GB2045135A - Forming dies and methods of forming tubular fittings - Google Patents

Abstract

A composite die for forming an elbow from a straight tube pushed therethrough comprises a tubular inlet guide section 28, a swaging section 30 in the form of a truncated cone connected and opening at the large end to one end of the section 28 and arranged so that the tube while pushed therethrough is subjected to circumferential swaging forces varying from a maximum at one location on the circumference to a minimum value at another opposed location on the circumference and is subjected to an offset of die forces producing a force moment, to cause bending of the tube about the location subjected to the minimum swaging forces, partial forming of the elbow and reduction in tube diameter, and a tubular bending section 32. There may also be a second swaging section 34 and a sizing section 36. <IMAGE>

Description

SPECIFICATION Forming dies and methods of forming tubular fittings This invention relates to forming dies and methods of forming tubular fittings.

Numerous methods of forming elbow and return bend fittings have been developed over the years.

U.S. Patent No. 3354681 discloses a method and apparatus for forming elbows from a tubular section by pushing through a forming die. A portion of this apparatus consists of a 'tapered land' which the inventor claims to cause bending by differential friction, the friction force being greater on the inside radius of the bent tubular section than on the outside radius, which is in direct contradiction to the finding of our invention.

According to the present invention there is provided a composite die for forming an elbow from a straight tube pushed therethrough, the die comprising a tubular inlet guide section, a swaging section in the form of a truncated cone connected and opening at the large end to one end of the inlet guide section and constructed and arranged so that the tube while pushed therethrough is subjected to circumferential swaging forces varying from a maximum at one location on the circumference to a minimum value at another opposed location on the circumference and is subjected to an offset of die forces producing a force moment, to cause bending of the tube about the location subjected to the minimum swaging forces, partial forming of the elbow and reduction in tube diameter, and a tubular bending section, forming a passageway of uniform diameter connected and opening at one end to the small end of the cone of the swaging section and constructed and arranged so that the tube while pushed therethrough is subjected to further bending further to form the elbow.

According to the present invention there is also provided a method of forming an elbow from a straight tube in a composite die having in sequence a tubular inlet guide section, a swaging section and a tubular bending section of uniform diameter, the method comprising pushing the tube through the inlet guide section and through the swaging section to subject itto circumferential swaging forces varying from a maximum value at one location on the circumference to a minimum value at another opposed location on the circumference and to subject it to an offset of die forces producing a force moment, to cause bending of the tube about the location subjected to the minimum swaging forces, partial forming of the elbow and reduction in tube diameter, and pushing the tube through the bending section to further bend the tube and further form the elbow, while maintaining a uniform tube diameter.

The invention will now be described by way of example with reference to the accompanying draw ings, in which: Figure 1 shows generally a side view of a typical arrangement for carrying out a method according to the invention; Figure 2 shows a sectionalised plan view taken along lines 2-2 of Figure 1; Figure 3 shows a cutaway plan view of a typical forming die insert; Figure 4 depicts generally a cutaway plan view of a first swaging section of the forming die insert showing a particular form of a bilaterally symmetric die composed of conical sections, with a tubular member therein; and Figure 5 shows an alternative first swaging section of that shown in Figure 4.

The invention is generally concerned with methods of forming tubular fittings or elbows, such as 450 and 900 elbows and 1800 returns, of high quality and of circular cross-section. Referring to Figures 1 and 2, a die support assembly 10, comprising an upper die support fixture 12 and a lower die support fixture 14, rests on a base plate 16. The assembly 10 houses a forming die 17. Confined within the upper support fixture 12 is an upper forming die insert 18, and likewise confined in lower support fixture 14 is a lowerforming die insert 20.

Together, inserts 18 and 20 comprise the die 17. A tubular member (hereinafter referred to as a tube) 22, treated with a commercial lubricant, is typically pushed into the assembly 10 by a pushing bar 24 which moves towards the die assembly under the action of a power-driven ram 26. A typical inlet guide section 28 (Figure 2) aligns the tube 22 for proper entry into the die 17 shown as the lower die insert 20 in Figure 2. While inlet guide section 28 is illustrated as being of uniform diameter throughout the length, the exit end may be proportioned and arranged to change the cross-sectional geometry of the tube 22 prior to entering a first swaging section 30 (Figure 3).

The formed fitting 29 exits the die 17.

The elbow forming may be thought of as consisting of separate, although interrelated, forming operations. One of the possible combinations employs four sequential forming sections: (a) Initial bending via a first swaging section (b) Bending with no swaging (c) Additional bending via a second swaging section (d) Sizing with no swaging.

The four operations are preferably carried out sequentially in one forming die.

Figure 3 illustrates one-half of a composite die 17 for carrying out the above listed operations sequentially. The composite die 17 is comprises of the tubular inlet guide section 28 of uniform diameter, the first swaging section 30, a tubular bending section 32 of uniform diameter, a second swaging section 34, and a tubular sizing section 36 of uniform diameter. Although Figure 3 shows a cavity which extends around a 900 arc from the start of the section 30 to the end of the section 36, this is not necessarily a requirement of the design. The cavity may be shortened to less than 900 or lengthened to more than 90 , depending upon the overall design requirements and number of forming sections used.

The first swaging section 30 may be fashioned for differential swaging or for swaging on that portion of the tube 22 which is referred to as the extrados of the fitting 29. In either instance, the operation of the first swaging section 30 is significantly influenced by percent reduction of the outer diameter (hereinafter referred to as OD reduction) and the subsequently defined tilt angle T (Figure 4).

The bending section 32 opens at an end 31 to a throat 42 of the first swaging section 30 and forces the tube 22 to conform to a tighter radius than it normally would just exiting the section 30, thus promoting additional bending. The bending section 32 does not cause diameter reduction but does influence the bend radius of the tube 22. The curvature of the bending section 32 is very important, but generally should have an inner radius close to that of the fitting 29.

The second swaging section 34 opens at the large end 35 to the other end 33 of the bending section 32.

As in the first swaging section 30, the second swaging section 34 also swages the tube 22 and has certain similar geometric features. That portion of the die 17 contacting the inner radius of the tube 22 is preferably a continuation of the inner radius 38 of the bending section 32. The second swaging section 34 increases the compression in the prior bending section 32 forcing the tube 22 to 'fill out' the inner and outer radii of the bending section 32. It also ideally completes bending ahead of the sizing section 36 and forces the tube 22 against the inner radius feeding into the sizing section 36.

The sizing section 36 opens at one end 39 to the small end 37 of the second swaging section 34 and is similar to the bending section 32 in that neither causes diameter reduction of the tube 22. However, the sizing section 36 exhibits a tighter outer radial measurement than does the bending section 32, and is used mainly for dimensional control.

The tube wall thickness changes as the tube 22 passes through the various sections in the following general manner: In the first swaging section 30, the wall thickens at both the inner and outer radius. In the bending section 32, the inner radius wall thickens and the outer radius wall thins. In the second swaging section 34, the outer radius wall thickens. In the sizing section 36 the wall, preferably does not change, but in actuality can change in either direction depending upon the design of the previous three forming sections.

The first swaging section 30 has bilateral symmetry. In the particular embodiment shown, the first swaging section 30 may be described as similar to a tilted die. The die shown is essentially a conventional forming die with the axis tilted with respect to the axis of the incoming tube 22. The use of tilted dies in a tube forming process and critical limits pertaining thereto are disclosed in our co-pending application No. (reference N66/7) of even date. Referring to Figure 4, the combination of the first swaging section 30 with the tube 22 being pushed therein is characterised by certain geometric considerations.

The section 30 may be a truncated hollow conical section the entrance cone 40 of which may be described with respect to the tube 22 by reference to the following symbols: C = the die cone angle (often called the semicone angle) which is the angular relationship between the surface of the cone and the centreline of the cone.

T = die tiltangle which is theangularrelation ship between the die or cone centreline and the entering tube centreline.

lx = maximum die inlet angle, equal to C + T.

Is = minimum die inlet angle, equal to C - T.

Rc = inner radius of curvature of the bent tube.

It will be observed that lx and li define oppositely located sections of the entrance cone 40 with respect to the centreline of the tube 22.

The unbent tube 22 is pushed through the cone 40 and passes through a throat 42 which represents the minimum opening of the conical section. The tu be 22, which started with an original diameter ODs, is deformed by passage through the section 30 to a bent tube or partially formed fitting 48 exhibiting a diameter ODf.

As the tube 22 is pushed through the section 30, the upper portion (Figure 4) of the tube circumference experiences a larger swage (diameter reduction) than the lower portion, the larger swage occurring at that portion of the cone associated with the maximum inlet angle lx, thus causing greater elongation in the upper portion of the tube 22 and resulting in bending. It will be noted that during pushing of the tube 22 through the section 30, a portion of the circumference of the tube 22 closest to the Ii element 46 of the entrance cone 40 contacts the section 30 prior to the opposed portion contacting the 1x element 44 of the entrance cone 40.This offset of initial contact in the entrance cone 40 results in an offset of die forces normal to the tube 22, thus producing a couple (or moment) which promotes further tube bending. It is understood that the above description of the section 30 is only an example of a particular class of bilaterally symmetric dies.

Subsequent to the tube 22 passing through throat 42, the tube 22 successively passes through the bending section 32 for further forming, the second swaging section 34 for still further forming, and the sizing section 36 for completion of the fitting 29, which then exits from the die 17. The formed fitting 29 may then be cut to the appropriate length. An alternative method of forming the tubular fittings comprises cutting the straight length of tubing into the desired lengths of the finished product and then pushing these pre-cut lengths through the die 17 in series. Different cut lengths result in different types of fittings, such as 450 and 900 elbows and 1800 returns. This disclosure thus teaches a method by which fittings of a particular set of dimensions can be formed from a long straight tube section or from pre-cut lengths of tubing in a semi-continuous or continuous process.

The foregoing description applies to the preferred embodiment and is illustrated in the drawings.

However, other die arrangements are possible and various combinations can be used, depending on the desired design of the finished product, such as: (a) An inlet guide section, a swaging section, and a bending section (b) An inlet guide section, a swaging section, a bending section, and a sizing section.

(c) An inlet guide section, a first swaging section, a bending section, and a second swaging section.

(d) An inlet guide section, a first swaging section, a bending section, a second swaging section, and a sizing section (e) An inlet guide section, a first swaging section, a first bending section, a second swaging section, and a second bending section (f) An inlet guide section, a first swaging section, a first bending section, a second swaging section, a second bending section, and a sizing section.

More complicated arrangements involving more sections are possible, but, because of complexity, are impractical.

Figure 5 shows an alternative form of the first swaging section 30 designated as section 50. The basic difference between sections 30 and 50 is that in section 50 the minimum die inlet angle Ij is 0 , and no swaging occurs on that element of the tube circumference contacting the lower face 54. As shown, tube 22, with an outer starting diameter of ODs, is pushed into the section 50 passing through a truncated conical section 52. The tube 22 remains in contact with the lower face 54 (Ij = 0 ), while experiencing diameter reduction by contacting the upper face 56 of the cone 52. The lower face 54 is tangential to the inner radius 38 of the bending section 32 (Figure 3) at the point where the sections 50 and 32 meet. The tube 22 is forced through the throat 42 and feeds into the bending section 32 (not shown in Figure 5) and continues as previously described.

The methods described and concomitant fittings exhibit numerous advantages as compared to existing methods. For example, the methods require no internal tube support, which makes possible the rapid forming of fittings from long tube sections. The methods are applicable to any ductile material able to withstand the forces associated with the methods.

The methods can be used cold, warm or hot.

Because no internal tools are used, the fittings are free of any internal scarring and have been found to have uniform wall thickness along their entire length, relatively little or no wall thinning on their outer radius, and outside diameters that are circular along their entire length.

Claims (12)

1. Acomposite dieforforming an elbow from straight tube pushed therethrough, the die comprising a tubular inlet guide section, a swaging section in the form of a truncated cone connected and opening at the large end to one end of the inlet guide section and constructed and arranged so that the tube while pushed therethrough is subjected to circumferential swaging forces varying from a maximum at one location on the circumference to a minimum value at another opposed location on the circumference and is subjected to an offset of die forces producing a force momentto cause bending ofthetube about the location subjected to the minimum swaging forces, partial forming of the elbow and reduction in tube diameter, and a tubular bending section, forming a passageway of uniform diameter connected and opening at one end to the small end of the cone of the swaging section and constructed and arranged so that the tube while pushed therethrough is subjected to further bending further to form the elbow.

2. A die according to claim 1 further comprising a second swaging section connected to the opposite end of the bending section and constructed and arranged so that the tube while pushed therethrough is subjected to circumferential forces varying from a maximum at one location on the circumference to a minimum value at another opposed location on the circumference and is subjected to an offset of die forces producing a force moment to cause further bending of the tube about the location subjected to the minimum swaging forces, further reduction in tube diameter and further forming of the elbow.

3. A die according to claim 2 further comprising a tubular sizing section forming a passageway of uniform diameter connected to the exit end of the second swaging section and constructed and arranged so that the tube while pushed therethrough is subjected to final formation of the elbow.

4. A method of forming an elbow from a straight tube in a composite die having in sequence a tubular inlet guide section, a swaging section and a tubular bending section of uniform diameter, the method comprising pushing the tube through the inlet guide section and through the swaging section to subject it to circumferential swaging forces varying from a maximum value at one location on the circumference to a minimum value at another opposed location on the circumference and to subject it to an offset of die forces producing a force moment, to cause bending of the tube about the location subjected to the minimum swaging forces, partial forming of the elbow and reduction in tube diameter and pushing the tube through the bending section to further bend the tube and further form the elbow, while maintaining a uniform tube diameter.

5. A method according to claim 4 further comprises pushing the tube through a second swaging section to subject it to circumferential swaging forces varying from a maximum value at one location on the circumference to a minimum value at another opposed location on the circumference and to subject it to an offset of die forces producing a force moment, to cause further bending about the location subjected to the minimum swaging forces, further reduction in tube diameter and further forming of the elbow.

6. A method according to claim 5 further comprises pushing the tube through a tubular sizing section of uniform diameter for forming the elbow.

7. A method according to claim 4, claim 5 or claim 6 wherein the formed elbow is cut to length upon exiting the die.

8. A method according to claim 4, claim 5 or claim 6 wherein the straight tube length is cut to desired finished lengths and then pushed through the die in series.

9. A composite die substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

10. A composite die substantially as hereinbefore described with reference to Figures 3 and 5 of the accompanying drawings.

11. A method of forming tubular fitting, the method being substantially as hereinbefore de scribed with reference to Figures 3 and 4 of the accompanying drawings.

12. A method of forming tubular fittings, the method being substantially as hereinbefore described with reference to Figures 3 and 5 of the accompanying drawings.