Method for making light alloy components

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

[0001] The invention relates to the technical sector of the production of light alloy components, particularly aluminium, obtained from casting, forging and similar methods.

[0002] A specific method called “COBAPRESS” is disclosed in European patent EP 119,365 that combines casting and forging techniques of aluminium or aluminium alloy components.

[0003] As a reminder, the method in question consists in casting aluminium or aluminium alloy in a mould and, after the casting operation, in stripping the component (called a preform) while still hot at between approximately 400° C. and 500° C., of positioning the component between two dies or sections of a die that define an impression the measurements of which are slightly smaller than those of the mould and are those of the end component, the two shells or die sections being then pressed tightly together to exert a combined effect of core pressing and superficial hammering on the cast preform positioned between the sections of the dies.

[0004] An improved method of the type mentioned above is disclosed in French patent FR 2,778,125 the purpose of which is to use the preheating operation in order to perform the thermal treatment operation simultaneously thereby saving on the standard thermal treatment operation which usually follows the heading operation. Between the casting of the preform and the forging operation said cast preform is transferred to a furnace where the solution heat treatment of said cast preform is carried out at the solution heat treatment temperature of the material in which the component is produced. The component is then positioned between the two sections of the heading die for the forging operation with ambient, accelerated or hardening cooling.

[0005] The improved method called COBAPRESS 2 therefore considerably reduces the production time and cost while achieving the same characteristics of the components as the COBAPRESS method disclosed in European patent EP 119,365.

[0006] As standard in the forging sector, implementation of the two versions of the method described above requires the forging die to be sprayed with a solution of water plus liquid graphite in order to facilitate the creeping of the forged metal and the stripping of the end component.

[0007] In practice, spraying the forging die with a graphite solution is an operation which, depending on the complexity, of the rough end component, is relatively long and expensive and does not always enable the less accessible sections of the component to be sprayed uniformly; finally, it dirties the work station considerably.

[0008] American U.S. Pat. No. 4,683,742 is also known and discloses preheating the billets before they are coated with a graphite or similar coating. The billets are then forged are being sent through a drying installation.

[0009] The purpose of the invention is therefore to optimise the initial COBAPRESS method for cast-forged light alloy.

[0010] Japanese patent JP 6,005,433 is also known which describes forging billets using a graphite coating.

[0011] Regarding all the above-mentioned prior art, the applicant has attempted to optimise the COBAPRESS method as defined in the previous patents referred to above.

[0012] The initial approach focused on improving the conditions under which the graphite is deposited in the forging die by spraying a graphite solution on the forging die using robots to achieve improved control of the distribution. In practical terms this solution is less than satisfactory as it nevertheless requires human participation and the same costs and environmental issues are still present.

[0013] The applicant therefore focused unexpectedly on another possibility available between the two main casting and forging phases. The approach in question ensures the graphite solution is distributed uniformly on the preform and, moreover, provides characteristics which are particularly advantageous by improving the productivity of the method.

[0014] According to a first aspect, the method for producing light alloy components is of the type which implements the following phases:

[0015] casting the preform at between approximately 250° C. and 500° C.,

[0016] transferring the heated preform to a die that defines an impression the measurements of which are slightly smaller than those of the mould, the two sections of the die being then pressed together to exert the forging and die-stamping effect on the rough end component,

[0017] cooling the rough component at ambient temperature, the method being characterised in that after casting the heated preform and before transferring it to a forging die said preform, which is at the end of casting temperature, is transferred and totally submerged in a graphite coating tank to enable the graphite solution to be deposited on the preform, then when the preform is removed from the tank the temperature of the preform enables the water to evaporate naturally such that the preform is coated uniformly with graphite.

[0018] There is therefore no further need to reheat the component for the resistance of the coating product or to provide a system to evaporate the water as this occurs naturally.

[0019] According to another aspect, the improved method for making light alloy components is of the type which implements the following phases:

[0020] casting the preform at between approximately 250° C. and 500° C.;

[0021] transferring the cast preform obtained to a furnace where the solution heat treatment of said cast preform is carried out at the solution heat treatment temperature of the material in which the component is produced;

[0022] when the preform, which has been subjected to the solution heat treatment, is removed from the furnace, transferring it to a die that defines an impression the measurements of which are slightly smaller than those of the mould, the sections of the die being then pressed together to exert the forging and die-stamping effect on the rough end component;

[0023] ambient temperature, accelerated or hardening cooling of the component obtained, the method being characterised in that after casting the heated preform and before transferring it to the tunnel furnace said preform, which is at the end of casting temperature, is transferred and totally submerged in a graphite coating tank to enable the graphite solution to be deposited on the preform, then when the preform is removed from the tank at this stage the temperature of the preform and that of the previous phases enables the water to evaporate naturally such that the preform is coated uniformly with graphite, said preform being then returned to a temperature in the tunnel furnace that homogenises the temperature of the graphite-coated preform.

[0024] These and other aspects will become apparent from the following description.

[0025] The object of the present invention is described, merely by way of example, in the accompanying drawings in which FIG. 1 shows the implementation of the method of the invention.

[0026] The method for producing light alloy components of the invention requires an installation with five successive specific zones that cover the various stages of the method.

[0027] First zone (Z1) is where the light alloy is cast in a mould (1) enabling a preform (2) to be obtained under the temperature conditions described above.

[0028] Second zone (Z2) is where heated preform (2) is transferred into a tank (3) to be immersed and undergo graphite coating. The bath is a graphite and water solution.

[0029] Adjacent to the tank used for graphite coating or in the plane above the tank a drying phase (Z3) is provided for the preformed component outside the bath.

[0030] The following zone (Z4) is where the dried graphite-coated preform is transferred into tunnel furnace (4) to be subjected to temperature homogenisation. The following zone (Z5) is where the preform leaves the tunnel furnace to be forged in a die (5) which is rapidly lubricated using minimum lubrication limited to the land according to the conditions specified above before being subjected to ambient temperature, accelerated or hardening cooling.

[0031] The optimised method of the invention provides components thus treated with specific advantages.

[0032] There are many advantages to the optimised method of the invention.

[0033] Advantage is taken of the preform temperature to enable the graphite to adhere to the preform and then the water to evaporate before the subsequent operations.

[0034] a finer surface quality of the component due to the graphite solution which is deposited uniformly and which has an effect on the breakage test conditions;

[0035] improved resistance in fatigue tests;

[0036] increased service life of the heading tooling;

[0037] improved working environment;

[0038] increased productivity;

[0039] reduced and less complex human training, an important aspect in terms of skilled labour recruitment, which is always difficult, or simpler automation;

[0040] when the temperature of the component is homogenised in the tunnel furnace the black from the graphite bath improves calorie storage and therefore improves the structural and mechanical characteristics of the component;

[0041] furthermore, a shade of colour could meet appearance and colour requirements. A subtler shade could be used for safety and particularly suspension-chassis components to prevent them from shining under the bodywork and distracting the drivers near the vehicle in question.

[0042] There are therefore many advantages. The method is optimised according to the invention and provides unexpected and recent improvements that justify its development.

Claims

1. Method for producing light alloy components of the type which implements the following phases:

casting the preform at between approximately 250° C. and 500° C.,

transferring the preform to a die that defines an impression the measurements of which are slightly smaller than those of the mould, the two sections of the forging die being then pressed together to exert the forging and die-stamping effect on the rough end component;

cooling the rough component at ambient temperature, the method being characterised in that after casting the heated preform and before transferring it to a forging die said preform, which is at the end of casting temperature, is transferred and totally submerged in a graphite coating tank to enable the graphite solution to be deposited on the preform, then when the preform is removed from the tank the temperature of the preform enables the water to evaporate naturally such that the preform is coated uniformly with graphite.

2. Improved method for making light alloy components of the type which implements the following phases:

casting the preform at between approximately 250° C. and 500° C.;

transferring the cast preform obtained to a furnace where the solution heat treatment of said cast preform is carried out at the solution heat treatment temperature of the material in which the component is produced;

when the preform, which has been subjected to the solution heat treatment, is removed from the furnace, transferring it to a die that defines an impression the measurements of which are slightly smaller than those of the mould, the two sections of the die being then pressed together to exert the forging and die-stamping effect on the rough end component;

ambient temperature, accelerated or hardening cooling of the component obtained, the method being characterised in that after casting the heated preform and before transferring it to the furnace said preform, which is at the end of casting temperature, is transferred and totally submerged in a graphite coating tank to enable the graphite solution to be deposited on the preform, then when the preform is removed from the tank the temperature of the preform and that of the previous phase enables the water to evaporate naturally, it is dried such that the preform is coated uniformly with graphite, said preform being transferred to the furnace where the solution heat treatment is performed on the graphite-coated preform.

3. Method as claimed in either of claims 1 and 2, characterised in that a shade of colour is introduced into the graphite coating bath.

4. Installation to implement the method of any of claims 1 to 3, characterised in that it comprises the following 5 successive zones:

a first zone (Z1) where the light alloy is cast in a mould (1) enabling a preform (2) to be obtained;

a second zone (Z2) where preform (2) is transferred into a tank (3) to be immersed and undergo graphite coating;

a drying phase (Z3) of preformed component (2) outside the graphite bath in tank (3);

a fourth zone (Z4) where the dried preform is transferred into a tunnel furnace (4) to be subjected to temperature homogenisation;

a fifth zone (Z5) where the preform leaves tunnel furnace (4) to be forged in a die (5) before being subjected to ambient temperature, accelerated or hardening cooling.