EP0331539B1 - Method of making forged blanks from bar material by upsetting, in particular for compressor blades, and tooling equipment for carrying out the method - Google Patents

Description

The present invention relates to a process for manufacturing blanks forged at the foot of a turbomachine compressor blade by upsetting as well as a tool intended for the implementation of said process according to the preamble of claims 1 and 5.

It is common in the manufacture of certain parts such as compressor blades from forged blanks to carry out a pressing operation at the end of a cylindrical bar in order to obtain the volume of material by increasing the section. necessary, for example, for the realization of the foot in the case of a dawn.

• des paramètres technologiques tel que le taux de refoulage t, défini par :
  
  $\text{t = (Lo - Ll)/Do}$
  
  
  
  où Lo est la longueur initiale de la portion de barre à refouler,
  Ll est la longueur de cette même portion après refoulage,
  Do est le diamètre initial de la barre à refouler ;
  Lo - Ll représente la course utile du poinçon de la machine de forgeage utilisée et la limite supérieure de cette course est une donnée de construction de ladite machine ;
• des paramètres métallurgiques et notamment le rapport de réduction r défini par :
  
  $\text{r = Lo/Ll = Sl/So = (Dl/Do)²}$
  
  
  
  où So est la section transversale initiale de la barre,
  Sl est la section transversale de la barre après refoulage et Dl est le diamètre correspondant.

In the data for defining such a pumping operation, two types of parameters can be retained:

• technological parameters such as the delivery rate t, defined by:
  
  $\text{t = (Lo - Ll) / Do}$
  
  
  
  where Lo is the initial length of the portion of bar to be driven back,
  Ll is the length of this same portion after upsetting,
  Do is the initial diameter of the bar to be driven;
  Lo - Ll represents the useful stroke of the punch of the forging machine used and the upper limit of this stroke is a data of construction of said machine;
• metallurgical parameters and in particular the reduction ratio r defined by:
  
  $\text{r = Lo / Ll = Sl / So = (Dl / Do) ²}$
  
  
  
  where So is the initial cross section of the bar,
  Sl is the cross section of the bar after upsetting and Dl is the corresponding diameter.

In the various known applications of the upsetting process, it appears that to avoid unacceptable defects on the blanks obtained, the process is subject to geometric limitations. These defects due to insufficient control of the deformation during the operation consist in particular of folds which may be due to a phenomenon of buckling of the portion of bar to be driven back or to a disturbed fiber drawing, due to a phenomenon of torsion of the bar after buckling.

Figures 1a, 1b, 1c, 1d of the accompanying drawings illustrate the production of a delivery on a bar B, placed in a container A, during which during four successive operations corresponding respectively to the four figures, a reduction in length l₁, l₂, l₃ and l₄ is obtained and the phenomena which have just been reported (buckling then twisting) appear leading to the defects which have been noted (folds and disturbed fiber drawing).

It is commonly accepted that to avoid these defects, an upper limit value of the delivery rate t of 4 when the delivery is carried out in one operation or of 6 when it is carried out in two successive operations must be respected. A limitation of the Dl / Do ratio of 1.5 to 2 depending on the type of alloy concerned is also sometimes fixed.

Various attempts at improvement have sought to overcome the geometric limitations imposed so far without incurring the appearance of defects. An attempt was thus made to carry out the pushing-back operation by means of a tool animated by a nutation movement on the end to be pushed back of the bar, the latter being simultaneously moved towards the working area of a length corresponding to the volume to be deformed. Attempts have also been made to push back in several passes by advancing successively, with each pass, the bar of a length corresponding to the volume to be deformed. Examples of such embodiments are given by FR-A-2050 483, FR-A-2050 484, and by FR-A-2220 328. In these methods, the results have not been entirely satisfactory and in particular a sufficiently regular orientation fiberizing cannot be guaranteed.
Also known from SU-A-804 163, which represents the closest state of the art, is a die-forging tool for roughing an object with a polygonal section such as a nut.

• (a) une première étape de refoulage durant laquelle, au moins à partir d'un premier stade de déformation, un contact est maintenu entre au moins trois génératrices de ladite portion de barre et la surface intérieure d'un premier conteneur qui comporte, entre deux desdites lignes de contact respectivement, une excroissance en creux longitudinale formant en section transversale une partie lobée,
• une deuxième étape de refoulage durant laquelle, au moins à partir d'un premier stade de déformation, un contact est maintenu entre les génératrices de sommet des excroissances longitudinales obtenues sur la première ébauche à l'issue de la première étape (a) et la surface intérieure d'un deuxième conteneur, ladite surface intérieure de cavité présentant une forme de contour enveloppant ladite première ébauche,

et en ce que ledit taux de refoulage t obtenu en deux passes est au moins égal à 8.This tool has an internal working cavity with convex faces connected by rounded angles whose radius of curvature is such that the contour leaves the limits of the contour of the impression of the finishing tool.
The process for manufacturing blanks forged in bar by upsetting which makes it possible to avoid these drawbacks is characterized in that it comprises at least two successive stages:

• (a) a first upsetting step during which, at least from a first deformation stage, contact is maintained between at least three generatrices of said bar portion and the interior surface of a first container which comprises, between two of said contact lines respectively, a longitudinal hollow outgrowth forming a lobed part in cross section,
• a second upsetting step during which, at least from a first deformation stage, contact is maintained between the crown generators of the longitudinal protuberances obtained on the first blank at the end of the first step (a) and the inner surface of a second container, said inner cavity surface having a contour shape enveloping said first blank,

and in that said delivery rate t obtained in two passes is at least equal to 8.

A discharge tool wrapping a bar forged blank intended for the implementation of said method is defined by the combination of characteristics of claim 5.

Advantageously, the first container has a cruciform section cavity, the cylindrical bar being in contact with the interior surface of the container along four generatrices located at 90 ° from one another and the second container has a square section cavity , with rounded corners, the tops of the protuberances or lobes of the cruciform section of the bar obtained at the end of the first step being in contact respectively with one side of said square.

In certain applications relating to titanium alloys, discharge rates of 8 to 10 obtained in two operations by the process in accordance with the invention required by the prior processes previously known at least five successive operations. According to the quality criteria imposed and according to the applications, in particular according to the alloys used, higher upsetting rates can be obtained and in all cases, higher than the previous results. In addition, metallographic examinations carried out on the forged blanks obtained by the upsetting process according to the invention have shown a marked improvement in the orientation of the fiber drawing compared to these previous processes as well as a total absence of defects. These improved results come directly from the application of the method according to the invention and can be explained by its characteristics. In fact, during the first step of the process, the bar is held in support at least along three generatrices, thus avoiding any deformation by buckling, while the flow of the alloy can only be done in the direction hollow parts of the container, thus making any torsional deformation impossible. Similarly, during the second step, the contact maintained between the end generators of the blank and the walls of the container prevents any deformation by buckling or twisting.

• les figures 1a, 1b, 1c, 1d qui ont été précédemment décrites représentent schématiquement les déformations d'une barre lors d'opérations successives de refoulage n'appliquant pas l'invention :
• les figures 2a, 2b représentent la barre dans sa forme initiale avant refoulage, respectivement en vue de face et en vue selon une section transversale,
• les figures 3a, 3b représentent schématiquement la barre représentée aux figures 2a, 2b au cours de la première étape de l'opération de refoulage selon le procédé conforme à l'invention, respectivement en vue suivant une coupe longitudinale et selon une section transversale ;
• les figures 4a, 4b représentent schématiquement l'ébauche obtenue à l'issue de la première étape, au cours de la deuxième étape de l'opération de refoulage selon le procédé conforme à l'invention, respectivement, selon des vues analogues aux figures 3a et 3b, suivant une coupe longitudinale et selon une section transversale ;
• la figure 5 représente une vue de l'ébauche forgée finale obtenue par le procédé conforme à l'invention, selon une section transversale ;
• la figure 6 représente selon une vue analogue à la figure 4b, en section transversale, une variante de mise en oeuvre de la deuxième étape du procédé conforme à l'invention ;
• les figures 7a, 7b, 7c montrent des variantes de mise en oeuvre d'étapes du procédé de refoulage conforme à l'invention.

Other characteristics and advantages of the invention will be better understood on reading the following description of an embodiment of the invention, with reference to the appended drawings in which:

• FIGS. 1a, 1b, 1c, 1d which have been previously described schematically represent the deformations of a bar during successive upsetting operations not applying the invention:
• FIGS. 2a, 2b show the bar in its initial shape before upsetting, respectively in front view and in view in a cross section,
• Figures 3a, 3b schematically show the bar shown in Figures 2a, 2b during the first step of the upsetting operation according to the method according to the invention, respectively in view in a longitudinal section and in a cross section;
• Figures 4a, 4b schematically show the blank obtained at the end of the first step, during the second step of the upsetting operation according to the method according to the invention, respectively, according to views similar to Figures 3a and 3b, along a longitudinal section and along a cross section;
• FIG. 5 represents a view of the final forged blank obtained by the method according to the invention, according to a cross section;
• 6 shows a view similar to Figure 4b, in cross section, an alternative implementation of the second step of the method according to the invention;
• Figures 7a, 7b, 7c show alternative embodiments of steps of the upsetting process according to the invention.

The method for manufacturing blanks forged by upsetting according to the invention applies in particular to bar products such as a cylindrical bar 1 shown in its initial form in FIGS. 2a and 2b. As shown schematically in Figures 3a and 3b, for the realization of the first step (a) of the upsetting process according to the invention, the bar 1 is placed in a first container 2 secured to a forging press or machine repress of a type known per se which is not shown in more detail in the drawings. During this first pushing step (a), one end 1a of the bar 1 is subjected to the pushing action of a punch 3 moved by the pushing and control means of said machine. The portion 1b of the bar 1 subjected to the upsetting thus tends to occupy the available volume of the container 2 limited by the face of the punch 3, which results in a reduction in length of said portion 1b, accompanied by an increase in the corresponding cross section. . In the embodiment of the invention shown in Figures 3a and 3b, the first container 2 used during the first step of the upsetting process comprises a cavity 4 which has in cross section a generally cruciform shape composed of four lobed parts 4a, 4b, 4c, 4d arranged symmetrically in pairs, thus providing four generators 5a, 5b, 5c, 5d located at 90 ° one from the other, which cooperate with four corresponding generatrices of the repressed portion 1b of the bar 1 while maintaining, from a first deformation stage, permanent contact with them during the repression step . Said contact following the generators between container and bar becomes necessary from the moment when during the upsetting operation there are risks of creating irreversible defects by buckling or twisting. Contact can be made from the start of the operation. It is often in practice easier, for ease of implementation, to provide a radial clearance at the start between said generators which can go in the present embodiment up to 0.5 mm. The action, in the direction of the force applied and of the displacement obtained, of the punch 3 is exerted according to the arrow F while the arrows f symbolize the directions of flow of the alloy constituting the bar 1 during the upsetting .

For the second step (b) of the upsetting process according to the invention, the progress of which is similar to that of the first step (a) which has just been described above, the intermediate blank 1c obtained at the end of the first step (a) is placed in a second container 6, as shown diagrammatically in FIGS. 4a and 4b, and its end is again subjected to the pushing action of a punch 7. In the embodiment of the The invention shown in Figures 4a and 4b, the second container 6 has a cavity 8 which has in cross section a generally square shape, with rounded corners. Intermediate draft 1c has a cruciform section which reproduces the shape of the cavity 4 of the first container 2 and the generators 1d, 1e, 1f and 1g corresponding to the vertices of the lobed parts of this cruciform section of the intermediate blank 1c are placed in contact with lines of corresponding support of the sides of the square of cavity of the second container 6 and in a similar manner to the first step (a), during the second step (b) of delivery, the contact is also maintained permanently, from a first deformation stage, at the level of these four symmetrical generators two by two, between the external surface of the blank 1c and the surface of the cavity 8 of the second container 6. As before, a variable radial clearance, from O to O, 5 mm in the present application, can be provided at the start of the second step between the cooperating generators of the bar and of the container.

At the end of this second step (b) of the upsetting process according to the invention, the initial upsetting portion 1b has a final section 1d of forged blank as shown in FIG. 5 in the embodiment which comes from 'be described. This repressed portion of bar 1b may in particular be intended to constitute the base of a turbomachine blade obtained by forging.

Various embodiments applying the characteristics of the upsetting process according to the invention which have been described can be envisaged. In particular, depending on the nature of the alloys concerned, parts whose manufacture is envisaged, the desired upsetting rate, a different number of steps in the upsetting process can be applied. Different forms of cavity of the container used, or according to the associated steps, can also be associated provided that, in accordance with the invention, permanent contact is made during a step between several generators of the blank and of the container cavity surface. The second container 6 used during the second upsetting step (b) in the embodiment which has been described and the section of which is shown in FIG. 4b may, for example, include a cavity 8a delimited by a surface which is shown by a circular section in FIG. 6. FIGS. 7a, 7b, 7c respectively represent, in a schematic section, other usable forms of container cavity 9a, 9b, 9c, respectively associated with a portion of bar to be driven back section 10a, 10b, 10c, 10c, 10d. This bar section at the start is of a shape adapted to the final part to be obtained and, in addition to being cylindrical, can in particular be rectangular or square.

Claims (8)

1. Process for manufacturing blanks for turboshaft engine compressor blade roots by upsetting forged bar, in which at least one portion of bar (1b), of initial length Lo and of initial section So, of diameter Do, is transformed by upsetting a portion of bar (1d) of final length L1 and final section S1, of diameter D1 such that Lo > L1, So < S1, Do > D1, a technological parameter t or rate of upsetting being represented by $\text{t = (Lo - L1)/Do}$

   

   , the said bar (1) placed in a supporting tool or container (2, 6) being subjected to the action of upsetting by a forging press punch (3), exerting itself on the end of the bar, characterised in that it comprises at least two successive stages:

   - (a) a first upsetting stage during which, at least from a first stage of deformation, a contact is maintained between at least three generatrixes of the said portion of bar and the inner surface of a first container (2) which comprises, between two of the said lines of contact (5a, 5b, 5c, 5d) respectively, a protuberance (4a, 4b, 4c, 4d) of longitudinal trough shape forming in cross section a lobed part;

   - (b) a second upsetting stage during which, at least from a first stage of deformation, a contact is maintained between the peak generatrixes of the longitudinal protuberances obtained on the first blank (16) at the end of the first stage (a) and the inner cavity surface of a second container (6), the said inner cavity surface presenting a shape of the contour enveloping the said first blank, and in that the said upset rate (t) obtained in two passes is at least equal to 8.
2. Process for producing blade root blanks by upsetting forged bar in accordance with Claim 1, in which during the first stage (a), the first container (2) presents in cross section an inner contour of generally cruciform shape and the first blank (1b, 1c) upset is maintained during the course of the said first stage (a) in accordance with four longitudinal generatrixes (5a, 5b, 5c, 5d) peripherally spaced at 90° to each other and presents at the end of the first stage (a) four longitudinal protuberances oriented at 90° from each other.
3. Process for producing blanks by upsetting forged bar in accordance with either of Claims 1 and 2 in which during the second stage (b), the second container (6) presents in cross section an inner contour of generally square shape, with rounded corners.
4. Process for producing blanks by upsetting forged bar in accordance with either of Claims 1 and 2 in which during the second stage (b), the second container (8a) presents in cross section a circular inner contour.
5. Upsetting tool enveloping a blank (1b, 1c) forged from bar, designed for putting into practice a production process conforming to any of Claims 1 to 4 consisting of two containers (2, 6) each comprising a cavity (4, 8) in which is placed the said blank (1b, 1c) characterised in that the first container (2) suited to the carrying out of the first stage (a) of the said process presents an inner cavity surface geometry (4) such that before forging the blank (1b) is in contact, at least from a first stage of deformation, at least in accordance with three generatrixes, with the matching generatrixes (5a, 5b, 5c, 5d) of the container (2) and such that trough-shaped longitudinal protuberances (4a, 4b, 4c 4d) are formed between the said generatrixes (5a, 5b, 5c, 5d) and in that the said second container (8)[sic. 8a] adapted for the carrying out of the second stage (b) of the said process presents an inner cavity surface geometry (8) such that the cross sectional contour envelopes the inner surface cavity geometry contour of the first container and that the inner surface cavity contour shapes of the said first (2) and second containers (6) are tangents in accordance with at least three generatrixes and are secants at no point.
6. Tools designed for carrying out the process of manufacturing blanks by upsetting forged bar in accordance with Claim 5 characterised in that the said first container (2) comprises a cavity presenting a cruciform cross section with four lobes, spaced at 90° from each other.
7. Tools designed for carrying out the process of manufacturing blanks by upsetting forged bar in accordance with either of Claims 5 or 6 characterised in that the said second container (6) comprises a cavity (8a) of generally square shape, with rounded corners, the length of one side of the square representing the distance between two peaks of protuberances diametrically opposite (1d-1f, 1e-1g) the first container.
8. Tools designed for carrying out the process of manufacturing blanks by upsetting forged bar in accordance with either of Claims 5 or 6 characterised in that the said second container comprises a cavity (8a) presenting a circular cross section whose circumference envelopes the cavity section (4) of the first container (2).

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