EP1250204B1 - Method for making light alloy components - Google Patents

Abstract

The invention concerns a method for making alloy components characterised in that after casting the preform (2) and before transferring it into a forging matrix (5), said preform, still hot at the end of casting, is transferred and completely immersed in a vessel (3) for graphitization coating, then, on coming out of the vessel, the preform temperature enabling the water to be evaporated so that the preform is homogeneously coated with graphite.

Description

The invention relates to the technical sector of the manufacture of light alloy parts, in particular aluminum, obtained in foundry, forging and similar processes.

EP 119.365 discloses a specific process called COBAPRESS which combines the techniques of foundry and forging of aluminum or aluminum alloy parts.

Remember that this process consists of casting aluminum or aluminum alloy in a mold and after casting, to release the part still hot called preform at a temperature of the order of 400 ° C at 500 ° C, we place it between two matrices or parts of a matrix defining a footprint of dimensions slightly smaller than those of the mold, which correspond to those of the final piece, the two shells or parts being strongly pressed against each other to exert on the casting preform put between the parts of the dies a combined effect of core pressing and surface dressing.

We also know, from patent FR 2,778,125, a method of aforementioned improved type which aims to take advantage of the preheating operation for simultaneously perform the heat treatment operation saving thus on the conventional heat treatment operation after the typing operation. Between the casting of the preform and the forging, we transfers said preform poured into an oven ensuring the dissolution of said preform poured at the dissolution temperature of the material component and then placed between the two parts of the striking matrix for the forging operation with ambient, accelerated or tempered.

This improved process called COBAPRESS 2 therefore makes it possible to reduce production time and manufacturing cost so significant parts, while obtaining the same characteristics of the parts compared to the teaching of the COBAPRESS process described in the EP patent 119,365.

The implementation of the above method in both versions requires commonly in forging activity to spray on the die forging a water solution plus graphite in the liquid state, which aims to facilitate the flow of the material thus forged and the release of the part final.

In practice, the spraying of the graphite solution on the forging die is an operation which, depending on the complexity of the shapes of the raw final part, is relatively long and costly, which does not systematically allow uniformity of spraying. in the parts of difficult access of the part, and finally which is very messy for the work station.
We also know US Patent 4683742 which provides preheating of the billets before applying a coating of graphite type and then the billets being forged after passing through a drying installation.

The aim sought after according to the invention was therefore to ensure optimization of the initial COBAPRESS process of cast-forged light alloy.
We also know from JP 6005433 the forging of billets with the use of a graphite coating.
Faced with all of the aforementioned prior art, the applicant has attempted to optimize the COBAPRESS process as defined by the aforementioned prior patents.
A first step was to focus on improving the conditions for depositing graphite in the forging matrix by spraying the graphite solution on the forging matrix, with better control of the distribution using robots. In practice, this solution is not very satisfactory, because it still requires human intervention, and the costs and environmental problems are still there.

The applicant's approach was therefore unexpectedly oriented on another possibility which is inserted between the two main phases of casting and forging, possibility which offers all the guarantees in a homogeneous distribution of the graphite solution on the preform, and which at surplus brings interesting particular characteristics, in improving the productivity of the process.

• coulage de la préforme à une température de l'ordre de 250° à 500°C,
• transfert de la préforme chauffée dans une matrice définissant une empreinte de dimensions légèrement inférieures à celle du moule, les deux parties de la matrice étant pressées l'une contre l'autre pour exercer l'effort de forgeage, de matriçage de la pièce brute finale,
• refroidissement de la pièce brute à la température ambiante, le procédé étant caractérisé en ce que après coulage de la préforme chauffée et avant le transfert de la préforme dans une matrice de forge, ladite préforme, à température de fin de coulée est transférée et immergée totalement dans un bac pour graphitage par enduction, pour autoriser le dépôt de la solution graphite sur la préforme, puis en sortie de bac, la température de la préforme permettant l'évaporation naturelle de l'eau de sorte que la préforme est recouverte d'une manière homogène de graphite.

According to a first characteristic, the process for manufacturing the light alloy parts is of the type implementing the following phases:

• pouring the preform at a temperature of the order of 250 ° to 500 ° C,
• transfer of the heated preform into a matrix defining an imprint of dimensions slightly smaller than that of the mold, the two parts of the matrix being pressed one against the other to exert the forging effort, forging the final blank ,
• cooling of the blank to ambient temperature, the process being characterized in that after casting the heated preform and before transferring the preform into a forging die, said preform, at end of casting temperature, is transferred and completely immersed in a graphitation tank by coating, to allow the graphite solution to be deposited on the preform, then at the tank outlet, the temperature of the preform allowing the natural evaporation of water so that the preform is covered with a homogeneous graphite.

• coulage de préforme à une température de l'ordre de 250° à 500°C ;
• transfert de la préforme coulée obtenue dans un four assurant la mise en solution de ladite préforme coulée à la température de mise en solution du matériau constitutif ;
• transfert de la préforme mise en solution en sortie du four dans une matrice définissant une empreinte de dimensions légèrement inférieures à celles du moule, les parties de la matrice étant pressées l'une contre l'autre pour exercer l'effort de forgeage, de matriçage de la pièce brute finale ;
• refroidissement de la pièce brute obtenue à la température ambiante, en accéléré ou trempé, le procédé étant caractérisé en ce que, après coulage de la préforme chauffée et avant le transfert dans le four tunnel, ladite préforme, à température de fin de coulée, est transférée et immergée totalement dans un bac pour graphitage par enduction, pour autoriser le dépôt de la solution graphite sur la préforme, puis en sortie de bac, à ce stade, la température de la préforme et celle du procédé en amont permettant l'évaporation naturelle de l'eau, de sorte que la préforme est recouverte d'une manière homogène de graphite, ladite préforme étant ensuite remise en température dans le four tunnel assurant l'homogénéisation en température de la préforme graphitée.

Thus, there is no longer any need to reheat the part to hold the coating product or to have a system for evaporating the water, the latter being natural.
According to another characteristic, the improved process for manufacturing light alloy parts is of the type implementing the following phases:

• casting of preform at a temperature of the order of 250 ° to 500 ° C;
• transfer of the casting preform obtained in an oven ensuring the dissolution of said casting preform at the dissolution temperature of the constituent material;
• transfer of the preform dissolved in the outlet of the furnace in a matrix defining an imprint of dimensions slightly smaller than those of the mold, the parts of the matrix being pressed one against the other to exert the effort of forging, forging of the final blank;
• cooling of the blank obtained at room temperature, accelerated or quenched, the process being characterized in that, after pouring the heated preform and before transferring it to the tunnel oven, said preform, at the end of casting temperature, is transferred and completely immersed in a tray for graphitation by coating, to authorize the deposition of the graphite solution on the preform, then at the exit of the tray, at this stage, the temperature of the preform and that of the upstream process allowing natural evaporation water, so that the preform is homogeneously covered with graphite, said preform then being brought back to temperature in the tunnel oven ensuring the temperature homogenization of the graphite preform.

These and other characteristics will become apparent from the following the description.

To fix the object of the invention illustrated in a nonlimiting manner to the drawing figures where Figure 1 shows the implementation diagram of the process according to the invention.

The process for manufacturing the light alloy parts according to the invention requires installation with five successive specific zones covering the different stages of the process.

The first zone (Z1) corresponds to the casting of the light alloy in a mold (1) enabling a preform (2) to be obtained under the conditions previously recalled.

The second zone (Z2) corresponds to the transfer of the preform (2) heated in a tank (3) for immersion and graphitation by coating the preform (2). The bath is a solution of graphite and water.

Adjacent to the tray for graphitation by coating, or in its upper plane, a phase (Z3) of drying the preformed part is provided out of the bath.

The following zone (Z4) corresponds to the transfer of the preform dried graphite in the tunnel oven (4) for homogenization in temperature. The following zone (Z5) corresponds to the exit of the tunnel oven from the preform to be then forged in a matrix (5) which is the object less and faster lubrication limited to the burr bead depending on the conditions mentioned above, then cooled to temperature ambient or accelerated or drenched.

The optimized process according to the invention appears to give the parts thus treated specific benefits.

• une qualité d'état de surface plus affiné de la pièce grâce à une homogénisation du dépôt de solution graphite qui a une influence sur les conditions d'essai de rupture ;
• une meilleure tenue en essai de fatigue ;
• une longévité accrue de l'outillage de frappe
• une amélioration de l'environnement ;
• un gain de productivité ;
• une formation humaine moindre et moins complexe, ce qui est important en regard du recrutement de main d'oeuvre qualifié, ce qui est toujours difficile ou une automatisation plus simple ;
• au moment de l'homogénisation en température dans le four tunnel pour homogénéisation en température, la couleur noire issue du bain graphité permet de mieux emmagasiner les calories et donc d'améliorer les caractéristiques de structure et mécaniques de la pièce ;
• De plus, une nuance de couleur pourrait répondre à un besoin d'esthétique et de coloris. Une plus grande discrétion pour des éléments de sécurité et plus particulièrement de suspension - châssis pour éviter l'effet de brillance sous carrosserie visible par les conducteurs voisins au véhicule concerné.

The advantages of the optimized method of the invention are numerous.
We take advantage of the temperature of the preform to allow the graphite to hang on the preform and then the water to evaporate before the following operations

• a more refined surface finish quality of the part thanks to a homogenization of the graphite solution deposit which has an influence on the failure test conditions;
• better resistance in fatigue test;
• increased longevity of impact tools
• improvement of the environment;
• increased productivity;
• less and less complex human training, which is important with regard to the recruitment of qualified labor, which is always difficult or simpler automation;
• at the time of temperature homogenization in the tunnel oven for temperature homogenization, the black color resulting from the graphite bath makes it possible to better store calories and therefore to improve the structural and mechanical characteristics of the part;
• In addition, a shade of color could meet a need for aesthetics and colors. Greater discretion for safety elements and more particularly suspension - chassis to avoid the shine effect under the body visible by drivers next to the vehicle concerned.

The advantages are therefore numerous. The process is optimized according to the invention and makes unexpected and recent improvements that justify His development.

Claims (4)

1. Process for manufacturing light alloys parts involves the following operations :

   Having a casting preform at about 250°C to 500°C

   transferring the cast preform in a furnace to solution heat treat the preform material.

   transferring the cast preform thus obtained from the preheat furnace directly to the forging press between two halves of a die that defines a cavity having dimensions that are slightly less than those of the mould, the two halves being forced together in order to exert an impact forging force

   cooling the rough forging thus obtained at room temperature or accelerated cooling or cooling by quench

   What makes the invention specific is that after the casting of the as said preform and before the forging operation, the as said hot preform is transferred and dipped in a graphite solution container for lubrication.. Outside of the container, the preform temperature allows the water to evaporate and the graphite to stick to the preform creating an homogeneous graphite skin all around it.
2. Process for manufacturing light alloys parts involves the following operations :

   Having a casting preform at about 250°C to 500°C

   transferring the cast preform in a furnace to solution heat treat the preform material.

   transferring the cast preform thus obtained from the preheat furnace directly to the forging press between two halves of a die that defines a cavity having dimensions that are slightly less than those of the mould, the two halves being forced together in order to exert an impact forging force

   cooling the rough forging thus obtained at room temperature or accelerated cooling or cooling by quench
   What makes the invention specific is that after the casting of the as said preform and before the forging operation, the as said hot preform is transferred and dipped in a graphite solution container for lubrication.. Outside of the container, the preform temperature allows the water to evaporate and the graphite to stick to the preform creating an homogeneous graphite skin all around it.

   The as said preform is after transferred in a tunnel furnace for temperature homogenization.
3. Process as claimed in claim 1 and 2, characterized in that we can introduce color in the lubrication container.
4. The process of this invention needs an installation of five successive specific areas .

   The first zone (Z1) corresponds to the casting of the alloy in a mold in order to obtain a preform in hot temperature conditions.

   The second zone (Z2) corresponds to the transfer of the hot preform (2) in a container (3) for a graphite solution dipping for lubrication. The bath is a graphite and water solution.

   On the side of the lubrication container, or above it, is the drying sequence (Z3) of the preform out of the bath.lubrication,

   The next (Z4) area corresponds to the transfer of the graphite lubricated preform in the tunnel furnace (4) for temperature homogenization. The (Z5) area is the exit of the preform from the tunnel furnace then brought to the forging die which is only slightly and therefore quicker lubricated and this only inside the cavity limited to the rib around it according to the above conditions. The part is then cooled naturally, or in an accelerated process or quenched.

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