ELECTROPOLISHING METHOD AND ELECTROLYTE FOR SAME

Abstract

The invention relates to an electrolyte for electropolishing metal surfaces, said electrolyte comprising methanesulphonic acid and additionally at least one phosphonic acid, as well as to an electropolishing method for same.

Claims

1. An electrolyte for electropolishing metal surfaces, wherein the electrolyte comprises methanesulfonic acid and at least one phosphonic acid.

2. An electrolyte according to claim 1, wherein the at least one phosphonic acid is selected from the group consisting of mono-, di-, and polyphosphonic acids and mixtures thereof.

3. An electrolyte according to claim 1, wherein the at least one phosphonic acid is contained at a concentration of from 0.1% by weight to 10% by weight.

4. An electrolyte according to claim 1, further comprising at least one polyalcohol.

5. An electrolyte according to claim 4, wherein the at least one polyalcohol is contained at a concentration of up to 10% by weight.

6. An electrolyte according to claim 1, further comprising one or more additives selected from the group consisting of mineral acids at a concentration of up to 50% by weight, fluorides at a concentration of up to 20% by weight, and amines at a concentration of up to 15% by weight.

7. An electrolyte according to claim 1, wherein the electrolyte contains additional additives, inhibitors or complexing agents.

8-11. (canceled)

12. An electropolishing method for metal components produced in 3D printing, wherein at least one component to be machined functions as a first electrode and at least one second electrode is provided as a counter electrode, and at least a partial removal of a portion of the component surface occurs in an electrolyte bath with an electrolyte according to claim 1 by applying current to the component, wherein the current is applied in the form of repeating pulse sequences, wherein at least one anodic pulse is provided, the current intensity of which displays a steady increase over the course of time up to a specifiable value.

13. A method according to claim 12, wherein the increase is linear, non-linear or exponential.

14. A method according to claim 12, wherein the anodic pulse displays micropulses subsequent to the increase.

15. A method according to claim 12, wherein at least one second pulse adjoins the at least one anodic pulse, wherein the at least second pulse is different from the first pulse, and the at least first pulse and the at least second pulse form a repeating pulse sequence.

16. A method according to claim 12, wherein the pulses have an average current density of 0.5 A/dm.sup.2 to 30 A/dm.sup.2.

17-18. (canceled)

19. An electrolyte according to claim 2, wherein the polyphosphonic acid is amino-tris(methylenephosphonic acid).

20. An electrolyte according to claim 4, wherein the polyalcohol is selected from the group consisting of glycol, glycerin, polyvinyl alcohol, inositol, sorbitol, and mixtures thereof.

21. An electrolyte according to claim 6, wherein the mineral acid comprises phosphoric acid or sulfuric acid.

22. An electrolyte according to claim 6, wherein the fluoride is ammonium difluoride.

23. An electrolyte according to claim 6, wherein the amine is selected from the group consisting of ethanolamines and isopropanolamines.

24. An electrolyte according to claim 7, wherein the additional additives comprise a wetting agent.

25. A method according to claim 15, wherein the repeating pulse sequence is interrupted by a pulse pause, a cathodic pulse, or a combination thereof.

Description

[0025] The invention will be explained in further detail below on the basis of non-limiting exemplary embodiments. Percentages are herein understood as percent by weight, unless otherwise specified.

[0026] In preparation for the electrochemical post-machining of 3D-printed parts, a mechanical cleaning, for example by blasting or shot peening, is carried out in a first step in order to remove metal powder not attached to the component, which metal powder adheres loosely or, respectively, has accumulated in cavities and undercuts.

[0027] After this cleaning step, the component is mechanically fixed at a suitable location, electrically contacted, dipped into the electrolyte according to the invention and anodically loaded according to an electrochemical method adapted to the material and the geometry of the component.

[0028] In doing so, the concentrations of the individual components of the electrolyte are adjusted such that a predefined final roughness of the component surface is achieved.

[0029] Depending on the requirement, the current that is used can be a direct current, a unipolar pulse current or a bipolar reverse pulse current. The combination of different methods is possible as well.

[0030] The bath temperature is between 20 C. and 75 C. and is also adapted to the workpiece to be treated.

[0031] An improvement of the results is achieved if an agitation of the electrolyte by pumping and/or stirring is provided in order to achieve an effective electrolyte circulation in places where the largest removal is to occur.

EXAMPLE 1: POST-TREATMENT OF A 3D-PRINTED COMPONENT MADE OF TI6AL4V

[0032] A 3D-printed component for technical applications made of the titanium alloy Ti6Al4V is removed from the 3D printer, mechanically pre-cleaned and electrically contacted. Subsequently, the component is treated for 30 minutes in an electrolyte bath consisting of 98% methanesulfonic acid, 2% amino-tris(methylenephosphonic acid) at a temperature of 50 C., at an average voltage of 20 V and at an average current density of 12.5 A/dm.sup.2 using a pulse current. Subsequently, the component is rinsed with deionized water and dried by means of compressed air.

[0033] In FIG. 1, an SEM image of a surface area of the component is depicted before the implementation of the method according to the invention as described above. FIG. 2 shows this surface after the implementation of the method according to the invention. In this case, the Ra value of 15 m is reduced to 3 m after the post-treatment according to the invention.

EXAMPLE 2: POST-TREATMENT OF A 3D-PRINTED COMPONENT MADE OF ALMGSI10

[0034] After mechanical cleaning and electrical contacting, a 3D-printed component made of the alloy AlMgSi10 with high silicon content is smoothed for 40 minutes in an electrolyte consisting of 4.4% methanesulfonic acid, 45.6% phosphoric acid, 32.7% sulfuric acid, 4.5% triethanolamine, 0.4% amino-tris(methylenephosphonic acid) and 12.4% ammonium hydrogen difluoride at a voltage of 18 V and a current density of 4 A/dm.sup.2. Subsequently, the component is rinsed with deionized water and dried by means of compressed air.

[0035] FIG. 3 and FIG. 4 again show an SEM image of the surface of the component before and, respectively, after the implementation of the method according to the invention, wherein the determined Ra value has decreased from 1.4 m to 0.3 m.

EXAMPLE 3: POST-TREATMENT OF A 3D-PRINTED COMPONENT MADE OF TI6AL4V

[0036] A 3D-printed component for technical applications made of the titanium alloy Ti6Al4V is removed from the 3D printer, mechanically pre-cleaned and electrically contacted. Subsequently, the component is treated for 30 minutes in an electrolyte bath consisting of 98% methanesulfonic acid, 1.5% amino-tris(methylenephosphonic acid) and 0.5% inositol at a temperature of 45 C., at an average voltage of 20 V and at an average current density of 5 A/dm.sup.2 using a pulse current. Subsequently, the component is rinsed with deionized water and dried by means of compressed air.

[0037] The surface of the component is shown in FIG. 5, and it has an Ra value of 15 m. After the treatment of the component in the manner as described above by the method according to the invention, the Ra value was only 3 m. In FIG. 6, the smoothing of the surface of the component treated according to the invention is evident.

EXAMPLE 4: POST-TREATMENT OF A 3D-PRINTED COMPONENT MADE OF TI6AL4V

[0038] After mechanical cleaning and electrical contacting, a 3D-printed component for medical applications is smoothed for 60 minutes in an electrolyte consisting of 90% methanesulfonic acid, 1.5% 1-hydroxyethane-(1,1-diphosphonic acid), 3% amino-tris(methylenephosphonic acid) and 5.5% glycol at a voltage of 22 V and a current density of 10 A/dm.sup.2 using a direct current. Subsequently, the component is rinsed with deionized water and dried by means of compressed air.

[0039] As shown in FIG. 7 in an SEM image of the surface, this component has a lattice-like structure, the roughness of which is caused by powder residues from 3D printing which adhere to the surface. After the treatment by means of the method according to the invention, those particle residues are removed virtually completely (FIG. 8).

[0040] In FIG. 9, a typical pulse sequence of 100 is illustrated which, according to the invention, comprises an anodic pulse 110, the current intensity j+ of which displays a steady increase 111 over the course of time up to a specifiable value J1. This anodic pulse 110 maintained over a certain time t1 is superimposed with micropulses 112, i.e., higher-frequency multipulses. A cathodic pulse 120 in rectangular shape adjoins this anodic pulse 110.

[0041] This pulse sequence 100 consisting of an anodic pulse 110 and a cathodic pulse 120 is repeated until the desired removal and, associated therewith, the desired surface quality are achieved. The duration and magnitude of the steady increase 111, namely the slope or, respectively, ramp, depends on the initial roughness and the consequent necessary etching time. Number and height of the micropulses 112 are material-dependent.

EXAMPLE 5: SMOOTHING OF A COMPONENT MADE OF A TITANIUM ALLOY (TI6AL4V)

[0042] The 3D-printed component with an initial roughness of Ra=20 m made of a titanium alloy is treated as follows: [0043] Cleaning of the component, especially degreasing and rinsing [0044] Deburring by means of electrochemically supported etching and another rinsing [0045] Smoothing of the surface of the component using the method according to the invention:
In this case, the anodic pulse consists of a ramp with a current density of 0 to 5 A/dm.sup.2 and rising and a subsequent pulse pattern of 5 A/dm.sup.2 and 20 A/dm.sup.2 at a frequency of 2 Hz.

[0046] The electrolyte consists of: [0047] 98% methanesulfonic acid [0048] 1% amino-tris(methylenephosphonic acid) [0049] 1% water [0050] The temperature of the electrolyte bath is 50 C. [0051] Rinsing [0052] Drying

[0053] The roughness of the machined component is reduced by this surface treatment to Ra=1.8 m. The resulting surfaces meet the requirement with regard to the surface roughness for the given application, further machining is not required therefor. However, depending on the application, a further functionalization of the surface may occur.