EP1362934B1 - Fixing device for at least one workpiece - Google Patents

Description

The present invention relates to a holder according to the preamble of claim 1.

To improve the surface properties of hard metal workpieces, such as the life and / or efficiency of tools, in particular indexable inserts, drills, milling cutters, forming tools, stamping tools, it is common today, such workpieces with a hard material layer, such as titanium nitride or titanium carbonitride to coat. As the coating method, widely used vacuum coating methods are preferably used. Since carbide workpieces, especially in complex forming, for example, according to the above-mentioned tools, are expensive, it is attempted to save the workpiece, if it is mis-coated, or in particular, if the workpiece has been worn through use, shape-forming and re-coating , For this purpose, the affected workpieces must first be stripped. The stripping of workpieces of the type mentioned is a difficult and challenging technical problem. Whether this problem is fed to a solution which can be used economically is ultimately of crucial importance as to whether the mentioned workpieces are being overworked or disposed of in economic terms. Even with careful procedure during the coating, process defects or process interruptions that can lead to inadequate coating of the hard metal workpieces with the hard material layer often occur. Also, contract coating companies may be confused with customer requirements for layer type and layer thickness. The resulting scrap costs are with carbide workpieces especially high. The cost of the uncoated workpiece - the base body - can easily amount to three times ten times the layer value.

For the stripping of steel workpieces is from the DE-41 01 843 For some time a method is known which allows the detachment of the hard material layer. This method uses a solution of hydrogen peroxide which dissolves titanium compounds and other hard material compounds. This is about the fact that the workpiece itself is not attacked in an inadmissible manner and thus damaged. For example, the use of acids and alkalis would unduly damage the steel workpieces. For hard metal, which consists predominantly of the hard material tungsten carbide and the chemically unstable cobalt, this method is completely unsuitable because the carbide body of the workpieces would be destroyed faster than the hard material layer dissolves.

For this reason, mechanical processes are largely used today for faulty coated hard metal workpieces or for such workpieces which are to be coated again for the stripping of the hard material layer. The hard coating is abraded or polished off. The costs are high. For this reason, such methods are used very rarely, and in their place erroneous workpieces are disposed of.

Now, from "Research Disclosure", April 1996, under the heading No. 38447, a method for stripping a hard material layer applied on a hard metal workpiece has become known, in which stripping is performed by electrolytic passivation. In this case, a tungsten oxide layer is electrolytically formed between the hard material layer and the hard metal base body. This passivation of the tungsten carbide is carried out by anodic polarization of the workpiece in a suitable electrolyte. Due to the transformation of tungsten carbide into Tungsten oxide loses the hard material layer its adhesion to the body and flakes off.

The decoating conditions to be chosen are extremely critical. With incorrectly selected parameters, the layer is either not removed or the workpiece is irreparably damaged.

The state of the art is also the re-coating of tools without prior stripping. For this purpose, the tools, preferably shank tools made of hard metal, such as milling cutters, drills and hobs, are reground on the cutting surfaces and then coated again. This method has the disadvantage that only the cutting surfaces are free of layers by the regrinding, but the remaining areas of the tool remain coated. During the subsequent overcoating, therefore, the thickness of the hard material layer in the non-reground areas steadily increases. As the layer thickness increases, the residual stresses in the urea layer increase, which leads to a reduction in the service life of the tool compared to a tool coated once only. The residual stresses often lead to breakouts in the area of the transition from the coated to the uncoated part during regrinding of a coated tool and reduce the performance of the tool.

From the DE 11 03 103 It is known to provide the shaft of a poppet valve in a dip by electrolytic chromium deposition with a uniform, dimensionally accurate chrome coating. In this case, the valve stem end is performed by a plug-in hole in a bottom of an insulating cup. The hole diameter is just so large that the aforementioned plug hole closes the threaded portion of the valve stem as liquid-tight as possible. The projecting from the Isoliernapf part of the valve stem is exposed to the electrolytic chromium deposition under current application.

From the US 5,405,518 It is known to etch disk-shaped, electrically conductive workpieces electrochemically one-sided. For this purpose, the not to be etched disk surface is encapsulated by the electrochemical etching. A first seal is provided along the periphery of the disc surface to be treated. A circumferential clamping frame braces this seal and another circumferential seal, the latter between clamping frames and the housing of an encapsulation chamber. This results in the disc surface to be treated, a space encapsulated by electrochemical action, wherein said disc surface is protected from electrochemical etching.

Similar to the US 5,405,518 is it from the DE 40 24 576 It is also known to protect one side of a wet-etchable wafer from etching by sealing the wafer along its periphery between two plate-shaped members, one of which is annular to allow access of the etching solution to the one surface of the wafer enable.

It is an object of the present invention to provide a holder of the type mentioned for another type of workpiece.

This is achieved by means of a holder, which is characterized by the characterizing part of claim 1.

The holder is, as far as known today, for stripping all commonly used conductive hard coatings, such as hard coatings of nitrates, carbides, carbonitrides of metals or metal compounds, such as TiAlN, TiAlNC, WC, WCN, etc., but also of chromium-containing hard coatings . such as Cr, CrN, CrC, CrNC and combinations of these hard material layers or multilayer arrangements.

For certain workpieces, such as hob cutters - an essential field of application of the present invention - it is impossible to immerse surface areas where the hard material layer is provided and which are to be stripped into the electrolyte simultaneously with surface areas where no hard material layer is provided. In hob cutters, essentially constructed as a hollow cylinder, the inner surface is namely hard material layer, while the outer surface, the working surface, is coated hardstoff. In order to be able to fulfill the requirement in the last-mentioned case of not bringing hard-material-free areas of the workpiece into contact with the electrolyte, the holder according to the invention is used.

The sealing elements can be moved axially relative to each other to be clamped against the workpiece end faces.

Furthermore, an electrical contact arrangement is provided on the rod section provided between the sealing elements, the electrical supply to the contact arrangement more preferably being guided through the rod.

In one embodiment of the last-mentioned holder, a tensioning body which is expandable or contractible by axial clamping radially with respect to the rod axis is provided on the rod portion located between the sealing members, on the periphery of which the contact elements are provided. In this case, acting on the support in the direction of the support rod axis clamping members are provided for the clamping body to clamp the contact elements, by clamping the clamping body against the workpiece. This makes it possible, regardless of the diameter of the passage opening, to contact the workpiece optimally electrically in wide areas.

But preferred is a simplified embodiment in which a radially resilient contact body is inserted into the passage opening and without additional clamping ensures the electrical contact.

It is imperative that parts of the holder come into contact with the electrolyte. Therefore, it is further proposed on the holder, that on both sides of the sealing elements outwardly located support portions have an outer surface made of a plastic, preferably made of Teflon.

As mentioned, the holder according to the invention is particularly suitable for the workpiece holder when carrying out the method according to the invention mentioned in the introduction.

The inventive holder is suitable for workpieces with passage opening, in particular for hobbing.

For the time being, the procedure for the stripping of workpieces will be further described by means of examples.

In an electrolytic solution of 2 mol / l of acetic acid and 2 mol / l of ammonium nitrate, at pH = 2, hob cutters were stripped off with the aid of the holder according to the invention. By using the mentioned, to be described in detail holder was taken care that only the hard-coated working surfaces of the cutter were contacted with the electrolyte. With an approximate effective area size of 1'000 cm ² , even at an initially generated maximum current density of 0.02 A / cm ^{2, the} hobs were stripped within 3 minutes. Generated by applying a constant voltage, this resulted in an initial maximum current, corresponding to the required maximum current density, of 25 A per simultaneously treated cutter, which dropped in the mentioned period of 3 min. To less than 4 A per hob.

Furthermore, a hob in the ammonium nitrate-acetic acid electrolyte was stripped within 3 minutes by applying a voltage of 15 V, an initial current of about 300 A and a passive current of about 50 A.

In addition to the acetic acid-ammonium nitrate electrolytes used in the examples, it is also possible to use other electrolyte compositions which lead to the passivation of the cemented carbide. For example, a sodium nitrate-acetic acid, ceric ammonium nitrate-acetic acid, ceric ammonium nitrate nitric acid or ceric ammonium nitrate perchloric acid electrolyte can be used.

Subsequently, the inventive holder for workpieces will be explained with reference to a figure.

In the single figure, an embodiment of the inventive holder is shown in longitudinal section, schematically and simplified.

On a metallic tube 1, a clamping body 3 is screwed with threaded blind bore 5, terminal. Detachably mounted along the tube 1, a counter-clamping block 7 is provided. At the facing end faces 7 _u and 3 _{o of} the two parts 3 and 7 sealing elements 9 ₇ and 9 _{3 are} provided. Dashed in the figure, a workpiece 11 to be held, in the form of a hob. As can be seen, the workpiece 11 is clamped between the end faces 7 _u and 3 _{o of} the parts 7 and 3. The sealing elements, for example O-rings 9 ₇ and 9 ₃ , sealingly abut end faces of the workpiece 11 in the region of the passage opening 11 _o . This results in an encapsulation of the uncoated workpiece inner surface 11 _i relative to the coated outer surface 11 _a , which latter can now be subjected to a processing by means of an electrolyte B, without thereby the encapsulated inner surface 11 _i would be impaired.

It is immediately apparent that the mount as described so far, excellent suitable for the inventive stripping of workpieces 11, what only the outer surface 11 is to be stripped _A - by contact with the above-mentioned electrolyte - while the inner surface 11 _i from the electrolyte should remain undisturbed.

The electrical contacting of the workpiece 11 takes place on the inner surface 11 _i via an electrical contact arrangement 13, wherein the electrical connection for a (not shown) power supply, as shown with E _e , via the metallic tube 1 outside the electrolyte.

In order optionally to take into account deviations or scattering of the inner diameter φ _{i of} the cylindrical inner wall 11i of the workpiece 11, the electrical contact arrangement 13 can now be applied to the periphery of a resilient, for example rubber-elastic, actively tensioned clamping body 5, as shown in the embodiment according to the FIGURE , which rests on a shoulder 17 on the tube 1. The clamping body 15 is fixedly connected to the body 7, both riding axially slidable on the tube 1. By means of an actuator 19, such as an adjusting nut on a threaded end of the tube 1, the clamping body 15 can be axially actively more or less compressed, which As shown by the arrows r, leads to a more or less pronounced radial, outward-evasion and thus moving the contact assembly 13. The electrical signal is carried out, as mentioned, via pipe 1, collar 17, bottom 15 _{u of} the clamping body 15, at its periphery. When inserting the resilient contact 13, 15 between the tool and the power supply the electrical connection is created.

The workpiece 11 is mounted here as follows:

The clamping body 3 is removed from the tube 1. Thereafter, the workpiece is placed over the clamping body 15 in abutment with the seals 9 and _{7 created} by tightening the screw 19 and expanding the clamping body 15 in the context of its inherent elasticity an optimal electrical contact with the inner surface 11 _{i of} the workpiece 11.

Thereafter, the body 3 is placed and clamped by screwing the workpiece 11 between the seals 9 ₇ and 9 ₃ , whereby both the inner surface 11 _{i of} the workpiece against the environment U, in particular with the electrolyte B, is encapsulated and further optimal electrical contact Largely tolerance-independent is created.

In a preferred, much simpler embodiment of the spring-trained clamping body 15 rides fixed on the tube 1, and the electrical contact with the workpiece inner surface 11i is carried out by resilient application in invagination of the clamping body 15 in the opening of the workpiece.

In this preferred embodiment, the workpiece 11 is slipped over tube 1 with its fixed thereto provided resilient clamping body 15, after which the body 7 is placed from above the pipe 1, and there is the sealing clamping of the workpiece 11 between the sealing elements 9 ₇ and 9 respectively ₃ by means of the actuator 19, for example an adjusting nut, which is screwed onto the external thread of the tube 1.

Those parts which come into contact with the electrolyte U for the workpiece outer surface 11 _a , ie in particular with the electrolyte bath B in preferred use in connection with the electrolytic Entschichtungsverfahren according to the invention, are made of materials which neither affect the intended treatment nor by the intended treatment yourself be affected. The clamping body 3 and at least the facing this games of the counter-clamping body 7, preferably its entire surface are made of a plastic, preferably made of Teflon. In the preferred simplified embodiment of the holder - as explained - waived the radial adjustability of the contact assemblies 15.

Claims (4)

1. Fixing device for at least one workpiece, at which at least a first surface area is to be treated under impact of electrolyte, at least a further surface area not, wherein an encapsulation at the fixing device for the further surface area of the workpiece and at least an electrical contact in the encapsulation for the further surface area are provided, characterized in that for a workpiece, which is furnished with a recess formed as a passage opening, at which the inner surface of the recess or the outer surface is to be treated, the fixing device comprises a pair of sealing elements being arranged in fitting manner at the workpiece at the front around the opening , which, being axially offset, are arranged along a carrier rod, of which a section lying between the sealing elements is dimensioned for feeding through the passage opening.
2. Fixing device according to claim 1, characterized in that a contact arrangement is provided between the sealing elements in a provided section of the bar, wherein preferably an electrical input to the contact arrangement is lead through the bar.
3. Fixing device according to one of the claims 1 or 2, characterized in that the fixing sections subsequent on both sides to the outside of the sealing elements comprise an outer surface out of Wolfram and/or Tantalum and/or a resin, preferably Teflon.
4. Use of the fixing device according to one of the claims 1 to 3 for workpieces, at which a hard material layer comprises at least one of the following materials:

   - a nitride, carbide, carbon nitride of a metal or of a metal compound , like for example TiAlN, TiAlNC, WC, WCN, WN;

   - CrN, CrC, CrNC or Cr.

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