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BACKGROUND I~ND SU~lMARY OF TIIE INVENTION
This invention relates to honing, polishing, reducing, or otherwise abrading, in which irnproved means and methods are employed for abrasion of workpieces in general, and at least seleeted internal portions of workpieces sueh as bores, passages, and eavities in particular. In general, the abrasion is accom-plished by the use of an abrasive medium, and more particularly by the use of a visco-elastie, abrasive medium.
In one embodiment, this abrasive medium eomprises a visco-elastic, rheopectic matrix, having the eonsisteney of putty (at room temperature and with no pressure applied~ which is permeate with finely divided and evenly dispersed abrasive particles. When passed across and against a work surface in the proper manner, this abrasive medium provides maximum abrasive action and unifor-mity of finish. In the context of this invention, "rheopeetic"
defines the property of a composition in which the viscosity inereases with time under shear or a suddenly applied stress.
Stated another way, this property of the abrasive medium is exaetly opposite of "thixotropy".
The invention also deals with the disçovery that viseo-elastie materials adhere strongly to porous or roughened surfaces and to silicone rubber. When using an abrasive medium eomprising a mixture of a visco-elastie matrix and abrasive partieles, this "bonding" property allows adherence of at least a portion of the matrix to sueh a surface to provide resistanee to abrasion by tl-le particles or grit. This "bonding" property also may be utilized for artieles of manufaeture such as belts for belt sanders, abra-sive pads for manual use, and deviees for inereasing the abrasion of seleeted work surfaee areas--partieularly seleeted work sur-faee areas of internal bores.
The invention further deals with selectively maskiny a workpiece with a ceramic or the like in order to control surface finishing by a flowable abrasive. Due to such mask-ing, abrasion of selected areas of the workpiece may be reduced controllably, or prevented, while normal abrasion is allowed to occur on other areas of the workpiece.
It is known to extrude a visco-elastic abrasive medium through workpieces to accomplish abrasive finishing of sel-ected surfaces of the work, as disclosed in U.S. Patent No.
3,634,973 -McCarty. Other references directed to this ap-proach are U.S. Patent Nos. 3,802,]28 -Minear,Jr., et al.;
3,819,343 - Rhoades; and 3,521,412 - McCarty. The disclos-ures of the above patents are herby incorperated by refer-ence.
It is also known, as in Japanese Utility Model Public-ation 55-53320, to space a work surface opposite from a deformable, elastic member and force a flowable abrasive mixture therebetween, with the elastic member deforming to reduce flow restriction caused by the work.
It is also known to hone or lap gears, as in U.S.
Patent No. 3,618,272 - Whalen, et al., in which a thickened, flowable abrasive medium is used. Other references disclos-in~ this same general approach are U.S. Patent Nos.
3,2g3,805 - Davies; 3,955,327 ~ Franco; 2,986,856 - Fehr;
and 3,169,349 - Findley. A meshing (usually driving) rel-ationship is required between two surfaces, whether or not one or both are the work surfaces to be treate~.
It is also known, as in U.S. Patent No. 3,593,410 -Taylor, to chemically alter the surface of one of a pair of generally mating die surfaces, to place abrasive grains or grits between the die pair, and to impart relative motion between the die pair to remove any protuberances from the ~2~
chemically altered surface.
It is als Q known, as in Japane 5 e Utility Model Publication 50-29197, to abrade a workpiece cavity by use of a mating mandrel having an elastic, deformable surface attached thereto and abrasives applied to the elastic surface Other known processes of finishing surfaces employ:
vapor blasting, sand blasting, shot blasting, and vibratory finishing. Vapor blasting incorporates an abrasive slurry which is forced against the product at relatively high velocity. The impingment of the abrasive particles on the surface of the product erodes or abrades away the surface.
This process has no effect on surfaces located interiorly of the product. Sandblasting involves the use of abrasive part-icles thrown at high speed by compressed air or a mechanical flinger. This process also has little value for interior surface finishing. Shot blasting uses cast iron shot, steel shot, or glass beads at high velocities as in the case of sand blasting. This operation is more nearly a peening over of burrs or the like rather than a clean removal. Vibratory finishing agitates the product in a mixture of abrasive particles, stones, or jacks, and is carried out at low pres-sure. The more exposed surfaces receive the most action.
~lere again, interior surfaces receive little or no abrasive effect.
~ .S. Patent Nos. 2,799,789 - ~olfskill and 3,247,572 -Munk disclose prior methods of masking of small objects, such as piezoelectric crystals and minature magnetic cores for micro-circuits, in order that surfaces o-f the devices may be selectively abraded by the above-mentioned sandblast-ing, tumbling, shot-peening, or the like. The material used to mask these small objects comprises a laquer, varnish, ~2~ 6 paint, ink, or the like which provides a resilient covering having doubtful masking capabilities when used with a flow-able, visco-elastic abrasive. Also this maskinq material was required to be diluted to assure "a surface tension of appropriate magnitude so that the resulting coating on the objects pulls away from... sharp projections and collects on [theJ broad surfaces of [the] objects..." Further, these patents disclose abrasive processes which do not provide for good abrasion of internal work surfaces or cavities.
The present invention incorporates the use of an abras-ive medium haviny a plastic or semisolid matrix containing abrasive particles distributed substantially uniformly throughout. The purpose of the semisolid matrix is to trans-port the abrasive particles through or across selected por-tions of a workpiece being treated in order to permit the abrasive particles to remove upraised metal and to round or radius corners as it passes, or to otherwise uniformly remove or finish these portions.
Another purpose of the semisolid matrix is to hold the abrasive particles in suspension so that thay will be pres-sed firmly against the workpiece, as taught hereinafter, so that the abrasive effect is at a maximum and is uniformly distributed over the surface or edge being treated.
Another purpose of the semisolid matrix is to provide a relatively firm backing for the abrasive when the medium is under pressure, in order to increase the cutting action of the abrasive against the workpiece portion being treated, while still being plastic enough to flow through or across the product in order to reach all required surfaces and edges. Although abrasion of the workpiece is only accom-plished by the abrasive particles which come in contact with it, the other,non-contacting particles and their flow, are s just as important as the particles that actually do the abrading of the workpiece. (Larry, please elaborate, if possible, on this statement.) It should be noted that a liquid slurry carrying an abrasive material and pumped through the same kind of work-piece as treated by this invention, would not have the required abrasive action nor would it strike all surface uniformily. Such a liquid slurry would require high Elow velocity to provide maximum impingement of the abrasive particles against the treated surface. Under such con-ditions some areas requiring abrasion would receive no ab-rasion would receive no abrasion at all.
One embodiment of the instant invention is especially useful in polishing mold cavities of complex shapes in which the internal peripheral surface to be worked or polished is of a varying radius. One such workpiece is the internal surface of a plastic injection mold for a telephone receiv-er. These mold cavities are usually polished manually by a skilled die maker at a time consuming rate of approximately 1-4 hours per square inch of work surface. ~dditionally, piece-by-piece, manual polishing of these mold cavities is not constantly repeatable, and human error accounts for workpiece wastage. On the contrary, the invention provides a time-wise and materials-wise efficient method and means for repeatably abrading, honing,or polishing such workpieces in an inexpensive manner. By this embodiment,the abrasive med-ium is displaced positively against and across a portion of a workpiece which is utilized as the displaccement chamber or as the displacer, or as both. In this context, the abras-ive medium acts as a positively displaced abrading tool.
There is no need for engagement, such as meshing, between the opposing surfaces, nor is there a need for mating o-f these surfaces although, in practice, it may be desirable to use such an arrangement. Further, there is no need to chem-ically alter the work surface prior to or during the abrad-ing thereof.
Throughout the description of the invention the term "relative motion" between the opposed surfaces is used to indicate that either or both surfaces may be moved to accom-plish positive displacement of the flowable abrasive medium.
Further, this movement may be gyratory, orbital, recipro~at-ory, or any combination of these, so long as postive dis-placement of the abrasive medium is accomplished against and across the work portion to be treated in a manner allowing the uniform abrasion offered by a flowable preferably visco-elastic, abrasive media.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1-4 are partial cross-sectional views of an internal passageway of a workpiece, illustrating various means of practicing one embodiment of the invention.
Figures 5 and 6 are isometric views, partially broken away, illustrating another embodiment of the invention .
Fiyure 7 is a schematic side elevation of a belt sander incorporating another feature of the invention~
Figure 8 is a partial isometric with parts broken away illustrating still another embodiment of the invention.
Figure 9 is a side cross-sectional view of another embodiment and illustrating a reciprocatable mandrel within a mold cavity.
Eigure 10 is a side, cross-sectional view illustrating an alternate embodiment of Figure 9.
Figure 11 is a top view taken along the lines 11-11 oE
Figure 10 Figures 12-1~ are top views depictiny various opposed surface profiles and arrangements.
Figure 15 is a plan view of another embodiment of the nvention.
Figure 16 is a plan view, partially in section, illus-trating still another embodiment of the invention.
Figure 17 is an approximate cross-section of arrows 17 17 of Figure 16.
Figure 18 is a front view of a machine suitable for use in the invention.
Figures 19-21 are schematic cross-sections illustrating flow of a visco-elastic abrasive medium through a workpiece.
Figures 22 and 23 are partial schematic cross-sections of a workpiece to illustrate masking and selective protect-ion of one surface of a workpiece which would be directly subjected to abrasion during treatment of an adjacent por-tion of the workpiece.
Figure 25 is a schematic cross-section of a workpiece to illustrate masking and protection of surfaces which are indirectly subjected to abrasion during treatment of an adjacent portion of the workpiece.
Throughout the drawings, like parts are indicated by like numbers.
DETAILED DESCRIPTION OF Tl-iE INVENTION
Referring to Figure 12, a workpiece 10 having internal bore 12 is provided with a protrusion 14 formed of or coated with silicone rubber or the like and is secured or held in place by any of various means within the skill of the art, opposite from a selected portion of the internal surface of bore 12, to form a restriction. Due to this restriction and the properties of a visco-elastic abrasive meclium used in the invention, the internal surface may be selectively re-duced, as indicated in phantom lines at 16. Because of the property of bonding to silicone rubber of the matrix of some of the media used in this invention, a surface layer of the matrix, as indicated at 18, adheres strongly to protrusion 14 to further restrict bore 12. It has been found that layer 18 also provides abrasion resistance to silicone rubber.
A change of flow direction of the medium tends to increase the abrasive action at a conjuction of surfaces.
Since protrusion 14 is protected from abrasion by layer 18, the increased abrasive action of the medium is directed against the portion of the internal surface of bore 12 which is opposite of protrusion 14. Arrows 20 indicate the flow of the medium without protrusion 14, and phantom-lined arrows 22 indicate the altered flow of the medium due to protrusion 14.
Protrusion 14 may be composed in its entirety of a silicone rubber-like material as shown in Figure 1, or it may be coated with a layer of silicone rubber-like material.
Figure 2 discloses a molded silicone rubber plug 30 which is opposite the selected area of abrasion. Although plug 30 is shown in Figure 2 as protruding into bore 12, it may also be "even" with or slightly "recessed" relative to the internal surface of bore 12, so long as a surface layer 18 of the matrix adheres strongly to the plug so as to provide a restriction of bore 12. In this regard, it should be men-tioned that the invention is applicable to increased or directed abrasion for surfaces other than internal bores, such as selected portions of cavities or even external surfaces.
Additionally, as indicated generally at 42 in Figure 3, the material for causing the restriction of the passageway may also be any porous material 40, such as woven fibers or material ~ith a porous surface, such as an oxidized iron or steel since it has been found that some oE the ~atrices used in the invention adhere strongly to such surfaces also.
Figure 4 illustrates a restrictor 50 for Einishing or undercutting a hore 12 peripherally at 13.
Figures 5 and 6 illustrate hand tools such as abrasive pads ar blocks, generally indicated at 60, with the abrasive medium adhered thereto. In Figure 5, substrate 62 is provided with a silicone rubber coating 64 -to whic~ visco-elastic matrix 66 adheres. ~lternatively, substate 62 could be sili-cone rubber material in its entirety? and coating 64 could be eliminated. In Figure 6, a porous substrate 68 is covered with the matrix 66 as by dipping. The various substrates used may have varying degrees of stiffness or flexibility, according to the use intended.
Figure 7 schematically illustrates a porous, or sili-cone rubber, or silicone rubber coated belt 72 for a port-able belt sander 70. A supply reservoir 74 is provided for periodical or continual resupply of a visco-elastic abrasive medium to the work engaging portion of the belt 72. With this arrangement, the useful life of the belt 72 as an abrader is greatly, if not indefinitely, extended.
Figure 8 depicts one blad2 82 of a turbine 80, the surface of which must be finished to a required tolerance, as by extruding or otherwise passing a flowable abrasive medium between blade 82 and guides 84 of a tooling jig.
Prior to the invention, guides 84 were subject to abrasion during the extrusion process, thus causing continuous widen-ing of the gap between guides 84 and blade 82 and reduction in abrasion of subsequently treated blades 82 due to this widening gap. This presented a costly problem in the finish-ing of workpieces such as blades 82. ~lowever, by molding guides 84 of a silicone rubber-like material 86 or coating portions 8~ of guides 84 wit~ s~ ~icone rubber, and by using an abrasive medium which is a mixture oE a visco-elastic matrix and abrasive particles, a film of the matrix adheres to the silicone rubber and protects the surfaces of guides 84 such that a reliable, repeatable finishing of a multitude of blades is realized while using the same tooling jigO
Because of the relative inexpense in molding guides 84 from a silicone rubber-like material, they are easil~ replaceable if eventually abraded out of the required tolerance.
The spacing between the work surface and the opposed wor~ing surface (protrusion 1~ of Figure 1 or guides 84 of Figure 8) is selectable according to such parameters as:
matrix visosity, grit size, work surface finish desired~
input energy, and amount of relative displacement normal to the opposed surfaces. This spacing should be at least great-er than the diameter of the largest abrasive grit when using a generally non-deformable working surface; and a spacing of at least four times the grit diameter is preferable. Al-though not necessary, the profiles of the opposed surfaces may be substantially mating in shape.
Figures 9-15 disclose alternate embodiments for treat-ing, polishing, or abrading internal and external three-dimensional work sur~aces~ ~s with the other embodiments, an abrasive medium comprising a visco-elastic matrix permeated with abrasive pariticles or grit is used. A preferred abras-ive medium for use in the invention has a visco-elastic, rheopectic matrix of silicone bouncing putty (borosiloxane) interspersed with abrasive particles.
In the embodiment of Figure 9, the abrasive medium is used to treat the internal surface 12 of a mold 10 by util-izing a mandrel 14 having a profile smaller than (and gener-ally mating with) that of the mold cavity. ~xternal surface 16 of mandrel ]4 is spaced from internal surface 12 ofrnold 10 to define a gap 22 through and across which the abrasive medium is displaced positively in the general direction of arrows 24 by relative movement between mold 10 and mandrel 14. This relative movement may take the form of reciproc-ation, oscillation, rotation, orbital motion, or any conb-ination of these motions of either or both of the mold 10 and mandrel 14. In this particular embodiment, mandrel 14 includes a passage 18 through which the abrasive medium is fed into the cavity as indicated by the arrow 20. After a sufficient amount of abrasive medium has been fed into the mold cavity, passage 18 may be sealed before imparting the relative movement between mold 10 and mandrel 14. In Figure 9, mandrel 14 is illustrated as the working displacer formed from or coated with an abrasion-resistant material such as a polyurethane. Alternatively, when using an abrasive medium having a visco-elastic matrix, the working surface may be composed of or coated with a silicone rubber-like material or the surface of the working surface may be roughened or porous such that a portion of the visco-elastic matrix adheres or "bonds" thereto to provide this abrasion resist-ance. Although Figure 9 illustrates external surface 16 as the working surface and internal surface 12 as the work surface, it should be understood that these roles could be changed such that either or both of the opposed surfaces 12, 16 receive treatment by the abrasive medium.
In Figure 10, passageway 18 has been eliminated and a removable cavity sealing member 30 has been added. Sealer 30 and/or mandrel 14 may be raised or removed to allow intro-duction of the abrasive medium (generally indicated at 40) into the cavity. As may be appreciated by reference to Figures 10 and 11 (Fi~ure 11 is a cross-section in the ~2~ 6 direction of arrows 11-11 of Figure 10) arrows 32 are meant to indicate relative reciprocatory, rotary, oscillatory, or orbital movement, or any combination thereof, hetween the mandrel 14 and mold 10.
Figures 12-14 are cross-sections illustrating various profiles of work surfaces 12 and working surfaces 16 which are applicable to practice of the invention. In Figure 13, external surface 12 is the work surface and internal surface 16 is the working surface. It is thought that this substant-ial likeness in profiles enhances the postive displacement and abrasive action of the medium when relative movement is imparted between the two surfaces.
E`igure 15 illustrates another structural embodiment of the invention in which a screw conveyor 50 is rotated about and/or reciprocated along longitudinal axis 52. Surrounding conveyor 50 is a coaxial tubular enclosure 60 comprising an internal surface facing and opposed to the external surface of screw conveyor 50. The edges of flights 54 of conveyor 50 may be spaced from or in rubbing contact with the internal surface of enclosure 60. As in the other embodiments of the invention, either or both the internal and external surfaces may be the work surface and all or selected portions of the working surface may be provided with the abrasion resistance as taught by this invention. Additionally~ the conveyor 50 or the enclosure 60, or bo-th, may be tapered or have varying radii and still be within the scope of the invention when the abrasive medium is used for polishing or honing or the like.
In the embodiments of Figures 9-14, it is generally preferred that there is always a gap between the opposed surfaces of sufficient spacing that the largest ahrasive grit being used cannot bridge this gap and engage both .
surfaces simultaneously, and -there is no need for the gap to be any smaller when using a visco-elastic matrix as taught by the invention. However, as may be appreciatecl from Figure 11, working surface 16 may be temporarily deformable by tne abrasive grit and the spacing between the work and working surfaces may be smaller than the largest abrasive grit being used. With such a deformable working surface, any flowable abrasive medium may be used, according to the desired treat-ment of the work surface.
A still further embodiment of the invention is dis-closed in Figures 16 and 17, in which workpiece 90 has a cavity 92 which is to be polished, honed, or the like by means of the abrasive medium of the instant invention. In this embodiment, a plurality of tubes 94 are loosely held together such that they may conform substantially to the cavity 92, as by assumimg various vertical heights according to engagement of their lower ends with cavity 92. Having substantially conformed to this surface, they are then tightly held or clamped together as by metal strap 96 and adjustable machine screw 97 such that they may be removed from cavity 92 while still retaining the general shape thereof at their lower ends. Although Figure 17 discloses tubes 94 to be of varying diameters, it is contemplated also that all of the tubes 94 may have the same general diamet-ers. In implementing this embodiment, the clamped together tubes are then again lowered into cavity 92 such that they are sightly spaced from the surface of cavity 92 and work-piece 90 is moved in a plane generally perpendicular to the vertical axes of tubes 94 by imparting orbital, reciprocat-ing, rotational, or any combination of these movements to a table or the like upon which workpiece 90 is mounted. Alter-natively, workpiece 90 could remain stationary with the same general type of motion imparted to the clamped together group of tubes 94. It is also contemplated that both the workpiece 90 and clamped together tubes 94 coul~3 have motion imparted thereto. The purpose of the tubes 94 is to provide flow passages for the abrasive medium of the instant inven-tion. The abrasive medium is caused to flow, as by an ap-plied pressure through the tubes 94 into the gap between the lower ends of tubes 94 and cavity 92. ~lthough tubes 94 are illustated as having circular cross-sections, various other cross-sections, including rectangular and triangular, are contemplated. Additionally, relative vertical reciprocation between the clamped tubes 94 and workpiece 90 may be impart-ed. Although Figure 16 illustrates tubes 94 as only partially covering the internal surface cavity 92, it is contemplated that a sufficient number of tubes 94 may be provided such that substantially the entire surface of cavity 92 is covered by tubes 94. Although Figure 16 discloses this embodiment as used upon a generally concave work surface, it is also contemplated that a generally convex, or outwardly protruding, work surface may be treated using the same general concept. Further, when more than one cavity of the same three-dimensional shape is to be abraded, polished, honed, or the like, such an arrangement of tubes 94 may be permanently attached together as by braising, adhesives, or the like.
Figure 18 illustrates a maching suitable for imparting relative motion between opposed surfaces during machining of at least one of the surfaces while using a visco-elastic, preferably rheopectic, abrasive medium. The machine includes two vertically opposed platens 102 and 104, either or both or which are provided with means for imparting reciprocating motion in the vertical direction and orbiting, gyrating~
oscillating, reciprocating, and the like motions in a gener-ally horizontal direction. Platen 104 has workpiece 106 attached thereto, with workpiece 106 having a work surface 105 to be machined. Fastened to platen 102 is a complement-ary model 103 which is generally a mirror image of work surface 105. Rather than imparting the relative motion to platens 102 and 104, suitable devices (not shown) may be attached to platens 102 and 104, with these suitable devices supporting complementary model 103 and workpiece 106 and imparting the relative motion therebetween. Devices for imparting relative motion between two surfaces are generally known to be old in the art and are not, per sel the inven-tion. A visco-elastic abrasive medium is fed from a supply 108 via supply tube 110 to the interface between surfaces 103 and 105. Working surface 103 is formed from a plurality of tubes or is provided with pre-drilled holes through which the abrasive medium is transported to the interface. In operation, top platen 102 is lowered into contact with platen 104 according to the accepted method in such mach-ines. Relative motion commences with the two platens 102, 104 slowly being forced further toward each other as the work surface 105 is machined. During the course of this operation, the abrasive medium is replaceable by advancing refeed piston 112, with the older, used medium simply being forced out of the work surface 105 and onto platen 104 for collection by the operator of the machine.
It should be noted that the opposed surface 103, 105 need not be exact complements as suggested by the figure.
Ratherl by using a visco-elastic, rheopectic abrasive med-ium, the working surface needs to be only a rough approxi-mation of the work surface. ~se of such a machine combines the full, three-dimensional machining capabilities of orb-ital abrasion with the uniform abrasion offered by a visco-elastic abrasive medium.
Previously, the basic technique of having ~wo opposed surfaces undergo relative motion while in con~act relied upon a "working" surface being embedded with an abrasive grit to Eorm, polish or in some way machine the work sur-face. Machining methods utilizing visco-elastic abrasive mediums previously achieved the abrasive action only by hydraulically forcing the media through or across the ~"ork surfaces. In contrast, the machine and method of use des-cribed above and illustrated in Figure 18 allows gyrating, orbiting, reciprocating, or any combination of these motions to be imparted between opposed surfaces while using a visco-elastic abrasive medium and thus facilitating a smooth and uniform abrasion of a workpiece.
In certain instances, a workpiece will include areas that must be abraded or machined and which lie directly adjacent to other areas that, due to critical tolerance, must be left intact and untouched by the abrasive medium.
Prior to another embodiment of this invention, it was neces-sary to protect certain areas of the workpiece from abrasion by means of fixtures and mandrels designed specifically for the workpiece. These fixtures and mandrels represented a tooling cost, in both time and money, beyond that of the actual abrasive flow machining. Additionally, particular areas of a workpiece were very difficult, if not impossible, to protect from abrasion during such flow machining. To overcome these vast difficulties, the instant invention also involves masking of these particular areas of a workpiece in order to selectively protect and abrade various workpiece portions as explained hereinafter.
Referring to Figure l9, abrasive grains 120 are carried ~2~
in a semi-solid matrix (not shown) and forced to flow across or through a workpiece 122. By way of example, a particular abrasive grain 121 contained in the matrix cuts into or abades workpiece 122 to remove a small, yet predictable, portion of the workpiece surface as the abrasive medium is caused to flow in the general direction of arrow 124. Thous-ands of these particles 120 act together to evenly abrade the surfaces of a workpiece. In this respect, arrow 130 illustrates the force of the abrasive grain generally paral-lel to flow direction 124 and arrow 132 illustrates an angled force that determines the depth of cut of the abra-sive grain 121 into the workpiece. Angled force 132 is determine by the restriction of the passageway through the workpiece and the pressure with which the abrasive medium is forced to flow. As seen in Figure 20, the abrasive medium should be made to flow evenly through the passageway to uniformly polish passageway surfaces 126, with the evenness of flow indicated by parallel lines 128. ~lowever, when it is desired to radius an entrance to a passeway, as at 134, then the flow of the abrasive medium should be faster through the center of the passageway than at the edges thereof, as illustrated by curved flow lines 129, wherein edges 134 at the passageway entrance are abraded more than surfaces 126 of the passageway.
~ owever, there are instances in which particular edges or surfaces of a workpiece must be abraded or machined while other surfaces lying directly adjacent thereto must not be machined because of critical tolerancess. As applied to Figure 21, this would be a situation where edges or corners 134 must be radiused but the distance between adjacent surfaces 126 must be held constant. Accordingly, surfaces 126, although directly in the flow path of the abrasive medium, must not be abraded. In this embodiment of the invention, a ceramic mask is applied to the area to be protected, such as surfaces 126 of Figure 21. After the mask cures, the workpiece is machined by a flowable abrasive mediumO ~hen subjected to the abrasive action, the mask remains relatively intact to protect surfaces 126 while surfaces 134 are subjected routinely to the machining oper-ation, One manner in which such selective machining may be accomplished will be better understood by reference to Fig-ures 22 and 230 In Figure 22, a workpiece 140 has a passage-way similar to that illustrated in Figure 20 with an edge or corner 142 at the entrance to the passageway which needs to be radiused or abraded while surface 148 of the passageway must be left unabraded. Accordingly, a ceramic mask is applied to surface 148 and, due to the natural character-istics of the abrasive flow or other abrading process to provide more abrasive action at the corner near 142 than along the remaining portion of surface 148. Although ceramic mask 146 resists abrasion during machining of the workpiece by this abrasive process, some of mask 146 will be removed abrasively such that corner 142 will be radiused, as in-dicated by phantom lines, at 144 in Figure 22. Accordingly, there is a smooth blend between radius 144 and unabraded surface 148, as illustrated in Figure 23. After the machin-ing process, mask 146 is removed by soaking the workpiece in a detergent suitable for removal of the ceramic coa-ting.
There are other instances, as in Figure 24, in which the corners and internal walls of a passageway (generally indicated as 152) must be machined while other surfaces 150 which are indirectly subjected to the abrasive action of the flowable abrasive medium should not be machined. Surfaces 150 are sometimes very difficult, if not impossible, to protect from such abrasive action. By the instant invention, it is only necessary to apply the ceramic mask 1~6 to sur-face 150 in order to provide the necessary protection.
Other uses for this embodiment of the invention include the prevention of abrasion where a special finish has been placed on the surface or where the abrasive medium would leave a cosmetically unacceptable mark on the workpiece. As may be appreciated from the above description, the mask provides protection of workpiece areas which are subjected to both direct and indirect flow machining. This protective mask could also be used in vibratory, spindel, tuh, barrel, or gyro finishing processes, all of which use an abrasive medium to finish a workpiece. The mask may be comprised of ceramic, silicone, or similar substances which may be paint-ed or dipped onto critical areas to protect them, while allowing other areas of a workpiece to be abraded normally.
Typical parameter ranges for the embodiments of Figure 9-14, and 18 include: grit sizes of 6 microns to 16 mesh, gap distances of 0.002-0.500 inches, time oE treatment of 5-60 minutes, vibrations per minute of 20-2,000, and amplitude of vibration of 0.025-0.500 inches. Specifically, after substantially filling the gap with a rheopectic abrasive medium, the mandrel of Figure 9 could be operated at 500 vibrations per minute with an amplitude of 0.05 inches for 5 minutes and a gap of 0.005 inches would be sufficient for a grit size of 10 microns.
It is preferable that the plastic carrier matrix have sufficient body at moderate pressure and low velocity to press the abrasive particles against the work surface with sufficient force to produce the result desired. One mixture successfully used in the invention is MV70 Extrude-Hone media, comprising 50~ by volume of silicone carbide abrasive grit and 50% by volume of silicone bouncing putty (borosilo-xane) carrier (matrix) having a ratio of approximately 2:1 by weight.
By definition, silicone bouncing putty (borosiloxane) exhibits many of the characteristics of a fluid. Under suddenly applied pressure it becomes less flowable and more like a solid. It conforms exactly to the shape of whatever confines it and this helps in abrading intricate shapes and details. It should be noted that silicone bouncing pu-tty (borosiloxane) is particularly useful in the invention as it is well known that this material becomes harder when sub jected to sudden shear force such as when squeezed in the gap between the opposed surfaces as they are moved relative to one another. This increased stiffness enhances abrasion of the workpiece by holding the abrasive particles more firmly in place and tranferring the drive force of the working member to the abrasive grains at the work surface.
A non-rheopectic abrasive medium suitable for use in some situations is that described in U.S. Patent No.
3,819,343 - Rhoades.
This invention may be utilized to hone or abrade mach-ined parts, die castings, forgings, sand casting, investment castings and extruded shapes. It is applicable to all mat-erials such as steel, aluminum, brass, bronze, plastics, glass and other compositions and materials as needed.
Obviously, the abrasive used in the carrier matrix will be varied to suit the job. A satisfactory abrasive to use in working on steel is boron carbide (BC) which is readily obtainable from the Norton Company in standard grit sizes.
Another abrasive which is useful for many applications is aluminum oxide. Other abrasives might include diamond dust, silicone carbide, rouge, cor-rundum, garnet, alundum, glass or, in some unusual operations, softer material such as fiber or shell material. Commonly, the abrasive will vary from about 2 to 4 pounds of abrasive particles per pound of the matrix material.
The above-mentioned visco-elastic honing mediums act as a surface abrading tool and are unique for the reason that the abrasive grit is held or contained in a random reposit-ioning arrangement in a plastic matrix. The grain particles in use in the process of this invention are sharp until the sum of all points or edges have been exposed many times, as opposed to the traditional concept of an abrasive "stone" or lap wherein the grain particle is fixed and presents one cutting point or edge which is maintained until dulling causes removal by means of a dressing operation.
The fastest cutting action, which is also consistent with most uniform results, occurs when the medium exhibits an oily non-adhering contact with the work surface. It would appear that when in this condition the medium has the great-est opportunity to pass through the gap at a constant cross-sectional pace. This is contrary to a fluid flow which is greatest through the center and supposedly "zero" along the wall.
It is to be understood that the present invention is not limited to the preferred embodiments disclosed herein, and that many modifications in construction, arrangement, use and operation are possible within the true spirit of the invention. Accordingly, the present invention is to be con-sidered as including all such modifications and variations coming within the scope of the appended claims.