Method and device for the plasma electrolytic processing of a workpiece surface

Abstract

The invention relates to a method (1) and a device for the plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3), wherein at least one electrolyte is conveyed by means of a supply unit (5) to a discharge unit (4), by means of which an electrolyte jet is applied at least intermittently to the surface (2) of the workpiece (3), between the surface (2) of the workpiece (3) to be processed and an electrode (6), which at least partially contact the electrolyte, an electrical voltage is applied by an electrical energy source (7) such that the electrode (6) forms a counter electrode to the surface (2) of the workpiece (3) during the processing such that a vapor plasma film is produced in the region of the processed surface (2) of the workpiece (3). It is essential for the technical solution described that at least one flow property of the electrolyte jet is set in such a way that, on account of the kinetic energy of the electrolyte jet, a pressure acting on the phase transition between liquid electrolyte and the vapor plasma film is generated such that a stable electrical jet resistance of at most 1200 Ω ∙ cm² is set between the electrode (6) and the surface (2) of the workpiece (3) to which the electrolyte jet is applied.

Description

[0001] Method and apparatus for plasma electrolytic processing of a workpiece surface

[0002] 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.

[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. 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.

[0004] 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. In this way, particularly smooth and glossy surfaces can be produced in a very short time and without form-bound tools. Furthermore, it is not necessary to pretreat the workpiece or remove any oils or lubricants that may be present on the surface.Furthermore, depending on the material being processed, plasma electrolytic treatment can create a workpiece surface with inhibited corrosion. 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. 2, which is why plasma polishing is currently limited to approximately 2,500 cm² due to technical and economic restrictions. 2 The component surface area is limited to approximately one DIN A3 sheet.

[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 a surface to be processed and the application of the voltage required for plasma generation between the outlet opening through which the electrolyte jet emerges and the workpiece surface, surface areas are processed in a manner adaptable to the component geometry. Here, the dynamic plasma treatment (DPH) is formed 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 jet plasma polishing. A generic method 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 oriented vertically upwards, can be positioned in space. Using the described system, it should be possible to plasma electrolytically process even larger workpieces by continuously scanning the surface.

[0008] 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.

[0009] 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. 2 up to 0.2 A / cm 2 treated surface.

[0010] A breakdown of the DPH (dielectric plasma 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.

[0011] 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 erosion 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 precisely as possible.According to the jet plasma polishing method described in Rll 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 opening, 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.

[0012] 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.

[0013] 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 current 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.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 processing of individual workpieces, reproducibly and with high quality, 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] The method according to the invention is characterized in that the flow properties 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, so that a stable electrical jet resistance in a range of 100 Q ■ cm is established between the electrode and the surface of the workpiece exposed to the electrolyte jet.2 up to 1200 Q ■ cm 2 The term "stable" in this context means that the jet resistance value fluctuates only slightly over time and / or does not exhibit any major jumps. This is because 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 has 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 jumps in current strength are primarily due to an unstable process and / or partial destruction of the vapor-plasma skin, which is undesirable according to the invention.

[0019] 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 directed towards the workpiece surface, which is primarily determined by its flow velocity, can thus be varied as required. This allows the hydrodynamic pressure acting in the impact zone, and therefore at least indirectly on the vapor-plasma skin forming in the processing area, to be modified depending on the specific requirements of the workpiece processing.

[0020] 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, which are smaller than the area of ​​the outlet, does the effective area correspond to the workpiece surface bathed by the electrolyte.

[0021] 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 value remains almost constant within certain limits even when the beam length is varied. However, the linear dependence on the effective area from the model analysis remains. The system for plasma electrolytic processing of a workpiece surface can therefore be clearly defined by the aforementioned jet resistance with the unit Q ■ cm. 2 or Q ■ m 2 This jet resistance represents the link between the complex, plasma electrolytic influencing factors and the measurable and controllable system parameters, since it can be determined based on the voltage set and / or measured at the energy and / or voltage source and the strength of the current flowing in the processing area, especially in the area of ​​the vapor plasma skin.

[0022] 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.

[0023] 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 a basis for adjusting the flow characteristics to achieve the desired jet resistance.

[0024] 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.

[0025] 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.

[0026] 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 processing systems for workpieces, for example, systems that differ in size, orientation, and parameterization, can be advantageously compared, designed, and controlled.

[0027] 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.

[0028] 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.

[0029] 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. 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 volume flow rate of the electrolyte jet, is characterized by: the formation of a stable and, due to the pressure exerted by the electrolyte jet, precisely compressed vapor plasma film; comparatively high current densities on the surface of the workpiece; and a high material removal rate without quality loss, which would otherwise be unattainable.The second operating state described above can be advantageously achieved by reducing the jet resistance to a maximum value of 1200 Q ■ cm. 2 is set, preferably to a value between 400 Q ■ cm 2 and 800 Q ■ cm 2 . Reaching the hydrodynamic stability zone, e.g. by reducing jet drag starting at high values ​​above 1200 Q ■ cm 2 In addition to the properties mentioned above, this is usually accompanied by a sudden, milky clouding of the electrolyte jet.

[0030] 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 in such a way 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. 2This results in a material removal rate approximately six to ten times higher than previously possible. This enables comparatively fast processing while still producing the familiar mirror-like shine. The specified jet resistance values ​​are universal, and the resulting electrical resistance measurements depend on the selected or set diameter of the electrolyte jet, which can be adjusted, in particular, by choosing a suitable dispensing element, preferably a circular or rectangular nozzle.

[0031] According to the invention, a jet resistance in the range of no more than 1200 Q ■ cm enables 2 High-quality and reproducible workpiece processing is achieved through plasma electrolytic processing with an electrolyte jet, i.e., jet plasma polishing. The process can also be used for deburring or cleaning.

[0032] 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.

[0033] This limits the hydrodynamic stability zone with respect to the values ​​for jet drag.

[0034] Experiments have confirmed the above statements regarding the limits of the hydrodynamic stability zone. It should be emphasized that while its lower limit depends on system-related parameters, it is always characterized by a sudden reduction in jet resistance. By changing the flow conditions, particularly by intensifying them, this resistance can be largely freely adjusted within the hydrodynamic stability zone and then drops abruptly upon leaving the process window. Accordingly, it can be stated that at a jet resistance below 200 Q ■ cm 2 , especially below 150 Q ■ cm 2 and certainly below 100 Q ■ cm 2 No stable plasma electrolytic processing process in accordance with the invention is feasible.

[0035] In jet plasma processing, particularly jet plasma polishing, the process voltage is preferably adjusted, while the process current 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. 2 and 80 cm 2 , especially preferred between 5 cm 2 and 10 cm 2 If this is determined by the size of the outlet opening, then 7 cm corresponds to... 2 approximately a round nozzle with a 30 mm diameter. With previous jet plasma processing, especially jet plasma plating, in the quasi-hydrostatic stability zone, a process current of between 0.8 A and 1.2 A would be expected, corresponding to a jet resistance of 3.092 Q ■ cm. 2 or 2.062 Q ■ cm 2This corresponds to the target value for efficient jet plasma processing. However, according to the essential properties of the inventive method, the target value would be reaching the hydrodynamic stability zone, i.e., reaching a jet resistance value of 1,200 Q ■ cm. 2 does not exceed. The flow conditions are preferably set comparatively more intensely, so that after overcoming the first instability region a stable process current of 2.1 A is achieved, which is usually accompanied by a sudden clouding 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 Q ■ cm. 2 up to 800 Q ■ cm 2 , therefore, in the example mentioned, 3.1 A to 6.2 A process current.

[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 according to the size of the outlet opening for identical process conditions. In the known prior art, the following values ​​are used per 1 cm²: 2 The surface area of ​​the outlet opening is determined by proposed values ​​for the electrolyte flow rate in the range of 5.3 to 10.6 l / h (RLI2681239C1) and 1.1 l / h (EP0955393A1). According to a particular embodiment of the invention, however, to achieve the hydrodynamic stability zone, normalized flow rate values ​​of 100 l / h to 400 l / h, preferably 250 l / h to 300 l / h, are provided. 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 7.1 cm², the following applies: 2If the system exhibits a certain characteristic, 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 the jet drag of 1200 Q ■ cm 2This 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 changed 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.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.

[0041] 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.

[0042] It is particularly advantageous for the invention if the electrolyte jet, in relation to an outlet opening of the dispensing unit with an area of ​​1 cm², 2The electrolyte is dispensed from the dispensing unit at a flow rate of 100 to 400 l / h, particularly 250 l / h to 300 l / h, towards the workpiece surface being processed. A supply unit conveys the required quantity of electrolyte, for example from an electrolyte reservoir, towards the dispensing unit, where it is then shaped and ultimately dispensed from an outlet at the aforementioned flow rate.

[0043] In a specific embodiment of the invention, it is provided that the electrolyte jet exiting the dispensing unit simultaneously processes an area of ​​0.8 cm² during the processing. 2 up to 80 cm 2 the surface of the workpiece is subjected to impact and thus material is removed.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 has a maximum value of 1200 Q ■ cm. 2assumes that if the movement changes the orientation of the dispensing unit in space, in particular by rotating, tilting or inclining, a special embodiment of the method according to the invention 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.

[0050] 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 and has a control unit for the targeted adjustment of at least one property of the electrolyte jet. The control unit provided according to the invention generates a control signal that is transmitted to at least one actuating element for adjusting at least one flow property of the electrolyte jet and ensures that the flow property, preferably the volume or mass flow rate, is set to the desired value.Preferably, the actuating element is part of a pump for at least temporarily conveying the electrolyte jet towards the processing area, wherein, most preferably, the rotational speed of the conveying element, in particular a conveying impeller, of the pump can be adjusted to set the desired volumetric flow rate of the electrolyte stream. Alternatively or additionally, it is conceivable that the control unit acts on other actuators, such as valves and / or orifices.

[0051] According to a further particular embodiment of the invention, the control unit is coupled to a control system or integrated into a control loop in terms of circuitry, so that the adjustment of at least one property of the electrolyte current can be carried out automatically depending on a predetermined, stored, adjustable, and / or measured setpoint. A preferred setpoint used as the basis for adjusting the at least one property of the electrolyte jet is the instantaneous value or a stored value of the jet resistance.

[0052] In a particular embodiment of the device according to the invention, at least one measuring element for detecting the intensity of the process current flowing 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 current 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 volumetric 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 dispensing unit, through which an electrolyte jet can be dispensed in the direction of the workpiece surface to be processed, so that the electrolyte jet has a jet resistance of a maximum of 1200 Q ■ cm. 2 The jet resistance is set to a certain value. Once this value is reached, particularly fast surface processing with consistent quality is possible. This is because an electrolyte jet is emitted at a comparatively high flow velocity towards the workpiece surface, 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 has a maximum value of 1200 Q ■ cm. 2Another 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.

[0055] 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:

[0056] Fig. 1: Schematic side view of a nozzle during plasma electrolysis

[0057] Machining of a workpiece surface

[0058] Fig. 2: Representation of the temporal course of the process flow during the plasma electrolytic processing of a workpiece surface using a process control known from the prior art, as well as

[0059] Fig. 3: Representation of the temporal course of the process flow during the plasma electrolytic processing of a workpiece surface in a process control according to the invention.

[0060] Fig. 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. For clarity, only the dispensing unit 4 and the workpiece 3 to be processed are shown in the illustration in Fig. 1 during the processing of the workpiece surface 2. Also shown, only schematically, are a supply unit 5, which delivers the electrolyte used to the outlet opening as needed, a reservoir 16 for storing an electrolyte, an electrical power source 7, which generates the voltage required to produce a vapor plasma film, and a control unit 9, which controls the individual system components.

[0061] With the device 1 for plasma electrolytic processing shown in Fig. 1, 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 an electrolyte jet from a reservoir at an outlet opening 10 to a delivery unit 4, so that an electrolyte jet is directed towards and impacts the workpiece surface 2. A voltage is applied between the electrode 6, which according to the illustrated embodiment is part of the delivery 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 during this process, resulting in surface roughness R aSurface finishes of up to 0.02 pm are achievable. Using the device shown in Fig. 1 and the inventive method explained in more detail below, it is advantageously possible to produce particularly high-quality surfaces in a comparatively short time, even on components with complex geometries, by means of 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] During the machining process, a DC voltage is applied between the electrode 6, which, according to the embodiment shown in Fig. 1, is part of the dispensing unit 4 and is formed by a tube section whose end forms the outlet opening 10, and the workpiece surface 2. A key aspect of the invention 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 processing cases where the area to be processed, 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 workpiece surface being processed. 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 set such that the jet resistance has a value of 1200 Q ■ cm during the processing of the workpiece. 2does not exceed this value of the jet resistance. As soon as this value 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.

[0066] According to the embodiment shown in Fig. 1, 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 rate of 1200 to 2200 l / h can be directed towards the workpiece. At the start of the processing, a voltage of 310 V is applied using the electrical power source 7, and the volume flow rate of the electrolyte jet is adjusted such that a current of 2.0 A is measured in the gap between the electrode 6 and the workpiece surface, and thus in the area of ​​the forming vapor-plasma skin. In the control unit, an electrical resistance of 155 Ω is calculated 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, an effective area of ​​A = 3.14 cm². 2 , which in this case corresponds to the cross-sectional area of ​​the outlet opening.

[0067] 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.

[0068] From the values ​​determined in the control unit for the effective area A of 3.14 cm² 2 and the electrical resistance of 155 Q is a jet resistance JW = R * A with a height of 487 Q ■ cm. 2 determined. This value is below the limit value of 1200 Q ■ cm provided for in the invention. 2 and within the hydrodynamic stability zone. Therefore, in this case, it can be assumed that a stable, compressed vapor-plasma skin forms on the workpiece surface in the processing area.

[0069] If, instead of a discharge unit with a diameter of 20 mm, a discharge opening with a diameter of 30 mm were used, the effective area would increase to A = 7.1 cm². 2 Assuming that the jet resistance is also 487 Q ■ cm 2Given a value of 68.6 Ω, 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 power source is 310 V and the electrolyte jet flow rate is adjusted using a 30 mm diameter outlet 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 a 20 mm diameter outlet and a modified electrolyte jet flow rate.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 that use different process parameters and / or system configurations comparable.

[0070] 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.

[0071] According to the embodiment shown in Fig. 1, 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 this purpose and fixed in this position. Subsequently, the discharge unit with the exit opening 10 is extended into its machining position.

[0072] The following section explains in more detail the inventive method for the plasma electrolytic processing of a workpiece surface 2, as schematically illustrated in Fig. 1, as well as its differences and advantages compared to methods known from the prior art, with the aid of the diagrams shown in Figures 2 and 3. 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 was recognized that a jet resistance of 1200 Q ■ cm during plasma electrolytic processing 2The system does not exceed the specified volume flow rate, generating a compressed yet particularly stable vapor-plasma skin, 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 rate, the vapor-plasma skin is compressed too much and direct contact between the electrolyte and the workpiece surface occurs, at least temporarily, plasma electrolytic workpiece processing within the meaning of the invention no longer takes place, since a stable vapor-plasma skin and therefore a stable processing process are no longer present.The transition from a stable plasma electrolytic processing state to an operating state in which the vapor-plasma skin is highly compressed and temporarily destroyed is characterized by a sudden increase in the current flowing in the processing area by a factor of 10 to 20. Accordingly, it can be assumed that with a jet resistance below 200 Q ■ cm. 2 , especially below 150 Q ■ cm 2 and certainly below 100 Q ■ cm 2 No stable plasma electrolytic processing process in accordance with the invention is feasible.

[0073] Figure 2 shows diagrams of the current intensity over time in the processing area during plasma electrolytic treatment of the workpiece surface in three partial views (a), (b), and (c). The parameters used here are based on methods known from the prior art. The processing differs in the three operating conditions shown in Figure 2 (a), (b), and (c) by the respective volumetric flow rate of the electrolyte jet. The curve in Figure 2 (a) shows the current intensity over time at an electrolyte jet flow rate of 12 l / h, Figure 2 (b) at a flow rate of 65 l / h, and Figure 2 (c) at a flow rate of 520 l / h. A discharge unit with an outlet opening having a cross-sectional area of ​​10 cm² was used. 2It has a diameter of 35.7 mm. The effective area to be considered further is therefore 10 cm². 2 to.

[0074] During 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. From this, it can be deduced that under this operating condition, 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 of the jet plasma polishing. The system behaves like a locally superheated electrolyte bath.

[0075] If the electrolyte jet flow rate is increased to 65 l / h, a current of approximately 1.1 A flows in the processing area at a nearly constant current intensity, as shown in Fig. 2 b). 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. With the operating parameters selected according to Fig. 2 b), the jet resistance assumes a value of 2818 Q ■ cm. 2and therefore significantly exceeds the limit value provided for in the invention. If the volume flow in this system is again increased to a value of 520 l / h, Fig. 2 c) shows an occurring, pulse-like instability of the process flow over time. This has previously been used as a reason to limit the process window of jet plasma polishing to the hydrodynamic stability zone.

[0076] It can be deduced from this that, with the aforementioned operating parameters, in particular an electrolyte jet with a volume flow rate of 65 l / h, a stable vapor-plasma film can indeed be generated. However, as the inventors recognized, this 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 Q ■ cm is achieved, 2Once the temperature is reached, a second stability zone is achieved. This area, known as the hydrodynamic stability zone, enables particularly effective and rapid plasma electrolytic processing of a workpiece surface, as a particularly stable, permissiblely compressed vapor-plasma skin forms in the processing area.

[0077] Figure 3, in partial views a), b), and c), exemplifies the current profile over time when the volume flow rate is consistently increased, particularly when the operating parameters are selected according to the invention. Figure 3 a) shows the current profile over time when using a discharge unit which, like the one in Figure 2, has an outlet opening with a cross-sectional area of ​​approximately 10 cm². 2The system features an electrolyte jet with a 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 slightly, provided the electrolyte is dispensed uniformly and with minimal pulsation. The instability shown in Fig. 2 c) is overcome, and the hydrodynamic stability zone is reached, enabling effective processing with the developing, compressed vapor-plasma skin. The jet resistance in this case is 1192 Q ■ cm. 2 , thus just below the maximum value of 1200 Q ■ cm provided for in the invention. 2As a rule, 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 ranges depends on the process parameters, particularly the combination of material and electrolyte, as well as the process voltage. If the volumetric flow rate of the electrolyte jet is further increased, 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). According to the described embodiment, the current has a magnitude of 7.5 A and is almost constant over the depicted time period. This results in a jet resistance of 419 Q ■ cm. 2a. The process therefore also takes place here in the form according to the invention within the hydrodynamic stability zone and exhibits even more effective processing due to the more highly compressed vapor-plasma skin compared to Fig. 3 a).

[0078] Starting from the operating condition shown in Fig. 3 b), if the volume flow rate of the electrolyte jet is further increased to a value of 3200 l / h, the current flowing in the processing area exhibits the temporal profile shown in Fig. 3 c). According to the operating condition described here, the vapor-plasma film collapses, at least temporarily, due to the pressure profile acting on the phase interface, resulting in a sudden increase in current intensity 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 values ​​given, the jet resistance decreases by a factor of 10 to 20 compared to the operating condition shown in Fig. 3 b), fluctuates considerably, and at least temporarily falls below 100 Q ■ cm. 2Plasma electrolytic processing of the surface of a workpiece is not possible under this operating condition, or only possible by accepting poor manufacturing results.

[0079] As the above explanations clearly show, by increasing the volume flow of an electrolyte jet used for workpiece processing, in such a way that a nearly constant or only slightly fluctuating jet resistance is achieved, which is below 1200 Q ■ cm 2 This is due to the fact that a particularly effective and rapid plasma electrolytic processing of workpiece surfaces can be achieved through 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 process for workpiece surfaces. Reference list

[0080] 1 Device for plasma electrolytic processing of an electrically conductive workpiece surface

[0081] 2 Surface

[0082] 3 workpieces

[0083] 4 output units

[0084] 5 supply unit

[0085] 6 electrode

[0086] 7 electrical energy source

[0087] 8 Actuator

[0088] 9 Control unit

[0089] 10 Exit opening

[0090] 11 Adjustment unit

[0091] 12 actuators

[0092] 13 Electrolyte supply

[0093] 14 Electrolyte removal

[0094] 15 processing unit

[0095] 16 storage containers

[0096] 17 Sensor unit

[0097] 18 heating element

[0098] 19 dosing units

[0099] 20 Temperature sensor

[0100] 21 nozzle head

Claims

Patent claims 1. Method (1) for plasma electrolytic treatment 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, an electrical voltage is applied between the surface (2) of the workpiece (3) to be treated and an electrode (6) which at least partially touches the electrolyte by an electrical energy source (7), such that the electrode (6) forms a counter electrode to the surface (2) of the workpiece (3) during treatment, so that a vapor plasma skin is generated in the area of ​​the treated surface (2) of the workpiece (3), characterized in that at least one flow property of the electrolyte jet is adjusted in such a way thatthat, due to the kinetic energy of the electrolyte jet, a pressure is generated acting on the phase transition between the liquid electrolyte and the vapor-plasma skin, so that a stable electrical jet resistance in a range between 100 Q ■ cm is established between the electrode (6) and the surface (2) of the workpiece (3) exposed to the electrolyte jet. 2 and 1200 Q ■ cm 2 adjusts.

2. Method according to claim 1, characterized in that at a jet resistance of a maximum of 1200 Q ■ 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 in that a current intensity 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 one of the preceding claims, characterized in that an 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 one of the preceding claims, characterized in 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 one of the preceding claims, characterized in that the surface (2) exposed to the electrolyte jet is limited and / or modified at least temporarily by supplying gases, preferably compressed air.

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

8. Method according to one of the preceding claims, characterized in that upstream of a discharge opening of the discharge unit the electrolyte is at least temporarily dammed up to generate desired properties of the electrolyte jet exiting the discharge opening.

9. Method according to one of the preceding claims, characterized in that the flow characteristics of the electrolyte jet are changed at least temporarily by the supply unit (5) and / or dispensing unit (4).

10. Method according to one of the preceding claims, characterized in that the at least one discharge opening of the discharge unit (4) is rotated, pivoted and / or tilted at least temporarily relative to the workpiece to be processed during the processing of the surface (2) of the workpiece.

11. Method according to claim 10, characterized in that while at least the discharge opening of the discharge unit (4) is rotated, pivoted and / or tilted, at least one flow property of the electrolyte jet is changed taking into account the jet resistance.

12. Device for plasma electrolytic processing of an electrically conductive surface (2) of a workpiece (3), which is configured to carry out the method according to at least one of the preceding claims, and has at least one control unit for adjusting the at least one flow property of the electrolyte jet.

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

14. Device according to claim 12 or 13, characterized in that the control unit is configured to change the rotational speed of a pump for at least temporary delivery of the electrolyte jet.

15. Device according to claim one of claims 12 to 14, characterized in that the dispensing unit has a cross-sectional constriction, a grid, a Tesla valve or another suitable dam element for influencing flow characteristics of the electrolyte jet upstream or at a dispensing opening of the dispensing unit.

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

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

18. Device according to one of claims 12 to 17, characterized in 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 the at least one flow property of the electrolyte jet.

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