Process and device for the treatment of non conducting metal bonded hard materials

A process and a device for the treatment of non conducting metal bo)1d non hal’d materials

LACH Spezial-IVerkzeuge GmbH

The present invention relates to a process and to a device for the treatment of metal bound working pieces of not conducting hard materials. Treatment in connection with the present invention means change of the shape or of the condition of the material, it may e.g. be separating, sharping, post-sha״_jping, sharpening, post-sharpening, etc.

The metal bound working pieces of not conducting material may be tools or parts of tools. The hard materials may consist of, e.g., polycrystalline diamonds, borom nitrides, oxide ceramics, etc. The tools may be, for example, saws, cutting edges, rotating tools, chissels, drills, milling cutters, trueing blocks, trueing rollers, grindings discs, etc.

The high strength properties of said materials give the tools made from said materials longer stability and shorter working steps in comparison with other tools. However, said properties cause difficulties in the course of the manufacture or post grinding of said tools. Said positive properties have a negative influence in the manufacture and post-treatment of said high valuable tools and cause the manufacturer of same many problems. Therefore the manufacturers are always looking for finding special methods for the manufacture and posttreatment of such tools, which methods should be economic and precise. There have been several processes which enable sharping of the specific tool materials, e.g. synthetic diamonds and the like.

In the later time there have been made experiments to treat said non conducting working materials by electrical means

Thus in one method (U.S. 2 552 582, DE-PS 8874 6ל) the non conducting crystals are treated mechanically in a complicated process, that, for example, in addition to the drilling subsequently an electrical discharge can be performed. In accordance with another method (U.S. 4 102 157) small parallel guided wire electrodes are brought near to the diamond or brought into contact with same in such manner that the discharge acts on the diamonds. However said experiments did not result in the industrial manufacture of tools. They may be utilised for special problems which occur, e.g. in space travels.

There are also know processes (EP-A2 1O276=EA-A1 79 10J 948.8) in which the metallic binding material between the crystals of synthetic diamonds is attacked by way of electro- or spark erosion. These processes have advantages in particular in the manufacture or post-treatment of cutting surfaces of polycrjistalline synthetic diamonds. The surface roughness obtained obtained may be useful for certain cutting patterns. However if higher surface qualities are required, such surface roughness which result from the distribution and size of the parts of the hard material canot longer be allowed.

It is therefore the object of the present invention to make available a process and a device for the manufacture and post treatment of the above tools made from metal bond non conducting materials of high strength and stability which tools require an even higher quality of the surface.

- I The present invention thus consists in a process for the treatment (as herein defined) of working pieces, tools, parts of tools and the like of metal bond non conducting hard materials by way of electro erosion in which the part to be treated constitutes an electrode of the electro erosive system on which acts a second electrode which is moved characterised in that a rotating tool which acts also mechanically is used as second electrode which tool a is made also of/metal bond non conducting hard material®

It is !mown to use movable metal parts as electrode for pure treatment of metals but not for treatment of working pieces of hard materials such as polycrystalline synthetic diamonds. Thus, in the course of electro erosive sinking in metal rotating copper electrodes are used. The rotating metal part acts herein only in an electric manner. The spark is distributed by the rotation and an overheating of the electrode is avoided. The electrode and the working piece never contact each other. Such contact is even avoided by way of a complicated steering in order to avoid the destruction or deformation of the electrode which is made of a soft metal.

Moreover it is known to use for the pure treatment of metals wire spark erosion machines in which the thin wire substantially made of copper is moved quickly in the direction of its axis, however also in this process there is no contact between the metal working piece and wire used as electrode.

In the process according to the present invention one utilises opposite working pieces made of very hard working materials, e.g. polycrystalline synthetic diamonds which are to be shaped as tools, as electrode a moving, for example rotating,tool which normally serves, which contacting the working piece»to remove material mechanically. Said tool is steered like an electrode in such a manner that at the beginning there is no mechanical contact, but over a pre-determined small distance a material removing spark over is obtained from the working piece. In this manner one can obtain on an industrial scale in an economical manner the desired high quality of the surface. A precise explanation for this process can so far not be given. Most probably the electric discharges between the metallic part of the rotating tool and between the metallic part of the working piece which is to be shaped into a tool and is normally at rest, at first remove in the desired depth the metallic bond which surrounds the embedded non-conducting hard materials.

Due to the fact that the non conducting small, e.g. polycrystailine particles are not caught by the electrical change or only indirectly the discharge to the directly adjacent metallic areas, said particles remain as small residues in the form of elevations which are in a short moment caught and broken mechanically by the rotating tool. In the course of this short mechanical contact with a small particle no discharge occurs at this place. It can eventually occur that simultaneously with the mechanical catching of a non-actuating elevation set free from the metal bond,a discharge surrounds the adjacent metallic areas which favours and facilitates the mechanical removal.

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Thus there exists a significant difference between the treatment technique known from U.S. 4,236,985 in which there is performed a surface grinding of a pure metal piece. In said technique the grinding disc with a determined electrical // potential is kept in a permanentie-mechanical contact with the surface to be treated. Thus discharges occur only in the border region of the continuous mechanical treatment. Moreover the grade of effectivity of the additive discharge is not big as the electric conducting grinding disc is always short circuited with the working piece. This is also the case for a part of the other known technique in which the mechanical grinding disc is simultaneously or alternatively post treated electro erosively, due to the fact that said post treating electrode is pressed with a spring constantly on the grinding disc.

In accordance with the known technique one works, for example, with a stable electrode in the so called sinking process. The wire-spark erosion known from the metal treatment technique for cutting of certain profiles in electric electrolyte liquids is used for spark erosive treatment. Contrary thereto in the process according to the present invention a rotating or quickly moving used tool/as electrode is moved at the begining without any contact along a surface to be treated which is covered with a hard material in particular polycrystalline synthetic diamonds.

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Only when one obtains / the stream of sparks or of the voltage \ spark-petentien-a signal indicating that for the time or at the spot no electro erosive removal is longer possible, a mechanical removal is started which however is performed by the same tool. Thus the tool is on the one hand metallic and electrically conductive and on the other hand mechanically erosive. For this purpose there are in particular suitable synthetic materials such as polycrystalline diamonds in which the non-conductive part act mechanically erosive and the conducting part electrically erosive. The quick movement of the tool of the working piece enables that with both treatment methods and without any translation period all parts of the working piece can be treated. The finest profiles can be manufactured. Any contour can be manufactured or treated.

It is suitable to use for the performance of the process according to the present invention a tub closed at all sides in order to avoid that the liquid required at the treatment spot and thro^wn away by the rotating tool, leaves the device.

In accordance with an embodiment of the present invention the room surrounding rhe treatment spot may be completely filled with the treatment liquid so that the rotating tool is completely dipped into said liquid.

The rotating treatment tool, can for example, be a metal bond grinding disc. which may also comprise diamonds. Said diamonds may also be polycrystalline synthetic diamonds so that a grinding process is performed in addition to the spark erosive treatment between the rotating tool and the tool surface to be treated. For this purpose the rotating tool is guided al&g the expansion direction of the surface to be treated« Whereas the spark erosive treatment deals with the electrically conducting parts of the bond, the elevated non conducting parts are simultaneously treatedin the same manner as in an usual grinding process. This gives exceptionally good treatment results which makes any post treatment superfluous.

It should be stressed that the process according to the present invention concerns a genuine electro erosive treatment and it is not an electrolytic grinding# The electrolyte usually used for the spark erosion can be substituted by any other liquid suitable for the required heat transport . Even water may be utilised. However in this case a rust preventing agent is advantageously added.

The process according to the present invention differs also from the known electro erosive sinking by which metallic working pieces are treated and in which the electrode sinking into the working piece rotates.

In said electroerosive sinking a pure electrical process occurs, no contact between the electrode and the working piece is contemplated and such contact, if occuring would not improve the treatment process. Contrary thereto the process according to the present invention constitutes a combination between the contactless spark erosion and at the parts where it is required a genuine grinding.

Moreover the rotating tool does not move into the working piece, but it moves along the expansion direction of the working a piece. In this respect there exists also/difference to the wirespark erosion technique.

Advantageously there is utilised, according to the present invention, a grinding disc. This disc comprises the non conducting hard particles in a metal embedding and is caused to rotate. In the course of the rotating treatment the grinding disc remains, like an electrode, in a steered distance over the working piece.

The steering is advantageously performed independently in dependence on the electrical parameters of the spark discharge. For simple treatments, e.g. for the manufacture of cutting surfaces at saws, drillers or millers the working piece may perform below the rotating tool a for - and backward movement. However there are also other path movements of the tool and/or the working piece possible to enable the treatment of complicated profiles. These profiles pathes can be steered automatically by a program memory.

Therefore the known steering techniques may be performed for the steering of the feed in at least two levels, in order not only to post-accomplish electronic stored shape giving movements, but also in order in dependence of the electric parameters on the spark distance to perform post regulation in order to optimise the material removal«

In addition the angle velocity of the tool in dependence on the electrical parameters of the spark distance may be regulated or post-regulated in order to optimise also in this manner the material removal both in respect of an improved surface quality and of a rational finish.

Should, in the course of the scaning of the electrical parameters at the spark distance, a change be determined which can be identified, electrically or over an electronic interpretation as belonging to a non conducting region, then the electric not contacting removal is automatically transformed in a very short time mechanical contact removal in order to include the non conducting regions into the desired shape.

Normally the working piece will be at rest in the course of the treatment with the exception of an index movement in the course of the treatment breaks״ However in accordance with one embodiment according to the present invention it is possible when a rotation symmetric tool is to be manufactured from a working piece to let said working piece rotate.

Said rotation may take place clockwise or anti-clockwise in relation to the treatment tool. The relative angle velocity obtained may also be varied over a treatment process. Thus, for example, one may for an intensive electro erosive treatment of a metallic region maintain the relative circumferential velocity small at the treatment spot should this favour the electrical removal and to increase the relative velocity should the mechanical removal be thereby favoured.

When the process according to the present invention has been tested it has been shown that the transition between both manners of treatment occur in a short time and completely automatically and that said transitions are not visible without special measurements at the machine. The treatment noise changes. However as a change of the treatment noise occurs continuously due to the continuous post-regulating, the transition of the contactless into the contact treatment condition and vice versa is not visible. Only a change in the spark colour can appear for a short time and be observed as an indication of the different kind of treatment. Tests of the quality of the surface have shown that all roughness resulting from the non-conducting inclusions are smoothed.

The spark generator may be adjusted to various frequencies, current waves or pulses. The voltage and ¹ may also be adjusted in accordance with the requirements of the material. Moreover the spark distance may be over bridged with an adjustable capacity in a manner known per se from the metal treatment.

In practice it has been shown that the treatment may be performed in such a manner that after fhe manufacture of the surface having the desired quality with the adjustment of the various electrical parameters said surface may be sealed in such a manner that finally on a thin non conducting layer is made on the entire surface by mere working over in the same device with the same tool. This layer is constituted by treatment with or of synthetic diamonds of pure carbon.

The present invention will now be illustrated with reference to the accompanying drawings without being limited by same.

In said drawings:

Fig. 1 shows a perspective schematically view of a machine according to the present invention;

Fig.2 shows in detail a cooperation of tool and working piece;

Fig.3 shows a detail changed in respect to Fig.2 of another tool with another working piece;

shows in

Figs.4 to 8/shhematic section five successive steps of a treatment process;

Fig.9 shows a schematical black diagram;

Fig.9a shows a preferred wave form obtained from the spark generator;

Fig.10 shows a profile of a rotation symmetric tool obtained from a working piece; and

Fig. 11 shows a schematical perspective view of another embodiment of the machine provided with a tub as antiflash or for a dipped in treatment.

In machine stand 10 are arranged in an usual manner working piece carriages 12 and 14 which are movable one against the other in the X-direction. Carriage 14 carries tiol holder in which may move thereon/the !-direction. Working piece 20 which may swivel around axis 18 is clamped into holder 16. Opposite said working piece 20, of which in the illustration a finger miller may be made, is tool 22 which is movable in the X-direction. In this illustration the tool is a grinding disc with angled grinding rim 24 which is driven by a motor (not shown) in the direction of the arrow shown in Fig, 2.

Another use is shown in Fig.3. On the index axis is arranged four-cutter miller 21 with a metal main body 28 carrying cutting edges 24 made of fillets with polyorystalline synthetic diamonds. These are normally treated in an electro gap erosive manner over -s-l-i-t- 30 with the aid of the grinding disc and top disc 23 with grinding surface 26. Top disc 23 performs a rotation movement in the direction of the drawn arrow. Tool holder 16 may perform simultaneously a for- and backward movement in the !-direction. The feeding in the Xdirection occurs automatically on the basis of index values adjusted by operating board 40. The steering automation will be explained hereinafter in detail with reference to Fig. 9.

For the cooling of the treament spot and for the disposal of the removed material serves a medium stream being under pressure. Said stream is directed by adjustable jet 42 onto said treament spot. Jet 42 is connected via medium conduit 44 to medium storage 46. Below the treament spot the medium is collected in reservoir 48. The medium may be a light electrolyte or an air mixture with finely distributed demineralised water drops which do not cause harm to the electric discharge.

Advantageously a protecting gas, e.g. argon, may be used as medium, a

The material removal is apparently performed in accordance with the sections shown In Figs. 4-8 with respect to crossline B-B in Fig.2. (Said explanations have so far not entirely be ascertained.)

Both tool 22 as well as working pieie 20 which moves in the Y-direction are made of non conducting hgrd material particles in a metallic embedding. Working piece 20 comprises schematically in metal embedding 50 non conducting inclusions 52. In electrically surrounding 54 non conducting hard material inclusions 56 are also present in grinding tool 22. Fig. 4 sfeows how spark 60 splashes over from metallic part 54 over gap

6H4r30 to metallic region 50 and removes same. A feed move/ axis went in the direction of the X-ax-16- does not occur at this moment. Previously mechanically removed part 55 of non conducting inclusion 52 is still shown by dashed lines is gap however no longer present in-slit 50. Does the spark formation slow down in the course of the Y-movement, as a further non conducting inclusion 52 is caught, the electrical parameters change and eventually there occurs a subsequent feed in the X-direction. (Fife. 5) this continues nipt0 the mechanical contact with the next non conducting region 52 which according to Fig.6 is mechanically removed. Due to the fact that here occurs a contact of a non conductor with a non conductor, until eventually occurs a contact of conducting parts 54 with conducting parts 50, there may be obtained an electric signal which starts a backward movement in the X-direction (Fig. 7) and transmits over to the pure electro erosive gap '⁷treatment over slit=30 (Fig. 8). The change between electric and short time mechanical treatment occurs very quickly and speed with a rotation ntunber of the tool of 500-800 rotations/min is not directly visible.

Fig. 9 describes the steering in a schematical manner, adjusting switch

Spark generator 70 is adjustable by citoxrsing־lever 72 to various pulse forms depending on the material to be treated. The frequency is adjustable between 10 and 100 kHz. The voltage is between 100 and 300 Volt and corresponds to the relative velocity between tool 22 and working piece 20. The electrical energy generated in spark generator 70 is forwarded via leads

Aonduit-s. 74 and 76 to tool 20 and working piece 22, respectively, which are insulated from each other so that between both gap a spark can splash over־s±i־t 30. gap

Parallel to spark -distance- 50 is provided a stepwise adjustable capacity 31. Said capacity is known from the metal treatment for the performance of adjustments.

The feed of the tool may be regulated in dependence on current 102. The value of the current, being proportional gap 0 to spark distanee 50, may be forwarded to a comparator in which it is compared with an index value. As long as the value of the current is high this is an indicating signal for an intensive treatment in the course of a movement in the !-direction and no further feed is forwarded in the X0 0 direction. The moment the comp^ratir indicates that only a little current flows a further feed is forwarded in the Xdirection which enables a deeper penetration into the tool surface. By choosing the various index values the grade of treament can be pre-determined from rough to finest treatment.

Servomotor 94 is steered for the movement along the Y lead axis via steering conduit90 ־ and signal convertor 92.

Servomotor 94 can in the course of the treatment of straight k cutting edges perform a for- and backward movement. The scale of said for-and backward movement may be chosen from program memory 104 or from the back-coupled electrical values gap '

100, 102 of the spark -di-e-tanee-of steering circuit 40.

However, also a simple re-steering by an end switch is possible. Lead

GSAdult 106 provides a Z-signal to steering circuit 108 , from which servomotor 100, used for the height adjustment of tool 22, is influenced.

Finally the rotation number of driving motor 112 for tool may be adjusted via a /- signal which is created in circuit ׳ lead

114 in dependence on a signal forwarded to -eendui-t- 116.

Should working piece 20 have to be brought after each treatment step with an index movement into another position, motor 118 is provided as index motor which is steered by steering circuit 120 in accordance with an a-signal forwarded ' lead τ 0-c-ondtri-t-12 2. As indicated above motor 118 may be used continuously as rotating drive when working piece 20 is to be treated as rotation body and should rotate around its axis in the course of the treatment. Rotation symmetric tools may,in particular, be provided with a profile, e.g. that shown in Fig. 10, by a program stored in program memory 104. In said Fig. is schematically shown working piece 150 with non conducting hard inclusions 154 embedded in metal embedding 152. Said tool 150 should, with the aid of tool 156. receive profile 150. For this purpose a program is prepared in an analogous or digital manner, which program may be called from program memory 104 the moment tool 150 is clamped on axis 118 and ready for treatment. Motor 118 working drives then/pieee|150 and motor 112 drives tool 156, which normally is guided with-sH-Jtt 50 over profile 150 according to the steering signals.

Fig. 9a shows a prefered pulse form , which is forwarded gap from spark generator 70 to spark -d-lstanoe- 50. Is has been found to be favourable to choose a pulse form which is switched on one third of the period and switched off two thirds of the period.

Fig. 11 shows another embodiment with tool 21 which corresponds approximately to Fig. 5י

Segments 24a which contain polycrystalline synthetic diamonds may be treated, in dependence on the use of tool 21 on the front surfaces 24b (in working position in rotation direction of tool 21), on circumferential surfaces 24c or on both surfaces 24b and 24c simultaneously.

The present invention relates to the treatment ofjfront surfaces 24b or circumferential surfaces 24c shown herein by way of example« The following description deals with the treatment of circumferential surface 24c. However, it is readily understood that front surface 24b can be treated in the same manner the moment the parts of the device are brought into the required position. Tool 21 is mounted on axis 18 in order to bring it into the treatment position. Axis 18 is connected to index device 16 which may be adjusted by hand or automatically. Said device 16 sets the tool before each treatment in the required manner into the exact position.

Index device 16 is schematically described herein as an automatically steered index device. Baid device 16 is connected with an electrical cable to the above described steering circuit 120.

In the illustrated position a spark erosive treatment of circumferential surface 24c, shown in the left part of the drawing, is performed. Rotating electrode 22a, which advantageously is a tool covered with polycrystalline diamonds is used for the spark erosive treatment. In the illustration said electrode 22a is a metal bound grinding disc with synthetic diamonds. Grinding disc 22a is mounted on a shaft which is caused to rotate by electric drive 112. The steering of this speed rotation and thus the regulation of the rotation-number of grinding disc 22a is performed via steering circuit which provided drive 112 preferably with direct voltage. Direct voltage is prefered as it enables to build a small unit and ascertains a good regulation. Moreover, it enables to work with a low voltage which decreases the insulation problems, as drive 112 and grinding disc 22a should be able, in this case, to work partially or completely in a dipped in position.

The mechanical unit constituted by grinding disc 22a and 88 drive 112 is hung on steerable and movable arm58־. the movement possibilities are indicated by drawn arrows. The regulation of the performance of certain treatment-, feed- or taking off movements is carried out via steering circuits 86, 92 and 108 to which steering arm 88 is connected.

In the shown case there occurs in the course of the treatment of circumferential surface 24c on tool 21 an axial movement, by way of spark erosion of rotating grinding disc ^2a, in the direction of the axis extending towards drive 112, in addition to the rotation of grinding disc 22a.

Spark generator ?0 is provided for the spark formation between grinding disc 22a and circumferential surface 24c. lead

Electrical conduit-74, connected to generator 70, is connected to a shaft which is insulated from the other parts. In this manner said shaft forwards electrical current to grinding disc 22a and thus causes grinding disc 22a to be one electrode lead in the spark erosive treatment. The other electrical-conduit— 76 from spark generator 70 leads to the unit, electrically insulated from the other parts, constituted by axis 18 and tool 21 , which tool 21 is mounted on said axis 18 and electrically connected thereto. Thus tool 21 become^ the second electrode of the spark erosion. The spark flash over slit JO together with the rotating grinding movement, which catches the non conducting parts of the diamond embedding, ascertains a quick and very precise treatment.

speed

The spark frequency, the rotation־rramher and the distance at which rotating electrode 22a is moved along surface 24c , as well as the size and the direction of the shaft in its axial direction may be adjusted by a program into the optimal and desired values. For this purpose steering circuits 120, 114, 80, 92, 108, 42 and 36 and spark generator 70 are connected to each other via process steering device 40. Thus, the gap ,spark frequency of erosion spark di^ance 30 may be coupled via generator 70 with steering circuit 114 for drive 112 in speed such a manner with steering circuit 40, that the rotation mmrbei of drive 112, the spark frequency and the voltage harmonise with each other in a maximal manner. The spark frequency is dependent on the kind and the circumference of rotatable tool 22a. The rotation number of drive 112 must be so regulated that the spark does not tear off or does not ignite again.

As dimension for the post-regulation one may use the differing spark voltage or the changing spark current.

The spark erosive treatimait is performed in liquid 162. For this reason the treatment station with tool 21 to be treated and treatment tool 22a are in tub 164 which is filled with liquid 162» the feeding of the treatment spot with liquid and the removal of heat is ascertained by adjustable direct conduit 44.

In case that the treatment is not performed in a complete dipped in position, liquid particles are whirled by rotating tool 22a and tub 164 may be closed with cover 166. Tool 21 to be treated, rotating treatment tool 22a and its drive 112 can be arranged within tub 164. Index device 16 may be outside tub 164» One has to take care about the insulation of the passages through the walls of tub 164 and of cover 166. Cover 166 may be provided with a bellow like sealing, which seals off the outward extending parts of steering arm 88 but does not hinder the movement thereof. Liquid 162 may be an usual electrolyte, a suitable lubricant or a suitable cooling agent. It is also possible to work in water to which optionally a rust preventing agent has been added.