MIRROR FINISH POLISHER

Abstract: Described herein is a mirror finish polisher, including; a tool base to be attached to the fore end of a spindle and constituted by a disk-like front plate and a rear plate forming liquid pools along the outer periphery of the front plate; a polishing liquid supply opening formed at the center of the rear plate around a spindle; a liquid supply tube opened into the liquid supply opening; a multitude of liquid outlet holes formed in the front plate along and slightly inward of the outer periphery thereof, and a liquid-permeable visco-elastic polishing member attached to the front plate, the visco-­ elastic polishing member retaining abrasive grains thereon and being deformable in conformity with the profile of a work surface. The polishing liquid is temperarily stored in the liquid pool in the tool base through the liquid feed tube and continuously distributed into the visco-elastic polishing member by the action of centrifugal force resulting from rotation of the tool.

Description: This invention relates to a mirror finish polisher for mirror-finishing workpiece surfaces, and more particularly to a polisher which removes material at an extremely small rate and amount as compared with the case of the improvement of shape accuracy using a conventional electrochemical machine, and which can improve the surface roughness up to the level of 1/100 µm. The present invention also relates to an automatic polishing machine which incorporates such a polisher. Mirror-finished stainless steel sheets are increasingly used as architectural interior and exterior furnishings and as silicon solar cell base plates. As users have come to put more severe criteria on the degree of mirror finish required, products bearing grain lines as a result of conventional buffing are now classified as "semi-mirror finish products", increasing the demands for perfect mirror finish products. Besides, the conventional buffing operation entails another problem in that it is difficult to improve the working environment by suppressing the dust which is scattered in a considerable amount during the polishing operation. With regard to the technology which can give a perfect mirror finish to a workpiece surface in place of the above-mentioned buffing, it seems relatively easy to develop a polishing machine which is directed to workpieces with specific geometrical surfaces such as plane or cylindrical surfaces. However, it is difficult to develop a polishing machine which can be applied to polishing of arbitrary curved free surfaces, and so far no satisfactory machine has been proposed in the art. Further, it is extremely advantageous to perform the mirror finishing of a free curved surface automatically, fitting in with the undulations of the free curved surface. In order to achieve this by the techniques generally known in the art, it is necessary to move a polishing tool along the profile of a free curved surface on the basis of dimensional data of the curved surface profile which are measured either beforehand or simultaneously with the polishing operation by the use of very complicated and costly automation equipment. Accordingly the automation of the buffing operation itself is extremely difficult and expensive. It is therefore an object of the present invention to provide a mirror finish polisher which can be applied to mirror polishing of workpieces with a certain degree of irregular surface variations or arbitrary free curved surfaces. US-A-4140598 discloses a mirror finish polisher for achieving mirror finishing of a workpiece by means of a combined electrolytic-abrasive polishing. This prior art polisher comprises: a liquid-permeable polishing member defining a work face retaining abrasive grains; a rotary drive for rotating the polishing member; a conductive tool base having a surface to which the polishing member is attached and comprising a disk-shaped front plate attached to the tip of the rotary drive, the polishing member and the conductive tool base together forming a tool electrode; an electrolyte supply pipe for supplying electrolyte to the tool base; and a plurality of electrolyte outlets provided in the disk-shaped front plate of the tool base. However, this prior mirror finish polisher is designed for polishing substantially planar, large workpieces and its construction is such that it would be unsuitable for use with workpieces having curved, i.e. non-planar surfaces. The mirror finish polisher in accordance with the present invention has the same constructional features of US-A-4140598 which have been set forth in the preceding paragraph but is characterised by the following additional features, namely: in that the polishing member is formed by a visco-elastic material which is deformable in conformity with both flat and free curved surfaces of a workpiece; in that the rotary drive includes a spindle to the tip of which the front plate of the conductive tool base is attached; in that the conductive tool base also comprises a rear plate which is integrally joined to the front plate at the peripheral edges of the plates, the front and rear plates together forming an electrolyte pool on the side of the front plate opposite the polishing member, the electrolyte pool being open to the atmosphere, and the rear plate having an electrolyte supply opening provided around the spindle of the rotary drive at the centre of the rear plate; in that the electrolyte outlets are provided at positions slightly inward from the periphery of the front plate; and in that the electrolyte supply pipe has an open end inserted in the electrolyte supply opening. Furthermore, whereas US-A-4140598 only teaches the use of abrasive grains adhered to the polishing member, it is within the scope of the present invention that, in addition to or instead of the work face of the polishing member retaining abrasive grains, such abrasive grains may be supplied with the electrolyte. The present invention also provides a polishing machine which comprises a guide provided on a carriage movable within a two-dimensional plane of an automatic two-dimensional feed mechanism, the guide being extended in a direction perpendicular to the two-dimensional plane, and a mirror finish polisher in accordance with the present invention supported slidably along the guide and tiltable for adjustment of the angle of inclination of the polishing member. Upon rotating the polishing member of a mirror finish polisher of this invention by means of the rotary drive while supplying an electrolyte through the electrolyte inlet, the visco-elastic polishing member fits the shape of a workpiece by deforming itself in conformity with the undulations on the surface of the workpiece, if any, thereby to make it possible to give a mirror finish to an arbitrary free curved surface. In this instance, the electrolyte which has been supplied to the tool base is temporarily reserved in the peripheral electrolyte pool and distributed stably to the entire contacting area of the visco-elastic polishing member and the workpiece by the centrifugal force resulting from the rotation of the tool base, without high pressure and permitting the polisher construction to be simplified to a marked degree. The electrolyte is uniformly distributed to the entire machining surface of the visco-elastic polishing member, without forming the separate, split streams where the contact pressure of the visco-elastic polishing member with the workpiece is lower or where a gap is formed due to existence of undulations on the surface of the latter, that are unavoidable when the flow is supplied under high pressure from the center of the tool base. Accordingly, it is possible with the polisher of the present invention to polish a workpiece by contacting therewith only the peripheral portions of the visco-elastic polishing member. Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: Fig. 1 is a partly sectioned view of a mirror finish polisher according to one embodiment of the present invention; Fig. 2 is a partly cutaway front view showing the polishing member and tool base of the polisher of Fig. 1; Fig. 3 is a partly sectioned view showing a polishing operation using the polisher of Fig. 1; Fig. 4 is a partly cutaway front view of an embodiment of an automatic polishing apparatus according to the invention; Fig. 5 is a partly cutaway side view of the apparatus of Fig. 4; Fig. 6 is a schematic side view of an automatic two-dimensional feed mechanism of the apparatus of Fig. 4; Fig. 7 is a schematic front view of major components of the automatic feed mechanism; and Fig. 8 is a sectional view taken on line A-A of Fig. 7. Referring first to Figs. 1-3, the illustrated embodiment of the mirror finish polisher 10 includes a pistol-shaped housing 11 accommodating a rotational drive motor 12 and a reducer 13 coupled with the output side of the motor to rotate a spindle 14 which is protruded from the housing 11 and has a polishing tool 20 attached to the fore end thereof whereby a workpiece may be polished by means of combined electrolytic-abrasive polishing. As shown particularly in Figs. 1 and 2, the polishing tool 20, which functions as an electrode for accomplishing electrolytic polishing, is constituted by a conductive tool base 21 substantially of a disk-like shape and a visco-elastic polishing member 22 attached to the surface of the tool base. The tool base 21 includes a disk-like front plate 24 releasably attached to the fore end of the spindle 14, and a rear plate 25 which is integrally joined to the front plate 21 at the peripheral edges thereof to form an electrolyte pool 26 around and on the back side of the front plate 24 to store the electrolyte temporarily before it is fed to the workpiece as described in more detail below. The front plate 24 is centrally provided with a recess 29 to receive therein a head portion of a screw 28 which fastens the tool base 21 to the spindle 14, and with a multitude of liquid outlet holes 30 at positions slightly inward of its peripheral edges. The rear plate 25 is formed with an electrolyte supply opening 31 centrally around the spindle 14, and a sliding contact surface 32 around the opening 31 for contact with a power supply shoe 33 which supplies electrolytic current as will be described hereinlater. The visco-elastic polishing member 22 which is attached to the surface of the tool base 21 is constituted by a liquid permeable visco-elastic material including sponge-like materials such as foamed polyurethane or other foamed synthetic resins or non-woven nylon fabric, which is in the form suitable for attachment to the surface of the tool base 21. In case where a sponge-like material is employed as in the particular embodiment shown, it is provided with a cavity 34 which fits on the tool base 21 and detachably mounted on the spindle 14 by fastening same to the spindle together with the tool base 21 by a screw 28 through a doubling plate 35. In case the visco-elastic polishing member 22 consists of non-woven nylon fabric or the like, its peripheral portions can be fixed to the surface of the tool base 21 by an adhesive or other suitable means and fastened to the spindle 14 through the doubling plate 35. The visco-elastic polishing member 22 may hold abrasive grains dispersed on its surface or throughout its entire body. In such a case, abrasive grains of alumina or the like may be fixedly bonded on an non-woven nylon fabric sheet or the like by the use of a synthetic resin bond which is mixed with the abrasive grains. Alternatively, instead of fixing abrasive grains in the just-mentioned manner, loose abrasive grains may be supported in meshes of non-woven fabric. A multitude of liquid outlet holes 30 are formed in the front plate 24 at positions slightly inward of the peripheral edges of the tool base 21 for the purpose of feeding the electrolyte to the workpiece. Accordingly, while the tool 20 is rotated, the electrolyte which flows out continuously through the electrolyte outlet holes 30 is fed to the contacting area between the visco-elastic polishing member 22 and a workpiece around the peripheral portions of the tool 20 under the influence of centrifugal force. In addition, since the tool 20 has a high liquid holding capacity, it is possible to feed the electrolyte liquid stably not only to a horizontally disposed curved surface but also to almost vertically disposed curved surface. An electrolyte feed pipe 38 which supplies the electrolyte to polishing areas in the peripheral portions of the tool 20 has its inlet end 40 opened into one end of the housing 11 and its outlet end 41 opened into the tool base 21 through the electrolyte supply opening 31 which is formed centrally in the rear plate 25 around the spindle 14. In this manner, the electrolyte is simply poured into the pool 26 which is open to the atmosphere, so that it is possible to simplify the equipments for feeding the electrolyte under pressure. For example, the electrolyte can be fed to the polisher without resorting to a pump, simply by locating an electrolyte reservoir at a slightly higher position that of the polisher. In place of or in addition to the abrasive grains which are carried by the visco-elastic polishing member 22, free abrasive grains may be admixed into the electrolyte which is supplied through the feed pipe 38. Especially in case of a polishing operation using fine grains, it is advantageous to use such free abrasive grains which can be uniformly distributed over the entire surface of the visco-elastic polishing member 22. A power supply terminal 43 is provided at one end of the housing 11 to supply electrolytic current to the tool 20 through the power supply shoe 33 and the sliding surface 32 which is in contact with the shoe 33, and connectible to a power source (not shown) to conduct current across the workpiece and tool 20 serving as positive and negative electrodes, respectively. Indicated at 44 is a switch member which is manipulatable to actuate the rotational drive 12. The above-described electrolytic-abrasive polisher can be used as a portable machine which is lightly pressed by hand against a surface of a workpiece which needs polishing, or it can be mounted on a carriage which is freely movable in a horizontal plate to perform the polishing operation. As illustrated in Fig. 3, in order to polish a free curved surface of a work 45, current of several amperes is passed across the tool electrode 20 and work 45 at a voltage of several to some ten volts, while supplying thereto an aqueous solution of NaNO₃ or KNO₃ through the liquid feed pipe 33 and rotating the tool electrode 20 by the rotational drive 12, with the peripheral portions of the visco-elastic polishing member 22 on the tool electrode 20 held in pressed contact with the free curved surface of the workpiece 45. In a case where the tool electrode 20 has a diameter of about 12 cm, it can give a mirror finish even to a work surface containing a certain degree of undulations, since the peripheral portions of the visco-elastic polishing member 22 are suitably deformed into a shape which fits the surface profile of the workpiece when pressed thereagainst at a rotational speed of about several hundreds r.p.m. In this instance, the pressure which is imposed by the tool 20 on raised portions of the contacting surface of the workpiece 45 is naturally greater than the pressure imposed on lower surface portions, so that the amount of stock removal by the abrasive becomes greater on the raised surface portions. However, since relatively large raised and depressed surface portions are finished substantially to the same degree of roughness, work can be polished efficiently in a case where accuracy in shape is not a severe requirement. It suffices to supply the electrolyte at a flow rate of one litre per minute or less. The combined electrolytic-abrasive polishing can be suitably applied to polishing of free curved surfaces of various metallic products, particularly to surface polishing of stainless steels or the like. Illustrated in Figs. 4 to 8 is an automatic polishing machine utilizing the above-described electrolytic-abrasive polisher 10. As seen in Figs. 4 and 5, this automatic polishing machine includes a machine frame 50 formed by joining angles which are extended along the respective edges of a rectangular parallelepiped, and a two-dimensional automatic feed mechanism 53 is mounted on a support plate 51 which is in turn mounted on top of the machine frame 50. The automatic feed mechanism 53, which moves the polisher head 10 on a carriage 54 freely in perpendicularly intersecting X and Y directions in a horizontal plane, includes paired parallel X-direction guide rods 58 between a pair of support members 56 and 57 at the opposite ends of a base plate 55 which is fixed to the support plate 51. A feed screw 60 which is rotationally driven by a motor 58 on the support plate 55 is rotatably supported also in the support members 56 and 57 and threadedly engaged with the X-direction carriage 61 in which the guide rods 58 are slidably inserted to guide the movements of the carriage 61 in X-direction. Accordingly, upon rotating the feed screw 60 by the motor 59, the X-direction carriage 61 is moved in the X-direction under guidance of the guide rods 58. Further, slidably inserted in the X-direction carriage 61 are a pair of Y-direction guide rods 63 and a feed screw 64 which are disposed perpendicular to the X-direction guide rods 58. These guide rods 63 are fixedly mounted between support members 65 and 66 at the opposite ends of the carriage 54, and the feed screw 64 is rotatably supported on the two support members 65 and 66, with one end of the feed screw 64 coupled with a motor 68 mounted on the carriage 54. Accordingly, upon rotating the motor 68, the carriage 54 is moved in the Y-direction relative to the X-direction carriage 61. The motors 59 and 68 of the above-described feed mechanism 53 are connected to a controller, not shown, which controls the operation of these two motors to move the carriage 54 along predetermined paths of movements. For this purpose one may utilize a controller known to be used in two-dimensional feed mechanisms of this sort. As shown particularly in Figs. 6 to 8, a pair of guides 70 and 71 are opposingly suspended from the carriage 54 to support the polisher head 10 slidably in a direction Z vertical to planes X and Y. These guides 70 and 71 are provided with slots 72 and 73 extending in the longitudinal direction thereof. The polisher 10 is fixed in a holder 74 which is arranged to hold the polisher 10 in-between a pair of split members 75 and 76 with projecting support rods 77 and 78, split support members 79 and 80 located opposingly to the split members 75 and 76, and a connecting plate 81 linking the split members 75 and 76, which are integrally fastened by bolts 82 and 83. Slide members 85 and 86 of square shape on outer side are rotatably fitted on the support rods 77 and 78 which are secured to the split members 75 and 76, and fixed in position by butterfly nuts 87 and 88. These slide members 85 and 86 are slidably received in the afore-mentioned slots 72 and 73. An angle indicator plate 89 with a dial of angle of inclination is fixed on the slide member 85, and a pointer plate 90 is fitted in the support rod 77 in such a manner as to permit its axial sliding movement while blocking its rotational movement. Consequently, as illustrated in Fig. 4, if the butterfly nuts 87 and 88 are fastened with the polisher 10 in a suitable inclined position, the square slide members 85 and 86 are fixed in the same inclined positions and the polisher 10 can be slided freely in the direction Z in the tilted state since the slide members 85 and 86 are slidable freely within the slots 72 and 73 of the guides 70 and 71. At this time, the angle of inclination is known from the graduation on the angle indicator plate 89, on which the pointer plate 90 registers. In order to reduce the resistance of sliding movement of the slide members 85 and 86 along the slots 72 and 73, it is possible to employ various kinds of linear slide mechanisms of known arrangement. In use of the automatic polishing machine of the above-described construction, a workpiece is set in the machine frame 50 and the polisher 10 is tilted suitably, depending upon the surface profile of the workpiece, and, in the tilted state, peripheral portions of the visco-elastic polishing member are contacted with the work surface as explained hereinbefore in connection with Fig. 3. At the same time, the carriage 54 is moved two-dimensionally by the controller along courses which have been preset beforehand according to the surface profile of the work. In the automatic polishing operation, it is necessary to maintain the angle of inclination of the spindle of the tool within the afore-mentioned appropriate range relative to the work surface in contact with the visco-elastic polishing member. If this is not possible, the polishing operation is at once stopped, and resumed after changing the angle of inclination. While the polisher 10 is two-dimensionally moved by the automatic two-dimensional feed mechanism 53, the visco-elastic polishing member is pressed on the work surface by the weight of the polisher 10 itself. Therefore, it is necessary for the polisher 10 to have a suitable weight for this purpose. However, in a case where the weight of the polisher 10 itself is insufficient, a spring may be interposed between the carriage 54 and polisher 10. The provision of such a spring is also necessary to secure the required pressing force of the visco-elastic member when polishing a vertical surface of a workpiece by a polisher head 10 on the above-mentioned horizontal type automatic polishing machine. The force with which the visco-elastic polishing member is pressed on the work surface is as small as several tens kPa, and the chipping action of abrasive grains is far weaker than that of the conventional solid grinder namely, not stronger than mere scratching action on the work surface, so that the major portion of the frictional resistance in the polishing operation is considered to take place between the visco-elastic polishing member and the work surface. Since the head pressing force is light as mentioned hereinbefore, the polisher head 10 can be automatically moved in the Z-direction along the surface profile of a work simply by feeding the polisher head 10 two-dimensionally by the above-described two-dimensional feed mechanism 53. Although the automatic polishing machine has been shown as having the hand-operable polisher head of Figs. 1 to 3 fixedly mounted on a holder 74, it may of course use a polisher head in accordance with this invention which is constructed exclusively for the automatic polishing machine.

Claims: A mirror finish polisher (10) for achieving mirror finishing of a workpiece by means of combined electrolytic-abrasive polishing, comprising: a liquid-permeable polishing member (22) defining a work face retaining abrasive grains, and/or being adapted to retain abrasive grains supplied with electrolyte; a rotary drive (12,13,14) for rotating said polishing member; a conductive tool base (21) having a surface to which said polishing member (22) is attached and comprising a disk-shaped front plate (24) attached to the tip of the rotary drive (12,13,14), said polishing member (22) and conductive tool base together forming a tool electrode (20), an electrolyte supply pipe (38) for supplying electrolyte to said tool base; and a plurality of electrolyte outlets (30) provided in said front plate (24), characterized in that said polishing member (22) is formed by a visco-elastic material which is deformable in conformity with both flat and free curved surfaces of a workpiece, in that said rotary drive (12,13,14) includes a spindle (14) to the tip of which said front plate (24) of said conductive tool base (21) is attached, in that said conductive tool base (21) also comprises a rear plate (25) which is integrally joined to said front plate (24) at the peripheral edges of said plates, said front and rear plates together forming an electrolyte pool opposite said polishing member (22), said electrolyte pool (26) being open to the atmosphere, and said rear plate (25) having an electrolyte supply opening (31) provided around said spindle (14) of said rotary drive at the centre of said rear plate (25), in that said electrolyte outlets (3) are provided at positions slightly inward from said periphery of said front plate (24), and in that said electrolyte supply pipe (38) has an open end (41) inserted in said electrolyte supply opening (31). A mirror finish polisher according to Claim 1, wherein abrasive grains are fixedly retained on the work face of said polishing member (22). A mirror finish polisher according to Claim 1 or Claim 2, wherein said polishing member (22) is constituted by a sponge-like material and is detachably fixed to said conductive tool base (21). A mirror finish polisher of Claim 1 or Claim 2, wherein said polishing member (22) is constituted by non-woven nylon fabric having abrasive grains retained thereon by a resin. A mirror finish polisher according to any preceding claim, wherein a power supply shoe (33) is held in contact with the rear plate (25) of said conductive tool base (21) for supply of electrolytic current. A polishing machine, comprising a guide (70,71) provided on a carriage (54) movable within a two-dimensional plane of an automatic two-dimensional feed mechanism (53), said guide (70,71) being extended in a direction perpendicular to said plane, and a mirror finish polisher (10) according to any preceding claim supported slidably along said guide (70,71) and tiltable for adjustment of the angle of inclination of the polishing member (22). A polishing machine according to Claim 6, wherein said mirror finish polisher (10) is adapted to be pressed against the surface of a workpiece by the weight of said mirror finish polisher (10) itself. A polishing machine according to Claim 6, wherein said mirror finish polisher (10) is adapted to be pressed against the surface of a workpiece by action of a spring.

Inventors: NAKAGAMI, KENJI, SEIMIYA, KOUICHI C/O MECHANICAL ENGINEERING LAB.
Applicants: AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY, MIRACLE COMPANY LIMITED
Application year: 1986
Main classification: B24D13
IPC codes: B24B29, B23H5, B24D13