Electron beam brazing

Abstract

ELECTRON BEAM BRAZING The invention relates to a method for brazing a workpiece (4) comprising a weld area (7), within a vacuum chamber (3), characterized in that it comprises the following steps: deposition of a brazing filler metal (5) onto the workpiece (4), evacuation of the chamber (3), heating of the brazing filler metal (5) by an electron beam (20) until a weld is formed. Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: ELECTRON BEAM SOLDERING TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of strong brazing, that is to say carried out with a filler metal whose melting temperature is greater than 450°C.

[0002] The present invention relates in particular to strong brazing for aeronautical parts. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Brazing consists of the assembly by capillarity of two metal parts with a filler metal whose melting temperature is lower than that of the parts to be assembled or to repair cracks for example. For strong brazing, the parts to be welded will be for example stainless steel, cobalt and nickel based steels. Strong brazing means brazing according to the NF EN ISO 4063 standard for the nomenclature of welding and brazing processes.

[0004] Strong solder has high mechanical resistance which allows its use in particular in the aeronautical field.

[0005] Today, aeronautical parts are brazed in a vacuum furnace which allows for uniform heating of the entire part, limiting deformations linked to temperature heterogeneities. Working under vacuum prevents any oxidation and avoids the use of flux. However, there are still general deformations of the components linked to the thermal cycle which require specific tools to limit them; it is not possible to make local retouches without potential impact on the rest of the part. On the other hand, the cycle time is long because the furnace must be heated to a temperature between 1040°C and 1150°C, which results in a significant cost for the brazing operation.

[0006] Indeed, for the brazing of several parts, the carrying out of multiple passages in a vacuum furnace of the elements to be brazed generates internal stresses in the material which result in geometric deformations of the part. These geometric deformations induce arrangements of specific ranges or ranges of retouching. Summary of the invention

[0007] The invention provides a solution to the problems mentioned above, by allowing high-precision and inexpensive soldering.

[0008] The invention relates to a method for brazing a part comprising an area to be welded, in a vacuum enclosure, characterized in that it comprises the following steps: • depositing a brazing filler metal on the part, • placing the enclosure under vacuum, • raising the temperature of the brazing filler metal by an electron beam until a weld is formed.

[0009] Targeted heating of the welding area, or brazing zone, and the speed of the welding limit the deformation of the parts to be joined. The electrical energy / heat conversion rate is also very high, reaching 75% efficiency, compared for example to 10% for laser methods. Electron beam welding makes it possible to obtain ultra-resistant joints with minimal deformation of the joined parts. In addition, replacing the heat energy provided by the vacuum furnace heating means with an electron beam consumes less energy. The power of the electron beam can be adjusted to adapt to the melting temperature of the filler metal.

[0010] Advantageously, the temperature rise is achieved with the defocused electron beam. This makes it possible to heat a larger surface area and to adapt the temperature on the filler metal.

[0011] According to a first embodiment, the electron beam is static on the area to be welded. Thanks to the defocusing of the electron beam it is possible to weld statically, in particular round welds.

[0012] According to a second embodiment, the electron beam performs a scan over the area to be welded. This makes it possible to weld continuously over a more or less significant length, in one or more passes.

[0013] Advantageously, the feed rate of the electron beam is 8 to 12 mm / min, preferably 10 mm / min (min=minute).

[0014] Advantageously, the electron beam heats the filler metal to a temperature between 1000°C and 1250°C. This temperature is adapted to the filler metal chosen.

[0015] Advantageously, the heating of the filler metal lasts 3 to 4 minutes, this duration depends on the assembly and the filler metal used. This duration is sufficient in static and sweeping mode for a weld of approximately 20 mm long and with two passes.

[0016] Advantageously, the electron beam is emitted at a distance from the filler metal of between 100mm and 200mm, preferably 150mm. This distance will be chosen according to the size of the part relative to the machine.

[0017] Advantageously, the power of the electron beam is between 0.37kW and 2.5kW, preferably 0.75kW. This parameter is determined during development depending on the assembly to be produced.

[0018] Advantageously, the filler metal is a nickel alloy. It will be possible to use, for example, according to the SAE International standard: AMS 4777, AMS 4779, DF4B, BNi81. These metals can be in the form of a paste: a powder with a binder, a preform in a roll or a laminated strip.

[0019] The table below gives the brazing temperature ranges to be applied depending on the filler metal: Filler metal (ISO 3677) Recommended brazing temperature Allowed brazing temperature range DF4B 1100°C 1064- 1122°C BNi81 1100°C 1060- 1210°C BNi82 (AMS 4777) 1040°C 1010- 1175°C BNi95 (AMS 4779) 1130°C 1100- 1175°C

[0020] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0021] The figures are presented for information purposes only and in no way limit the invention.

[0022] [Fig. 1] is a view of an electron beam soldering device,

[0023] [Fig.2] shows a part having several holes with a filler metal before the brazing,

[0024] [Fig.3] shows the part of [Fig.2] after brazing carried out according to the invention,

[0025] [Fig.4] shows a part having an oblong hole with filler metal before the brazing

[0026] [Fig.5] shows the part of [Fig.4] after brazing carried out according to the invention. DETAILED DESCRIPTION

[0027] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0028] The brazing device 1 illustrated in [Fig.l] comprises an electron gun 2 which emits an electron beam 20 into a vacuum-sealed enclosure 3. A workpiece 4 is placed under the electron gun 2 and a filler metal 5 is placed on the workpiece 4. The electron beam 20 will heat the filler metal 5 and thus enable brazing.

[0029] According to a first embodiment, illustrated in figures 2 and 3, the part to be brazed 40 comprises several circular holes 41 to be plugged, in some of which a thermocouple 6 has been placed which it is desired to fix to the part 40.

[0030] The electron gun 2 is placed at a distance d, called the firing distance, from the part 5. This distance d is calculated as a function of the melting temperature of the filler metal 5 and the power of the electron gun 2. Once the electron gun 2 is positioned in the enclosure 3, the electron beam 20 is focused on the part 40 in the area to be brazed 7.

[0031] Thus for a brazing of BNi81 or DF4B on a KCN22W alloy support, the firing distance d is 150mm for an electron beam power of 0.75kW.

[0032] Prior to brazing, the components are degreased, then assembled in the enclosure 3, the filler metal 5 is placed on the brazing zones 7, then the enclosure is placed under vacuum. The electron beam 20 is directed perpendicular to the part 40 towards the filler metal then defocused, then the filler metal 5 rises in temperature in a range between 1000°C and 1250°C for 3 minutes to melt completely. The defocusing is sufficient to melt the filler metal 5 in static mode, the brazing zone 7 being restricted.

[0033] The visible finished part 40 [Fig.3] shows a first solder 50 filling a hole or crack and a second solder 51 bonding the thermocouple 6 to the part 40.

[0034] According to the second embodiment, visible in figures 4 and 5, the part to be brazed 42 has a hole or an elongated crack 43 and an area to be refilled 44. The materials used in this example are the same as for the first embodiment.

[0035] The electron gun 2 is arranged according to the same method as for the first embodiment.

[0036] Prior to brazing, the part 42 is degreased and placed in the enclosure 3, the filler metal 5 is placed in the brazing zone 7. The enclosure 3 is placed under vacuum. The electron beam 20 is directed perpendicular to the part 42 towards the filler metal 5, then defocused and scans the zone to be brazed 7 to raise the temperature of the filler metal 5 in a range between 1000°C and 1250°C to melt it. In the example illustrated, the feed rate of the electron beam is 10 mm / min for 4 minutes and two back and forth movements are sufficient to completely melt the filler metal 5.

[0037] The result obtained illustrated [Fig.5], shows the repaired crack.

[0038] A non-destructive test of the assembly is then carried out.

Claims

Claims

1. Method for brazing a part (4, 40, 42) comprising a zone to be welded (7), in a vacuum enclosure (3) characterized in that it comprises the following steps: - depositing a brazing filler metal (5) on the part, - placing the enclosure (3) under vacuum, - raising the temperature of the brazing filler metal (5) by an electron beam (20) until a weld is produced, the electron beam (20) performing a scan over the zone to be welded (7) with a speed of 8 to 12 mm / min.

2. Brazing method according to claim 1, characterized in that the temperature rise is carried out with the defocused electron beam (20).

3. Brazing method according to one of the preceding claims, characterized in that the electron beam (20) heats the filler metal to a temperature between 1000°C and 1250°C.

4. Brazing method according to one of the preceding claims, characterized in that the heating of the filler metal lasts 3 to 4 minutes.

5. Brazing method according to one of the preceding claims, characterized in that the electron beam (20) is emitted at a distance d from the filler metal of between 100mm and 200mm, preferably 150mm.

6. Soldering method according to one of the preceding claims, characterized in that the power of the electron beam (20) is between 0.37kW and 2.5kW, preferably 0.75kW.

7. Brazing method according to one of the preceding claims, characterized in that the filler metal (5) is a nickel alloy.

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