DE2137829B2 - Process for the production of the material for a spark erosion electrode - Google Patents

Description

The invention relates to a method for producing the material for a spark erosion electrode Consists of 18 to 22% copper, 0.5 to 1% nickel, the remainder tungsten, in which the tungsten powder mixed with paraffin dissolved in petroleum ether, the petroleum ether removed by evaporation that with the paraffin homogenized and set powder is pressed and impregnated with copper.

The use of copper, brass, cast iron, tungsten or of pseudo-alloys W-Cu for the The manufacture of electrodes for use in electrical discharge machining machines is known.

The copper, brass and cast iron electrodes have the disadvantage of low volumetric Efficiency that leads to faster wear due to spark erosion when machining workpieces • Uses cemented carbides as well as stainless and heat-resistant steels.

In addition, these known materials cause difficulties in precision machining, while Rolled copper and brass are sensitive to deformation during operation because of their fiber structure Are.

The use of tungsten and the pseudo-alloys W-Cu is technically limited by the fact that these materials have to be produced at very high temperatures above 2000 ^° C., which is technically difficult and affects profitability.

From DT-AS 12 53 919 is the powder metallurgy Production of spark-erosion-resistant molded bodies made of tungsten and copper is known, with the tungsten powder is pressed into the desired shape and the unsintered compact is impregnated with copper will. A mixture of copper powder and tungsten powder can also be used according to a known method pressing and then sintering, whereby there is no impregnation with copper. It is also known that To press tungsten powder and to sinter it, whereupon copper is introduced into the porous pressed body by impregnation will. Nickel is never present. The areas of application for tungsten-copper materials are limited.

From F. Eisenkolb, "Advances in Powder Metallurgy", Vol. II, 1963, p. 432 is the technology of sintering tungsten in the presence of nickel additions from 1 to 2%, i.e. without copper, known So far as an influence on the sintering behavior tungsten is described by other metal additives, such as nickel and, to a lesser extent, cobalt, A sudden increase in density is reported for nickel additions in the range from 0.025 to 0.1%; further it is reported that higher nickel contents give no further improvement. Such materials are sufficient does not meet the high demands of electrical discharge machining.

The DL-PS 50 751 describes the production of envisaged by Tränklegierungen use of a highly porous sintered material made of tungsten powder in a mixture with reducible tungsten compounds, the pressed to give moldings and is sintered in hydrogen between 900 and 1200 ⁰ C. With such tungsten materials, between pressing and soaking (with copper or silver), a sintering process at temperatures between 900 and 1200 ^° C. can also be switched on according to a known procedure. Nickel is not involved. The impregnating alloys to be produced are used to produce contact materials, which naturally have different technical requirements than spark erosion electrodes.

Finally, one takes from "Berg- und Hüttenmännische monthly books", Vol. 94, 1949, pp. 284 to 294, in particular P. 287 that in the case of known, excessively porous process products obtained after impregnation - obviously due to insufficient wettability of the tungsten powder by copper - the wettability thereby can be increased that you add metals to the skeletal body, which are also with the impregnation metal alloy, e.g. B. nickel to tungsten, which improves the impregnation of this metal with copper. These however, general versions do not contain detailed instructions for the manufacture of High performance electrodes.

Therefore, the object of the invention is to provide a process for the production of a high-performance material for spark erosion electrodes, which has a high, volume-related level of performance for both roughing and fine machining offers.

This object is achieved according to the invention in that the tungsten powder is mixed with a nickel nitrate solution and treated in a reducing manner before mixing with the paraffin and that the pressed body with removal of the paraffin and without deformation at a heating rate of 200 ° / hour while maintaining constant temperatures in each case ' / 2 hours with increasing the temperature by 100 ° in each case in the temperature range from 300 to 600 ° C and then ^{heated to 1170 to 1200 0} C and sintered at this temperature for 1 hour before the impregnation.

The invention is explained in more detail below using an exemplary embodiment.

example

The material for the production of electrodes, consisting of 18 to 22% Cu, 0.5 to 1% Ni, remainder W, is by activating sintering of the nickel-containing tungsten powder with subsequent soaking with copper in

the W-Ni sintered product obtained by homogenizing the tungsten powder with a concentrated nickel nitrate solution. The nickel content is calculated stoichiometrically; after previous drying the mixture in Wasserstoffstro.T "is reduced at about 600 ⁰ C.

The resulting W / Ni mixture is then mixed with a solution of paraffin in petroleum ether mixed evenly to increase powder density. Instead of the substance that evolves in the course of the subsequent Heat treatment completely volatilized, copper is made by soaking by means of capillary action brought in

After the petroleum ether has been completely removed, the mixture bound with paraffin is pressed into a geometric shape that approximates the desired electrode as closely as possible. The pressing is carried out in heat-treated tool steel matrices using hydraulic or mechanical-hydraulic presses customary in powder metallurgy at a specific pressure of 3 t / cm ² . The compacts obtained in this way are subjected to an activating sintering with Ni as the activating agent. The activating effect of nickel in the sintering of tungsten consists in the transfer of part of the free electrons of the W atoms, which results in a reduction in the energy consumption of the entire system and enables sintering at relatively low temperatures.

The activating sintering in the hydrogen atmosphere takes place at a temperature of 1170 to 1200 ^° C. for one hour. The heating rate to reach the sintering temperature is selected such that it enables the paraffin separation, ie 200 ° / hour in stepwise paragraphs of each '/ 2 hour from 100 ⁰ C to 100 ⁰ C starting from 300 ° C up to and including 600 ° C.

The W-Ni sintered workpieces obtained in this way are then subjected to copper impregnation, which takes place at 1150 ^° C. in a hydrogen atmosphere or in a vacuum, the copper originally in the form of powder, tape or wire with a 10 to 15% excess over that for the Preservation of the given composition stoichiometrically calculated amount is introduced.

The copper is placed on the bottom of a crucible made of refractory bricks according to the dimensions and the shape of the various workpieces introduced.

At the specified temperature, the copper is in a liquid state and quickly penetrates the pores of the sintered W-Ni material created by the paraffin precipitation, whereby a dense Material is obtained which is practically pore-free and in which the copper is uniformly distributed.

The workpieces obtained after the copper soaking are used to remove the excess copper and to obtain the shape and final dimensions of the electrode as well as the desired surface finish mechanically processed.

These materials are particularly advantageous in that the electrodes obtained have a high have volumetric efficiency in both roughing and finishing; the machined surfaces are of excellent quality with high dimensional accuracy; aside from that this material can be produced easily and very economically.

Claims (1)

Paterl claim: Process for the production of the material for a spark erosion electrode, consisting of 18 up to 22% copper, 0.5 to 1% nickel. Remainder tungsten, in which the tungsten powder with dissolved in petroleum ether Paraffin mixed, the petroleum ether removed by evaporation, which homogenized with the paraffin and set powder is pressed and impregnated with ι ο copper, characterized in that the tungsten powder before mixing with the paraffin with a nickel nitrate solution is mixed and treated reducing and that the pressed body with removal of the paraffin and without deformation at a heating rate of 200 ° / hour while maintaining constant temperatures in each case 1/2 hour long when the temperature is increased by 100 ° in the temperature range from 300 to 600 ° C and then heated to 1170 to 1200 ° C and at this temperature sintering for 1 hour before soaking.