Patent Application
20050160783
The present invention relates generally to forming a shaped tubular member and, more particularly, to a method of making pre-formed tubular members for hydroformed metal tubing used in assembling automotive structures.
It is known to hydroform tubular components. Hydroformed tubular components are becoming increasingly popular in automotive body structural applications. Moreover, curved hydroformed tubular components are used for some of these applications. In general, curved hydroformed tubular components require bent pre-forms before going to the final hydroforming dies for final part shapes. To make good final parts, usually good bent pre-forms are required, which are free of splits or deep wrinkles.
Conventional methods for bending a tube usually employ rotary draw bending machines with a set of bend dies, a mandrel, and other tools. The bent tubes from those bending machines usually have circular cross-sections along the whole length and free of split and deep wrinkles.
Using this traditional practice, there are some limitations regarding a ratio between bend radius (R) and tube diameter (D) of the tube to be acceptable for subsequent hydroforming operation (R/D>2). For lower ductility materials such as high-strength steel and aluminum, the ratio should be larger. In some applications, this limitation on using larger bend radius could restrict some hydroform applications that require tight-bend design features or using alternative light-weight materials.
Another potential problem with a bent tube is wrinkle on its compressive surface, especially for thin gage tube or tightly bent tube. Some of these wrinkles could be flattened out by high pressure used in the hydroforming process, but not for somewhat deep wrinkles. The common practice is to use a wrinkle-free pre-form to ensure successful subsequent hydroforming operation.
As a result, it is desirable to provide a method of making curved hydroformed tubular members. It is also desirable to provide a method of pre-forming tubular members that improves hydroforming formability for a wider range of hydroforming applications. It is further desirable to provide a method of pre-forming tubular members that minimizes thinning and avoids splitting during a bending process. Therefore, there is a need in the art to provide a method of making pre-formed tubular members that meets these desires.
It is, therefore, one object of the present invention to provide a new method of making pre-formed tubular members.
It is another object of the present invention to provide a method of making bent pre-formed tubular members.
To achieve the foregoing objects, the present invention is a method of making a pre-formed tubular member. The method includes the steps of providing a tubular member extending longitudinally and providing a set of bending tools having a mandrel with at least one ball and a bending die. The method also includes the steps of positioning the at least one ball inside of the tubular member. The method further includes the steps of bending the tubular member about the bend die to form a bent pre-formed tubular member having at least one curved portion having a recess therein.
In addition, the present invention is a method of making a curved hydroformed tubular member. The method includes the steps of positioning a bent pre-formed tubular member having at least one curved portion with a recess therein between open die halves mating with one another to define a tubular cavity portion. The method also includes the steps of progressively closing the die halves to progressively deform the bent pre-formed tubular member within the tubular cavity portion. The method includes the steps of applying hydraulic pressure to expand and conform the bent pre-formed tubular member to the tubular cavity portion to form a curved hydroformed tubular member. The method further includes the steps of separating the die halves and removing the curved hydroformed tubular member from the die.
One advantage of the present invention is that a method of making curved hydroformed tubular members is provided for a vehicle. Another advantage of the present invention is that a method of making bent pre-formed tubular members is provided to hydroform curved tubular members to assemble hydroframe structures. Yet another advantage of the present invention is that the method improves hydroforming formability of light-weight materials such as high-strength steel and aluminum. Still another advantage of the present invention is that the method further expands the hydroforming process to tightly-bent parts (R/D<1.5) such as some suspension components for a vehicle. A further advantage of the present invention is that the method improves hydroformed part quality by ensuring more uniform straining. Yet a further advantage of the present invention is that the method is less expensive than conventional deep drawing processes.
Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.
Referring to the drawings and in particular
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The bending assembly 28 also includes at least one, preferably a plurality of, more preferably a first, second, and third ball 32, 34, and 36, respectively, connected to the mandrel 30. The first, second, and third balls 32, 34, and 26 are generally cylindrical in shape with a generally kidney cross-sectional shape similar to the mandrel 30 and have a cross-section less than a cross-section of the mandrel 30 as illustrated in
The bending assembly 28 further includes a bend die 44 as illustrated in
The method includes the step of positioning the balls 32, 34, and 36 and mandrel 30 inside or in the interior 26 of the tubular member 24 and positioning the tubular member 24 adjacent the bend die 44. The method includes the step of bending the tubular member 24 to form the bent pre-formed tubular member 16. The mandrel 30 is moved relative to the bend die 44 by the actuator 54 to bend the tubular member 24 around the bend die 44 to form the curved portion 20. As the tubular member 24 is bent on the bend die 44, the balls 32, 34, and 36 cause a wall of the tubular member 24 to cave in or collapse to form the caved in portion 22. Due to the different height between the second and third balls 34 and 36, an indented portion 52 is formed opposite the caved in portion 22 in the bent pre-formed tubular member 16. It should be appreciated that the method allows the tensile surface of the tubular member 24 to “cave in” as much as required to reduce “tensile strains” to minimize thinning and avoid splitting during the bending process. It should also be appreciated that, to avoid deep wrinkles on the compressive surface, the method requires the profile of the mandrel 30 illustrated in
A method, according to the present invention, of making the curved hydroformed tubular member 10 is disclosed. The method includes the step of hydroforming the bent pre-formed tubular member 16 to form the curved hydroformed tubular member 10. The bent pre-formed tubular member 16 is placed in a die set comprised of an upper die half (not shown) and a lower die half (not shown). The upper die half includes a tubular forming cavity portion. Likewise, the lower die half includes a tubular forming cavity portion.
The ends of the bent pre-formed tubular member 16 are sealed and hydraulic fluid is pumped into the bent pre-formed tubular member 16 under pressure. The upper die half and lower die half are progressively closed so that the bent pre-formed tubular member 16 is progressively deformed and the pressurized fluid captured therein expands the walls of the bent pre-formed tubular member 16 into the cavity portions of the die.
The die halves are fully closed upon one another with the bent pre-formed tubular member 16 being tightly clamped between the die halves. During this closing of the die halves, a relatively constant hydraulic pressure may be maintained within the bent pre-formed tubular member 16 by incorporating a pressure relief valve (not shown) into the seal enclosing the ends of the bent pre-formed tubular member 16 so that hydraulic fluid may be forced from the bent pre-formed tubular member 16 as it collapses.
Once the die is closed, the bent-pre-formed tubular member 16 is then expanded to a final cross-sectional profile by increasing the hydraulic pressure sufficient to exceed the yield limit of the bent pre-formed tubular member 16 so that the bent pre-formed tubular member 16 is forced into conformity with the tubular forming cavity portions of the die halves. The die halves 26 are then opened to permit removal of the finished or curved hydroformed tubular member 10 from the die halves. The curved hydroformed tubular member 10 may be assembled into a vehicle body (not shown) or some other desired vehicle component. It should be appreciated that, because of the reduced strains from the bending process in the bent pre-formed tubular member 16, there is much ductility of the material left for the hydroforming process to use and thus a greater range of curved hydroformed components can be produced.
The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.
Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.
