Method of manufacturing hollow one-piece axle blanks, and axle blanks obtained

The present invention relates to a hollow axle blanks manufacturing process in one piece, comprising a body provided with flares at both ends, for the equipment of wheeled vehicles, road or not, in particular commercial vehicles towed such as trailers or semi-trailers.

There are basically two families of methods for the production of hollow axles blanks.

A first family of processes enables the production of composite blanks axles, that is to say formed of several assembled pieces. It is known thus generating a longitudinal axle blanks by joining two halves .constituées each of a starting material, in particular sheet metal or flat profiles, for example, U-shaped with a variable section, by stamping or forging, rockets being pre-made on the starting material. It is also known to provide hollow axle blanks by assembling a tubular body on which is reported by any suitable processes including welding, of independently manufactured rockets.

The second family of axle blanks manufacturing processes allows the production of blanks piece axles, that is to say in a single piece. usually starts with a smooth tube of uniform wall thickness, of appropriate section, for example round, oval, rectangular or square that is shrinking the ends by forging or hammering for the reduction of area corresponding to the rockets, a final heat treatment on the whole of the axle from the complete forming. hot. The heat treatment that is subjected to the axle draft depends on the characteristics of the steel used. According to it, is subjected to the axle blank is quenching followed by annealing, a normalization processing. The heat treatment process has the disadvantage of causing the axle blank which is a product of variable section deformities requiring further training which is a source of residual stresses on the axle over.

Axles obtained from the axle drafts known to date have the disadvantage of not presenting all points of their length of dimensional and mechanical characteristics related to the stresses in operation. To ensure a sufficient lifetime to the axle Builders are thus led to oversize the axles, or particular areas thereof, which increases the weight of the axle and its manufacturing cost.

The present invention proposes to provide a method for producing economical manner of hollow axles blanks in one piece for obtaining axles in particular with appropriate mechanical properties in different areas of the axle to the constraints experienced in service , while for the same operating characteristics of a smaller thickness at the body for a given diameter compared to conventional axles.

The method according to the invention is characterized by the fact that after a heated steel tube is subjected to a quenching operation, in particular with water over its entire length, followed by annealing, is then carried out to ends of the tube, after localized rapid heating and without scale formation for example by induction of said end zones, discharge operations to create a thickness in the transition zone between the body and the spindle and necking, and then is carried out a localized thermal annealing treatment on both ends of the axle blank.

In a first embodiment, is carried out the quenching operation on great length pipes, for example, as taught in French patent application 79 08 911 (FR-A-24 53 902) of the applicant, after which Revenue is carried out at great length tube and, after making him suffer a dimensional calibration and training, desired is cut to the length corresponding to that of the axle draft.

In a second embodiment, the quenching operation is performed and income on previously bucked tubes to length to the axle draft.

According to the invention, the forging operations and refoulement and annealing can be done in the same production line as a result of treatment of quenching and tempering. Alternatively, provision may be made to perform processing independently of quenching and tempering, and after optionally stored quenched and tempered tubes are subsequently subjected to the following steps of the method according to the invention.

The steel used according to the invention is of tempered steel building types in particular to water and weldable.

discharge operations and shrink for forming the fuses and the transition zone therebetween and the body are preferably made in a single operation after rapid local heating without scale formation for example by induction, of the area of corresponding ends of the pre-soaked tube and income, sawed, as indicated above and performing a hammering on internal mandrel of appropriate shape, in a machine for engagement with axial rotation of the tube, an axial thrust of the end being exerted on the tube .

It is of course possible according to the invention to perform the discharge and necking operations in two successive operations, the displacement being obtained by axial thrust of the tube, including mandrel after heating a corresponding zone of the tube, by necking forging or hammering is then carried out after obtaining by upsetting the desired thickness in the transition zone between the body and the spindle.

The annealing operation, after shaping, may advantageously be accomplished by performing successively with relatively short time, heating in an induction furnace to rapid increase in temperature and equalization in the same furnace or another furnace, particularly an electrical resistance furnace.

In the method of the invention, there is thus limited to performing localized heat treatments at both ends of the blank of axles, that is to say located at the two rockets and two transition zones, without this disrupt the metallurgical center (or body) of the axle. The process maintains thereby the mechanical properties data initially to the central part of the axle by the heat treatment performed on the blank in the tube state, before forging rockets.

The method avoids having to perform any final metallurgical treatment of the axle as a whole. It avoids, therefore, local deformation, and the need to perform, as in the prior art, a final straightening of the whole of the blank after forging rockets. This final dressage is usually very harmful residual source of local constraints.

The axle blank obtained by the implementation of the method according to the invention is characterized by different metallurgical structure in the body and in rockets, with a continuous transition of the metallurgical structure between the body and each rockets.

Thanks to the implementation of the method according to the invention, it is possible to achieve, for a given diameter, with axle blanks whose thickness the body of the level is less than the thicknesses may be used for the properties of comparable operating under standardized axle blanks obtained by conventional methods. We can quantify this wall thickness reduction and thus axle weight to about 13% vis-à-vis traditional axles normalized steel at comparable properties of use or operating performance.

The thickness of the blank axle obtained by the invention is maximum at the connection area between the conical body and each of the fuses and a minimum at the body, this thickness decreasing from the connection zone to the body external extrimité of the rocket, the thickness at the rocket being always greater than the thickness of the body. The bulge at the connection between the body and the rocket is larger than that which would be produced by a continuous variation due to a simple metal necking by forging or hammering.

For one axle, the draft produced by the method according to the invention is then machined to form in rockets bearings receiving areas, and is provided with the necessary equipment to use.

With the aim of better understanding the invention will now be described, for example limiting in any way, an embodiment with reference to the accompanying drawings in which:<ul><li>Figure 1 shows an axle blank obtained by implementing the method according to the invention,</li><li>Figure 2 is an enlarged sectional view of one end of the axle of Figure 1.</li></ul>

Seen, in Figures 1 and 2, an axle having a body 1 provided at both ends of rockets 2.

Rockets 2 have a cylindrical inner wall surface 3 or slightly conical.

Between the stub axles and the body is a transition zone wherein the inner wall of the axle has a frustoconical surface 3, increasing the thickness of wall to be maximum in a bulge area 4 and 5, this thickness decreasing subsequently until a minimum value in the body. The body 1 of the wall thickness is always less than the thickness of wall 3 in rockets 2.

Has thus been produced according to the invention, in a steel according to the AFNOR designation 20MV6 an axle blank a standard diameter of 152.4 mm with a wall thickness of the body of 10 mm, the minimum thickness may be obtained by conventional methods for the same diameter in standard steels being 12 mm. For a length of the axle blank obtained 2100 mm, the weight is 82.5 kg, while the weight is, for a traditional axle blank of the same diameter and comparable properties of use of 95 kg.

To achieve this axle was subjected to water quenching a tube as described in the French patent 79 08 911 (FR-A-24 53 902). After Revenue tube was conducted dimensional calibration followed by dressage.

The tube was then cut up in lengths of 2300 mm.

To achieve the flares and the transition zone between the rocket and the body was heated by induction successively each of the ends of the tube cut along a length of the order of 450 mm at a temperature of the order of 1 200 ° C . was then to each of the method ends in a hammering on an inner mandrel by engagement with axial rotation of the tube in a hammering machine by exerting an axial thrust on the tube end.

The maximum thickness of material in the transition zone, obtained by upsetting, is 24.5 mm, the thickness at the ends of rockets being 15 mm.

We then proceeded to annealing of each rocket starting from the transition region to the end of the spindle in an induction furnace at 950 ° C followed by passage through an equalizing furnace, e.g. an electrical resistance furnace of which the area of ​​use is between 900 and 1000 ° C. This finishing treatment has the advantage of not causing deformation requiring further dressing, source of residual stresses.

The axle obtained is characterized by a yield stress in the body, greater than or equal to 588 N / mm2 and in the upper rockets or equal to 441 N / mm2.

It is also characterized by a resilience at 0 ° in the upper body or 6,5 Daj / cm 2 and in the upper rockets or equal to 5.5 Daj / cm2. The elongation means in the transition zone is greater than or equal to 20%.

While the invention has been described in connection with a particular embodiment, it is obvious that it is not limited.