FR3011493A1 - METHOD FOR ASSEMBLING PARTS OF A GAS GENERATOR - Google Patents

Abstract

A method of assembling a first piece (10) on a second piece (20), the first piece (10) being metallic with at least one male part (11) arranged to fit into a female part of the second piece (20) and passing therethrough, the male portion (11) protruding a predetermined height from the second piece (20), the method comprising at least one step of exerting a force on the male part (11) and simultaneously heating the latter so that the force is sufficient to plastically deform the protruding part of the male part (11), so as to form a retaining deformation of the second part (20) on the first part (10).

Description

The present invention relates generally to a method of assembling parts of a security module mounted on a motor vehicle and in particular of parts of a gas generator used in a vehicle. these security modules.

It is known in the prior art assemblies parts by deformation of a male part of a first piece protruding from a female part of a second part, to create a retaining deformation of the second part on the first piece . In general, a riveting method is used, but such a process is performed by applying significant forces to the first piece. When this first part is fragile or if the assembly must be precise, the efforts can deform the first part or even the complete assembly and make them unfit for use. An object of the present invention is to meet the disadvantages of the prior art mentioned above and in particular, first of all, to propose a method of assembling a first piece with a second piece, by deformation of a male portion of the first piece protruding from a female part of the second piece, the method being provided to limit the risk of deformation of the first piece or the assembly. For this, a first aspect of the invention relates to a method of assembling a first part on a second part, the first part being metallic with at least one male part arranged to fit into a female part of the second part and passing through the latter, the male portion protruding from a predetermined height of the second piece, the method comprising at least one step of exerting a force on the male part and simultaneously heat the latter so that the effort is sufficient to deform plastically the protruding part of the male part, so as to form a retaining deformation of the second part on the first part. The method according to the present implementation comprises, at least partly simultaneously with the step of applying the force, a heating step to reduce the resistance of the male part of the first part, and thus limit the efforts to apply to form the holding deformation, such as a bead or a retention bend, with respect to deformation performed at ambient temperature. The risk of deformation of the rest of the first part are thus limited. The force sufficient to plastically deform the protruding part of the male part, so as to form a holding deformation of the second part on the first part is less than a deformation force of the rest of the first part. It is conceivable to design the first part so that the male part has a section or volume much lower than the rest of the structure of the first part, to limit the heating in the male part, so that the rest of the first piece does not heat and retains a significant mechanical strength and does not deform or little. According to one embodiment, a section of said at least one male portion is less than or equal to 45% of a section immediately adjacent to the rest of the first piece. More particularly, the section of said at least one male portion is less than or equal to 40% of the immediately adjacent section. According to one embodiment, the step of applying the force and simultaneous heating is a step during which the male portion is heated so as to reduce the mechanical strength of 60% or more of the male part when is at room temperature. According to one embodiment, the heating step is a step during which the male part is heated to at least 50% of the melting temperature of the material of the first part. According to one embodiment, the first part comprises several male parts, each arranged to fit into and pass through a female part of the second part, and the step of applying a force and heating is simultaneous on all the protruding parts of the male parts. The process, with this simultaneous heating-deformation step, makes it possible to quickly assemble the two parts. According to one embodiment, the step of applying the force is performed with a single monolithic tool for all the male parts. According to one embodiment, the heating step is a step of independent and simultaneous heating of each protruding part of each male part. The independence of the heating circuits guarantees a good control of the process and allows the rapid identification of a production problem. According to one embodiment, the step of forming the holding deformation leads to a play-free embedding of the second piece in the first piece. A second aspect of the invention is a device comprising: - a first part, - a second part to be assembled on the first part, the first part 20 being metallic with at least one male part arranged to fit into a female part of the second piece and passing through the latter, the male part protruding from a predetermined height of the second piece, a tool arranged to exert a force on the male part protruding from the second piece and to simultaneously heat the protruding part of the part male, so as to form a holding deformation of the second piece on the first piece. According to one embodiment, the first part comprises several male parts, each arranged to fit into a female part of the second part and pass through the latter, and in which the tool is arranged to simultaneously apply a force and a heating on all male parts. According to one embodiment, the tool is arranged to independently heat and simultaneously each male part.

According to one embodiment, the system comprises a third piece mounted in a sliding connection between the first and the second part and arranged to slide between them. A third aspect of the invention is a gas generator comprising an assembly of a first piece with a second piece, made according to the method according to the first aspect of the invention. It is vital for a gas generator to ensure that the assembly in question is compliant and can provide its function properly during its operation to inflate the airbag. A fourth aspect of the invention is an automotive security module comprising a gas generator according to the third aspect of the invention. A fifth aspect of the invention is a motor vehicle comprising a security module according to the fourth aspect of the invention. A final aspect of the invention is a method of assembling a first piece to a second piece, the first piece being metallic with a predetermined mechanical strength at room temperature, and having at least one male part arranged to fit in a female portion of the second piece and passing therethrough, the male portion protruding a predetermined height from the second piece, the method comprising: - a step of exerting a force on the male part and simultaneously heating the latter to reduce a mechanical strength of the protruding portion of the male part; - a step of plastically deforming the protruding part of the male part by applying to it a stress lower than the predetermined mechanical strength at room temperature, so as to form a deformation of retaining the second piece on the first piece. Other features and advantages of the present invention will appear more clearly on reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the appended drawings, in which: FIG. 1 shows a perspective view of an assembly of a first, a second and a third part, before the creation of a retaining deformation of the second part on the first part with the process according to the invention; - Figure 2 shows two side views of the assembly of Figure 1, before and after the creation of the retaining deformation of the second part on the first part. In the present application, the mechanical strength is defined as the tensile strength Rm. For metallic materials such as iron, steel, copper or aluminum, it is well known that this mechanical strength drops when they are heated. Figure 1 shows a perspective view of a first U-shaped member 20 which supports a second piece 20 which is generally plate-shaped. A third piece 30 is mounted between the first piece 10 and the second piece 20. The first piece 10 comprises a plurality of male portions 11 which engage female portions of the second piece 20, in order to position the second piece 20 on the second piece 20. first piece 10. Thus, the third piece 30 may be mounted in sliding connection relative to the first piece 10 and relative to the second piece 20, and will be perfectly positioned and guided by the assembly formed by the first piece 10 and the second piece 20.

In order to make the assembly shown in FIG. 1 integral, the male parts 11 protrude from the second part 20, so that they can be deformed in order to form a retaining deformation of the second part 20 on the first part 10.

Due to the U-shape of the first piece 10 and its thickness, the application of a vertical force on the male parts 11 can deform the first piece 10 or cause a shift between the latter and the second piece 20, this which can lead to a questioning of the slide connection of the third piece 30.

In order to avoid these risks of non-compliance (deformation of the first part 10 and / or jamming of the third part 30), the method according to the invention proposes to heat the male parts 11 in order to reduce locally the mechanical strength of the first piece 10. FIG. 2 shows two side views of the assembly of FIG. 1, before and after the formation of the retaining deformation of the second piece 20 on the first piece 10. The method according to the invention proposes therefore to apply a force on the male parts 11 and heat them simultaneously with a tool 40. The tool 40 is arranged to pass an electric current in each male portion 11, when the force is applied to them. The passage of the current will thus cause a heating of the metal Joule effect, until a significant decrease in the mechanical strength of the male parts 11. In order to limit the risk of drift of the method, the tool comprises a portion 40a in contact with one of the male parts 11, independent of a portion 40b in contact with another of the male parts 11. Thus, the current flowing in each male portion 11 is controllable and measurable, to verify that each male portion 11 is well crossed by a suitable heating current.

During the heating step, the parameters of current and heating time are determined so as to heat each male part so that their mechanical strength drops by at least 60%. For example, for a first U-shaped piece of steel of length 37 mm and thickness 2.5 mm as shown, having six male parts 11 each having a section of 5 × 2.5 mm, exceeding by 5.3 mm, a current of 18,000 can be applied. amperes for 400 milliseconds and easily obtain a deformation with a bearing force of 9000N. The left view of FIG. 2 shows the tool 40 in contact with the first part 10, during the application of the force and heating step, before the temperature of the male parts 11 allows the formation with a reduced force of the holding deformation of the second piece 20 on the first piece 10. The right view of FIG. 2 represents the tool 40 which has formed the deformation of the second piece 20 on the first piece 10, by a descent represented by the arrows on each side of the tool 40. As the male parts 11 have been heated, the deformation force has been low, and no spurious deformation has deformed the remainder of the first part 10, neither the assembly of the first piece 10 with the second piece 20.

It should also be noted that the heating of the male parts 11 limits the risk of crack creation in the deformed parts. It should be noted that the step of simultaneous heating with the application of a force improves the contact between the tool 40 and the first part 10, which reduces the contact resistance.

As can be seen in FIG. 1, the male parts 11 have a section and a mass that is much smaller than the rest of the first part 10, so that the passage of the heating current in the male parts 11 causes only localized heating. in these last ones. The remainder of the first part 10 is not sufficiently heated to reduce its mechanical strength by more than 10% for example. It can also be envisaged to locate the ground electrodes as close as possible to the male parts 11 to limit the passage of the heating current in the remainder of the first part 10. An advantage of the method according to the invention is that it can easily be implemented with a resistance welding machine, which limits investment. It will be understood that various modifications and / or improvements obvious to those skilled in the art can be made to the various embodiments of the invention described herein without departing from the scope of the invention defined by the appended claims.

Claims (11)

REVENDICATIONS1. A method of assembling a first piece (10) on a second piece (20), the first piece (10) being metallic with at least one male part (11) arranged to fit into a female part of the second part (20) and passing therethrough, the male part (11) protruding by a predetermined height from the second part (20), the method comprising at least one step of exerting a force on the male part (11) and simultaneously heat the latter so that the effort is sufficient to plastically deform the protruding part of the male part (11), so as to form a retaining deformation of the second part (20) on the first part (10). 2. Method according to the preceding claim, wherein the step of applying the force and simultaneous heating is a step during which the male part (11) is heated so as to reduce the mechanical strength of 60% or more of the male part (11) when it is at ambient temperature. 3. Method according to one of the preceding claims, wherein the first piece (10) comprises several male parts (11), each arranged to fit into and pass through a female part of the second piece (20), and wherein the step of applying a force and heating is simultaneous on all the protruding parts of the male parts (11). 4. Method according to the preceding claim, wherein the step of applying the force is performed with a single tool (40) monolithic for all the male parts (11). 5. Method according to one of claims 3 or 4, wherein the heating step is a step of independent and simultaneous heating of each protruding portion of each male portion (11). 6. Method according to one of the preceding claims, wherein the step of forming the holding deformation leads to a fitting without play of the second part (20) in the first part (10). 7. Device comprising: - a first piece (10), - a second piece (20) to be assembled on the first piece (10), the first piece (10) being metallic with at least one male part (11) arranged for s inserting into and passing through a female part of the second piece (20), the male part (11) projecting from a predetermined height of the second piece (20), a tool (40) arranged to exert a force on the male part (11) protruding from the second part (20) and simultaneously heating the protruding part of the male part (11), so as to form a holding deformation of the second part (20) on the first part ( 10). 8. Device according to the preceding claim, wherein the first part (10) comprises a plurality of male parts (11), each arranged to fit into and pass through a female part of the second part (20) and into which The tool (40) is arranged to simultaneously apply force and heat to all male portions (11). 9. Device according to the preceding claim, wherein the tool (40) is arranged to heat independently and simultaneously each male portion (11). 10. Device according to one of claims 7 to 9, further comprising a third part (30) mounted in sliding connection between the first and the second part (10,20) and arranged to slide between them after assembly. 11. A gas generator comprising an assembly of a first part (10) with a second part (20), produced according to the method of one of claims 1 to 6. Automotive safety module comprising a gas generator according to the preceding claim. 13. Motor vehicle comprising a security module according to the preceding claim.