System and electrode apparatus for electrochemical polishing of channels

Abstract

The invention relates to a system, apparatus and method for the effective provision of a polishing effect on surfaces of a wall of a channel of a workpiece using electrochemical polishing. The invention includes an electrolyte solution into which the workpiece is placed and an electrode member which is passed along the channel with the wall which is to be polished. The electrode member includes a conductive core and an insulating assembly. The insulating assembly is provided to maintain a gap between the surface of the conductive core and the wall of the channel so as to prevent short circuiting whilst allowing the polishing effect to be achieved. The insulating assembly includes one or more insulating members spaced along the conductive core and depending outwardly therefrom and the electrode member is sufficiently flexible so as to pass along the channel and follow the form of the channel, thus ensuring a substantially uniform polishing effect is created on the wall of the channel.

Description

[0001] System and Electrode Apparatus for Electrochemical Polishing of Channels

[0002] The present invention relates generally to the field of electrochemical polishing, and more specifically to a system and electrode apparatus for achieving relatively uniform electrochemical polishing of the surfaces of a wall of a length of an internal channel of a workpiece.

[0003] Electrochemical polishing is a widely used technique for the finishing of metal components by inducing a reduction reaction across the surface of the same, as it offers a variety of benefits such as improved surface quality, reduced friction, and enhanced corrosion resistance. The process of electrochemical polishing involves locating a positively charged workpiece to be polished within a chamber and also providing within the chamber a negatively charged member which acts as a cathode and submerging the two electrodes in an electrolyte solution (typically a mixture of acids, salts or the like) held in the chamber. An electrical current, typically a DC current, is passed through the solution and the current causes the metal at the surface of the metal workpiece to dissolve, and in particular causing surface irregularities and peaks to dissolve preferentially, thus creating a relatively smooth, uniformly polished surface. The process can be used to deburr, remove imperfections, and improve the surface finish of various metal workpieces.

[0004] The rate of reduction at the surface of the workpiece is typically directly proportional to the distance between the surface of the workpiece to be polished and the cathode.

[0005] Internal surfaces of a workpiece, and particularly channels formed through the workpiece, are often not directly facing the cathode and as such the level of reduction is reduced or minimal and hence creates a reduced and / or non-uniform polishing effect. This often leads to internal channels that have a lower quality polished effect relative to the external surface areas of the workpiece, and this may require a secondary polishing process using conventional mechanical means to be used which requires additional tooling, time and associated costs.

[0006] However, if the cathode is brought into direct mechanical and hence electrical contact with the workpiece, a short circuit occurs wherein the electron transfer across the power supply occurs at the contact point between the electrodes, rather than across and through the electrolyte solution. This results in a highly localised area of reduction which may damage the wall surface and so does not achieve the desired polishing effect on the workpiece wall surface.

[0007] An aim of the present invention is therefore to provide apparatus to achieve effective and uniform electrochemical polishing of a relatively complex surface, such as the wall surface of an internal channel of a workpiece. A further aim is to provide a means to ensure there is a reduced risk short-circuiting occurring between the electrodes of the electrochemical polishing apparatus when being used in relatively complex shapes.

[0008] In a first aspect of the invention, there is provided a system for use in the electrochemical polishing of a workpiece, said system including an electrolyte solution into which the workpiece is placed; a power supply for connection to the workpiece and an electrode member selectively placed into the electrolyte solution and along a channel formed in the workpiece and wherein the electrode member includes a conductive core connectable to the said power supply so as to be oppositely charged to the said workpiece and an insulating assembly configured such that the conductive core is spaced from electrical contact with walls of the channel by the said insulating assembly.

[0009] In one embodiment of the invention the said insulating assembly is configured along the conducting core such that the core is prevented from contacting the workpiece channel walls when in use.

[0010] Typically the insulating assembly is formed so as to significantly resists the passage of electrical current through the same.

[0011] Thus, the contact of the conductive core with the workpiece, which would otherwise short-circuit the system and prevent electrochemical polishing through the electrolyte solution taking place, is prevented by the provision of the insulating assembly. Typically the insulating assembly includes a plurality of insulating members interspaced along a length of the conductive core. In one embodiment the insulating member is formed by one or more brisdes extending substantially perpendicularly from the conductive core. Typically the bristles are resiliently biased towards extending outwardly from the conductive core.

[0012] In another embodiment the insulating member is an expandable member. In one embodiment the insulating member is expandable by the flow of fluid from a pumping means flowing into the extendable member and acting on an internal surface of the expandable member.

[0013] In one embodiment the expansion of the expandable member is controlled by a control means. In another embodiment the expandable member is configured to expand to substantially the same diameter as the diameter of the channel in which the electrode member is to be inserted in use.

[0014] In one embodiment the insulating assembly includes a deburring element such that the wall of the channel of the workpiece is mechanically deburred by the electrode member as it is passed through the channel in use. Typically the deburring element includes one or more portions of a relatively hardened material located on an external surface of the insulating assembly.

[0015] In one embodiment the electrode member includes an insulated stop member. In one embodiment the said stop member is located at a leading end of the electrode member with respect to the direction of insertion of the electrode member through the channel such that the stop member prevents contact between the conductive core and an end wall of, for example, a blind channel into which the electrode member is inserted.

[0016] In one embodiment the electrode member is a degree of flexibility sufficient to allow the electrode member to flex when it is inserted along a channel of the workpiece with a non-linear profile and to follow the form of the same.

[0017] Typically the electrode member has an elongate profile. Typically the conductive core is formed of a conductive metal material.

[0018] Typically relative movement between the electrode member and wall of the channel is possible such that the core member and / or the insulating member are variably exposed to the wall of the workpiece channel so as to provide a substantially uniform polishing effect along the channel. In one embodiment said movement is linear along the longitudinal axis of the channel and / or rotatable about the said longitudinal axis.

[0019] Typically the electrode member is negatively charged and the workpiece is positively charged when connected to the power supply in use.

[0020] In one embodiment the electrolyte solution is an ionic solution. Typically the electrolyte solution includes sodium chloride and / or sodium nitrite.

[0021] In one embodiment the electrolyte solution includes a particulate material to provide a physical polishing effect on the workpiece wall of the channel as it flows along the same and provide a physical polishing effect.

[0022] In one embodiment the insulating members of the insulating assembly extend outwardly from the conductive core such that the insulating members substantially span the gap between the outer surface of the conductive core and the wall of the channel in which the electrode member is inserted in use.

[0023] In one embodiment, the insulating assembly includes a series of insulating member in the form of bead elements of insulating material. In one embodiment the bead elements are typically spaced apart at respective fixed locations along at least part of the conductive core. Typically in this embodiment, in which the conductive core may litde rigidity, the electrode member is inserted along the channel with the assistance of a compressed gas and / or a fluid which is pumped into and along the said channel.

[0024] In one embodiment, the insulating assembly includes a series of insulating members configured to receive the conductive core to form, in combination, the elongate electrode member. Typically the conductive core is formed by a number of pivotally connected elements so as to maintain electrical connection along the conductive core.

[0025] Typically the electrode member is capable of flexing about at least one axis so as to allow the same to flex as it follows the form of the channel wall as it moves therealong and retain a gap between the conductive core and the channel wall. In one embodiment the electrode member is capable of flexing about a plurality of axes perpendicular to the longitudinal axis of the elongate member.

[0026] In a further aspect of the invention, there is provided an electrode member for use in electrochemical polishing, said electrode member including a conductive core and an insulating assembly located at least partially therealong and wherein the insulating assembly is configured to prevent contact between the conductive core and a wall of a channel win which the electrode member is inserted in use.

[0027] Specific embodiments of the invention will be described with reference to the following figures, wherein:

[0028] Figure 1 illustrates an electrochemical polishing system in accordance with one embodiment of the invention;

[0029] Figure 2 illustrates an electrode member in accordance with one embodiment of the invention;

[0030] Figure 3 illustrates a cross section of a linear blind channel of a workpiece being electrochemically polished by the electrode member of Figure 2;

[0031] Figure 4 illustrates a cross section of a non-linear through channel of a workpiece being electrochemically polished by the electrode member of Figure 2;

[0032] Figure 5a illustrates a cross section of an expandable electrode member in an unexpanded configuration in accordance with another embodiment of the invention;

[0033] Figure 5b illustrates a cross section of the expandable electrode member of Figure 5a in an expanded configuration; and Figures 6a- b illustrate the expansion of the electrode member of Figures 5a-b within a non-linear through channel of a workpiece to be electrochemically polished.

[0034] Figure 7a illustrates an electrode member in accordance with one embodiment of the invention; and Figures 7b-c illustrates a cross section of a non-linear through channel of the workpiece being electrochemically polished by the electrode member of Figure 7a;

[0035] Figures 8a-f illustrates an electrode member in accordance with one embodiment of the invention; and

[0036] Figure 8g illustrates a cross section of a non-linear through channel of the workpiece being electrochemically polished by the electrode member of Figures 8a- f;

[0037] Referring firstly to Figure 1, there is illustrated a system for electrochemically polishing one or more surfaces of a workpiece 2. In this embodiment the workpiece includes a plurality of channels 4,6. Channel 4 is a linear blind channel of a fixed diameter along its length extending from an external face of the workpiece 2 towards the centre of the same. Channel 6 is a non-linear channel that extends from a first face of the workpiece along a curved profile to emerge from a second, perpendicular face and the apparatus and system is particularly provided to achieve an effective polishing effect of the wall of these types of channels.

[0038] To perform the electropolishing effect the workpiece 2 is submerged in an ionic electrolyte solution 8 contained within a chamber 10. In addition an electrode member 12 is provided within the electrolyte solution 8, separate from the workpiece 2. Both the electrode member 12 and the workpiece 2 are connected to a power supply 14 such that a conductive core of the electrode member 12 is connected to a negative terminal of the power supply 14 so as to be negatively charged and the workpiece 2 is connected to a positive terminal of the power supply 14 so as to be positively charged when the power supply 14 is activated. Thus, the workpiece 2 and electrode member 12, upon activation of the power supply 14, act as an anode and cathode respectively. The rate of reduction on the channel wall 2 is determined by the distance between the wall and the cathode which is the conductive core of the electrode member 12. However if the electrode member 12 is located remotely from the channels within the solution 8, the walls of the channels 4,6 experience little to no reduction, and are therefore unable to be polished.

[0039] This problem is overcome in the current invention by the provision of the electrode member in the form as will now be described as, upon activation of the power supply 14, with the electrode member inserted along one of the channels 4 or 6, the electrolyte solution 8 allows for reduction of the metal at the wall of the said channel of the positively charged workpiece 2 and, thus, the said wall is electrochemically polished.

[0040] The electrode member 12 in accordance with the invention is movable with respect to the workpiece 2 and has an elongate and flexible profile. The electrode member 12 may be inserted within and along a selected channels 4,6 so to bring the gap between the conductive core of the electrode member 12 and the channel wall to a distance so as to enable effective reduction and polishing to occur on the wall of the channel in which it is inserted.

[0041] Referring to Figure 2, there is illustrated the electrode member 20 in accordance with one embodiment of the invention. The electrode member 20 includes a conductive core 22 and an insulating assembly formed by a series of insulating members 24. The core 22 is formed of an elongate, flexible and electrically conductive material such that the core may act as the electrode. The insulating members 24 in this example are groups of bristles, with the brisdes being elongate members of a resiliently biased material, such as plastic, that is substantially resistant to electrical current passing through the same, such as plastic.

[0042] In this embodiment the electrode member 20 includes an insulating member 26 extending from an end 28 of the core. The electrode member 20 further includes a cable 30 extending from the core 22 to connect the same to the power supply 14 to charge the same. Figure 3 illustrates the insertion of the electrode member 20 along the length of the channel 4 of the workpiece 2. The conductive core 22 extends substantially along the length of the channel 4, and so allows reduction and hence polishing to occur along the length of the channel. The bristles 24 which extend perpendicularly from the surface of the conductive core 22 ensure that there is a gap between the conductive core 22 and the wall of the channel 4, preventing an electrical short circuit. The end bristle 26 extends perpendicular to the face of the end 28 of the core and prevents the core 22 from contacting the end wall of the blind channel 4 whilst ensuring the same experiences reduction.

[0043] Figure 4 illustrates the insertion of the electrode member 20 along the through channel 6 of the workpiece. The flexible material of the electrode core 22 allows the same to follow the profile of the channel as it curves between the two perpendicular faces of the workpiece 2 and ensures that the entire length of the channel 6 experiences reduction and hence uniform activation of the power supply 14.

[0044] The bristles 24 at their free ends may include end caps of a hardened material, such as metal, that may act to deburr the walls of the channels 4,6.

[0045] Figures 5a-b illustrate a further embodiment of an electrode member 40 formed of a conductive core 42 and an insulating assembly including a plurality of insulating members 44. The core 42 includes an internal passage 46 with an inlet connected to a supply line 48 which is connected to a pump (not shown). The core 42 includes a plurality of outlets 50 interspaced along its length.

[0046] Pivotably connected with the core 42 are a number of insulating members 44 that are movable between a retracted position as shown in Figure 5a and an expanded position as shown in Figure 5b. The insulating members 44 are formed of an insulating material, and have a curved profile to direct the flow of expelled electrolyte towards the rear of the core 42. In the retracted position, the insulating members 42 partially overlap. The pivotable connection includes a stop to limit the movement of the insulating members 42 in the expanded position. The conductive core 42 is electrically charged via cable connection 43 to the power supply. In use, the pump is activated, and a fluid is supplied along the supply line 48 into the internal passage 46 and is expelled through the plurality of outlets 50. The fluid expelled from the outlets 50 as indicated by arrows 52 act on an internal surface of the insulating members 52 and forces the same outwards and away from the core 42 in the expanded position. If the flow of the pump is reversed, the insulating members 44 are drawn towards the core 42 in the retracted position. In this example, the fluid supplied by the pump is electrolyte solution 8 drawn from the chamber 10.

[0047] In another example, the pivotable connections of the insulating members 44 are biased towards the retracted position such that the insulating members 44 are in the retracted position when the pump is deactivated.

[0048] Figure 6a illustrates the insertion of the electrode member 40 along the through channel 6 of the workpiece 2. On insertion of the electrode 40, the pump flow is reversed such that the insulating members 44 are drawn into the retracted position, as shown in Figure 6a. The electrode member is then passed along the length of the chamber 6 such that reduction may occur along its entire length. On insertion of the electrode member 40, the core 42 is located closer to one wall of the channel 6 than the other, which may otherwise result in unequal polishing of the walls of the channel.

[0049] The pump is activated and the insulating members 44 expand to the expanded position as shown in Figure 6b. The uniform output of fluid from the outputs 50 ensure that an equal expansion force is applied to the insulating members 44 and the longitudinal axis of the conductive core 42 is substantially aligned with the longitudinal axis of the channel 6, ensuring equal reduction along the length of the channel 6.

[0050] Figure 7a illustrates another embodiment of an electrode member 52. In this embodiment the electrode member 52 includes a conductive core 54 and an insulating assembly formed by a plurality of insulating members 56 in the form of insulating bead members and located at, typically fixed, locations along the conductive core. The core 54 is formed of an elongate, flexible and electrically conductive material such that the core may act as the electrode. The series of insulating bead members 56 in this embodiment are interspaced along the length of the core 64 so that, in combination with the conductive core, there is formed an electrode member 52 that is capable of bending in at least one, but typically around all axes perpendicular to the longitudinal axis of the electrode member. The insulating bead members 56 are comprised of a material that is substantially resistant to electrical current passing through the same.

[0051] Figure 7b-c illustrates the insertion of the electrode member 52 in electrolyte solution 8 through a through channel 53. Insertion of the electrode member 52 can be achieved by application of a compressed gas and / or a fluid through the channel in the direction indicated by arrow 58. The insulating bead members 56 prevent contact between the wall of the channel 53 and the conductive core 54 so that the core can be located along the length of the channel 53 such that reduction and polishing effect occur along the length of the channel on activation of a power supply.

[0052] Figure 8a-f illustrates another embodiment of an electrode member 60. The electrode member 60 in this embodiment includes an insulating assembly formed by a plurality of insulating members 64 and a conductive core 62 formed of electrically conductive material elements which are pivotally connected 67 so as to maintain electrical connection along the core and hence the electrode member. The series of insulating members 64 are in the form of blocks containing at least one recess 65. The recesses 65 are configured to receive the core elements therein and which pass therethrough in pivotal interconnection 62. Thus, in this embodiment the electrode member 60 is formed of a length of interchanging elements of core 62 and insulating members 64 wherein there is pivotal connection 67 between the elements of the core between each other and possibly also with the insulating members so as to form an articulated electrode member 60 such that the same is capable of bending in at least one direction. Figure 8g illustrates the insertion of the electrode member 60 in electrolyte solution 8 through the through channel 53. On insertion of the electrode member 60, the bendable, articulating length of the same allows for enhanced manoeuvrability of the electrode member along the non-linear through channel 53. The core 62 is located along the length of the channel 53 such that reduction and polishing effect occur along its length on activation of a power supply. It should be appreciated that aforementioned embodiments of the electrode member may provide a further enhanced polishing effect in the event that the electrode member is moved back and forth and / or in a progressive manner longitudinally and / or rotatably through and / or along the channel. For example, in Figure 8g the electrode member 60 is moveable relative to the through channel 53 in the directions indicated by arrow 66. Movement of the electrode member 60 would allow regions of the through channel 53 to be variably exposed to the core 62 and the insulating members 64 in order to provide an enhanced polishing effect to the through channel due to increased exposure to the conductive core and thereby removing the possibility of any masking effect on the conductivity which may be caused by the insulating members being held at the same location in the channel for the duration of the polishing operation.

[0053] It will be appreciated by a person skilled in the art that the polarities of the electrodes could be swapped and with the appropriate electrolyte solution the electrochemical process applies a plating effect of the channel wall, rather than a polishing effect.

[0054] Thus, there is provided a means to pass an electrode member through an internal channel of a workpiece to allow a substantially uniform electrochemical process to occur along its length. There is also provided a means to insulate the electrode, such that there is a reduced chance of a short circuit caused by the electrodes contacting each other, whilst the electrode is passed through the channel.

Claims

CLAIMS1.A system for use in the electrochemical polishing of a workpiece, said system including an electrolyte solution into which the workpiece is placed; a power supply for connection to the workpiece and an electrode member selectively placed into the electrolyte solution and along a channel formed in the workpiece and wherein the electrode member includes a conductive core connectable to the said power supply so as to be oppositely charged to the said workpiece and an insulating assembly configured such that the conductive core is spaced from electrical contact with walls of the channel by the said insulating assembly. A system according to claim 1 wherein the insulating member is formed of a material that significantly resists the passage of electrical current through the same and is configured so as to prevent mechanical contact between the said conductive core and walls of the channel.

2. A system according to claim 1 wherein the insulating assembly includes a plurality of insulating members interspaced along a length of the conductive core.

3. A system according to any preceding claims wherein the electrode member is elongate with a longitudinal axis and is sufficiently flexible to allow the same to flex as it is inserted along the said channel and so follow the shape of the wall of the channel and retain a gap between the conductive core and the channel wall.

4. A system according to claim 3 wherein the electrode member is capable of flexing about a plurality of axes perpendicular to the longitudinal axis of the elongate member.

5. A system according to any preceding claim wherein the electrode member is selectively moveable relative to the channel along the longitudinal axis of the channel and / or around said longitudinal axis such that the polishing effect by the conductive core on the channel wall is substantially uniform along the channel.

6. A system according to any of the preceding claim wherein the conductive core is formed of a conductive metal material.

7. A system according to any of the preceding claims wherein the electrode member is negatively charged and the workpiece is positively charged by the power supply.

8. A system according to any of the preceding claims wherein the electrolyte solution is an ionic solution.

9. A system according to claim 8 wherein the ionic solution includes sodium chloride and / or sodium nitrite.10.A system according to any of the preceding claims wherein the electrolyte solution includes a particulate material to provide a physical polishing effect on the wall of the channel as the electrolyte solution flows therealong.

11. A system according to any of the preceding claims wherein the insulating assembly includes insulating members formed by one or more bristles extending substantially perpendicularly from the conductive core.

12. A system according to claim 11 wherein the insulating members are located at spaced intervals along and / or or around the conductive core.

13. A system according to any of claims 1-10 wherein the insulating assembly includes one or more expandable members.

14. A system according to claim 14 wherein the expandable member is expanded by the flow of the electrolyte solution from a pumping means into the expandable member to act on an internal surface of the expandable member15. A system according to claims 13-14 wherein the expansion of the expandable member is controlled by a control means.

16. A system according to any of the preceding claims wherein the free end of the at least one insulating member is biased away from the conductive core to retain a gap between the surface of the conductive core and the wall of the channel.17.A system according to claims 1-10 wherein the insulating assembly includes a bead element located on the conductive core.

18. A system according to claim 17 wherein a plurality of beads are provided at spaced locations along the conductive core.

19. A system according to any of claims 1-10 wherein the insulating assembly includes a series of insulating members configured to receive the conductive core to form said electrode member.

20. A system according to claim 19 wherein the conductive core is formed of a plurality of elements pivotally and electrically connected such as to allow flexing of the conductive core and to maintain electrical connection along the conductive core.

21. A system according to any of the preceding claims wherein the electrode member is inserted along the channel by application of a compressed gas and / or a fluid through the same.22.A system according to any of the preceding claims wherein the insulating assembly includes one or more deburring elements such that the wall of the channel of the workpiece is deburred by the electrode member as it is moved along the channel.

23. A system according to claim 22 wherein the deburring elements are formed of a relatively hardened material located on an external surface of the insulating assembly.

24. A system according to any of the preceding claims wherein the electrode member includes an insulating stop member located at an end of the electrode member to prevent contact between the conductive core and an end wall of the channel of the workpiece25. An electrode member for use in electrochemical polishing, said electrode member including a conductive core and an insulating assembly located at least partially therealong and wherein the insulating assembly is configured to prevent contact between the conductive core and a wall of a channel win which the electrode member is inserted in use.

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