Method and device for the electrochemical polishing of metal workpieces

Abstract

The invention relates to a method and a device for electrochemically polishing metal workpieces, wherein an electrolyte medium, which contains solid granular particles and a liquid electrolyte, is added to a container and conductively connected to a first electrode, wherein the metal workpiece is conductively connected to a second electrode and immersed in the electrolyte medium located in the container, wherein the electrodes are applied with an electrical voltage in such a way that the first electrode in contact with the electrolyte medium has a negative voltage and the second electrode in contact with the workpiece has a positive voltage, and wherein the workpiece is moved relative to the plurality of solid granular particles of the electrolyte medium in order to electrochemically polish it. According to the invention, the polarity of the electrical voltage applied to the electrodes, during the electrochemical polishing of the workpiece, is temporarily reversed at least once, in particular periodically, such that the first electrode in contact with the electrolyte medium temporarily has a positive voltage and the second electrode in contact with the workpiece temporarily has a negative voltage.

Description

[0001] Method and apparatus for the electrochemical polishing of metallic workpieces

[0002] The invention relates to a method for the electrochemical polishing of metallic workpieces, wherein an electrolyte medium, which on the one hand contains a plurality of solid granular particles and on the other hand contains at least one liquid electrolyte, is placed in a container and electrically connected to a first electrode, wherein the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium in the container, wherein the electrodes are subjected to an electrical voltage such that the first electrode, which is in conductive contact with the electrolyte medium, has a negative voltage and the second electrode, which is in conductive contact with the workpiece, has a positive voltage, and wherein the workpiece is moved relative to the plurality of solid granular particles of the electrolyte medium in order to polish it electrochemically.

[0003] The invention further relates to a device particularly suitable for carrying out such a method for the electrochemical polishing of metallic workpieces, comprising:

[0004] - at least one container for holding an electrolyte medium which contains, on the one hand, a plurality of solid granular particles and, on the other hand, at least one liquid electrolyte;

[0005] - at least one first electrode, which is arranged inside the container and / or is in electrically conductive contact with the container;

[0006] - at least one workpiece holder that can be moved relative to the container for the detachable fastening of the workpieces;

[0007] - at least a second electrode which is in electrically conductive contact with at least one workpiece holder;

[0008] - at least one voltage source to apply an electrical voltage to the electrodes such that the first electrode has a negative voltage and the second electrode has a positive voltage; and

[0009] - a control and / or regulating device programmed to control and / or regulate the voltage applied between the electrodes.

[0010] For surface finishing of workpieces, so-called drag finishing processes are known, in which the workpiece is immersed in a bed of solid abrasive or polishing granules contained in a container and moved relative to the granules within the bed. Drag finishing machines are typically used for this purpose; these machines are a special type of vibratory finishing machine in which the workpieces to be processed are detachably fixed, for example, individually or on one or more clamping devices of a workpiece holder in the machine, in order to polish or grind them as a result of the relative movement with respect to the bed of granules. Such drag finishing machines often include a usually rotating part, essentially in the form of, for example, a...A rotaryally driven plate, driven by a suitable gearbox, to which the workpiece holders are attached directly or indirectly, for example via lifting devices. This is done particularly eccentrically with respect to the axis of rotation of the rotating part of the drag finishing machine. This part...

[0011] As the so-called plate of the drag finishing machine rotates, the workpiece holders attached to it describe a trajectory path. The workpieces, supported by the clamping devices of the workpiece holders, are immersed in the container, which is filled with a load of granular particles, often with the addition of liquid processing media such as water, surfactants, etc. Due to the relative movement of the workpieces with respect to the granules, their surface is treated in the form of a vibratory finishing process. Such drag finishing machines are known, for example, from DE 102 04 267 Gl, DE 200 05 361 Ul, or DE 10 2010 052 222 Al.

[0012] Alternatively or additionally, the container holding the granular particles and the liquid processing medium can be moved relative to the workpieces, which are also moving (e.g., rotated around their own axis) or stationary, for example, around its own axis and / or along a path, such as a circular track. If only the container is moved and the workpieces themselves do not undergo any translational movement, this is also referred to as "immersion grinding" or "immersion polishing" as a special form of drag finishing. Machines in which the workpiece holder supporting the workpiece during surface processing is essentially stationary are also called immersion finishing machines.

[0013] The granules can be of a wide variety of origins, depending on the workpieces being treated. These can be of natural origin (e.g., organic material such as walnut or coconut shells, wood, cherry pits, etc.), mineral origin (e.g., silicates, oxides, etc.), and / or synthetic origin (e.g., plastics). Furthermore, as already mentioned, vibratory finishing can be performed dry or wet, using a liquid processing medium such as water, which may contain additives such as surfactants.

[0014] To provide a rotational movement of the workpieces, such as around their own axis, as an alternative or additional to a translational movement relative to the granule particles, resulting in even more effective surface treatment, the workpiece holders of known drag finishing machines are often rotary-driven, for example by means of suitable motors (see, e.g., DE 10 2010 052 222 Al). Furthermore, workpiece holders for drag finishing machines are known whose clamping devices for the detachable fastening of the workpieces are rotatably mounted and can be set in rotation via a shaft rotatably mounted in the workpiece holder. For this purpose, the workpiece holder has, e.g.,A planetary gear with a central sun gear, which meshes with planet gears that are in turn rotationally fixed to a support shaft of a respective clamping device and are arranged around the circumference of the sun gear of the workpiece holder. Due to such movement of the clamping devices rotatably mounted on the workpiece holder with the workpieces, which consists of a translational movement (in the direction of rotation of the support part or the "plate" of the drag finishing machine) and a rotational movement (about the axis of the respective clamping device or about the workpiece axis), by the processing medium, a uniform processing quality is achieved with shorter processing times compared to a purely translational movement. Furthermore, alternatively or additionally, the workpiece holder itself can be rotatably fixed to the support part of the drag finishing machine in a corresponding manner (see, e.g.,(DE 20 2009 008 070 Ul). Furthermore, conventional drag finishing processes for polishing or grinding metallic workpieces of the aforementioned type have been further developed into electrochemical polishing processes in such a way that, on the one hand, the metallic workpiece is electrically connected to a positive electrode (anode), and on the other hand, the granule particles flooded with a liquid electrolyte are electrically connected to a negative electrode (cathode), whereby the electrodes are subjected to an electrical voltage and the workpiece is moved relative to the majority of solid granule particles, e.g., in the manner described above. The latter are part of an electrolyte medium which, in addition to the granule particles, comprises a liquid, electrically conductive electrolyte.The surface quality of the processed workpieces can often be improved in this way, and such electrochemical polishing is also a process of abrasive surface treatment. When the electrodes are subjected to an electrical voltage via a voltage source, in addition to the purely mechanical surface treatment of the metallic workpieces, a current flows due to the electrical conductivity of the liquid electrolyte, which causes the surface, anodic removal of material from the metallic workpieces. The electrodes can be supplied with either direct current or pulsed voltages, with the workpiece being connected to the positive electrode (anode), while the electrolyte medium or the container holding it is connected to the negative electrode (cathode).Typically, the workpieces are also moved in the electrolyte medium to ensure the desired relative movement of the workpieces with respect to the solid granule particles and to minimize the concentration gradient that forms on the surface of the workpieces. A generic method for the electrochemical polishing of metallic workpieces is known, for example, from WO 2024 / 056315 Al.

[0015] Furthermore, recent attempts have been made to improve methods for the electrochemical polishing of workpieces by using special electrolyte media, which on the one hand comprise a plurality of solid porous granular particles based on polymers, e.g. in the form of ion exchangers, and on the other hand a liquid electrolyte consisting of an electrically conductive, hydrophilic liquid, in particular from the group of strong inorganic acids and sulfonic acids. The liquid electrolyte is absorbed exclusively in the pores of the granule particles and is otherwise contained within the cavity volume of the granule particles in a gas or air atmosphere (see, for example, WO 2017 / 186992 Al, WO 2019 / 145588 Al, WO 2020 / 099699 Al, WO 2020 / 174112 Al, WO 2020 / 099700 Al or WO 2021 / 156530 Al) or a non-electrically conductive liquid that is immiscible with the liquid electrolyte, e.g.in the form of mineral or silicone oils, which, similar to the aforementioned gas atmosphere, serve as a dielectric (see, for example, EP 4 249 647 Al). However, due to the current flow being induced only at specific points as a result of contact between a single granule particle and the workpiece being processed, surface treatment of the workpieces in this way is very time-consuming. Therefore, electrolyte media are preferable, in which the liquid electrolyte is absorbed in the interparticle spaces of the granule particles.

[0016] However, it has been shown that the liquid electrolyte must be adapted to the material of the metallic workpieces being processed. This is both time-consuming and often done using a trial-and-error method. Furthermore, particularly with precious metals or alloys containing them, it sometimes leads to unsatisfactory polishing results, leaving the workpieces with a matte surface. This applies, for example, especially, though not exclusively, to precious metal alloys such as gold-palladium and white gold-palladium alloys, with a palladium (Pd) content between approximately 5 and 25% by mass and / or with a silver (Ag) content of up to approximately 20% by mass.

[0017] The invention is based on the objective of further developing a method and a device for the electrochemical polishing of metallic workpieces of the type mentioned above, while at least largely avoiding the aforementioned disadvantages, in a simple and cost-effective manner, such that a flawless surface quality of the electropolished workpieces can be achieved, particularly, though not exclusively, with precious metals, while avoiding even local corrosion, thus improving the efficiency of electropolishing.

[0018] In terms of process engineering, this problem is solved in a process for the electrochemical polishing of metallic workpieces of the type mentioned above by temporarily reversing the polarity of the electrical voltage applied to the electrodes at least once during the electrochemical polishing of the workpiece, so that the first electrode, which is in conductive contact with the electrolyte medium, temporarily has a positive voltage and the second electrode, which is in conductive contact with the workpiece, temporarily has a negative voltage.In terms of the device technology, the invention further provides for solving this problem in a device for the electrochemical polishing of metallic workpieces of the type mentioned above that the control and / or regulating device is designed to at least temporarily reverse the polarity of the electrical voltage applied to the electrodes during operation, so that the first electrode temporarily has a positive voltage and the second electrode temporarily has a negative voltage.

[0019] The invention therefore provides that, in contrast to generic electrochemical polishing processes in which the electrodes are supplied with a continuous direct current or with a pulsed direct current (i.e., with short interruptions of the voltage source) such that the first electrode (cathode) in conductive contact with the electrolyte medium has a negative voltage and the second electrode (anode) in conductive contact with the workpiece has a positive voltage, the polarity of the electrical voltage applied to the electrodes is temporarily reversed at least once during the electrochemical polishing of the workpiece, so that the first electrode in conductive contact with the electrolyte medium temporarily has a positive voltage and the second electrode in conductive contact with the workpiece temporarily has a negative voltage.Surprisingly, it was found that this method can also produce a perfectly smooth, glossy surface on metallic workpieces that are otherwise only inadequately electropolished (resulting in a matte surface with a kind of "needle structure"). This applies particularly—though not exclusively—to workpieces containing or consisting entirely of precious metals, such as gold-palladium and white gold-palladium alloys. Furthermore, the inventive method ensures reproducible, homogeneous material removal and guarantees very high processing efficiency.While metallic workpieces, which are usually subjected to a positive voltage via the second electrode (anode), experience material removal on their surface, particularly at the roughness peaks, under the influence of the granule particles, and metal oxides are locally generated, which can reduce diffusion, it is assumed that the inventive temporary reversal of the electrical voltage (i.e., the workpieces are briefly subjected to a negative electrical voltage) is capable, on the one hand, of reducing such locally present metal oxides and thus increasing the mobility of surface metal atoms, and on the other hand, in particular – supported by the granule particles moving relative to the workpiece – of causing a rapid dissolution and deposition of metal ions in the roughness valleys on the surface of the workpiece, so that roughness valleys are "filled".

[0020] As already indicated, an advantageous embodiment provides for the use of an electrolyte medium in which the interparticle spaces between the granule particles are at least partially, and in particular substantially completely, filled with the liquid electrolyte. In this way, not only can time-efficient surface treatment of the workpieces to be electropolished be achieved, but it is also ensured that, when the workpieces are exposed to the electrical voltage gradient applied to the electrodes according to the invention, a rapid dissolution and deposition of surface metal ions of the workpiece occurs, by ensuring very high mobility of metal ions on the surface of the workpiece.

[0021] In terms of the device design, it is provided that the container for receiving the electrolyte medium receives an electrolyte medium in which the interparticle spaces between the granule particles are at least partially, and in particular essentially completely, filled with the liquid electrolyte.

[0022] Regarding the solid granular particles of the electrolyte medium, the invention fundamentally allows the use of virtually any known granular particles used for polishing or grinding metallic workpieces. In addition to glass and ceramic particles, granular particles made of polymer materials have proven particularly advantageous. These polymers possess a lower hardness than mineral and metallic materials and, in particular, can have a rounded shape, preferably substantially spherical, and / or a mean particle diameter between approximately 10 µm and approximately 5 mm, preferably between approximately 100 µm and approximately 3 mm. With regard to the typically acidic environment of the electrolyte, the polymer materials of the granular particles should expediently be acid-resistant and, with regard to the electrochemical polishing process, expediently oxidation-resistant.The solid granules can, for example, be selected from the group of ion-exchange polymers. In principle, any ion-exchange polymer can be used, but preferably cationic ion-exchange polymers capable of absorbing metal ions released during the electrochemical polishing of the metallic workpieces. Examples of advantageous ion-exchange polymers include copolymers of styrene with sulfonated ethylstyrene and / or with sulfonated divinylbenzene, acrylic resins with acrylic acid and / or methacrylic acid units, and the like, such as ion exchangers available under the trade name "AMBERLITE," preferably in the form of sodium ion exchangers. Furthermore, the solid granules can be compact or porous and / or gel exchangers, as is often the case with the aforementioned polymer materials due to their manufacturing properties.

[0023] The liquid electrolyte of the electrolyte medium, which—as already mentioned—at least partially, and preferably substantially completely, fills the interparticle spaces between the granule particles, can also be any electrolyte liquid such as those already used for the electrochemical polishing of metals, whereby the liquid electrolyte can be adapted to the respective metal material of the workpieces to be processed in a manner known as such. An example composition for an electrolyte suitable for precious metal alloys is given below (percentages are given in mass%):

[0024] - 3% thiourea;

[0025] - 10% thiocyanate, such as ammonium, sodium or

[0026] Potassium cyanate;

[0027] - 20% sulfate, such as ammonium, sodium, potassium or

[0028] Magnesium sulfate;

[0029] - 5% nitrate, such as ammonium, sodium or potassium nitrate;

[0030] - 5% ethoxylated isotridecanol (mixture of isomers of

[0031] Tridecanols);

[0032] - 7% surfactants, such as ethoxylated isotridecanol, C10-C13 sec-alkyl derivatives of benzenesulfonic acid, triethanolamine and / or sodium N-(2-carboxyethyl)-N-(2-ethylhexyl)-beta-alaninate;

[0033] - 4% solubilizers (hydrotropes), such as benzene,

[0034] 1,1-oxybis-tetrapropylene derivatives, sulfonated, sodium salt and / or dipropylene glycol methyl ether; and

[0035] - Remaining water.

[0036] From a process engineering perspective, the polarity of the electrical voltage applied to the electrodes can preferably be temporarily reversed several times during the electrochemical polishing of the workpiece, particularly at essentially equal time intervals, so that the first electrode, which is in conductive contact with the electrolyte medium, repeatedly exhibits a positive voltage and the second electrode, which is in conductive contact with the workpiece, repeatedly exhibits a negative voltage. This means that the electrical voltage applied to the electrodes is reversed at periodic, short intervals, resulting in particularly efficient electropolishing of metallic workpieces, including those made of precious metals.

[0037] In terms of the device design, it may be advantageously provided that the control and / or regulating device is designed to repeatedly reverse the polarity of the electrical voltage applied to the electrodes, particularly at essentially equal time intervals, during operation, so that the first electrode temporarily has a positive voltage several times and the second electrode temporarily has a negative voltage several times, which can be done, for example, by means of a pulse-reverse rectifier.Furthermore, it proves advantageous if, during the electrochemical polishing of the workpiece, the total duration during which the polarity of the electrical voltage applied to the electrodes is temporarily reversed is shorter than the total duration during which the first electrode in conductive contact with the electrolyte medium has a negative voltage (cathode) and the second electrode in conductive contact with the workpiece has a positive voltage (anode), i.e., during the electrochemical polishing of the workpiece, the total duration of the temporary reversal(s) of the polarity of the electrodes is shorter than the total duration during which a positive voltage is applied to the workpiece in the usual manner to ensure anodic oxidation.Advantageously, during the electrochemical polishing of the workpiece, the ratio between the total duration during which the first electrode, in conductive contact with the electrolyte medium, has a negative voltage and the second electrode, in conductive contact with the workpiece, has a positive voltage, and the total duration with temporarily reversed polarity of the electrical voltage applied to the electrodes can be determined.

[0038] - at least about 1.1, preferably at least about 1.3, most preferably at least about 1.5; and / or

[0039] - at most about 20, preferably at most about 10, most preferably at most about 4, are set.

[0040] From a device engineering perspective, it can therefore be advantageously provided that the control and / or regulating device is further designed to control and / or regulate the total duration during which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed during operation to a value smaller than the total duration during which the first electrode has a negative voltage and the second electrode has a positive voltage; wherein the control and / or regulating device is particularly designed to control and / or regulate the ratio between the total duration during which the first electrode has a negative voltage and the second electrode has a positive voltage and the total duration with temporarily reversed polarity of the electrical voltage applied to the electrodes to

[0041] - at least about 1.1, preferably at least about 1.3, most preferably at least about 1.5; and / or

[0042] - can be formed in a maximum of about 20, preferably in a maximum of about 10, most preferably in a maximum of about 4.

[0043] Regarding the magnitude of the voltage applied to the electrodes, it has proven advantageous to set the magnitude of the electrical voltage applied to the electrodes (or, in the case of repeated reversals of the electrode polarity, the magnitude of the amplitude of the electrical voltage) between approximately 5 V and approximately 20 V, particularly between approximately 6 V and approximately 15 V, and preferably between approximately 8 V and approximately 12 V. Furthermore, when the polarity is reversed, the magnitude of the electrical voltage applied to the electrodes (or, in the case of repeated reversals of the electrode polarity, the magnitude of the amplitude of the electrical voltage) can preferably remain essentially unchanged; that is, when the polarity of a respective electrode is temporarily reversed, only the sign of the electrical voltage changes, while its mathematical magnitude remains essentially unchanged.In terms of the device design, it is advantageous in this context that the control and / or regulating device for controlling and / or regulating the electrical voltage applied to the electrodes is designed such that the magnitude of the electrical voltage (or, in the case of repeated reversals of the electrode polarity: the magnitude of the amplitude of the electrical voltage) is at least between approximately 5 V and approximately 20 V, in particular at least between approximately 6 V and approximately 15 V, preferably at least between approximately 8 V and approximately 12 V. Alternatively or additionally, it is preferably provided that, when the polarity is reversed, the magnitude of the electrical voltage applied to the electrodes (or, in the case of repeated reversals of the electrode polarity: the magnitude of the amplitude of the electrical voltage) remains essentially unchanged.The latter can be achieved, for example, by means of a bridge circuit also known as an "H-circuit".

[0044] If, during the electrochemical polishing of the workpieces, the polarity of the electrical voltage applied to the electrodes is temporarily reversed several times, particularly in periodic succession, it may preferably be provided that the sum of each time interval in which the first electrode, in conductive contact with the electrolyte medium, has a negative voltage and the second electrode, in conductive contact with the workpiece, has a positive voltage, and of a subsequent time interval in which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed, is between approximately 0.001 s and approximately 0.1 s (corresponding to a frequency of approximately 10 Hz to approximately 1000 Hz), in particular between approximately 0.002 s and approximately 0.05 s (corresponding to a frequency of approximately 20 Hz to approximately 500 Hz), preferably between approximately 0.005 s and approximately 0.02 s (corresponding to a frequency between approximately 50 Hz and approximately 200 Hz); i.e., within the aforementioned time intervals, a processing phase takes place in which the workpiece is anodically contacted (with positive voltage) in the usual manner, as well as a processing phase in which the polarity of the electrical voltage has been reversed and the workpiece is subjected to a negative, but e.g., equal in magnitude, electrical voltage.

[0045] In terms of the device design, it can therefore be advantageously provided that the control and / or regulating device for controlling and / or regulating the electrical voltage applied to the electrodes is designed such that the sum of each time interval in which the first electrode has a negative voltage and the second electrode has a positive voltage, and of a subsequent time interval in which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed, is at least between about 0.001 s and about 0.1 s, in particular at least between about 0.002 s and about 0.05 s, preferably at least between about 0.005 s and about 0.02 s.

[0046] Furthermore, in the advantageous embodiment of the inventive method, in which the polarity of the electrical voltage applied to the electrodes is temporarily reversed several times, particularly in periodic sequence, during the electrochemical polishing of the workpieces, the electrical voltage applied to the electrodes can be, for example, essentially rectangular, triangular, or wave-shaped, although other voltage shapes, such as sawtooth or the like, are also conceivable. In this case, a corresponding electrochemical polishing device has, for example,a voltage source designed to generate an essentially rectangular, triangular and / or wave-shaped electrical voltage; and / or the control and / or regulating device of the apparatus may, for example, be designed to control and / or regulate the electrical voltage applied to the electrodes to an essentially rectangular, triangular and / or wave-shaped electrical voltage.

[0047] As already mentioned, the inventive method is particularly suitable – although not exclusively – for the electrochemical polishing of metallic workpieces which contain at least one metal from the group consisting of gold (Au), silver (Ag), platinum (Pt) and palladium (Pd) or are essentially entirely composed of these metals, but which are also suitable for workpieces which contain other precious metals, such as ruthenium (Ru), rhodium (Rh), osmium (Os) and / or iridium (Ir), and / or semi-precious metals, such as copper (Cu), or consist practically entirely of these metals. It has also proven particularly effective for precious metals which, according to the state of the art, can only be processed inadequately with a residual roughness leading to a matte appearance, such as gold-palladium and white gold-palladium alloys with a palladium (Pd) content between approximately 5 and 25% by mass, especially between approximately 8 and 20% by mass.- % , and / or with a silver (Ag) content of 0 to approximately 20 mass%, in particular up to approximately 16 mass%.

[0048] In the inventive method for the electrochemical polishing of metallic workpieces, the relative movement of the metallic workpiece with respect to the solid granular particles of the electrolyte medium can, in principle, be carried out in any manner, as is known, for example, in conventional drag or immersion finishing processes. With regard to such relative movement of the workpiece with respect to the solid granular particles of the electrolyte medium during surface treatment, this can, for example, involve...

[0049] - a rotational movement of the workpiece and / or the container, in particular essentially about an axis of symmetry of the workpiece and / or the container; and / or

[0050] - a translational movement of the workpiece in relation to the container, in particular essentially in the form of a trajectory curve; and / or

[0051] - This involves exciting the workpiece and / or the container with vibrations, e.g., using ultrasound, piezo actuators, unbalanced drives, or the like. Furthermore, to prevent damage to the workpieces from colliding with each other and / or with the container wall, it is advantageous to clamp the metallic workpiece on a workpiece holder that is movable relative to the container and also allows for easy electrical contact with the (respective) workpiece.

[0052] A corresponding device for the electrochemical polishing of metallic workpieces is therefore preferably designed such that the relative movement of the at least one workpiece holder with respect to the container is achieved by at least one relative movement from the group

[0053] - rotational movement of the workpiece holder and / or the container, in particular essentially about an axis of symmetry of the workpiece holder and / or the container;

[0054] - translational movement of the workpiece holder in relation to the container; and

[0055] - Vibration excitation of the workpiece holder and / or the container takes place, wherein the control and / or regulating device is also designed, in particular, to control and / or regulate the respective movement of the workpiece holder and / or the container.

[0056] The control and / or regulating device may further preferably include an input device, such as a keyboard, a touchscreen, or the like, which is designed for inputting at least the parameters of the electrical voltage applied to the electrodes (such as the magnitude of the voltage or its amplitude, frequency, waveform, etc.) and, in particular, also the movement parameters of the workpiece holder and / or the container. Furthermore, the control and / or regulating device may preferably include a display device, which is designed for displaying at least the parameters of the electrical voltage applied to the electrodes and, in particular, also the movement parameters of the workpiece holder and / or the container.

Claims

Patent claims 1. A method for the electrochemical polishing of metallic workpieces, wherein an electrolyte medium, which on the one hand contains a plurality of solid granular particles and on the other hand contains at least one liquid electrolyte, is placed in a container and electrically connected to a first electrode, wherein the metallic workpiece is electrically connected to a second electrode and immersed in the electrolyte medium in the container, wherein the electrodes are subjected to an electrical voltage such that the first electrode, which is in conductive contact with the electrolyte medium, has a negative voltage and the second electrode, which is in conductive contact with the workpiece, has a positive voltage, and wherein the workpiece is moved relative to the plurality of solid granular particles of the electrolyte medium in order to polish it electrochemically, characterized in thatthat the polarity of the electrical voltage applied to the electrodes is temporarily reversed at least once during the electrochemical polishing of the workpiece, so that the first electrode, which is in conductive contact with the electrolyte medium, temporarily has a positive voltage and the second electrode, which is in conductive contact with the workpiece, temporarily has a negative voltage.

2. Method according to claim 1, characterized in that an electrolyte medium is used in which the interparticle spaces between the granule particles are at least partially, in particular substantially, borrowed completely, filled with the liquid electrolyte.

3. Method according to claim 1 or 2, characterized in that the polarity of the electrical voltage applied to the electrodes is temporarily reversed several times, in particular at substantially equal time intervals, during the electrochemical polishing of the workpiece, so that the first electrode, which is in conductive contact with the electrolyte medium, has a positive voltage several times temporarily and the second electrode, which is in conductive contact with the workpiece, has a negative voltage several times temporarily.

4. A method according to any one of claims 1 to 3, characterized in that, during the electrochemical polishing of the workpiece, the total duration during which the polarity of the electrical voltage applied to the electrodes is temporarily reversed is less than the total duration during which the first electrode in conductive contact with the electrolyte medium has a negative voltage and the second electrode in conductive contact with the workpiece has a positive voltage, wherein, during the electrochemical polishing of the workpiece, the ratio between the total duration during which the first electrode in conductive contact with the electrolyte medium has a negative voltage and the second electrode in conductive contact with the workpiece has a positive voltage,and the total duration with temporarily reversed polarity of the electrical current applied to the electrodes, Voltage, in particular, at least 1.1, preferably at least 1.3, most preferably at least 1.5; and / or - at most 20, preferably at most 10, most preferably at most 4, is set.

5. Method according to one of claims 1 to 4, characterized in that the magnitude of the electrical voltage applied to the electrodes - is set between 5 V and 20 V, in particular between 6 V and 15 V, preferably between 8 V and 12 V; and / or - remains essentially unchanged when the polarity of the electrical voltage applied to the electrodes is reversed.

6. Method according to one of claims 3 to 5, characterized in that the sum of each time interval in which the first electrode, which is in conductive contact with the electrolyte medium, has a negative voltage and the second electrode, which is in conductive contact with the workpiece, has a positive voltage, and of a subsequent time interval in which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed, is set between 0.001 s and 0.1 s, in particular between 0.002 s and 0.05 s, preferably between 0.005 s and 0.02 s.

7. Method according to one of claims 3 to 6, characterized in that the electrical voltage applied to the electrodes is essentially rectangular, triangular or wave-shaped.

8. Method according to one of claims 1 to 7, characterized in that the electrochemically polished metallic workpieces contain at least one metal from the group of precious metals, in particular from the group of gold (Au), silver (Ag), platinum (Pt) and palladium (Pd), or are substantially entirely composed of such metals.

9. Method according to any one of claims 1 to 8, characterized in that the relative movement of the metallic workpiece with respect to the electrolyte medium contained in the container is controlled by at least one relative movement from the group - rotational movement of the workpiece and / or the container, in particular essentially around an axis of symmetry of the workpiece and / or the container; - translational movement of the workpiece in relation to the container; and - Vibration excitation of the workpiece and / or the container occurs.

10. Method according to one of claims 1 to 9, characterized in that the metallic workpiece is clamped on a workpiece holder movable relative to the container.

11. Device for electrochemical polishing of metallic workpieces, in particular for carrying out a method according to one of the preceding claims, comprising: - at least one container for holding an electrolyte medium which contains, on the one hand, a plurality of solid granular particles and, on the other hand, at least one liquid electrolyte; - at least one first electrode, which is located inside the arranged in the container and / or in an electrically conductive connection with the container; - at least one workpiece holder that can be moved relative to the container for the detachable fastening of the workpieces; - at least one second electrode which is in electrically conductive contact with the at least one workpiece holder; - at least one voltage source to apply an electrical voltage to the electrodes such that the first electrode has a negative voltage and the second electrode has a positive voltage; and - a control and / or regulating device programmed with respect to the electrical voltage applied between the electrodes, characterized in that the control and / or regulating device is designed to at least once temporarily reverse the polarity of the electrical voltage applied to the electrodes during operation, so that the first electrode temporarily has a positive voltage and the second electrode temporarily has a negative voltage.

12. Device according to claim 11, characterized in that the container receives electrolyte medium in which the interparticle spaces between the granule particles are at least partially, in particular substantially completely, filled with the liquid electrolyte.

13. Device according to claim 11 or 12, characterized in that the control and / or regulating device is designed to repeatedly reverse the polarity of the electrical voltage applied to the electrodes, particularly at substantially equal time intervals, during operation, so that the first electrode temporarily has a positive voltage several times and the second electrode temporarily has a negative voltage several times.

14. Device according to one of claims 11 to 13, characterized in that the control and / or regulating device is further configured to control and / or regulate the total duration during which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed during operation to a value smaller than the total duration during which the first electrode has a negative voltage and the second electrode has a positive voltage, wherein the control and / or regulating device is particularly configured to control and / or regulate the ratio between the total duration during which the first electrode has a negative voltage and the second electrode has a positive voltage and the total duration with temporarily reversed polarity of the electrical voltage applied to the electrodes to a value smaller than the total duration during which the first electrode has a negative voltage and the second electrode has a positive voltage. - at least 1, 1, preferably at least 1, 3, most preferably at least 1, 5; and / or - at most 20, preferably at most 10, most preferably at most 4, is trained.

15. Device according to one of claims 11 to 14, characterized in that the control and / or regulating device for controlling and / or regulating the electrical voltage applied to the electrodes is designed such that- The fact is that the magnitude of the electrical voltage - at least between 5 V and 20 V, in particular at least between 6 V and 15 V, preferably at least between 8 V and 12 V; and / or - remains essentially unchanged when the polarity of the electrical voltage applied to the electrodes is reversed.

16. Device according to one of claims 11 to 15, characterized in that the control and / or regulating device for controlling and / or regulating the electrical voltage applied to the electrodes is designed such that the sum of each time interval in which the first electrode has a negative voltage and the second electrode has a positive voltage, and of a subsequent time interval in which the polarity of the electrical voltage applied to the electrodes has been temporarily reversed, is at least between 0.001 s and 0.1 s, in particular at least between 0.002 s and 0.05 s, preferably at least between 0.005 s and 0.02 s.

17. Device according to one of claims 11 to 16, characterized in that - the voltage source for generating an essentially rectangular, triangular and / or wave-shaped electrical voltage and / or - the control and / or regulating device for controlling and / or regulating the electrical voltage applied to the electrodes is designed to produce an essentially rectangular, triangular and / or wave-shaped electrical voltage.

18. Device according to one of claims 11 to 17, characterized in that the relative movement of the at least one workpiece holder with respect to the container is effected by at least one relative movement from the group - rotational movement of the workpiece holder and / or the container, in particular essentially about an axis of symmetry of the workpiece holder and / or the container; - translational movement of the workpiece holder in relation to the container; and - Vibration excitation of the workpiece holder and / or the container takes place, wherein the control and / or regulating device is also designed, in particular, to control and / or regulate the respective movement of the workpiece holder and / or the container.

19. Device according to one of claims 11 to 18, characterized in that the control and / or regulating device - an input device designed for inputting at least the parameters of the electrical voltage applied to the electrodes, in particular also the movement parameters of the workpiece holder and / or the container; and / or - a display device which is designed to display at least the parameters of the electrical voltage applied to the electrodes, in particular also the movement parameters of the workpiece holder and / or the container.