heat input into the electrolyte, turbidity of the electrolyte, and / or temperature development are detected and considered in the transformation function when determining the state indicator. Such measures increase the accuracy of the inventive method for assessing the state of the electrolyte used during plasma electrolytic processing.

[0025] According to a particular embodiment of the invention, a limit value of the state indicator corresponds to a number of workpieces that can be plasma electrolytically processed while meeting at least one quality criterion, without requiring additional filtering, cleaning, conditioning, and / or replacement of the electrolyte. Based on the current state indicator and its limit value, the number of workpieces that can still be processed while meeting a predetermined quality criterion can then be determined with particular advantage. The current state indicator is always determined by means of a transformation function based on the charge introduced into the electrolyte at the time of measurement.

[0026] According to these embodiments, the limit value of the status indicator thus contains, from the start of a plasma electrolytic processing operation, information about the maximum number of workpieces that can be processed while adhering to the specified quality criterion. Furthermore, it is advantageous if the current status indicator, the limit value of the status indicator (i.e., the maximum permissible value of the status indicator for the respective plasma electrolytic processing operation), and / or a difference between the limit value of the status indicator and the current status indicator are displayed to a system operator, for example, via a display.Alternatively or additionally, it is advantageous if, particularly in the context of automated operation of a system for the plasma electrolytic processing of workpieces, a violation of the limit value for the status indicator, especially reaching or exceeding the limit value of the status indicator, leads to at least a temporary stoppage of the processing process.

[0027] Based on the current state indicator, which is determined using a transformation function based on the current introduced into the electrolyte during a measurement period, and the limit value of the state indicator, which is determined before the start of the processing process and is available for further evaluation, effective use of the electrolyte used for each processing process is enabled, and rejects in the plasma electrolytic processing of workpieces are prevented, or at least the risk is minimized.

[0028] In a further embodiment, information about the electrolyte's state is output based on a measurement of the current flowing through the electrolyte during a measurement period, the current state indicator determined from this measurement using a transformation function, and a comparison of the current state indicator with a maximum or minimum permissible limit value. This output can be visual, for example, via a display, a light, or another indicator unit, and / or audible, for example, by means of a loudspeaker or a signal horn.Preferably, this information could also be transmitted to a central production control room and / or used to control a processing process, in particular the monitored plasma electrolytic processing process.

[0029] According to a particular embodiment of the invention, the relative charge, i.e., the charge introduced into the electrolyte within a given time period, is determined in relation to the volume of the electrolyte. This enables evaluation and condition monitoring that is independent of the electrolyte volume and thus takes into account, for example, that the condition of an electrolyte stored in a small tank deteriorates more rapidly than the condition of an electrolyte in a large tank.

[0030] Furthermore, a specific embodiment of the invention is characterized by the fact that the state parameters temperature, pH value, and / or electrical conductivity of the electrolyte are assumed to be constant during the determination of the state indicator. This specific embodiment of the invention thus allows the assessment of the electrolyte's state to be limited to the quantifiable deterioration of the electrolyte, which is not known from the prior art, since the comparatively easily controllable parameters of temperature, pH value, and electrical conductivity are assumed to be constant. Based on this assumption, a comparatively simple yet accurate method for the quantifiable assessment of the state of an electrolyte used for the plasma electrolytic processing of workpieces can be implemented.

[0031] A particular embodiment of the invention provides that, to determine a limit value for the condition indicator, in particular a limit value of the condition indicator, a number of workpieces made from a predetermined metallic material are preferably determined before the start of the actual industrial machining process. These workpieces must be producible without preparation and / or without at least partial replacement of the electrolyte while adhering to at least one quality criterion. Preferably, this number of workpieces is stored in a database as a material-specific limit value of a condition indicator. Furthermore, it is advantageous if the limit value of a condition indicator for the combination of a material to be machined with the electrolyte used for machining is stored in a database.Furthermore, it is conceivable, alternatively or additionally, to determine limit values ​​of a condition indicator and to store or make them available for further use, which are specific to a certain workpiece size and / or geometry.

[0032] Essential to the embodiments described above is the determination and storage of a limit value for a condition indicator. If this limit value is violated, particularly if exceeded, it is highly likely that, without intermediate electrolyte regeneration, the workpiece produced after exceeding the limit value will no longer meet the specified quality criterion due to the deterioration of the electrolyte's condition. By outputting, storing, and / or using a corresponding limit value in the control system of a plasma electrolytic processing system for workpieces, it is thus possible to ensure, in a particularly efficient manner, that the processed workpieces meet a specified quality criterion while simultaneously preventing the premature replacement, cleaning, and / or regeneration of the electrolyte.The threshold value of the condition indicator allows for a quantitative statement about the state of an electrolyte and thus a suitable, easily verifiable comparison between a current value and the relevant threshold value. This advantageously enables the detection of a deterioration in the electrolyte's condition due to workpiece processing, with quantification taking into account the charge introduced into the electrolyte. The threshold value of the condition indicator therefore correlates with a threshold value for the introduced charge; if this threshold is exceeded, the processed workpieces no longer meet a predefined quality criterion.According to the invention, a transformation function is used to determine both the current state indicator and the limit value for a state indicator. This transformation function is designed such that the respective state indicator can ultimately be determined from the measured strength of the current flowing through the electrolyte. If several determinations of a limit value are carried out for a specific material-electrolyte combination, the values ​​of the various determined limit values ​​will follow a normal distribution.

[0033] In a particularly specific embodiment of the invention, it is provided that a plurality of limit values ​​of the condition indicator, each specific to a material, a material-electrolyte combination, a workpiece size, and / or a workpiece geometry, are stored in a database. Preferably, it is possible in this way to store a large number of different such limit values ​​of condition indicators and make them available for use, in particular for plasma electrolytic processing of metallic workpieces, whereby the limit value that is relevant for the processed workpiece and / or the electrolyte used is always taken into account.

[0034] According to a particular embodiment, it is conceivable in this context that data is stored and provided that takes into account the type, in particular the geometric shape and design, of a component to be processed. Advantageously, the data described above is made available to the control system of a system for the plasma electrolytic processing of workpieces, with suitable interfaces for wired and / or wireless data transmission being provided so that the corresponding data can be taken into account in the control unit, for example, after a system operator has selected the combination of a material to be processed and the electrolyte intended for processing using an input unit.Subsequently, it is possible to compare the current status indicator determined during the operation of the plasma electrolytic processing system for workpieces with the specific limit value of a status indicator stored in the control unit. If this limit value is exceeded, particularly as soon as the current status indicator exceeds the limit value of the status indicator, the workpiece processing is at least temporarily interrupted and corresponding information is issued to the system operator. In this context, it is therefore preferable that the plasma electrolytic processing of components is automatically stopped when the stored limit value is reached, exceeded, or fallen below.

[0035] Furthermore, a particular embodiment of the invention provides that the shape, size, and / or configuration of a holder specifically used for processing a workpiece is taken into account when determining the condition indicator. According to this embodiment, the shape of a holder and / or its arrangement is thus considered during processing with an electrolyte when assessing the condition of the electrolyte used.

[0036] Furthermore, it is advantageous to consider the degree of contamination of the workpiece being processed and / or a workpiece holder when determining the condition indicator. This contamination can vary, particularly when integrating a plasma electrolytic processing system into a complex industrial production process. Such contamination is often caused by the coolants and / or lubricants used and can be detected with optical and / or electrical sensors.

[0037] According to a further particular embodiment of the method according to the invention, a correlation is established, particularly using statistical means, between the limit value for the status indicator and / or for the charge introduced into the electrolyte and the failure to meet at least one quality criterion, and the relevant limit value is determined over a predetermined confidence range. Furthermore, it is advantageously conceivable that an operator of a system implementing the method according to the invention receives feedback on the fulfillment of at least one quality criterion, and that this feedback is taken into account when determining the limit value, taking into account the respective value of the status indicator.

[0038] Furthermore, a specific embodiment of the invention provides that a system operator has the option of inputting information regarding the degree of fulfillment of at least one quality criterion. Preferably, this information can then be used to consider data based on this information when determining the condition indicator and setting the limit value for the condition indicator. In this way, a practical adaptation of the method is possible.

[0039] In addition to a method for assessing the condition of an electrolyte used during the plasma electrolytic processing of workpieces, the invention also relates to a device for monitoring and / or controlling a device for the plasma electrolytic processing of a workpiece. According to the invention, the device is designed such that the method according to the invention can be carried out in its general form or according to one of the previously described embodiments. In this context, it should be noted that the invention also relates to the material components required for the realization of the method according to the invention, in particular their suitable composition.Furthermore, the invention also relates to a computer program product that is configured to effect the execution of the method according to the invention in its general form or according to one of the previously described further developments at least temporarily in a device for monitoring and / or controlling a device for plasma electrolytic processing of an electrically conductive surface of a workpiece.

[0040] The invention will now be explained in more detail with reference to specific embodiments and the figures mentioned, without limiting the general concept of the invention. These figures show: Fig. 1: Device for plasma electrolytic processing of workpieces; Fig. 2: Curve of the development of the state indicator over time, taking into account a theoretical system behavior; Fig. 3: Graphical representation of the limit values ​​of the state indicator for various material-electrolyte combinations; and Fig. 4: Curve of the development of the state indicator over time, taking into account a real system behavior.

[0041] The invention relates to a method for monitoring and evaluating the condition of an electrolyte used in the plasma electrolytic processing of workpieces with a metallic surface. Using the method according to the invention, which will be described in detail below, the deterioration of the electrolyte's condition can be quantified, something that was previously impossible or only possible to a very limited extent. According to the specific embodiment of the invention described below, the parameters temperature, pH value, and electrical conductivity of the electrolyte are initially disregarded; instead, these parameters are assumed to remain constant during the processing process for the purpose of evaluating the electrolyte's condition.

[0042] The method implemented according to the embodiment of the invention described below can advantageously be realized in a system such as that described in Fig. 1 shown.

[0043] Fig. 1 Figure 1 shows a schematic top view of a device 1 for plasma electrolytic processing, preferably for deburring and / or polishing, of a surface 2 of a workpiece 3, in which the inventive method for determining the state of the electrolyte used is advantageously employed. The device 1 shown has a supply unit 5 that supplies the electrolyte required for the plasma electrolytic processing of a workpiece surface 2 to a delivery unit 4. The supply unit 5 has a pump that, during operation, delivers the electrolyte almost pulsation-free from a reservoir 16 to several nozzle openings 10 of the delivery unit 4.The electrolyte delivery begins after the workpiece 3, whose surface 2 is to be machined, has been fixed in the machining position. A plurality of electrolyte jets from the individual outlet openings 10 then strike the workpiece surface 2 from different directions. The number of outlet openings 10 through which the electrolyte is dispensed, as well as their design, orientation, and means of movement (if the nozzles are to be actively moved), are selected depending on the contour of the workpiece surface 2 and the machining task.

[0044] In the plasma electrolytic processing device described here, the application unit 4 has a movable nozzle head 21 with three nozzle-shaped outlet openings 10. Different electrolyte jets can be applied to the workpiece surface 2 to be processed via the outlet openings 10 as required. The supply of electrolyte to the individual outlet openings 10, the control of the application unit 4, and the processing of the electrolyte extracted from the workpiece surface 2 are carried out as previously described. The individual nozzle-shaped outlet openings 10 are movable relative to the workpiece 3 during processing, and according to the illustrated embodiment, three nozzle-shaped outlet openings 10, together with a nozzle head 21, are moved relative to the workpiece 3 as indicated by the arrows.

[0045] The controlled movement of the outlet openings 10 and the dispensing of the electrolyte are dependent on the contour of the workpiece 3, which is fixed or clamped in its processing position. The movement of the nozzle head 21, the supply of electrolyte to the individual outlet openings 10, the switching on and off of the electrodes 6 arranged in the area of ​​the outlet openings 10, and the adjustment of the voltage applied between an activated electrode 6 and the workpiece surface 2 to be processed are changed as required, in particular depending on the contour of a surface area currently being processed. During the processing process, the nozzle head 21 with its nozzle-shaped outlet openings 10 is then moved in such a way that the desired contour of the workpiece surface 2 is processed.

[0046] According to the in Fig. 1 In the illustrated embodiment, a workpiece 3 previously manufactured in a mechanical series production process is to be deburred using the device 1 according to the invention. Due to the integration of plasma electrolytic processing of workpieces into an industrial manufacturing process, it is unavoidable that contaminants, such as lubricants and / or cooling fluids, from upstream mechanical processing steps are introduced into the electrolyte. Furthermore, during the plasma electrolytic processing of workpieces, the properties of the electrolyte change, which is also referred to as electrolyte consumption.

[0047] The device 1 shown has a control unit 9, which controls the supply unit 5, as well as an electrical power source 7 used as a voltage source and the individual actuating elements 8 of the device 1, with which the output of electrolyte jets and the properties of the electrolyte jets can be adjusted and changed as required. In order to achieve suitable control of the different elements, a measuring unit 22 with suitable sensors for the continuous or discontinuous measurement of at least one property of the surface 2, in particular the surface roughness, is also provided for determining a distance between the output unit 4 and the surface 2 and / or for determining the position and / or orientation of the output unit 4 relative to the surface 2.The measuring unit 22 and the control unit are in unidirectional or bidirectional data exchange via a data transmission link, which can be wireless and / or wired.

[0048] In this way, both the electrical voltage applied between the electrodes 6 of the device 1 and the workpiece surface 2 during processing can be varied, and the individual outlet openings 10 can be selectively closed and opened. Furthermore, the flow velocity and volume flow of the individual electrolyte jets can be changed as required.

[0049] Essential for the in Fig. 1 The device shown includes a sensor unit that measures the current introduced into the electrolyte during workpiece machining. Alternatively or additionally, the current intensity in the area of ​​the electrodes 6 can be detected. Based on the detected current intensity and the measurement period, the charge introduced into the electrolyte is determined in an evaluation element, which, according to the illustrated embodiment, is part of the control unit 9. As will be explained in detail below, a state indicator is derived from the determined charge using a transformation function. The current state indicator, determined continuously or at discrete time intervals during workpiece machining, enables a quantitative assessment of the electrolyte's condition.In this context, it is essential that the current status indicator, preferably via the control unit, is compared with a previously determined limit value for the status indicator specific to the respective processing operation and provided to the control unit 9 from a database. Before the workpiece processing begins, the machine operator enters the relevant material-electrolyte combination into an input unit of the device, so that the required limit value can be provided to the control unit 9.If the current status indicator approaches the limit value and eventually falls within a predefined tolerance range, corresponding information is displayed visually or audibly via an output unit. This allows the operator to visually check the electrolyte's condition, clean or replace the electrolyte, interrupt the processing operation, or take any other appropriate action. If the plasma electrolytic processing continues without further intervention and / or the current status indicator reaches or exceeds the stored limit value, the processing operation is automatically stopped, and a notification is issued.

[0050] At the in Fig. 1 In the device shown, the electrolyte stored in a reservoir 16 is preheated by means of a heating element 18 and then conveyed via the electrolyte supply 13 to the individual outlet openings 10 by means of a plurality of pumps, so that the individual outlet openings 10 can be supplied with the electrolyte separately. The supply of the electrolyte to the outlet openings 10 is further controlled by actuating elements 8, such as valves, with which the flow characteristics can be specifically varied. In this way, at least two electrolyte jets with different properties are applied simultaneously or sequentially to the workpiece surface 2 to be processed via the outlet openings 10.

[0051] During the processing operation, a connection is made between at least one electrode 6, which according to the in Fig. 1 In the illustrated embodiment, each section is formed by a tube, the end of which forms the respective outlet opening 10, and a DC voltage of 200 V to 450 V is applied to the workpiece surface 2. As soon as the electrolyte jet strikes the workpiece surface 2 to be processed, gas or vapor is generated, and a gas plasma shell forms on the surface 2, beneath which the desired material removal occurs. A sensor unit is located on the tube section, which measures the current flowing through the electrolyte. From the current intensity thus measured and the duration of the current flow, the charge introduced into the electrolyte is calculated, which is taken into account in the control unit to determine the current status indicator.A sensor unit for measuring the current of the electrolyte used in plasma electrolytic processing is located at each nozzle through which electrolyte is applied, at least temporarily, to the workpiece surface being processed. The charges measured at each nozzle are summed to determine the total charge introduced into the electrolyte during the charging process and to calculate the current status indicator.

[0052] After the electrolyte comes into contact with the workpiece surface 2, it is extracted from the supply unit 5 via an electrolyte discharge unit 14 and fed to a processing unit 15 for electrolyte treatment. In a first step, suspended particles are removed using a cyclone filter. Subsequently, the turbidity, pH value, and electrical conductivity of the discharged electrolyte are measured using at least one sensor unit 17. If the electrolyte is particularly contaminated, a precipitating agent is added from a tank via a dosing unit to induce a precipitation reaction in the electrolyte, and the electrolyte is then pumped into a separate treatment tank. Furthermore, depending on the measured values ​​for the conductivity and pH value of the electrolyte, salt and / or a pH regulator are added from appropriate storage containers with suitable dosing units 19, if required.Following this, the processed electrolyte returns to the storage tank 16. A temperature sensor 20 and a heating element 18 are provided in the storage tank 16 to ensure that the electrolyte is always heated to the required temperature before being fed to the dispensing unit 4 with its multiple outlet openings 10. As will be explained in more detail below, each of the aforementioned electrolyte processing measures is taken into account in the transformation function. It follows that the state indicator in a plasma electrolytic processing system for workpieces changes more slowly if electrolyte processing measures are carried out during the processing than if the system is operated without electrolyte processing.

[0053] With the in Fig. 1 The device 1 shown allows for two different forms of continuous processing of a workpiece 3. The dispensing unit 4 with its nozzle head 21 can be set up and positioned such that the outer contour of the workpiece 3 to be processed is reproduced exactly or approximately. Once the appropriate positioning is complete, the workpiece 3 is guided along the dispensing unit 4 with the nozzle head 21 and its outlet openings 10. If individual surface areas of the workpiece 3 guided along the dispensing unit 4 are not to be processed, it is possible to interrupt the dispensing of electrolyte jets and / or the application of a voltage in these areas, in particular via an actuating device 12.

[0054] The strength of the current introduced into the electrolyte during a specific time interval is measured, and the charge introduced into the electrolyte is determined. The control and evaluation unit then takes into account the volume of electrolyte used in the plasma electrolytic processing system for the workpieces, so that a value for the relative charge is ultimately used to further determine the state of the electrolyte.Furthermore, characteristic curves are stored in a database, which is connected to the control unit via suitable data transmission. Each of these curves contains a limit value for a condition indicator for a specific combination of components made from a particular material and an electrolyte. This limit value corresponds to the number of workpieces that can be processed consecutively with the electrolyte without changing or reprocessing it, in order to meet a predefined quality criterion. If the condition indicator determined during the processing process violates or exceeds the limit value stored in the database for the specific electrolyte-workpiece combination, it is highly likely that the subsequently processed workpieces will no longer meet the predefined quality criterion.For this reason, if the limit value for the condition indicator is exceeded, the operator is advantageously informed and / or the processing process is automatically stopped. If the operator only receives such information without the processing process being automatically stopped, the operator at least has the option of deciding whether the processing process should continue without further intervention in the system or whether the electrolyte used should first be replaced or reprocessed.

[0055] Essential to the described, controlled process for plasma electrolytic processing of a workpiece is the monitoring and consideration of the electrolyte's state during process control. For this purpose, the electrical charge introduced into the electrolyte is determined, and a current state indicator is calculated using a transformation function. This current state indicator is then compared to a previously determined limit value. A specific charge, i.e., the charge introduced per unit volume, is used to determine the respective state indicator. This takes into account that a larger quantity of electrolyte is consumed less during processing than a smaller quantity.The limit value of the specific charge, which corresponds to a limit value of the condition indicator, is reached during the machining process when the state of the electrolyte no longer permits further processing of the workpieces while adhering to at least one predefined quality criterion. A just-acceptable condition indicator is thus reached when the last workpiece that meets at least one predefined quality criterion has been produced. The value of the condition indicator chosen in this case therefore corresponds to the number of workpieces that can be machined without additional preparation or replacement of the electrolyte while adhering to the predefined quality criterion.

[0056] The in Fig. 2 The observed trend of the condition criterion is due to the fact that the condition indicator increases during workpiece machining, while remaining constant during machining breaks. Additionally, in Fig. 3 In the partial views a), b) and c) a total of three diagrams are shown, which are for the plasma electrolytic processing of workpieces made of steel of material number 1.4404 ( Fig. 3a )), steel of material number 1.4542 ( Fig. 3b )) and from 1.4301 ( Fig. 3c )) each shows the number of workpieces that can be machined up to a limit value of the condition indicator, above which a specified quality criterion is no longer met by the machined workpieces. While 70 workpieces made of steel of material number 1.4404 ( Fig. 3a )) and 45 workpieces of steel of material number 1.4542 ( Fig. 3b )) can be processed in compliance with a specified quality criterion, this applies to the plasma electrolytic processing of 1.4301 ( Fig. 3c )) only 25 workpieces. It is expressly pointed out here that the stated numerical values ​​are merely examples and may differ from the values ​​obtained in reality.

[0057] Out of Fig. 3 This means that an electrolyte with a condition indicator value of 35 can no longer be used for machining 1.4301, but can certainly be used for machining workpieces made of steels with material numbers 1.4404 and 1.4542.

[0058] In this way, if the limit value of the condition indicator for a specific electrolyte-material combination has been previously determined or is known, the number of components that can still be processed while complying with the required quality criterion can be determined from the current condition indicator of an electrolyte without having to replace or reprocess the electrolyte used.

[0059] In contrast to the theoretical approach described above, a real-world system for the plasma electrolytic processing of workpieces must also consider additional parameters that influence the processing and the state of the electrolyte. These include, in particular, the influence of system components that remove erosion products from the electrolyte.

[0060] When determining the appropriate condition indicator for a real-world system, further system characteristics must be considered in the transformation function, such as whether cross-flow filtration, electroplating, continuous screen filters, or paper filters are used. For batch systems, it is also advisable to consider the individual electrolyte preparation steps and the batch filtration stages. Fig. 4 In this context, a state curve is shown, depicting the progression of the state indicator over time. It is clearly visible that the state of the electrolyte changes.

[0061] In a real-world system with intermediate electrolyte regeneration, the changes occur more slowly than predicted by the previously described theoretical approach. The [unclear] Fig. 4The depicted function curve is based on a transformation function that takes into account the components present in the actual system for electrolyte preparation, and in particular their functional influence. This function, determined for real-world conditions, primarily considers the filtering effect of the system and leads to a state indicator that can be used for monitoring and control in real-world processes. In this way, the state monitoring of the electrolyte can be quantified and objectified even for real plasma electrolytic processing with intermediate electrolyte preparation, enabling it to be carried out without relying on the expert knowledge of individual system operators.

[0062] Furthermore, the transformation function allows us to consider that the state indicator is also influenced by the complex interplay of material removal products, impurities, consumption of complexing agents, degradation of surface tension-modifying substances through plasma-physical reactions, and the aging of organic substances. The geometry of the component being machined also affects the change in the electrolyte's state and thus the state indicator. It was found that large, flat surfaces and bores, in particular, reduce the state indicator's threshold value. This is because, as the electrolyte's state deteriorates, machining differences become visible, and material removal products can accumulate in bores. Reference symbol list

[0063] 1 Device for plasma electrolytic processing of an electrically conductive workpiece surface 2 Surface 3 Workpiece 4 Dispensing unit 5 Supply unit 6 Electrode 7 Electrical power source 8 Actuating element 9 Control unit 10 Outlet opening 11 Adjustment unit 12 Actuating device 13 Electrolyte supply 14 Electrolyte discharge 15 Processing unit 16 Storage container 17 Sensor unit 18 Heating element 19 Metering unit 20 Temperature sensor 21 Nozzle head 22 Measuring unit 23 Sensor unit for measuring current

Claims

1. Method for monitoring an electrolyte state during the plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3), in which at least one property of an electrolyte that is stored, conveyed in a circuit and / or applied to the surface (2) of the workpiece (3) is recorded, characterized by the fact that a strength of an electric current passed through the electrolyte is measured and a charge is determined, such that a state indicator is determined on the basis of the determined charge by means of a transformation function, wherein the state indicator takes into account a limit value, if the violation of which a plasma electrolytically processed workpiece (3) does not meet at least one predetermined quality criterion.

2. Method according to claim 1, characterized by the fact thata value of the condition indicator corresponds to a number of workpieces (3) that can still be machined from a time of charge determination until reprocessing and / or at least partial replacement of the electrolyte, while adhering to at least one quality criterion.

3. Method according to any of the preceding claims, characterized by the fact that The state indicator determined on the basis of a measurement of the strength of the current flowing through the electrolyte is compared with a maximum permissible limit value of a state indicator, and information about the state of the electrolyte is output as soon as the determined state indicator exceeds the maximum permissible limit value of a state indicator.

4. Method according to any of the preceding claims, characterized by the fact that the relative charge per unit volume of the electrolyte (A·s / m³) 3) determined and the state indicator is determined taking into account the relative charge per unit volume.

5. Method according to any of the preceding claims, characterized by the fact that The state parameters temperature, pH value and / or electrical conductivity of the electrolyte are assumed to be constant during the determination of the state indicator.

6. Method according to any of the preceding claims, characterized by the fact that a number of workpieces (3) made from a given metallic material is determined which can be produced without preparation and / or without at least partial replacement of the electrolyte while fulfilling at least one quality criterion, and this number is stored in a database as a material-specific limit value of a condition indicator.

7. Method according to any of the preceding claims, characterized by the fact thatA plurality of limit values ​​of the condition indicator, each specific to a metallic material, are stored in a database.

8. Method according to claim 7, characterized by the fact that The condition indicator, determined on the basis of a measurement of the strength of the current flowing through the electrolyte, is compared with the material-specific limit value stored in the database.

9. Method according to any of the preceding claims, characterized by the fact that When a condition indicator exceeding a maximum permissible limit is reached, the plasma electrolytic processing of components is automatically stopped.

10. Method according to any of the preceding claims, characterized by the fact that Heat input into the electrolyte, turbidity of the electrolyte and / or temperature development are detected and taken into account in the transformation function when determining the state indicator.

11. Method according to any of the preceding claims, characterized by the fact that a shape and / or size factor that is specific to the workpiece (3) to be machined and / or to a holder for receiving the workpiece (3) is taken into account when determining the condition indicator.

12. Method according to any of the preceding claims, characterized by the fact that The degree of contamination of the workpiece (3) to be processed and / or of a holder for receiving the workpiece (3) is taken into account when determining the condition indicator.

13. Method according to one of the preceding claims characterized by the fact that The violation of the limit value and the failure to meet at least one quality criterion are statistically correlated, and the relevant limit value is determined over a predetermined confidence range.

14. Device for monitoring and / or controlling a device for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3), which is suitable for implementing the method according to one of the preceding claims.

15. Computer program product configured to effect the execution of the method according to one of claims 1 to 14 at least temporarily in a device for monitoring and / or controlling a device for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3).

Images