Tailored tubes are made from tubes with different properties, wall thickness and/or different diameter. in a similar manner as tailored blanks, in which two blanks of different thickness and properties are welded together. The current state of tailored tube technology is to use at least two different tubes with the desired properties and sizes which are butt welded together along the orbital seam as shown in Figure I. For example, a substantially thicker tube can be used at the location of a bend or joint and the thinner tubing welded to each end. This allows the heavier and more expensive tubing to be utilized at the point of greater stress (particularly non-axial loading), and the less expensive and lighter tubing to be used elsewhere, reducing both the cost and weight of the structure. Another approach is to put a sleeve around the tube where reinforcement is needed and which is welded to the main tube as shown in figure 2. This similarly adds material only to the areas where reinforcement is required. These straightforward approaches are relatively simple methods for tailoring the properties of the finished part. but they also require processes which can deliver precise edge quality and tight tolerances in creating the reinforcing pieces to accomplish high-quahty welds. For example, the butt welding of tubes of various diameters requires Hxturing and space to precisely position. clamp and rotate the tubing. Also. typically a bulky structure is required for supporting a precision driven laser. as well as sufficient room to load and unload the tubing, and room for any additional processing. Plant space has become an increasing portion of the overhead cost involved in manufacturing, as efficiency in manufacturing processes has improved : thus, it is preferred to reduce or eliminate such space-consuming operations wherever possible. Further, the equipment to perform the necessary orbital welding is expensive and the process is relatively time consuming. Further still. subsequent forming tvpicallv requires smoothing of the edges formed by the reinforcing material, which often causes problems due to the abrupt or step-like change of wall thickness at the joint or slceve. This discontinuity acts as a stress riser and impacts the material flow during forming and thus requires special dies and forming technologies. Further still, the material around the seam, in the heat-affected zone. typically displays a hardness different from the remaining bulk tube material, which also has a negative impact on the formability of the reinforced area.

The reinforcing material used in the present invention is a metal foam which has recently become commercially available in various shapes, based on a powder metallurgy process developed and patented by the Assignee of this invention. Typical automotive uses of these metal foams are to insulate and stiffen automotive panels. such as the front firewall. the rear luggage compartment panel, and floor panels. These foams are also used currently for weight reduction and increased stiffening in some convertible bodies. Metal foams are typically used to greatest advantage when used in combination with other materials of construction. For example. it has been demonstrated that aluminum foam sandwich panels used as firewalls can provide 8 times the torsional stiffness of a conventional stamped steel part with a 50% reduction in weight.

The unique compression behavior of aluminum metal foams - in which the foams absorbed high amounts of deformation energy at nearly constant and low mechanical stresses-makes them very attractive material to absorb crush energy to improve vehicle crashworthiness. Because of the high amount of controlled porosity, metal foams are not generally used as stand-alone materials in components requiring high tensile strengths.

SUMMARY OF THE INVENTION The present invention relates to a new structurally reinforced tubing and a method of making same. The invention is cost effective and structurally superior as it allows for tubing to be easily reinforced, thus reducing or eliminating the need for multiple sizes of tubing. expensive manufacturing floor space. and time consuming processing.

The invention involves incorporating a metal foam insert within the tubing at critical loading areas where structural reinforcement is desired. In one embodiment, the metal foam is activated inside the hollow tube. causing the metal foam to expand in volume and thus fill the interior of the tube. This provides substantial stiffening, which mav be particularly necessary in areas such as bends in the tubing or at joints which result in non-axial, torsional. or bending loading of the tubing. In another embodiment to produce ready-to-use custom tubing, the metal foam can be activated inside a shaped tool cavity to form a molded foam insert. which is subsequently inserted into the tubing.

This new method of reinforcing structural tubing takes advantage of the newly emerging lightweight metal foam materials technology. All sections requiring higher stiffness. increased damping, increased torsional strength, increased bending strength or increased crashworthiness can be internally reinforced using metal foam. Further. the resultant reinforced tubing is lightweight and has an aesthetically pleasing uniform outer diameter.

This innovative technology does not have the aforementioned drawbacks of the state-of- the art and combines tailoring of the mechanical properties of the finished part with easy lormability, uniform exterior profile and low production costs.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 1 illustrate tailored tubes made according to the known art. showing tubes with different wall thickness butt welded together.

Figure 2 shows another tailored tube according to the known art. having a reinforcing sleeve around a base tube.

Figure 3 shows a tube according to the claimed invention with metal foam precursor inserts.

Figure 4 shows the tube of Figure 3 inserted after tacking and forming of the tube.

Figure 5 shows the tube of Figure 4 after the metal foam is activated.

DETAILED DESCRIPTION OF TIIE PREFERRED EMBODIMENT The present invention allows the use of a single tube for shaping into a finished part that is locallv reinforced to meet the varying structural requirements of the finished part. A typical tube reinforced with metal foam in specific sections according to the present invention is shown in Figures')-5. illustrating the placement of the foam preform, the forming of the tube and the activation of the foam to fill a section of the tube.

The two essential steps of the present invention are to position a foam"preform"12 at a desired position within the tube 14. and to activate the preform to fill the tube and thus reinforce the desired area. To allow for reinforcement of tubes or hollow shapes of varying cross-sectional geometry, a metal foam precursor is inserted in the tubing before activation and before the tubing is formed into its desired structural shape (see Fig. 4). This allows the tubing with inserted metal preform to be formed with conventional methods, such as bending or hydroforming. After the tubing has been formed into the desired geometry, the foam can be activated. typically by temperature. Upon thermal activation, the metal foam preform typically expands by a factor of about 400% in volume to I III the tube interior.

The foam preforms can be cut to size to allow proper filling of the tubular section for achieving the designed stiffness, the stiffness to be achieved will be designed by tailoring the material, the mechanical properties and the amount of metal foam put into the specific section.

Metal foam is commercially available in a wide variety of different materials and characteristics.

Aluminum foams can be produced in essentially any alloy composition or commercial grade for which metal powders are available. For example, aluminum foams have been produced from Al- Si. AI-Mg. AI-Cu. AA606I. AA506. and AA7093 alloys, among other. Foams can be fabricated to have porosity levels over the broad range 40-90 vol% porosity. Cell sizes typically vary over the range of 1 to 10 mm. A widely used metal foam alloy is Al-Si which metallurgically bonds to the inner surface of AA6061 tubes during Other foams in aluminum, steel, zinc, and other alloys are also available. It is contemplated that other foam compositions, such as aluminum alloys. steels. ceramic particle-reinforced aluminum metal matrix composites, copper alloys, zinc allovs. titanium, intermetallics. could also be utilized as the foaming reinforcement.

The foamable precursor is produced in extruded lengths containing a foaming agent that is activated by heating to elevated temperature. The precursor preforms can be extruded in various cross-sectional shapes and sizes for the specific component design. For example, the preform can be tapered to increase the amount of material toward the center of the tube or could be curved to better fit within the tube.

The preforms are sold in sheets of desired thickness which can be cut to size depending on the expansion characteristics of the foam used and the size tube filled. These foam preform pieces are inserted into the tube and tacked into position. From the outside of the tube using high power laser beams (as shown in Figure ure 4). Another preferred approach for positioning the foam preform is to set the preform in place upon the flat tube blank prior to forming the blank into a tube. In this case the inserts would be placed and tacked into position before the tube is closed by rollers and sealed by longitudinal welding, typically by means of a laser beam. This allows very cost-effective production due to minimized part handling effort and verv high production rates of the tube manufacturing process. The preform can also be positioned with a spot weld or adhesive or any other known positioning means. It should be appreciated that the tacking operation is not a precision process. as the tacking need only be sufficient to hold the foam preform pieces in place during the tube forming, shipment and assembly. The tacking is not a structural bond and need not be precisely located, and could also be performed by brazing. soldering or adhesive bonding.

After the preform or preforms have been fixed in position, the tube can be formed or bent into the desired structural shape through any of the various know industrial methods, such as a <BR> <BR> <BR> <BR> <BR> <BR> conventional hydroforming process. Plastic or composite tubing can be formed utilizing known heating and bending processes. To assure that the material How of me tube during forming is not at all impacted by the inserted preform. the volume of individual foam preforms is preferably kept relatively small and the tacking is located toward the center of the preform to minimize stress on or exerted bv the preform. Thus. it is preferred to use multiple small preforms that each fill only a fraction of the cross-sectional area or a fraction of the intended length of reinforcement at any point. rather than one large preform. Once activated, the metal foam generated from these multiple preforms will bond into an homogenous foam reinforcement. Further, tacking performed toward the center of the preform will allow the ends of the preform to separate from the tube as the tube is bent. Further still. it should be appreciated that the preforms are preferably affixed to the portion of the tubing that will form the inner radius of a bend or curve as shown in Figure 4 to enable this separation as opposed to the deformation that would occur to the preform.

Another approach is to have extruded preforms of a tapered or keystone shape which would allow for tube bending without effecting the preform. Since the outer surface of the tube is smooth. no special dies or technologies need to be developed for the hydroforming process.

In order to position the preform of foamable precursor material in existing tubing, it is anticipated that any type of pusher rod or sufficiently stiffened wire wouid suffice, with the distance the preform is to be inserted to be measured on the pusher rod or wire. A disk of circumference slightly less than the inner diameter of the tube can be included at the end of the pusher rod or wire to facilitate insertion. In this type of application, the preform can be attached to one or more soft foam disks of circumference slightly greater than the inner diameter of the tubing, which creates an interference fit within the tubing sufficient to hold the preform in place until the preform is activated. but which allows easy insertion and movement of the preform within the tube. These soft foam disks would merely effect the necessary temporary positioning of the preform and would have no structura) effect.

Another method of positioning the foam precursor is to tack the foam inserts into a position prior to roll forming of the tube. In this case the inserts would be placed and tacked into position before the tube is closed by the rotters and scaled by longitudinal welding. typically by means of a laser beam. This attows very cost-effective production due to minimized part handling effort and very high production rates of the tube manufacturing process.

After the tube with the foam precursor inserts has undergone forming (such as hydroforming) the tube will be heated at an elevated temperature (of about 650-700 degrees Celsius for aluminum foam) with a laser or other means to cause the foam inserts to expand and to fill the tube in a section where it is needed. The foam can also be activated with microwaves. chemically or through other activation means known in the art. The composition. density. cell size, and resulting mechanical properties of foam material utilized in the tailored tubes determine the final mechanical properties of the finished component in the sections of the shape. It is anticipated that this process can be used for tubing of various materials. such as steels, aluminum alloys, aluminum metal matrix composites, high temperature superalloys. titanium. and copper alloys. Of course. there is an advantage to choose a foam that will bond to the tubing interior. which will significantly improve the strength and stiffness of the tubing at the reinforcement, and thus the preferred choice of metal foam will vary with the type of tubing materials. increase this bonding, it is preferred with certain tubing to pre-treat the tube interior as is known in the art.

It may be preferable in certain applications to provide metal foam reinforcing inserts activated prior to insertion. Due to the stiffness of the activated foam. this approach is generally limited to linear tubing segments. However, if it is desired to reinforce joints such as"T" sections, or to reinforce a tube before forming a bend. and the activation step is preferably eliminated. an activated"slug"of metal foam can be inserted to the structural tube. This slug can be manufactured by placing the desired amount offoamable preform materiai into a iliold having an inner diameter the same as the specified tubing and activating the foam. Although the foam reinforcement will not bond with the tubing when inserted, due to the tight tolerances possible with the foam. any deformation of the tube under loading (or forming) will clamp the slug in place. It is also contemplated that a second activation could be achieved once the slug is in place, whether by completing an incomplete reaction from the molding phase or by performing a second independent reaction utilizing a secondary foaming agent.

The resulting reinforced tubing can be used in a variety of structural applications. For custom structures. the tubing can be delivered in straight pieces of stock lengths with one or more preforms unactivated. so that the customer can form the desired shape and activate the necessary preforms to reinforce joints or bends and cut the tubes to length.

As can be appreciated from the disclosure, there is a wide variety of anticipated applications and embodiments of the present invention.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which the invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.