FR3124750A1 - Electroerosion process of an amorphous metal alloy sample - Google Patents

Abstract

The invention relates to a method for cutting an amorphous metal alloy sample, comprising at least two steps of wire EDM producing electrical discharges on a sample to remove material from the sample so as to obtain a cut sample according to a reference trajectory and maintained in the amorphous state, in which the amorphous metal alloy (AMA) has a critical diameter Dc of less than 8 millimeters and/or a difference ΔTx between the crystallization temperature Tx and the glass transition temperature Tg less than 80°C, and/or a quotient ΔTx/(TI-Tg) of the difference ΔTx between the crystallization temperature Tx and the glass transition temperature Tg and of the difference between the liquidus temperature TI and the temperature of glass transition Tg less than 0.16. The method includes at least one roughing EDM step and at least one finishing EDM step. The invention also relates to a method of manufacturing an AMA component and such a component. Abstract Figure: Figure 5

Description

Electroerosion process of an amorphous metal alloy sample

The present invention relates to the field of methods for machining metal microcomponents, in particular amorphous metal alloy (AMA) parts. Indeed, amorphous alloys have particularly interesting mechanical characteristics for technical fields involving very small parts.

It is known to obtain amorphous metal preforms by injection into molds of specific shape. By cooling the injected metal sufficiently quickly, the crystallization of the alloy can be avoided and an amorphous type structure can be obtained. This type of amorphous alloy structure is also called metallic glass.

In order to obtain a mechanical part ready to be integrated for example in a clockwork mechanism, it is sometimes necessary to machine the molded preform.

In the general field of alloys, in particular crystalline alloys, many machining and/or shaping techniques have been developed (stamping, micro-milling, etc.). However, these techniques cannot be easily transposed to AMAs which have particular chemical compositions and generally much higher mechanical properties than crystalline alloys. Machining is therefore more complex to master (obtaining the desired precision and surface conditions, perpendicularity of the sides, tool life, production speed compatible with industrial constraints, etc.).

On the other hand, many of these techniques cause thermal heating at the level of the machined zones, thus implying a local recrystallization of the alloy and the loss of the amorphous structure of the AMA at the level of the machined zones. This is all the more true for AMAs with low thermal stability. Indeed, among the AMAs, some have a lower thermal stability than the others. This low thermal stability reflects the ease/speed with which the structure of the alloy can be affected by a temperature variation (temperature increase beyond the glass transition temperature Tg, too slow cooling, etc.). AMAs with lower thermal stability therefore have an ability to evolve to a faster crystalline state above the glass transition temperature Tg.

Electroerosion processes are suitable for the manufacture of components, in particular microcomponents in crystalline metal alloys. Electroerosion makes it possible to overcome the mechanical characteristics of materials, the machining of hard materials is indeed possible, and makes it possible to achieve machining precision of the order of a few micrometers. Nevertheless, its thermal nature, the high temperatures involved and the long machining times make EDM a priori a poor candidate for the machining of amorphous metal alloys. As indicated above, the latter and more particularly those with low thermal stability, are in fact much more sensitive to temperature than crystalline alloys.

Thus, the difficulty is to carry out these machining operations of AMAs while preserving their amorphous structure, guaranteeing a quality of the surface state of the machined part and maintaining a high cycle time adapted to a production. industrial. Indeed, a machining operation that would lead to excessive heating of the material would cause crystallization of the heat-affected zone and would therefore lose the advantageous properties conferred by the amorphous structure of the material.

There is therefore a need to have a machining process that makes it possible to maintain an amorphous microstructure while allowing an industrial level manufacturing rate. Another requirement is to be able to obtain a surface finish with very low roughness and/or excellent perpendicularity of the flanks in the cutting zone, in order to fully exploit the intrinsic qualities of the AMA.

Summary

To this end, the invention proposes a method for cutting a sample 1 of amorphous metal alloy, comprising at least two steps of electroerosion by wire 2 producing electric discharges on a sample 1 to remove material from the sample. 1 so as to obtain a sample 1 cut according to a reference trajectory TRef and maintained in the amorphous state,
in which :
the amorphous metal alloy has:
- a critical diameter Dc of less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or
- a difference ΔTx between the crystallization temperature Tx and the glass transition temperature Tg of less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or
- a quotient ΔTx/(TI-Tg) of the difference ΔTx between the crystallization temperature Tx and the glass transition temperature Tg and of the difference between the liquidus temperature TI and the glass transition temperature Tg of less than 0.16, preferably less than 0.14 and even more preferably less than 0.12; And
wherein the successive spark erosion steps are such that they comprise:
- at least one spark erosion step, called "roughing", of the sample 1 along a reference trajectory TRef+n to produce a roughing 5 or 51 according to a trajectory TRef+n, n being the number total of electroerosion steps, called “roughing”, the discharge energy E per roughing step being less than 5000 μJ per millimeter of thickness of sample 1 to be cut; And
- at least one spark erosion step, called "finishing", of the sample 1 along a reference trajectory TRef to remove material from the sample 1 along the reference trajectory TRef, the discharge energy E per finishing step being less than 200 μJ per millimeter of thickness of sample 1 to be cut; And
- the reference trajectory or trajectories TRef+n being translated by a given distance gn from the reference trajectory TRef+(n-1) which is directly adjacent to it and which is closest to the final part 4, in the opposite direction to that of the final piece 4 cut out; And
- the given distances gn between two directly adjacent reference trajectories, identical or different, are such that the electrical discharges removing material from the sample 1 to be cut on the reference trajectory TRef+n, also remove, at least partially, of the material of sample 1 to be cut on the reference trajectory TRef+(n-1) which is directly adjacent to it.

According to another aspect, there is proposed a method for manufacturing a part 4 of amorphous metal alloy, comprising the steps:
- melt a mixture of metals to obtain a piece of alloy, and
- injecting the slug obtained into a mold and cooling the cast alloy with a cooling rate greater than a critical rate of crystallization of the alloy, to obtain a sample 1 of amorphous alloy, and
- cutting at least one surface of the sample 1 according to the cutting process as described above to obtain a part 4 of amorphous alloy according to a predetermined geometry, and
- optionally performing a finishing step on at least the surface of the machined sample 1, preferably a tribofinishing step or a chemical treatment.

There is also proposed a component made of amorphous metal alloy comprising at least one surface cut according to the cutting method previously described or manufactured according to the manufacturing method above.

The characteristics exposed in the following paragraphs can, optionally, be implemented. They can be implemented independently of each other or in combination with each other.

According to one embodiment, the cutting process comprises at least two so-called "roughing" electroerosion steps whose successive energy levels E are decreasing, the first roughing step(s) being carried out with electric discharges whose the discharge energy E is between 2000 μJ and 5000 μJ per millimeter of sample 1; and the last roughing step or steps being carried out with electrical discharges whose energy level (E) is between 200 µJ and 2000 µJ per millimeter of sample 1.

According to one embodiment of the cutting process, the diameter of the wire 2 is less than 200 μm, preferably less than 100 μm and even more preferably less than 75 μm.

According to one embodiment of the cutting process, sample 1 is a stack of samples.

Advantageously, the current of each electrical discharge at the terminals of wire 2 is less than 200 amps.

Preferably, the voltage across the terminals of wire 2 is less than 200V.

Advantageously, the pulse duration during which sample 1 is subjected to an electric discharge is less than 1000 μs, preferably less than 400 μs or even more preferably less than 100 μs.

The flank obtained by spark erosion of sample 1 cut out advantageously has a surface whose roughness Ra is less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm and even more preferably less than 300 nm.

The cutting by spark erosion of a first surface P1 of the sample 1 results in obtaining a second surface P2 of the sample (1) cut and, at each point of intersection between the first remaining surface P1 and the surface P2 created, said surfaces P1 and P2 advantageously form between them an angle Ad of 90° ± 1.5°, preferably 90° ± 1° and even more preferably 90° ± 0.5°.

Other characteristics, details and advantages will appear on reading the detailed description below and on analyzing the appended drawings, in which:

shows an X-ray diffraction analysis of an amorphous metal alloy.

shows an X-ray diffraction analysis of a partially amorphous metal alloy.

shows an X-ray diffraction analysis of a crystalline metal alloy.

is a schematic top view illustrating an implementation embodiment of the cutting process,

is a schematic side view detailing a method for cutting a stack of samples,

is a schematic top view illustrating the cutting process comprising roughing EDM steps and a finishing EDM step,

is a schematic side view illustrating a cutting process for obtaining a part having excellent sidewall perpendicularity,

is a diagram showing the results of the bending tests of Example 1.

Claims (11)

Method for cutting a sample (1) of amorphous metal alloy, comprising at least two steps of wire spark erosion (2) producing electrical discharges on a sample (1) to remove material from the sample (1) so as to obtain a sample (1) cut according to a reference trajectory (TRef) and maintained in the amorphous state,
in which :
the amorphous metal alloy has:
- a critical diameter (Dc) less than 8 millimeters, preferably less than 6 millimeters, and even more preferably less than 4 mm, and/or
- a difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) of less than 80°C, preferably less than 70°C, and even more preferably less than 60°C, and/or
- a quotient (ΔTx/(TI-Tg)) of the difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) and of the difference between the liquidus temperature (TI) and the temperature glass transition (Tg) of less than 0.16, preferably less than 0.14 and even more preferably less than 0.12; And
wherein the successive spark erosion steps are such that they comprise:
- at least one spark erosion step, called "roughing", of the sample (1) along a reference trajectory (TRef+n) to produce a roughing (5; 51) along a trajectory (TRef +n), n being the total number of EDM steps, called “roughing”, the discharge energy (E) per roughing step being less than 5000 µJ per millimeter of sample thickness ( 1) to cut; And
- at least one spark erosion step, called "finishing", of the sample (1) along a reference trajectory (TRef) to remove material from the sample (1) along the trajectory reference (TRef), the discharge energy (E) per finishing step being less than 200 μJ per millimeter of thickness of sample (1) to be cut; And
- the reference trajectory or trajectories (TRef+n) being translated by a given distance (gn) from the reference trajectory (TRef+(n-1)) which is directly adjacent to it and which is closest to the final part (4), in the direction opposite to that of the final piece (4) cut; And
- the given distances (gn) between two directly adjacent reference trajectories, identical or different, are such that the electric discharges removing material from the sample (1) to be cut on the reference trajectory (TRef+n), remove also, at least partially, of the material of the sample (1) to be cut on the reference trajectory TRef+(n-1) which is directly adjacent to it. Process according to claim 1, such that it comprises at least two so-called "roughing" electroerosion steps, the successive energy levels (E) of which are decreasing, the first roughing step(s) being carried out with electrical discharges whose discharge energy (E) is between 2000 µJ and 5000 µJ per millimeter of sample (1); and the last roughing step or steps being carried out with electrical discharges whose energy level (E) is between 200 µJ and 2000 µJ per millimeter of sample (1). Method according to any one of the preceding claims, characterized in that the diameter of the wire (2) is less than 200 µm, preferably less than 100 µm and even more preferably less than 75 µm. Method according to any one of the preceding claims, characterized in that the sample (1) is a stack of samples. Method according to any one of the preceding claims, characterized in that the current of each electrical discharge is less than 200 amperes. Method according to any one of the preceding claims, characterized in that the voltage is less than 200V. Method according to any one of the preceding claims, characterized in that the pulse duration during which the sample (1) is subjected to an electric discharge is less than 1000 µs, preferably less than 400 µs or even preferably less than 100 µs. Process according to any one of the preceding claims, such that the side obtained by electroerosion of the sample (1) cut has a surface whose roughness Ra is less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm and even more preferably less than 300 nm. Method according to any one of the preceding claims, such that the cutting by spark erosion of a first surface P1 of the sample (1) results in obtaining a second surface P2 of the sample (1) cut and that, at each point of intersection between the first remaining surface P1 and the surface P2 created, said surfaces P1 and P2 form between them an angle Ad of 90° ± 1.5°, preferentially 90° ± 1° and even more preferentially 90° ± 0.5° between them. Method of manufacturing a part (4) in amorphous metal alloy, comprising the steps:
- melt a mixture of metals to obtain a piece of alloy, and
- injecting the slug obtained into a mold and cooling the cast alloy with a cooling rate greater than a critical rate of crystallization of the alloy, to obtain a sample (1) of amorphous alloy, and
- cutting at least one surface of the sample (1) according to the cutting method of one of claims 1 to 11 to obtain a part (4) of amorphous alloy according to a predetermined geometry, and
- optionally performing a finishing step on at least the machined surface of the sample (1), preferably a tribofinishing step or a chemical treatment. Amorphous metal alloy component comprising at least one surface cut according to the cutting method of one of Claims 1 to 11 or according to the manufacturing method according to Claim 12.