FR3096907A1 - Method of making a mechanically reinforced part - Google Patents

Abstract

This concerns a process for producing a part in steel or titanium and which corresponds to a sheet or a plate. In this process: - if the part (1) is made of steel, bainitic or martensitic steel is used, and the part is heated to a heating temperature between temperatures AC1 and AC3, - if the part is made of titanium, we heating to a heating temperature of between 700 ° C and 1050 ° C, then forming a rib (3c) on said part, at a room temperature corresponding to the heating temperature, to within 10 ° C. Figure to be published with the abstract: 3

Description

Process for producing a mechanically reinforced part

Technical field of the invention

This concerns the production of a part in a material which is steel or titanium and which corresponds to a sheet or a plate.

The intended field of application is in particular that of an aircraft turbine engine or an aircraft.

State of the prior art

In the art, mechanically welded metallurgical assemblies from metal sheets or plates are known.

It is the thickness that distinguishes a sheet from a plate. It will be considered that a sheet has a thickness up to 3 to 4mm, a plate beyond. Its thickness will be able to go until it can be formed as below on a forming tool, such as in particular a bending tool.

A metal sheet or plate is characterized by two flat parallel faces of identical area (except for the specific machining of the edges and the tolerances) with consequently a constant thickness between these two surfaces (within the tolerances). The thickness has a much smaller dimension (at least 10 times) than the two other dimensions which are the width and the length of the sheet or plate.

Often, metallurgical assemblies are objects or parts that delimit a volume or separate two different volumes.

Typically, either they can close on themselves in at least one of the three directions (conventional axes X, Y, Z) by welding or bolting (riveting or any other means of fixing), or they can delimit two volumes by fixing on one or more supports by welding or bolting (riveting or any other means of attachment).

The volumes in question can be made up of gases, fluids, liquids, a multitude of solid pieces, etc.

Here, the elements which can be obtained from the sheets or plates produced according to the invention can, for example and in particular, be containers, tanks, casings, ferrules, boxes, hulls, instrument boxes, or assemblies whose function is to contain the projection of exogenous bodies, also called shielding.

Among the targeted elements, there may in particular be some which will have to structurally resist a difference in pressure on either side of the sheet or plate (structuring function of the assembly), and this in the field elasticity of the material constituting the sheet or plate. This pressure difference can be induced for example: by different pressures on either side, by the local force undergone by a surface which can be associated for example with the stopping of a projection of an external body (case shielding for example) or other elements which can induce bending of the sheet or plate.

Thus are particularly targeted aeronautical applications including turbomachines (in particular turbofans) for propelling flying machines.

Mechanically welded assemblies are required to guarantee a minimum elastic displacement in bending. This displacement in bending corresponds to the "deflection" out of the plane of the sheet or plate (the term deflection is also possible).

This is the consequence of the elastic deformation of the sheet under the difference in pressure existing on either side of the surface.

In the case of the present invention, it is desired not to plastically deform the sheet or plate

A known practice, to meet such a need for reduction of deflection (movement in bending) without plastic deformation, leads to stiffening the sheet or plate by stiffeners.

These stiffeners can in particular be positioned at intermediate distances between the fixing or support points of the sheet or plate, dividing the surface of the sheet or plate segments then defined. These stiffeners can be of a length close to the dimensions of the sheet or plate segments and can be arranged longitudinally and/or transversely to the length of the sheet or plate.

A known practice is thus to weld such stiffeners to the sheet or plate

The welds can be penetrating: the sheets or plates are cut and welded to the stiffeners. Welds may also be only partially penetrating. In this case, the stiffeners are welded directly to one of the faces of the sheet or plate. These two cases are not exhaustive.

In the context of the invention, the geometry of the stiffeners will be of little importance. They can be any.

A major disadvantage of welding stiffeners is to weigh down the mechanically welded assembly compared to the situation where it would not have been necessary to take into account a minimum deflection.

At the welds, the metallurgy is different from that of the sheets or plates concerned. The welds present a raw metallurgical microstructure of solidification (with the presence of dendrites and porosities) which are different from the recrystallized microstructures of wrought materials found in sheets and plates. Therefore, the mechanical properties differ between the two microstructures. The welds have reduced mechanical properties (tensile, elongation, tenacity, fatigue) compared to the wrought metal of the sheet or plate. Practice therefore leads to sizing the mechanically welded assembly to the minimum of the properties of these welds.

To compensate for this reduction or reduction in mechanical properties, it is then necessary to increase the thickness of the sheet or plate compared to a situation where there would have been no need to weld stiffeners. This increase in thickness results in an increase in the mass of the mechanically welded assembly. In addition, the size of the stiffeners adds volume, therefore additional mass. This increase in mass is all the more important as the Young's modulus of the sheet or plate is low. For example, mechanically welded assemblies in titanium alloy have more stiffeners than in those made of steel because of a Young's modulus almost half.

The object of the invention is to provide a solution to at least some of the above problems and drawbacks.

Presentation of the invention

It is planned to hot form a rib in order to make it possible to form a stiffener and a part having the expected performance, once a specific range of temperatures has been chosen where the material constituting the sheet or plate will have superplastic properties. .

It is recalled that superplasticity is one.

Especially for obtaining ribs via folds greater than 135° (see below fold at 180° to within 10°), the notion of superplasticity sought here is not linked to the melting temperature but to a two-phase microstructure (therefore to the chemical composition), that is to say alpha and beta for titanium, and austenite and pearlite, between AC1 and AC3, for steels. Naturally, the more the deformation temperature will increase, the more the classical plasticity (property of plastic deformation at high temperature T (with T≥0.5Tf, where Tf is the melting temperature of the metal expressed in kelvins) of a material which is characterized by large elongations at break which may exceed 1000% during a tensile test) will increase. The flow stress (force necessary to ensure a plastic deformation) will on the other hand decrease with the increase in temperature.

In the case of superplasticity defined here, the temperatures are among the lowest, while the flow stresses are among the highest. But, contrary to the law mentioned above which states that the elongation at break decreases with a decrease in temperature (associated with an increasing flow stress), we will find ourselves in this case in a range temperatures where the elongation at break will increase, with potentially and for example elongations at break of more than 1000%.

A rib is considered here as any protruding part on a part (in this case sheet or plate). Synonyms are elongated stiffener, elongated protrusion, elongated edge, elongated projection, all in one piece with the sheet or plate, said elongation extending along (one of the faces of) said sheet or plate.

An essential aspect is that this rib is not linked to the sheet or the plate by any weld bead.

More specifically, at least part of the solution of the invention thus provides a method for producing a part in a material which is steel or titanium and which corresponds to a sheet or a plate, in which process:
- if the part is made of steel, a low or high alloy, bainitic or martensitic steel is used, and the part is heated to a heating temperature between the temperatures AC1 and AC3,
- if the part is made of titanium, it is heated to a heating temperature of between 700°C and 1050°C, then
- a rib is formed on said part, at a temperature of the part corresponding to the heating temperature, to within 30°C, and possibly within 10°C (the expression “within X °C” meaning: at + or – X°C).

Low-alloy steels are Fe-based alloys with a C content ≤ 2.1% by mass and with a content of other alloying elements whose minima meet standard NF EN 10020 and whose individual maxima, for example alloying element, remain ≤ 5% by mass.

High-alloy steels are Fe-based alloys with a C content ≤ 2.1% by mass and with a content of at least one of the alloying elements and > 5% by mass.

Forming the part by at least one hot stamping at the aforementioned temperatures may make it possible to optimize the forming industrially.

From the outset, situations can be reached in which the forming of the rib on said part includes:
- a first fold of the part, so as to obtain a part folded over an angle less than or equal to 120°, then
- a second fold made on the folded part and on an angle less than or equal to 120°.
However, to promote the achievement of even more marked angles or folds (fold(s) of angle(s) greater than 135°, to within 10°), with therefore high superplastic properties of the material constituting the sheet metal or plate, it may usefully be preferred that at least one of the following characteristics be satisfied:
- if said part is made of titanium, that the heating temperature is 800°C, to within 30°C, and possibly within 10°C,
- if said part is made of titanium, that the titanium has a two-phase alpha and beta microstructure,
- if said part is made of steel, that the steel has a two-phase microstructure of austenite and pearlite.

In this text, the term (first then second, etc.) "folding" should not be misused. “Bending” consists of making a bend, whether by (a) stamping tool, by (a) bending tool, or by forging, with the effect of obtaining a “fold”.

In any situation, sheet metal or plate, steel or titanium, it may further be provided that, to obtain a said rib in the shape of an arch with a bulbous apex, the forming of the rib on said part comprises:
- either :
-- a first fold of the part, so as to obtain a first part folded over an angle of 90°, to within 10°, with respect to an unfolded part then
-- other successive folds combining folds of a maximum of 120° each, with an association of incoming angles and outgoing angles until obtaining a last folded part which closes the shape along said first folded part, at the opposite of the unfolded part, then
-- a final fold made on said last folded part, so as to obtain a terminal folded part on an angle of 90°, to within 10°, towards the opposite of the unfolded part,
- either :
-- a first fold of the part, so as to obtain a part folded over an angle less than or equal to 120°, then
-- a second fold made on the folded part and on an angle less than or equal to 120°.

Indeed, the bend angles involved (relatively limited) and the superplastic properties then presented by the sheet or the plate will make it possible to achieve the realization of the rib integrated into the desired sheet or plate.

Given the advantages of folds linked to the expected superplastic properties, it may be necessary to:
- during the forming of the rib on said part, to control the temperature of the part, and
- if the temperature of the controlled part drops more than 20°C, within 5°C, below the heating temperature, to reheat the part to the heating temperature, at 10°C, before resuming forming.

Again thanks to the superplastic properties, and the resulting high elongation at break, it will be possible to obtain, in safety, an arch-shaped rib, in particular a hairpin, with a forming of the rib on said part comprising:
- a first fold of the piece, so as to obtain a first part folded over an angle between 90° and 135°, to within 5°, with respect to an unfolded part then
- a second fold made on the first folded part, so as to obtain a second part folded over an angle between 90° and 180°, to within 5°, along the first folded part, towards the opposite part unfolded, then,
- a third fold made on the second folded part, so as to obtain a third part folded over an angle between 90° and 135°, to within 5°, with respect to the second folded part, towards the opposite part unfolded.

The use of the aforementioned temperature control will secure the target achievement of said angle between 90° and 135°, to within 5°.

In addition to the foregoing, the invention also relates to a tool for implementing the aforementioned method.

Favorably, such a tool may include:
- a male matrix having a convex arcuate outer surface, provided with movable drawers adapted, in an extended state, to protrude from the arcuate outer surface,
- a female die having, complementary to the male die, a concave arcuate inner surface, provided with cavities adapted to receive the movable drawers, in the deployed state,
- first means of relative displacement between the male die and the female die and second means of displacement of the movable drawers with respect to the male die, so that the male die can be engaged in the female die, with the movable drawers engaged in the cavities of the female matrix, and
- Means for heating the male die and/or the female die.

Thus, we can obtain ribs from the rib itself.

In addition to the foregoing, yet another aspect of the invention relates to a metallic element of an aircraft turbine engine or of an aircraft, the metallic element comprising at least one part obtained via the method according to any one of the claims above and in which said part must resist, in the elastic range of the material, a pressure difference on either side of the part which can be between 0.03 GPa and 50 GPa.

Indeed, it was mentioned earlier that, among the elements targeted, there may in particular be some which will have to structurally resist a significant pressure difference on either side of the sheet or plate (function structuring of the assembly), and this in the elastic range of the material constituting the sheet or plate.

Other elements targeted, or even the same on other physical aspects, could require mechanical resistance, particularly to tearing or shearing.

Also, in particular for these cases, is proposed a metal element of an aircraft or aircraft turbomachine which will comprise at least one part obtained via the aforementioned process, with all or part of its characteristics and in which the rib of said part would define a flange for attaching said metallic element to another element of the aircraft turbine engine or the aircraft

Brief description of figures

represents a local diagram of a first part having a rib that can be obtained with the method of the invention,

represents a local diagram of a second part having a rib that can be obtained with the method of the invention,

represents a local diagram of a third part having a rib that can be obtained with the method of the invention,

represents a local diagram of the second part that can be obtained with the method of the invention and having fixing holes,

represents a partial diagram of a tool for forming by stamping a ribbed part that can be obtained with the method of the invention,

represents an alternative local embodiment of the tool of [FIG. 5], at the location of detail VI, and

represents a local diagram of a rounded and ribbed part which can also be obtained with the method of the invention.

Detailed description of the invention

As explained, the invention therefore aims to produce by forming at least one stiffener or rib, at ambient pressure (10 ⁵ Pa) and at a predetermined temperature, directly from a large sheet or a large plate already manufactured.

The forming of the part can be done by at least one of the following techniques: stamping, bending, forging.

As for the advantages of forging over other techniques, we can note:
- improvement of the mechanical characteristics of the metal,
- savings in material used and reduction in machining time.

A specific feature is linked to the material of part 1 (sheet or plate) to be obtained, which is such that:
- if the part is made of steel, a low or high alloy bainitic or martensitic steel is used, and the part is heated to a heating temperature Tc between the temperatures AC1 and AC3,
- if the part is made of titanium, it is heated to a heating temperature Tc between 700°C and 1050°C, then, in each of these cases,
- Is produced on said part, by forming, a rib, such as 3a, 3b, 3c Figures 1-3, at a temperature of the part corresponding to the heating temperature Tc, to within 10 ° C.

In the context of the present invention, it is not required that the part 1 (sheet or plate) has been pretreated by a heat treatment, such as at least one quenching which may be followed by tempering, before the forming of the rib.

On the other hand, a quality heat treatment can be judiciously applied once the part has been shaped.

For steels, this heat treatment will favorably consist of quenching (or normalization) followed by tempering.

After quenching or normalizing the steel will be martensitic or bainitic. Then tempering at a lower temperature will best guarantee the expected working properties.

For titanium alloys, the heat treatment may include (or not) quenching. If there is none, we will take advantage of the shaping temperature. After quenching, we can provide an income.

Given the temperatures involved, quenching or the forging temperature will act on the dual, and therefore two-phase, structure. Tempering confers the mechanical properties (elimination of stresses and embrittlement caused by quenching).

For the record, for steel parts:
- the structure of the steel can be modified by such heat treatments: the rapidity of the transformation does not allow the carbon to diffuse and then blocks it in the centered cubic mesh, which deforms to give martensite; the crystals form small needles. A slower quenching, or a quenching staged in temperature, allows the formation of bainite,
- AC are the transformation temperatures of the iron-carbon alloys with a sufficiently rapid heating not to respect the equilibrium temperatures. This term is used to indicate that the transformation temperature increases with the heating rate: AC1>A1 and AC3>A3, it being specified that:
- A1 is the transformation temperature of iron-carbon alloys meeting the following criteria: it is:
-- the temperature from which austenite begins to appear during very slow heating,
-- the temperature from which austenite completely disappears during very slow cooling,
- A3 is the transformation temperature of hypo-eutectoid iron-carbon alloys (up to 0.77%C) meeting the following criteria: it is:
-- the temperature above which the structure is totally austenitic during very slow heating,
-- the temperature from which austenite begins to transform into ferrite during very slow cooling (source: https://www.isgroupe.com/fr/savoir-faire/glossaire/glossaire_soudage/Pages/ default.aspx).

Furthermore, forming by bending or stamping or forging, as mentioned above, will make it possible to use conventional tools, the implementation of which is perfectly mastered, inexpensive and with which one can very effectively control the height of the stamping (H ; see below).

Therefore, it will not be necessary to increase the thickness of the initially selected sheet or plate.

The invention thus makes it possible to approach the ideal situation where it would not have been necessary to add a stiffener. The only excess weight will then come from the additional mass of the stiffener itself. By standardizing the masses, with as reference 100, that of the previous situation, table 1 specifies the standardized masses (the mass of the object is divided by the mass of the object having at least one welded stiffener) that it is possible to achieve for the different solutions below.

The columns represent from left to right:
• a solution where it is not planned to add a stiffener; ideal case where the displacement of the deflection of the part is not to be taken into account in the dimensioning, for a mechanically welded assembly in steel or titanium alloy,
• a previous solution where it is necessary to weld stiffener(s) to meet a minimum deflection criterion; this mass is used to carry out the normalization calculations for each of the mechanically welded assemblies considered in steel or titanium (alloy);
• a solution in accordance with the invention to form one (the) stiffener (s) cold or at controlled temperature as above, this for each of the mechanically welded assemblies in steel or titanium alloy;

In addition to the mass advantage, the cost of making a bend by hot forming in the superplastic temperature range of the material is significantly reduced compared to a stiffener created by welding.

Sheets or plates may be received in any metallurgical condition. Then, if necessary, they will be divided into elementary parts in the implementation format.

These (elementary parts of) sheets or plates will be heated to a target temperature with which the material therefore exhibits superplastic behavior.

This makes it possible to obtain a better malleability of the material via an improvement in its rate of elongation A compared to what can be observed at room temperature; 20°C, within 10°C.

For the aforementioned steels, in the low or high alloy bainitic or martensitic families, the target temperature to reach the superplastic capacity will then be included in the intercritical range, namely between the temperatures AC1 and AC3, corresponding respectively:
- at the temperature where the transformation of bainite or martensite into austenite begins during heating,
- and the one where this transformation ends, still under heating.

For titanium parts (Ti base therefore), all grades can be used and more particularly grades with a two-phase Alpha and Beta microstructure, for example: titanium-based alloy of type 6242 or 6246 or Ti 6-4, this at the superplastic forming temperature of part 1.

The (elementary parts of) sheets or plates will thus be brought to temperatures corresponding therefore to said superplastic capacity, ie to a temperature between 700° C. and 1050° C., and more particularly to 800° C., to within 20° C.

It should be noted that due to the superplastic deformation reached, the part will have good shear strength because the titanium alloy can then flow better during forming.

The sheets or slabs can then be brought to the shaping tools.

If such conditions are met, for the aforementioned respective materials, the rib diagram 3b of Fig. 2 can be aimed at.

To obtain a rib 3b in the shape of an arch, which can be described as a hairpin, it is indeed then possible that the forming, in particular by forging, of the rib on the part 1 comprises:
- a first fold 5a of the part, so as to obtain a first part 7b folded over an angle between 90° and 135°, to within 5°, with respect to an (initially) unfolded part 7a then,
- a second fold 5b made on the first folded part 7b, so as to obtain a second part 7c folded over an angle (α) between 90° and 180°, to within 5°, along the first folded part 7b, this towards the opposite of the unfolded part 7a, then,
- a third fold 5c (which may be the final fold) made on the second folded part 7c, so as to obtain a third folded part 7i, folded over an angle between 90° and 135°, to within 5°, relative with second folded part 7c, towards the opposite of said (initially) unfolded part 7a.

It is in particular for the angle α that it will be necessary to be vigilant and that the rounding at the location of this angle is as progressive as possible.

As, and even more so than in the cases of Figures 1 and 3 where the bend angles are less marked, one will be vigilant that after the first fold 5a of the part, a sufficient height H is ensured at the rib in training course, in order to achieve rigidity, without intimate physico-chemical weakening (one remains in the elastic domain of the material constituting the sheet or plate).

This height H may typically be greater than 1 cm.

In this case, the limit of this height will be linked to the radius of curvature of the bend zones concerned and to the need for support points of the forming tools.

The height H will be defined as the distance between the apex or the edge of the fold (3b figure 2) and the plane from which the previous fold or the following fold was made (plane P figure 2 where the said respectively extend (initially) unfolded part 7a and said end folded part 7i).

An additional advantage with a 180° fold like figure 2 is that the rib or protrusion 3b produced can serve as a flange 9, as shown schematically in figure 4.

On this rib 3b, other usage functions can be added, such as holes 11 (drilled) which can, for example, receive screws for fixing between parts. This leads to additional improvements: lightening (no need to re-weld a flange taking into account a knocked-out area, etc.), cost reduction (elimination of costs relating to preparation and welding operations, etc.) .

If, however, the superplasticity is not sufficient, the hairpin shape is not achievable and one must either significantly change the shape of the rib, as with that of figure 3, or else circumvent the difficulty by multiplying the folds, each one being d a limited angle, as shown schematically in Figure 1: the characteristic of the sheet or plate in the corresponding metallic grade then has a bend radius well below 180° at the temperatures allowing superplasticity. This is verified by a typical control test.

In the case of Figure 3, the rib 3c defines a shoulder.

The forming of this rib could indeed be carried out as follows:
- a first fold 5a of the piece, so as to obtain a first folded part 7b over an angle of at most 120°, here 90°, with respect to an (initially) unfolded part 7a,
- then (at least) another fold, here a single 5b which will therefore define the final fold, of a maximum of 120° (each), here of 90°, made on the last part (then still) folded (here said first folded part 7b), so as to obtain a terminal folded part 7j, over an angle of 90°, to within 10°, towards the opposite of the (initially) unfolded part 7a.

To obtain a rib in the shape of an arch with a bulbous apex, as marked 3a in figure 1, the forming of this rib on the part will, on the other hand, be longer and can be carried out with the following bends:
- a first fold 5a of the piece, so as to obtain a first folded part 7b, folded over an angle of 90°, to within 10°, with respect to an (initially) unfolded part 7a then,
- other successive folds 5b to 5e combining folds of a maximum of 120° each, with an association of incoming angles (as for the 5b or 5f fold) and outgoing angles (as for the 5c or 5e fold) up to 'to obtain a last folded part 7h which, via the penultimate folded part 7g - before the part 7h is created) closes the arch shape with a bulbous apex along the first folded part 7b, opposite of the (initially) unfolded part 7a, then
- a terminal fold 5g made on said last part (then still) folded 7f, so as to obtain a terminal folded part 7h, over an angle of 90°, to within 10°, towards the opposite of the part (initially) not folded 7a.

In fact, successively, the following procedure could have been followed, in order to obtain such a rib in the shape of an arch 3a with a bulbous apex:
- a first fold 5a of the piece, so as to obtain a said first part 7b folded over an angle of 90°, to within 10°, with respect to the unfolded part 7a, then
- a second fold 5b made on the first folded part, so as to obtain a second folded part 7c over an angle between 90° and 120°, to within 5°, towards said unfolded part 7a, then,
- a third fold 5c made on the second folded part 7c so as to obtain a third part 7d folded over an angle between 90° and 120°, to within 5°, towards the opposite of said unfolded part 7a, then,
- a fourth fold 5d made on the third folded part 7d so as to obtain a fourth folded part 7th over an angle of 90°, to within 10°, with respect to the third folded part 7d, towards the opposite of said part not bent 7a, then,
- a fifth fold 5th made on the fourth folded part 7th so as to obtain a fifth folded part 7f which closes the fold in the direction of the second fold 5b,
- a sixth fold 5f made on the fifth folded part 7f, so as to obtain a sixth folded part 7g at an angle of 90°, to within 10°, with respect to the fifth folded part 7f, towards the opposite of said part unfolded 7a, then,
- a seventh fold 5g (also called terminal fold) made on the sixth folded part 7g, so as to obtain a seventh folded part 7h (also called terminal folded part) at an angle of 90°, to within 10°, towards opposite of said (initially) unfolded part 7a.

Another form that can be reached, even if the superplasticity, as below, is insufficient (see remark above on this insufficient superplasticity): that marked 3a in figure 3 defining a shoulder.

The forming of this rib could indeed be carried out as follows:
- a first fold 5a of the piece, so as to obtain a first folded part 7b over an angle of at most 120°, here 90°, with respect to an (initially) unfolded part 7a,
- then (at least) another fold, here a single 5b which will therefore define the final fold, of a maximum of 120° (each), here of 90°, made on the last part (then still) folded (here said first folded part 7b), so as to obtain a terminal folded part 7h, over an angle of 90°, to within 10°, towards the opposite of the (initially) unfolded part 7a.

Since the superplastic state of the material is a critical element, we may find useful:
- that during the forming of the rib such as 3a, 3b or 3c on part 1, the temperature of this part is controlled, and
- that, if the temperature of the controlled room drops more than 20°C, to within 5°C, below the aforementioned heating temperature Tc, room 1 is heated to the heating temperature, at 10°C, before resuming forming on the tool.

Various known forming tools may be used, in particular a bending tool or a forging tool adapted to be, for example by electrical resistors, heated and preferably preheated, before placing the sheet or plate to be formed therein.

As an important part of such a tool (see reference 13 in FIG. 5), at the place of a die 15 and a punch 17, one could however in particular provide:
- a male punch 17 having at least one convex arcuate outer surface 17a, provided with movable drawers 17b adapted, in an extended state, to project relative to the fixed part 17c of the male punch, so as to then form a projecting la ( the) convex outer arcuate surface(s) 17a,
- A female matrix 15 having, in a complementary manner to the male matrix, at least one concave arcuate inner surface 15a and provided for this purpose with one or more cavities 15b adapted to receive the mobile drawers, in the deployed state.

In addition to the first conventional means (typically cylinders) - symbolized by the double arrow 19 in FIG. 5 - to ensure the approximation and the relative spacing between the fixed part 17c of the male punch and the female die 15, the tool will in this case include second means for moving the movable drawers 17b relative to the fixed part 17c and to the female die 15, so that the punch 17 can be engaged in the female die, with the movable drawers 17b engaged in the cavities 15b of the female die ; see the double arrows 21 symbolizing said second displacement means, figure 5.

In addition to this, means 23 for heating the die and/or the fixed part 17c of the punch may therefore be desired.

A less sophisticated stamping tool solution would be to replace the movable drawer(s) 17b with as many protrusions 17d forming the convex outer arcuate surface(s). (s) 17a, as shown schematically in Figure 6.

If the tool 13 is used, it is possible, depending on the shape of the surfaces facing the die and the punch, to obtain parts 1 of various shapes from sheet metal or plate, such as the part schematically shown in part in FIG. , with its ribs 3b standing on a base 23 arched.

From the foregoing, it will be understood that the solution of FIGS. 1 and 3 is general, since there is no fold at 180° (in fact less than 135°). It may be preferred to achieve such folds by stamping and/or hot bending, rather than by forging. The solution of figures 2,4,7, with their fold at more than 135° (which can therefore reach 180°, within 10°) is a choice without technical conditions. We will then work if necessary at relatively low strain rates to increase the radius of curvature.

Claims (11)

Process for producing a part in a material which is steel or titanium and which corresponds to a sheet or a plate, in which:
- if the part (1) is made of steel, a low or high alloy bainitic or martensitic steel is used, and the part is heated to a heating temperature (Tc) between the temperatures AC1 and AC3,
- if the part is made of titanium, it is heated to a heating temperature (Tc) between 700°C and 1050°C, then
- a rib (3a, 3b, 3c) is formed on said part, at a temperature of the part corresponding to the heating temperature, to within 30°C. A method according to claim 1, wherein the forming comprises at least one of stamping, bending, forging the part. Process according to one of Claims 1 or 2, in which, if the said part is made of titanium, the heating temperature is 800°C, to within 30°C. Method according to any one of the preceding claims, in which, if the said part is made of titanium, the titanium has a biphasic alpha and beta microstructure. A method according to any preceding claim wherein, if said part is steel, the steel has a biphasic microstructure of austenite and pearlite. A method according to any preceding claim, wherein forming the rib (3c) on said part comprises:
- a first fold (5a) of the part, so as to obtain a part folded over an angle less than or equal to 120°, then
- a second fold (5b) made on the folded part and on an angle less than or equal to 120°. A method according to any one of claims 1 to 5 wherein, to obtain a rib in the shape of an arch with a rounded apex, the forming of the rib on the said part comprises:
- a first fold (5a) of the part, so as to obtain a first part folded over an angle of 90°, to within 10°, with respect to an unfolded part (7a) then
- other successive folds (5b-5f) combining folds of a maximum of 120° each, with an association of incoming angles and outgoing angles until obtaining a last folded part which closes the shape along said first folded part, opposite the unfolded part, then
- a terminal fold (5g) made on said last folded part, so as to obtain a terminal folded part (7h) at an angle of 90°, to within 10°, towards the opposite side of the unfolded part (7a). Method according to any one of Claims 1 to 5, in which, in order to obtain an arch-shaped rib (3b), the forming of the rib on the said part comprises:
- a first fold (5a) of the piece, so as to obtain a first part (7b) folded over an angle between 90° and 135°, to within 5°, with respect to an unfolded part (7a), then
- a second fold (5b) made on the first folded part, so as to obtain a second part (7b) folded over an angle between 90° and 180°, to within 5°, along the first folded part, towards the opposite of the unfolded part, then,
- a third fold (5c) made on the second folded part, so as to obtain a third part (7c) folded over an angle between 90° and 135°, to within 5°, with respect to the second folded part, towards the opposite the unfolded part (7a). A method according to any preceding claim, wherein:
- during the forming of the rib (3a, 3b, 3c) on said part, the temperature of the part is controlled, and
- if the temperature of the controlled part drops more than 20°C, to within 5°C, below the heating temperature (Tc), the part is reheated to the heating temperature, at 10°C, before resuming forming . Metallic element of an aircraft turbine engine or of an aircraft, the metallic element comprising at least one part (1) obtained via the method according to any one of the preceding claims and in which the said part must resist in the elastic range of the material at a pressure difference on either side of the part of between 0.03GPa to 50GPa. Metallic element of an aircraft turbine engine or of an aircraft, the metallic element comprising at least one part obtained via the method according to any one of claims 1 to 9 and in which the rib of the said part defines a flange ( 3b) to attach said metallic element to another element of the aircraft turbine engine or of the aircraft.