METHOD OF MANUFACTURING A CLOSED PROFILE

Description

[0001] The present invention relates to a method for manufacturing a closed profile, for example in the form of a pipe in a profile structure.

[0002] When manufacturing profile structures, where the cross-section and/or shape of the profile or the pipe have been changed, you usually start from materials preferably of steel or aluminium with good forming properties. During the forming operation a certain strain hardening is achieved but this is not the crucial reason for the choice of forming method or the structural form of the product.

[0003] US 4 649 728 shows integral joint forming of work-hardenable high alloy tubing. A pre-form tube is cold forged or cold rolled from the outside using a counterstay within the tube in order to increase the strength along substantially its entire length and substantially uniformly.

[0004] Furthermore, a profile material is not chosen or the manufacturing process is not controlled so that you achieve any substantial strategical variations in thickness of the material of the final product. By starting from a profile having an even wall thickness you often will use considerably more material as compared to a structure that is optimised in weight.

[0005] The object of the present invention is to provide a method for manufacturing a closed profile in a profile structure, for example a pipe that is constituted by iron and alloyed to provide a strong strain hardening during plastic cold forming in combination with maintaining a good ductility of the alloy at the same time as the pipe achieves a yield point of above 1000 MPa as the final product. Another object of the invention is that the closed profile is manufactured according to a method through hydroforming and/or mechanical treatment of the same, to provide a strategically varying wall thickness axially and/or in the cross-section of the profile. The characterising features of the invention are stated in claim 1.

[0006] Thanks to the invention a method and device for manufacturing a closed profile in a profile structure and a closed profile manufactured according to the method have now been provided that in an excellent manner fulfil their purposes at the same time as the manufacture can take place very rationally and at low cost. By forming the profile, which is manufactured according to the invention, with varying wall thickness and/or diameter the weight of the profile can be reduced to more than half the weight of profiles in previously known construction solutions. Examples of such solutions may be different girders and frame structures in cars and other means of conveyance and also other components where closed profiles, for example in the form of pipes, may be incorporated.

[0007] The invention is described in more detail below with the aid of the following embodiments.

[0008] According to the invention the closed profile is constituted for example in the form of a pipe that is manufactured from a metal material of iron, which is alloyed with chromium, nickel and carbon in predetermined proportions. In the example chosen the iron is alloyed with 17% chromium, 7% nickel and 0,1% carbon, wherein a strong strain hardening is obtained when plastically cold forming the profile in combination with maintaining a good ductility of the alloy. The alloyed metal material forming the profile is formed through hydroforming and/or through expanding preferably by means of a mandrel with a cylindrical or other shape or through shrinking through axial elongation by pulling with or without a matrix, in order to increase the yield point of the metal material from an original, low yield point of about 300 MPa to a final product that completely or partially obtains a yield point of more than about 1000 MPa.

[0009] In an embodiment according to the invention in which a closed profile is manufactured with varying diameter you start for example from a pipe of the kind above-mentioned having a diameter of 40 mm, a wall thickness of 2 mm and a yield point of 300 MPa. By means of a mandrel or internal liquid pressure the pipe is expanded along half its length to a diameter of 60 mm, wherein the wall thickness of the pipe is decreased to about 1.5 mm along said half of the pipe and the yield point of the pipe can be increased to 1000 MPa or more at the same time as the other half of the pipe is left untreated. Then a pulling force is applied on the ends of the pipe, wherein the half that still has a diameter of 40 mm, a wall thickness of 2 mm and a yield point of 300 MPa is extended under a certain reduction in diameter until the wall thickness has been reduced to about 1.5 mm and the yield point has been increased to about the same level as in the other end of the pipe, and thereafter the process is interrupted.

[0010] The wall thickness and/or the circumference of the final closed profile may also be varied axially by applying two or more profiles partially into each other with the short profile external on the longer profile. The wall thickness and/or the circumference may be varied further after the forming of the closed profile by using welding to join so called starting profiles with walls of different thickness and/or with different diameters. To optimise the strength of the profile the wall thickness may be varied in the same cross-section, so that the material will be strategically placed just over the areas where an expected maximum strain may take place. As an alternative you may combine a heavily strain hardening alloy with other alloys to provide the final product certain strength characteristics and/or cost optimisation. As starting material for the closed profile according to the invention a metal material of the above-mentioned alloy having low strength is used.

[0011] According to an embodiment of the invention the material in the profile is cooled to or is kept at a controlled temperature before and during the forming operation to achieve a controlled, maximal strength independently of the degree of deformation during the forming operation. For example, the temperature that the material is cooled to or the temperature that is maintained during the forming operation is -196° ≤ T ≤ 70°C.

[0012] According to another embodiment the final product is cooled to or is kept at a controlled temperature for achieving a controlled maximal strength independently of the degree of deformation during the forming operation. For example, the temperature that the final product is cooled to or the temperature that is maintained during a limited time after the forming operation is -196° ≤ T ≤ 70°C.

[0013] Alternatively, the profile described in the application intended to be incorporated in a current profile structure may be constituted by any closed profile design intended to be incorporated in the current profile structure.

Claims

1. A method of manufacturing a closed profile at which the initial metal work piece used is constituted of iron, alloyed with chromium, nickel and carbon in predetermined proportions and then plastically cold working the closed profile, characterized by cold working through hydroforming and/or through expanding, preferably by means of a mandrel with a suitable shape, or through shrinking through axial elongation by pulling with or without a matrix to increase the yield point of the metal material from an original low yield point to a final product that completely or partially obtains a high yield point.

2. A method according to claim 1, characterized in that the metal material of iron in the form of the closed profile, which is plastically worked, is alloyed with 17% chromium, 7% nickel and 0.1% carbon.

3. A method according to claim 1, characterized in that the original low yield point amounts to about 300 MPa and the high yield point is preferably equal to or amounts to more than 1000 MPa.

4. A method according to claim 1, characterized in that the wall thickness of the final closed profile is varied axially by applying two or more profiles partially into each other with the shorter profiles external on the longer profiles, by joining profiles having different wall thickness and/or different diameter through welding before the forming operation, or by varying the wall thickness in the same cross-section to achieve a strategic position of the profiled material and optimisation of the strength.

5. A method according to claim 1 or 4, characterized in that the strength of the final profile is varied in different portions of the profile by partially more or less extending the material.

6. A method according to any of the preceding claims, characterized in that the material in the profile is cooled to or is kept at a controlled temperature before and during the forming operation to achieve a controlled, maximal strength independently of the degree of deformation during the forming operation.

7. A method according to any of the preceding claims, characterized in that the temperature that the material is cooled to or the temperature that is maintained during the forming operation is -196° ≤ T ≤ 70°C.

8. A method according to any of the preceding claims, characterized in that the final product is cooled to or is kept at a controlled temperature for achieving a controlled maximal strength independently of the degree of deformation during the forming operation.

9. A method according to claim 9, characterized in that the temperature at which the final product is cooled or the temperature that is maintained during a limited time after the forming operation is -196° ≤ T ≤ 70°C.

Ansprüche

1. Verfahren zur Herstellung eines geschlossenen Profils, bei dem das ursprünglich benutzte metallene Werkstück aus Eisen besteht, das mit Chrom, Nickel und Kohlenstoff in vorbestimmten Anteilen legiert wurde, mit anschließender plastischer Kaltverformung des geschlossenen Profils,
gekennzeichnet durch,
Kaltverformung mittels Hydroformung und/oder durch Expandieren, insbesondere mittels einer Spindel mit geeigneter Form, oder durch Schrumpfen mittels axialer Elongation mittels Ziehen mit oder ohne einer Matrize, zur Erhöhung der Streckgrenze des metallenen Materials von einer ursprünglich niedrigen Streckgrenze zu einem Endprodukt, das vollständig oder teilweise eine hohe Streckgrenze erhält.

2. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, dass
das metallene Material aus Eisen in Form eines geschlossenen Profils, das plastisch bearbeitet wurde, mit 17% Chrom, 7% Nickel und 0,1% Kohlenstoff legiert ist.

3. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, dass
sich die ursprünglich niedrige Streckgrenze auf etwa 300 MPa bemisst und die hohe Streckgrenze bevorzugt gleich oder größer ist als 1.000 MPa.

4. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, dass
sich die Wandstärke des endgültigen geschlossenen Profils axial verändert, indem zwei oder mehrere Profile teilweise ineinander angeordnet werden, indem die kürzeren Profile außerhalb an den längeren Profilen angebracht sind, indem Profile mit unterschiedlichen Wandstärken und/oder unterschiedlichen Durchmessern mittels Schweißen vor der Formbehandlung miteinander verbunden werden oder indem die Wandstärke in demselben Querschnitt verändert wird, um eine strategische Anordnung des profilierten Materials und um eine Optimierung der Festigkeit zu erreichen.

5. Verfahren nach Anspruch 1 oder 4,
dadurch gekennzeichnet, dass
die Festigkeit des endgültigen Profils in unterschiedlichen Bereichen des Profils verändert wird, indem das Material teilweise mehr oder weniger ausgezogen wird.

6. Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet, dass
das Material in dem Profil auf einer geregelten Temperatur gehalten wird oder auf diese abgekühlt wird, bevor oder während der Formung, um eine kontrollierte maximale Festigkeit zu erhalten, unabhängig vom Grad der Deformation während der Formung.

7. Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet, dass
die Temperatur, auf die das Material herabgekühlt wird, oder die Temperatur, die eingehalten wird während der Formung, -196° ≤ T ≤ 70° C ist.

8. Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet, dass
das endgültige Produkt auf eine geregelte Temperatur herabgekühlt wird oder auf dieser gehalten wird, um eine kontrollierte maximale Festigkeit zu erreichen, unabhängig vom Grad der Deformation während der Formung.

9. Verfahren nach Anspruch 8,
dadurch gekennzeichnet, dass
die Temperatur, auf die das endgültige Produkt heruntergekühlt wird, oder die Temperatur, die während einer limitierten Zeit nach der Formung eingehalten wird, -196° ≤ T ≤ 70° C ist.

Revendications

1. Procédé de fabrication d'un profilé fermé, dans lequel la pièce métallique initiale utilisée est constituée de fer allié à du chrome, du nickel et du carbone en des proportions déterminées à l'avance, puis le profilé fermé est travaillé à froid plastiquement, caractérisé en ce que l'on travaille à froid par hydroformage et/ou par expansion, de préférence, au moyen d'un mandrin d'une forme appropriée ou par retrait par allongement axial en étirant avec ou sans une matrice pour augmenter la limite apparente d'élasticité du matériau métallique d'une limite apparente d'élasticité basse à l'origine à un produit final qui a, en tout ou partie, une grande limite apparente d'élasticité.

2. Procédé suivant la revendication 1, caractérisé en ce que le matériau métallique en fer sous la forme du profilé fermé qui est travaillé plastiquement est allié à 17 % de chrome, à 7 % de nickel et à 0,1 % de carbone.

3. Procédé suivant la revendication 1, caractérisé en ce que la basse limite élastique d'élasticité d'origine s'élève à environ 300 MPa et la grande limite apparente élastique est de préférence égale ou supérieure à 1 000 MPa.

4. Procédé suivant la revendication 1, caractérisé en ce que l'on fait varier l'épaisseur de paroi du profilé fermé final axialement en appliquant deux ou plusieurs profilés partiellement l'un dans l'autre, les profilés les plus courts étant disposés à l'extérieur des profilés les plus longs en réunissant des profilés ayant des épaisseurs de paroi différentes et/ou un diamètre différent par soudage avant l'opération de formage ou en faisant varier l'épaisseur de paroi dans la même section transversale pour atteindre une position stratégique du matériau profilé et une optimisation de la résistance.

5. Procédé suivant la revendication 1 ou 4, caractérisé en ce qu'on fait varier la résistance du profilé final en des parties différentes du profilé en allongeant partiellement plus ou moins le matériau.

6. Procédé suivant l'une quelconque des revendications précédentes, caractérisé en ce que l'on refroidit ou on maintient à une température réglée le matériau du profilé avant et pendant l'opération de formage pour obtenir une résistance maximum réglée indépendamment du degré de déformation pendant l'opération de formage.

7. Procédé suivant l'une quelconque des revendications précédentes, caractérisé en ce que la température à laquelle le matériau refroidit ou la température qui est maintenue pendant l'opération de formage est telle que -196° ≤ T ≤ 70°C.

8. Procédé suivant l'une quelconque des revendications précédentes, caractérisé en ce qu'on refroidit le produit final ou on le maintient à une température réglée pour obtenir une résistance maximum réglée indépendamment du degré de déformation pendant l'opération de formage.

9. Procédé suivant la revendication 8, caractérisé en ce que la température à laquelle le produit final est refroidi ou la température qui est maintenue pendant une durée limitée après l'opération de formage est telle que -196° ≤ T ≤ 70°C.