BACKG ROUND OF THE I NVENTION

[0001] The present invention relates to a roll form appa ratus and method to form sheet material into an elongated tubula r beam of generally uniform cross section, but where the tubula r beam has latera l deformations forming crush initiators in side walls of the beam to intentiona lly affect longitudi nal impact strength of the beam and to intentiona lly create both a high strength initia l resistance to im pact but also a colla pse that is predicta ble and that i nsures multi ple bending locations for optimal impact energy absorption. The present invention a lso i ncludes crush tubes manufactured by roll forming apparatus, and that are used to mount a bumper reinforcement beam to vehicle side frame ra ils.

[0002] Roll forming a pparatus and processes include forming rolls that are well adapted to form sheets of very high strength material into tubes at relatively high speed and with good dimensiona l consistency. The forming rolls provide opposing rolling contact against the sheet when deforming the sheet. As a result, the forming rolls can be made durable for long service life (i.e. more parts ca n be made prior to wear causing a need for refurbishing the forming rolls). A problem with roll forming is that it is not typica lly used for elongated products having longitudinally non-uniform cross sections, because the longitudina lly non-uniform cross sections would interferingly engage the forming rolls.

[0003] Stamping processes utilize opposing dies that "pound" against each other to form sheet material. A problem is that, when the sheet is high strength, stamping dies tend to wear relatively q uickly, such that they require constant maintenance and refurbishing.

[0004] Crush tubes are often used to mount bumper reinforcement beams to vehicle frame rails. The crush tubes extend longitudinally of the vehicle, and m ust be sufficiently strong to support a bumper beam, but preferably incl ude crush initiators so that the tubes colla pse predicta bly a nd consistently during a vehicle impact in a longitudi nal direction in a multi-point crumpling ma nner providing a maximum amount of energy absorption. Sometimes, crush tubes are made of higher strength materia ls to allow thinner wa lls for reduced weight. However, higher strength and thinner materials have an even greater need for crush initiators to prevent pre-mature catastrophic colla pse and to facilitate multi-point crumpling for good energy absorption. [0005] Historically, crush tubes are stamped components, such as two-piece clam shell designs welded together, since this a llows consistent placement and formation of crush initiators in side walls of the crush tubes, and allows a high degree of design freedom. For example, see Hirano U.S. Patent No. 4,272,114 (Fig. 13). Historically, crush tubes are not roll formed, since the existence of crush initiators require a manufacturing process capable of making non-uniform cross sections. Heatherington U.S. Patent No. 7,617,916 does disclose a crush tube that is initially roll formed with longitudinal channels and then finally formed in a secondary operation by expanding portions of the channels. However, the tube in Heatherington requires substantial secondary processing to expand the roll formed tube, with the secondary processing requiring considerable cycle time and also placing stress on any welded a reas during expansion.

[0006] A roll form apparatus and method of making crush tubes is desired, and also a roll formed crush tube is desired that is capable of being made on a roll form apparatus and method, where the process is simple, reliable, and does not require substantial secondary processes, and further where the crush tube minimizes weight and cost of manufacture, including minima l secondary processing.

BRIEF SUMMARY OF THE INVENTION

[0007] In one aspect of the present invention, a roll form apparatus comprises an

unroller device for unrolling an elongated sheet of material from a roll of the material, an embossing device for embossing a series of crush initiating embossments into the sheet, and a roll former with rolls configured to deform the sheet into a continuous tubular beam defined by walls, each wall defining a plane with some of the embossments extending from the plane in at least one of the walls, the walls being joined by corners with the embossments spaced from the corners. The apparatus further includes a welder welding abutting edges of the sheet together to fix the tubular beam, with the abutting edges being located inboard of an adjacent one of the corners but outboard of an outboard edge of adjacent ones of the embossments, and a cutoff device for cutting the continuous tubular beam into beam segments with the beam segments being

substantially finally formed as crush initiator tubes. [0008] In a narrower form, the apparatus includes a slitter to trim edges of the sheet prior to roll forming in orde r to eliminate distortion of the edges from the embossing device.

[0009] In a narrower form, the cutoff device i ncl udes a cutoff blade that cuts one end of the beam segments at an a ngle different than 90 degrees to a longitudina l length of the tubular beam .

[0010] In another aspect of the present invention, a method includes unrolling an

elongated sheet of material from a roll of the material; embossing a series of crush initiating embossments into the sheet; roll forming to form the sheet into a continuous tubular beam defined by walls, each wa ll defining a plane with some of the embossments extending from the pla ne i n at least one of the walls, the wa lls being joined by corners with the embossments spaced from the corners; welding abutting edges of the sheet together to fix the tubula r beam, with the abutting edges being located inboa rd of an adjacent one of the corners but outboa rd of an outboard edge of adjacent ones of the embossments; a nd cutting the contin uous tubular beam into beam segments, with the bea m segments being substa ntia lly fina lly formed as crush initiator tubes.

[0011] In a narrower form, the method includes a step of slitting edges of the sheet after embossing a nd prior to roll forming in order to eliminate distortion of the edges from the embossing step.

[0012] In a nother aspect of the present invention, a roll form apparatus includes an embossing device for embossing a series of crush initiators into the sheet, a roll former with rolls configured to deform the sheet into a continuous tubular beam defined by wa lls, the wa lls being joined by corners with the crush initiators spaced from the corners, the rolls being configured to avoid contact with portions of the sheet having the crush initiators placed therein, a welder welding edges of the sheet together at a location inboa rd of the corners but outboa rd of an outboa rd edge of adjacent ones of the crush initiators, and a cutoff device for cutting the continuous tubular beam into crush tubes.

[0013] In a nother aspect of the present invention, a crush tube product made by a roll form process comprises a sheet having opposing edges that is deformed to have embossed crush initiators and that is roll formed into a tubular shape and cut to length for use as a crush tu be for mounting a bumpe r beam on a vehicle front end. The crush initiators are formed perpendicula rly into the sheet inboa rd of the opposing edges, and the elongated tubular shape has a longitudina l centerline caused by roll forming the sheet so that the opposi ng edges abut, with the tubula r shape having a constant cross section except for the crush initiators, the constant cross section having side walls defining corners. A weld secures the opposing edges together to fix the elongated tubular sha pe, with some of the crush i nitiators being between the weld line and a n adjacent one of the corners. A section of the e longated tubular shape is cut into a desired length to thus form a crush tube configu red to support a bumper beam on a vehicle frame and configured to longitudina lly crush with a predicta ble force/deflection curve when impacted parallel the longitudinal centerline.

[0014] These and other features, adva ntages, a nd objects of the present invention will be further understood and a ppreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

BRI EF DESCRI PTI ON OF TH E DRAWINGS

[0015] Fig. 1 is a perspective view of a vehicle frame with crush tubes mounting a

bumper reinforcement beam to the vehicle frame rail tips, the crush tubes being roll formed a nd including embossed crush initiators on side walls.

[0016] Fig. 1A is a perspective view of the roll formed beam in Fig. 1A, including showing a beam segment cut from the end of the beam to form the crush tube of Fig. 1 a nd a lso showing dashed lines representing a second bea m segment ready to be cut.

[0017] Fig. IB is a fragmenta ry perspective view of the roll formed continuous beam after the welder in Fig. 1A.

[0018] Figs. 1C and ID are cross sections taken at locations 1C and ID in Fig. 1A.

[0019] Fig. 2 is an enlarged perspective view of the crush tube in Fig. 1.

[0020] Figs. 3-5 are perspective views of modified crush tubes similar to Fig. 2.

[0021] Fig. 6 is a perspective view of a bumpe r reinforcement beam mounted by crush tubes to vehicle frame rail tips.

[0022] Figs. 7-8 are front and rear perspective views of the crush tubes in Fig. 6.

[0023] Fig. 9 is a schematic top view of a bumper system not unlike Fig. 6, including a bumper reinforcement beam mou nted by crush tubes to vehicle frame rail tips.

[0024] Fig. 10 is a schematic top view of the roll formed tubular continuous beam in Fig.

1A, with angled cutting pla nes overlaid on the continuous beam to show how adjacent portions of the continuous beam a re cut to form similar but "180-degree flipped" crush tubes.

[0025] Fig. 11 is a perspective view of a crush tube having a partial internal leg

supporting sidewalls of the crush tube.

[0026] Fig. 12 is a graph showing a force-deflection curve for the crush tube shown in Fig.

11.

[0027] Figs. 13 and 14 are perspective and cross sectional views of a modified crush tube.

DETAILED DESCRIPTION

[0028] A bumper system 10 (Fig. 1) includes a frame with side rails 11 (sometimes called or including "frame rail tips"), a high-strength swept tubula r bumper reinforcement beam 12, and two crush tubes 41 supporting the beam 12 on the side rails 11. The bumper system 10 is typically covered by a colored fascia (not specifically shown) for aesthetics.

[0029] An apparatus 20 (Fig. 1A) com prises an uncoiling device 21 for unrolling an

elongated sheet 22 of coiled material, an embossing device 23 (e.g. reciprocating stamping device with dies, or forming rolls with mating protrusions and recesses) for repeatedly embossing a series of crush initiating embossments 24 into the sheet, optionally a slitter 23A (at a downstream end of the embossing device 23) for trimming sheet edges back to a straight line (which is needed when the sheet's edges are distorted, i.e. "sucked in", when forming the embossments into the sheet), trimming edges of the unrolled sheet that are a nd a roll former 25 with stations having opposing forming rolls 26 configured to deform the sheet into a continuous tubular beam 27 (Fig. IB) with walls 28-31 each including some of the embossments, with the rolls 26 being configured to clear the embossments 24 but accurately form corners 32 joining the walls.

[0030] The appa ratus 20 (Fig. 1A) further includes a welder 33 with welding tip 33A

welding a weld bead 34 to bond a ligned abutting edges 35-36 of the sheet together to fix a cross section of the tubular beam 27. It is noted that a welding tip 33A is illustrated, but it is contemplated that any type welding can be used, including an induction welding process or laser welding process (neither of which use a weld tip per se). The abutting edges 35-36 are coplanar and located inboa rd of an adjacent one of the corners 32 but outboard of an outboa rd edge of adjacent ones of the embossments 24, and a cutoff device 37 is positioned for cutting the continuous tubular beam 27 into beam segments 38 as it exits the roll form apparatus. Notably, the slitter is used when the edges are so distorted by the embossments that the edges don't abut properly unless the edges are re-trimmed. A wa ll-trimming device 39 is provided in a secondary operation, and is configured to form a longitudinally-extending flange 40 on an end of the segment 38 to finally form the crush tube 41. Notably, the embossments 24 can be any shape and depth. The cross section of the illustrated crush tube 41 is orthogonal (i.e square or rectangular), and the embossments 24 a ll extend inward of the tubes.

[0031] The illustrated welder 33 (Fig. 1A) includes internal and external mandrels 42-43

(Fig. ID) that support a cross sectional shape of the beam 27, holding the abutting aligned edges together in a coplanar condition during the welding process. It is noted that the weld is offset from a centerline of the beam 27 so that the welding line avoids the crush initiator embossments 24. Further, the internal mandrels 42 (anchored upstream by a cable 42A secured at anchor 42B) include channels and/or clear-outs (see Fig 1C) so that they do not interferingly engage and reform the embossments 24.

Notably, the edges 35-36 are preferably a butting and coplanar in order to avoid a double- thickness wall portion, which double-thickness wall portion may unacceptably cause a strong corner to the crush tube 41.

[0032] As noted above, the crush tube 41 (Fig. 2) includes four walls 28-31 connected by radiused corners 32. The illustrated walls 28 and 30 are slightly longer in width than walls

29 and 31, such that the crush tube 41 forms a rectangular shell shape. The wa lls 28 and

30 each include two crush initiating embossments 24 that are elongated in a longitudinal direction to be about twice as long as wide. The flanges 40 extend coplanar from walls 28 and 30. The walls 29 and 31 each include three crush initiating embossments 24 that are elongated in a lateral direction to be a bout three times as long as wide. A preferred depth of the illustrated embossments 24 is about 1-3 times a thickness of the material forming the walls 28-31, though it is contemplated that the depth can be more or less deep. The weld bead 34 is located outboard of an adjacent embossment 24, but is located on a flat portion of the wall (i.e. offset from the radiused corner).

[0033] It is contemplated that the material used for the crush tube can be a variety of different thicknesses and material strengths, depending on the functional requirements of a particular application. For example, the illustrated material of crush tube 41 can be

1.0-3.0mm thick, or more preferably about 1.2-1.6mm thick. The material is preferably steel having a tensile strength of at least about 50 KSI, or higher tensile strengths of 120 KSI or higher. The em bossments 24 are a ll illustrated as extending inward, but it is contemplated that some or all of them could be designed as extending outward, as shown in Fig. 4, and that they can be different shapes, as shown in Fig. 5.

[0034] Figs. 3-14 are perspective views of modified crush tubes similar to Fig. 2. Similar features, characteristics and aspects are identified using the same numbers, but adding a letter "A" or "B" or etc. This is done to reduce redundant discussion.

[0035] Fig. 3 illustrates a crush tube 41A similar to crush tube 41, but crush tube 41A has

45 degree "flat/angled" corners 32A (rather than fully radiused corners 32 as in crush tube 41). Further, the embossments 24A in crush tube 41A all are elongated laterally, three embossments 24A being on each side wall 28A-31A. Also, flanges (40) are eliminated, with both ends being perpendicularly trimmed. Also, a cross section of the crush tube 41A is modified to match a corresponding shape of the mating frame rail tip on the vehicle. It is contemplated that one of the ends can be trimmed at an angle to fully engage a swept reinforcement beam (see Fig. 1).

[0036] Fig. 4 illustrates a crush tube 41B that is similar to crush tube 41, but crush tube

41B only includes embossments 24B on two opposing side walls 29B and 31B, and does not include any embossments on the other side walls 29B and 31B. Crush tube 41B does include flanges 40B.

[0037] Fig. 5 illustrates a crush tube 41C that is similar to crush tube 41B, but the

embossments 24C are shaped to form non-uniform channels. For example, two embossments 24C are illustrated, one being a T-like shape, and one being an X-like shape.

[0038] Fig. 6 is a perspective view of a bumper reinforcement beam 12E mounted by crush tubes 41E to brackets on the vehicle frame rail tips HE. A lower pedestrian impact bar 14 mounts to brackets 15 extending vertically from the beam 12E. Figs. 7-8 are front and rear perspective views of the crush tubes 41E. Notably, a rear end of the crush tubes 41E is cut square (i.e. at 90 degrees to a length of the crush tube), but the front end is cut at an angle to the length of the crush tube (so that walls 29E and 31 E stablyl abut a rear surface of a longitudinally swept beam 12E). (See Fig. 6 and also Figs. 9-10.) Also, one or both of the ends of the crush tubes 41E are cut to include features that locate and orient the crush tube 41E on the bumper beam 12E and/or on the frame rail tip, and that facilitate fastener attachment or welding. As illustrated in Fig. 10, by cutting the continuous roll formed beam first with a square cut and then with an angled cut, successive beam segments cut to a final shape of the crush tubes 41E with less wasted material, since a "long side" (Dl) of successive beam segments alternates between high and low positions on the continuous beam.

[0039] Fig. 11 is a perspective view of a crush tube 41F having a partial-length internal leg 49F supporting sidewalls of the crush tube. It is noted that the internal leg 49F only extends a short distance longitudinally, such that it does not add significant weight to the crush tube 41F. Each end of the internal leg 49F has a flange 49F' that is secured to the opposing walls of the crush tube. The flanges 49F' of the internal leg 49F can be attached by welding, adhesive, or other means. By making the internal leg 49F from a relatively narrow strip, it helps minimize weight. At the same time, the internal leg 49F provides stability to the side walls, even when the internal leg is a relatively thin material, such as only 1.0mm thick or less, and when the leg 49F has only a limited width, such as only 2- 4mm width. Also, the channel 24F' is formed in each wall 28F-31F, and replaces the stamped embossments (24).

[0040] Fig. 12 is a graph showing a force-deflection curve for the crush tube shown in Fig.

11. The graph illustrates that the present roll formed crush tube 41F provides surprisingly good strength and energy absorption during a length of its crush stroke along an impact longitudinally aligned with a centerline of the crush tube 41F and into the frame rail to which it is attached.

[0041] Figs. 13 and 14 are perspective and cross sectional views of a modified crush tube

41G. The crush tube 41G includes an internal leg 49G similar to Fig. 11, but in Figs. 13-14, the interna l leg 49G extends a length of the crush tube 41G. This allows the crush tube

41G to be made from a single sheet of material, as shown in Fig. 14. Edges of the sheet are folded into abutting contact and welded to other parts of the sheet to form two tubes, with the internal leg forming a common center leg. It is contemplated that the single sheet for forming the crush tube 41G can include adjacent strips (welded together prior to roll forming) of different material properties and different thicknesses. For example, the partial strip of material in the original sheet that ends up forming the internal leg could be a m uch thinner and/or weaker and/or cheaper material than the remaining portions of the sheet forming the two tubes. This arrangement allows crush tubes to be made in a roll former while minimizing secondary processing, and optimizing material location and weight, yet without making a center of the crush tube 41G being undesirably strong (i.e. and hence wasting material and leading to excess weight).

[0042] It is believed to be surprising and unexpected to produce a bumper crush tube by roll forming without substantial additional secondary processing, since roll forming tends to produce a beam of constant cross section. Yet the present crush tube product is made by a roll form process without substantial secondary processing. Specifically, a sheet having opposing edges is deformed to have embossed crush initiators and is then roll formed into a tubular shape and cut to length for use as a crush tube for mounting a bumper beam on a vehicle front end. The crush initiators are formed perpendicularly into the sheet inboard of the opposing edges, and the elongated tubular shape has a longitudinal centerline caused by roll forming the sheet so that the opposing edges abut, with the tubular shape having a constant cross section except for the crush initiators, the constant cross section having side walls defining corners. A weld secures the opposing edges together to fix the elongated tubular shape, with some of the crush initiators being between the weld line and an adjacent one of the corners. A section of the elongated tubular shape is cut into a desired length to thus form a crush tube configured to support a bumper beam on a vehicle frame and configured to longitudinally crush with a predictable force/deflection curve when impacted parallel the longitudinal centerline.

[0043] It is to be understood that variations and modifications can be made on the

aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.