Method for producing a door element of an automotive vehicle and door element of an automotive vehicle

A method for producing a door element comprising a planar panel (30) and protruding edges (32a, 32b, 32c), each edge (32a, 32b, 32c) being joined to at least one adjacent edge (32a, 32b, 32c) by a joining edge, comprising: —providing a rectangular planar blank, —cutting out said blank to retrieve a corner part being adapted to form a joining edge (34), —stamping the cut-out blank to obtain a door element part (52) comprising the panel (30) and the edges (32a, 32b, 32c), said edges (32a, 32b, 32c) being separated one from the others, —joining the adjacent edges (32a, 32b, 32c) by attaching a joining part (54) to the door element part, said joining part (54) being made of a material different from the material of the door element part (52) and forming a joining edge.

The present invention concerns a method for producing a door element of an automotive vehicle, in particular a tailgate of a cargo box of a pickup truck.

Pickup trucks generally a cargo box, also called bed, for carrying various types of cargo loads.

A cargo box for a pickup truck typically includes a base panel bounded by upstanding walls to form a container. The walls generally include two side walls, a front wall and a rear wall. The rear wall, which forms a door element, is pivotably mounted to provide a tailgate facilitating the insertion or removal of articles in the cargo box.

The tailgate generally comprises an inner panel being a structural part and an outer panel being an ornament panel. The inner panel comprises a substantially planar panel and protruding edges extending around the planar panel in planes substantially perpendicular to the planar panel. Each protruding edge is adjacent to at least one other protruding edge, and each protruding edge is joined to the adjacent edge(s) by joining ends.

The inner panel is generally made of a metallic material, for example steel. For example, it is known to produce the inner panel by providing a one-piece steel blank, i.e. a blank obtained by cutting a single steel sheet, and by cold stamping the blank so as to shape the inner panel.

When designing such a cargo box, several requirements, often conflicting with each other, must be complied with. Indeed, it is desirable to design the cargo box, in particular the tailgate, so that it may resist to impacts, in particular resist the impacts of loads received in the cargo box, or resist impacts resulting from a collision of the vehicle. It is thus desirable that the tailgate may absorb an important quantity of energy when subjected to impact loads, and may deflect significantly before failure. Furthermore, it is desirable to reduce the overall weight of the vehicle, in order to reduce the energy consumption of the vehicle, so as to meet the future environment requirements. It is thus desirable to reduce the thicknesses of the parts forming the vehicle, in particular the tailgate. However, simply reducing the thickness of the tailgate leads to a degraded resistance to impacts.

It has thus been proposed to form the tailgate in a high strength steel, for example having a tensile strength greater than 780 MPa.

However, with steels having such a high tensile strength, problems for stamping the blank may arise, due to the lower formability of these steels. In particular, thickening of the steel may happen during the cold stamping.

The object of the invention is to solve the above-mentioned problems, and in particular to provide a method for producing a door element having a reduced weight and an improved resistance to deformation, which does not lead to compression or thickening of the steel.

To that end, the invention relates to a method for producing a door element of an automotive vehicle, said door element comprising a substantially planar panel and protruding edges extending around the panel in planes substantially perpendicular to the panel, each edge being adjacent to at least one other edge, each edge being joined to the or each adjacent edge by a joining edge, said method comprising the following steps:providing a substantially rectangular planar blank,cutting out said blank to retrieve at least one corner part of said blank, said or each corner part being adapted to form a joining edge of two adjacent edges of the door element,stamping the cut-out blank in order to obtain a door element part comprising the panel and the edges extending around the panel, said edges being separated one from the others,joining the adjacent edges by attaching at least one joining part to the door element part, said or each joining part being made of a material different from the material of the door element part and forming a joining edge.

Forming the door element part and the joining parts as two distinct parts made of different materials allows choosing for each of the door element part and the joining parts a material which is suitable for shaping these parts by stamping blanks, without obtaining necking or thickening of the steel.

According to other advantageous aspects of the invention, the method comprises one or more of the following features, considered alone or according to any technically possible combination:the dimensions of the corner parts retrieved from the blank are calculated such that the edges of the door element part are each deformed according to a single direction during the stamping of the cut-out blank;the material of the door element part has a tensile strength greater than or equal to 780 MPa;the material of the joining parts has a yield strength inferior to the yield strength of the material of the door element part;the joining parts are obtained by stamping;the joining parts are at least partly subjected during stamping to a deformation rate greater than a critical deformation rate of the material of the door element part;the joining parts are attached to two adjacent edges and to the panel by bolting;the method comprises, prior to cutting out the blank, a determination step for determining the location of the corner parts to be retrieved, said determination step including evaluating the deformation rate that should be applied on each point of the blank to shape the door element part and the joining parts, and determining which points of the blank would be subjected to a deformation rate higher than a deformation rate threshold for the material of the door element part.the corner parts are determined as corner portions of the blank including the points that would be subjected to a deformation rate higher than the deformation rate threshold.

The invention also relates to a door element for an automotive vehicle, comprising a substantially planar panel and protruding edges extending around the panel in planes substantially perpendicular to the panel, each edge being adjacent to at least one other edge, each edge being joined to the or each adjacent edge by a joining edge, the panel and the edges outside the joining edges being made of a single door element part and the or each joining edge being made of a joining part attached to the door element part.

According to other advantageous aspects of the invention, the door element comprises one or more of the following features, considered alone or according to any technically possible combination:the or each joining part is made of a material different from the material of the door element part;at least part of the or each joining edge has a deformation rate greater than a critical deformation rate of the material of the door element part.each joining part comprises two branches extending in substantially perpendicular directions, each branch being attached to one of two adjacent edges in order to join said edges together.the door element forms at least a part of a tailgate of a pick-up vehicle.

A cargo box6of a pickup truck is illustrated onFIG. 1.

A pickup truck generally comprises a cab portion for carrying passengers and a cargo box6, also called bed, for carrying various types of cargo loads. The cab portion and the cargo box6are mounted on a front and a rear end respectively of the frame of the pickup truck.

The cargo box6comprises a base8and four side walls including right and left side walls10, a front wall14, and rear wall16forming a tailgate of the cargo box6.

The base8has a substantially rectangular shape.

The front wall14extends in a transversal plane, and protrudes upwardly from a front edge of the base8.

Each side wall10substantially extends in a vertical longitudinal plane. In particular, each side wall10protrudes upwardly from a side edge of the base8.

The tailgate16is pivotally mounted at a lower edge16aadjacent to a rear edge of the base8. The tailgate16may thus pivot between a closed position and an open position. In the closed position, the tailgate16protrudes upwardly and substantially vertically from the rear edge of the base8. In the open position, the tailgate16extends substantially horizontally in the extension of the base8.

As illustrated onFIG. 2, the tailgate16comprises a door element20, forming an inner panel of the tailgate16, and an outer panel22.

The door element20is a structural part of the cargo box6.

The door element20comprises an inner face oriented towards the inside of the cargo box6, and an outer face destined to face an inner face of the outer panel22.

The outer panel22is an ornament panel. The outer panel22comprises an inner face destined to cover the outer face of the door element20and an outer face oriented towards the outside of the pickup truck.

The door element20comprises a substantially planar panel30and protruding peripheral edges32a,32b,32c. The peripheral edges32a,32b,32cextend around the panel in planes substantially perpendicular to the panel.

In particular, the panel30has a substantially rectangular shape, and extends vertically (when the tailgate is closed) between a lower end30aand an upper end30b, and transversally between two side ends30c,30d.

The peripheral edges protrude perpendicularly from at least some of the lower, upper and side ends of the panel20.

In the illustrated embodiment, the peripheral edges comprise a lower edge32aprotruding from the lower end30aof the panel30, and two side edges32c,32dprotruding from the side ends30c,30dof the panel30.

Thus, each peripheral edge32a,32b,32cis adjacent to at least one other peripheral edge32a,32b,32c.

Each peripheral edge32a,32b,32cis joined to each adjacent edge by a joining edge34. The joining edges34thus form the corner parts of the door element20.

In the illustrated embodiment, the joining edges34include two lower joining edges, each joining a side edge32c,32dto an end of the lower edge32a.

Each peripheral edge32a,32b,32ccomprise an inner portion38, which protrudes perpendicularly to the panel30, and an outer portion40, substantially parallel to the panel30, which protrudes outwardly from the inner portion38.

Each joining edge34comprises an inner portion44, which protrudes perpendicularly to the panel30and joins the inner portions38of two adjacent peripheral edges32a,32b,32c, and an outer portion46, substantially parallel to the panel30, which protrudes outwardly from the inner portion34.

Furthermore, each joining edge34comprises two branches extending in substantially perpendicular directions, each branch being attached to one of two adjacent peripheral edges32a,32b,32cin order to join the two edges together.

As illustrated onFIG. 3and explained in further details below, the panel30and the peripheral edges32a,32b,32care made of a single door element part52, and the joining edges34are each made of a joining part54. The door element part52and the joining parts54are distinct three-dimensional parts made of different materials, for example different steels, which are attached to each other.

The door element part52is preferably obtained from a one-piece steel blank, i.e. a blank obtained by cutting a single steel sheet.

For example, the door element part52is made of a first material, and the joining parts54are made of a second material, different from the first material.

The first material is a steel, for example having a tensile strength greater than or equal to 780 MPa, preferably greater than or equal to 980 MPa. For example, the steel has a yield strength greater than or equal to 450 MPa, preferably greater than or equal to 550 MPa.

For example, the first material is a dual-phase steel, having a yield strength to tensile strength ratio inferior to 0.6, preferably inferior to 0.5.

Indeed, a dual-phase steel provides both a good mechanical resistance and a good drawability, and provides enhanced energy absorption properties during an impact as compared to a usual high strength low-alloy steel (so called HSLA) having the same yield strength.

The first material may be uncoated or coated, for example galvannealed or galvanized by any suitable process such as hot dip coating, electrodeposition, vacuum coating.

The door element part52has a thickness preferably comprised between 0.5 mm and 1.2 mm, for example 0.8 mm.

The second material is preferably a steel having a better drawability than the first material.

Indeed, the joining parts54have more complex shapes than the door element part52, i.e. have an overall deformation rate, resulting from the stamping, higher than the door element part52. In particular, the highest deformation rate of the joining parts54is greater than the highest deformation rate of the door element part52.

More specifically, the deformation rate of the joining parts54is such that, if the joining parts54were made of the first material, thickening or necking would occur on at least some parts of the joining parts54.

The use of a material having a better drawability than the first material to form the joining parts54allows avoiding these phenomena.

For example, the second material is a high strength low-alloy steel. For example, the steel has a yield strength comprised between 420 MPa and 520 MPa and a tensile strength comprised between 470 MPa and 590 MPa.

The second material has preferably a yield strength inferior to the yield strength of the first material.

Preferably, the second material has a total elongation greater than or equal to 17%.

Preferably, the second material has a higher total elongation than the first material.

The second material may be uncoated or coated, for example galvannealed or galvanized by any suitable process such as hot dip coating, electrodeposition, vacuum coating.

The joining parts54have a thickness preferably comprised between 0.6 mm and 1.3 mm, for example 0.9 mm. For example, the joining parts54have a greater thickness than the door element part52.

The joining parts54are attached to the panel30, for example by bolting, or by welding.

The door element20further comprises a handle60, which protrudes perpendicularly from the panel30, and which is destined to be received in a corresponding through hole62formed in the outer panel22.

Preferably, the handle60is made of a three-dimensional part distinct from the door element part, and is made of a third material different from the first material.

For example, the third material is the same as the second material.

A method for producing the door element20will now be described.

The production of the door element20comprises producing the door element part52and the joining parts54separately, and attaching the joining parts54to the door element part52.

Additionally, the production of the door element20comprises producing the handle60separately from the door element part52and the joining parts54, and attaching the handle60to the door element part52.

The production of the door element part52comprises forming an intermediate blank of the first material, by cutting a sheet of the first material to the appropriate shape, i.e. a shape adapted so that the blank could be stamped to form the door element part52and the joining parts.

The intermediate blank is for example a substantially rectangular planar blank.

The production of the door element part52further comprises determining the location on the intermediate blank of corner parts to be retrieved.

These corners parts correspond to the portions of the intermediate blank which, if the intermediate blank was stamped as such, without retrieving the corner parts, would form the joining edges34.

Preferably, the determination of the location of the corner parts include evaluating the deformation rate that should be applied on each point of the intermediate blank to shape the door element part52and the joining parts54, and determining which points of the blank would be subjected to a deformation rate higher than a deformation rate threshold for the first material. The threshold is for example determined as a critical deformation rate corresponding to the highest deformation rate that could be applied by cold stamping without inducing thickening or necking at these points. This determination is for example carried out by using forming limit diagrams.

The corner parts are for example determined as corner portions of the intermediate blank including all the points that would be subjected to a deformation rate higher than the deformation rate threshold.

Furthermore, the dimensions of the corner parts are preferably such that the edges of the door element part are each deformed according to a single direction during the subsequent stamping of the blank.

The intermediate blank is then cut-out to retrieve the corner parts from the intermediate blank, to form a cut-out blank.

The cut-out blank is then cold stamped to shape the three dimensional door element part52. Once stamped, the cut-out blank forms the panel30and the peripheral edges32a,32b,32cextending around the panel, the peripheral edges32a,32b,32cbeing separated one from the others.

The joining parts54are each produced by forming a joining part blank of the second material, by cutting a sheet of the second material to the appropriate shape.

The joining part blank is substantially planar.

The joining part blank is then cold stamped to shape the three-dimensional joining part54.

Besides, the handle60is produced by forming a handle blank of the third material, by cutting a sheet of the third material to the appropriate shape, i.e. a shape such that the handle blank could be stamped to form the handle60.

The handle blank is substantially planar.

The handle blank is then cold stamped to shape the three-dimensional handle60.

The joining parts54are then each attached to two adjacent edges of the door element part52, for example by bolting.

The handle60is also attached to the panel30, for example by bolting.

Forming the door element part52and the joining parts54as two distinct parts made of different materials allows choosing for each of the door element part52and the joining parts54a material which is suitable for shaping these parts by stamping blanks, without obtaining necking or thickening of the steel.

It further allows choosing for each of the door element part52and the joining parts54a material and a thickness offering an optimal performance, in function of the stress which they may be submitted to, so that both the resistance of the structural part and its weight may be optimized.

In particular, the joining parts54can thus be made of a material having a better formability than the door element part52, without necessitating forming the whole door element20with this material, and thus allows forming the door element part52in a material having a good resistance when submitted to impacts.

It must be understood that the example embodiments presented above are not limiting.

For example, according to another embodiment, the door element part52comprises four peripheral edges, each peripheral edge being adjacent to two peripheral edges, and being joined to each adjacent peripheral edge by a joining edge34. In this embodiment, the door element20thus comprises four joining edges34, and the step of cutting out the intermediate blank comprises retrieving four corner parts of the blank.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments.