EP0524098B1 - Method and punch for deep-drawing containers with a continuous wall - Google Patents

Abstract

The invention relates to a method for deep-drawing blanks of flat metal products having undergone a drawing or rolling operation, with a view to carrying out subsequent deep-redrawing or repeated-passing operations or with a view to manufacturing flanged containers, in particular cylindrical containers, characterised in that a punch is used whose tip has a variable transition (coupling) radius which is determined as a function of the anisotropic characteristics of the blank material. Advantageously the next step is an operation for grinding the bottom of the container by using a punch having a constant transition (coupling) radius. Application to the manufacture of metal tumblers. <IMAGE>

Description

The present invention relates to a method of stamping blanks for the manufacture of containers which may have a flange corresponding to the non-stamped part of the blank.

The blanks are generally made of a metal which has undergone a drawing or rolling operation so that this metal has an anisotropy as regards the resistance to thinning. As a result, when containers with flanges of cylindrical section are produced in circular blanks, for example in steel having undergone significant skin-pass operations, during stamping, different thinning and thickening operations are created. on the body of stamped objects and the collar obtained is irregular; it has a sinuous profile comprising "horns" and "hollow horns".

In the case of a stamped without collar, the irregularity is located at the end of the wall. This irregularity creates significant obstacles during subsequent operations (case of re-stamping or ironing).

As a result, the irregular flange which, during an additional cutting operation, creates significant losses of base material.

To reduce this effect of horn formation, a minimum reserve is generally used under a blank holder, that is to say that one works at the minimum blank holder pressure, at the limit of the appearance of folds. on the collar. In this solution, the stamping operation swallows a larger quantity of metal into the matrix and in order to always obtain the same dimension of flange, it is necessary to increase the dimensions of the starting blank.

The present invention therefore proposes to provide a method which makes it possible to reduce the formation effect. horns without increasing the amount of material used.

   dans laquelle ε₂ est la déformation en largeur et ε₃ la déformation en épaisseur.The subject of the invention is a process for stamping blanks of flat metal products having undergone a drawing or rolling operation, with a view to carrying out subsequent operations of deep drawing or ironing or with a view to manufacturing flanged containers in particular for cylindrical containers, characterized in that a punch is used whose nose has a variable connection radius which is determined according to the anisotropic characteristics of the blank material, the low value connection radii being located in the area where the LANDFORD coefficient is low and the connecting radii of high value being located in the zone where the LANDFORD coefficient is high, the LANDFORD coefficient being defined by the following formula:

in which ε₂ is the deformation in width and ε₃ the deformation in thickness.

The punch therefore has a variable or evolving connection radius which is determined so as to compensate for the anisotropic nature of the material used. The connection radius is determined as a function of the resistance to thinning of the material considered or LANDFORD coefficient. It is thus possible to determine for each base material and each container to be produced the ideal profile of the punch nose which makes it possible to obtain a practically regular flange.

Advantageously, it is then possible to carry out an additional operation of rectifying the bottom of the container obtained by using a punch with a constant radius of connection.

This rectification operation makes the shape of the bottom of the container obtained more regular.

According to another characteristic of the invention, this rectification operation is only carried out in certain areas of the bottom of the container. This is done in particular in the case where the difference between the minimum and maximum radii of connection of the stamping punch is significant.

This rectification operation can be used so as to create bosses in the bottom of the container; advantageously these bosses are four in number. They serve as a support zone for the container obtained, the bottom of which is not in contact with its support. This avoids damaging, for example by scratching, an illustration carried by the outer wall of the bottom of the container.

The subject of the invention is also a stamping machine punch for implementing the aforementioned method, characterized in that its nose comprises zones having a maximum connection radius and separated by zones with minimum connection radius.

Advantageously, the nose of the punch comprises four zones distributed at right angles, having a maximum connection radius and separated by zones with minimum connection radius.

According to an embodiment of the invention, the maximum radius of connection of the nose of the punch is equal to five times its minimum radius.

• les figures 1 à 3 représentent respectivement les récipients obtenus dans un procédé d'emboutissage de type connu, dans un procédé d'emboutissage selon l'invention et dans un procédé d'emboutissage selon l'invention dans lequel on a effectué ensuite une opération de rectification ;
• les figures 4 à 6 sont des courbes correspondant respectivement aux figures 1 à 3 et représentant l'épaisseur du matériau en différents points A,B,C,D et E de la paroi latérale du récipient obtenu ;
• les figures 7 à 9 sont des courbes représentant l'épaisseur de la paroi latérale du récipient obtenu dans un procédé d'emboutissage de type connu et dans un procédé d'emboutissage selon la présente invention, respectivement pour une direction transversale, longitudinale et oblique par rapport à la direction d'étirage ou de laminage ; et
• la figure 10 est une vue partielle en perspective d'un poinçon d'emboutisseuse conforme à une forme de l'invention.

Other advantages of the invention will emerge from the description which follows of an exemplary embodiment of the invention, made with reference to the appended drawings in which:

• Figures 1 to 3 respectively represent the containers obtained in a drawing process of known type, in a drawing process according to the invention and in a drawing process according to the invention in which a rectification operation was then carried out;
• Figures 4 to 6 are curves respectively corresponding to Figures 1 to 3 and showing the thickness of the material at different points A, B, C, D and E of the side wall of the container obtained;
• FIGS. 7 to 9 are curves representing the thickness of the side wall of the container obtained in a drawing process of known type and in a drawing process according to the present invention, respectively for a transverse, longitudinal and oblique to the direction of stretching or rolling; and
• Figure 10 is a partial perspective view of a stamping punch according to one form of the invention.

Figure 1 shows an exploded perspective view of the container obtained by a stamping process of known type using a punch whose nose has a constant radius of connection; in the example shown which relates to the manufacture of metal cups from thin iron blanks of 0.18 mm thick which has undergone a significant skin-pass operation, the connection radius of the nose of the punch is 2 mm for a cup with a diameter of 65 mm and a height of 45 mm.

In this case, it can be seen that the collar 1 has an irregular shape and has horns 2 separated by horn recesses 3. The radius of connection of the punch nose is found at the bottom of the container and the radius of connection of this bottom 4 with wall 5, R1 or R2, is constant and equal to 2 mm.

The associated curve 4 represents the thickness of the wall of the container at different points designated A, B, C, D and E; the curve in solid line corresponds to a direction of formation of hollow of horn and the curve in broken line to a direction corresponding to the formation of horns.

   dans laquelle ε₂ est la déformation en largeur et ε₃ la déformation en épaisseur. Les directions de formation de cornes correspondent à un coefficient de LANDFORD élevé et les directions de formation de creux de corne à un coefficient de LANDFORD faible.These horns and hollow corns correspond to different values of the coefficient of resistance to thinning of the material used or LANDFORD coefficient which is defined by the following formula:

in which ε₂ is the deformation in width and ε₃ the deformation in thickness. The horn formation directions correspond to a LANDFORD coefficient high and the troughs of horn formation at a low LANDFORD coefficient.

Figures 2 and 5 correspond to Figures 1 and 4 and show the product obtained in a rolling radius drawing process according to the invention. It can be seen that the collar 11 is very regular and that there is no longer any horn or hollow of the horn. Furthermore, it appears from FIG. 5 that the distribution of the thickness of the wall is much more regular than in the stamping method of known type, the thickness differences between the directions with low LANDFORD coefficient and the directions with a high LANDFORD coefficient are more reduced.

The profile of the cup obtained corresponds to the profile of the punch used. The radius R11 of connection in a zone normally corresponding to a formation of recess, that is to say to a coefficient of low LANDFORD, is of small value for example 1 mm while the radius of connection R12 corresponding to a direction of horn formation, i.e. at a high LANDFORD coefficient, is higher, for example 5 mm. It can be seen that the modulation of the radius of connection of the nose of the punch as a function of the LANDFORD coefficient makes it possible to eliminate the formation of horns and hollows while using the same starting blank, that is to say the same amount of material. In addition, a normal hold down pressure is used.

Figures 3 and 6 correspond to the case where the stamping method according to the invention was used by carrying out an additional operation of rectification of the bottom of the container using a punch with a regular profile. This treatment practically only concerns the bottom of the container, without stretching the wall. During this treatment, the shape of the collar 21 remains unchanged, but the large connecting radii are "caught up" corresponding to a high LANDFORD coefficient (formation of horns). For example, the radius R12 in FIG. 2 is reduced from 5 mm to a value R22 of 2 mm, the radius R21 corresponding to the low LANDFORD coefficient remaining unchanged.

In FIG. 6, it can be seen that the dashed line curve which corresponds to the directions with a high coefficient, that is to say for which the rectification operation is carried out, is slightly modified in particular in the connection zone A.

This rectification operation cannot generally be pushed until a regular profile is obtained for the bottom of the box when materials having a significant anisotropy are used such as steels having undergone a significant skin-pass operation. This rectification operation is carried out so as to create slight bosses 26 projecting from the bottom of the container in the rectified zones; these bosses, which are four in number, constitute bearing surfaces of the container on its support, which makes it possible to preserve the external face of the bottom from contact with its support. In this way, it is possible to avoid degradation, for example by scratching, of a decorative motif affixed or produced on the external face of the base 24.

Figures 7 to 9 are curves representative of the thickness of the wall of the container obtained according to a known type process (solid lines curves) and according to a process according to the present invention (dashed lines) in a perpendicular direction in the direction of rolling (Figure 7), parallel to the direction of rolling (Figure 8) and in a 45 ° direction relative to the first two (Figure 9).

In FIG. 7, the curve in solid lines corresponds to a connection radius equal to 2 mm and the curve in broken lines to a radius of 1 mm, that is to say according to a direction where the LANDFORD coefficient is high; FIG. 8 corresponds to the same conditions and in these two cases, the connection radius for the known type drawing process (curves in solid line) is 2 mm and the connection radius for the known type process (curves in broken line) is 1 mm.

FIG. 9 corresponds to the oblique directions which form an angle of 45 ° with respect to the rolling direction and which are not preferred orientations such as the regions perpendicular or parallel to the rolling direction (Figures 6 and 7). In the case of FIG. 6, the radius of connection of the curve in solid lines is 2 mm and the radius of connection of the curve in broken lines corresponds to radius R11 of FIG. 2 and is equal to 5 mm.

From the examination of these FIGS. 7 to 9, it will be seen that the method according to the invention makes it possible to obtain a more regular distribution of the thickness of the walls of the container in all directions.

   e0 étant l'épaisseur d'origine et e1 l'épaisseur moyenne après emboutissage. Les valeurs de ce coefficient α pour un procédé de type connu et le procédé selon l'invention respectivement sont de 1,035 et 0,997 selon la direction perpendiculaire au sens de laminage (figure 7), 1,006 et 0,971 pour la direction parallèle au sens de laminage (figure 8) et 0,969 et 0,972 pour la direction à 45° (figure 9).Indeed, the invention makes it possible to reduce the thinning coefficient α which is defined by:

$$\text{α =}\frac{\text{e1}}{\text{e0}}$$

e0 being the original thickness and e1 the average thickness after stamping. The values of this coefficient α for a known type process and the process according to the invention respectively are 1.035 and 0.997 in the direction perpendicular to the rolling direction (FIG. 7), 1.006 and 0.971 for the direction parallel to the rolling direction ( Figure 8) and 0.969 and 0.972 for 45 ° steering (Figure 9).

It can be deduced therefrom that the method according to the invention makes it possible to obtain a better circumferential distribution of the thickness, the coefficient Δα passing from the value 0.025 for the known method to the value 0.006 for the method according to the invention, and a greater stretch over the height of the box, the coefficient α passing from the value 0.995 to the value 0.978 for the method according to the invention.

$$\text{α =}\frac{\text{e1}}{\text{e0}}$$

   α(L), α(T) et α(45°) étant les valeurs des coefficients d'amincissement α dans les directions longitudinale, transversale et oblique à 45°.These two coefficients Δα and α , which are well known in the stamping technique, are defined as follows:

$$\text{α =}\frac{\text{e1}}{\text{e0}}$$

α (L), α (T) and α (45 °) being the values of the thinning coefficients α in the longitudinal, transverse and oblique directions at 45 °.

FIG. 10 partially shows in perspective a stamping machine punch intended for implementing the method which has just been described. This punch 41, the working face of which has essentially been represented, has a connection nose with an evolving connection radius. It has four zones 43 where the connection radius is high. These zones 43 correspond to directions making an angle of 45 ° with the rolling axis 44 and the transverse axis 45; the zones corresponding to the axial direction 44 and the transverse direction 45 are zones where the radius of connection is minimal. As indicated above, the minimum radius is for example 1 mm and the maximum radius 5 mm.

The Applicant has manufactured metal cups having the dimensions indicated above in thin iron blanks 0.18 mm thick having undergone a significant skin-pass operation. She found that you get a 20% gain on the surface additional residual of the collar, a gain of 5% on the hollow diameter of the horn which can result in a reduction of more than 3% of the surface of the initial blank. In addition, it was possible to reduce the holding forces under blank holder by 50%.

The amplitude of the horns was reduced by 42% on the collar. This is particularly important in the case where cups having patterns are produced from preprinted blanks. Indeed, in this case, the illustration of the cups is much more regular.

In the directions with low LANDFORD coefficient, the connection radius has been halved compared to the usual connection radius and multiplied by two in the directions with high coefficient. This comparison was made with respect to stamping methods considered to be the most efficient according to the prior art.

We see that the invention allows both to obtain a gain in material and better regularity of the thickness of the collar and the walls of the container obtained, which increases the mechanical strength of the latter.

The drawing area of a material in terms of holding force under blank holder is increased.

This invention also applies to cups which require, for their obtaining, several stamping and re-stamping sequences, in these cases where the horns and hollow of the horn are an obstacle during re-stamping operations, the intermediate cups do not have flange. The regularity of the thickness of the walls of the stampings is a success factor during subsequent operations.

Claims (8)

1. Method of deep-drawing blanks of flat metal products which have undergone a drawing or rolling operation, with the purpose of carrying out subsequent deep-drawing or flattening operations or for the purpose of manufacturing flanged containers, particularly cylindrical containers, characterised in that a punch (41) is used, the nose of which has a variable connecting radius which is determined as a function of the anisotropic characteristics of the material of the blank, the connecting radii of low value (R11) being situated in the zone where the Landford coefficient is low and the connecting radii of high value (R12) being situated in the zone where the Landford coefficient is high, The Landford coefficient being defined by the following formula:

   

   wherein ε₂ is the deformation in width and ε₃ is the deformation in thickness.
2. Method of deep-drawing according to claim 1, characterised in that a rectifying operation is then carried out on the bottom of the container using a punch having a constant connecting radius.
3. Method of deep-drawing according to claim 2, characterised in that the rectifying operation on the bottom of the container is carried out only in certain zones of the latter.
4. Method of deep-drawing according to claim 3, characterised in that the rectifying operation is such that it creates bosses in the bottom of the container.
5. Method of deep-drawing according to claim 4, characterised in that the rectifying operation creates four bosses.
6. Method of deep-drawing according to claim 1, characterised in that the maximum connecting radius of the nose of the punch is equal to about five times its minimum radius.
7. Deep-drawing punch for carrying out the process according to any one of claims 1 to 6, characterised in that its nose (41) has zones (43) having a maximum connecting radius (R12) which are separated by zones (44, 45) having a minimum connecting radius (R11).
8. Deep-drawing punch according to claim 7, characterised in that its nose (41) comprises four zones (43) arranged at right angles, having a maximum connecting radius (R12) and separated by zones (44, 45) having a minimum connecting radius (R11).

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