EP1649949B1 - Method of heating forging tools in a forging device, and releasable furnace element for heating such tools - Google Patents

Description

The present invention relates to the field of forging by means of pressure forging machines such as hydraulic presses.

As the performance of aeronautical turbomachines increases, the parts constituting them must have increased mechanical characteristics; it is especially to avoid the appearance of cracks or other defects in the mass. Thus for aeronautical applications the use of titanium alloys has developed to meet both the requirements of mass reduction and obtaining the best compromise between the mechanical characteristics and the service life corresponding to the improvement of the performances. .

For this purpose, forging techniques have been developed. Pre-heated equipment is now used to ensure a better distribution of temperatures in the workpiece during the pressing operation.

It is possible to use an isothermal forging technique in which the workpiece and the tooling are brought to the same temperature, but this is cumbersome to implement.

It is also possible to use conventional forging machines with so-called hot-die tools

The invention relates in particular to the latter technique.

However, the temperature of the steel tool can not exceed 450 to 500 ° C, due to the thermomechanical limitations of the material.

In order to be able to increase the forging temperature without using an isothermal forging technique, it has been necessary to use stronger alloys, such as nickel-based superalloys. It is thus possible to heat the tooling up to 750 ° C.

The simplest design would be to produce one-piece tools. However, the cost would be high and the feasibility made difficult by the volume of alloy material to be involved.

We have therefore designed bi-metallic tools. The active part, ie the etched matrix, is a nickel-based refractory superalloy. It is mounted removably and wedged in a support, said insert door, steel. The latter has the function of distributing the forces exerted by the press and storing the calories.

For the implementation of this technique, the two elements constituting this tooling are separately heated in furnaces heated respectively to 450-500 ° C. and 750 ° C. The die is placed in the insert holder by adjusting its position by means of appropriate wedging keys and the whole is carried on the machine where they are fixed on the trays. These operations are performed for the two tools, lower and upper.

• On doit immobiliser deux fours extérieurs à l'engin de forgeage.
• Les transferts et l'assemblage de pièces chaudes génèrent des situations à risques pour les opérateurs.
• L'assemblage des pièces chaudes nécessite des jeux importants entre les deux éléments, néfastes au bon fonctionnement.
• Elle manque de souplesse lors d'incidents de fabrication avec interruption car il est alors nécessaire de démonter les outillages pour la réchauffe.

The method outlined above has several disadvantages:

• Two furnaces must be immobilized outside the forging machine.
• Transfers and assembly of hot parts generate risk situations for operators.
• The assembly of hot parts requires significant play between the two elements, detrimental to the proper functioning.
• It lacks flexibility during manufacturing incidents with interruption because it is then necessary to disassemble the tools for the heating.

The document US 4,088,000 discloses a hot forging installation comprising tool preheating units disposed near the forging machine. These units include burners that are placed between the tools.

To reduce the manipulations, one can carry out the heating of the tools by means of a room known as martyr. However the quality of heating is very poor. There is no control over the temperature. We must always immobilize two furnaces, one at high temperature for the martyred piece, of the order of 1000 ° C.

Another method would be to heat the tools on the spot by means of gas ramps but the tests have shown as previously poor quality of heating with low performance.

The applicant has set itself the goal of developing a method of heating tooling machines or forging presses that overcomes the disadvantages reported above.

According to the invention, the method of heating a forging machine tool comprising an insert holder and an insert having a free face with a forging cavity, in preparation for a forging operation in said forging machine, is characterized in that the tooling being in place in the forging apparatus is provided on the insert-holder an oven element comprising at least one burner and a gas evacuation stack, forming with said face of the inserting a closed heating chamber, said enclosure is heated until the insert reaches a predetermined temperature, the furnace element is removed. Advantageously, said enclosure is heated by combustion of a combustion fluid inside thereof.

In particular, the removable oven element has the function of overheating the insert relative to the insert holder. Preferably, the assembly of the insert holder and the insert has been preheated in an oven to a first temperature below said predetermined temperature.

• On supprime les opérations d'assemblage à chaud de l'insert dans le porte - insert et on réduit les manipulations à chaud et les risques qui y sont associés.
• Le temps d'immobilisation de l'engin de pression est réduit.
• Par la formation d'une enceinte de chauffage à proximité immédiate de l'insert, on en assure un chauffage homogène, avec possibilité d'une régulation précise de la puissance de chauffe et de la montée en température.
• En cas d'incident de fabrication e t d'interruption de l'opération de forgeage, il n'est pas nécessaire de démonter l'outillage pour la réchauffe, on peut la reprendre aisément.

The solution of the invention has the following advantages:

• The hot assembly operations of the insert in the insert holder are eliminated and the hot handling and the risks associated with it are reduced.
• The downtime of the pressure craft is reduced.
• By forming a heating chamber in the immediate vicinity of the insert, it ensures homogeneous heating, with the possibility of precise control of the heating power and the rise in temperature.
• In case of manufacturing incident and interruption of the forging operation, it is not necessary to disassemble the tooling for the heating, it can be taken easily.

The method makes it possible to adapt to each type and geometry of tools.

Thus, according to another characteristic, when the forging machine comprises two tools with a holder and insert each, a ring-shaped furnace element is used. This furnace element is placed in abutment between the two inserts-holders so as to constitute said heating enclosure.

When the tool is deep cavity such as a spinning pot, a bell-shaped oven element with a bottom wall is used. This element is placed on the tooling so as to constitute said heating chamber.

According to a particularly advantageous application of the method, it is advantageous that the materials constituting the insert and the insert holder have different coefficients of expansion. The insert is in particular nickel superalloy and the steel insert holder. The insert is mounted in the insert holder in such a way that it has a negative clearance, that is to say that it is shrunk, when the insert is brought to said determined temperature, while being dismountable when returns to a temperature below the first temperature, especially at room temperature.

The advantages of this particular solution are:

• on améliore la robustesse
• on réduit la dispersion dans les cotes géométriques en supprimant les jeux,
• on améliore la qualité et la géométrie des pièces forgées car l'insert est contenu fermement dans le porte -insert et les efforts sont repris par ce dernier.

Elle permet de maintenir en outre la géométrie de l'insert lorsqu'il vient à présenter des criques. La sécurité et la durée de vie de l'insert en sont accrues. Enfin, elle permet de réduire les coûts de fabrication par la réduction de la quantité de superalliage nécessaire.Compared to tools with the use of matrix locking keys in the insert holder,

• we improve the robustness
• we reduce the dispersion in the geometric dimensions by eliminating the games,
• the quality and the geometry of the forgings are improved because the insert is firmly contained in the holder and the forces are taken up by the latter.

It also maintains the geometry of the insert when it comes to present cracks. The safety and the lifetime of the insert are increased. Finally, it reduces manufacturing costs by reducing the amount of superalloy required.

The invention also relates to a removable oven element for the implementation of the method; according to a characteristic, it comprises a metal wall, internally coated with a layer of insulation, with at least one burner and a flue gas discharge chimney. Preferably, the burner is oriented tangentially to produce a swirling flow along the wall.

The furnace element is advantageously part of a removable heating assembly comprising a means for supplying combustion fluids and means for regulating the power and the heating time.

• la figure 1 représente, en coupe selon un plan vertical, une installation de chauffage conforme à une première application de l'invention,
• la figure 2 montre l'élément de four de la figure 1, vu de dessus,
• la figure 3 montre une installation pour une deuxième application de l'invention.

Other features and advantages will appear on reading the following description of an embodiment of the invention with reference to the drawings in which:

• FIG. 1 represents, in section along a vertical plane, a heating installation according to a first application of the invention,
• FIG. 2 shows the oven element of FIG. 1, viewed from above,
• Figure 3 shows an installation for a second application of the invention.

Forging is produced by placing a blank between two dies, each having an appropriate impression, and then bringing the latter closer to each other with sufficient pressure to deform the blank to obtain a part whose geometry corresponds to that of the footprints.

FIG. 1 shows two matrices 1 and 3 each with an imprint for the manufacture of a part, here for example an aeronautical turbomachine rotor disc made of titanium alloy. The two matrices or inserts are mounted in two insert holders 11 and 13 respectively. The two inserts can be constituted by assembling several parts, here 11a and 11b, for one, and 13a and 13b for the other, or be in one piece each. The insert assembly 1 and insert holder 11 constitutes the lower tooling 111. The insert assembly 3 and the insert holder 13 constitutes the upper tooling 313. For the forging operations the two tools are mounted in the machine or forging press which is not represented. This is in itself well known. Regarding the object of the invention any type of forging gear by pressure is suitable.

The installation of Figure 1 comprises a removable oven element 20 placed between the two tools, so as to form a closed chamber. This enclosure is delimited laterally by the wall of the element 20 and transversely by the two inserts 1 and 3. It is observed that the element 20 is in vertical support on the vertical walls of the two inserts 11 and 13 respectively, of such way that these are outside the enclosure.

The wall of the furnace element has an opening through which a burner 30 opens into the enclosure. The burner is supplied with fluids for combustion by tubes 31 and 32 flexible connected to a feed unit 38, here mobile. This unit comprises fluid control means 33, and means 34 for controlling this power supply to adjust the power of the heating, possibly with a means for regulating the temperature. For example the fluid supply valve for combustion can be controlled by a temperature controller. This is to heat the enclosure, preferably as quickly as possible, so as to reduce heat loss through the wall of the insert holder.

Figure 2 shows the element 20, isolated and viewed from above. This element comprises a metal wall 21 lined inside an insulating material 22. A non-radial opening 24 is formed in the wall and the insulator. The burner 30 is mounted on the wall 21 and opens into the opening.

A second opening passes through the wall 21 and is connected to a chimney 27 for evacuation of the combustion gases. Finally, it is observed that ears 25 are welded to the wall 21 and form plugs for handling the furnace element.

• On démonte les outillages inférieur et supérieur de la presse.
• On préchauffe les outillages - insert et porte insert ensemble - dans une étuve à ladite première température. Celle -ci, lorsque le porte-insert est en acier, est entre 450 et 500°. Elle correspond au niveau de température que peut supporter le porte -insert sans dommage.
• On remet en place les deux outillages dans la presse en les fixant sur leur plateau respectif.
• On dispose l'élément de four amovible 20 sur le porte-insert inférieur. La géométrie de l'élément 20 est compatible avec celle de l'outillage.
• On abaisse le plateau supérieur jusqu'à ce que l'outillage supérieur vienne dans la position de la figure 1. Le bord supérieur de la paroi de l'élément de four est en contact avec la partie verticale du porte -insert 13. On a formé ainsi une enceinte fermée. Celle -ci est délimitée par la paroi de l'élément de four, d'une part, et par les deux inserts, d'autre part.
• On commande l'alimentation du brûleur en fluides de combustion, gaz et air. La flamme produite est tourbillonnante ce qui permet une bonne homogénéisation de la température. On fait en sorte que la température monte rapidement afin de réduire les pertes de chaleur par les porte - inserts.
• Lorsque la température, 750°c pour le superalliage, est atteinte, on arrête le chauffage, et on retire l'élément de four.
• La presse est prête pour effectuer le forgeage des pièces.

The tools are heated as follows:

• We dismantle the lower and upper tools of the press.
• The tools - insert and insert holder - are preheated in an oven at said first temperature. This, when the insert holder is steel, is between 450 and 500 °. It corresponds to the temperature level that can bear the door-insert without damage.
• The two tools are put back into the press by fixing them on their respective plates.
• The removable oven element 20 is disposed on the lower insert holder. The geometry of the element 20 is compatible with that of the tooling.
• The upper plate is lowered until the upper tool comes into the position of Figure 1. The upper edge of the wall of the furnace element is in contact with the vertical portion of the insert holder 13. We have thus formed a closed enclosure. This is delimited by the wall of the furnace element, on the one hand, and by the two inserts, on the other hand.
• The burner feed is controlled by combustion fluids, gases and air. The flame produced is swirling which allows a good homogenization of the temperature. The temperature is increased rapidly to reduce heat loss through the inserts.
• When the temperature, 750 ° C for the superalloy, is reached, the heating is stopped, and the furnace element is removed.
• The press is ready to perform forging parts.

According to a particularly advantageous embodiment, the inserts 1 and 3 are sized relative to their housing in their respective insert holder, so that there is a slight play at room temperature. This game allows easy assembly and disassembly of the inserts.

This clearance is chosen, preferably, so that it is absorbed when the tools leave the oven at the first temperature, between 450 and 500 ° C.

Then, when the inserts are overheated by the above method, they continue to expand, and they come to collapse in the door-insert. The game is said to be negative.

They form a very resistant assembly to the stresses undergone during the forging of parts.

The invention is not limited to the application that has just been described.

Figure 3 schematically shows an application of the method of the invention to the overheating of an insert having a deep etch. It can be a spinning pot.

The tool 200 consists of an inset holder 210, made of steel, for example, in the form of a cylindrical pot with a bottom, containing an insert 201 in a superalloy. The insert 201 covers the inner wall of the pot. The shape is intended to allow the introduction of a punch, vertically in the pot for the extrusion of a metal that is in the bottom of the pot.

During the heating operation the pot does not include the punch or any part.

In order to ensure that the insert 201 is overheated, a bell-shaped removable oven element 120 is placed in abutment on the edge of the insert holder 210. The element 120 consists of a cylindrical metal wall 121 , coated with an insulator 122, and a bottom cross wall 123. The diameter is determined by that of the insert holder. On this wall 123, there is a burner 130 with its combustion fluid supply tubes. The burner 130 extends to the bottom of the pot by a tube 131, so that the combustion occurs as close as possible to the bottom of the insert. The arrows show the circulation of the hot combustion gases along the inner face of the insert. These are then evacuated by the chimney 127 fixed on the wall 121.

When it comes to overheating the superalloy insert relative to the insert holder. 210, the furnace element 120 is used by placing it on the pot 200 so as to constitute a closed enclosure, defined by the insert 201 on the one hand and the inside of the bell 120 on the other hand. A combustion is produced in the enclosure so as to heat the insert and to bring it up to the desired temperature. When the temperature is reached, the bell 120 is removed and the forging operation is carried out.

Claims (11)

1. A process for the heating of a forging machine tool, including an insert holder (11, 13, 200) and an insert (1, 3, 201) with one free face bearing a forging impression, in preparation for a forging operation in the said forging machine, characterised by the fact that the insert holder (11, 13, 200) includes a furnace element (20, 120) that has at least one burner (30, 130) and one flue for removal of the gases (27, 127), forming with the said face of the insert (1, 3, 201) a closed heating chamber, the said chamber being heated until the insert (1, 3, 201) reaches a given temperature, then the furnace element (20, 120) is removed.
2. A process according to claim 1, in which the said chamber is heated by the combustion of a combustible fluid within the latter.
3. A process according to claims 1 or 2, in which the assembly (111, 313, 200) of the insert holder and the insert is heated beforehand in an oven, up to a first temperature that is less than the said given temperature.
4. A process according to one of claims 1 to 3, in which the forging machine includes two tools (111, 313) each with an insert holder (11, 13) and an insert (1, 3), where the said furnace element (20) is in the form of a cylindrical ring, and the furnace element (20) is placed against and between both insert holders (11, 13) so as to constitute the said heating chamber.
5. A process according to one of claims 1 to 3, in which said machine tool (200) is an extrusion vessel, the said furnace element (120) is in the form of a bell with a bottom wall, and in which the furnace element is positioned on the extrusion vessel so as to constitute the said heating chamber.
6. A process according to one of the preceding claims, in which the materials constituting the insert (1, 3, 201) and the insert holder (11, 13, 210) have different expansion coefficients, and are positioned in relation to each other so as to create negative play when the insert is at the said given temperature while still being removable when it is at a temperature below the first temperature, and in particular at ambient temperature.
7. A removable furnace element (20, 120) for implementation of the process according to one of claims 1 to 6, including a metal wall (21, 210) that is coated on the inside with a layer (22, 201) of insulation, having at least one burner (30, 130) and a flue (27, 127) for removing the combustion gases.
8. A removable furnace element according to claim 7, in which the burner (30) is oriented tangentially so as to produce a vortex-like flow along the wall.
9. A removable furnace element according to one of claims 7 and 8, which is of annular shape.
10. A removable furnace element according to one of claims 7 and 8 in the form of a bell.
11. A removable heating assembly that includes a removable furnace element according to one of claims 7 to 10, a means of feeding with combustion fluids and a means of regulating heating power and time.

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