Patent Application
20080203743
The present invention relates to a method to manufacture an impact absorbing device, such as a vehicle bumper beam and a vehicle door beam. The invention also relates to the impact absorbing device thus obtained.
Impact absorbing devices such as impact absorbing bumper or door beams are well known in the art.
At present, such impact absorbing devices may be provided out of a matrix being a metal such as steel or aluminum. Such metal impact absorbing devices have the drawback of being heavy, which is a disadvantage when to be used for automotive or transport applications. Due to their production method they are not flexible towards function integration. The weight causes additional fuel consumption as the weight is to be carried along with the vehicle.
An alternative for such heavy impact absorbing devices is found in the use of composite material as matrix material, usually glass fiber, aramid fibers, high modulus PET fibers or C-fiber reinforced polymers. Such composite articles have the disadvantage of possible scattering into small parts once they are subjected to significant impact. In spite of the fact that under such significant impacts, the vehicle may be preserved from damage, the parts of polymer material scattered from the broken impact absorbing device may cause on its turn damage to parts of the vehicle being present behind the impact absorbing device, such as e.g. puncture of the gasoline tank or damage to the motor block.
Even more, once a fiber reinforced composite has been subjected to some load, small cracks may occur, which cracks decrease the safety and absorbing property of the impact absorbing device to a large extent. Usually, once subjected to some impact force, the whole impact absorbing device is to be replaced due to safety reasons.
The use of elongated metal elements such as metal wire or metal cords, e.g. steel wire or steel cords, as such or in the form of a woven grid such as from U.S. Pat. No. 5,290,079, as additional reinforcement to the composites out of polymer matrix and glass or C-fibers, is also known.
The design and manufacturing of such metal wire or metal cord reinforced impact absorbing means, envisages however some problems. As an example, the fixation of the elongated metal elements in the device during press molding of the device, may cause difficulties. Also the beam should be designed to have no undercuts, to make them moldable, what limits strongly the design freedom of such type of reinforced beams.
Also, in case one is willing to replace an existing impact absorbing device out of metal or out of composite material by a metal reinforced composite impact absorbing device, such replacement causes the matrix volume of the impact absorbing device to be redesigned, causing new press molds to be designed and produced, and many more technical and economical problems.
It is an object of the present invention to avoid the problems of the prior art.
It is a further object of the present invention to increase the impact resistance of impact absorbing devices, without the necessity to redesign the matrix volume of the impact absorbing device.
It is also an object of the present invention to partially restore and increase the impact resistance of impact absorbing devices which have been subjected to impact forces, which did not cause rupture of the whole device.
It is yet another object of the present invention to provide a method to avoid scattering of the matrix volume of existing composite impact absorbing devices, such as glass- or C-fiber reinforced polymer impact absorbing devices.
It is another object of the present invention to increase the part integrity of impact absorbing devices, in case such have been subjected to an impact force.
It is further an object of the present invention to provide an increase of energy absorption capacity of impact absorbing devices.
It is further an object of the present invention to provide an increase of energy absorption capacity of impact absorbing devices without the necessity to redesign the matrix volume of the impact absorbing device.
It is finally an object of the present invention to provide a method to generate more design freedom in producing reinforced beams.
According to a first aspect of the invention, there is provided a method to manufacture an impact absorbing device as claimed in accordance with claim 1.
The two-step approach, namely first press-molding the matrix volume and thereafter attaching the tape-like device allow to reach more complex structures which cannot be made by means of a single press-molding operation.
The presence of elongate metal elements, such as metal steel wire or metal cords such as metal steel wire and metal steel cords, provide additional impact absorption to the existing matrix volume of the impact absorbing device. However, the re-design of the whole impact absorbing device is avoided.
It is understood that the matrix volume as such may serve as an impact absorbing device itself. Attaching a tape like device to the matrix volume increases the impact resistance to the matrix volume and improves the impact absorbing capacity of the matrix volume.
In case the matrix volume has been used as impact absorbing device as such, and in case the matrix volume has been subjected to an impact force, causing minor ruptures of the matrix, the attaching of a tape-like device may restore the impact absorbing capacity and resistance to required levels. It so-to-say restores the impact absorbing characteristics of the matrix volume to at least its original level. It is understood that the tape like device may be attached to the matrix volume, so increasing the impact resistance to the matrix volume and improves the impact absorbing capacity of the matrix volume prior to use of the impact beam, e.g. in case the requested impact absorbing capacity is to be increased due to changing legislation, or changing expectancy.
By making a choice in mechanical properties of the elongated metal elements, such as Young's modulus, elongation under specific load, number of elongated metal elements in the tape-like device, specific strength of the used metal alloy, coating type, which coating may influence the adhesion between the elements and polymer matrix, mechanical anchoring, flexibility, such choice may provide an increase of the impacts resistance without being obliged to change the design dimensions of the matrix volume of the impact absorbing device. The interaction of the matrix volume of the impact absorbing device with the elongated metal elements is not to be taken into account during production of the matrix volume.
Additionally, by attaching in a separate step of the production phase a tape-like device to an impact absorbing device, it becomes possible to have impact absorbing devices with complex structures, e.g. with so-called undercuts. As an example, a U-shaped matrix volume of an impact absorbing device can be foreseen from a tape-like device, being attached to the two extremes of the U-shape, so providing a substantially hollow rectangular impact absorbing device. Such devices cannot be made using a single press-molding process step.
The matrix volume may be made of different possible matrices, such as aluminum or out of a polymer matrix, such as thermoplastic polymers e.g. polyolefins, polyamides, polyethylene, polypropylene, polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides and polyether imides, or thermoset polymers such as polyesters. This polymer matrix of the impact absorbing device may further comprise reinforcing material such as glass fibers, C-fibers or any other reinforcing fiber, either man-made fibers or natural fibers, either random or oriented in woven or other sheets. As an example, LFT- and GMT-polymer matrices may be used.
In order to benefit most of the impact improvements due to the presence of the tape-like device comprising elongated metal elements, the elongated metal elements are preferably present substantially parallel to the impact surface of the impact absorbing device.
The impact surface of the impact absorbing is to be understood as the surface of the impact absorbing device, on which impact forces are to apply during use of the device.
Preferably, the shearing strength between the tape-like device and the matrix volume of the impact absorbing device is larger than the cohesion strength of the matrix volume of the impact absorbing device. This to provide the additional advantage that in case the impact absorbing device is subjected to a too high impact load, parts of the matrix volume which would scatter from the impact absorbing device, may still adhere to the tape-like device. Scattering of parts may be avoided to a large extent.
Typical for impact absorbing devices with the shearing strength between the tape-like device and the matrix volume of the impact absorbing device being larger than the cohesion strength of the matrix volume of the impact absorbing device, is the failure system which is noticed when these impact absorbing devices are subjected to a three point bending test.
The impact absorbing device is placed on two supporting points, being rods with radius 30 mm, and the axes of these rods are on an distance of 900 mm from each other. The impact surface of the impact absorbing device is directed away from the supporting rods. A force is execute in the middle of the distance between these two rods, by means of a tubular curved surface with radius 135 mm. The force is executed until failure of the impact absorbing device. The failure system which is noticed in case the shearing strength between the tape-like device and the matrix volume of the impact absorbing device is larger than the cohesion strength of the matrix volume of the impact absorbing device, is that the matrix volume is cracked or broken, causing failure of the impact absorbing device, whereas the attachment of tape like device and matrix volume remains intact.
As at the moment of failure, the shearing strength has not been reached, the tape-like device and the parts of the impact absorbing device will still cohere, resulting in no or fewer parts being scattered. The part integrity will be realized and the scattering of parts will be avoided to a large extent.
In case the shearing strength exceeds the cohesion strength, the tape-like device will not come loose prior to rupture of the impact absorbing device.
Possibly the elongated metal elements are provided by means of a woven fabric, such as e.g. in WO-A1-01/44549, hereby incorporated by reference. It is understood that the elongated metal elements may be present either in warp and/or weft direction. The tape-like product as used in the invention method preferably comprises additional polymer matrix material, which is substantially enveloping the elongated metal elements. This may be obtained in many different ways, e.g. by extrusion of a polymer matrix coating around the elongated metal elements, or by laminating the elongated metal elements between two or more layers of polymer sheet or by a hotdip process, by co-extrusion or pulltrusion.
For the polymer matrix material, all thermoplastic polymers are suitable, as an example polyolefins, polyamides, polyethylene, polypropylene, polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides and polyether imides.
Possibly, the tape-like device additionally comprise glass- or C-fibers, as short fibers, or as uni- or multidirectional woven or nonwoven felt. Such fibers may also be present as short fibers in the polymer matrix material.
Attachment between impact absorbing device and tape-like device may be obtained in many different ways. The tape-like device may be glued to the surface of the impact absorbing device, using e.g. contact glues, hot melt glues, glue-tapes, bi-component glues, epoxy adhesives, poly-functional silanes or any other type of glues. Alternatively, the tape-like device and the matrix volume of the impact absorbing device may be attached to each other by means of ultrasonic or high frequent welding. The tape-like device may be attached to the matrix volume of the impact absorbing device by bolts and nuts or screws, staples, rivets clips or any other means alike.
As an alternative, in case the tape-like device comprises thermoplastic polymer matrix material, attachment can be obtained by first heating the polymer matrix material to partially melt or soften the polymer matrix, and subsequently bringing the partially melted or softened polymer matrix material in contact with the surface of the matrix volume of the impact absorbing device, where the polymer matrix material is cooled to solidify and attached to the surface of the volume matrix of the impact absorbing means.
Preferably some pressure is used during this step.
Alternatively, in case the volume matrix of the impact absorbing device is provided out of material that can be molten, the surface of the matrix volume on which the tape-like device is to be attached, may be subjected to heat in order to melt or soften partially this matrix of the impact absorbing means. Subsequently, the tape-like device is brought into contact with the partially molten or softened matrix of the impact absorbing device. Preferably some pressure is used during this step.
As an example, flame, laser or plasma heating may be used.
Prior to attaching, such as by heating or gluing, the surface of the volume matrix of the impact absorbing device and/or the tape-like device may be roughened to obtain better attachment. This may e.g. be done by mechanical or chemical abrasion, e.g. etching with sulfuric or chromic acids, or e.g. by means of corona or plasma etching.
According to the present invention, elongated metal element may be metal wires or metal cords comprising metal wires.
The metal wires may have a diameter, being a diameter of a radial cross section of the metal elements, which is equal or larger than 100 μm, more preferred larger than 125 μm e.g. more than 150 μm or even more than 175 μm. All possible metal alloys may be used to provide the metal wires. Possibly, oil hardened steel wires are used.
More preferably, metal cord are used in the tape-like device for use in an impact absorbing device. Most preferred are metal cords of a type which can absorb relatively high amounts of impact energy. However also other metal cords may be used.
Examples here are:
multi-strand metal cords e.g. of the m×n type, i.e. metal cords, comprising m strands with each n wires, such as 4×7×0.10 or 3×3×0.18; the last number is the diameter of each wire, expressed in mm.
compact cords, e.g. of the 1×n type, i.e. metal cords comprising n metal wires, n being greater than 8, twisted in only one direction with one single step to a compact cross-section, such as 1×9×0.18 or 1×12×0.18; the last number is the diameter of each wire, expressed in mm.
layered metal cords e.g. of the l+m(+n) type, i.e. metal cords with a core of l wires, surrounded by a layer of m wires, and possibly also surrounded by another layer of n wires, such as 2+4×0.18; the last number is the diameter of each wire, expressed in mm. Other examples are 0.20+18×0.175, 0.365+6×0.35 or 3×0.24+9×0.225.
single strand metal cords e.g. of the 1×m type, i.e. metal cords comprising m metal wires, m ranging from two to six, twisted in one single step, such as 1×4×0.25; the last number is the diameter of each wire, expressed in mm.
open metal cords e.g. of the m+n type, i.e. metal cords with m parallel metal wires surrounded by n metal wires, such as disclosed in U.S. Pat. No. 4,408,444, e.g. a metal cord 2+2×0.25; the last number is the diameter of each wire, expressed in mm.
All cords as described above can be equipped with one or more spiral wrapped wires to increase the mechanical bond of the cords in the polymer matrix of the polymer material being part of the tape-like device, and/or to bundle the n single parallel crimped or non-crimped but plastically deformed wires if the cord is provided using such parallel wires.
Preferably however, the metal cord used in the context of the present invention may be a metal cord with a high elongation at fracture, i.e. an elongation exceeding 4%, e.g. an elongation between 5% and 10%. High elongation metal cord has more capacity to absorb energy.
Such a metal cord is:
either a high-elongation or elongation metal cord (HE-cords), i.e. a multi-strand or single strand metal cord with a high degree of twisting (in case of multi-strand metal cords: the direction of twisting in the strand is equal to the direction of twisting of the strands in the cord: SS or ZZ, this is the so-called Lang's Lay) in order to obtain an elastic cord with the required degree of springy potential;
an example is a 3×7×0.22 High Elongation metal cord with lay lengths 4.5 mm and 8 mm in SS direction;
or a metal cord which has been subjected to a stress-relieving treatment such as disclosed in EP-A1-0 790 349; an example is a 2×0.33+6×0.33 SS cord.
as an alternative or in addition to a high elongation metal cord, the metal cord may be composed of one or more wires which have been plastically deformed so that they are wavy. This wavy nature additionally increases the elongation. An example of a wavy pattern is a helix or a spatial crimp such as disclosed in WO-A1-99/28547.
high impact cords such as e.g. 5×0.38.
With respect to the required properties of the tape-like device, all metal cords may be identical, or alternatively, different metal cords may be used to constitute the tape-like device.
The metal wires used to provide these metal cords may have a diameter, being a diameter of a radial cross section of the metal wires, which is equal or larger than 100 μm, more preferred larger than 125 μm e.g. more than 150 μm or even more than 175 μm. All metal wires of a metal cord may have the same diameter, or the diameters of the metal wires may differ from each other. Preferably, the optical diameter of the metal cord is larger than 200 μm, or even larger than 250 μm, such as larger than 300 μm or more. The optical diameter of the metal cord is to be understood as the diameter of the smallest imaginary circle, encompassing the radial cross section of the metal cord.
Most preferably steel cords are used in the invention. Presently known steel alloys may be used to provide the steel cords. Preferably, the steel cords are subjected to a stress relieving thermal treatment, e.g. by passing the steel cord through a high-frequency or mid-frequency induction coil of a length that is adapted to the speed of the steel cord during production. It was observed that, increasing the temperature to more than 400° C. for a certain period of time, a decrease in tensile strength of the steel cord (a reduction of approximately 10%), but at the same time, an increase of the plastic elongation of the cord before rupture of more than 6% may be obtained. Such steel cords are hereafter referred to as stress relieved steel cords.
Possibly, the elongated metal elements may be coated with a polymer coating layer, such as a layer out of e.g. polyolefin, polyamide, polyethylene, polypropylene, thermoplastic polyester, polycarbonate, polyacetal, polysulfone, polyether ketone, polyimide or polyether imide.
The tape-like device is attached to the impact absorbing device in such a way that the elongated metal elements are substantially parallel to the impact surface of the impact absorbing device.
The term ‘impact surface’ is to be understood as the surface on which impact forces are intended to act when the impact absorbing device is in use.
The tape-like product may be attached to the impact surface. Preferably however, the tape-like product is attached to the surface of the impact absorbing device, opposite to this impact surface. This because in such circumstances, the elongated metal elements will be brought under tension in case impact forces act on the impact surface. In such circumstances, the elongated metal elements will provide the largest increase of impact resistance to the impact absorbing means. In a possible embodiment, the tape is placed at both sides of the impact absorbing device (sandwich structure). The tape can be the same or may comprise another cord composition. This in function of the required properties in the compression and the tensile zone.
Tape-like devices may also be provided at the other surfaces of the impact absorbing device.
In an embodiment, the tape is placed over the total length of the matrix volume of the impact absorbing device. The tape can be fixed on the crash cone, e.g. by means of bolts. In another embodiment the tape can be placed on a part of the length of the volume matrix of the impact absorbing device. This is function from desired requirements and limitation of weight.
An impact absorbing device having increased impact resistance, is characterized by a matrix volume, and a tape-like device which is attached to the matrix volume at an outer surface of the matrix volume.
The matrix volume may be provided out of different materials. The tape-like device is attached to this matrix volume at at least one outer side of the matrix volume, so providing an interface between matrix volume and tape-like device. This interface may comprise a glue which is to attach the matrix volume and the tape-like device. The interface may be characterized by comprising a layer of melted and re-solidified polymer, either resulting from melting and solidifying of the volume of the matrix, or resulting from melting and solidifying of the polymer matrix of the tape-like device.
The impact absorbing device with increased impact resistance may be used for several applications. As an example, vehicle bumper beams or vehicle door beams are impact absorbing devices of which the impact resistance may be increased by the invention method. Alternative uses are e.g. cross-car beams, A-pillars, B-pillars or C-pillars in vehicles.
The invention will now be described into more detail with reference to the accompanying drawings wherein
a and
a shows a cross-section of a prior art impact absorbing device and
As shown in
At the extremities 106 of the U-shape of matrix volume 101, a tape like device 107 comprising metal cords 108 was attached at the locations 109 where both matrix volume 101 and tape-like device 107 meet, so providing an impact absorbing device.
The metal cords 108 used to provide the tape-like device 107 were 3×0.26+9×0.245 steel cords. 89 cords equally spaced one from the other were used to provide a tape having a width, equal to the width of said impact absorbing device 102, being 90 mm. Around these cords, a layer of polypropylene, having a thickness 113 of 2 mm was provided by laminating 2 sheets of polypropylene around the cords. The cords were located substantially in the middle of this thickness 113.
The tape-like device 107 and the matrix volume 101 Of the impact absorbing device 100 were attached to each other by softening the polypropylene of the tape-like device 107, and laminating the tape-like device 107 to the extremities of the legs of the U-shaped matrix volume 101, where tape-like device 107 and matrix volume 101 are to attached.
Alternatively, tape-like device 107 and the matrix volume 101 of the impact absorbing device 100 may be attached to each other by a hot melt adhesive Plastoflex® 9065, applied at the contact zones between tape-like device and impact absorbing device.
As shown in
The failure noticed at the point 331 of the test (curve 303) of the impact absorbing device 100 with tape-like device attached, was a rupture of the GMT of the impact absorbing device. The tape-like device was not loosened from the polymer of the impact absorbing device. The shearing strength between tape-like device and impact absorbing device was found to be higher than the cohesion strength of the GMT.
The impact absorbing device without tape-like device attached (curve 304) fails at a lower deflection and at a lower force applied. Failure is cracking of matrix volume at point 341.
It is clear that the impact absorbing device with tape-like device absorbs substantially more energy (surface between curve and abscissa), as compared to the one without tape-like device., next to the fact that the maximum force which could be withstand by the impact absorbing device is significantly higher as the identical impact absorbing device without tape-like device attached.
As already mentioned, the separate steps of first press-molding the matrix volume and thereafter attaching a reinforced tape-like device, allows a greater freedom in the design of impact absorbing devices and allows to obtain impact absorbing devices with geometries that are not obtainable with a single press-molding step. This is illustrated in
a shows a prior art embodiment. A matrix material 402 already contains a tape 404 reinforced with steel cords 406. The matrix material 402 with the tape 404 is press-molded by means of a molds. Only the upper mold 408 is shown. The upper mold 408 exercises an action in the direction of arrow 410 and thus creates a concave part in the cross-section of this prior art impact absorbing device. This cross-section does not show so-called undercuts. This means that in a direction 412 opposite to the action 410 of the upper mold 408 no cross-sectional material of the impact absorbing device is met.
b, similar to the cross-section of
c illustrates a second type of embodiments according to the invention. Here again, a matrix material 402—with or without reinforcing elements or reinforcing tapes—is press-molded so that a U-type of shape is obtained. Two strips 418′ and 418″ with steel cord or steel wire elements 406 are attached to both legs of the U-form. Unlike the embodiment of
| Number | Date | Country | Kind |
|---|---|---|---|
| 04105472.7 | Nov 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/54908 | 9/29/2005 | WO | 00 | 5/3/2007 |
