RU2248857C2 - Method for making metallic part such as part of wheel designed for motion of transport vehicle and wheel - Google Patents

Abstract

FIELD: manufacture of metallic part such as rim or disc of transport vehicle wheel.

SUBSTANCE: method comprises steps of strengthening structure of part (after shaping wheel part from aluminum or magnesium base alloy) by quenching and subsequent tempering; cold working with use of bombarding particles at least of one part of disc surface or rim surface for plastically deforming it. Wheel for transport vehicle motion has metallic disc shaped according to invention.

EFFECT: enhanced mechanical properties, lowered mass of wheel.

10 cl, 3 dwg, 1 ex

Description

The present invention relates to a method for manufacturing a metal part, for example, a part of a wheel for a vehicle, and a wheel made in this way. The invention is used, in particular, for the manufacture of a metal part of a wheel such as a light disk of a light metal, for example aluminum or magnesium, or of a metal, which allows a substantial reduction in the weight of the part, for example, titanium, or an alloy of one of the above-mentioned metals.

Metal alloy wheels, such as aluminum alloy, are forged or forged or molded.

The first of the above methods, although it ensures the production of rims having satisfactory mechanical and aesthetic characteristics, has a very significant drawback, which is its high cost.

Over the years, for the implementation of the second of the above methods, it is preferable to use a material that is a metal alloy previously converted to a semi-solid and thixotropic metallographic state. The thixotropic state can be characterized by the structure of the alloy, which contains the primary non-dendritic phase formed by structural particles having a substantially spherical shape.

European patent EP-A-710515 describes such a molding method for casting using a starting material in the form of a thixotropic and semi-solid alloy and a molding matrix for implementing this method.

European Patent EP-A-439981 describes a process for the preparation of the aforementioned thixotropic state.

This molding method, often called "thixoforming," includes both the principle of molding or injection molding (called thixolithing) and the principle of molding / forging on a vertical machine (called thixo molding).

Wheel disks molded using the aforementioned method have the following advantages precisely because of the metallographic state of the alloy, which can be determined by spherical structural particles of reduced size (usually less than 120 microns) distributed almost uniformly in the mass.

These rims can have a reduced thickness and, therefore, reduced dead weight compared to rims of cast or molded alloys in a different state.

In addition, such rims have reduced porosity, i.e. compactness and increased uniform mechanical strength, as well as improved ability to heat treatment.

This molding method also has other advantages:

a wide range of possibilities for giving the resulting rims an aesthetic appearance, for example, obtaining thin walls or significant changes in the cross section;

high accuracy of measured parameters of the obtained rims, which minimizes the necessary subsequent machining operations;

high productivity due to the short time of the technological cycle and the possibility of automating technological operations;

significantly increased service life of molding dies in comparison with the service life of foundry molds, which are used in conventional casting processes when a liquid metal such as aluminum is supplied under pressure.

The objective of the invention is to provide a method for manufacturing a metal part, which initially comprises forming a part from a metal material having a thixotropic structure and semi-solid state, so that the part has improved mechanical properties and reduced weight compared to the above-mentioned characteristics.

To solve this problem, the manufacturing method in accordance with the invention comprises, at a subsequent stage of cold working, cold working of the part by means of collisions of the bombarding particles with at least part of the part for its plastic deformation.

In accordance with an embodiment of the invention, the manufacturing method comprises, at the stage following the initial stage, dispersion hardening of the structure of the moldable part.

In accordance with a specific method of implementing the present invention, the method comprises an intermediate step of stamping the moldable part, performed after the initial stage, but before dispersion hardening of the structure.

An alloy based on a metal selected from the group consisting of aluminum, magnesium, titanium, iron, chromium, cobalt, nickel, copper, zinc, silver, tin, lead and antimony is preferably used for the initial molding step.

In a preferred embodiment, an aluminum-based alloy is used, for example, an alloy containing, in addition to aluminum, from 6.5% to 7.5% by weight of silicon and from 0.5% to 0.6% by weight of magnesium.

Such an aluminum-based alloy reduces the corrosion process.

In accordance with another distinguishing characteristic of the invention, the initial molding step consists in thixoforming, which may be either thixol casting, or casting or casting in semi-solid phase.

It should be noted that the thixolithic method comprises a first stage, which consists in filling the injection mold with a thixotropic metal material in a semi-solid state, and a second stage, which consists in compacting this material in the injection mold under high pressure, having a value of the order of 100 MPa.

"Re-casting" consists in mechanically mixing a liquid alloy to obtain a semi-solid state and in subsequent direct casting of the semi-solid alloy thus obtained without the cooling step prior to molding.

In accordance with another characteristic of the invention, the method includes quenching followed by tempering at the stage of dispersion hardening of the structure.

According to an exemplary embodiment of the method of this invention, at least one of the cold work operations is to use corundum grains having bombardment particles ranging in size from 75 to 150 microns.

According to another embodiment of the present invention, at least one cold working operation consists in using glass beads as bambarding particles.

In accordance with yet another possible embodiment of the present invention, at least one cold working operation consists in using steel or cast iron shots with a grain size in the range of 200 μm to 800 μm as bombarding particles.

According to a preferred characteristic of the invention, the initial molding step is to form a wheel for the vehicle, the wheel comprising a wheel disk and a rim so that the wheel is a metal part to be manufactured, and the cold working step consists in processing by means of collisions using bombarding particles throughout or parts of at least one surface of the rim and / or rim.

According to another embodiment of the invention, the initial molding step is to form a part of the wheel for the vehicle, the part of the wheel being formed by the rim or rim so that the part of the wheel is a metal part to be manufactured, and cold working is carried out by impact processing with bombarding particles the entire or only part of at least one surface of the rim or rim.

The wheel in accordance with the invention for a vehicle comprises a rim on which a metal disk is fixed by welding, which is made by the method defined in one of the claims.

Other characteristics and advantages of the invention will be better understood from the following description, which is not restrictive, with reference to the accompanying drawings, in which:

figa and 1b depict flowcharts of a method for manufacturing a metal part in accordance with two variants of implementation of the invention;

figure 2 - device for the ejection of bombarding particles used to implement the manufacturing method in accordance with the invention;

figure 3 - the rim and rim of the wheel (section) in the position of their connection in such a way as to form a wheel, which is a metal part in accordance with the invention.

A method of manufacturing a metal part in accordance with the first embodiment (Fig. 1a) of the present invention consists in the first step 10 of molding the part by thixolithic metal material having a thixotropic structure and semi-solid state, then in the second step 20 of the choice in the implementation of the operation of dispersion hardening of the structure the molded part and then, during the next third step 30, processing at least a part of the metal part by means of collisions with bombarding parts Tsami.

On figb schematically presents a second embodiment of the method in accordance with the invention, which consists in the implementation of the first step 110, similar or similar to the first step 10, in the implementation then of the second step 120, which consists in stamping the molded part thus, and in the subsequent implementation the third stage 130 of the choice, which consists in the implementation of the dispersion hardening of the structure of the part, which differs from the similar operation in stage 20, and the subsequent implementation of the fourth stage 140 holo hydrochloric processing by collisions with the bombarding particles, which is identical or similar to step 30.

To carry out the first step, 10 or 110 are introduced into a mold (not shown in the figures given in the appendix, since it is described in detail in European patent EP-A-710515), cylindrical rods of a predetermined length or a blank of an alloy based on light metal, such as like aluminum or magnesium.

In a preferred embodiment, an aluminum based alloy is used. The aluminum alloy is preferably an alloy belonging to the family of aluminum-silicon alloys.

As the most preferred embodiment, this alloy meets the designation A-S7GO, 6 in accordance with the requirement of standard NF A 02-004. This alloy, in addition to aluminum, contains the following components in wt.%:

from 6.5% to 7.5% silicon

0.15% iron;

0.03% copper;

0.03% manganese;

0.90% magnesium;

0.03% nickel;

0.05% zinc;

0.03% lead and tin;

0.20% titanium and

0.05% strontium.

In the following presentation, references will be made specifically to this alloy of the A-S7G0.6 grade to describe the second embodiment and to compare the results of mechanical strength and weight reduction tests obtained using the first variant or second variant.

Before being fed into the injection mold, at the first stage, the thixotropic metallographic structure intended for introducing into the metal alloy is preliminarily given, and then, at the second stage, this alloy is transferred to the semi-solid state.

The first stage is carried out, for example, by subjecting the alloy billet to stirring using electromagnetic induction in accordance with the method and using the devices described in European patent EP-A-439981 to obtain thixotropic blanks.

To obtain at the second stage thixotropic preforms in a semi-solid state, induction heating of the preforms to a temperature of T in ° C is carried out, which satisfies the following inequality:

T _fe <T <T _fe +10, where T _fe is the melting point of the eutectic (which in this case, for the preferably used alloy grade A-S7G0.6, is 577 ° C).

The thixotropy of the alloy introduced into the mold is such that the maximum size of the spherical particles characterizing it is less than 120 microns.

Other methods can be used to obtain a thixotropic structure and semi-solid state. In particular, mention may be made of a method known to those skilled in the art as "re-casting" or semi-solid casting, which consists mainly in mixing an alloy, whether or not associated with the chemical refining of dendritic grains.

In the molding process, the material introduced into the injection mold is compacted under pressure having, for example, a value of about 100 MPa. The magnitude of the seal pressure may vary depending on the alloy used or the method used.

Then the molded material is left to cool until a solid state is reached, after which the manufactured part is removed from the mold. In this way, a metal part is obtained which is molded in accordance with the working cavity of the mold.

In accordance with the second step 20 of the first embodiment of the method according to the invention, it is preferable to immediately after removing from the mold the dispersion hardening of the structure, consisting successively in hardening the part and in its tempering. Dispersion hardening of the structure may not be carried out.

In the quenching process, which is carried out using an appropriate liquid, such as water, and which lasts several seconds, the liquid is maintained at a temperature in the range of 30 ° to 60 ° C and preferably in the range of 30 ° to 40 ° C.

As for the vacation, it is carried out at a temperature of 170 ° C and lasts for 6 hours.

The temperature parameters and the duration of the heat treatment, which are used for the dispersion hardening of the part structure, are adapted to obtain the specified values of the strength / ductility pair.

In the third step 30 of the first embodiment of the method in accordance with the invention, the metal part is processed by cold plastic deformation, subjecting this part to collisions with bombarding particles at normal ambient temperature.

These collisions with bombarding particles are provided, for example, by means of a device 1 (FIG. 2) for ejecting bombarding particles 2, the construction of which is shown schematically in FIG. 2.

The device 1 contains at least one inlet part 3a associated with the hopper 4 for storing the bombarding particles 2, and at least one outlet part 3b for ejecting the jet J.

A device 1 is used with the suction of air contained in the hopper 4, so as to create a vacuum in it. This device is known as the "Giffard".

The device 1 used in this embodiment includes a first flexible pipe 5a, the ends of which form an input 3a and an output 3b, respectively. The inlet is connected to the lower part of the hopper 4, which contains an air intake P, equipped with means R for regulating the flow rate of intake air.

The second compressed air supply pipe 5b (in the direction of arrow A) is connected to the outlet 3b in its front part. The air supplied through this pipeline 5b is designed to eject bombarding particles 2 through the outlet 3b, which are continuously removed from the bottom of the hopper 4 (in the direction of arrow B) by creating a vacuum in this hopper 4. The regulator 5c of compressed air flow and, therefore, flow ejected bombarding particles mounted on the pipeline 5b.

The outlet 3b of the pipeline 5a and the rear end of the pipeline 5b are hermetically connected to the gun 6, ending at the outlet with an ejection nozzle 6a designed to emit jets J.

It should be noted that the device 1 can be used using instead of air a liquid, for example water, as a carrier fluid.

You can use the device 1 of a different design than that shown in figure 2, for example, a device that creates gravity, overpressure, direct pressure inside the hopper 7 or a machine with a turbine provided for the mechanical ejection of bombarding particles 2.

You can also use the device 1 of the ultrasonic or electromagnetic type to accelerate the bombarding particles, or to create intense vibration of these particles against the workpiece, or to use an explosive device, or a device that generates a laser strike.

In the General case, it is clear that you can use any device that ejects bombarding particles on the treated surface. Moreover, the device must be such that its mechanical, thermal and ballistic parameters are adapted to the nature and intensity of the required processing.

EXAMPLE OF IMPLEMENTATION OF STAGES 30, 140

At steps 30, 140, the surface 7a of the rim 7 is subjected to cold working using the device 1 (see FIG. 3). In this case, the rim 7 is made of the aforementioned alloy of the A-S7G0.6 grade and is a metal part that has been preformed in accordance with step 10, 110.

In this example, bombarding particles 2 were used, which are brown corundum grains (alumina). Brown corundum, which was used in this case, has the following chemical composition in wt.%:

Al ₂ O ₃ from 89% to 94%

TiO ₂ from 2% to 4%

SiO ₂ from 0.4% to 1.5%

Fe ₂ O ₃ from 1.5% to 3.5%

CaO + MgO from 0.3% to 0.5%

Na ₂ O + K ₂ O from 0.01% to 0.02%

Magnetic particles - less than 4%.

In addition, grains 2 had sizes ranging from 75 to 150 μm and were characterized by an angular shape.

Compressed air was used at a pressure of 4 bar to propel the grains 2 through conduit 5b and nozzle 6b, the ejection direction was essentially perpendicular to the surface 7a of the machined wheel 7 and the ejection distance of the bombarding particles was 100 ml relative to surface 7a.

An attempt was made to characterize the condition of the surface 7a of the rim 7, which was thus treated by collisions with grains 2, and for this, criteria or roughness parameters were used that are precisely defined in norm NF / E05-015 (visual tactile roughness reference sample N10b on Rugotest No. 3 in accordance with NF / E05-051).

Parameter Reference sample After impact treatment Ra 2 microns 11 microns Rt 40 microns 120 microns Rz 24 μm 94 μm Rmax 36 μm 111 μm

where Ra represents the arithmetic mean deviation of the characterized profile; Rt represents the maximum height of the profile, Rz represents the height of the roughness at 10 points, and Rmax represents the maximum height of the roughness of the profile.

You can also use other materials with a different particle size distribution as mentioned bombarding particles 2, for example, grain 2 of white corundum (crystallized aluminum oxide) instead of brown corundum, or ceramic grains, or dry or wet glass beads, or steel or cast iron with medium sizes in the range of 200 to 800 microns, and preferably of 400 microns.

You can also use bombarding particles 2 with or without coating, materials, mass, shape and size of which are suitable for thermomechanical impact on the treated surface, to subject this surface to compression stress of a given degree and depth, and / or to provide the desired condition of the treated surface (for example , roughness or creases), and / or give this surface a definite aesthetic appearance, for example, gloss, reflectivity, matte finish, satin effect Ania or color.

Stage 30 cold processing by collisions with the bombarding particles 2 can be performed in one or in several operations. In the latter case, the conditions of the ejection, for example, the speed of movement of the bombarding particles 2, the angle of their incidence on the treated surface and the degree of its overlap are appropriately adapted for each operation to obtain the above results.

As for the second embodiment of the method of manufacturing a metal part in accordance with the invention, the second stamping step 120, which is performed after the casting is completed at step 110, is similar to the step described in European patent EP-A-119365.

The temperature in the core of the part extracted from the mold has a value of about 450 ° C, in the range from 400 ° C to 500 ° C, during the stamping operation, that is, in the process of pressing the part between two matrix elements.

The third stage 130 of dispersion hardening of the structure cast from the stamped part consists in reheating, which is designed to transfer magnesium in the alloy grade A-S7G0,6 into a solid substitution solution in aluminum, and then in quenching with subsequent tempering, and the operations are carried out in the same way as in step 20 of the first embodiment.

Reheating is carried out over time in the range from 1 hour to 10 hours and to a temperature in the range from 520 ° C to 540 ° C to obtain a solid solution.

Quenching aims to retain magnesium in a supersaturated solid solution in aluminum, while tempering aims to create a thin precipitate of magnesium in aluminum, completing the required diffusion hardening of the alloy structure.

As for the fourth step 140 of the second option, it is essentially similar to step 30 of the first option, as mentioned earlier.

Below are the results of tests of fatigue resistance to bending during rotation (fatigue limit or fatigue strength L _f and relative weight reduction e), which were obtained for a rim 7 with a diameter of 15 inches (37.5 cm) from an A-S7G0.6 thixotropic alloy manufactured by the first or second embodiments of the method in accordance with the invention, with the only difference being that the first disk D 'was processed by means of collisions with bombarding particles during steps 30 and 140 on only one side 7a, while the second disk D ″ was subjected to the same processing from two sides.

For testing, two reference or control wheels were also used.

The first control wheel disk D1 is a thixotropic disk structure and cast in accordance with the invention, but was not subjected to processing by means of collisions with bombarding particles, as is done in the above steps 30 or 140.

The second control wheel disk D2 is a disk of a deformable and malleable alloy known under the brand name 6082T6 (European norm NF EN 573-3), that is, containing, in particular, aluminum, magnesium and silicon, this alloy being converted into a solid solution, hardened and then tempered. As in the case of the first control wheel, the second control wheel was not subjected to processing by means of collisions with bombarding particles.

The fatigue limit L _f (expressed in MPa) was estimated during bending during rotation for the realized number of cycles of 6 · 10 ⁶ .

The relative weight loss e (expressed in%) was estimated under load Q at failure, set for 6 · 10 ⁶ cycles (in kilograms of force) in accordance with the ratio:

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

where for bending during rotation n = 2/3.

All tested D ’, D’ ’, D1 and D2 rims had the same diameter of 15 inches (37.5 cm).

In addition, the thickness of each rim was determined taking into account the reference thickness e _{0 of a} similar reference rim. The reference rim is made of an aluminum alloy of type A-S7G0.6 U33 in accordance with NF A / 02-004 and was obtained using the "die casting" method, also known to experts in the art as low pressure casting . In addition, the reference rim was characterized by a fatigue limit L _{f1 of} 105 MPa.

RESULTS Fracture force Q (in kg of force) at 6.10 ⁶ cycles L _f (MPa) e (%) Disk D1 0.75 e ₀ thick 705 126 14,4 Disk D2 with a thickness of 0.84 e ₀ 790 119 11.0 Disk D 'with a thickness of 0.75 e ₀ 820 147 22.6 Disk D '' with a thickness of 0.7 5 e ₀ 1020 183 33.3

In conclusion, it should be noted that the results on the fatigue limit and relative weight reduction are better for the disks D 'and D' 'in accordance with the invention with respect to the control disk D1 obtained by thixol casting and not subjected to processing by impacts with bombarding particles, and in relation to the forged control disk D2, also not subjected to collision processing, and this improvement is especially pronounced for just one disk D ''.

Figure 3 schematically shows an example of attaching to the rim 8 of the disk 7, which is a sample of a metal part manufactured by the method in accordance with the invention, to obtain a wheel 9.

The rim 8 is made of a light metal such as aluminum or magnesium, or an alloy of such a light metal, or any other known material to reduce its weight and obtain a sufficiently high mechanical strength. The rim 8 may also be made of iron or an alloy based on iron.

In a preferred embodiment, the attachment is realized by welding, known as MIG, that is, arc welding in an inert gas atmosphere such as argon, and with the supply of metal. This type of welding favors the thixotropic structure of the alloy of which the disk 7 is made.

Any other suitable method for connecting the rim 7 to the rim 8 can be used, for example, mechanical fastening thereof.

It should be noted that in this case, you can use different profiles of the wheel 9, different from the profile shown in figure 3. In particular, a rim profile 7 may be used, for example, of a type of profile marketed under the name Full Face ™, or of a rim profile 8, for example, of a type of profile marketed under the name PAX ™ or under the name Single ™.

Regarding the application of two variants of the method for manufacturing a metal part in accordance with the invention for the manufacture of a wheel 9 for a wheeled vehicle, it should be noted that the initial molding step 10, 110 is not limited to molding the rim 7, but may also apply to molding the entire wheel 9 formed by the disk 7 and the rim 8, so that the resulting part is a wheel 9 as a whole.

In this case, the cold working step 30, 140 consists in processing by collision with the bombarding particles 2 the entire or at least part of the surface 7a of the disk 7 and / or the surface of the rim 8.

In relation to the wheel 9 as a whole, it should also be noted that the initial molding step 10, 110 may consist in forming the rim 8 (i.e., one or the other part 7, 8 of the wheel 9) instead of the disk 7, so that the metal part is formed by a cast rim 8.

In this case, the cold treatment 30, 140 is carried out by means of collisions with the bombarding particles 2 of the entire or at least part of the surface of said rim 8.

In cold working 30, 140, which is carried out in the form of a single operation for treating a disk 7 on one of its surfaces 7a by means of collisions with bombarding particles 2, this surface 7a can preferably be that surface which should be on the inside of the wheel 9 due to the not quite smooth appearance of this treated surface 7a.

Claims (10)

1. A method of manufacturing metal parts such as a disk and a rim of a wheel, including at the initial stage forming a part from a metal material having a thixotropic structure and a solid-liquid state, characterized in that after molding, the structure of the part is strengthened by quenching and subsequent tempering, and then cold working bombarding particles of at least part of the surface of the disk or rim for plastic deformation, while an aluminum-based alloy is used for molding Nia or magnesium. 2. The method according to claim 1, characterized in that they carry out an intermediate step of stamping the part molded at the initial stage before hardening the structure. 3. The method according to claim 1, characterized in that at the initial stage of molding an aluminum-based alloy is used, having in its composition an additional from 6.5 to 7.5% by weight of silicon and from 0.5 to 0.6% by weight weight of magnesium. 4. The method according to claim 1, characterized in that at the initial stage of molding carry out thixoforming. 5. The method according to claim 1, characterized in that, at the initial stage of molding, a thix casting operation is performed. 6. The method according to claim 1, characterized in that at the initial stage of molding carry out the operation of casting. 7. The method according to any one of claims 1 to 6, characterized in that in at least one cold working operation corundum grains having sizes from 75 to 150 microns are used as bombarding particles. 8. The method according to any one of claims 1 to 7, characterized in that at least one cold working operation or at least other operations use glass beads as bombarding particles. 9. The method according to any one of claims 1 to 8, characterized in that in at least one cold working operation or at least one of the indicated operations, steel or cast iron particles with grain sizes from 200 to 800 μm are used as bombarding particles. 10. A wheel for moving a vehicle, comprising a rim on which a metal disk is fixed, characterized in that the metal disk is made by the method according to any one of claims 1 to 9.

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