_PRO C _{ESS AND PL} A _{NT FOR PR} ODUCING COMPONENTS MADE OF THIXOTROPIC BILLETS OF ^A N _AL UM _{INIUM ALLO} Y _FOR VEHICULES, AND COMPONENTS OBTAINED THEREBY

The present invention refers to a process and a plant for producing components made of an aluminium alloy for vehicles and white goods, to the material to be used for producing such components, and to the components obtained through the above-stated process, plant and material.

In the field of parts made of an aluminium alloy for vehicles, no process of this type has ever been put in practical use. In fact, as regards the xest of the components in the motor vehicles field, but also in the railway and aeronautical fields, and in the field of white goods, the aluminium alloy in a thixotropic version has not yet been used, for the difficulties linked to its industrial production. Obviously, such type of material would be ideal in these applications, given its light weight and the chance of withstanding all wording loads and operating stresses that such applications impl_y.

Object of the present invention is solving the above prior-art problems, by providing components made of an aluminium alloy for vehicles and white goods whose weight is very low and whose cost is much lower than the current one and that keep, and preferably highly improve, the quality characteristics of current products.

A further object of the present invention is providing a process and a plant that are adapted to realise components as mentioned above and that are such that the end product needs only reduced workings: this allows simplifying the production processes and highly reducing their costs, obviously at a benefit for the end product.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained by a process, a plant, a material and an end product as those claimed, respectively, in Claims 1, 9, 23 and from 24 to 32. Preferred embodiments and non-trivial variations of the present invention are claimed in the dependent Claims .

The present invention will be better described by some preferred embodiments thereof, given as a non-limiting example, with reference to the enclosed drawings, in which the only Figure 1 is a schematic diagram of the plant adapted to realise the process of the present invention to produce the inventive components.

The process and the plant of the invention will be disclosed hereinbelow in their embodiment that is adapted to produce components for motor vehicles as listed below. It is obvious that the process and the plant could be used, practically without modifications apart from the dimensional ones, for producing components similar to those listed below.

The components that have been discovered as able to be produced through the plant, the process and the material of the present invention are as follows:

vehicle body elements, such as internal bodywork, door panels, instrument-holding dashboard, framework for seats, framework for steering wheels and other

internal vehicle parts ; internal door panels integrated with door drive moving functions ; structural and aesthetic elements of car body and/or motorbyke chassis , engine blocks and motorbyke components ; components for cars and motorbykes such as front and r ear car suspensions , engine supporting frame and o ther component parts ; vehicle engines ; a eronautical elements , such as wheels , seats and panels for aeroplanes ;

.railway elements , such as seats and panels for trains ; components of machines in the white goods sector, such as washing machines, dish washing machines, small white goods and the like.

F±g. 1 is a schematic view of the plant for producing components for vehicles of the invention; first of all, such plant comprises means 5 for heating the crop ends formed of thixotropic billets made of an aluminium alloy (as can be better seen below) , in which such billets are sized depending on the ratio between weight and size of the component to be realised. The means 5 are fed by a loader 4 and heat the crop ends in a range of temperatures during which both solid phase and liquid phase coexist with a prevalence in the solid phase (more than 50%) , and in the preferrred embodiment of the invention are composed of heating furnaces 5, that in particular are electromagnetic induction furnaces 5 comprising modular stations that are able to be composed. The induction heating furnace

guarantees, in addition to keeping the temperature within very restricted tolerances, an energy induction into the billets, which guarantees that a perfect metallographic structure re-forms at an intermediate physical state between the solid state and the liquid state. Therefore, the temperature of the piece is detected by measuring the active power of tine induced energy in the material in a predetermined period of time. The inventive plant further comprises means 9 for loading the heated crop ends in a vessel for further workings, that must have specific characteristics for products of the "Semi Solid Material"

(S. S. M.) type; the loading means 9 are composed of a first handling robot, that is an anthropomorphic robot equipped with a mechanical gripping hand adapted to handle the vessel in which "the billets are placed in order to be heated and transported. The plant then comprises means 11 for forming a molding, which operate with injection steps that are specific of the S. S.M. process; in particular, such means 11 for forming are composed of a die-casting machine, that is equipped with a die 8 adapted to produce components in S. S -M. The die 8 is lubricated by lubricating means 12 before every injection of metal through a detaching agent. Preferably, the die-casting machine 11 is equipped with an ±njection unit controlled by a closed-loop system, that allows a real-time control of a first and a second injection steps and of a third gearing step. With the above-mentioned arrangements, the press with which the die-casting machine 11 is equipped has a very powerful injection system that is able to manage the injection step with a high dynarnicity, and a maximum increasing speed of the injection force according to the construction specifications. This is made possible by controlling the injection process through a closed-loop system that allows

a real-time control. A high dynamicity is then realised not only as regards the speed, but also for acceleration. , braking and repeatability and programmability of th_e process. The closed loop allows a programmability on at least ten injection variables with 0.1 m/s resolutions. Thie suitably- adjusted press injects the billet inside ttie recesses of the die 8.

Further preferably, the lubricating means 12 are composed of a lubricating robot equipped with a lubricating head adapted to spray water, air and a detaching agent onto the die 8; such operation can also be performed through a manual nozzle.

Retmrning to Fig. 1, t:he plant of the invention further comprises means 13 fox extracting the molding, and means foar depositing the molding from the extracting means 13 onto a. conveyor belt 15, that are preferably composed of a second handling robot or of extracting means 13 of a manual type.

In a variation of the inventive plant, the means ffor depositing the molding are replaced by means 16 ffor previous Iy cooling the molding, and means for depositing the cooled molding onto a shearing die installed on a shearing" press 17 for shearring feedheads and/or riserrs, that are unloaded through unloading means 20.

In particular, the means 16 for previously cooling can be composed of a tank 16 containing heated and heat- adjusted water. In Fig. 1 a station 26 is further provided for cleaning the vessel prepared when going out of "the furnace 5.

Finally, the inventive plant comprises means for controlling the quality of the obtained molding, before sending the molding to downstream mechanical worki ngs and/or an heat treatment. Such means for controlling the

quality of the obtained molding are composed of a device 27 for detecting the presence of the molding, a control pulpit 29, control panels 31 for the billet heater, process control panels 33, a control panel 35 of the extractor 13 and a control panel 37 of the conveyor 15 for the finished pieces .

In the above-described plant, the die 8 installed on the press for producing components can be equipped with one or more carriages fox defining possible channels of the components and is equipped with air vents. The die 8 can be further equipped with shearing or tearing plates in order to remove the feeheacL from the molding, and with internal heat-adjusting channels.

In order to use such a die 8, the plant can be further equipped with units 25 for heat-adjusting the die 8 itself, that are composed of a modular system equipped with resistances or gas boilers for heating water or diathermic oil, and with pipings for flowing such water or oil from a pump of the unit insi_de the heat-adjusting channels of the die 8.

The above-described plant is adapted to realise the process for producing components for vehicles and white goods of the invention, which process comprises the steps of: providing thixotropic billets made of an aluminium alloy; sizing said billets depending on the ratio between weight and size of the component to be produced, thereby obtaining crop ends of material; heating the errop ends in a range of temperatures during which both solid phase and liquid phase coexist with a prevalence in the solid phase (more than 50%) in heating means 5 (of the modular induction furnaces t;ype) ;

loading, through loading means 9, the heated crop ends in a vessel for further workings with machines with specific characteristics for products of the "Semi Soli_d Material" (S. S. M.) type; forming a molding with a die-casting machine 11 with injection steps that are specific of the S. S. M. process; extracting the molding through extracting means 13; depositing the molding from the extracting means ZL3 onto a conveyor belt 15; and controlling the quality of the obtained molding, and then sending the molding itself to downstream mechanical workings and/or an heat treatment _

Alternatively, the process of the invention can be realised so that the step of depositing the molding is replaced by the steps of: previously cooling the molding in a tank 16 containing heated and heat-adjusted water; and depositing the cooled molding onto a shearing die installed on a shearing press 17 for shearing feedheads and/or risers.

In order to allow an optimum use of the above-stated process and plant, it is also necessary to provide a suitable material, that has an innovative composition ≡ind concept when is applied to such process and plant. Thiis material allows producing components in an aluminium alILoy for vehicles and white goods of the invention and is composed of an aluminium alloy having the following characteristics : centesimal chemical composition; and finely-divided, metallographic structure of "the globular type, that is a thixotropic structure. The globular microstructure provides the billet with a h_igh

fluidodynamic property even with high fractions of matter at a solid state. This allows performing the die-casting process at temperatures that are near the solidification one .

The main characteristic of the aluminium alloys that are die-cast with the thixotropic system consists (when they are in a partial solidification phase) in the dreastic reduction of the so-called "casting errors", "that are the macro- and micro-cavities from shrinking or gas. The production cycle of a part produced with a thixotropic alloy can have different results according to the system being used for the mixing action and the degassing system used in the billet-production step.

With the above-described process and system, and using the above material, it is possible to realise components made of an aluminium alloy whose characteristics are equal to or better than those of similar currently-marketed components .

In particular, the advantages of the die -casting with the S. S. M. process when producing components for vehicles are as follows: product with high metallurgic and mechanical performance characteristics; innovative solutions that are able to improve the reliability under operating conditions; high health of the part; reduction of scraps; reduction of mechanical workings; exceptional mechanical characteristics with a possible heat treatment:

• minimum traction strength: 300 mpa

• minimum ultimate tensile strength: 225 mpa

• minimum elongation: 12%

(all the above results being obtained with reference to an A 356.0 alloy) .

It is further necessary to point out the positive results due to the S. S.M. process that cannot be directly- measured on the product, but are connected thereto, such as for example lower working temperatures that have as a direct consequence energy savings, lower emissions of smokes and powders and consequently better environmental conditions .