Method, device and computer program product for monitoring an electrolyte state

Abstract

The invention relates to 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), wherein at least one property of an electrolyte, which is stored, conveyed in a circuit and / or applied to the surface (2) of the workpiece (3), is detected. The described technical solution is characterized in that a strength of an electrical current conducted through the electrolyte is measured and a charge is determined, and 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, beyond which a plasma-electrolytically processed workpiece does not satisfy at least one predefined quality criterion.

Description

[0001] Method, apparatus and computer program product for monitoring an electrolyte state

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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. Such 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.

[0006] 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.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.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.

[0009] A facility for implementing the previously described procedure is made from the

[0010] WO 2024 / 003401 A1 is known. A key feature of the plasma electrolytic processing system for workpieces described in this document is the provision of multiple nozzles for emitting electrolyte jets, enabling the processing of a material surface with differently shaped and / or oriented electrolyte jets. This allows even comparatively complex component geometries to be plasma electrolytically processed, manufactured, 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 16 and by a computer program product implemented according to claim 17. 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 an 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, conveyed in a circuit and / or applied to the surface of the workpiece.The method according to the invention is characterized in that the strength of a current passed through the electrolyte is measured and an electrical charge introduced into the electrolyte is determined, that a state indicator is determined on the basis of the determined electrical charge by means of a transformation function, wherein at least one process, operating and / or system parameter prevailing, detected and / or specified during the processing of the electrically conductive surface of the workpiece is taken into account and processed data-wise, and that a limit value is specified for the state indicator, upon reaching, exceeding and / or falling below this limit, i.e., upon violation thereof, a plasma electrolytically processed workpiece does not meet at least one specified quality criterion.Preferably, this allows information to be output and / or a signal to be generated, at least when a limit value is reached, providing information about the state of the electrolyte. In this context, it is conceivable that a signal is generated when a 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 at least temporarily and automatically interrupted. For the purposes of the invention, reaching and / or exceeding a limit value is understood to mean compliance with, or exceeding and / or falling below, a predetermined, stored, or otherwise determined limit value.Essential to 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 derived from this charge using a transformation function. This state indicator provides quantifiable information about the state of the electrolyte, ultimately forming the basis for deciding whether a currently manufactured and / or a future workpiece meets a quality criterion, without requiring additional measures that influence the electrolyte's state, 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 state, of the electrolyte used to be advantageously quantified. Here, the electrical charge introduced into the electrolyte is converted into a state indicator using a transformation function. This transformation function is implemented depending on the system components present and / or process or operating parameters that influence the properties of the electrolyte, for example, those intended for the removal of erosion products from the electrolyte system and / or those that influence the properties of the electrolyte.With the help of the transformation, at least one recorded, prevailing, set, specified and / or stored process, operating and / or plant parameter is mapped to the state indicator by means of mathematical and / or data processing, and thus the current state indicator specific to the state of the electrolyte is determined, taking into account the respective relevant or defined relevant process, operating and / or plant parameters.

[0016] The transformation function advantageously considers at least one process parameter, preferably a plurality of process parameters, especially the electrical charge introduced into the electrolyte, in order to determine a state indicator. This indicator ultimately allows for a statement about how many components with a specific geometry and / or made of a particular material can still be processed with the electrolyte present in the plasma polishing system to meet a predetermined quality criterion. Accordingly, the state indicator determined using the transformation function is compared with a limit value, which depends in particular on the type of material being processed.The condition indicator and its limit value can be used to take into account, for example, that with the same electrolyte a first number of components made of a first material or a second number of components made of a second material that differs from the first number can still be processed while adhering to a specified quality criterion.

[0017] Preferably, the at least one process parameter included in the transformation function is multiplied by a factor so that the relevance, the structure of the system and / or the importance of individual properties of the system or of operating parameters for the state of the electrolyte are taken into account, so that the state indicator is determined from the individual process parameters, preferably by a weighted addition, or is composed of the individual process parameters.

[0018] According to a particular embodiment of the invention, the transformation function takes into account the relative charge introduced into the electrolyte and the amount of water added during processing as process parameters. Furthermore, the value of the relative charge is multiplied by a first factor, e.g., 0.8, and the amount of water added is multiplied by a second factor, e.g., 0.25, so that the influence of the respective process parameter on the quality of the electrolyte and thus the state indicator can be considered. The factors used are preferably determined empirically, in particular by measurements in comparative tests. According to the example described above, the transformation function thus takes into account, via the relative charge, the length of the polishing process already carried out and the amount of water added during this time.Refilling the water is particularly important because a considerable amount of water evaporates from the electrolyte during the polishing process.

[0019] In this context, a limit value for the condition indicator of an electrolyte during the machining of simple components made of a first material, particularly conventional stainless steel, would be higher than the limit value for the condition indicator during the machining of complex or sensitive components made of a second material that is more sensitive to machining and contains an iron-nickel alloy, such as stainless steel 1.3912, known under the designations Invar 36, Nilo alloy 36, Nilvar, NS 36, Permalloy D, Radio metal 36, and Vacodil 36. The relevant limit values ​​of the condition indicator for each machining operation are also preferably determined empirically, particularly on the basis of comparative tests.

[0020] 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.

[0021] 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.

[0022] A specific embodiment of the invention is characterized by the fact that, upon reaching, exceeding, and / or falling below the limit value for the status indicator, a control signal is generated to output information about the status indicator and / or to automatically change at least one operating and / or system parameter during the electrolytic processing of at least one surface of the workpiece. According to this embodiment of the invention, a targeted control intervention in the plasma polishing process can advantageously be carried out based on a violation of the limit value of the status indicator, thus preventing, in particular, the production of defective components that do not meet a predetermined quality criterion, impermissible contamination of the electrolyte, and / or damage to the plasma polishing system.

[0023] Furthermore, it is particularly advantageous to generate a control signal when the limit value for the status indicator is reached, exceeded and / or fallen below, which initiates a control and / or regulation process for the processing of at least one surface of the workpiece.

[0024] According to a particularly preferred embodiment of the invention, the state indicator Z is determined using the transformation function specified below:

[0025] Z = A * RLM + B * P1 + C * P2, where:

[0026] RLM: amount of charge introduced into the electrolyte

[0027] A: Factor that takes into account the design of the plasma polishing system, e.g., the properties of the filters used;

[0028] P1: First process parameter

[0029] B: Factor of influences on the first process parameter taken into account

[0030] P2: at least one second process parameter

[0031] C: Factor of influences on at least one second process parameter taken into account

[0032] 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.

[0033] 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 machined at that point will no longer meet the quality criterion after machining is completed. 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 machined material, 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.

[0034] 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.

[0035] According to a preferred training program, the previously described influencing factors are classified into different quality requirement levels, for example:

[0036] Q1: Difficult-to-machine materials, complex flow conditions in the electrolyte,

[0037] Q2: Standard materials to be machined, workpieces with non-complex geometry, normal flow conditions

[0038] Q3: Simple workpiece geometries, low surface requirements

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 relevant to the processed workpiece and / or the electrolyte used is always taken into account. According to a particular embodiment, it is conceivable in this context that data is stored and made available that takes into account the type, in particular the geometric shape and design, of a component to be processed.Advantageously, the data described above are made available to the control system of a plasma electrolytic processing plant for 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 plant operator has selected the combination of a material to be processed and the electrolyte intended for processing by means of 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.

[0049] 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 during processing with an electrolyte is thus considered when assessing the condition of the electrolyte used.

[0050] 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.

[0051] 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 setting the limit value, taking into account the respective value of the status indicator.

[0052] Furthermore, a specific embodiment of the invention provides that a system operator has the option of entering 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.

[0053] 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.

[0054] 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:

[0055] 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;

[0056] Fig. 3: Graphical representation of the limit values ​​of the condition indicator for various material-electrolyte combinations; as well as

[0057] Fig. 4: Curve of the development of the state indicator over time, taking into account real system behavior.

[0058] 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.

[0059] The method implemented according to the embodiment of the invention described below can advantageously be realized in a system as shown in Fig. 1.

[0060] Fig. 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 illustrated device 1 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 supply 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.

[0061] 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.

[0062] 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.

[0063] According to the embodiment shown in Fig. 1, 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.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.

[0064] 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.

[0065] Essential to the device shown in Fig. 1 is the provision of a sensor unit that measures the current introduced into the electrolyte during workpiece machining. Alternatively or additionally, it is conceivable that the current intensity in the area of ​​the electrodes 6 is 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 could 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.

[0066] In the device shown in Fig. 1, 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 selectively varied. At least two electrolyte jets with different properties are thus applied simultaneously or sequentially to the workpiece surface 2 to be processed via the outlet openings 10.

[0067] During the processing operation, a DC voltage of 200 V to 450 V is applied between at least one electrode 6, which, according to the embodiment shown in Fig. 1, is formed by a tube section whose end forms the respective outlet opening 10, and 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.

[0068] 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 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 status 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.

[0069] The device 1 shown in Fig. 1 allows, in principle, 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, particularly via an actuating device 12. The strength of the current introduced into the electrolyte at a specific time interval is measured, and the charge introduced into the electrolyte is determined.The control and evaluation unit takes into account the volume of electrolyte used in the plasma electrolytic processing system for the workpieces, thus determining the relative charge for further analysis of the electrolyte's condition. Furthermore, a database connected to the control unit via a suitable data transmission system contains characteristic curves. These curves define a limit value for a condition indicator for each specific combination of components made from a particular material and electrolyte. This limit value corresponds to the number of workpieces that can be processed consecutively without replacing or reprocessing the electrolyte to meet a predefined quality criterion. If this limit is exceeded, the system will automatically adjust the parameters accordingly.If the condition indicator determined during the machining process exceeds the limit value stored in the database for the specific electrolyte workpiece combination, it is highly likely that the workpieces subsequently machined will no longer meet the specified quality criteria. Therefore, if the condition indicator limit value is exceeded, the machine operator is notified and / or the machining process is automatically stopped. If the machine operator only receives this information without the machining process being automatically stopped, the operator has the option to decide whether the machining process should continue without further intervention or whether the electrolyte should first be replaced or reprocessed.

[0070] 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.

[0071] The condition indicator curve shown in Fig. 2 is due to the fact that the condition indicator increases during machining, while remaining constant during machining breaks. In addition, Fig. 3 shows three diagrams in partial views a), b), and c). These diagrams illustrate the number of workpieces that can be machined up to a certain condition indicator threshold for the plasma electrolytic machining of workpieces made of steel material number 1.4404 (Fig. 3a), steel material number 1.4542 (Fig. 3b), and steel material number 1.4301 (Fig. 3c). Exceeding this threshold means that the machined workpieces no longer meet a specified quality criterion. While 70 workpieces made of steel material number 1.4404 (Fig. 3a) and 45 workpieces made of steel material number 1.4542 (Fig. 3b) are shown, the number of workpieces that can be machined is significantly higher.3b)) while adhering to a specified quality criterion, only 25 workpieces can be processed using plasma electrolytic machining of 1.4301 (Fig. 3c)). It is expressly pointed out here that the numerical values ​​given are merely examples and may differ from the values ​​obtained in reality.

[0072] Fig. 3 shows that an electrolyte with a state 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.

[0073] 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.

[0074] 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.

[0075] When determining the appropriate state 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. Figure 4 shows a state curve illustrating the state indicator's behavior over time. It is clearly evident that the electrolyte's state in a real-world system with intermittent electrolyte preparation changes more slowly than predicted by the previously described theoretical approach. The state indicator shown in Figure 4...The function curve shown in Figure 4 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 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.

[0076] 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)

[0077] 1 Device for plasma electrolytic processing of an electrically conductive workpiece surface

[0078] 2 Surface

[0079] 3 workpieces

[0080] 4 output units

[0081] 5 supply unit

[0082] 6 electrode

[0083] 7 electrical energy source

[0084] 8 Actuator

[0085] 9 Control unit

[0086] 10 Exit opening

[0087] 11 Adjustment unit

[0088] 12 actuators

[0089] 13 Electrolyte supply

[0090] 14 Electrolyte removal

[0091] 15 processing unit

[0092] 16 storage containers

[0093] 17 Sensor unit

[0094] 18 heating element

[0095] 19 dosing units

[0096] 20 Temperature sensor

[0097] 21 nozzle head

[0098] 22 Unit of measurement

[0099] 23 Sensor unit for measuring current

Claims

Patent claims 1. A method for monitoring the 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, circulated, and / or applied to the surface (2) of the workpiece (3) is detected, characterized in that the magnitude of an electric current passed through the electrolyte is measured and a charge is determined, that a state indicator is determined on the basis of the determined charge by means of a transformation function, wherein the transformation function takes into account and processes at least one process, operating, and / or system parameter prevailing during the processing of the electrically conductive surface (2) of the workpiece (3), and that a limit value is specified for the state indicator, upon reaching which,Exceeding and / or falling short of at least one specified quality criterion is achieved if a plasma electrolytically processed workpiece (3) does not meet at least one specified quality criterion.

2. Method according to claim 1, characterized in that, upon reaching, exceeding and / or falling below the limit value for the status indicator, a control signal is generated to output information about the status indicator and / or to automatically change at least one operating and / or system parameter during the electrolytic processing of at least one surface (2) of the workpiece (3).

3. Method according to claim 2, characterized in that when the limit value for the status indicator is reached, exceeded and / or fallen below, a control signal is generated by which a control and / or regulation process for the processing of the at least one surface (2) of the workpiece (3) is started.

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

5. Method according to any of the preceding claims, characterized in 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.

6. Method according to one of the preceding claims, characterized in 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.

7. Method according to one of the preceding claims, characterized in 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.

8. Method according to one of the preceding claims, characterized in that a number of workpieces (3) made from a predetermined 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.

9. Method according to one of the preceding claims, characterized in that a plurality of limit values ​​of the condition indicator, each specific to a metallic material, are stored in a database.

10. Method according to claim 9, characterized in that the state 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.

11. Method according to one of the preceding claims, characterized in that the plasma electrolytic processing of components is automatically stopped when a condition indicator exceeding a maximum permissible limit value is reached.

12. Method according to one of the preceding claims, characterized in that a heat input into the electrolyte, a turbidity of the electrolyte and / or a temperature development are detected and taken into account in the transformation function when determining the state indicator.

13. Method according to one of the preceding claims, characterized in that a shape and / or size factor, which 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.

14. Method according to one of the preceding claims, characterized in that a 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.

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

16. 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.

17. Computer program product configured to effect the execution of the method according to one of claims 1 to 15 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).

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