FR2783184A1 - METHOD FOR MANUFACTURING A DRAWING TOOL IN HYDRAULIC CONCRETE COVERED AT LEAST PARTIALLY WITH A METAL HULL - Google Patents

Abstract

The tool is made from a metal outer shell (9) made to the required shape and acting as a mold for a fiber-reinforced concrete filling, poured in after applying an adhesive compound which has a liquid adhesive phase (13) and a solid phase (14) to anchor the concrete in place. The liquid and solid phases are applied in sequence, so that the solid phase projects partially from the liquid phase to provide an anchoring surface for the concrete. The metal shell is produced by electrodeposition in a polymer mold.

Description

Method for manufacturing a concrete stamping tool

  hydraulics at least partially covered with a metal shell.

  The invention relates to tools for stamping steel sheets made of hydraulic concrete and the methods of manufacturing these tools. Stamping consists in manufacturing, from a precut sheet of thin metal called "blank", a piece of complex shape not

  developable called <"stamped".

  A stamping installation includes several stamping tools: a "punch" with a "head", a "die" with a "bottom" and a "blank holder"; the punch head and the die bottom are shaped according to the complex shape of the stamp to be obtained, and according to a complementary shape adapted to be able to obtain a complete nesting of the punch head

in the bottom of the matrix.

  To obtain a stamped according to the imprint of the bottom of the die (or of the punch head) from a pre-cut blank, while maintaining the blank in the blank holder, using the punch, the blank is drawn towards the bottom of the die until engagement and complete fitting of the head into the bottom. For the production of stampings in large series, one generally uses

  stamping tools in cast iron or steel.

  For the production of stampings in small and medium series, less expensive stamping tools can be used, for example in resin directly molded to the shape of the tool or in machined resin, in hydraulic concrete or

  resin on a surface gel coat.

  However, given the poor mechanical characteristics of the materials of the "working surface" of these tools, these tools wear out quickly in contact with the sheet metal to be stamped, which leads to too many series.

short stamping.

  To improve the surface condition and the wear resistance of these tools, it is therefore necessary to keep a metallic material at the level of these working surfaces; these tools can then be provided with a metallic "skin" or "shell", as described for example in document FR 2 669 842 or in the article entitled "A functional approach to die and process development: the" composite "die and hydroforming "- Authors:

  G.GALLINARO - Review: ATA - Ingegneria Automotoristica, November-

  December 1997, vol.50, no 11/12, pp. 635-646; the metal "skin" or "shell" then serves as a support for hydraulic concrete or resin; it forms, at least partially, the "working surface" of the tool which comes into contact

  of sheet metal during stamping.

  The invention relates to a hydraulic concrete stamping tool with

of a metallic skin.

  To make a hydraulic concrete stamping tool whose surface intended to come into contact with the sheet metal blank to be stamped is covered at least partially with a metal shell, a process is known comprising the steps consisting in: - preparing a metal shell having a so-called "external" face corresponding to the predetermined shape of the stamping and an opposite so-called "internal" face, preparing a mold for the stamping tool using said shell as the bottom or element of the mold, internal side facing inside the mold, and using, if necessary, other molding elements, applying a bonding composition to said internal face, - pouring into said mold a composition for preparing said concrete, and solidifying said composition, - demolding said composition solidified by removing any other molding elements, while keeping the hull in place bonded to the

solidified concrete.

  The shell itself can be prepared by stamping; it can be prepared by different methods, such as by spraying metal particles as described in document FR 2 669 842, or by

  electrodeposition, or by vapor deposition.

  This metal shell generally has more than 1 mm thickness.

  This produces a hydraulic concrete stamping tool with a

  metal shell, the working surface of which is that of the metal shell.

  A drawback of such stamping tools lies in the weakness of the connection between the shell and the concrete, that is to say of the adhesive joint ensuring this connection. The metal shell and the concrete have very different mechanical characteristics; during a stamping cycle, in particular at the end of the cycle, the adhesive joint is stressed by very high shear stresses, in particular in areas having a small radius of curvature; these high loads can cause local breaks in the connection between the concrete and

  the shell, which limits the performance of the tool.

  Furthermore, it has been found that the bond between an applied adhesive and a "fresh" or "wet" concrete generally exhibits much poorer performance, in terms of shear strength, than the bond between the same

  adhesive and "old" concrete, ie "set" and dry concrete: example 1 above

  after illustrates this performance degradation.

  However, to make the stamping tool out of concrete, the hydraulic concrete composition is poured onto the metal shell coated with a film of glue; it is therefore a shell connection on "wet" concrete; this bond presenting

  degraded performance, the performance of the tool is then limited.

  The invention aims to improve the performance of a hydraulic concrete stamping tool with a metal shell forming the working surface of the tool, in cases where this tool is prepared by pouring

  hydraulic concrete on said hull.

  To this end, the invention relates to a method of manufacturing a stamping tool in hydraulic concrete, suitable for the preparation of stampings of predetermined shape from sheet metal blanks, tool whose surface intended to come to the contact of the sheet metal blank to be stamped is covered at least partially with a metal shell, comprising the steps consisting in: - preparing a metal shell having a so-called "external" face corresponding to the predetermined shape of the stamped and an opposite face called "internal", - prepare a mold for the stamping tool by taking said shell as the bottom or element of the mold, internal face facing the interior of the mold, - applying a bonding composition on said internal face, - pouring into said mold a composition for preparing said concrete comprising aggregates, - solidifying said composition, characterized in that said bonding composition contains means

concrete anchoring mechanisms.

  The invention may also have one or more of the following characteristics: - to apply said bonding composition, a layer of conventional glue is applied first in the fluid state, then said anchoring means are applied to said layer partially penetrating the layer

glue in the fluid state.

  - The anchoring means are applied so that part of said anchoring means emerges from the free surface of said layer of adhesive

applied.

  - Said adhesive is thermosetting under the solidification conditions of

said concrete composition.

  - The dimension of said anchoring means which extends perpendicular to the surface of the shell is greater than the thickness of the adhesive layer

applied.

  the mechanical anchoring means are aggregates, preferably of

same nature as those of concrete.

  - concrete contains reinforcing fibers.

  In the case where the shell is prepared by electrodeposition, the invention may also have one or more of the following characteristics: - said shell preparation comprises the steps consisting in: - making a replica having a surface corresponding to the predetermined shape of the stamped, - if necessary, make said replica surface conductive, - coat said replica surface or, where appropriate, said conductive surface, with a metal layer by electrodeposition until forming a metal shell, the internal face of the shell then corresponding to the metallic deposit of

end of plating.

  - said metal layer is based on nickel and the electroplating is

  performed in an electroplating bath based on nickel sulfamate.

  - said replica is made of polymer material and / or the conductive surface of

the replica includes graphite.

  The invention also relates to a hydraulic concrete stamping tool whose surface intended to come into contact with the sheet metal blank to be stamped is covered, at least partially, with a metal shell linked to the concrete by means bonding, capable of being obtained by the method according to the invention, characterized in that said bonding means comprise

  mechanical means for anchoring to concrete.

  The invention may also have one or more of the following characteristics: - said bonding means comprising a layer of adhesive applied to said metal shell, said mechanical anchoring means are embedded

  for one part in the adhesive layer and for the other part in the concrete.

  the mechanical anchoring means are aggregates, preferably of

same nature as those of concrete.

  - concrete contains reinforcing fibers.

  The invention will be better understood on reading the description which follows

  o the shell is prepared by electrodeposition, this description being given

by way of nonlimiting example.

  The examples which follow this description serve to illustrate it more

  precisely, always without limitation and with reference to: - in Figure 1 which is a block diagram of the shear tests of

Example 1.

  - Figures 2 to 4 which correspond to different stages of manufacturing a stamping tool by the method according to the invention as described in Example 2: Figure 2: making the replica - Figure 3: manufacturing the

  shell - Figure 4: stamping tool according to the invention.

  The method for manufacturing a stamping tool according to the invention therefore mainly comprises the following steps: preparation of the metal shell, preparation of a concrete pouring mold integrating this shell, preparation of a concrete composition, preparation and application of a bonding composition for the concrete-shell connection, concrete pouring,

  solidification of the concrete and crosslinking of the adhesive, demoulding of the concrete.

  To prepare a metal shell by electrodeposition or electroforming, document DE 40 21 384 describes a process comprising the steps consisting in: - making a replica having a surface corresponding to the predetermined shape of the stamping, - if necessary, making said conductive surface of the replica, - coating said conductive surface with a metallic layer by electrodeposition until forming a metallic shell, the internal face of the shell then corresponding to the layer thickness

  metal deposited at the end of electrodeposition.

  We can make a replica for example by pre-cutting a block of soft material and then machining it to bring it exactly and precisely to

desired dimensions.

  As soft material, it is possible to use a composite material with an organic matrix, prepared for example from a thermosetting resin added with fillers; if these charges are conductive, one can obtain a

  electrically conductive composite material.

  We can also make a replica by molding on a "master-

  model "of a resin, a resin concrete or a hydraulic concrete on a" gel-coat "(in English) or any other material compatible with the constraints of electroforming; these constraints relate in particular the temperature and the chemistry of the electroplating bath and the surface condition of the replica. One of the faces of the replica must therefore correspond to the predetermined shape of the stamping; the state of this surface will condition that of the

  surface of the stamping tool and also the ease of replica separation-

  shell, generally after concrete has been poured; it is therefore particularly important to control this surface condition, and surface treatments,

  such as polishing, can be useful for this purpose.

  In order to guarantee the geometry of the electroformed part, and in particular when the electroplating is carried out in a bath at a temperature different from ambient temperature, it is advisable to use, for the replica, a material whose coefficient of expansion is as close as possible as that of the metal of the electrodeposited metal shell. Thus, it is common to make copper shells in electroplating baths at room temperature, while nickel shells are prepared by electrodeposition at temperatures generally more

high of around 55 C.

  If the material used to make the replica is not conductive, it is then advisable to make conductive the face of the replica which corresponds to the shape of the stamping, so that, by immersing this surface in a bath of electroplating, you can pass an electroplating current

  between this surface and a counter-electrode immersed in the bath.

  The surface can be made conductive, for example by applying a layer of conductive paint or by chemical or physical deposition of a conductive material (silver or palladium, for example); preferably, the

  conductive material includes graphite.

  If the thickness of the deposited layer is too great with regard to the dimensional tolerances of the tool, it will be advisable to carry out beforehand a draft of the surface of the replica to a depth corresponding to that of the layer of paint; the surface quality of the deposited layer is also

  important than that of the replica as previously described.

  In order to limit the thickness of this layer and obtain a conductive surface more faithfully reproducing that of the replica, it is preferred

  proceed by chemical or physical deposition, rather than by painting.

  The next step includes an electroplating operation suitable for coating the conductive surface with a metallic layer of a thickness

  suitable for forming the metal shell of the stamping tool.

  As a plating material capable of forming a stamping tool shell, nickel, or copper, or alloys of these, can be used.

  metals such as nickel-cobalt alloys.

  The thickness of the metal shell is a function of the shape of the stamping, the mechanical characteristics of the concrete of the tool and the metal of its shell, and the expected conditions of use of the tool; thus for example, complex stamped shapes, having small radii of curvature, will cause significant stresses on the shell and require a greater thickness; The thickness which should be given to the shell can be evaluated by methods known in themselves which will not be described

  here in detail; this thickness is generally greater than 1 mm.

  For electrodeposition, the conductive surface is therefore immersed in an electrodeposition bath and a current of electrodeposition is passed between

  this surface and a counter-electrode immersed in the bath.

  The electrodeposition conditions, such as the composition and the temperature of the bath, such as the current density and the electrodeposition charge are adapted in a manner known per se depending on the composition and the thickness of the layer. metallic to deposit;

  this deposited layer forms the metal shell of the stamping tool.

  Thus, in the case of nickel shells, it is preferable to use baths containing mainly sulfamate and nickel chloride, and boric acid; can be added to these baths organic additives suitable for

  improve the mechanical properties of the metal shell.

  Since the deposition at the start of electrodeposition is intended to constitute the working surface of the stamping tool, the deposition conditions are particularly important during this phase; in particular, in the event of low conductivity of the conductive layer of the replica and / or so as to obtain a homogeneous electrodeposition of good quality and low roughness, it is advisable to apply during this phase a very low, very lower current density at 1 A / dm2; the current density is then increased according to the performances authorized by the bath and according to the internal stress limits

  permitted in the thickness deposited.

  Baths containing nickel sulfamate allow to reach

  high deposition rates, which reduces manufacturing costs.

  For average current densities generally less than 10 A / dm2, it is thus possible to obtain thick metallic layers of nickel having a Vickers hardness of between 150 and 250 HV, an elastic limit stress of between 250 and 660 MPa, a stress limit of

  rupture between 370 and 1050 MPa.

  The addition of cobalt in the bath makes it possible to increase the hardness of the metal obtained; the increase in current density generally causes a

decrease in hardness.

  After electrodeposition, a metallic shell is obtained applied against the replica by its so-called "external" face, the free surface of the shell constituting the so-called "internal" face of the shell which corresponds to the layer thickness

  metal deposited at the end of electrodeposition.

  At this point, you can separate the shell from the replica; we prefer

  however, perform this separation later.

  From molding elements, a mold is then prepared for the stamping tool, the metal shell being used as the bottom or mold element, "internal" side facing the interior of the mold; other molding elements are arranged on the periphery of the shell so as to form a mold adapted to the dimensions of the stamping tool to be manufactured; these others

  elements can be fixed on the replica of the hull.

  One then prepares in a manner known per se a hydraulic concrete composition suitable for the manufacture of a stamping tool; it is generally a so-called "BHP" or High Performance Concrete composition which contains, in addition to the conventional components of concrete, namely a binder

  hydraulic and aggregates, fumed silica and a superplasticizer.

  The aggregates are for example made up of sand and / or gravel.

  For these "BHP" compositions, the proportion of mixing water and the

  shrinkage upon solidification are very small.

  The complete solidification of these concretes can be obtained by storage at room temperature for at least 28 days; she can also be

  obtained in an accelerated manner by heat treatment.

  For these compositions, after complete solidification, concretes are obtained whose ultimate tensile stress exceeds 50 MPa in compression and

7 MPa in traction.

  Preferably, the concrete preparation composition that is used contains reinforcing fibers; these metallic fibers make it possible to limit the propagation of cracks in the concrete, which makes it possible to increase its resistance to compression, especially to traction and to fatigue and to further improve the performance of the stamping tool. A bonding composition is then prepared and applied to the face

  internal metal shell, bottom or mold element.

  One proceeds for example as described in tests n 4 to 6, or n 13 to of example 1; according to these tests in accordance with the invention, to prepare the bonding composition, a conventional adhesive suitable for bonding on is used

  concrete and mechanical means for anchoring to concrete.

  Preferably, this adhesive is based on thermosetting polymers,

  for example of epoxy type; these types of glues are generally bi-

  components, the mixing of the organic components being carried out just before application; preferably, this adhesive is suitable for crosslinking

  completely under the conditions of concrete solidification.

  The use of adhesives based on thermoplastic polymers should be avoided, since the shell-concrete cohesion of the tool could be degraded by the heating of the stamping tool during use.

  high rate, which would seriously affect the performance of this tool.

  The mechanical anchoring means have at least one dimension which extends perpendicular to the surface of the metal shell so as to protrude from the surface of the layer of adhesive applied to this shell, so that, after pouring the concrete , these anchoring means are drowned

  for one part in the adhesive layer and for the other part in the concrete.

  These mechanical anchoring means can be isolated elements, such as the aggregates or the nails mentioned in example 1; they can be constituted by a "two-dimensional" wire of the "barbed wire" type or by a "three-dimensional" lattice having regularly distributed elements extending transversely to the general direction of the wire or lattice respectively, of which the ends are intended to be embedded in the concrete. To apply the bonding composition, one generally begins by coating the internal face of the metal shell with a uniform layer of conventional adhesive in the fluid state and then applying the means of anchoring by making them penetrate the layer of glue in the fluid state; it is very important that these anchoring means are partially embedded in the adhesive layer and that the other portion emerges from the free surface of the adhesive layer so that they can be embedded later in the concrete; after pouring the concrete, the anchoring means must be inserted both into the thickness of the

layer of glue and into concrete.

  Preferably, the dimension of the anchoring means which extends perpendicular to the surface of the shell or to the surface of the layer of

  glue is greater than the thickness of the layer of glue applied.

  When using isolated anchoring elements, these elements are preferably applied by distributing them uniformly over and

in the glue layer.

  The advantage of using a wire or a lattice as an anchoring means is that the anchoring elements carried by this wire or this lattice are regularly pre-distributed. We can then proceed to the casting operation of the composition of

concrete in the mold.

  Before casting: - depending on the nature of the conventional adhesive used, it is possible, in a manner known per se, to partially allow the adhesive to crosslink; - if necessary, concrete reinforcement can be provided and

  metal inserts which are then placed in the mold.

  The concrete composition is then poured into the mold, the concrete is vibrated in a fluid state so as to degas and densify it, then this concrete is allowed to solidify in a manner known in itself and suitable for concrete composition used; under solidification conditions, the glue

  the bonding composition is completely crosslinked.

  After solidification or at least after beginning of solidification, while the adhesive of the adhesive composition is completely crosslinked, it is removed from the mold by removing the other molding elements, except the metal shell which is

  secured to concrete by the bonding composition.

  When the adhesive is suitable for crosslinking completely under the conditions of solidification of the concrete, it is not necessary to provide a

  separate crosslinking step after pouring the concrete.

  The glue then provides a chemical bond between the shell and the concrete, while the mechanical anchoring means essentially provide a mechanical bond since they are embedded both in the layer of crosslinked glue and in the solidified concrete; preferably, when aggregates are used as mechanical anchoring means, aggregates of the same type are chosen as

those of concrete composition.

  It is also advisable, if this has not yet been done, to separate the replica from the metal shell, which uncovers the external surface of the shell.

  which corresponds to the working surface of the stamping tool.

  Advantageously, when the replica is made of polymer material and / or when the conductive layer applied to this replica is based on

  graphite, this separation is facilitated.

  A stamping tool in hydraulic concrete is thus obtained, suitable for the preparation of stampings of predetermined shape from sheet blanks, tool whose surface intended to come into contact with the sheet blank to be stamped is

  covered, at least partially, with a metal shell.

  The manufacturing of the tool can be completed by a light machining to correct if necessary the dimensions of the tool and / or by a treatment of the working surface to harden it and / or to adapt its roughness and / or to improve

  the effect of lubrication in stamping.

  We can practice on the metal shell of the tool the same surface treatments as those used on conventional stamping tools in cast iron; for heat treatments, care must be taken not to reach temperatures which could damage the crosslinked adhesive of the

  bonding composition which ensures the connection between the shell and the concrete.

  Thanks to the invention, the stamping tool that is obtained offers significantly improved performance compared to those of the same type of the prior art, because the connection between the shell and the concrete is very resistant, in particular to shear stresses; Improving the resistance of

  this connection with respect to the prior art is illustrated in Example 1 below.

  Thanks to the invention, it is possible to manufacture, at reduced cost, stamping tools which can be used for larger series of stamping production and / or for stamping of more complex shapes, ie

  shapes with small radii of curvature.

  The following examples complete the description.

Example 1:

  The purpose of this example is to illustrate the effect of the solid anchoring means added to the glue on the strength of the connection between the shell of a tool.

  stamping and the concrete that is poured into this shell.

  To assess this effect, we measure the shear strength of glue joints applied between a concrete block and a metal plate according to the protocol defined in 1 below, for several types of glued joints defined.

  in 2 below; the results are reported in 3.

  1 - Protocol for measuring the shear strength of glue joints applied between a concrete block and a metal plate:

  The principle of measurement is illustrated in Figure 1.

  1.1- Preparation of the assembly of a concrete block 1 and a plate

  metallic 2 secured with an adhesive joint 3, to be characterized.

  The metal plate 2 is made of a bare sheet steel of thickness 1.5

  mm; the plate is degreased using trichlorethylene.

  After having, if necessary, mixed the different components of the adhesive, one of the faces of the plate 2 is coated with adhesive, the method of coating

  being adapted to the type of glue used (see below).

  Then, if necessary, the mechanical anchoring means according to the invention are applied (see below); the collage composition then includes the

  glue itself and the mechanical anchoring means.

  The preparation of the assembly then differs depending on whether it is

  assembly on "old>" concrete or assembly on "wet" concrete.

  1.1.1 - Assembling on "old" concrete: From the concrete composition n 1 (without fibers) described in Example 2 (Table III), a concrete block I with parallel faces is prepared; after keeping at least 28 days in the conservation room, the block obtained has a

  compressive strength of the order of 55 MPa.

  To obtain the assembly, we then apply the plate 2 glued on one

of the faces of block 1.

  After drying under conditions suitable for the adhesive used, the bond

  3 between block 1 and plate 2 is then provided by the bonding composition.

  1.1.2 - Assembling on "wet" concrete: On the glued side of the plate 2, and after a start of polymerization of the adhesive (1 to 2 hours depending on the type of adhesive used), a block I of concrete is molded from a concrete composition identical to that described in

paragraph 1.1.1 above.

  After vibrating the composition in the fluid state, the concrete is allowed to set in bulk and dry under the same conditions as those described in paragraph 1.1.1 above, that is to say that the assembly is maintained at least

28 days in the conservation room.

  As in paragraph 1.1.1, connection 3 between block 1 and plate 2 is

  then provided by the bonding composition.

  1.2 - Measurement of shear resistance: The measurement of the shear resistance of the connecting joint 3 is then carried out as follows: by maintaining the block 1 between a support 4 on its lower face and another support 5 on its upper face, apply a vertical force F to the plate 2 (see arrow in figure 1) and measure the force

  Fr of the joint connection 3.

  The stress on the joint 3 is then essentially in shear.

  To obtain a more precise evaluation of the shear resistance of a joint 3 of connection, one carries out at least three assemblies using the same joint of connection and one measures the resistance to rupture Frl, Fr2, Fr3 of each assembly ; the average of the three measurements obtained gives an evaluation

  more precise shear strength of the joint 3.

  The choice of a metal sheet of steel can be explained as follows: rupture tests were previously carried out using electroformed plates as the metal plate under the same conditions as those of the metal shell of the stamping tool according to the invention; it was then observed that the rupture of the bond of the adhesive joint always occurred at the concrete-adhesive interface; it has therefore been deduced that measurements carried out using metallic steel plates would give the same results as those carried out on electroformed plates; to simplify the tests, we have

  so then carried out most of the measurements on steel plates.

  2 - Type of concrete-metal connections tested: 2.1 - Nature of the adhesives used and suitable application method: Three adhesives were tested:

  - "Sikadur 31" (from the company SIKA: it is a bi-

  components, suitable for bonding metals and fresh concrete to old concrete; this glue can be considered as a resin mortar; this glue is applied using a tooth squeegee

triangular 2 mm high.

  - "Sikadur Impregnation" (from the SIKA Company: bi-

  components, fluid, suitable for bonding fresh concrete to old concrete and for resumption of concreting; it is a pure resin which impregnates well in concrete; this glue is applied to

brush.

  - "Mybond Epiphen" (1800 "from LAMBIOTTE: two-component, fluid epoxy resin; it is a pure resin generally used for the manufacture of laminated composites and resin concretes; this adhesive is applied to 1 to 2 mm thick by pouring into a mold, the bottom of which is the metal plate; before application to the plate, it is left to partially crosslink for approximately 2 hours, so as to obtain an adhesive of higher viscosity but still sufficiently fluid to be poured into 2. 2 -Preparation of "composite" bonding compounds on "wet" concrete: Three types of composite bonding have been tested on "wet" concrete, the last two corresponding to bonding compositions according to the invention: - Double layer of glue: "Sikadur 31" glue + "Sikadur Impregnation": first apply a layer of "Sikadur 31" on the metal plate, let this glue partially crosslink p lasts for approximately 2 hours, then a layer of "Sikadur Impregnation" is applied to this partially crosslinked layer,

bonding on porous materials.

  - "Sikadur 31" glue + "mineral" bond: the polymerization of the glue being more difficult in a humid environment, the objective is to complete the bond with mechanical bonds of the same kind as concrete; after application of the adhesive layer on the metal plate, aggregates are dispersed on this layer, before the start of polymerization; the average diameter of the aggregates is much greater than the thickness of the layer of adhesive applied; the coverage rate of the dispersed aggregates is adapted so that the average space between the aggregates is of the same order of magnitude as the average size of the aggregates; the granules are brought into the

layer of glue.

  - "Sikadur 31" glue + "metallic" bond: the polymerization of the glue being more difficult in a humid environment, the objective is to complete the bond with metallic bonds comparable to concrete reinforcements; after application of the layer of glue on the metal plate and before the start of polymerization, nails of about 40 mm long are dispersed on this layer, by embedding the head of these nails in the layer of glue, the general direction of the nails being transverse to the surface of the plate; the coverage rate of the dispersed nails is adapted so that the minimum spacing between each nail is greater than the minimum diameter of the

concrete gravel.

  3 - Results of the shear strength measurements of the various concrete-metal bonds: The results obtained as well as the type and location of the failure

  after test are reported in Table I below.

  Table I - Shear strength of different concrete-metal bonds.

  Type of test Effort at Type and location of failure LINK n failure (kN) Sikadur 31 25 11.5 at the adhesive / old concrete interface on concrete 26 14.4 same as "old" 27 17.2 same as Sikadur 31 1 7 , 9 progressive - at the adhesive / concrete interface on concrete 2 9.2 same as "wet" 3 6.5 same as Sikadur 22 8.6 at the adhesive / steel interface Impregnation on 23 6.3 same as "wet" concrete 24 10.1 same as Lambiotte Resin 16 9.4 at the adhesive / steel interface on concrete 17 13.5 same as "wet" 18 10.2 identical to Sikadur 31 + 19 10.6 progressive - at the adhesive / adhesive interface Impregnation. .. out of 20 15.5 as in "wet" concrete 21 14.3 as in Sikadur 31 + connection 4 19.2 at the adhesive / steel and adhesive / "mineral" concrete interface out of 5 18.2 at the adhesive / concrete "wet" concrete 6 19.4 at the glue / steel interface Sikadur 31 + connection 13 20.3 at the glue / steel interface at "metallic" on 14 22.6 ditto "wet" concrete 15 22.6 ditto La comparison of the results of tests 1, 2 and 3 with those of tests 25, 26 and 27 shows that an adhesive applied to "fresh" or "wet" concrete generally has much poorer performance, in terms of shear strength, than the same adhesive applied to concrete

  "old", ie concrete "set" and dry.

  It is precisely an essential aim of the invention to avoid or compensate for this deterioration in performance.

  The performance obtained with other adhesives on wet concrete (tests n 16 to 18 and n 22 to 24) may be slightly higher but still insufficient to withstand the high stresses between the concrete and the shell

  metal of a stamping tool.

  It is also an object of the invention to propose a concrete-

  metal much better resistant to shearing.

  Thus tests no 4 to 6 and no 13 to 15, in accordance with the invention, show that the composite connections according to the invention resist shear much better than the "adhesive" connections according to the prior art, on wet concrete (tests n 1 to 3 and n 16 to 24); The invention therefore relates to the use of a bonding composition comprising mechanical anchoring means such as

  aggregates (tests no 4 to 6) or metal nails (tests no 13 to 15).

  By using this type of composite connection for the manufacture of a concrete stamping tool provided with a metal shell, the cohesion between the shell and the concrete is substantially improved and, consequently, the

tool performance.

  An advantage of the composite bond according to the invention lies in the reliability of the resistance of this bond: the dispersion of the results of the tests carried out on composite bond is indeed much lower than that of the results of the tests carried out on conventional bonded bond (see Table 1); this advantage therefore improves the reliability of the stamping tools manufactured according to the invention.

Example 2:

  The purpose of this example is to illustrate the manufacture of a concrete mold

  hydraulics according to the invention, with reference to Figures 2 to 4.

  1.- Creation of replica 6 with reference to Figure 2.

  We pre-cut a block of soft material then we machine it to bring it exactly and precisely to the desired dimensions and so that

  that one of the faces 7 corresponds to the predetermined shape of the stamped.

* As soft material, one can take one of the polymeric materials

described in Table II below.

  Table II - Examples of polymeric materials for the replica.

  Base polymer: poly- -carbonate epoxy -urethane Commercial reference: Lexan LAB 900 Ren Shape Company characteristics: Axson CIBA Density (g / cm;) 1,2 1,62 1,65 Water absorption at 24 h: 0 , 3% 0.2% 0 Compressive strength (MPa) 77 120 73 Elongation at break (%) 60-100 50 90 Modulus of elasticity in bending (GPa) 2.24 4.5 5 Hardness M70-R118 88 ShoreD 90 ShoreD Resistance temperature to 120 123 (Tg) 110 (Tg) heat (C) (Tg: glass transition) Coefficient of thermal expansion (/ C) 70.10- 55. 10 '45.10-5 Action of weak acids null resistant Action strong acids slow attack The materials described in this table It have the following characteristics: coefficient of expansion greater but relatively close to that of nickel (17.10-6 approximately) in the temperature range 20 - 100 C, density greater than 1 kg / dm3 to facilitate immersion in the electroplating bath, glass transition temperature euse well above the temperature of use of the bath, good resistance to the acidic chemical action of the bath and to swelling with water, - good machinability due to the mechanical properties (resistance to

  compression, elongation at break, hardness).

  - excellent surface condition after machining, especially at the

  roughness and porosity, which facilitates the shell-replica separation.

  After degreasing, the face 7 is then made conductive by applying a very thin layer of a conductive paint containing silver particles: the replica 6 is then provided with a conductive film 8 on its surface 7

  the thickness of the conductive film 8 is of the order of a micrometer.

  It is also possible to use a paint containing particles of

  graphite, which facilitates the shell-replica separation.

  2. Manufacturing by electrodeposition of a 0.8 mm nickel shell 9

  approximately thick, with reference to Figure 3.

  By electrodeposition in a bath, the conductive film 8 is therefore coated with a layer of nickel, which will form the metal shell 9 of the tool.

stamping.

  Composition of the electroplating bath - boric acid H3BO3: 80 g / I nickel chloride, NiCI2, 6 H2O 5 to 10 g / I - nickel sulfamate Ni (NH2 SO3) 2,200 g / l 15 ... so that obtain INi2 + l = 40 g / I - wetting agent <1% by weight Electrodeposition conditions - Bath: 4.2 <pH <4.8 and temperature between 50 and 55 C, - current density: 0.1 A / dm2 at the start, gradually increased to 5

A / dm2.

  Mechanical characteristics of the nickel obtained - yield stress (at 0.2%): 485 MPa, - Modulus of elasticity: 182.5 GPa, stress at break: 840 MPa, - Elongation at break: 8, 3% - hardness on the external face (to film 8): 210 HV - hardness on the internal face (mold base) 238 HV We also evaluated the value of the residual stresses in the thickness of the nickel layer by carrying out measurements on layers

  deposited under the same conditions, but on a steel sheet.

  On this substrate and unlike the conductive film 8 or on the surface of the replica 7, nickel is deemed to be strongly adherent; after depositing nickel, a deformation gauge is bonded to the uncoated face of the sheet and the relaxation which appears when removed by

  electroerosion of the successive layers of the nickel deposit.

  These measurements made it possible to estimate that the residual stresses are between 90 and 150 MPa in tension. The low level of residual stresses makes it possible to limit the risks of "detachments" from certain areas of the shell relative to the replica during electrodeposition or before pouring of the concrete, which makes it possible to further guarantee compliance with the geometric tolerances of the surface

working the tool.

  After electrodeposition, there is therefore obtained on the replica 6, a metal shell 9 having a so-called "external" face in contact with the conductive film.

  8 and an opposite face called "internal".

  Given the shape of the shell 9 described in Figure 3, no molding element is here to add to form the concrete casting mold. 3 - Preparation of the concrete composition: Preparations are made with the following constituents - hydraulic binder of the cement and sand type: mortar called Clavex Lanko 701 from the company LAFARGE; this mortar is already formulated with

  additives limiting shrinkage such as fumed silica.

  - gravel with a particle size between 3 and 8 mm, - reinforcing fibers: amorphous cast iron fibers in the form of very thin flexible ribbons of dimensions approximately 15 x 1 x 0.03 mm,

  called Fibralex from SEVA.

  - fluidifier or superplasticizer: called Sikament FF86 of the

SIKA company.

- mixing water.

  The aggregates are therefore here formed by the sand of the mortar and the gravel.

  Three types of composition are prepared differing in the proportions of these

  constituents, as indicated in Table III.

  Table III - Concrete compositions for stamping tool.

  Concrete Fibers Mortar Gravel Water W / C Fluidifier nl 0 1270 1250 200 0.41 1.35 (0.3%) n 2 36 (0.5%) 1250 1133 200 0.42 4.75 (1%) n 3 72 (1%) 1500 480 240 0.42 5.7 (1%) In this Table III, the proportions are indicated by density (kg / m3), the figures in parentheses indicate: - in the column "fibers", the volume of fibers in relation to the volume of concrete, - in the "fluidizer" column, the volume of fluidizer in relation to

volume of cement.

  The W / C ratio designates the weight of water divided by the weight of cement.

  4 - Preparation and application of the bonding composition on the face

internal of the metal shell 9.

  In Example 1, two types of bonding composition are used: the first corresponding to tests n 4 to 6, and the second corresponding to tests n 13 to 15; the bonding composition is prepared and applied to the

metal plate 2.

  In this case, either the first or the second bonding composition is used in the same way, on the metal shell 9 still supported by the

reply 6.

  - Pouring and solidification of the concrete with reference to Figure 4 in the case

  the use of the first bonding composition (mineral bonds).

  Before casting, metal inserts 10 and 11 are positioned.

  The concrete composition is then poured into the mold formed by the shell 9 supported by the replica 6, then the concrete is vibrated in the fluid state at

  using a vibrating needle suitable for this purpose.

  As the shell 9 forms the mold corresponding to the shape of the tool to be manufactured, there are no other molding elements here and there is therefore no

subsequent release step.

  The concrete is then left to set under the following conditions, conservation for 28 days in an atmosphere at constant temperature (21 ° C.) and constant humidity (approximately 95%), protecting from

  desiccation of fresh concrete surfaces exposed to the atmosphere.

  Test pieces of the same concrete are prepared under conditions

  identical, to assess the mechanical properties.

  It is noted that the withdrawal at 30 days is of the order of 0.05 mm / m for the

three concrete compositions.

  The mechanical properties are evaluated in the following manner: - compressive strength cr max.c: on test pieces with diameter mm and length 220 mm; - tensile strength C max.t1i: by bending tests (of the "three point" type) with imposed displacement on test pieces of dimensions: 70 x 70 x 280 mm; - tensile strength c max.t2: by bending tests (of the "three point" type) with force imposed on pre-notched test pieces of dimensions: 47

  x 70 x 280 mm; these tests are carried out at one year.

  - modulus of elasticity in compression Ec and in bending Ef.

  The results obtained are reported in Table IV for each concrete composition (see 3 above)

  Table IV - Mechanical properties of concretes from Tab.lll.

  Concrete Smaxc (MPa) Smaxtl (MPa) Smaxt2 (MPa) Ec (GPa) Et (GPa) n 1 55.5 8.5 9.4 33.6 43.4 n 2 67.5 10.6 11.1 34 , 5 46.7 n 3 62.7 17.1 16.4 37.3 45.6 This table illustrates the reinforcing effect of the fibers introduced into the

concrete composition.

  After casting and solidification, the replica 6 is separated from the metal shell 9 secured to the solidified concrete part 12, and the tool is obtained.

  stamping as shown in Figure 4.

  FIG. 4 illustrates the connection between the concrete part 12 and the shell 9 provided by the bonding composition comprising crosslinked glue 13 and

aggregates 14.

  The combination of the chemical bonding effect provided by the adhesive 13 and the mechanical bonding effect provided by the aggregates 14 makes it possible to achieve a

  very strong cohesion of the shell 9 and the concrete part.

  The inserts and the part of the surface of the tool which is made of concrete are machined in order to obtain the desired dimensions and centering; the electroformed shell 9 does not require any special treatment before using the tool in a stamping press. A particularly efficient stamping tool is thus obtained, very resistant to wear and allowing high-speed production of

stamped quality.

  A comprehensive study on stamping friction and in particular on the effect of nickel as a tool surface material has shown that practically equivalent friction conditions are obtained with a steel tool surface material and with a material tool surface in electroformed nickel; on a steel sheet simply coated with a lubricating film for temporary corrosion protection, the coefficient of friction has been

estimated at around 0.22.

  The stamping tools obtained have been tested on an industrial press and have given satisfaction under conventional stamping conditions; tests have shown that a single tool can perform several hundred

thousands of stamps.

Claims (17)

  1.- Method of manufacturing a hydraulic concrete stamping tool (12), suitable for the preparation of stampings of predetermined shape from sheet blanks, tool whose surface intended to come into contact with the sheet blank to be stamped is covered at least partially with a metal shell, (9) comprising the steps consisting in: - preparing a metal shell (9) having a so-called "external" face corresponding to the predetermined shape of the stamped and an opposite face said "internal", prepare a mold for the stamping tool by taking said shell (9) as the bottom or element of the mold, internal face facing the inside of the mold, - applying a bonding composition to said internal face, pouring into said mold a composition for preparing said concrete comprising aggregates, - solidifying said composition, characterized in that said bonding composition contains means   (14) mechanical anchoring of concrete.   2.- Method according to claim 1 characterized in that, to apply said bonding composition, first applying a layer of conventional glue (13) in the fluid state, then applying said means (13) anchor (14) by making them partially penetrate the layer of glue (13) in the fluid state.   3.- Method according to claim 2 characterized in that one applies the anchoring means (14) so that part of said means   anchor emerges from the free surface of said layer of applied glue (13).   4.- Method according to any one of claims 2 to 3 characterized   in that said adhesive is thermosetting under the conditions of   solidification of said concrete composition.   5.- Method according to any one of claims 2 to 4 characterized   in that the dimension of said anchoring means (14) which extends perpendicular to the surface of the shell is greater than the thickness of the layer of adhesive (13) applied.   6.- Method according to any one of the preceding claims,   characterized in that the mechanical anchoring means are aggregates (14). 7.- Method according to claim 6 characterized in that said   aggregates are of the same nature as those of said composition of concrete.   8.- Method according to any one of the preceding claims   characterized in that said concrete preparation composition contains reinforcing fibers.   9.- Manufacturing method according to any one of claims   previous characterized in that said shell is prepared by plating.   10.- Method according to claim 9 characterized in that said shell preparation comprises the steps consisting in: - making a replica (6) having a surface (6) corresponding to the predetermined shape of the stamped, - if necessary, making said replica surface conductive, - coating said replica surface or, where appropriate, said conductive surface (8), with a metal layer by electrodeposition until forming a metal shell (9), the internal face of the shell corresponding then to the metal deposit at the end of electrodeposition.   11.- Method according to any one of claims 9 to 10,   characterized in that said metallic layer is based on nickel and in that said electrodeposition is carried out in an electrodeposition bath   essentially containing nickel sulfamate.   12.- Method according to any one of claims 9 to 1 1,   characterized in that said replica (6) is made of polymeric material.   13.- Method according to any one of claims 9 to 12,   characterized in that, before electrodeposition, the conductive surface of said replica includes graphite.   14.- Hydraulic concrete stamping tool whose surface intended to come into contact with the sheet metal blank to be stamped is covered, at least partially, with a metal shell (9) linked to the concrete (12) using bonding means, capable of being obtained by the method according to any one of   previous claims, characterized in that said bonding means   comprise mechanical means (14) for anchoring to the concrete.   15.- Tool according to claim 14 characterized in that, said bonding means comprising a layer of adhesive (13) applied to said metal shell, said mechanical means (14) for anchoring are embedded for a   part in the adhesive layer (13) and for the other part in the concrete (12).   16.- Tool according to any one of claims 14 to 15, characterized   in that the mechanical anchoring means are aggregates.   17.- Tool according to claim 16 characterized in that said aggregates   are of the same nature as those of concrete.