Apparatus and method for the noncircular bending of tubes

A tube bending apparatus adapted for the noncircular bending of a tube includes a modified bend die, a modified wiper die, a translatable and pivotable element and an actuator. The bend die presents a noncircular bending profile having a linearly or nonlinearly increasing radius of curvature. The wiper die is configured to accommodate the maximum radius presented by the profile, and the element and actuator present an inclined rack and pinion configuration. The bend die presents an involute of a circle having a radius equal to the product of the radius of the pinion and the sine of the angle of inclination, so that the bend die engages the tube at a fixed point in space during bending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tube bending apparatuses, and more particularly to an improved die and tube bending apparatus configured to produce noncircular bends in tubes.

2. Discussion of Prior Art

Conventional tube-bending apparatuses primarily employ compression, press and rotary draw methods to bend tubes along circular arcs. These apparatuses and methods are commonly utilized in various industries, including automobile and aircraft assembly, plumbing and fire protection, and equipment/conduit manufacture. These apparatuses typically include a set of dies and a drive mechanism that cooperate to impart pressure upon the tube, so that the tube bends to a predetermined form. More particularly, a bend die is positioned adjacent to a section of the tube and the apparatus is configured to conform the section to the circular profile defined by the bend die. The engaging surface of the bend die is-formed by a constant radius, and therefore produces a change in radius at the beginning of the bend equal to the difference between the constant radius and the radius of the virtually straight tube prior to the bend. Once released, a minor degree of spring-back occurs to result in the final orientation of the bent tube.

These conventional apparatuses and methods, however, present a plurality of concerns to those ordinarily skilled in the art, as well as the targeted consumer. Of primary concern, is deformation that frequently occurs during the bending process. During these deformed bends, the tube collapses on the outer side, and compresses on the inner side of the tube to produce flat or concave spots and wrinkles respectively; and the likelihood of deformation is based in part on the outer tube diameter, wall thickness, and radius of curvature of the bend. These deformed bends may result in increased costs and inconvenience, both during the fabrication and utilization of the tube. For example, where a mandrel is initially inserted into the tube to facilitate bending, a small degree of deformation may inhibit the removal of the mandrel, and thereby result in inefficiencies to the overall fabrication process, where the tube is utilized as a conduit, the reduced cross sectional area of the deformed bend results in a decreased capacity of flow, and finally, where the bent tube is utilized proximate an operator/end user, as in a bicycle frame, the wrinkles may result in abrasions to the operator or damage to fabric coming in contact therewith.

Even where properly formed, conventionally bent tubes present concerns. During the network installation of a bent tube, for example, the lack of geometric flexibility in the configuration of the produced bends limits the efficient use of space. This can be seen in the congested space of the undercarriage of an automobile, where the limitations to circular and combinations of circular bends of exhaust tubing often limit design configurations. Where utilized as a conduit, the abrupt change in radius caused by conventional apparatuses and methods also results in a greater dissipation of fluid energy.

Accordingly, there is a need in the art for an improved apparatus for and method of bending tubes that reduces the likelihood of deformation and provides greater geometric flexibility during installation.

BRIEF SUMMARY OF THE INVENTION

Responsive to these and other concerns caused by conventional tube benders, the present invention concerns an apparatus for and method of noncircularly bending a tube. Among other things, the invention provided hereof, is useful for reducing the likelihood of deformed bends, and providing additional choices of geometric configuration of bends during installation.

A first aspect of the present invention concerns an apparatus adapted for the noncircular bending of a tube. The apparatus includes a holding element engaging a first section of the tube, and a bending element configured to apply a bending force to a second section of the tube. The bending and holding elements are cooperatively configured to retain the first section in a fixed position relative to the bending and holding elements, and to bend the second section into a final condition, wherein the second section presents a noncircular bend having a gradually increasing radius of curvature. The bending element includes a bending die having a tube-engaging surface, wherein the surface presents a longitudinal cross section having a noncircular circumferential profile. The bending element is further configured to compress the second section of the tube against the surface, so as to conform the second section to the noncircular profile of the surface. The bending element includes a rotatable spur gear removably connected to the die, and a driven gear rack interconnected with the gear and configured to cause the rotation and linear displacement of the gear and die relative to the rack. The gear has a radius equal to R, and the gear rack presents a lead incline edge that defines an angle Φ and a vertex with respect to horizontal. The rack is pivotable about the vertex so as to adjust the angle Φ, and the profile defines an involute of a circle concentrically aligned with the gear and presenting a radius equal to R sin Φ, so that the die engages the tube at a fixed point during bending.

A second aspect of the present invention concerns a die adapted for interconnecting to an apparatus, wherein the die and apparatus are cooperatively configured to bend a tube. The die includes a tube-engaging surface having a holding portion and a bending portion. The bending portion presents first and second longitudinal ends, and a longitudinal cross section having a noncircular circumferential profile. The surface is configured to engage the apparatus during bending, so that a first section of the tube is held in a fixed position relative to the die adjacent to the holding portion and a second section of the tube conforms to the profile adjacent to the bending portion.

A third aspect of the present invention concerns a method for noncircularly bending a tube, wherein the tube presents first and second sections and a bending strength. The method includes the steps of applying a vector force component greater than the bending strength to the first section, and securing a tube-engaging surface adjacent to the first section and opposite the vector force direction, wherein the surface presents a longitudinal cross section having a noncircular circumferential profile and the profile presents a linearly increasing radius of curvature.

It will be understood and appreciated that the present invention provides a number of advantages over the prior art, including, for example, providing an apparatus for and method of noncircularly bending a tube. This invention decreases the likelihood of deformation during bending by gradually decreasing the radius of curvature. The present invention also provides more flexibility in design consideration.

DETAILED DESCRIPTION OF THE INVENTION

As shownFIG. 2, the present invention concerns a bending apparatus10configured to noncircularly bend a tube (or pipe)12. The apparatus10is described and illustrated herein, with respect to rotary draw bending; however, it is well within the ambit of the present invention to utilize certain improvements and inventive aspects of the apparatus10in conjunction with other conventional tube-bending methods, such as compression, and press bending. As described herein, the tube12is formed by a longitudinal tube wall that presents a round cross sectional configuration and defines an outer diameter (o.d.), inner diameter (i.d.) and corresponding tube wall thickness, W. The preferred tube12presents a hollow cylindrical object having first and second open ends linearly separated by a tube length, inner and outer surfaces22,24and a longitudinal axis (See,FIG. 1a). The tube12may consist of any material of suitable strength to prevent deformation under normal operating conditions, including aluminum, stainless steel, copper (Type K and L), poly-butyrene (PB), etc. Finally, it is appreciated by those ordinarily skilled in the art that the tube may function structurally or as a conduit. However, it is certainly within the ambit of the invention for the apparatus10to be utilized and/or modified to bend other conventional members, such as square tubing, finned tubing, pipe, flat stock, Chromolly, solid rod, etc.

The die components of a conventional rotary draw bender are shown inFIG. 1, and typically include a clamp die14, a bend die (or draw die)16, a pressure die (or follower die)18, and a wiper die20. These dies may be configured to form an interlocked position, such as the reversed interlocked position shown inFIG. 1a, so as to deter slippage or misalignment during bending.

An actuator (not shown) is communicatively coupled to the bend die16, and configured to apply the bending force to the tube12. The actuator may be driven by any of a plurality of conventional means, including manual, mechanically assisted manual, electrical, hydraulic, and electro-hydraulic drive systems to effect the rotary function of the bender. The rotary function of a conventional rotary draw bender is to move the bend die so that the point at which bending takes place is stationary and the die lies tangential to the incoming line of the tube. To achieve this intended function the actuator need only rotate the conventional circular die.

Turning to the configuration of the illustrated embodiment of the present invention,FIG. 2shows a preferred rotary draw bender10having a modified bend die26, modified wiper die28, support structure30(see,FIG. 4), and a pivotable element32. The apparatus10includes other components of a conventional rotary draw bender, such as the previously described pressure and clamp dies, that will not be further described herein with the understanding that the other components are conventionally configured.

In the illustrated embodiment, the apparatus10generates a motion of the modified bend die26by attaching it to a gear or pinion32that forms the pivotable element. More preferably, one of a plurality of modified bend dies of varying curvature is removably connected to the gear32, as shown inFIG. 4, so as to be easily replaceable by an operator where desired. The gear32is pivotably coupled to the structure30, and pivotable about an axis34(see,FIG. 3) within the range of 0° to 360°, and more preferably, approximately equal to 180°. To reduce the frictional energy of rotation, the gear32and structure30are pivotably coupled via a series of ball bearings36as shown inFIG. 4. Alternatively, a solid or fluid lubricant can be utilized in lieu of or addition to the bearings36intermediate movable surfaces.

The preferred structure (or base)30is constrained to move on a line perpendicular to a line followed by the tube path, so that the bend die26, gear32, and structure30are linearly translatable. A biasing mechanism, such as the spring38shown inFIG. 4(alternative biasing mechanisms may include pneumatic or hydraulic means), urges the structure30towards an initial position shown inFIG. 2.

The apparatus10further includes an actuator communicatively coupled to the gear32and configured to cause the gear32to pivot about an axis34and translate. More preferably, a gear rack40propelled by a ram (not shown) moves parallel to the incoming tube12and engages the gear32along an inclined engagement surface42, so as to force the gear32to simultaneously roll on the rack40and linearly translate along a line perpendicular to the line followed by the incoming tube12. Thus, the gear32and rack40forms a traditional rack and pinion configuration. It is well within the ambit of the present invention, however, to utilize separate actuating mechanisms for causing the element32to pivot and the structure30to correspondingly translate, and to programmably interconnect the mechanisms.

In the illustrated embodiment, the modified bend die26presents a bending surface44, and a linear clamp surface46. During bending the clamp surface46cooperates with the clamp die to hold a first section of the tube12in a fixed position relative to the die26. The first section of the tube12presents a minimum length, L1, sufficient for clamping. Alternatively, where the bend begins at or near a distal end of the tube12, a conventional clamp plug (not shown) may be utilized. The die26is configured to gradually engage the bending surface44and a second section of the tube at a fixed pressure point, so that the second section conforms to the curvature of the bending surface44. To effect the noncircular bending of the tube12, the bending surface44presents a noncircular configuration.

More preferably, the surface44presents a noncircular, or strict monotonically changing, curve of either linearly or nonlinearly changing radius with respect to the angle of bending. For example, the surface profile may present one or a combination of the group consisting essentially of clothoids, circular involutes, elliptical involutes, semi-parabolic and quarter-elliptical shapes. As shown inFIG. 5, the preferred bending surface44presents a minimum radius of curvature, R2, and a maximum radius, R1. As the modified die26bends the tube12, the centerline radius of the bend, Rx, as measured from the axis of rotation34to the longitudinal axis of the tube12, increases towards R1. Finally, as previously mentioned, the bend angle, A, has a preferred maximum value of 180°.

Most preferably, the apparatus10is configured to bend tubes into a family of shapes that are sections of curves known as circular involutes. As shown inFIG. 6, the involute of a circle can be traced by a point on a thread kept tangent to the circle as it is unwound from the circle. The radius of curvature of an involute grows linearly with the unwound angle around the circle. In other words, the radial difference of the involute between equal sectors of a circle remains the same. Thus, for a circle of radius r, a segment of its involute that has a starting radius of curvature ρowill have, after bending through an angle of θ, a final radius of curvature ρf=ρo+θr, so that ρ, r and θ determine the shape of the segment.

If the bend surface44presents the involute of a circle of radius r=Rsin Φ, where R denotes the radius of the gear32greater than r, and Φ equals the angle of the engagement surface42of the gear rack40with respect to horizontal (See,FIGS. 2 and 3), then the motion of the bend die26causes it to meet the tube tangentially at a fixed point in space. It is appreciated that the fixed point of bending allows the pressure die, wiper die and the mechanism that feeds the tube to remain in a relatively fixed position, thereby simplifying construction. Where another non-circular surface profiles is presented, it is further appreciated that a different configuration, including a different shaped horizontal gear rack, would be required to provide the fixed point of contact.

More particularly, as shown inFIGS. 7 and 8, however, where R denotes the radius of the circular gear and Cithe initial location of its center, the tangency of the gear rack40at Tiand the origin on a line perpendicular to the horizontal linear directional movement of the rack40and passing through the center of rotation provide that the center has coordinates:
Ci=(0,−R/cos Φ).

As shown inFIG. 8, the horizontal movement of the gear rack40rotates the gear32through an angle θ and determines a consequent linear displacement that moves Cito the new position Cθwhere:
Cθ=Ci+(0,−θRsin Φ).

To ensure that B, the intersection of the vertical line passing through Tiand the involute, remains in a fixed position and still lie on the involute, the additional distance dθalong this line from Tθto the involute circle must satisfy:
θr=θRsin Φ;r=Rsin Φ
so that the radius of the involute is determined.

Different segments of the same involute of a circle of radius r can be bent by setting the initial position of the clamp appropriately at the point when the radius of curvature of the involute equals ρoand then bending the tube until the desired final curvature ρfis reached. To bend an involute from a circle of a different radius r′ requires that the bend die26be swapped with a new bend die and the engagement surface42of the gear racked40to be adjusted to an angle Φ′ by pivoting the rack about a vertex48, such that r′=R sin Φ′. Conventional circular arcs can be bent using a circular bend die and setting Φ′=0.

The modified wiper die28presents a distal end50that is configured to enable the rotation of the bend die26while abutting the die near the fixed point of bending. More particularly, the wiper die28presents a curved end50having a radius of curvature slightly larger than the maximum radius of curvature, R1, presented by the bend die26. As shown inFIGS. 2 and 3, an increasingly reduced gap between the curvature of the wiper end50and the bend die26results during bending. The wiper die28is sufficiently fixed during bending, so that the gap does not result in instability or create undue stresses in the tip of the wiper end50. However, since the proximity of the wiper die28relative to the fixed point of bending (i.e., the initial contact point between the first section of the tube and the bend die, wherein the bending force is applied and the tube is compressed) determines the efficiency of wrinkle prevention, the gap should be minimized. In this regard, the preferred wiper die28includes a vertically adjustable and horizontally retractable internal sleeve28a, as shown inFIGS. 2 and 3, wherein the retractable sleeve28aremains biased towards and in contact with the bend die26during bending. Alternatively, the wiper die28may be resistively slidable along a limited distance parallel to the tube path, so that the die28is gradually displaced as the radius of curvature increases.

Thus, a preferred method of noncircularly bending a tube is described herein, and includes a first step, wherein a vector force, greater than the bending strength of the tube, is applied to a first section of the tube. At a second step, the tube is secured against an engaging surface adjacent to the first section and opposite the vector force direction, so that the first section conforms to the profile of the engaging surface. The preferred surface presents a longitudinal cross section having a noncircular profile of linearly increasing radius of curvature. More preferably, at the second step a second section of the tube is secured in a fixed position relative to the tube engaging surface; the tube engaging surface is fixed to a rotatable and linearly translatable member having a radius equal to R; the member engages an incline surface defining an angle Φ with respect to horizontal, and is rotated and translated by translating the inclined surface perpendicularly to the path of the member. Most preferably, at the second step, the engaging surface defines an involute of a circle having a radius equal to R sin Φ, so as to draw the second section away from the longitudinal axis of the first section and gradually apply the vector force component to the first section at a fixed point in space. At a third step, the second section is released, so that the bent tube can be replaced by a new un-bent tube, and the process repeated.

It is appreciated by those ordinarily skilled in the art that the ability to bend tubes along noncircular curves has the advantage of better accommodation in packaging constraints. Noncircular bends may also provide better structural designs and may allow smoother transitions from bent to straight sections of a tube. This smoother transition further allows better quality in creating attach points should the attached point be optimally located at the transition. Finally, noncircular bends can improve the quality of hydroforming tubes by providing curves with smaller curvatures.

It is further appreciated that the present invention can be utilized in conjunction with various conventional accessories to facilitate the bending process. For example, a Plane of Bend Degree Dial, Model No. DD-996, manufactured by Baileigh Industrial of Manitowoc, Wis., can be utilized for more accurate multi-plane bending. Additionally, a mandrel (not shown) of proper size and material can be conventionally inserted within the tube12to facilitate the bending process described herein.

The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments and modes of operation, as set forth herein, could be readily made by those skilled in the art without departing from the spirit of the present invention. The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as it pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.