|
(11) | EP 0 109 845 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||||||
| (54) | Improved methods and apparatus for surface machining |
| (57) Methods and apparatus are provided for mechanical, electro-chemical, and chemical
machining of work surfaces with improved flushing of debris from the surfaces. One
embodiment of the invention utilizes a machining tool formed from a plurality of tubular
or rod-like elements easily conformable to the surface to be machined, while providing
increased flow of flushing fluids across the machined surface. Another embodiment
accomplishes improved work surface flushing via a porous tool. |
[0001] The field of invention is workpiece machining and is directed particularly to means and methods for forming a workpiece surface and/or improving the texture of a workpiece surface.
[0002] Machining processes in which the invention is applicable include: total form machining (TFM); electrochemical machining (ECM); electrochemical grinding (ECG); electrical discharge machining (EDM); and the like. In these processes, an abrasive cutting master, or an electrically conductive electrode used for electrochemical etching of or electrochemical deposition onto a workpiece surface, or a combination of abrasive cutting master and electrode are used. In all of these processes, it is necessary to flush the surface during machining to remove bits of the workpiece and/or electrode material. In electrochemical processes, sufficient flow must be imparted to the fluid to prevent "hot arid ECG spots". In ECM/ this flushing fluid is an electrolyte, whereas a dielectric oil or the like is used as a flushing fluid in EDM processes. For TFM processes, the flushing fluid is usually a filtered oil comparable to EDM oils used in the machining of graphite electrodes.
[0003] In the past, cutting masters for total form machining were manufactured by molding an epoxy, suspended with abrasive particles, in a mold cavity which is a mirror image of the workpiece to be machined. The master was also molded onto a special backing containing a large number of passages. When the master was com- pletely molded, holes were drilled through-the entire shape using the backing passages as guides for the drilling. These holes are used for transporting a flushing fluid pumped from the backing of the master to its front, workpiece-engaging surface. After drilling of the flushing holes, the cutting surface is usually finished by blasting with glass or the like. Examples of prior art TFM methods and apparatus may be found in U.S. Patent Nos. 4,132,038 and 3,663,786. The disclosures of these . two patents are incorporated herein by reference.
[0004] Accordingly, it is an object of the invention to improve the flushing of the surface of the workpiece by these fluids.
[0005] It is a further object of this invention to provide means and methods for forming electrodes, particularly electroconductive electrodes as are used in the ECM ECG and EDM processes.
[0006] It is a further object of the invention to improve the circulation of these flushing fluids across the surface of the workpiece.
[0007] It is a further object of this invention to provide an elec- =rode, or cutting master for forming an electrode, which is easily changeable for forming, or conforming to, different surfaces of three-dimensional workpieces.
[0008] One embodiment of the instant invention comprises an electrode, or cutting master for forming an electrode, in which plural tubes or rod-like elements are grouped together and changeably constrained, in order to form or conform to different surfaces to be machined. The hollow portions of the tubes and/or the interstices therebetween may serve as passageways for transporting a flushing fluid to the workpiece surface. When rod-like elements are used, the interstices between the rod-like elements may serve as the flushing fluid passageways. Alternatively, a combination of tubes and rod-like elements may comprise the group such that the tubes and/or the interstices between the various elements may be used as flushing fluid passageways. Additionally, some of these passageways may be used for passage of the fluid to the machined surface, while others are used for evacuation of the fluid therefrom.
[0009] In another embodiment of the invention, the electrode or cutting master may be formed from a plurality of particles or fibers, each precoated with an adhesive material, which are placed in or on a molding surface. Heat is applied sufficiently to bond the particles or fibers together by the adhesive but yet not allow adhesive to fill the interstices therebetween the particles or fibers thus permitting them to form a generally porous mass. The molded, porous mass is then cooled to set the adhesive material. The porosity of the mass allows flushing fluid to be passed to a workpiece surface during machining thereof. The particles or fibers may be abrasive in nature such that mechanical finishing of the workpiece surface is attainable, or the porous mass may be electrically conductive to act as an electrode in electrochemical machining of the workpiece surface. Alternatively, a combination of chemical and mechanical machining or a combination of electrochemical and mechanical machining may be performed on the workpiece surface. Rather than the above-described thermoplastic adhesive, a thermosetting adhesive such as an epoxy-like adhesive may be used for bonding the particles or fibers together. By controlling the proportion of adhesive to particles or fibers, the amount of interconnecting interstices within the mass, upon curing, is controllable.
[0010] In another embodiment, a layer or coating of a parting agent is applied to a mold surface, and magnetically orientable, oblong particles or fibers are applied onto the parting agent- While
a magnetic field is applied such that the oblong particles or fibers orient with each longitudinal axis thereof generally normal to the mold surface and touching the mold surface by penetrating the parting agent. An adhesive, such as an epoxy resin, is then introduced onto the portions of the particles or fibers which are not embedded in the parting agent and, upon curing of the adhesive, the molded mass is removed from the mold surface and parting agent for subsequent use. The thickness or depth of the parting agent upon the mold surface determines how much of the abrasive particles or fibers protrude from the finished abrasive mass of bonded particles. Again, the number and size of the particles as well as the amount and type of adhesive material used will determine the amount of porosity through the bonded abrasive particles or fibers. This embodiment provides a fairly uniform distribution of cutting or abrading points of the particles or fibers extending or protruding from the adhesive bonding agent such that a more uniform abrading pattern occurs during use of the tool in an abrading operation.
[0011] Additionally, relative motion may be imparted between the workpiece and machining tool, with this movement or motion being gyrating, orbiting, reciprocating, or any combination of these motions. Typical examples of apparatus for performing such relative motion may be found in U.S. Patent Nos. 4,230,926 - Gaumond; 4,152,570 - Inoue; and 4,075,897 - Schmidt.
[0012]
Figure 1 is a front elevation of one embodiment of the invention.
Figure 2 is a front elevation of another embodiment of the invention.
Figures 3-6 are cross-sectional views illustrating various embodiments of the individual cutting master or electrode elements of the invention.
Figures 7-9 are partial front elevations illustrating several different tip configurations for elements of a cutting master or electrode usable in the instant invention.
Figure 10 is a front elevation of another embodiment of the invention in which a porous cutting master or electrode is used.
Figures 11A-11B illustrate the prior art, and method of manufacture thereof, in tools of bonded abrasive particles.
Figures 12A-12D illustrate an alternative embodiment of a porous, cutting tool having aligned, oblong abrasive particles or fibers.
[0013] Referring to Figure 1., a loosely held group of rod-like or tubular elements 10 are placed onto a pattern of an EDM electrode, such that the elements may shift (vertically, as seen in Figure 1) and conform to the shape of the pattern 11. Having generally conformed to the shape of pattern 11, a band 16 or other form of clamping means is tightened around the group of elements to constrain them. As seen in Figure 2, the group of elements is then held by an adjustable chuck 18, or the like for use in machining a workpiece 12. A flushing fluid is supplied to the top of the group of elements 10 and is forced therethrough to the surface of workpiece 12 during machining thereof. It is contemplated that other means for holding the group of elements 10 may be used in the instant invention. For instance, adjustable chuck 18 could be replaced by a receptacle having an adhesive material therein which will bond to the group of elements 10 to form a more permanent attachment thereto. However, when the group of elements 10, as formed in Figure 1, are used to form or improve the surface texture of a limited number of workpieces, it may be advantageous to use an adjustable clamping means, such as band 16 and/or chuck 18 in order that the same group of elements 10 may be reconfigured for machining of workpiece surfaces of different shapes.
[0014] The elements of group 10 may have various cross-sectional configurations, some of which are illustrated in Figures 3-6. -n Figure 3, rods 22 are generally octagonal in cross-section and, when grouped together, have interstices 13 therebetween which provide passageways for the flushing fluid. Figure 4 discloses tubular elements 24 such that the hollow portions of tubular elements 24 may augment interstices 13 as passageways for the flushing fluid. In this regard, some of the passageways may be used to admit fluid to the workpiece surface, while others of the passageways may be used to exhaust fluid therefrom. Additionally, the various elements of group 10 may be adhesively attached together with some or all of the interstices 13 being partially or wholly filled with the adhesive. Figure 5 discloses an arrangement in which generally rectangular rods have been bevelled, as indicated at 27, in order that they may be constrained more securely as a group while providing a larger interstice 13 therebetween. The element of Figure 6 was originally circular in cross-section and has been modified to provide flat surfaces 31, while retaining curved portions 32. Although shown as a rod-like element 30, phantom lines 33 indicate that element 30 may be ;ubular.
[0015] In some applications of the instant invention, it is preferable to alter the tips of the workpiece approaching or engaging ends of the elements in order to more closely conform to the surface being machined. Additionally, alteration of the tips enhances flushing of the workpiece surface in some applications. When it is desired to conform the tips of the rods or tubes to a particular surface, the pattern 11 of Figure 1 may be formed from a material more abrasive than that of the elements and, by imparting relative motion between pattern 11 and element group 10, the tips of the elements may be abraded by pattern 11 in order to conform to the surface thereof more closely. Figures 7-9 disclose various other tip alterations in which Figure 7 discloses tubular element 40 having a double bevel arrangement 41. Figure 8 discloses tubular element 44 as having a bevel 45 and a flat portion 46, and Figure 9 discloses a rod-like element 48 having bevelled portion 49.
[0016] Figure 10 illustrates another embodiment of the instant invention in which an electrode 50, or a cutting master for forming an electrode, is a porous mass such that the flushing fluid may flow or be forced therethrough to the surface of a workpiece 12. Cutting master or electrode 50 may be formed by placing a plurality of individually coated particles or fibers into a mold cavity and molding a porous mass. The coating on the individual particles or fibers may be a% cyano-acrylate or other adhesive binder such that, when heated, it slightly melts to bond the particles or fibers together into a mass having a multitude of interconnected pores or interstices through which a flushing fluid may flow. Alternatively, the bonding agent may be a thermosetting adhesive, such as an epoxy-like adhesive.
[0017] There is no need to drill flush-out passages or holes through the cutting master and, since the flushing fluid may flow through a multitude of "pores" of the workpiece engaging or approaching surface of the cutting master, debris is washed away more effectively and machining takes place more efficiently. In order to direct or limit the flow of fluid from the outside surface of cutting master 50, it is contemplated that a non-porous coating, as indicated at 60, may be applied thereto.
[0018] Referring to Figures llA-D, prior art abrasive cutting masters are fabricated by placing a mass of adhesive with abrasive particles randomly dispersed therein onto the mold surface and curing the mass. Thereafter, a steel backing plate is often added for rigidity and the cured mass is then removed to expose a mirror image of the mold surface. An alternate prior art method comprises applying a thin coat of adhesive or bonding agent combined with abrasive particles to the mold surface and, upon curing of this thin coat of adhesive and abrasive, such as epoxy and a steel backing plate for added rigidity.
[0019] A problem is encountered when applying the mixture of adhesive and abrasive cutting particles to the mold surface. The particles are epoxy and randomly oriented and located causing an uneven distribution of abrasive particles onto the surface of the mold and a resulting uneven abrading surface. Further, the formed cutting master, upon being removed from the mold surface, must be roughened to expose cutting edges of the abrasive particles. Such roughening is usually accomplished by blasting the surface of the mass with glass fragments or the like as indicated in Figure 11C. During such blasting, some of the abrasive particles may be caused to .fall out of the mass because their shapes do not always lend themselves to good anchoring of the particles within the mass.
[0020] Such problems are overcome by the method and apparatus of the instant invention. Referring to Figures 12A-12D, generally oblong abrasive particles or fibers 75 are caused to be oriented normal to the surface 72 of mold 70 prior to or during application of a portion or all of the adhesive material 76. Orientation of the oblong particles 75 normal to mold surface 72 may be accomplished by electrostatic or magnetic or electromagnetic forces.
[0021] For instance, application of a properly oriented electro-magnetic field may-be used to-accomplish the orientation of the oblong particles or fibers 75. When magnetics or electromagn :tics is used for this orientation, the particles may be coated with a magnetically susceptible material such as a ferrous coating, or the particles 75 may be magnetically susceptible by virtue of the at least partly composed of fact that they are/iron or an appropriate alloy. In order to enhance the porosity of the cutting master, tubes may be randomly dispersed or applied onto the mold surface along with the abrasive particles 75, with such tubes treated or composed of similarly magnetically susceptible materials such that they are oriented normal to the mold surface 72 along with oblong particles 75.
[0022] Of course, the use of electrostatics to orient the oblong particles and tubes provides the advantage that they need not be magnetically susceptible. Additionally, the tubes used to provide flushing. fluid passageways may be rod-like or solid and may be (such term also meaning removable by melting or vaporization) selectively soluble/arter formation of the abrasive mass. It is contemplated that such soluble rods or tubes may be used in both the electrostatic and electromagnetic orientation methods in order to provide flushing fluid passageways through the finished abrasive mass. In using oblong particles or fibers 75, there is increased mechanical anchoring of the particles in the adhesive 76, such that the problem of particular particles falling out of the adhesive during roughening of the surface of the mass is avoided. Such anchoring also prevents scratches or gouges, which occur to a surface being treated abrasively, when a particle dislodges from the adhesive during the machining thereof.
[0023] It is also contemplated that chemical etching could be used in place of the aforementioned blasting in order to expose the cutting edges or points of the abrasive particles. Additionally, during formation of the abrasive mass, a sufficient thickness of parting agent 77 may be applied to mold surface 72 prior to application of the abrasive particles. The advantage of parting' agent 77 is that, upon removing the abrasive mass from the mold surface, little or no roughening of the mass will be necessary in order to expose the cutting edges or points of oblong particles 75.
[0024] Having discussed the general structures as illustrated in the drawings, the following discussion deals with other portions of the invention not easily discernible from the drawings. For instance, the cutting masters or electrodes may be used for mechanical abrasive machining, chemical machining, electrochemical machining, or combinations thereof. For instance, the elements of cutting master or electrode 10 may be abrasive or nonabrasive as may be the fibers or particles of cutting master or electrode 50. for electrochemical grinding, the abrasive Additionally / elements of cutting master or electrode 10 may be electrical insulators .and the adhesive material used in the formation of cutting master or electrode 50 may be electrically conductive. Further, if cutting master or electrode 50 is formed such that the fibers or particles engage each other; it may be sufficient to use a nonconductive adhesive binder. Still further, with the proper electrolyte, it may not be necessary that the elements or particles of the various embodiments be electrically conductive in order to act as an electrode for electrochemical machining.
[0025] Materials suitable for use as elements include metal, quartz, glass, and the like. In certain applications, it is preferred that the rod-like or tubular machining elements be flexible in nature, whereas other applications require that they be rigid.
[0026] One method of using the apparatus disclosed above comprises providing a three-dimensional body such as an electrode or a pattern of an electrode such as that used in the EDM process, placing the longitudinal elements 10 thereon as indicated in Figure 1, jogging or vibrating'these elements while they are loosely held together in order that they conform generally to a surface of the three-dimensional body, and constraining the elements'together as a group. Additionally, an adhesive material may be applied to the elements in order to hold them together, either prior to or after removal from the three-dimensional form. In addition to or in place of the adhesive, the group of elements 10 may be clamped in a chuck 18 or the like of a machine capable of supporting a workpiece in opposition to the newly formed three-dimensional tool and imparting relative motion between the tool and workpiece (as by gyrating, orbiting, vibrating, reciprocating, or combinations of these motions) in a plane generally perpendicu-In ECM or EDM I.ar to a direction of feed between the workpiece and tool./ A gap may be retained between the workpiece and tool during machining when a mechanical abrasive action is not desired. Alternatively, nonconductive during advance of the tool into the workpiece, there may be/ contact therebetween such that mechanical abrasion does occur.
[0027] The method of use of the cutting master or electrode 50 and that of Figures 12A-D, once formed, is much the same as the above example.
[0028] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
provding a three-dimensional body having a surface: providing a plurality of loosely grouped longitudinal machining elements-having first and second ends and orienting said elements with longitudinal axes thereof generally normal to said surface and said first ends proximate said surface;
displaying said elements and contacting said first ends with said surface such that said first ends generally conform to a profile of said surface;
constraining said elements together as a group having said first ends generally conforming to said surface profile and flushing fluid passageways through said group: and
removing said group from contact with said surface.
wherein said elements are rod-like such that interstices between said elements provide said passageways.
vibrating said elements.
clamping said elements together.
applying an adhesive material to said elements and setting,said adhesive, after said displacing, to provide said constraining.
machining said first ends to conform a first end of each of said elements to a portion of said profile.
imparting relative motion between said group and said surface; and
abrading said first ends to conform each of said first ends to a portion of said profile.
orbiting,
vibrating,
gyrating.
providing a mixture of abrasive particles and adhesive material;
placing said mixture against a mold surface;
causing adherence between said particles by said adhesive material into a porous, abrasive mass generally conforming to said mold surface; and
removing said mass from said mold surface.
coating a portion of said porous mass with a non-porous material.
controlling the proportion of said mixture to ensure internconnection interstices and porosity in said mass upon adherence of said particles.
thermoplastic.
providing soluble particles in said mixture; and dissplving said soluble particles to provide porosity to said mass.
applying abrasive particles onto a mold surface, each of said particles generally being oblong and magnetically orientable along an oblong axis;
applying a magnetic field and magnetically orienting said particles with said oblong axes generally normal to said mold surface;
applying an adhesive material to said particles and, after said orienting, curing said adhesive to form an abrasive mass generally conforming to said mold surface; and removing said moss from said mold surface.
controlling said adhesive material in amount such that, upon curing, interstices are formed between said particles and said abrasive mass is porous.
coating said particles with a ferrous material to cause said particles to be magnetically orientable upon application of said magnetic field.
applying a parting agent to said mold surface prior to said particles applying, such that said particles pierce said parting agent and contact said mold surface upon said orienting and protrude from said adhesive material by a thickness of said parting agent upon curing thereof: and
removing said parting agent from said mass.
applying abrasive particles onto a mold surface, each of said particles generally being oblong and electrostatically orientable along an oblong axis;
applying an electric field and inducing dipoles in each of said particles and orienting said particles with said oblong axes generally normal to said mold surface;
applying an adhesive material tos aid particles and, after said orienting, curing said adhesive to form an abrasive mass generally conforming to said mold surface; and
removing said mass from said mold surface.
applying a parting agent to said mold surface prior to said particles applying, such that said particles pierce said parting agent and contact said mold surface upon said orienting and protrude from said adhesive material by a thickness of said parting agent upon curing thereof: and
removing said parting agent from said mass.
dissolving said soluble particles to provide flushing fluid passageways through said mass.
a plurality of machining elements each having a generally longitudinal axis and first and second ends, said elements constrained as a group such that their longitudinal axes are generally parallel to each other and said first ends generally conform to a mirror image of said surface; and
means for admitting a flushing fluid to said surface through said group.
at least one tubular machining element or interstices between constrained elements.
quartz rods,
glass fibers,
metal rods,
glass tubes.
a porous mass having at least a portion of an outer surface thereof formed to provide generally a mirror image of said workpiece surface;
said porous mass having interstices throughout, such that a flushing fluid is passable therethrough.
abrasive particles bonded together by an adhesive material.
a thermosetting material
a cyano-acrylate.
said abrasive particles each protruding from said adhesive material a particular distance toward said workpiece surface during said machining.
plural machining elements, each having a longitudinal axis and first and second ends, grouped together with said first ends defining a locuse with is generally a mirror image of said specified shape;
means for constraining said elements together in a group to retain said locus;
a flushing fluid supply proximate said second ends;
means for flushing said fluid from said supply through said group to said surface;
means for feeding said group of elements into said surface; and
means for imparting relative motion between said elements and said surface, in a direction generally perpendicular to a direction of said feeding.
an adhesive material,
an adjustable chuck receiving and clamping said elements,
a band clamped around said group of elements.
a thermoplastic material or
a cyano-acrylate.
interstices,between said elements providing passageways for said fluid,
said elements being tubular to provide passageways for said fluid,
passageways through said group of elements, such that said relative motion causes pumping of said fluid across said surface during said machining.
means for reciprocating said group of elements generally parallel to their longitudinal axes.
a gyrating motion,
a reciprocating motion,
an orbital motion,
a rotary motion.
means for changing said locus and generally defining a mirror image of another specified shape.
an electrolyte or
a dielectric.
plural machining elements, loosely grouped together, each having a longitudinal axis and first and second ends and being individually displaceable generally along said longitudinal axis;
means for displacing said elements generally along said longitudinal axis such that said first ends are shiftable from a first position to a second position to define a locus of said first ends at said second position, said locus generally coinforming tosaid surface;
means for constraining said elements together as a group with said first ends defining said locus;
a flushing fluid supply proximate said second end;
means for flushing said fluid from said supply through said group to said surface; and
-means for imparting relative motion between said group of elements and said workpiece to finish said surface.
means for contacting said first ends with said surface to abrade said surface with said elements during said finishing.
means for spacing the first ends of said group from said surface to provide a gap therebetween during said finishing.
wherein said locus is determined by engagement of said first ends with said surface.
an electrolyte or
a dielectric.
a porous mass having at least a portion of an outer surface thereof formed to provide generally a mirror image of said workpiece surface;
said porous mass having interstices throughout, such that a flushing fluid is passable therethrough;
a fluid supply connectable to said porous mass;
means for feeding said porous mass into said workpiece surface and imparting relative motion between said workpiece and said mass, in a direction generally perpendicular to a direction of said feeding, to effect said machining; and
means for flushing said workpiece surface with said fluid from said supply via said interstices.
abrasive particles bonded together by an adhesive material.
an electrolyte or
a dielectric.