Method and device for plasma electrolytically processing a workpiece surface

Abstract

A method (1) and a device for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3) are described, in which at least one electrolyte is conveyed by means of a supply unit (5) to a delivery unit (4), through which the surface (2) of the workpiece (3) is at least temporarily exposed to an electrolyte jet, and an electrical voltage is applied between the surface (2) of the workpiece (3) to be processed and an electrode (6) which at least partially touches the electrolyte by means of an electrical energy source (7), so that the electrode (6) forms a counter electrode to the surface (2) of the workpiece (3) during processing, so that a vapor plasma skin is generated in the area of ​​the processed surface (2) of the workpiece (3).Essential for the described technical solution is that at least one flow property of the electrolyte jet is adjusted such that, due to the kinetic energy of the electrolyte jet, a pressure acting on the phase transition between the liquid electrolyte and the vapor plasma skin is generated, so that a stable electrical jet resistance of a maximum of 1200 Ω · cm2 is established between the electrode (6) and the surface (2) of the workpiece (3) exposed to the electrolyte jet.

Description

[0001] The invention relates to a method and a device for the plasma electrolytic treatment of an electrically conductive surface of a workpiece. A key feature of the described solution is that an electrolyte jet is directed precisely and controllably onto the workpiece surface to treat specific areas of the overall surface. For treatment, a high electrical voltage is applied between the surface to be treated and the outlet through which the electrolyte jet emerges, causing a vapor plasma film to form on the workpiece surface and resulting in the desired material removal.

[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. Depending on the specific quality requirements and the required surface finish of a workpiece, various machining or electrochemical processes are generally suitable. In this context, plasma electrolytic machining of electrically conductive surfaces represents a specific advancement of established methods for the electrochemical machining of metallic workpieces.

[0003] Plasma electrolytic machining processes are methods by which the properties of a workpiece surface, which 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 removing material. In contrast to electropolishing, this is achieved 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.By applying a DC voltage of 200 V to 450 V, preferably 300 V to 400 V, the electrolyte in contact with the workpiece evaporates and forms a vapor film surrounding it, which displaces the electrolyte solution from the workpiece surface. The polishing voltage drop across the vapor film leads to partial ionization and the formation of a plasma. The surface of the workpiece is uniformly smoothed and simultaneously freed from contaminants through a combination of physical, chemical, and electrochemical ablation processes.

[0004] 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.

[0005] A generic plasma polishing system is known from DE 10 2006 016 368 B4. 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 regulates the speed at which the workpiece is immersed in the electrolyte container depending on the current.

[0006] A crucial limitation for the applicability of the immersion bath process is the linear relationship between the power requirements of the process energy source (PEQ), which provides the voltage necessary to generate the vapor plasma skin (DPH), and the workpiece surface area. For stainless steels, this factor is approximately 70 W / cm², which is why plasma polishing is currently limited to a component surface area of ​​approximately 2,500 cm² – roughly the size of a DIN A3 sheet – due to technical and economic constraints.

[0007] There is an effort to overcome this linear dependency by localizing the processing. Besides plasma electrolytic processing of workpieces in an immersion bath, methods are also known in which, with the aid of an electrolyte jet directed at the surface to be processed and the application of the voltage required for plasma generation between the exit opening through which the electrolyte jet emerges and the workpiece surface, surface areas are processed in a manner adaptable to the component geometry. Here, diffuse plasma polishing (DPH) forms only in a locally limited area of ​​effect defined by the electrolyte jet. These methods are therefore also referred to as jet plasma polishing or beam plasma polishing.

[0008] A generic process of this type is known from RU 2 640 213 C1. This document describes a system for the plasma electrolytic processing of workpieces, in which a nozzle-shaped application unit, always directed vertically upwards, can be positioned in space. The described system is intended to make it possible to plasma electrolytically process even larger workpieces by continuously scanning the surface.

[0009] CN 110125734 A also describes a system for jet plasma electrolytic processing of workpiece surfaces. To enable the processing of workpieces with comparatively complex geometries according to requirements, it is proposed to use an industrial robot, with the discharge opening for the electrolyte jet being located at the end of a movable robot arm to allow for rapid changes in the direction and positioning of the electrolyte jet.

[0010] In plasma electrolytic processing of workpiece surfaces, the stability of the process and the quality of the processing result depend significantly on the degree of diffusion potential (DPP). In the immersion bath, this is primarily determined by the electrolyte used, which is tailored to the material being processed, its conductivity, pH, and temperature, as well as the process voltage provided by the plasma electrolytic capacitor (PEC). Crucially, the most uniform and stable film boiling possible is achieved along the component contour. This stability can be measured by the current-time profile. Ideally, this profile remains constant during immersion bath processing at current densities of 0.1 A / cm² to 0.2 A / cm² of the processed surface.

[0011] A breakdown of the DPH (dielectric plasma) leads to direct contact between the electrolyte and the workpiece surface, resulting in plasma misfires and unstable current peaks. The balanced interplay between electrochemical and plasma-physical material removal, which is responsible for the unique surface results achieved in plasma polishing, cannot be established. Etching and erosion mechanisms dominate. Excessive, unstable DPH formation, for example, due to an excessively high electrolyte temperature and a correspondingly small temperature differential to the electrolyte's boiling point, also leads to repeated process failures. Therefore, the process conditions prevailing at the interface between the liquid electrolyte and the DPH are crucial.

[0012] In the current state of the art, jet-based electrolyte delivery in jet plasma polishing is viewed solely as a technical solution for localized processing, thereby breaking the linear relationship between component surface area and electrical power. The minimal flow of the electrolyte jet serves only for the local supply of the electrolyte and the removal of abraded products. Naturally, the same process stability, or rather the stability of the phase boundary, must prevail within the operating area of ​​jet plasma polishing as is already known from immersion baths. However, the flow conditions of the electrolyte, acting directly on the phase boundary, are a crucial process parameter here, one that has previously been considered disruptive. Process stability is therefore ensured by adjusting these flow conditions to replicate the conditions in the immersion bath as closely as possible.According to the jet plasma polishing method described in RU 2 640 213 C1, with a vertically upward-pointing nozzle, the pressure of the pump delivering the electrolyte should be adjusted so that the height of the resulting jet corresponds to the distance to the workpiece. The flow velocity of the electrolyte, resulting from the volume flow from the outlet, its cross-sectional area, and the opposing force of gravity, should be virtually zero at the interface with the DPH (dielectric plasma polishing) and thus correspond to the conditions in the immersion bath.

[0013] As a result, local processing occurs at the same speed as expected in an immersion bath, typically between 30 and 300 seconds. This time is very fast for processing an entire workpiece surface in an immersion bath compared to other methods such as vibratory finishing or electropolishing. However, if a workpiece surface is processed using jet plasma polishing, with small areas being processed sequentially, the total processing time is many times longer. Cycle times of 30 minutes to several hours per individual part are quickly reached. Consequently, jet plasma polishing is currently often economically unattractive for workpieces in series production.

[0014] Up to now, electrolyte jets with low flow velocities have been used to enable the development of DPH (dielectric hydrostatic pressure) similar to that in an immersion bath. This approach assumes an optimal process window, which is limited at both the upper and lower ends as follows: at excessively low flow velocities, the insufficient supply of new electrolyte leads to a process more akin to a locally overheated electrolyte bath. The result is a process flow that fluctuates with the unstable thickness of the DPH and is usually excessive. Conversely, excessively high flow velocities disrupt the development of the DPH, leading to a polishing current interrupted by current spikes (plasma ignitions). This is attributed to the pressure acting on the phase interface, which partially breaks down the DPH. The process window between these two extremes is referred to as the quasi-hydrostatic stability zone.

[0015] Based on the prior art technical solutions for the plasma electrolytic processing of workpieces and the problems described above, particularly in jet plasma polishing, the invention aims to provide a device and a method with which a stable process for the plasma electrolytic processing of components using an electrolyte jet can be realized with a significantly reduced processing time and without loss of quality. This enables the economical, reproducible, and high-quality processing of individual workpieces by means of jet plasma polishing. In this way, a particularly flexible processing method, especially suitable for components with complex geometries, is to be made possible by means of jet plasma polishing.

[0016] In this context, it is important that the jet plasma polishing process can be controlled relatively easily and yet precisely using the specified solution, so that rapid yet high-quality and reproducible plasma electrolytic processing of workpiece surfaces, adaptable to the respective operating conditions, is possible.

[0017] Furthermore, it is desirable that the technical solution to be specified can also be integrated into existing systems for the plasma electrolytic processing of workpieces with at least one electrolyte jet, i.e., systems for jet plasma polishing, and can be integrated into known control systems and control methods, for example, through relatively simple adaptations.

[0018] The foregoing problem is solved by means of a method according to claim 1 and a device according to claim 12. 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. Features and details described in connection with the method according to the invention are also considered disclosed in connection with the device according to the invention, so that, with regard to the disclosure of the individual aspects of the invention, mutual reference is always made, or rather, can be made.

[0019] The invention relates to a method for the plasma electrolytic treatment of an electrically conductive surface of a workpiece, in which at least one electrolyte is conveyed by means of a supply unit to a discharge unit, through which the surface of the workpiece is at least temporarily exposed to an electrolyte jet. An electrical voltage is applied between the surface of the workpiece to be treated and an electrode that at least partially contacts the electrolyte by means of an electrical energy source, such that the electrode forms a counter electrode to the surface of the workpiece during treatment. The discharge unit has a discharge opening, preferably circular, which discharges a suitably shaped electrolyte jet into the surroundings and therein in the direction of the workpiece surface to be treated.Plasma electrolytic processing is thus carried out with at least one electrolyte jet and therefore, in contrast to processing in an electrolyte bath, only on a partial surface of the workpiece. Crucially, a vapor plasma film forms on the processed surface during the machining process. Such machining processes are therefore also referred to as jet plasma polishing.

[0020] The method according to the invention is characterized in that the flow characteristics of the electrolyte jet are adjusted such that, due to the kinetic energy of the electrolyte jet, a pressure profile acting on the phase transition between the liquid electrolyte and the forming vapor-plasma skin is generated, resulting in a stable electrical jet resistance of a maximum of 1200 Ω·cm² between the electrode and the surface of the workpiece exposed to the electrolyte jet. In this context, "stable" means that the jet resistance value fluctuates only slightly over time and / or does not exhibit any major jumps, which is due to the fact that the current flowing in the processing area also remains at least nearly constant and is therefore subject to only minor fluctuations.Preferably, the process current value exhibits a fluctuation range of no more than 5% around a mean value over time, and particularly preferably no more than 2% around a mean value. It can be taken into account that, in particular, sudden jumps in current intensity are due to an unstable process and / or partial destruction of the vapor-plasma skin, which is undesirable according to the invention. In this context, it is conceivable that a jet resistance value below 200 Ω·cm², particularly 150 Ω·cm², and especially 100 Ω·cm², is defined as the lower limit for the process for plasma electrolytic processing of a workpiece surface. The aforementioned setting enables stable plasma electrolytic processing with a well-defined, and in particular compressed, vapor-plasma skin.According to the invention, the kinetic energy of the electrolyte jet emitted in the direction of the workpiece surface to be processed, which is largely determined by its flow velocity, can thus be varied as required, so that the hydrodynamic pressure, which acts in the impact area and thus at least indirectly on the vapor plasma skin forming in the processing area, can be changed depending on the respective requirements of the workpiece processing.

[0021] The electrical jet resistance, or simply jet resistance, is the product of the respective effective area A, defined as the cross-sectional area of ​​the outlet or the workpiece surface bathed, whichever is smaller, and the electrical resistance R, which exists between the electrode and the workpiece surface and can be determined from the electrical voltage U and current I. The effective area A is thus usually determined by the size of the outlet. Only in the case of very small surfaces to be processed, smaller than the area of ​​the outlet, does the effective area correspond to the workpiece surface bathed by the electrolyte.

[0022] If, for the sake of simplicity, the electrolyte jet is assumed to be an electrical conductor, its resistance is equal to its resistivity, a material constant, multiplied by its length and divided by its cross-sectional area. However, a real electrolyte jet is not a homogeneous electrical conductor like a copper wire. Its electrical properties, particularly its resistance, result from a complex interaction between the relatively highly conductive electrolyte, the significantly less conductive, ionized vapor-plasma layer, and the interface between them. The vast majority of the voltage drops across the processing zone formed by the vapor-plasma layer. Therefore, considering the entire electrolyte jet, the electrical resistance does not increase linearly with its length.Rather, this resistance remains almost constant within certain limits, even when the jet length is varied. However, the linear dependence on the effective area from the model analysis remains. The system for the plasma electrolytic processing of a workpiece surface can therefore be unambiguously described by the aforementioned jet resistance with the unit Ω · cm² or Ω · m². This jet resistance represents the link between the complex plasma electrolytic influencing factors and the measurable and controllable system parameters, as it can be determined from the voltage set and / or measured at the energy and / or voltage source and the current flowing in the processing area, particularly in the area of ​​the vapor-plasma skin.

[0023] The process conditions acting within the electrolyte jet are crucial for the stability, speed, and quality of plasma electrolytic processing. These process conditions can be divided into classical plasma electrolytic parameters, such as the selection of the electrolyte used for processing, its conductivity, and temperature, and hydrodynamic parameters, which result in a pressure profile acting on the phase interface of the vapor-plasma skin. According to the invention, a specific jet resistance is achieved by appropriately adjusting the process voltage and the flow characteristics of the electrolyte jet, allowing the complex interplay of the various process parameters to be quantified and controlled, even for different specific system configurations.

[0024] The electrical resistance R can be calculated from the jet resistance by dividing it by the effective area A, and the process current I can then be calculated by taking the process voltage U into account. Unlike, for example, the variable thickness of the vapor phase film along the workpiece surface, these parameters are measurable, controllable, and technically monitorable. According to a particular embodiment of the invention, the process voltage and / or the process current are therefore measured continuously or at time intervals selected as required and used as the basis for adjusting the flow characteristics to achieve the desired jet resistance.

[0025] The consideration of the aforementioned classical plasma electrolytic influencing factors is already known from immersion bath processing. Preferably, these influencing factors are assumed to be constant when controlling a jet plasma polishing system. Crucial for the inventive method and device is the targeted adjustment of the jet resistance via the targeted variation of the hydrodynamic influencing factors, from which the pressure profile acting on the phase transition between the liquid electrolyte and the vapor phase skin—i.e., the profile of the pressure forces acting on the phase transition—results.

[0026] The jet resistance, as a characteristic quantity of the electrolyte jet, is thus the product of its effective area and the electrical resistance of the system.

[0027] For illustrative purposes, two specific embodiments of the invention are described, each with a different diameter of electrolyte jet. In the embodiments described here, a first electrolyte jet is provided for workpiece processing in the first embodiment, and a second electrolyte jet in the second embodiment. Each jet has an effective area that is at least nearly circular and is subject to the same plasma electrolytic influences. The second electrolyte jet has twice the diameter of the first, so that its effective area extends over four times the surface area, and thus, as a rule, significantly different process currents and electrical resistances are observed. The two systems are designed differently and are not directly comparable.However, the jet resistance allows for a quasi-normalization or comparability of the two systems, advantageously ensuring that when the same jet resistance is set in the systems according to the first and second embodiments, the flow and processing conditions in both systems are also identical. In this way, differently configured jet plasma machining systems for workpieces, for example, systems that differ in size, orientation, and parameterization, can be advantageously compared, designed, and controlled.

[0028] The invention is based on the remarkable discovery that jet plasma machining of workpieces, particularly jet plasma polishing, exhibits a further stable state within the previously considered non-relevant high-flow-velocity range, and that this state can be specifically adjusted by selecting the appropriate jet resistance. This second, stable machining range is hereinafter referred to as the hydrodynamic stability zone and is characterized in particular by a significantly increased machining speed.According to the invention, the targeted adjustment of hydrodynamic properties of an electrolyte jet used for workpiece machining, in particular the volume flow rate, is utilized and regulated based on the monitoring and / or adjustment of the jet resistance in such a way that safe and high-quality workpiece machining can be carried out even with high volume flows and thus in a comparatively short time.

[0029] According to a specific embodiment of the invention, it is provided that the hydrodynamic properties of the electrolyte jet are adjusted in such a way that, due to the flow conditions during jet plasma processing, state parameters are established at least in the processing area, in particular in the area of ​​the vapor plasma skin, which differ significantly from the conditions in the immersion bath.

[0030] According to a specific embodiment of the invention, the pressure profile acting on the phase interface is increased, for example, by increasing the flow velocity or volume flow rate of the electrolyte, so that, following the establishment of a first stable machining process and after a transition phase involving known instabilities, a second stable machining process for jet plasma machining of a workpiece is established. This second machining process, which is based on a comparatively high flow velocity or a high volume flow rate of the electrolyte jet, is characterized by: the formation of a stable and, due to the pressure caused by the electrolyte jet, definedly compressed vapor plasma skin, comparatively high current densities on the surface of the workpiece and a otherwise unattainable high material removal rate without loss of quality.

[0031] The second operating state described above can advantageously be achieved by setting the jet resistance to a maximum value of 1200 Ω·cm², preferably to a value between 400 Ω·cm² and 800 Ω·cm². Reaching the hydrodynamic stability zone, e.g., by reducing the jet resistance starting at high values ​​above 1200 Ω·cm², is generally accompanied, in addition to the properties mentioned above, by a sudden, milky turbidity of the electrolyte jet.

[0032] By adjusting the jet resistance within the range specified in the invention, an electrolyte jet is generated and directed towards the workpiece surface to be processed. This jet compresses the forming vapor-plasma skin to such an extent that a stable equilibrium is established between plasma electrolytic and electrochemical material removal. Compared to known systems, surface treatment is carried out here with comparatively high electrical current densities, preferably 0.5 to 1.0 A / cm², resulting in material removal that is approximately six to ten times greater than previously possible. This enables comparatively fast processing while still producing the familiar mirror-like gloss finish.The specified jet resistance values ​​are universal, and the resulting measured values ​​for electrical resistance depend on the selected or set diameter of the electrolyte jet, which can be adjusted in particular by a suitable choice of the dispensing element, especially preferably in the form of a circular or rectangular nozzle.

[0033] According to the invention, a jet resistance in the range of no more than 1200 Ω·cm² enables high-quality and reproducible workpiece processing by plasma electrolytic processing with an electrolyte jet, i.e., by jet plasma polishing. The process can also be used for deburring or cleaning.

[0034] As soon as the flow velocity or the pressure exerted by the electrolyte jet on the workpiece surface, and thus at least indirectly on the vapor-plasma skin, becomes too high, the vapor-plasma skin is compressed to such an extent that it can no longer fulfill its function as a machining zone. The result is a current-time profile that alternates between ignition currents on the order of ten times the process current for the formation of the vapor-plasma skin and a subsequent complete collapse. This limits the hydrodynamic stability zone with respect to the jet resistance values.

[0035] In jet plasma processing, particularly jet plasma polishing, the process voltage is preferably adjusted, while the process flow is determined by the process parameters. Crucially, a very uniform pressure distribution across the working area is essential. Stability, even at lower jet resistances, is therefore enhanced by larger working areas. The working area is preferably between 0.8 cm² and 80 cm², and particularly preferably between 5 cm² and 10 cm². If this is determined by the size of the outlet opening, 7 cm² corresponds approximately to a round nozzle with a 30 mm diameter. In the previous jet plasma processing, especially jet plasma polishing, in the quasi-hydrostatic stability zone, a process current of between 0.8 A and 1.2 A could be expected, which corresponds to a jet resistance of 3,092 Ω · cm 2< or 2,062 Ω · cm 2<.However, according to the essential characteristics of the inventive method, the target value for efficient jet plasma processing would be reaching the hydrodynamic stability zone, i.e., achieving a jet resistance value that does not exceed 1,200 Ω·cm². The flow conditions are preferably set to a comparatively higher intensity so that, after overcoming the first instability region, a stable process current of 2.1 A is achieved, which is generally accompanied by a sudden turbidity of the electrolyte jet.

[0036] Even within the hydrodynamic stability zone, the stability of the process flow, characterized by its fluctuation range over time, is not constant. Rather, there is a sub-region distinguished by particularly high process flow stability. Its position can be influenced, preferably, by changing the system design, the chosen electrolyte, and the material and geometry of the workpiece being processed. Given these parameters, the position can be determined by varying the jet resistance.

[0037] A particularly advantageous embodiment of the invention therefore provides to first reduce the jet resistance within the hydrodynamic stability zone until the process flow falls below a certain fluctuation range over time, preferably 5%, and then to further reduce it until it reaches the predetermined fluctuation range again. This ensures that processing takes place at the highest possible speed, yet remains stable. Particularly preferably, this results in a further increase in the flow velocity or volume flow of the electrolyte jet and thus an increase in the pressure acting on the phase boundary of the vapor-plasma skin, or the pressure profile, to the range for the jet resistance of 400 Ω cm² to 800 Ω cm², corresponding to a process flow of 3.1 A to 6.2 A in the example mentioned.

[0038] Preferably, to achieve the hydrodynamic stability zone, a comparatively high flow velocity of the electrolyte jet, or a high volumetric flow rate for the same effective area, is set. This volumetric flow rate should be selected depending on the size of the outlet opening for identical process conditions. In the known prior art, values ​​for the electrolyte volumetric flow rate in the range of 5.3 to 10.6 l / h (RU2681239C1) and 1.1 l / h (EP0955393A1) are proposed with reference to 1 cm² of outlet opening area. According to a particular embodiment of the invention, however, values ​​for the volumetric flow rate of 100 l / h to 400 l / h, preferably 250 l / h to 300 l / h, are provided to achieve the hydrodynamic stability zone, also normalized. When using a nozzle for dispensing the electrolyte jet, which has an outlet opening with a diameter of 30 mm and thus an outlet area of ​​approximately...If the surface area is less than 7.1 cm², a volume flow rate in the range of 1,775 to 2,130 l / h, e.g. 2,000 l / h, is preferably set.

[0039] In a particular embodiment of the invention, it is provided that the current supplied by the electrical energy source is measured and the flow conditions are changed and / or adjusted depending on a setpoint for the jet resistance density. This is done, for example, by controlling the pump speed.

[0040] Reaching the hydrodynamic stability zone by falling below a jet resistance of 1200 Ω·cm² is generally accompanied by a change in the optical properties of the electrolyte jet, in particular a sudden, milky, or colored turbidity. In a specific embodiment of the invention, it is therefore provided that at least one optical property of the electrolyte downstream of the electrode (6), in particular a sudden turbidity, is measured absolutely or in relation to another measuring point in the system, and at least one flow property of the electrolyte jet is modified and / or adjusted as a function of a setpoint for the jet resistance. The additional measuring point can be located, for example, in the area of ​​the pump, and by considering both measurements relative to each other, the elimination of other optical influences, such as erosion products, is permitted.

[0041] According to a further embodiment of the invention, the surface exposed to the electrolyte jet is limited by at least one limiting element arranged downstream of a discharge opening of the training unit. Such a limiting element can have a sealing lip, preferably movable, which limits the processing area at least sectionally and / or temporarily to a maximum required size or shape. Alternatively or additionally, it is also conceivable to use other means to limit the processing area exposed to the electrolyte jet, in which a vapor plasma skin forms.

[0042] In this context, a specific training course stipulates that a compressed air jet, e.g., in the form of a compressed air curtain, is directed at least temporarily towards the electrolyte jet, particularly in the area of ​​the workpiece surface being processed, using a compressed air source, thus actively influencing the shape and / or orientation of the electrolyte jet. It is also conceivable that an airflow at ambient air pressure, i.e., uncompressed, is used, at least temporarily.

[0043] A particular advantage of the invention is that the electrolyte jet, based on an outlet opening of the dispensing unit with an area of ​​1 cm², is dispensed from the dispensing unit towards the workpiece surface to be processed at a volume flow rate of 100 to 400 l / h, particularly 250 l / h to 300 l / h. A supply unit conveys the required quantity of electrolyte, for example from an electrolyte reservoir, towards the dispensing unit, where jet shaping and ultimately the dispensing of an electrolyte jet with the aforementioned volume flow rate from an outlet opening then take place.

[0044] In a special embodiment of the invention, it is provided that the electrolyte jet emerging from the dispensing unit simultaneously acts on an area of ​​0.8 cm² to 80 cm² of the surface of the workpiece during processing, thus removing material.

[0045] According to a specific embodiment of the invention, an electrolyte flow upstream of a discharge opening of the discharge unit, preferably the discharge opening of a nozzle, is at least temporarily dammed to generate desired properties of the electrolyte jet exiting the discharge opening. This is a particularly preferred embodiment when the flow velocity resulting from gravity is already too high for the hydrodynamic stability zone.

[0046] The dispensing unit has at least one suitable damming element for this purpose, which may be designed, for example, as a cross-sectional constriction, a special coating on the inner wall of the electrolyte-carrying flow channel, a grid, an open-pore sponge, a Tesla valve, or a specifically movable element, such as a valve closure, for coupling such damming elements into and out of the electrolyte flow. Such at least temporary damming of the electrolyte within the dispensing unit leads to an increase in hydrodynamic pressure upstream of the respective damming element and a reduction in the flow velocity to a defined value, while downstream of the damming element, a free change, in particular an increase in the flow velocity due to gravity, occurs.If the distance between the baffle element and the surface of the workpiece is small, it can be achieved that the flow velocity of the electrolyte prevailing at the phase interface corresponds almost to the flow velocity set by the baffle element.

[0047] In a particularly advantageous way, at least one damming element can be controlled in such a way that the damming effect of the damming element and thus the influence of the damming element on the electrolyte current on the flow properties is adjusted in a targeted and required manner depending on the desired machining of a workpiece, in particular the actual jet resistance prevailing in the machining area and / or a target jet resistance.

[0048] Furthermore, a specific embodiment of the invention provides that the supply unit and / or the dispensing unit has suitable means to effect a targeted adjustment or influencing of the properties of the electrolyte jet. It is conceivable that the flow characteristics, in particular the volumetric flow rate, its flow velocity, or even the composition of the electrolyte jet, are actively modified, for example, to change the flow pattern of the electrolyte, especially to generate turbulence, introduce gases, or remove impurities.

[0049] In a particularly advantageous way, the properties of the electrolyte jet are adjusted accordingly by the supply unit and / or the dispensing unit depending on a control signal that is generated in the control unit taking into account an actual or target value of the jet resistance, especially in the area of ​​the processing surface.

[0050] According to a further specific embodiment of the invention, the dispensing unit, or at least the dispensing opening, is directly or indirectly connected to a movement unit by which a targeted movement of the dispensing unit, in particular the dispensing opening, can be initiated. Advantageously, this enables movement of the dispensing unit, in particular the dispensing opening, for example in three spatial directions, in order to achieve targeted and demand-oriented processing even of workpieces with complex component geometries. It is essential that, even with a suitably movable dispensing unit and its dispensing opening, an electrolyte jet is generated and applied to the workpiece surface, the jet resistance of which assumes a maximum value of 1200 Ω·cm².If the movement changes the orientation of the dispensing unit in space, in particular by rotating, tilting or inclining, a special embodiment of the inventive method provides for changing the flow characteristics of the electrolyte jet by a control unit in such a way that the jet resistance remains constant despite the change in orientation.

[0051] In addition to a method, the invention also relates to a device for the plasma electrolytic processing of a workpiece using an electrolyte jet, i.e., a device for jet plasma polishing. The device is designed such that it can perform the method according to the invention with or without at least one of the previously described special embodiments.

[0052] In a particular embodiment of the device according to the invention, at least one measuring element for detecting the intensity of the process flow through the electrolyte jet, at least one element for determining the current actual jet resistance, and a control unit are provided by which the intensity of the process flow can be changed and / or adjusted depending on a target jet resistance and the actual jet resistance. It is particularly advantageous for the method according to the invention for achieving the desired jet resistance if the hydrodynamic properties of the electrolyte jet, in particular the flow velocity and / or the volume flow rate, are changed so that the pressure acting on the vapor plasma film and also the intensity of the current flowing in the electrolyte jet increase.It is essential that the device has suitable means, in particular at least one measuring unit, one control unit, and one delivery unit, through which an electrolyte jet can be directed towards the workpiece surface to be processed, such that a jet resistance of no more than 1200 Ω·cm² is established in the electrolyte jet. As soon as such a jet resistance value is reached, particularly fast surface processing with consistent quality is possible. This is due to the fact that an electrolyte jet is directed towards the workpiece surface at a comparatively high flow velocity, generating a comparatively high pressure profile upon impact, and achieving a state in which the vapor plasma film required for processing the workpiece surface is in a compressed but stable state.

[0053] Furthermore, it is particularly advantageous if the dispensing unit has a grid structure and / or a nozzle with a Tesla valve and / or other pressure-generating structures for influencing the flow characteristics of the electrolyte jet, which is or are arranged upstream or at a dispensing opening of the dispensing unit.

[0054] According to a further specific embodiment of the invention, the dispensing unit, or at least the dispensing opening, is connected, directly or indirectly, to a motion unit by which a targeted movement of the dispensing unit, in particular the dispensing opening, can be initiated. Advantageously, such a motion unit enables movement of the dispensing unit, in particular the dispensing opening, for example in three spatial directions, in order to achieve targeted and demand-oriented processing even of workpieces with complex component geometries. An industrial robot with a robot arm is particularly preferred as the motion unit, by which the dispensing unit, in particular the dispensing opening, can be positioned and moved quickly and with high accuracy in space relative to the workpiece to be processed.It is essential that, even with a suitably movable dispensing unit and its dispensing opening, an electrolyte jet is generated and applied to the workpiece surface, the jet resistance of which assumes a maximum value of 1200 Ω · cm 2<.

[0055] Another embodiment of the invention provides for a compressed air source and a compressed air delivery unit, wherein compressed air is generated by the compressed air source and can be delivered by the compressed air delivery unit, in particular in the form of a nozzle, in the direction of the electrolyte jet and / or the surface exposed to the electrolyte jet. The compressed air source and the compressed air delivery unit are preferably designed such that compressed air, in particular in the form of a compressed air jet or compressed air curtain, can be delivered in a controlled manner with regard to positioning and volume flow in the direction of the electrolyte jet, so that its shape and flow characteristics are actively influenced by the impact of the compressed air jet.The direction of the compressed air jet and / or the compressed air volume flow are preferably set by the central control unit, taking into account the workpiece properties, the workpiece geometry of the workpiece to be machined and the properties of the electrolyte jet, i.e. its composition and / or in particular the jet resistance.

[0056] The invention will now be explained in more detail with reference to specific embodiments and figures, without limiting the general concept of the invention. The figures show: Fig. 1: Schematic side view of a nozzle during the plasma electrolytic processing of a workpiece surface, Fig. 2: Representation of the time course of the process flow during the plasma electrolytic processing of a workpiece surface in a process control known from the prior art, and Fig. 3: Representation of the time course of the process flow during the plasma electrolytic processing of a workpiece surface in a process control according to the invention.

[0057] Fig. 1 Figure 1 shows a schematic side view of a device 1 designed according to the invention for plasma electrolytic processing, preferably for deburring and / or polishing, of a surface 2 of a workpiece 3. In the illustration according to Fig. 1 For clarity, only the output unit 4 and the workpiece 3 to be processed are shown during the processing of the workpiece surface 2. Furthermore, a supply unit 5, which delivers the electrolyte used to the outlet opening as needed, a storage container 16 for storing electrolyte, an electrical power source 7, which generates the voltage required to create a vapor plasma film, and a control unit 9, which controls the individual system components, are also shown schematically.

[0058] With the in Fig. 1 In the device 1 shown for plasma electrolytic processing, the surface 2 of the workpiece to be processed is polished using a plasma generated on the workpiece surface 2. For this purpose, the supply unit 5 provides a supply unit 4 with plasma from a reservoir at an outlet opening 10, so that an electrolyte jet is directed towards the workpiece surface 2 and impacts it. A voltage is applied between the electrode 6, which according to the illustrated embodiment is part of the output unit 4, and the surface 2 of the workpiece 3. This voltage is selected such that a vapor plasma skin forms in the area of ​​the surface to be processed. The desired material removal from the surface occurs, achieving surface roughness Ra of up to 0.02 µm. With the aid of the Fig. 1 The device shown and the inventive method explained in more detail below advantageously enable the production of particularly high-quality surfaces in a comparatively short time, even on components with complex geometries, using plasma electrolytic surface treatment. Compared to known methods, it is therefore possible to increase the number of workpieces processed per unit of time without any loss of quality, thus improving the efficiency and cost-effectiveness of workpiece processing.

[0059] The supply unit 5 delivers the electrolyte required for the plasma electrolytic processing of a workpiece surface 2 to a discharge unit 4 with an outlet opening 10. The supply unit 5 has a pump that, during operation, delivers the electrolyte almost pulsation-free from a reservoir 16 to the outlet opening 10 of the discharge unit 4.

[0060] The electrolyte supply begins after the workpiece 3, whose surface 2 is to be machined, has been fixed in the machining position, whereby an electrolyte jet from the outlet opening 10 impinges on the workpiece surface 2 to be machined. The electrolyte stored in the reservoir 16 is preheated by means of a heating element 18 and then pumped via the electrolyte supply 13 to the outlet opening 10, whereby various actuating elements 8, in particular valves, and / or other means for influencing the flow properties of the electrolyte are or may be provided.

[0061] The device 1 shown also has a control unit 9 with which the supply unit 5, an electrical energy source 7 used as a voltage source, and the respective actuating elements 8, such as valves, which will not be explained in detail below, can be controlled as required. Essential to the solution according to the invention is that the hydrodynamic properties of the electrolyte jet, in this particular embodiment the volume flow rate, can be changed as required. In this context, it has been recognized that by appropriately adjusting the flow velocity or...The formation and shape of the vapor plasma skin can be advantageously influenced by the volume flow of the electrolyte jet exiting the outlet opening 10 due to slight compression, such that a particularly stable vapor plasma skin is formed, which ensures not only high-quality but also comparatively fast processing of a workpiece surface.

[0062] During the processing operation, a connection is made between electrode 6, which is designed according to the specifications in Fig. 1 In the illustrated embodiment, the electrode 6 is part of the dispensing unit 4 and is formed by a tube section, the end of which forms the outlet opening 10, and a DC voltage is applied to the workpiece surface 2. A key aspect of the invention in this context is that the jet resistance is used as the control variable for the machining process. This jet resistance corresponds to the product of the electrical resistance prevailing in the machining area during machining, i.e., the gap between the electrode 6 and the workpiece surface 2, and the effective area. The effective area is the area relevant for machining, which in most cases corresponds to the cross-sectional area of ​​the outlet opening 10. Only in machining cases where the area to be machined, bathed by the electrolyte jet, is smaller than the cross-sectional area of ​​the outlet opening 10, does the effective area A correspond to the size of the machined workpiece surface.According to the invention, the resistance is determined from the voltage generated by the electrical energy source 7, which is measured separately, and the current flowing in the processing area, which is also measured. Taking into account the effective area A, which, according to the embodiment described here, is the cross-sectional area of ​​the outlet opening 10, the current jet resistance is calculated. According to the invention, the relevant operating parameters, in particular the volume flow rate of the electrolyte jet, are always adjusted such that the jet resistance does not exceed a value of 1200 Ω·cm² during processing of the workpiece.

[0063] As long as this value of the jet resistance is not exceeded, a comparatively stable vapor plasma skin forms, which also ensures a comparatively fast plasma electrolytic processing of a workpiece surface 2 over a longer period of time.

[0064] According to the in Fig. 1 In the embodiment shown, the workpiece 3 is processed with an electrolyte jet, wherein the outlet opening 10 has a diameter of 20 mm, through which an electrolyte jet with a volume flow of 1200 to 2200 l / h can be emitted in the direction of the workpiece.

[0065] At the start of the process, a voltage of 310 V is applied using the electrical power source 7, and the volume flow of the electrolyte jet is adjusted such that a current of 2.0 A is measured in the gap between electrode 6 and the workpiece surface, and thus in the area of ​​the forming vapor-plasma skin. The control unit calculates an electrical resistance of 155 Ω from the applied voltage and the current flowing in the processing area, and, taking into account the diameter of the outlet opening of 20 mm, determines an effective area of ​​A = 3.14 cm², which in this case corresponds to the cross-sectional area of ​​the outlet opening.

[0066] The strength of the current flowing in the machining area is specific to the selected nozzle. If a larger nozzle than described in the exemplary embodiment is used under otherwise identical conditions, for example with a diameter of 30 mm, the electric current flowing in the machining area will also be higher.

[0067] From the values ​​determined in the control unit for the effective area A of 3.14 cm² and the electrical resistance of 155 Ω, a jet resistance JW = R * A of 487 Ω · cm² is calculated. This value is below the limit value of 1200 Ω · cm² provided for in the invention and within the hydrodynamic stability zone. Consequently, it can be assumed in this case that a stable, compressed vapor plasma film forms on the workpiece surface in the processing area.

[0068] If, instead of a discharge unit with a diameter of 20 mm, an outlet opening with a diameter of 30 mm were used, the effective area increases to A = 7.1 cm². Assuming that the jet resistance is also 487 Ω cm², the electrical resistance in this case is 68.6 Ω, resulting in a current of I = U / R = 4.5 A flowing in the processing area.From this, it can be deduced that if the electrical voltage generated by the electrical energy source is 310 V and the volumetric flow rate of the electrolyte jet is adjusted using an outlet opening with a diameter of 30 mm such that a current of 4.6 A is measured in the processing area, the same conditions prevail in the processing area and the vapor-plasma skin as were previously achieved using an outlet opening with a diameter of 20 mm and a modified volumetric flow rate of the electrolyte jet. This can be easily derived from the determined jet resistance, which is the same in both cases and thus advantageously represents a value that makes plasma electrolytic workpiece processing methods using different process parameters and / or system configurations comparable.

[0069] As soon as the electrolyte jet strikes the workpiece surface 2 to be processed, gas or vapor is generated, and a vapor-plasma skin forms on the surface 2, beneath which the desired material removal occurs. After the electrolyte has struck 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. Here, suspended particles are removed in a first step 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.Depending on the measured values ​​for the conductivity and pH of the electrolyte, salt and / or a pH regulator are added as needed from corresponding storage containers with suitable dosing units 19. The processed electrolyte then returns to the storage container 16. A temperature sensor 20 and a heating element 18 are provided in the area of ​​the storage container 16 so that the electrolyte is always heated to the required temperature before it is fed to the dispensing unit 4 with the multiple outlet openings 10.

[0070] According to the in Fig. 1 In the illustrated embodiment, the workpiece surface 2 is machined by fixing or clamping the workpiece 3 in the area of ​​the discharge unit 4 of the device 1 designed according to the invention. The workpiece 3 is thus moved into the position provided for machining and fixed in this position. Subsequently, the discharge unit with the exit opening 10 is extended into its machining position.

[0071] The following describes the inventive method for plasma electrolytic processing of a workpiece surface 2, as described in Fig. 1 schematically illustrated, as well as its differences and advantages compared to the methods known from the prior art, using the methods described in the Figuren 2 and 3The illustrated graphics explain this in more detail. The operating parameters selected during the processing process, from which the magnitude of the jet resistance is derived, are essential for the invention, since it has been recognized that with a jet resistance during plasma electrolytic processing that does not exceed a value of 1200 Ω · cm 2, a compressed, yet particularly stable vapor plasma skin is generated, thus enabling comparatively fast and high-quality plasma electrolytic processing of a workpiece surface 2.If an operating condition is reached in which, due to the selected parameters, particularly a comparatively high volume flow, the vapor-plasma skin is compressed too strongly and direct contact between the electrolyte and the workpiece surface occurs, at least temporarily, plasma electrolytic machining of the workpiece within the meaning of the invention no longer takes place, since a stable vapor-plasma skin and thus a stable machining process are no longer present. The transition from a stable plasma electrolytic machining condition to an operating condition in which the vapor-plasma skin is very strongly compressed and temporarily destroyed is characterized by a sudden increase in the strength of the current flowing in the machining area by a factor of 10 to 20.Accordingly, it can be assumed that with a jet resistance below 200 Ω · cm 2< , in particular below 150 Ω · cm 2< and most certainly below 100 Ω · cm 2< a stable plasma electrolytic processing process in the sense of the invention is not feasible.

[0072] In Fig. 2 In the three partial views a), b), and c), the time course of the electric current flowing in the processing area during the plasma electrolytic processing of the workpiece surface is plotted in diagrams, whereby the parameters used here are based on processes known from the prior art. The processing differs in the three Fig. 2 a), b), und c) The operating situations depicted are determined by the respective volume flow rate of the electrolyte jet. The curve shows this as follows. Fig. 2 a) the time course of the current intensity at a volume flow rate of the electrolyte jet of 12 l / h, Fig. 2 b) at a volume flow rate of 65 l / h and Fig. 2 c) At a flow rate of 520 l / h, a dispensing unit with an outlet opening was used, which has a cross-sectional area of ​​10 cm², corresponding to a diameter of 35.7 mm. The effective area to be considered in the following analysis therefore has a value of 10 cm².

[0073] When processing according to Fig. 2 a) A significant fluctuation in the current flowing in the processing area can be observed, here between 1 A and 5 A. This indicates that under these operating conditions—i.e., a voltage of 310 V generated by the electrical power source and an electrolyte jet with a volume flow rate of 12 l / h—a stable vapor plasma film cannot be generated in the processing area. At such a low flow velocity, a stable temperature cannot develop in the electrolyte due to the local thermal energy input from the jet plasma polishing. The system behaves like a locally superheated electrolyte bath.

[0074] If the volume flow rate of the electrolyte jet is now increased to 65 l / h, a current with an almost constant current strength of approximately 1.1 A flows in the processing area, as described in Fig. 2 b) This is illustrated. Under these operating parameters, a stable vapor-plasma skin is generated in the processing area on the workpiece surface 2, which is only minimally affected by the low electrolyte flow. The system is in the quasi-hydrostatic stability zone, and the balanced interplay between electrochemical and plasma-physical material removal, which ensures the unique surface results of plasma polishing, can be established. According to Fig. 2 b) With the selected operating parameters, the jet resistance assumes a value of 2818 Ω · cm² and therefore significantly exceeds the limit value provided for in the invention. If the volume flow rate in this system is then increased to a value of 520 l / h, the following results are observed. Fig. 2 c) A pulse-like instability of the process flow occurs over time. This has previously been used as a reason to limit the process window of jet plasma polishing to the hydrodynamic stability zone.

[0075] It can be deduced from this that a stable vapor plasma film can indeed be generated with the aforementioned operating parameters, in particular an electrolyte jet with a volume flow rate of 65 l / h. However, as the inventors recognized, this film only exhibits processing speeds comparable to the classic bath process and is therefore regularly associated with very long cycle times as the sum of the local processing times. Processing at a higher volume flow rate is clearly superior to the prior art, as faster material removal can be achieved. In this context, the inventors recognized that as soon as the operating parameters, especially the volume flow rate of the electrolyte jet, are selected such that a jet resistance of a maximum of 1200 Ω·cm² is achieved, a second stability zone is reached.This area, known as the hydrodynamic stability zone, enables particularly effective and fast plasma electrolytic processing of a workpiece surface, as a particularly stable, permissiblely compressed vapor plasma skin forms in the processing area.

[0076] The examples shown in Fig. 3 The partial views a), b) and c) show the temporal course of the current intensity during a consistent continuation of the increase in volume flow, in particular with a selection of operating parameters according to the invention. Fig. 3 a) shows the time course of the current intensity when using an output unit, which, like in Fig. 2 The system features an outlet opening with a cross-sectional area of ​​approximately 10 cm² and delivers an electrolyte jet with a volume flow rate of 1300 l / h. As the diagram shows, the current, at a voltage of 310 V generated by the electrical power source, reaches a value of approximately 2.6 A and changes only slightly over time. Surprisingly, the value fluctuates only minimally, provided the electrolyte is dispensed uniformly and with minimal pulsation. The in Fig. 2 c) The observed instability is overcome, and the hydrodynamic stability zone is reached, enabling effective processing with the forming, compressed vapor-plasma skin. In this case, the jet resistance is 1192 Ω·cm², thus just below the maximum value of 1200 Ω·cm² provided for in the invention. Typically, falling below this limit is accompanied by a sudden, milky, or even colored turbidity of the electrolyte jet. The extent of the instability between the two stability zones depends on the process parameters, particularly the combination of material and electrolyte, as well as the process voltage.

[0077] If the volume flow rate of the electrolyte jet is now increased further, here to a value of 2600 l / h, without changing the voltage setting of the electrical power source, the current flowing in the processing area increases and exhibits a time profile as shown in Fig. 3 b) The current, according to the described embodiment, has a strength of 7.5 A and is almost constant over the depicted time period. A jet resistance of 419 Ω · cm 22 is established. The process thus also proceeds here, in the form according to the invention, within the hydrodynamic stability zone and, compared to Fig. 3 a) More highly compressed vapor plasma skin allows for even more effective processing.

[0078] Starting from the point in Fig. 3 b) In the operating state shown, the volume flow of the electrolyte jet is further increased to a value of 3200 l / h, resulting in a corresponding increase in the strength of the current flowing in the processing area. Fig. 3 c) The temporal progression shown is relevant. According to the operating condition described here, the vapor-plasma film collapses, at least temporarily, due to the pressure profile acting on the phase boundary, resulting in a sudden increase in current by a factor of 10 to 20. This is because the electrolyte jet now directly impacts the surface being processed, causing plasma re-ignition. According to the specified values, the jet resistance decreases compared to the operating condition described above. Fig. 3b The resistance is correspondingly 10 to 20 times higher, fluctuates considerably, and at least temporarily falls below 100 Ω·cm². Plasma electrolytic processing of a workpiece surface is either impossible or only possible with the acceptance of poor manufacturing results under these operating conditions.

[0079] As the above explanations clearly demonstrate, by increasing the volume flow rate of an electrolyte jet used for workpiece processing, in such a way that a nearly constant or only slightly fluctuating jet resistance is achieved, below 1200 Ω·cm², a particularly effective and rapid plasma electrolytic processing of workpiece surfaces can be realized due to the formation of a special vapor-plasma skin. This finding surprisingly enables a significant increase in the effectiveness and speed of the plasma electrolytic processing of workpiece surfaces. Reference symbol list

[0080] 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

Claims

1. Method (1) for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3), in which at least one electrolyte is conveyed by means of a supply unit (5) to a discharge unit (4), through which the surface (2) of the workpiece (3) is at least temporarily exposed to an electrolyte jet, and an electrical voltage is applied between the surface (2) of the workpiece (3) to be processed and an electrode (6) which at least partially touches the electrolyte by means of an electrical energy source (7), such that the electrode (6) forms a counter electrode to the surface (2) of the workpiece (3) during processing, so that a vapor plasma skin is generated in the area of ​​the processed surface (2) of the workpiece (3). characterized by the fact thatat least one flow property of the electrolyte jet is adjusted such that, due to the kinetic energy of the electrolyte jet, a pressure acting on the phase transition between the liquid electrolyte and the vapor plasma skin is generated, so that a stable electrical jet resistance of a maximum of 1200 Ω·cm is present between the electrode (6) and the surface (2) of the workpiece (3) exposed to the electrolyte jet. 2 adjusts.

2. Method according to claim 1, characterized by the fact that with a jet resistance of maximum 1200 Ω · cm 2In a first step, the volume flow of the electrolyte jet is increased until the electrical process current flowing between the electrode and the surface of the workpiece to be processed stabilizes, preferably not exceeding a fluctuation interval of 5% around a mean value over time, and in a subsequent second step, the volume flow is further increased until the process current again violates this stability criterion.

3. Method according to claim 1 or 2, characterized by the fact that a current strength of the current provided by the electrical energy source (7) is measured and at least one flow property of the electrolyte jet is changed and / or adjusted as a function of a setpoint for the jet resistance.

4. Method according to any of the preceding claims, characterized by the fact thatan optical property of the electrolyte downstream of the electrode (6), in particular a sudden turbidity, is measured absolutely or in relation to another measuring point in the system and at least one flow property of the electrolyte jet is changed and / or adjusted as a function of a setpoint for the jet resistance.

5. Method according to any of the preceding claims, characterized by the fact that the surface (2) exposed to the electrolyte jet is limited by at least one limiting element arranged downstream of a discharge opening of the discharge unit (4).

6. Method according to any of the preceding claims, characterized by the fact that at least temporarily the surface (2) exposed to the electrolyte jet is limited and / or altered by the supply of gases, preferably compressed air.

7. Method according to any of the preceding claims, characterized by the fact thatfrom the dispensing unit (4) during processing with the electrolyte jet an area of ​​0.8 cm² simultaneously 2 up to 80 cm 2 the surface (2) of the workpiece is acted upon.

8. Method according to any of the preceding claims, characterized by the fact that Upstream of a discharge opening of the discharge unit, the electrolyte is at least temporarily dammed to generate the desired properties of the electrolyte jet exiting the discharge opening.

9. Method according to any of the preceding claims, characterized by the fact that the flow characteristics of the electrolyte jet are at least temporarily altered by the supply unit (5) and / or the delivery unit (4).

10. Method according to any of the preceding claims, characterized by the fact thatwhich at least one discharge opening of the discharge unit (4) is rotated, swiveled and / or tilted at least temporarily relative to the workpiece being processed during the processing of the surface (2) of the workpiece.

11. Method according to claim 9, characterized by the fact that while at least the discharge opening of the discharge unit (4) is rotated, pivoted and / or tilted, which changes at least one flow property of the electrolyte jet taking into account the jet resistance.

12. Device for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3) according to the method according to at least one of the preceding claims.

13. Device according to claim 12, characterized by the fact thatat least one measuring element for detecting the strength of the electrical process current provided by the electrical energy source (7) and at least one control unit by which the current actual jet resistance can be determined and which, depending on a target jet resistance and the actual jet resistance, generates a control signal and transmits it to an actuating element which is configured to change at least one flow property of the electrolyte jet.

14. Device according to claim 12 or 13, characterized by the fact that The discharge unit has a cross-sectional constriction, a grid, a Tesla valve or another suitable dam element to influence the flow characteristics of the electrolyte jet upstream or at a discharge opening of the discharge unit.

15. Device according to one of claims 12 to 14, characterized by the fact thatthe dispensing unit is directly or indirectly connected to a movement unit by which the dispensing unit can be moved in a targeted manner.

16. Device according to one of claims 12 to 15, characterized by the fact that a compressed air source and a compressed air delivery unit are provided, wherein compressed air can be delivered through the compressed air source in the direction of the electrolyte jet and / or the surface (2) exposed to the electrolyte jet.

17. Device according to one of claims 12 to 16, characterized by the fact that at least one measuring element for detecting an optical property of the electrolyte downstream of the electrode (6) and at least one control unit by which the current actual jet resistance can be determined and which, depending on a target jet resistance and the actual jet resistance, generates a control signal and transmits it to an actuating element which is configured to change at least one flow property of the electrolyte jet.

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