EP0545145B1 - Manufacture of a porous copper-based material as a preform for a machining process - Google Patents

Description

The invention relates to a method for producing a semi-finished product from a copper material suitable for machining work, in particular a semi-finished product with improved machinability.

Semi-finished products made of copper alloys are widely used for the production of parts in which machining work such as turning, drilling and milling must be carried out. These alloys usually contain additives such as lead or tellurium, which act as chip breakers and at the same time facilitate the economic processing of semi-finished products in the form of tubes, rods, sheets or strips made of the alloys mentioned into small parts.

For hygienic reasons, attempts are made to limit the lead content in those parts which, for. B. come into contact with drinking water in supply lines, etc.

On the other hand, the addition of the chip breaker described is difficult because this also means the production of the preliminary products, such as. B. rods, tubes and profiles, is restricted by the usual manufacturing steps hot and cold forming. The reason for this is the inevitable side effect of these chip breaker additives, which have an embrittling effect on the base material.

Porous copper materials are also known; So far, however, the efforts of the professional world have always been directed towards the pores as far as possible to be completely eliminated in order to achieve the best possible properties of the copper material (cf. for example WO 90/11 852).

The invention has for its object to provide a method for producing semi-finished products suitable for machining work from copper materials without adding the harmful chip breaker additives such as lead or tellurium. The method enables in particular the economical production of semi-finished products with improved machinability. According to the invention, the basic idea leading to the solution of the problem is to use the pores contained in a porous preform made of copper material as chip breakers.

This object is achieved according to the invention in a method of the type mentioned at the outset by producing and sintering a porous preform from copper powder or copper alloy powder by powder metallurgy and by using cold and / or hot forming to produce the semifinished product from this preform in the form of rods, tubes, Profiles, wires, sheets or strips with a volume fraction of pores of 0.05 to 10% is produced. A preferred embodiment is characterized in that the average particle size of the copper or. Copper alloy powder is 2 to 3000 microns.

A further solution to the problem in a method of the type mentioned at the outset according to the invention is that a porous preform is produced by the spray compacting process, in that a metal melt made of copper or a copper alloy is broken down into metal droplets by atomization and the metal droplets are sprayed onto a base, whereby a gas-metal ratio of 0.05 Nm ³ / kg - 1.5 Nm ³ / kg is maintained, and that from this preform by means of cold and / or hot forming, the semi-finished product in the form of bars, tubes, profiles, Wires, sheets or strips with a volume fraction of pores 0.05 to 10% is generated. The mean droplet diameter is preferably 5 to 200 μm.

Furthermore, it is advantageous if the pores are gas-filled, since while the porous copper material is being processed, the remaining pores change their shape, but do not close completely because the cavities are stabilized by the gas. It is particularly advisable if the pores are filled with a gas which is insoluble in copper or a copper alloy, such as nitrogen, noble gas, helium or carbon dioxide. Further preferred embodiments of the method according to the invention are therefore characterized in that, in the case of a powder metallurgical method, the preform is sintered in an atmosphere which contains gaseous components which are insoluble in copper and copper alloys, and in the case of a spray compacting method as a spray gas in copper or in the copper alloy insoluble gas is used.

According to both solutions according to the invention, the pores generated in the copper material serve as chip breakers. The pores mean localized weakening of the material, which leads to the chips breaking during the cutting process. As usual, the pores can have three-dimensional dimensions; however, they can also be pressed into almost two-dimensional structures by mechanical deformation of the matrix. The pores take the place of additives acting as chip breakers, which are opposed to hygienic or technical concerns. The invention thus provides a semi-finished product which is hygienically perfect and very well suited for machining work is.

A method is known from US Pat. No. 2,881,511 in which a porous preform is made from copper alloy powder by powder metallurgy and sintered and the desired workpiece with a porosity between 2% and 13% is formed from this preform by steps of cold and / or hot forming. is obtained. However, this known method is used to produce objects which are particularly wear-resistant by adding nickel and titanium and which, if possible, have self-lubricating properties and are no longer intended for further machining. The known method is therefore not aimed at improving the machinability of the copper material produced in this way.

SU-A-511 362 describes a powder-metallurgically produced tungsten and calcium fluoride-containing copper alloy with a pore content of 15 to 20%, which is particularly stable and machinable against erosion. However, there are no steps involved in cold and / or hot forming following the sintering process.

The document Metals Handbook 1984, ASM, Vol. 7: "Powder Metallurgy" describes on pages 735 to 740 copper materials of various types produced by powder metallurgy, but contains no reference to cold and / or hot forming of the sintered preform to a specific pore fraction and for an improvement in machinability that can be achieved. On page 742 of the document, the good machinability of P / M aluminum compared to "wrought" aluminum is emphasized in connection with FIG. 1, but this is the case P / M aluminum referred to is only a preform obtained by powder metallurgy, which has subsequently not been subjected to any cold and / or hot deformation. - From pages 620, 667, 725 and 735 of the document, especially from Fig. 13 on page 620, there is the possibility of machining sintered parts, but in Fig. 13 there is obviously a step missing between the processing stages of sintering and machining cold and / or hot forming. 1 on page 667 are used for producing the workpiece, several successive stages of sintering and compacting pressing are used, but the production of the preform, which is then only machined, ends with a sintering process, so that the steps of cold and / or hot working are missing. Furthermore, it is known from page 725, FIG. 21 to hot-roll a preform produced by powder metallurgy and then to subject it to a heat treatment again before the semi-finished product thus obtained is machined. However, as can be seen from the description on page 724, hot rolling and the subsequent hot treatment serve precisely to remove the existing pores, so that this citation does not describe the invention, as was already explained at the beginning of WO 90/11 852, According to which porous copper materials are known as such, the efforts of the experts were directed towards removing the pores as completely as possible in order to achieve the best possible material properties. - The same applies to the spray compacting method known from pages 530 to 532 of the document, in which the subsequent hot forging of the porous preform likewise serves the most possible pore removal; in any case, this section of the document contains no indication that the hot forging only reduces the pores in the manner according to the invention to such an extent that the machinability is significantly improved.

Finally, it is known from EP-A-0 456 591 that end products made of copper material are produced by machining, starting from rod material which has been provided by means of spray compacting / hot forming. However, here too there is no indication that the hot forging did not serve to largely or completely remove the pores and that the machinability could improve if the hot forging had left a proportion of pores in the semifinished product according to the invention.

Brass and bronze alloys are preferably used for the processes according to the invention, but the application of the invention to other copper alloys is readily possible if required.

A suitable brass alloy contains in particular 1 to 45% zinc, aluminum (maximum 10%), nickel (maximum 20%), tin (maximum 6%), silicon (maximum 4%), iron (maximum) are recommended as individual components or in combination 2%), manganese (maximum 8%). Other optional components that can be added individually and in combination to achieve special strength properties are titanium, chromium, zirconium, beryllium, magnesium, phosphorus, antimony, each up to a maximum of 1%.

A suitable bronze alloy contains in particular 0.1 to 12% tin, zinc (maximum 6%), nickel (maximum 5%), iron (maximum 4%) as additional components individually or in combination are recommended as well as further optional components for setting special properties the elements phosphorus, chromium, zirconium, titanium, magnesium (maximum 1% each).

An aluminum bronze alloy which is also suitable for the processes according to the invention contains in particular 1 to 10% aluminum and, as optional components, individually or in combination iron (maximum 5%), nickel (maximum 8%), silicon (maximum 4%), manganese (maximum 5%), Tin (maximum 3%) and as additional optional components chrome, titanium, zircon, magnesium, phosphorus, up to a maximum of 1% individually or in combination.

A low-alloy copper alloy suitable for the processes according to the invention contains, as optional components, individually or in combination phosphorus (maximum 0.5%), iron (maximum 4%), tin (maximum 3%), nickel (maximum 4%), silicon (maximum 2%). ), Chrome (maximum 2%), cobalt (maximum 2%), beryllium (maximum 2%) and as further optional components titanium, zirconium, magnesium, manganese, arsenic, zinc up to a maximum of 1% individually or in combination.

Fig. 1a

den Längsschliff einer gesinterten Kupferprobe,

Fig. 1b

den Querschnitt einer gesinterten Kupferprobe,

Fig. 2

Spanformen der gesinterten Kupferprobe nach Fig. 1,

Fig. 3

Spanformen von einer konventionell hergestellten Kupferprobe,

Fig. 4

den Querschliff einer weiteren, gesinterten Kupferprobe und

Fig. 5

Spanformen der gesinterten Kupferprobe dre Fig. 4.

The invention is explained in more detail using the following exemplary embodiments. It shows

Fig. 1a

the longitudinal grinding of a sintered copper sample,

Fig. 1b

the cross section of a sintered copper sample,

Fig. 2

Chip shapes of the sintered copper sample according to FIG. 1,

Fig. 3

Chip forms from a conventionally produced copper sample,

Fig. 4

the cross section of another sintered copper sample and

Fig. 5

Chip shapes of the sintered copper sample dre Fig. 4.

Example 1:

A powder of copper with a grain size of 25 µm obtained by atomization is mixed with a lubricant (stearic acid) in the usual way and pressed to a green body of 95% density. The green body becomes after one Temperature program led up to the sintering temperature so that the lubricant is expelled. The sintering temperature is 1000 ° C, the sintering time 2.5 h.

Fission gas obtained from ammonia at atmospheric pressure is used as the sintering atmosphere. After sintering, the body now has a density of 98.5% of the theoretical and contains closed pores.

The sintered body is cold worked at room temperature by rolling by about 30%, the pores being stretched. This creates a structure as is characterized in FIG. 1a on a longitudinal section and in FIG. 1b on a transverse section (magnification 200: 1). The material is interspersed with evenly fine pore tubules.

The turning test on a lathe produces much shorter chips (Fig. 2 / L: longitudinal turning test, P: face turning test) than those of bars that were made from completely tight, continuously cast bolts by pressing and pulling (Fig. 3).

Example 2 :

The procedure is the same as in Example 1 , with the difference that now coarser powder with a grain size of 25 to 50 µm is used. This results in a somewhat coarser pore structure after cold forming, as can be seen from the cross section in FIG. 4. When turning on a lathe, low-cost chips are produced in this case, as shown in Fig. 5 (L: longitudinal turning, P: face turning).

Example 3 :

A melt of CuFe2P with the composition 2.3% iron, 0.022% phosphorus, the rest copper and usual impurities is sprayed with the help of the spray compacting process (OSPREY process) to an approximately 30 mm thick plate. Pure nitrogen is used as the spray gas. By suitable Selection of the spraying method, in particular the gas-metal ratio of 0.42 in the atomization stage, ensures that the consolidated plate has a density of 85% of the theoretical.

The plate is milled on the outside, then heated to 930 ° C and cold rolled by 40%. A piece for turning tests is worked out from the rolled sheet. This rod has a density of 98.5% of the theoretical.

In the face turning test, the bar again produces much shorter chips than those which were produced from a sample of cast and hot-rolled plate using the usual method.

Claims (18)

1. Process for the production of a semi-finished article from a copper material with improved machinability, wherein a porous preform of copper powder or copper alloy powder is first produced by powder metallurgy and sintered, characterized in that from this preform, by cold forming or hot forming steps the semi-finished article is produced in the form of bars, pipes, sections, wires, sheets or bands with a pore proportion of between 0.05 and 10% by volume.
2. Process according to Claim 1, characterized in that the average size of the particles in the copper powder or copper alloy powder is 2 to 3000 µm.
3. Process according to Claim 1 or 2, characterized in that the preform is sintered in an atmosphere containing gaseous constituents soluble in copper and copper alloys.
4. Process for the production of a semi-finished article with improved machinability, wherein a porous preform is first of all produced by the spray compacting method in which a metal welt of copper or of a copper alloy is sub-divided into metal droplets by atomization, the metal droplets being sprayed onto a base, characterized in that a gas-to-metal ratio of 0.5 Nm3/kg - 1.5 Nm3/kg is maintained and that, by cold and/or hot forming operations, the semi-finished articles are produced in the form of bars, pipes, sections, wires, sheets or bands with a pore proportion of between 0.05 and 10% by volume.
5. Process in accordance with Claim 4, characterized in that the average diameter of the droplets amounts to between 5 and 200 µm.
6. Process in accordance with any one of Claims 1 to 5, characterized in that the copper material contains gas-filled pores.
7. Process in accordance with Claim 6, characterized in that the pores contain a gas insoluble in copper or in a copper alloy.
8. Process in accordance with any one of Claims 1 to 7, characterized in that the copper material consists of a brass alloy with between 1 and 45% of zinc.
9. Process in accordance with Claim 8, characterized in that the brass alloy contains, as optional constituents, maximum proportions of 10% of aluminium, 20% of nickel, 6% of tin, 4% of silicon and 8% of manganese, as well as a maximum of 2% of iron, either separately or in combination with one another.
10. Process in accordance with Claim 9, characterized in that the brass alloy contains, as further optional constituents, one or more of the elements titanium, chromium, zirconium, beryllium, magnesium, phosphorus and antimony, in each case up to a maximum of 1%.
11. Process in accordance with any one of Claims 1 to 7, characterized in that the copper material consists of a bronze alloy with between 0.1% and 12% of tin.
12. Process in accordance with Claim 11, characterized in that the bronze alloy contains, as optional constituents, a maximum of 6% of zinc, a maximum of 5% of nickel and a maximum of 4% of iron, either separately or in combination with one another.
13. Process in accordance with any one of Claims 1 to 12, characterized in that the bronze alloy contains, as further optional constituents, one or more of the elements phosphorus, chromium, zurconium, titanium or magnesium, in each case up to a maximum of 1%.
14. Process in accordance with any one of Claims 1 to 7, characterized in that the copper material consists of an aluminium bronze with between 0.1 and 10% of aluminium.
15. Process in accordance with any one of Claims 1 to 14, characterized in that the aluminium bronze contains, as optional constituents, maximum proportions of 5% of iron, 8% of nickel, 4% of silicon and 5% of manganese as well as a maximum of 3% of tin, either separately or in combination with one another.
16. Process in accordance with Claim 15, characterized in that the aluminium bronze contains, as further optional constituents, one or more of the elements chromium, titanium, zirconium, magnesium or phosphorus, in each case up to a maximum of 1%.
17. Process in accordance with any one of Claims 1 to 7, characterized in that the copper material consists of a low-alloy copper alloy containing, as optional constituents, maximum proportions of 0.5% of phosphorus, 4% of iron, 3% of tin, 4% of nickel, 2% of silicon, 2% of chromium, 2% of cobalt and 2% of beryllium, either separately or in combination with one another.
18. Process in accordance with Claim 17, characterized in that the copper alloy contains, as further optional constituents, one or more of the elements titanium, zirconium, magnesium, manganese, arsenic or zinc, in each case up to a maximum of 1%.

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