APPARATUS AND METHOD FOR REDUCING THE DIAMETER OF TUBES

Abstract: An apparatus and a method for reducing the outside diameter of thin-walled, relatively soft, metal tubing (10) by using a deformation head, having relative axial movement, comprising a plurality of symmetrically radially spaced rollers (11), each having an arcuate surface (14), that engages the tubing (10) to plastically deform same. Variations in tubing profile and repeatability thereof can be produced in conjunction with a numerical control system. An optional feature of the apparatus is a suitably located cutting tool (15) used to remove material from tubing wall thickness (16) to produce finished wall thickness (17).

Description: APPARATUS AND METHOD FOR REDUCING THE DIAMETER OF TUBES The present invention relates to an apparatus for reducing the diameter of metal tubing and, in particular, to apparatus to reduce the diameter of thin walled metal tubing by plastic deformation. The invention further relates to apparatus to both reduce the diameter of thin walled metal tubing and, as required, reduce the thickness of the walls of said metal tubing. The invention is particularly useful in connection with aluminium (and alloys thereof) tubing. BACKGROUND ART Concerning apparatus and methods for producing a variable profile tube, at least four methods are known for doing this. One method involves cutting, pressing and re-welding. This method is slow and produces a profile that cannot easily be repeated, with poor metal quality plus some irregularity in wall thickness due to grinding of welds. A further method is hammer swaging. This technique increases the wall thickness dramatically and is limited to the shape and size of dies placed in the swaging machine. A further method involves a system of multi-rollers comprising the tube onto a mandrel. This method is limited to the shape, length and size of the mandrel so that any changes in profile requirements necessitate the production of a new mandrel. This method therefore is somewhat inflexible and consequently, especially for relatively short production runs, costly. A further known method is that of air spinning using a single roller. This method is known to give tapered tubes quickly and efficiently. However with this method, wall thickness cannot be below approximately 2mm otherwise harmonic problems occur. Furthermore it is known for this method to produce a longitudinal bend in the taper. The method of air spinning, then, has a relatively specific application. None of tne foregoing apparatus will allow for the —* production of tubing with a varied diameter profile, said varied profile being easily and accurately repeatable over long lengths. Further, methods and apparatus are known for reducing the thickness of the walls of the tubes. Further, none of the known methods or apparatus of the prior art provides a simple means for varying the diameter along the length of a tube as well as, as necessary, varying wall thickness of the pipe. It is an object of the present invention to provide an improved apparatus and method which will substantially overcome, or ameliorate, the abovementioned disadvantages. DISCLOSURE OF INVENTION According to the present invention there is disclosed an apparatus to reduce the diameter of thin walled metal tubing, said apparatus comprising a deformation head adapted to engage the tubing to plastically deform same, means to support said tubing, and means to cause relative movement between the tubing and deformation heads so that the tubing passes through the head along the longitudinal axis of the tubing, means to provide relative angular movement of said head about said longitudinal axis, and wherein said deformation head has a plurality of rollers which engage said tubing to plastically deform same. According to a further aspect of the present invention there is provided a method for the reduction of the outside diameter of metal tubing by the application of a plastic deformation force by means of a plurality of rollers, said rollers rotatively mounted on a deformation head such that they are rotatable about an axis spaced radially from the longitudinal axis of said metal tubing and extending generally parallel to and co-extensive with at least a portion of said metal tubing, said method including means to support said tubing, and means to cause relative movement between the tubing and deformation head so that the tubing passes through the head along the longitudinal axis of the tubing, said method further including means to provide relative angular movement of said head about said longitudinal axis. A preferre eature o t e presen nvent on includes, for the purpose of reducing the thickness of the walls of the tubing, as desired, at least one cutting tool arranged to move radially relative to the longitudinal axis of the tubing, the cutting tool located to remove metal from the tubing portion as the tubing portions exits from behind one of the rollers on the deformation head, the location being at the end of the form roller chain at which point the tube presents itself at the desired diameter. The point at which the cutter is removing metal from the tube is immediately behind the tangent point common to the roller and the tube. In a further preferred form, the invention entails the control by computer or equivalent programmed means of the position of the rollers, the position of the deformation head relative to the tubing, and the cutting action of the cutting tool in such a way that the precise control of all the mentioned variables allows for the production of profiles of tubing incorporating varied diameter and varied wall thicknesses along the longitudinal length of the tubing, the profile being easily reproducible. BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings; wherein Fig. 1 is a schematic part sectioned side elevation of a thin walled tubing being deformed by a plurality of rollers; Fig. 2 is a schematic part sectioned front elevation of the tubing and rollers through line II-II of Fig. 1; and Fig. 3 is a schematic section through a portion of a typical end-product. MODES OF CARRYING OUT THE INVENTION In Figs. 1 and 2 there is schematically depicted a length of thin walled tubing 10 having an undeformed portion 10A and a deformed portion 10B. It should be noted in Fig. 1 that the nearside lower roller has not been shown for clarity r-sasons. The tubing 10 is plastically deformed by a plurality of rollers 11 which are equally angularly spaced about the longitudinal axis 12 of the tubing 10. The rollers 11 are rotatably mounted on a deformation head so that they are rotatable about axes 13 spaced radially and equidistant from the longitudinal axis 12 and extending generally parallel and coextensive with respect thereto. Each of the rollers 11 has a peripheral surface 14 which engages the tubing 10 to cause plastic deformation thereof. The configuration of the peripheral surface 14 is arranged to provide the correct rate of plastic deformation of the tubing portion 10A. In the present embodiment, the axes 13 of the rollers are mounted parallel with the longitudinal axis 12 of the tube. The perpendicular cross-section through the axis of rotation 13 of the rollers is a disc shape, the diameter of the disc becoming progressively smaller in the direction of advance towards the unworked surface 10A. The deformation head, not depicted, is movably mounted on a frame so that it is moved parallel to the longitudinal axis 12 to thereby pass the tubing 10 through the deformation head. The tubing 10 is supported and is rotatably driven to thereby cause rotation of the rollers 11 by frictional engagement between the tubing 10 and rollers 11. Preferably the deformation head is driven along the tubing 10 by means of a power screw or hydraulic or pneumatic ram. It has also been found advantageous to provide a steadying sleeve mounted on the deformation head and which engages the tubing portion 10A to steady the tubing 10 as it is delivered to the deformation head. Also mounted on the deformation head is a cutting tool 15 which engages the tubing portion 10B to reduce the metal thickness and/or provide the peripheral surface of the tubing portion 10B with a relatively smooth appearance and finish. The cutting tool 15 is movable radially relative to the longitudinal axis 12. The cutting tool 15 removes metal from the tubing portion 10B at a position immediately behind one of the rollers 11 where the roller 11 engages the tubing portion 10B. At this point there is a minimum amount of tube surface flexing thus the amount of metal being removed is not affected by the wall thickness of the tube being varied. Depicted in cross-section in Figs. 1 and 2 is the material to be removed 16 in order to effect wall thinning. Also shown in cross-section is the remaining, thinned wall surface 17. In the present embodiment, two of the rollers 11 are used as steady rollers angularly spaced by 120° making sure that the tubing portion 10B to be thinned is held as steady as possible even- when the tube diameter is changing rapidly. The cutting axis intersects the angle between the two steady rollers 11 while being located in an opposing position with respect thereto. Movement of the rollers and cutting tool is effected by mechanical means, for example hydraulic or screw drive (not shown) . The axes of the rollers are moved toward or away from the longitudinal axis 12 as necessary, in order to effect the required tube diameter reduction. The movement is always in tandem so that the cross sectional dimensions of the assembly are symmetrical at all times. Preferably, the mechanical means is, in turn, computer controlled to ensure the product can be repeated. As an alternative to the above described preferred embodiment, the deformation head can be fixed on the frame and the tubing movably mounted in order to provide the relative movement between the deformation head and tubing. As a still further alternative, the rollers 11 may be driven together with the tubing 10 or the tubing 10 mounted for free rotation so as to be frictionally driven by the rollers 11. It may also be advantageous to tension the tubing 10 to effect stretching thereof during deformation by the rollers. The invention, incorporating the cutting tool, operates successfully upon very thin walled and soft tubing (for example aluminium) . Such tubing walls tend to flex between the rollers, whether the rollers are being used for forming the diameter of the tube or for thinning by means of'cutting in conjunction with forming. In this situation, by making the cutter tip act along the line drawn along the SUBSTITUTE SHEET central axis of one of the rollers and the central axis of the tube, the wall thinning process is carried out in a manner which is repeatable since, at this point, there is a minimum amount of tube surface flexing, the amount of metal being removed thus not being affected by the wall thickness of the tube. The particular configuration of two rollers opposed at 120° to the cutter axis ensures that the tube to be thinned is supported as steadily as possible, even when the tube diameter is being changed rapidly. In use, the required natural movements of the rollers and of the one or more cutters, as well as the speed of rotation of the tube and the relative longitudinal speed of the tube with respect to the roller assembly, is programmed into the deformation head controlling the system. One or more lengths of tube are then passed through the deformation head assembly resulting in a product whose overall diameter profile is as desired and whose wall thickness is independently controlled and is also as desired. Relatively complex profiles as for example, shown in Fig. 3, may be achieved. More importantly, such profiles may be repeatedly achieved a high degree of accuracy upon thin walled and soft tubing with a high degree of accuracy. The foregoing has described specifically the use of three rollers and one cutter operating through the axis of and immediately behind one of the rollers. This preferred juxtaposition of components provides apparatus which may be utilised, preferably in conjunction with programmed control means, to effect the profiling of metal tubing by means of diameter reduction. Further, the preferred embodiment is ideally suited to operate upon thin walled metal tubing in such a way as to effect both diameter reduction and/or wall thickness reduction in a repeatable manner. Parameters which may be varied include the number of rollers, the number of cutters, speed of throughput of the tubing and tensioning of the tubing. In particular, where high throughput speed and/or a significant amount of wall thinning is required, a cutter may be placed behind each roller on tne deformation head. Similarly, where a significant amount of diameter reduction is required, two or more deformation heads may be used to process the tube in series. In such a situation, only -the final deformation head may have cutters mounted on it. The invention is particularly useful in the tapering of aluminium tubes for use in items such as snow ski stocks, light poles and yacht masts. In articles such as yacht masts where a tapered section is often used over the top third of the mast it is desirable to obtain the maximum strength for the minimum weight. Thus, the invention allows for the mast to be tapered, work hardened in the plastic deformation stage and the wall thickness controlled to achieve the desired result. Modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

Claims: CLAIMS 1. An apparatus to reduce the diameter of thin walled metal tubing, said apparatus comprising a deformation head to engage the tubing to plastically deform same, means to support said tubing, and means to cause relative movement between the tubing and deformation heads so that the tubing passes through the head along the longitudinal axis of the tubing, means to provide relative angular movement of said head about said longitudinal axis, and wherein said deformation head has a plurality of rollers which engage said tubing to plastically deform same. 2. The apparatus of claim 1. wherein the rollers are rotatably mounted on a deformation head so that they are rotatable about an axis spaced radially from the longitudinal axis and extending generally parallel to and mutually coextensive with respect thereto over at least a portion of said longitudinal axis. 3. The apparatus of claim 1 or claim 2, wherein said rollers are spaced equally about the longitudinal axis of said tubing. 4. the apparatus of any preceding, claim, wherein the number of rollers is three. 5. An apparatus to reduce the diameter of thin walled metal tubing, said apparatus comprsing a deformation head to engage the tubing to plastically deform same, means to support said tubing, and means to cause relative movement between the tubing and deformation heads so that the tubing passes through the head along the longitudinal axis of the tubing, means to provide relative angular movement of said head about said longitudinal axis, and wherein said deformation head has a plurality of rollers which engage said tubing to plastically deform same and wherein at least one cutting tool is mounted on the deformation head, said cutting tool positioned to remove metal deformation head immediately behind one of said rollers. 6. The apparatus of claim 5. wherein a cutting tool is loc __ated behind two or more of said rollers. 7. The apparatus of any preceding claim, wherein the deformation head is fixed relative to a reference frame and the tubing is moved relative thereto. 8. The apparatus of any ' preceding claim, wherein said tubing is fixed relative to a reference frame and said deformation head is moved relative thereto. 9. The apparatus according to any preceding claim, wherein the rollers are driven together with the tubing. 10. The apparatus according to any preceding claim, wherein said tubing is mounted for free rotation so as to be frictionally driven by said rollers. 11. The apparatus according to any preceding claim, wherein movement of said rollers and said cutting tool is computer controlled to ensure product repeatability. 12. A method for the reduction of the outside diameter of metal tubing by the application of a plastic deformation force by means of a plurality of rollers, said rollers rotatively mounted on a deformation head such that they are rotatable about an axis spaced radially from the longitudinal axis of said metal tubing and extending generally parallel to and co-extensive with at least a portion of said metal tubing, said method including means to support said tubing, and means to cause relative movement between the tubing and deformation head so that the tubing passes through the head along the longitudinal axis of the tubing, said method further including means to provide relative angular movement of said head about said longitudinal axis. 13. The apparatus substantially as described herein with reference to and as illustrated by the accompanying drawings. 14. The method substantially as described herein with reference to and as illustrated by the accompanying drawings.

Inventors: RAWSON-HARRIS DOUGLAS, RAWSON-HARRIS, DOUGLAS
Applicants: HALBUN HOLDINGS PTY LTD, HALBUN HOLDINGS PTY. LTD.
Application year: 1985
Main classification: B21D22
IPC codes: B21D22