CN1355110A - Method for making metal element such as wheel unit and wheel made by said method - Google Patents

Abstract

The invention relates to a method for manufacturing a metal element such as a wheel component of a rolling system of a vehicle and to such a wheel. The method according to the invention for the manufacture of metal elements (7,8,9) comprises an initial step of forming said parts (7,8,9) from a semi-solid and thixotropic metallic material and includes a (2) A subsequent cold treatment step (30, 140) of spraying at least a portion of said part (7, 8, 9) to plastically deform it. The wheel (9) according to the invention comprises a rim (9) on which a metal disc (7) is welded, the disc (7) being obtained by said manufacturing method.

Description

Method for producing metal elements such as wheel parts and wheel produced by the method

The present invention relates to a method for the manufacture of metal elements such as wheel components for vehicle rolling systems, and to wheels produced by this method. The invention relates in particular to a metallic wheel component, such as a wheel disc, which consists of a light metal such as aluminum, magnesium or a metal which substantially allows a reduction in weight such as titanium, or which may consist of an alloy of one of these metals.

Discs constructed of metal alloys such as aluminum are typically manufactured by forging or casting methods.

The first method described above, although it produces discs with generally satisfactory mechanical and aesthetic properties, has the major disadvantage of higher costs.

In recent years, for the implementation of the second method described above, a material consisting of an alloy which can be transformed in advance into a thixotropic, semi-solid metallurgical state has been chosen. This thixotropic state is characteristic of an alloy structure comprising a non-dendritic primary phase consisting of substantially spherical globules or spherulites.

Reference can be made, for example, to European patent EP-A-710 515 for a description of this casting method utilizing thixotropic, semi-solid alloys and the molds for implementing the method.

A description of the method for achieving the above-mentioned thixotropic state can also be obtained with reference to European patent EP-A-439 981.

This forming method is generally expressed by the technical term "thixoforming", which includes the principle of die casting (ie, "thixocasting") and the principle of casting/forging on a vertical machine (ie, "thixoforging").

In particular, discs formed by this casting method have many advantages due to the formation of the exact metallurgical state of the above-mentioned alloys, which can be defined by small balls (typically smaller than 120 μm) in a substantially distributed in an even manner.

These discs can be thinner and thus lighter than discs cast from the alloy in other tempers.

In addition, they have less porosity, resulting in uniform, improved density and mechanical strength, and also improved heat treatability.

This forming method also has other advantages, in particular:

— wheels with aesthetic appearance are available in a wide range of options (e.g. thin walls or large cross-sectional variations can be achieved),

- the discs obtained have good dimensional accuracy, which reduces machining to a minimum,

- short cycle times and work automation leading to high productivity, and

- Increased tool life compared to traditional processes utilizing liquid metal such as aluminum injection molding.

The object of the present invention is to provide a method for the manufacture of metal elements, which method comprises, in an initial step, forming said elements from a semi-solid and thixotropic metal material, such that said elements are more durable than the aforementioned method The manufactured components have better mechanical properties and reduced weight.

To this end, the manufacturing method according to the invention includes a subsequent cold treatment step in which at least a part of said element is shot blasted in order to deform it plastically.

According to a variant of the invention, the method comprises a step of hardening said element tissue after said initial step and before said subsequent cold treatment step.

According to a particular embodiment of the invention, said method also comprises the step of subjecting said shaped element to an intermediate swaging, after said initial step and before said tissue hardening step.

Preferably said method comprises, for said initial forming step, the use of a metal alloy of the type comprising aluminum, magnesium, titanium, iron, chromium, cobalt, nickel, copper, zinc, silver, tin, lead and Antimony group.

Preferably an aluminum-based alloy is used which also contains between 6.5% and 7.5% by weight of silicon and between 0.5% and 0.6% by weight of magnesium.

This aluminum-based alloy has the advantage of reducing corrosion.

According to another characteristic of the invention, said initial shaping step comprises thixoforming, which may consist of thixocasting or rheocasting.

It should be noted that the thixotropic casting method comprises a first step of filling a mold with a semi-solid thixotropic metal material and a second step of compressing said material in the mold with high pressure, eg on the order of 100 MPa.

It should also be noted that, in a known manner, the generally described "rheological casting" method essentially consists of mechanically stirring a liquid alloy to obtain a semi-solid material, followed by direct casting of the semi-solid alloy, said casting being carried out at Carried out without any prior cooling step.

According to a still further feature of the present invention, the step of tissue hardening of the method includes quenching followed by annealing.

According to one embodiment of the method according to the invention, at least one operation of said cold treatment step comprises using corundum particles having a size between 75-150 μm as said shot peening.

According to another embodiment of the method according to the invention, at least one operation of said cold treatment step comprises using glass microspheres as said shot peening.

According to another embodiment of the invention, at least one operation of said cold treatment step comprises using steel or cast iron pellets with a size between 200-800 μm as said shot peening.

According to an advantageous characteristic of the invention, said initial forming step comprises forming a wheel of the rolling system of the vehicle, said wheel comprising a disc and a rim, in which case said wheel constitutes said manufactured metal element , and said cold treating step comprises blasting all or part of at least one surface of said wheel disc and/or said rim with said shot blasting.

According to an equally advantageous variant of the invention, said initial forming step comprises the formation of a wheel part for the rolling system of a vehicle, said wheel part comprising a wheel disc or a rim, in which case said wheel part constitutes the The metal element manufactured as described above, and the cold treatment step comprises blasting all or a part of at least one surface of the disc or the rim with the shot blasting.

A wheel according to the invention for a rolling system of a vehicle, said wheel comprising a rim on which is fastened, eg welded, a metal disc obtained by a manufacturing method according to one of the preceding claims of.

The above and other features of the present invention will be better understood after reading the description of the embodiments of the invention with reference to the accompanying drawings, which are given as non-limiting examples, wherein:

Figures 1a and 1b respectively represent a block diagram of a method of manufacturing a metal element according to two different embodiments of the present invention,

Figure 2 represents a schematic diagram of a shot blasting device for implementing the manufacturing method according to the invention, and

Figure 3 is a partial cross-sectional view of the disc and rim assembled into a wheel constituting the metal element according to the invention.

Referring to FIG. 1a, the method for manufacturing a metal element according to a first embodiment of the invention comprises, in a first step 10, forming said element by thixotropic casting from a semi-solid metal material having a thixotropic structure , then, in a second optional step 20, tissue hardening of said shaped element, and finally in a third step 30, at least part of said element is blasted.

Referring to FIG. 1 b, it can be seen that the method according to the second embodiment of the present invention includes first performing a first step 110 identical or similar to the aforementioned step 10, and then performing a second step 120 of swaging the formed metal element, An optional third step different from the step 20 is then carried out, that is, a tissue hardening step 130 , and finally a fourth step 140 of shot blasting cooling treatment which is the same as or similar to the step 30 is carried out.

To carry out the first step 10 or 110, a predetermined length of round rod or bar consisting of, for example, light metals such as aluminum and magnesium-based alloys is injected into a mold (not shown because of the same as described in European patent EP-A-710 515 Same).

Aluminum-based alloys are preferred. Preferably said alloy is an alloy belonging to the aluminum/silicon group.

Preferably said alloy is an alloy named A-S7G0.6 according to the NF A 02-004 standard, which alloy is such that, in addition to aluminum, it also specifically comprises the following components by weight percentage:

Silicon 6.5%-7.5%

Iron 0.15%

Copper 0.03%

Manganese 0.03%

Magnesium 0.06%

Nickel 0.03%

Zinc 0.05%

Lead and Tin 0.03%

Titanium 0.20%

Strontium 0.05%

In the remainder of this specification reference will be made to alloy A-S7G0.6, referring on the one hand to the description of the second example and on the other hand to the results of mechanical strength and weight reduction obtained by implementing said first and second examples .

Upstream of the mould, the alloy to be injected has previously been transformed in a first stage into a thixotropic metallographic structure and in a second stage into a semi-solid state.

More precisely, said first stage consists, for example, of agitating said alloy mass by means of electromagnetic induction according to the method described in European patent EP-A-439 981 and corresponding devices, in order to obtain a thixotropic material.

In order to ensure that the thixotropic material is also in a semi-solid state in the second stage, induction heating of the thixotropic material is then performed to heat the temperature of the thixotropic material to a temperature T (° C.), namely:

T _fe < T < T _fe +10, where T _fe is the eutectic melting temperature (577° C. for the preferentially used alloy A-S7G0.6).

It should be noted that the thixotropy of the alloy injected into the mold is such that the largest dimension of the pellets is less than 120 μm.

It should be noted that other methods can be used to obtain thixotropic structures and semi-solids. Particular mention can be obtained by the "rheological casting" process known to those skilled in the art, which essentially consists of agitating a semi-solid alloy, with or without chemically refining dendrites. Combination of granular methods.

When carrying out casting operations according to said European patent EP-A-710 515, it should be noted that the material injected into the mold is finally compressed at a pressure of, for example, 100MP (compression pressure values may vary with the alloy and method used).

The cast material is allowed to cool until it attains a solid state and then immediately demolded. This results in a metal element formed according to the mold cavity.

According to said second (optional) step (20) of the first embodiment of the method of the invention, the continuous tissue hardening comprises quenching and annealing said element, preferably immediately after said demolding. It should be noted that this tissue hardening can be omitted.

During said quenching, which is carried out for a few seconds with a suitable liquid such as water, said liquid is kept at a temperature between 30-60°C, preferably between 30-40°C.

The annealing is carried out at 170° C. for 6 hours.

It should be noted that the processing temperature and time parameters for tissue hardening of the elements are matched in such a way as to obtain a specific correlation between strength and toughness.

According to the third step 30 of said first embodiment of the invention, the metal element obtained in the second step 20 is subjected to cold plastic deformation, ie shot blasting treatment on the element at ambient temperature.

Shot peening is effected, for example, by means of a device 1 for injecting shot peening 2 , the structure of which is shown in simplified form in FIG. 2 .

The device 1 comprises at least one inlet 3 a connected upstream to a storage hopper 4 for shot blasting and at least one outlet 3 b for the jet stream J.

In the embodiment shown in Figure 2, the device 1 is of the type that sucks air contained in a hopper 4 to create a low pressure in the hopper, known to the public by the name "Giffard" injector Know.

More precisely, the device 1 shown in this embodiment comprises a first hose 5a whose ends respectively form an inlet 3a and an outlet 3b. The inlet 3a is connected to the bottom of the hopper 4, and it also includes an air inlet P with a control device R for controlling the flow of suction air.

A second hose 5b for conveying compressed air (arrow A) is connected upstream of said outlet 3b. The air delivered by this hose 5b creates a partial vacuum through said hopper 4 for the continuous extraction of shot from the bottom of the hopper 4 through said outlet 3b (arrow A). A regulator 5c for adjusting the flow rate of compressed air to adjust the blasting speed is installed on the hose 5b.

The outlet 3b of the hose 5a and the downstream end of said hose 5b open in a sealed manner on the spray gun 6 and end at a nozzle 6a designed to spray said stream J.

It should be noted that it is also possible to use a device 1 which utilizes a liquid such as water as the propelling fluid instead of air.

It should also be noted that it is possible to use devices 1 other than those shown in Figure 2, for example of the type generating gravity, overpressure or directional pressure in the hopper 4, or a turbine type for mechanical injection of shot peening 2, etc. type of device. It is also possible to use devices 1 of the ultrasonic or electromagnetic type to accelerate the particles or to vibrate them violently relative to the pretreatment element, or even devices 1 of the explosive type or of the generation of laser pulses.

In conclusion, it will be understood that any device can be used to inject shot peening on the surface to be treated as long as it guarantees that the mechanical, thermodynamic and ballistic parameters correspond to the desired properties and intensity of the treatment.

Example of implementing steps 30, 140

One surface 7 a (see FIG. 3 ) of the disc 7 is subjected to said cold treatment step 30 , 140 with said device 1 described with reference to FIG. 2 . Said disc 7 consists of said alloy A-S7G0.6 and constitutes said metal element already formed according to steps 10 , 110 .

In this example, the shot 2 used consists of brown corundum (aluminum oxide, especially containing titanium). More precisely, the composition of brown corundum is as follows, expressed in weight percent:

Al ₂ O ₃ 89%-94%

TiO ₂ 2%-4%

SiO ₂ 0.4%-1.5%

_{Fe2O3 1.5} %-3.5%

CaO+MgO 0.3%-0.5%

_Na2O + _K2O 0.01%-0.02%

A small amount of Mg ＜4%

Furthermore, the shot 2 has a size between 75-150 μm and an angular shape.

Furthermore, a compressed air pressure of 4 bar is used to propel the shot 2 through the hose 5b and the nozzle 6a, the direction of the shot is chosen substantially perpendicular to the surface 7a of the wheel 7 to be treated, the distance of the shot is chosen opposite to said surface 1a is 100mm.

To measure the surface state of the surface 7a of the disc 7 blasted with shot peening 2, the surface roughness standard or parameter (Rugotest No. 3 to standard NF/E05 N10b Surface Roughness Tactile and Visual Control of -051, Registered).

Parameters Control After Shot Peening

Ra 2μm 11μm

Rt 40μm 120μm

Rz 24μm 94μm

Rmax 36μm 111μm

it's here,

Ra is the arithmetic mean deviation of the feature profile,

Rt is the maximum height of the profile,

Rz is the irregular height at 10 o'clock,

Rmax is the maximum height of profile irregularities.

It should be noted that for the shot peening 2 other materials and particle sizes can also be used instead of the brown corundum, such as white corundum (crystalline alumina) or ceramic material particles 2, or dry or wet glass microspheres, or even Steel or cast iron pellets with an average size between 200-800 µm, preferably 400 µm.

In conclusion, it is possible to use shot peening 2, which may or may not be coated, whose material, weight, shape or dimensions are adapted in such a way to obtain the thermomechanical stress of the surface to be treated, i.e. subject it to a certain degree and depth of compressive stress, and/or to achieve control of the surface state (e.g. roughness, wrinkling), and/or to impart a particular aesthetic (in particular brightness, reflectance, diffuse reflectance, gloss) to said treated surface effects and colors, etc.).

It should be noted that the cold treatment step 30 including injection peening 2 may be carried out in one or more operations. In the latter case, the ejection conditions such as the speed of the shot 2, the angle of incidence, and the coverage are set for each operation so as to achieve the above-mentioned results.

Considering now a second embodiment of the method of manufacturing a metal element according to the invention, the second swaging step 120 carried out on the basis of the casting done according to step 110 is of the type described in European patent EP-A-119365. More precisely, during the swaging operation, i.e. when the cast element is compressed between two parts of the mould, the core temperature of the demolded element is approximately 450°C (between 400 and 500°C ).

The third step 130 of structure hardening of cast and swaged parts consists of heating in a first stage, designed to transform the magnesium of the alloy A-S7G0.6 into a substitutional solid solution in aluminum, followed by a A second stage, quenching followed by annealing as in step 20 of the first embodiment.

The heating time is 1 to 10 hours, and the temperature is 520° C. to 540° C. to obtain the above solid solution.

In this example, the purpose of quenching is to keep magnesium in a supersaturated solid solution of aluminum, while the annealing has the effect of causing a small amount of precipitation of magnesium in aluminum, thereby achieving the desired structure hardening.

The fourth step 140 of the second embodiment is similar to said step 30 of the first embodiment as described above.

The following are the rotational bending test results (fatigue limit or durability L _f and relative weight reduction rate e) obtained for a 15 inch diameter wheel 7 made of said thixotropic alloy A-S7G0.6 , manufactured using the first or second embodiment of the invention with the slight difference that the first disc D' according to the invention is only subjected to the blasting treatment of step 30 or 140 on one surface 7a, whereas The second disc D" according to the invention has been subjected to the same blasting treatment on both its surfaces.

Two "control" discs were used in these experiments.

A first control disk D1, consisting of a thixotropic cast wheel according to the invention, but not sprayed in step 30 or 140 .

The second control panel, D2, consists of a refined and wrought alloy 6082T6 (European Standard NF EN573-3), that is to say, an alloy comprising in particular aluminium, magnesium and silicon, which has been transformed into a solid solution, quenched and annealing. Like the first control disc, the second control disc is also unjetted.

The fatigue limit L _f (MPa) is assessed by rolling bending multiple 6.10 ⁶ cycles.

The relative weight reduction rate e (%) is evaluated according to the following formula under the breaking load Q (kg force) of 6.10 ⁶ turns:

e(%)=100(1-((L _f1 ) ⁿ /(L _f2 ) ⁿ )),

Here, n=2/3 for roll bending.

All test discs D', D", D1 and D2 have the same diameter of 15 inches.

In addition, the thickness of each disk is determined with reference to the thickness e ₀ , _which is the thickness of a similar reference disk. This reference disk is made of aluminum base alloy A-S7G0.3 from Y33 to standard NF A/02-004, obtained by the "shell casting" method, also known as "low pressure casting" to those skilled in the art. Furthermore, the fatigue limit L _f1 =105 MPa of the reference disc.

result

Breakage under 6 ^{* 106} circles L _f (MPa) e(%)

      Load Q(Kg force)

Roulette D1 705 126 14.4

Thickness = 0.75e ₀

Roulette D2 790 119 11.0

Thickness = 0.84e ₀

Roulette D’ 820 147 22.6

Thickness = 0.75e ₀

Roulette D" 1020 183 33.3

Thickness = 0.75e ₀

In conclusion, the results of the fatigue limit and weight reduction rate of the discs D' or D" according to the invention are significantly better than those of the control disc D1 obtained by thixocasting but without blasting and forged also without blasting. Control disk D2, this is more evident for disk D".

FIG. 3 shows an example of how a rim 8 is assembled with a disc 7 to obtain a wheel 9 constituting a metallic element produced according to the method of the invention. The rim 8 consists of, for example, a light metal such as aluminum and magnesium, or an alloy of such light metals and any other known material capable of achieving a satisfactory degree of weight reduction and sufficient durability.

This assembly is preferably realized with the known method of MIG welding, which is arc welding using an inert gas, such as argon, with the metal feed. It should be noted that the thixotropic structure of the disc 7 facilitates this type of welding.

However, any other method of connecting the disc 7 to the rim 8 is also feasible, such as mechanical fastening.

It should be noted that wheel profiles 9 other than those shown in Figure 3 may be used. In particular, for example the wheel profile 7 sold as Full Face ^™ or the rim profile 8 sold as PAX ^™ or Single ^™ can be used.

Regarding the application of the two embodiments of the method for manufacturing metal elements according to the invention to wheels 9 of vehicle rolling systems, it should be noted that the initial forming steps 10, 110 are not exclusively limited to the casting of the wheel disc 7, which It can also involve the casting of the entire wheel 9 , consisting of the disc 7 and the rim 8 , so that the element resulting from said process consists of said wheel 9 . In this case, the cold treatment step 30 , 140 consists in blasting all or part of at least one surface 7 a of the disc 7 and/or rim 8 with shot blasting 2 .

Also for this application on the wheel 9, it should be noted that the initial forming step 10, 110 may comprise forming a rim 8 (i.e. one or other part 7, 8 of the wheel 9) instead of said wheel disc 7, In this way, the element resulting from said process consists of said rim 8 . In this case, as in the case of the wheel disc 7 , the cold treatment step 30 , 140 consists in blasting all or part of at least one surface of the rim 8 with shot blasting 2 .

It should also be noted that in case the cold treatment steps 30, 140 are performed in a single operation comprising blasting only one surface 7a with shot peening 2, due to the uneven appearance of said blasted surface 7a, said surface 7 can preferably be designed as a surface located inside the wheel 9 .

Claims (16)

1. A method for manufacturing a metallic element (7, 8, 9), said method comprising, in an initial step (10, 110), forming said element from a semi-solid and thixotropic metallic material (7,8,9), characterized in that the method comprises, in a subsequent cold treatment step (30,140), blasting at least a part of said element (7,8,9) by spray peening (2) Cold treatment is carried out so that it can be plastically deformed. 2. The method for manufacturing metal elements (7, 8, 9) according to claim 1, characterized in that it comprises a step (20, 130) of tissue hardening of said elements (7, 8, 9) ), which step is after said initial step (10, 110) and before said cold treatment step (30, 140). 3. The method for manufacturing metal elements (7, 8, 9) according to claim 1 or 2, further comprising subjecting said shaped element (7, 8, 9) to an intermediate swaging step (120) after said initial step (10, 110) and before performing said tissue hardening step (20, 130). 4. The method for manufacturing metal elements (7, 8, 9) according to one of the preceding claims, characterized in that it comprises, for said initial forming step (10, 110), using a metal alloy , the metal belonging to the group comprising aluminium, magnesium, titanium, iron, chromium, cobalt, nickel, copper, zinc, silver, tin, lead and antimony. 5. The method for manufacturing metal elements (7, 8, 9) according to claim 4, characterized in that it comprises the use of an aluminum-based alloy for said initial forming step (10, 110). 6. The method for manufacturing metal elements (7, 8, 9) according to claim 5, characterized in that it comprises carrying out said initial forming step (10, 110) using an aluminum-based alloy which It also contains between 6.5%-7.5% by weight of silicon and between 0.5%-0.6% by weight of magnesium. 7. The method for manufacturing metal elements (7, 8, 9) according to one of the preceding claims, characterized in that said initial forming step (10, 110) comprises thixotropic forming. 8. The method for manufacturing metal elements (7, 8, 9) according to claim 7, characterized in that said initial forming step (10, 110) comprises thixocasting. 9. The method for manufacturing metal elements (7, 8, 9) according to claim 7, characterized in that said initial forming step (10, 110) comprises rheocasting. 10. The method for manufacturing metal elements (7, 8, 9) according to one of the preceding claims, characterized in that said step (20, 130) of structure hardening comprises quenching followed by annealing. 11. The method for manufacturing metal elements (7, 8, 9) according to one of the preceding claims, characterized in that at least one operation of said cold treatment step (30, 140) includes the use of dimensions between 75- Corundum particles between 150 μm are used as the shot peening (2). 12. The method for manufacturing metal elements (7, 8, 9) according to any one of claims 1-10, characterized in that at least one operation of said cold treatment step (30, 140) includes the use of glass Microspheres are used as the shot peening (2). 13. The method for manufacturing metal elements (7, 8, 9) according to any one of claims 1-10, characterized in that at least one operation of said cold treatment step (30, 140) includes Steel or cast iron balls between 200-800 μm are used as the shot peening (2). 14. The method for manufacturing metal elements (9) according to one of the preceding claims, characterized in that said initial forming step (10, 110) comprises forming a wheel (9) of a vehicle rolling system, said wheel (9) comprising a wheel disc (7) and a wheel rim (8), in this case said wheel (9) constituting said fabricated metal element (9) and during said cold treatment step (30, 140 ) includes spraying all or part of at least one surface (7a) of the wheel disc (7) and/or the rim (8) with the shot peening (2). 15. The method for manufacturing metal elements (7 or 8) according to any one of claims 1-13, characterized in that said initial forming step (10, 110) comprises forming a wheel for a rolling system of a vehicle ( 9), the part (7 or 8) of the wheel (9) comprises a wheel disc (7) or a rim (8), in which case the wheel part (7 or 8) constituting said fabricated metal element (7 or 8), and said cold treatment step (30, 140) comprising blasting said wheel disc (7) or said wheel rim (8) with said shot peening (2) All or part of at least one surface (7a) of the. 16. A wheel (9) for a vehicle rolling system, said wheel (9) comprising a rim (8) on which a metal disc (7) is fixed, characterized in that said metal wheel The disc (7) is obtained with a manufacturing method according to one of the preceding claims.

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