WO2000042334A1

WO2000042334A1 - Helical spring made of aluminium alloy wire

Info

Publication number: WO2000042334A1
Application number: PCT/FR2000/000037
Authority: WO
Inventors: David Mollet; Gérard Thomas
Original assignee: Pechiney Rhenalu
Priority date: 1999-01-13
Filing date: 2000-01-10
Publication date: 2000-07-20
Also published as: FR2788317A1; AU3052100A; FR2788317B1

Abstract

The invention concerns a helical spring made from an aluminium wire whereof the yield strength exceeds 350 MPa and preferably 400 MPa, and more particularly a spring having an endurance limit of at least 96 h under alternating compression at 50 % of its initial height at the rate of 100 cycles/mn, produced from an aluminium alloy wire with a cross-section ranging between 2 and 3 mm, said wire having a yield strength R0.2 > 400 MPa and a shear modulus G > 20 GPa, and preferably 25 GPa. The inventive springs are useful for making mattresses with light corrosion-resistant and non-magnetic springs, and for motor vehicle suspension elements.

Description

Coil spring in aluminum alloy wire

Field of the invention

The invention relates to a spring produced from metallic wire of circular section wound in a cylindrical helix and intended to be subjected to a compressive or tensile force along the axis of the helix.

State of the art

Helical springs made from steel wire have been used for many years. To form a spring which is suitable for industrial applications, the following properties are required: - sufficient mechanical resistance of the wire, expressed by the conventional elastic limit at 0.2% R _0; ;

- an appropriate stiffness of the spring allowing it to withstand sufficiently the compression and traction forces without however being too stiff;

- sufficient resistance to fatigue. For example, for the use of steel springs in a mattress, mattress manufacturers require a resistance of at least 96 h for an alternating stress of 100 cycles / min of a value corresponding to a compression of the spring at 50% of its initial height, i.e.

576,000 cycles in total.

Carbon steel coil springs meet these different conditions. However, for certain applications, these springs can have three types of drawbacks:

Given the high density of steel, these springs are heavy. There are many applications in which the user would prefer to have a spring which, with equal mechanical performance and durability, is lighter. For example, steel spring mattresses are heavy, which makes them difficult to handle. For suspension springs in cars or motorcycles, a weight saving is also an advantage for reducing the inertia of the moving masses and the total mass of the vehicle.

Furthermore, the corrosion resistance of carbon steel may be insufficient for certain applications where the spring is subjected to humidity or to aggressive atmospheres.

Finally, the ferromagnetic nature of steel can be troublesome in certain mechanical devices subjected to intense magnetic fields, or in certain electromagnetic devices of high precision. On the other hand, an increasing number of buyers would like to have mattresses that do not contain ferromagnetic materials, which can have an unfavorable influence on the quality of sleep. The invention therefore aims to remedy these drawbacks by allowing the use of coil springs in a light material, resistant to corrosion and non-magnetic and remaining of an acceptable cost for mass production. It can be noted that general publications on springs, such as for example the chapter "Springs" of Engineering Techniques, volume B5, Mechanical Engineering, sections B5430 to B5440, August 1984 (author Michel Duchemin), consider a fairly large number of ferrous or non-ferrous metallic materials for the manufacture of springs, but not aluminum alloys.

Subject of the invention

The invention relates to a helical spring produced from an aluminum wire whose elastic limit exceeds 350 MPa and preferably 400 MPa. This elastic limit can be reached, thanks to appropriate manufacturing ranges, either with hardening-hardened aluminum alloys, such as AlMg alloys, in particular alloys 5019, 5052, 5154A, 5251 or 5754 according to the EN standard. 573-3, i.e. alloys with structural hardening, such as AlCu alloys (and in particular alloys 2011, 2014, 2014A, 2017, 2017A, 2024 or 2117), AlSiMg or AlZnMg. More particularly, the invention relates to a spring, intended in particular for the manufacture of mattresses, having a fatigue resistance of at least 96 h under alternating compression at 50% of its initial height at the rate of 100 cycles / min , produced from an aluminum alloy wire with a section of between 2 and 3 mm, this wire having an elastic limit Ro, ₂ > 400 MPa and a Coulomb module G> 20 GPa, and preferably> 25 GPa.

Another object of the invention is a method of manufacturing a spring from an AlMg aluminum alloy wire, characterized in that a wire rod blank is subjected to one or more wire drawing passes followed by annealing, then work hardening greater than 100% and preferably 200%, before manufacturing a spring from this wire. Another object of the invention is a method of manufacturing a spring from an AlCu alloy wire, characterized in that a wire rod blank is subjected to one or more drawing passes followed by a annealing, then to a work hardening greater than 100% and preferably to 200%, to a dissolution followed by a quenching, to one or more wire drawing passes at a cumulative rate of work hardening greater than 20% and preferably greater than 30 %, and at maturation, before making a spring from this wire.

The springs according to the invention can also be used in the suspension or damping elements of land vehicles, agricultural machines or aircraft or in mechanical devices subjected to intense electromagnetic fields.

Description of the invention

The invention is based on the observation that it is possible, by choosing both alloy compositions and a suitable manufacturing range, to obtain helical springs of aluminum alloy wire having employment properties. at least equivalent to those of steel wire springs, with a wire diameter of the same order, and therefore a significant weight gain, good corrosion resistance and an absence of magnetism. The aluminum alloys used must lead, for the wire used to make the springs, to a high mechanical resistance, the elastic limit R _0ι2 exceeding 400 MPa, even 500 MPa. This can be obtained with alloys without heat treatment, but with a high capacity for hardening by work hardening, such as alloys AlMg (5000 series), with significant work hardening (at a rate of more than 100% and preferably more than 200%) during the last wire drawing pass. The Applicant has obtained good results with the alloy EN AW-5019 of general composition according to standard EN 573-3 (% by weight): Si <0.40 Fe <0.50 Cu <0.10 Mn: 0, 10 - 0.60 Mg: 4.5 - 5.6

Cr <0.20 Zn <0.20, with Mn + Cr 0.20 - 0.6 other elements 0.05 each and 0.15 in total.

Even better characteristics can be obtained with heat-treated alloys such as AlCu (series 2000), AlSiMg (series 6000) or AlZnMg (series 7000). The wire, before dissolving, is subjected to a work hardening of at least 100% and preferably of at least 200%. Then, it is subjected to a dissolution and a quenching, then to a last pass of wire drawing at a rate of work hardening of at least 20% and preferably of at least 30%, followed by maturation at ambient temperature. It is thus possible to reach an elastic limit greater than 500 MPa.

A particularly suitable alloy is the alloy EN AW-2017 according to standard EN 573-

3 of composition:

Si: 0.20 - 0.80 Fe <0.7 Cu: 3.5 - 4.5 Mn: 0.40 - 1.0

Mg: 0.40 - 0.80 Cr <0.10 Zn <0.25 The springs obtained using these wires are characterized by a high stiffness. This stiffness R, measured in N / mm, is given, for a wire of circular section, by the formula: R = (G xd ⁴ ) / (8n x D ³ ), in which d is the diameter of the wire, D the diameter of the helix, n the number of useful turns and G the Coulomb modulus (or transverse elasticity modulus) of the wire. For a given spring geometry, the stiffness is therefore proportional to the Coulomb module. The wires intended for the springs according to the invention must have a Coulomb modulus greater than 20 GPa and preferably greater than 25 GPa.

This stiffness (or rigidity) measurement is made by pressing the spring gradually, recording the applied force, and measuring the observed sinking. The relationship between applied force F and driving e being linear, we deduce the total stiffness R which is the quotient F / e. Examples

Example 1

A rough wire rod with a diameter of 9.5 mm in alloy 5019 of the following composition (% by weight) was produced by continuous casting on a wheel and continuous rolling between alternately horizontal and vertical roller trains. 0.06 Fe = 0.13 Cu = 0.01 Mn = 0.13 Mg = 4.8 Cr = 0.08 The blank, after lubrication, was drawn to the diameter of 7.5 mm, with a 60% work hardening. The wire was annealed, then greased again before being drawn to the final diameter of 2.5 mm, with a work hardening rate of 800%. This wire had the following mechanical characteristics (measured according to standard EN 1301-2): Resistance to rupture R _m : 466 MPa _Elastic limit R _0d : 427 MPa Elongation at break A (measured on a reference base of 100 mm ): 5% We made with this wire coil springs with an initial height of 120 mm and a helix diameter of 50 mm, comprising 4.7 useful turns. The total stiffness R of the spring was measured, which was 0.21 N / mm. We deduce a Coulomb module of 25.40 GPa. Using a rod-crank assembly, the spring was compressed to 50% of its initial value at the rate of 100 cycles / min for 96 h, for a total of 576,000 cycles, without finding any fatigue failure. These coil springs are intended for the manufacture of spring mattresses.

Example 2

A roughing wire rod 9.5 mm in diameter in 2017 alloy of composition 2017 (% by weight) was produced by wheel casting and continuous rolling: Si = 0.56 Fe = 0.13 Cu = 4.0 Mn = 0.64 Mg = 0.70 The blank was greased, then drawn to a diameter of 7 mm, with a work hardening rate of 84%, annealed, again greased and drawn to the final thickness of 2 , 2 mm, with a work hardening rate of 732%. The wire was then dissolved at 500 ° C, quenched in cold water, then subjected to a work hardening pass at a rate of 40%, and finally left to mature at room temperature for 3 days.

It then had the following mechanical characteristics (determined as in Example 1): R _m = 591 MPa R _{0> 2} = 582 MPa A = 6%

The same spring was produced with this wire as in the previous example, which was subjected to the same tests. A total stiffness R of 0.18 N / mm was obtained corresponding to a Coulomb modulus of 36.78 GPa, and an absence of fatigue rupture at 576,000 cycles.

These coil springs are intended for the manufacture of spring mattresses.

Example 3

A 2024 alloy wire of 4.0 mm diameter was produced from a blank with a diameter of 12.3 mm, by first carrying out a wire drawing with a work hardening rate of 40%, then an annealing and wire drawing to the final diameter. After dissolving, quenching and maturing, the wire had an elastic limit of 430 MPa. A spring was produced as in the previous example, which did not show fatigue failure after 640,000 cycles. This spring is intended for the manufacture of suspension elements for mopeds.

Example 4

An 1156 diameter 6056 alloy wire was produced from an annealed blank (state O) with a diameter of 12.2 mm. The drawn wire was dissolved and quenched, then wound up in the form of a helical spring comprising 11 turns, with an outside diameter of 55 mm. After returning to the mechanical resistance peak (state T6), the following mechanical characteristics were obtained: R _m = 460 MPa R _0; = 417 MPa

A = 17%

A total stiffness of 50 N / mm was measured. This spring is intended for the manufacture of mountain bike shock absorbers.

Claims

1. helical spring produced from a metal wire, characterized in that the wire is made of aluminum alloy, with an elastic limit R _0; > 350 MPa.

2. helical spring according to claim 1, characterized in that the wire has an elastic limit R ₀ , ₂ > 400 MPa.

3. Coil spring according to one of claims 1 or 2, characterized in that the aluminum alloy is an AlMg alloy.

4. Spring according to claim 3, characterized in that the alloy is chosen from alloys 5251, 5052, 5154A, 5754, 5019.

5. Spring according to one of claims 1 or 2, characterized in that the aluminum alloy is an AlCu alloy.

6. Spring according to claim 5, characterized in that the alloy is chosen from alloys 2011, 2014, 2014A, 2017, 2017A, 2117, 2024.

7. Spring according to claim 1, characterized in that the aluminum alloy is an AlZnMg alloy.

8. Spring according to claim 1, characterized in that the aluminum alloy is an AlSiMg alloy.

9. Coil spring according to one of claims 2 to 8, characterized in that it has a resistance to fatigue of at least 96 h under alternating compression to 50% of its initial height at the rate of 100 cycles / min , and that it is made from an aluminum alloy wire with a section between 2 and 3 mm, this wire having a Coulomb modulus G> 20 GPa and preferably G> 25 GPa.

10. Use of a spring according to one of claims 1 to 9 for the manufacture of suspension elements for land vehicles, agricultural machines or aircraft

11. Use of a spring according to one of claims 1 to 9 in mechanical devices subjected to intense electromagnetic fields.

12. A method of manufacturing a helical spring made of aluminum alloy AlCu wire according to claim 5, characterized in that a wire rod blank is subjected to one or more drawing passes followed by annealing, then hardening at a rate higher than 100% and preferentially higher than 200%, dissolving followed by quenching, one or more wire drawing passes at a cumulative hardening rate higher than 20% and preferentially more than 30%, and to a maturation, and that a spring is made from this wire.

13. The manufacturing method according to claim 12, characterized in that the work hardening which precedes dissolution is greater than 400%.

14. Method according to one of claims 12 or 13, characterized in that the wire is of 2017 alloy.

15. A method of manufacturing a helical spring made of aluminum alloy AlMg wire according to claim 3, characterized in that a wire rod blank is subjected to one or more drawing passes followed by annealing, then a work hardening greater than 100% and preferably greater than 200%, and that a spring is made from this wire.

16. The method of claim 15, characterized in that the work hardening is greater than 400%.

7. Method according to one of claims 15 or 16, characterized in that the wire is of alloy 5019.