GB1561637A - Composite bodies formed by expansion joining - Google Patents

Description

(54) COMPOSITE BODIES FORMED BY EXPANSION JOINING (71) We, YORKSHIRE IMPERIAL METALS LIMITED, a British Company, of Haigh Park Road, Stourton, Leeds LS1 IRD, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method of making bodies which can be used particularly, though not exclusively, as structural members.

There is a demand for structural bodies each comprising a tubular member and a honeycomb core. At present such bodies are produced by forming the core and the tubular member separately, and joining the core to the tubular member, for example by adhesive.

The present invention enables formation of the core at the same time as it is joined to the tubular member.

The present invention provides a method of making a body comprising locating a plurality of elements side by side, at least one of said elements being hollow, and expanding the one element, while restraining the plurality of elements as a whole against outwards movement, to cause the one element to join to an adjacent said element or adjacent said elements. The invention further relates to a body made by such expansion. The one element may be joined to adjacent elements over substantially the whole of its periphery. The method may therefore involve plastic deformation of the body over substantially the whole, or at least the greater part, of its periphery. In this specification, the term "side by side" excludes an arrangement in which any one of said elements is located within another of said elements.

The join may be mechanical, or it may comprise a metallurgical bond.

The expansion may be produced by a high energy rate technique, for example an explosive technique.

The elements may be formed separately from each other and assembled for joining.

They may be located in the assembly by mutual contact.

The expansion may be into a space left between the elements prior to expansion, and this space may be produced by the external configuration of the elements for example they may be of circular external cross-section.

More than one element may be expanded; preferably each element is expanded. The expansions may be carried out simultaneously and may be arranged so that directly opposing forces within the assembly substantially balance out.

The elements as a whole may be restrained against outwards movement during expansion by, for example, a boundary member that surrounds the elements. The elements, or the outermost elements, may be joined to the boundary member by the expansion. There may be a separate support for the boundary member during the expansion step, for example a supporting die in which the assembly is located.

The elements, and/or the boundary member, may be elongate, for example tubular.

Expansions may be effected by a longitudinally travelling shock front. Where a plurality of elements are expanded simultaneously, the longitudinal travel of each shock front should be initiated simultaneously, and the speed of its longitudinal travel should be the same for each element.

The expansion may be arranged to produce a collision front travelling at an angle to the direction of travel of the shock front. In particular, the collision front may have a substantial component of velocity in a direction encircling the direction of travel of the shock front, and preferably substantially normal to the direction of the shock front.

Thus, for a shock front travelling longitudinally of an elongate element the collision front preferably travels generally circumferentially of that element.

The conditions within the space or spaces may be such as to produce a weld. The necessary conditions are now well-known in the explosive welding art, and can be found, for example in "The Development of Explosive Welding and its Application in Engineering" by Professor B. Crossland in "Metals and Materials" December 1971.

Where the collision front travels at an angle to the shock front the velocity of the latter may be greater than 120% of the sonic velocity of the material having the higher sonic velocity, the resultant collision front travelling at a velocity below 120% of that sonic velocity because of the angle. Preferably the collision front velocity is below 100% of the sonic velocity. Where the shock front travels longitudinally of elongate elements but the collision front travels at an angle to the direction of travel of the shock front there may be continuous longitudinally extending regions of contact between elements prior to expansion.

The assembly prior to expansion may comprise an explosive charge within the or each element to be expanded, and the charge may be separated from its element by a suitable pressure transmitting insert, for example of polyethylene.

In its preferred embodiment, the invention provides a method of making a body by assembling a plurality of tubular elements with a bounding means, preferably enclosing them, and simultaneously expanding the elements into joining contact with each other and with the bounding means. The invention further provides an assembly for use in a method as defined comprising a plurality of elements arranged side by side, at least one such element having an explosive charge therein, the explosive charge being capable of expanding the one element into contact with an adjacent said element or said elements to join them together and means for restraining outwards movement of the plurality of elements as a whole during expansion of said one element.

By way of example some embodiments of the invention will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 shows an axial section through a body produced by a method in accordance with She invention; Figure 2 shows an assembly for producing the body shown in Figure 1; Figure 3 shows an assembly for producing a body having an alternative configuration; Figure 4 shows an axial section through a body produced from the assembly shown in -Figure 3.

The body shown in Figure 1 comprises an outer tube 10 of rectangular section, concontaining a generally rectangular lining 12 provided with an integral transverse rib 14.

The. body therefore forms a double box section. The lining 12 is welded to the tube 10 along substantially the whole of the interface therewith.

The body shown in Figure 1 can be produced from the assembly shown in Figure 2 which comprises the tube 10 of rectangular section and a pair of tubes 16 of circular section. The components are dimensioned so that tubes 16 contact each other, and also contact the tube 10 at locations spaced by 90" around the axis of each tube 16. This leaves spaces 18 within the assembly due to the external configuration of the tube 16. It is not essential that the components contact each other in the manner just described, but this is desirable in providing positive location of the components relative to each other prior to the joining operation now to be described.

Inserted within each tube 16 is a tubular polythene insert 20 containing an axially extending explosive charge 22 in the form of an explosive cord. A suitable cord is sold under the name of "Cordtex" (Registered Trade Mark). At one end, cords 22 are joined to a common detonator (not shown) which can initiate detonation of each of them simultaneously. The length of each cord between the end of its associated tube 16 and the detonator is the same, and the detonation velocity of each cord is the same, so that the resultant detonation fronts travel axially of the assembly in phase with each other.

As the detonation fronts progress along the tubes 16 those tubes are driven into the spaces 18 producing collision fronts with each other and with the enclosing tube 10. If the various components are suitably matched the collision fronts will occur on the dotted lines illustrated in Figure 2, and they will travel in the direction of the arrows indicated at those lines. The impact pressure at each collision front, and the velocity of that collision front can be arranged to produce welds as is now well-known in the explosives art as described in the above reference. Thus, each tube 16 suffers plastic deformation to a generally rectangular, or square, configuration and is simultaneously bonded to the adjacent tube 16 and to the enclosing tube 10 to form the body shown in Figure 1. The enclosing tube 10 may be supported in a suitable die during the expansion step to avoid distortion thereof.

In the assembly described above in which the elements contact each other prior to expansion, there will be no weld in the initial contact regions because the tubes 16 cannot be accelerated to the required impact velocity in those regions. Further, there may bean unbonded region at the junction of collision fronts, for example at the corners of the illustrated assembly. However, these unbonded regions can be made very small, and if.necessary- the assembly could be evacuated prior to-expansion to reduce them further.

Since the formation of a weld is dependent upon circumferentially travelling collision fronts, and not upon axially travelling collision fronts, the detonation velocity of the explosives charge may be greater than 120% of the sonic velocity of tube 16 or tube 10, which ever has the higher sonic velocity. The materials of these tubes will normally be metals, although other materials can be welded by explosive techniques. As is wellknown, different metals can be welded by such techniques, for example the outer tube 10 may be of brass and the inner tubes 16 of aluminium. In any event, the tubes 16 must have sufficient ductility to avoid rupture during the expansion step. Provided they have this ductility it is not essential to provide them with uniform axial section; for example the tubes could be of varying thickness or varying circumference to give a varying thickness to the lining 12.

The resultant body can be of substantial length, for example, it is believed that lengths up to 20 feet can be produced without difficulty. With increasing length it becomes increasingly difficult to ensure that the detonation fronts will remain in phase as they travel down the tubes 16, with increasing risk of bulging within the resultant body. However, assuming a sufficient degree of control, the length of the body is indeterminate.

It is not essential to have axially straight tubes 10 and 16. However, if the tubes are curved along their length difficulties are encountered if there are differing path lengths for the detonation fronts around the curve.

This can be allowed for by varying the detonation front velocity around the curve, although this would be difficult to achieve in practice. Where the curve does not produce differing detonation front path lengths, it can be incorporated without difficulty.

Figures 3 and 4 illustrate an alternative assembly and resulting body, comprising an enclosing tube 24 and seven reinforcing tubes 26. The elements are assembled in contact with each other to produce spaces 28 similar to the spaces 18 in the embodiment of Figure 2. Each tube 26 has an insert and an axial explosive cord (not shown) similar to the insert 20 and cord 22. Upon initiation of the cords the assembly of Figure 3 is deformed and bonded into the body of Figure 4, giving the honeycomb internal support structure 30 illustrated in that Figure. The mechanism by which this is produced is similar to that described with reference to Figure 2 and further detailed description is therefore considered unnecessary.

Tube 24 can be located in a suitable support die during the expansion step. It will be realised that the central tube 26 of the assembly of Figure 3 could also be mounted upon a suitable support die, instead of being provided with an expanding charge, to produce a resultant annular body.

In both of the illustrated embodiments, the enclosed tubes have been bonded to their enclosing tube (10 or 24). This is not essential, since the enclosure could act simply as a restraining means during bonding of the enclosed tubes. The bonded elements are not necessarily tubular, provided access can be gained to their interior during the expansion step for the application of expanding pressure.

Such pressure is not necessarily produced by an explosive means, since alternative high energy rate techniques are known. Further modifications will occur to those skilled in this art.

The rectangular-section tube 10 shown in Figures 1 and 2 may of course enclose more than one row of circular-section tubes 16.

The tubes in such multiple rows could be staggered to provide a honeycomb reinforcing structure within the rectangular bounding tube in a similar manner to the formation of the honeycomb structure illustrated in Figure 4. It would, however, be desirable to provide filler blocks in the diagonally opposed corners of the rectangularsection tube which are spaced furthest from the circular-section tubes in the assembly.

Such filler blocks could be formed during extrusion of the bounding tube.

The bounding means is not necessarily formed as a single member such as the tubes 10 and 24 shown in the drawings. The boundary means can be made up of a number of plates held together by a suitable die. In this event, only some of these plates might be bonded into the eventual structure.

It will be noted that the present invention enables plastic deformation of members of relatively simple formation to produce a unitary structure of relatively complex form.

In accordance with this invention it is not necessary to pre-form any parts of the eventual complex structure, although pre-formation of some parts of the structure is not to be excluded from the broad scope of the invention.

WHAT WE CLAIM IS: 1. A method of making a body comprising locating a plurality of elements side by side, at least one of said elements being hollow, and expanding the one element, while restraining the plurality of elements as a whole against outwards movement, to cause the one element to join to an adjacent said element or adjacent said elements.

2. A method as claimed in Claim 1 wherein the one element is joined to adjacent element over substantially the whole of its periphery.

3. A method as claimed in Claim 1 or Claim 2 wherein the elements are formed separately from each other and assembled for joining.

4. A method as claimed in any preceding

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   upon circumferentially travelling collision fronts, and not upon axially travelling collision fronts, the detonation velocity of the explosives charge may be greater than 120% of the sonic velocity of tube 16 or tube 10, which ever has the higher sonic velocity. The materials of these tubes will normally be metals, although other materials can be welded by explosive techniques. As is wellknown, different metals can be welded by such techniques, for example the outer tube

   10 may be of brass and the inner tubes 16 of aluminium. In any event, the tubes 16 must have sufficient ductility to avoid rupture during the expansion step. Provided they have this ductility it is not essential to provide them with uniform axial section; for example the tubes could be of varying thickness or varying circumference to give a varying thickness to the lining 12.

   The resultant body can be of substantial length, for example, it is believed that lengths up to 20 feet can be produced without difficulty. With increasing length it becomes increasingly difficult to ensure that the detonation fronts will remain in phase as they travel down the tubes 16, with increasing risk of bulging within the resultant body. However, assuming a sufficient degree of control, the length of the body is indeterminate.

   It is not essential to have axially straight tubes 10 and 16. However, if the tubes are curved along their length difficulties are encountered if there are differing path lengths for the detonation fronts around the curve.

   This can be allowed for by varying the detonation front velocity around the curve, although this would be difficult to achieve in practice. Where the curve does not produce differing detonation front path lengths, it can be incorporated without difficulty.

   Figures 3 and 4 illustrate an alternative assembly and resulting body, comprising an enclosing tube 24 and seven reinforcing tubes 26. The elements are assembled in contact with each other to produce spaces 28 similar to the spaces 18 in the embodiment of Figure 2. Each tube 26 has an insert and an axial explosive cord (not shown) similar to the insert 20 and cord 22. Upon initiation of the cords the assembly of Figure 3 is deformed and bonded into the body of Figure 4, giving the honeycomb internal support structure 30 illustrated in that Figure. The mechanism by which this is produced is similar to that described with reference to Figure 2 and further detailed description is therefore considered unnecessary.

   Tube 24 can be located in a suitable support die during the expansion step. It will be realised that the central tube 26 of the assembly of Figure 3 could also be mounted upon a suitable support die, instead of being provided with an expanding charge, to produce a resultant annular body.

   In both of the illustrated embodiments, the enclosed tubes have been bonded to their enclosing tube (10 or 24). This is not essential, since the enclosure could act simply as a restraining means during bonding of the enclosed tubes. The bonded elements are not necessarily tubular, provided access can be gained to their interior during the expansion step for the application of expanding pressure.

   Such pressure is not necessarily produced by an explosive means, since alternative high energy rate techniques are known. Further modifications will occur to those skilled in this art.

   The rectangular-section tube 10 shown in Figures 1 and 2 may of course enclose more than one row of circular-section tubes 16.

   The tubes in such multiple rows could be staggered to provide a honeycomb reinforcing structure within the rectangular bounding tube in a similar manner to the formation of the honeycomb structure illustrated in Figure 4. It would, however, be desirable to provide filler blocks in the diagonally opposed corners of the rectangularsection tube which are spaced furthest from the circular-section tubes in the assembly.

   Such filler blocks could be formed during extrusion of the bounding tube.

   The bounding means is not necessarily formed as a single member such as the tubes 10 and 24 shown in the drawings. The boundary means can be made up of a number of plates held together by a suitable die. In this event, only some of these plates might be bonded into the eventual structure.

   It will be noted that the present invention enables plastic deformation of members of relatively simple formation to produce a unitary structure of relatively complex form.

   In accordance with this invention it is not necessary to pre-form any parts of the eventual complex structure, although pre-formation of some parts of the structure is not to be excluded from the broad scope of the invention.

   WHAT WE CLAIM IS: 1. A method of making a body comprising locating a plurality of elements side by side, at least one of said elements being hollow, and expanding the one element, while restraining the plurality of elements as a whole against outwards movement, to cause the one element to join to an adjacent said element or adjacent said elements.
2. 2. A method as claimed in Claim 1 wherein the one element is joined to adjacent element over substantially the whole of its periphery.
3. 3. A method as claimed in Claim 1 or Claim 2 wherein the elements are formed separately from each other and assembled for joining.
4. 4. A method as claimed in any preceding

   claim wherein a plurality of elements are expanded simultaneously.
5. 5. A method as claimed in Claim 4 wherein directly opposing forces within the assembly during said expansion are arranged to substantially balance out.
6. 6. A method as claimed in any preceding claim wherein a boundary member surroun ding the elements is provided to restrain said plurality of elements as a whole against outwards movement during expansion of said element(s).
7. 7. A method as claimed in Claim 6 wherein the elements, or the outermost elements, are joined to the boundary member by the expansion.
8. 8. A method as claimed in any preceding claim wherein the elements, and the boundary member where provided, are elongate.
9. 9. A method as claimed in Claim 8 wherein said expansion is effected by a longitudin ally travelling shock front.
10. 10. A method as claimed in Claim 9 wherein said shock front is produced by an explosive.
11. 11. A method as claimed in any preceding claim wherein the expansion conditions are arranged to produce a weld between said elements.
12. 12. A method of joining a plurality of elements substantially as herein described with reference to the accompanying drawings.
13. 13. An assembly for use in a method as claimed in any preceding claim comprising a plurality of elements arranged side by side, at least one such element having an explosive charge therein, the explosive charge being capable of expanding the one element into contact with an adjacent said element or said elements to join them together and means for restraining outwards movement of the plurality of elements as a whole during expansion of said one element.
14. 14. A body when produced by a method as claimed in any one of Claims 1 to 12.