JP2003501273A - Joining method of metal parts using induction heated metal powder - Google Patents

Abstract

  (57) [Summary] The present invention relates to a method for joining metal parts at a high temperature without risking melting of the parts. It uses a powder that has a melting temperature above the melting temperature of the component material when the components are of the same type, and a melting temperature above the lowest melting temperature of the component material when the components are of different types. Is used. In the joining, the powder is melted without melting the part because the temperature of the powder is higher than that of the part by the induction heating. The invention is useful for joining any metal parts made of metals or alloys, especially when joining parts of the same type using powders of the same material.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to joining metal parts with a filler in a somewhat brazing-like manner. The induction heating process is adopted.

(Prior Art and Problems to be Solved) When a metal powder inserted between these two parts is used to join two metal parts of the same material or different materials, the purpose is metal powder. This is because the two parts are joined to each other with high rigidity when they are heated to be temporarily transformed into the molten material and when they are cooled. This is a brazing method that uses metal powder with a melting temperature below the melting temperature of the two parts to be joined. Furthermore, a brazing process by induction heating using a powder filler is known.
Many metals can be joined in this way, especially copper or stainless steel, using suitable fillers. In the case of copper, alloys with high copper and silver contents or zinc and copper alloys are usually used. The brazing temperature is about 700 to 800 degrees. In the case of stainless steel, the filling alloy is based on silver, copper, nickel or gold. Brazing is performed between 700 and 1100 degrees. Various powdery fillers are often mixed with flux. In these cases, the powdered filler, unlike the materials of the two parts to be joined, has a melting temperature below the melting temperature of the two parts.

Further, it is known to use the same kind of powder as the parts to be joined when the thickness of the joined part is large (about several millimeters). The powder of the metal to be bonded is always used with a filler whose melting temperature is lower than the melting temperature of the metal to be bonded. Pressure is constantly applied during the brazing process to eliminate porosity in the joint. (U.S. Pat. No. 581292
(See No. 5)

Further, in the case of two parts of the same type, for example, two parts of aluminum, a powder composed of a metal component having a melting temperature higher than the melting temperature of the parts, for example, in the case of joining aluminum, silicon and potassium fluoroaluminate are used. It is known that bonding can be performed using powder mixed with flux. In this case, the diffusion phenomenon between the powder and the part causes the formation of a phase below the melting temperature of the parts, so that a liquid phase can be achieved even below the melting temperature of the two parts.

There is another joining technique called diffusion joining. However, in that method, the powder inserted between the surfaces of the two parts does not change to a liquid during joining. It is a solid phase bonding process that is formed by the diffusion of powders placed between and in contact with metal surfaces by maintaining pressure and high temperature for long enough without adding chemicals.

SUMMARY OF THE INVENTION The main object of the present invention is a method of joining two metal parts by melting a filler material: -using induction heating, -the melting temperature being lower than the melting temperature of the parts. As a filler to prevent the formation of new phases, when the parts are the same material, the melting temperature of the parts to be joined is higher than the melting temperature of the materials of the parts. This is a joining method using powder having a melting temperature or higher. In particular, the combination of these two means
The use of chemical filler elements and pressurization at high temperatures is not necessary for the joining.

In the preferred embodiment of the invention, the two parts are of the same type, the powder is the same material as the part, and the melting temperatures of the powder and the part are equal.

[0008]   It is possible to compact the powder before inserting it between the two parts.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The present invention is somewhat similar to electromagnetic induction brazing, but is fundamentally different in the following respects.

The filler is a metal powder, and the melting temperature is higher than the melting temperatures of the two materials to be joined when the two parts are of the same type, and the melting temperature is lower when the two parts are of different types. Is above the melting temperature of the part.

The combination of metal powder fillers with induction heating creates a particular condition in which the powder does not melt but the parts do not melt as the temperature of the powder rises. The principle of induction heating of a homogeneous metal part is based on Lenz's law that an induced current is generated in a conductive material that is affected by a varying magnetic field. This current produces heat due to the Joule effect, which causes the temperature of the material through which the current flows to rise. The penetration depth of the induced current depends on the frequency of the magnetic field and the physical properties of the component such as permeability and electrical resistance. In the case of metal powder, the induction heating of the metal powder is due to the inhomogeneity of the metal powder, the induced current in the metal powder has a much more complex distribution than the induced current that occurs in dense parts of the same material It means that. Furthermore, the presence of an oxide film on the surface of the particles and the nature of the oxide film influence the flow of the induced current in the powder. Therefore, the temperature rise due to the flow of induced current is very different between powder and parts.

The observed phenomenon indicates that electromagnetic coupling is more efficient with powder than with metal parts. In other words, the temperature rise of the powder is larger than that of the dense parts.

It is necessary to clearly distinguish between the powder in the initial state, which does not serve as a source of the induced current, and the powder in which the metal contact between the particles is formed and the induced current can flow. In the initial state, in other words, at room temperature, the electric resistance of the powder used is very large because of the oxide layer on the surface of the particles, and the bonding state of the powder is usually not good. However, when heated, the temperature of the powder rises due to heat conduction from the dense parts. in this case,
The surface layer of the oxide, which may be present on the surface of the particles of the powder, is altered or removed in nature. Moreover, due to the influence of temperature, there are increasingly more metal contacts between the particles, increasing their surface area. Therefore, the heating causes a large change in the flow of the induced current in the powder, and the heating efficiency also changes significantly. If this condition of the powder is met, its temperature can be higher than that of the dense part. It is therefore possible to melt the powder without melting the part.

The efficiency of induction heating depends on whether the powder particles are in metal contact or electrically insulated from each other by an oxide film.

Therefore, using a preformed body of hot-formed powder, if there is contact between the particles before the heating cycle, an induced current will occur around the granular conductor and, for example, a cylinder Facilitates the joining of shaped parts.

The reaction is very different if the metal contact of the filled metal particles is not formed prior to joining. The formation of the first contact and the highly concentrated induced current cause a very large fluctuation of the voltage in the granular conductor. In contact covered by a film of insulator,
The "breakdown voltage" may be reached. In this case, melting occurs quickly at such contact points, and this phenomenon spreads throughout the granular conductor.

In order to promote the fixing of the materials to be joined between the parts, it is possible to compress the powder in advance.

Joining is performed in the same manner as brazing by utilizing the capillary phenomenon that occurs in a normal liquid phase.

The characteristics of the bond depend on the material with the various parameters, the initial characteristics of the powder and the temperature cycle.

[0020]   The metal parts and powder can be composed of pure metals or alloys.

[0021]   The powder may be composed of a mixture of different metal particles.

[0022]   This method is preferably applied when the metal part and the metal powder are the same material.

Induction heating must be stopped when all the powders have melted so that assembly can be performed when all the powders become liquid.

The basic procedure of this method is as follows. -Put a thin layer of metal powder between two dense metal parts of the material to be joined. Heating the powder and the limited part of the dense part, preferably near the joint, by induction heating. Therefore, it should be noted that the powder is first heated by the dense metal parts. These components are sources of induced currents that cause a rise in temperature. Then, heat is exchanged between the component and the powder. The effect of this heating is to increase metal contact between the particles. When sufficient metal contact is achieved, an induced current can flow between the powder particles. Consequently, the presence of dense parts is essential to enable these contacts and induction heating of the powder. -The powder melts because the temperature of the powder becomes higher than the temperature of the parts because the induction heating works more efficiently than the dense metal part. -Stop induction heating and cool the joint, resulting in solidification.

As an example, an example of joining copper pellets with copper powder will be shown. The two pellets are cylindrical with a diameter of 20 mm and a height of 5 mm. A few grams of copper powder are sandwiched between two copper pellets in order to create a thin layer of copper with a thickness of several μm that is distributed as evenly as possible over the entire surface of the pellet. The size of the particles is about 40 μm. Induction heating is performed using a high frequency generator with an output of 25 kw. The induction coil used has a diameter of 56 m
It is a two-turn induction coil with m and a height of 10 mm. Bonding is done under a secondary vacuum with a frequency of 155 kHz.

In this case, the following detailed operation is performed. -Put two copper pellets and powder of the material to be joined into the induction coil inside the vacuum chamber. -Close the vacuum chamber. -Create a primary vacuum. -Create a secondary vacuum. -Turn on the generator of the heating coil. -Adjust to a preset power level. -Turn on the high voltage switch. -Induction heating of pellets and powder. -Powder melting. -Switch off the high voltage. -Cooling under vacuum. -Open the vacuum chamber. -Take out the joined joined body from the vacuum chamber.

As another example, Z2CN18-10 stainless steel pellets, commonly known as AiSi. 304
There is an example in which the pellets are joined with Z12CN25-20 stainless steel powder, commonly called AiSi 310. As a result of the test, the mechanical strength of the bonded body is about 70% of the ultimate strength of the reference material.
Thus, the dimensional change due to elongation at failure is 90% of the dimensional change at failure of the reference material.

[0028]   The procedure and working method are the same as for copper.

[0029] (Advantages of the present invention)   The method is applicable to different metals and alloys.

The method has the same advantages as brazing at high temperature. Because: -It is possible to prevent the parts, which are the materials to be joined, from changing to liquid. This can prevent some metallurgical problems such as the appearance of cracks. -Allows the joined joint to be used at high temperatures.

Furthermore, since the parts are joined using powders made of exactly the same material, the impurities can be kept within the range during the joining, which is very important for parts used in corrosive environments. Be beneficial. Furthermore, there is no deterioration in the electrical characteristics of the joint. Therefore, the method can be advantageously used for connection.

Furthermore, the device preferably uses a high frequency generator as an induction heating device. Therefore, the present technique is very easy to implement and can immediately be used to replace conventional induction heating brazing to improve results.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Raille, Alain             France F-91610 Barrancourt,               Lupierre Duniz 3

Claims (3)

[Claims] 1. A method for joining metal parts by melting a filler, comprising: -heating the joint by induction heating; -melting to newly form a phase having a lower melting temperature than the melting temperature of the parts. As a filler, if the parts are made of the same material, the powder must be above the melting temperature of the parts to be joined, and if the parts are different, the powder must be above the melting temperature of the part that has the lowest melting temperature. The joining method to use. 2. The joining method according to claim 1, wherein the component and the powder are made of the same material. 3. The joining method according to claim 1, wherein the powder is compressed before being inserted between the two metal parts.