WO1998003310A1

WO1998003310A1 - Tube welding fixture and heat shield

Info

Publication number: WO1998003310A1
Application number: PCT/US1997/012641
Authority: WO
Inventors: Thomas E. Smith
Original assignee: Mcdonnell Douglas Corporation
Priority date: 1996-07-23
Filing date: 1997-07-18
Publication date: 1998-01-29
Also published as: AU3733597A

Abstract

A tube welding fixture (10) for holding and axially aligning cylindrical tubing pieces (22, 24) in an end-to-end butted relation, in preparation for welding and assembly. The fixture has clamping surfaces (27, 28) which fit tightly around the outer walls of the tubing pieces and compress each piece between a clamping yoke (16) and a clamping base member (12). The clamping yoke (16) is removably attached to the clamping base member (11) for insertion and removal of the tubing piece (22, 24). The fixture (10) is constructed from heat conducting material which acts as a heat shield and sink, and blocks excess welding heat from conducting down the tubing piece (22, 24) and damaging adjacent components.

Description

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Background of the Invention

This invention relates generally to the art of clamping cylindrical pieces in preparation for welding and more particularly, to the securing, axial alignment, and heat shielding of tubing end pieces in preparation for welding and assembly.

When preparing sections of tubing ends for welding and assembly, proper support and alignment are often critical. This support and alignment is typically achieved through the use of tube clamping devices. In many applications the available space for such clamping devices is limited as is common in aircraft assembly operations . In U.S. Patent No. 4,379,215, issued Apr. 5, 1983, for "Orbital Cassette Welding Head" , there is disclosed an apparatus for welding abutting tube sections. The apparatus includes, an orbital welding head unit and a separable U-shaped tube clamp unit which holds the tube sections to be welded in .abutting aligned relationship during the rotation of the weld head about the tube ends. The disclosed tube clamp unit uses wide rigid collets to hold the tube sections in alignment during welding and a jaw-like assembly for attachment and removal of the collets to the tubing sections. The clamp is specifically designed to function with the disclosed welding apparatus.

In U.S. Pat. No. 4,973,823, issued Jun. 28, 1989 for "Collet Assembly For Cylindrical Work Pieces", there is disclosed an apparatus for holding cylindrical work pieces. This apparatus, like the previously discussed apparatus, is disclosed as being suited for use as a tubing clamp unit in an orbiting head tube welder. The apparatus includes a clamping device which utilizes a jaw-like method of attaching the collets to the cylindrical member and various designs of interchangeable collets. The collets are specifically designed to compensate for tubing with various outer diameter tolerances.

Certain drawbacks have been encountered in these prior art devices. Particularly, in such devices, the jaw-like method of attachment to the tubing is restrictive in certain limited access or tight fit situations. These limited access applications are common in aircraft and military equipment assembly operations where space is often at a premium. In some applications, the available space is such that the prior art tubing clamp cannot be fit around the tubing pieces. In these instances, completing the tubing assembly often requires a series of cuts and welds in easier to access locations and then overall reassembly. Other drawbacks to existing tubing clamps includes their cost and complexity. The jaw-like clamping method requires the machining of a hinge assembly as well as a latch assembly and their associated hardware. Many of these devices require over thirty hardware pieces for a single clamp. Additionally, the outer diameter variances of modern tubing is generally improved over earlier manufactured tubing, especially when using tubing as typically required in military and aircraft assemblies. This higher tolerance tubing reduces the need for costly, specialized collet assemblies necessary to compensate for such variances. In addition, the use of various and specifically designed collets requires expensive machining as well as an operator who must be able to effectively install, remove and store the separate collet assemblies. Existing tube welding clamp assemblies do not address the need for heat shielding and dissipation during welding. Heat generated during welding can conduct along the tubing and without shielding and dissipation, can damage adjacent valves, seals and other assemblies.

For the foregoing reasons, there is a need for a tube welding fixture and heat shield that can support and align tubing end pieces in preparation for welding using various styles of tube welding devices that is inexpensive to manufacture, simple to use, has the ability to fit in tight locations, and that can shield critical parts from the heat generated by welding.

Summary of the Invention

Briefly, and in general terms, the present invention is directed to a tube welding fixture and heat shield for supporting and axially aligning pieces of cylindrical tubing, in an end-to-end butted relation, in preparation for welding and assembly. A tube welding fixture and heat shield having the features of the present invention comprises a generally U-shaped base member assembly having a rectangular lower member with a pair of rectangular side members extending perpendicularly away from the lower member. Each of the upper ends of the side members is substantially flat and has a centrally disposed semi-cylindrical cut therein. This semi-cylindrical cut extends across the upper surface of each side member and is of essentially the same diameter as the cylindrical tubing to be clamped. A pair of rectangular clamping yokes have a lower surface and an upper surface and are removably mounted to the side members of the base member assembly. The lower surfaces of the yokes are essentially flat and have a centrally disposed semi-cylindrical cut extending across the narrower width of the lower surface and are of substantially the same diameter as the tubing to be clamped. Each of the flat lower surfaces of the yokes is removably seated against the flat ends of the U- shaped base member wherein each of the semi cylindrical cuts align to create a cylindrical hole for clamping the tubing pieces and for removing heat generated from the welding process.

The apparatus, when installed onto tubing with an outer diameter essentially equivalent to the cylindrical hole or clarrping bore, securely supports the tubing ends in close proximity and in precise radial alignment to allow for welding and assembly.

An important aspect of the invention is its utility in difficult to access places, its simplicity, and its low cost. The ability to assemble the tube welding fixture onto tubing in many different positions allows for such high utility. The assembly, which includes only a few, relatively simple to manufacture parts, keeps the tube welding fixture and heat shield of the present invention simple and inexpensive.

Another irrportant aspect of the invention is the solid body construction and the tight fitting clarrp design which surrounds the entire outer diameter of the tubing. This design, in conjunction with the high heat conductivity of the fixture material, acts to absorb and dissipate heat, preventing the heat generated during welding operations from travelling along the tubing, past the fixture, and damaging adjacent components.

Another important aspect of the invention is the spacing between the tubing clamps. This spacing allows maximum utility for the welding apparatus and operation while minimizing space requirements for the overall clamp.

Another important aspect of the invention is the ability to clamp and support the cylindrical tubing in locations that could not otherwise be completed. This flexibility minimizes the need to make a series of expensive and time consuming tubing cuts and welds at easier to access locations and then reassembly because the fixture could not be fit into the desired location. For example, an L-shaped tube welding fixture and heat shield embodiment of the present invention, can be used alone or can be used in conjunction with the U-shaped tube welding fixture and heat shield embodiment, as described, to provide custom fitted tubing support. When used in pairs, the L-shaped tube welding bracket and heat shields can act as tubing clamps for use in very tight spaced and custom fit applications. The use of different combinations of different embodiments of the present invention allows for greater flexibility when making welds and assemblies in custom and tight spaced locations.

Thus, the tubing clamp of the present invention overcomes the problems of previous tubing clamps and provides a simple and inexpensive device without the need for extraneous parts or collets.

The invention, together with additional features and the advantages thereof, may be better understood by reference to the following description taken in conjunction with the accompanying illustrative drawings.

Brief Description of the Drawings

FIG. 1 is a front view of a tube welding fixture and heat shield formed in accordance with the present invention; FIG. 2 is a side view of the embodiment of FIG. 1 showing the clamping bore for supporting the tubing, and a cutaway section showing the engagement bores for retaining the clamping yoke; FIG. 3 is a side view of the embodiment of FIG. 1 showing the base member separated from the clamping yoke;

FIG. 4 is a front view of a second embodiment of a tube welding fixture and heat shield formed in accordance with the present invention;

FIG. 5 is a side view of the embodiment of FIG. 4 showing the clarrping bore for supporting the tubing;

FIG. 6 is a side view of the embodiment of FIG. 4 showing the opposite side of the tube welding fixture as FIG. 5;

FIG. 7 is a bottom view of the embodiment of FIG. 4 showing the side member fastener and the alignment pin locations; and

FIG. 8 is a front view of a third embodiment of a tube welding fixture and heat shield formed in accordance with the present invention showing a left hand bracket fixture, a right hand bracket fixture and an associated base plate.

FIG. 9 is a side view of the tube welding fixture and heat shield of FIG. 8 showing the clarrping yoke retaining fasteners.

FIG. 10 is a top view of the tube welding fixture and heat shield of FIG. 8 showing the fixture attachment holes as well as the clamping yoke retaining fasteners

Description of the Related Art

Referring now to FIGS. 1-3, a first preferred embodiment of the invention is illustrated. The tube welding fixture and heat shield assembly 10 is designed to securely hold two pieces of tubing 22 and 24 (FIG. 1) in end-to-end butted axial alignment so that a welding apparatus can have access to the entire seam and perform the desired weld. The tube welding and heat shield assembly 10 preferably includes a generally U-shaped base member assembly 12 having two generally rectangular side members 14 extending upwardly from a rectangular bottom member 26. The upper surfaces of each side member 14 are preferably flat with a semi-cylindrical cut 27 therein. A pair of clamping yokes 16 are removably attached to the flat upper surfaces of the side members 14. The clarrping yokes 16 are each fitted with a flat lower surface and have a semi-cylindrical cut 28 therein which matches and aligns with the semi-cylindrical cut 27 in the side members 14 of base member 12 (FIG. 2) . These matched semi-cylindrical cuts 27 and 28 form a generally cylindrical hole, or clarrping bore 29, in which the outer walls of tubing sections 22 and 24 are engaged. Each clarrping yoke 16 may be removably joined to the upper surface of each side member 14 using any conventional fastening means, such as, for example, bolts, machine screws, wing-nuts, ball-detent fasteners or the like. Markings 20 may be used to indicate which clarrping yoke 16 fits with which side section 14. This can simplify installation in tightly spaced situations and when a tube welding fixture is designed to mate with two different types or sizes of tubing. However, in most preferred embodiments, the clamping yokes 16 are generally interchangeable with either of the two side members 14 and no markings are necessary.

To create axially aligned clarrping bores 29 using a single machining operation, each clamping yoke 16 is attached to a corresponding side member 14 and then a cylindrical hole is machined. This method achieves a semi-cylindrical cut in both clarrping yokes 16 as well as both side members 14 using only one machining operation, such as a center bore. This single operation, in addition to reducing machining costs, generally assures precise tubing end piece to end piece alignment. For an appropriate compression fit and tolerancing, a thin shim (not shown) is generally inserted between the side members 14 and the clarrping yokes 16 prior to machining and then removed once the machining process is completed. By using shims during the machining process, the diameter of the cylindrical holes formed by the joining of the upper and lower members 14 and 16, respectively, is reduced when the shims are removed. This provides a good corrpressive fit to tubing having the same diameter as the machined clarrping bore without reducing alignment accuracy. A shim of approximately 0.004 inches has been found to be generally appropriate for ensuring proper clarrping of average quality tubing pieces. The shim thickness can be increased for tubing pieces having greater outer diameter tolerances, and the shims may not be employed at all in cases of precision tubing, such as tubing manufactured to military specifications. In a typical application, a first piece of tubing, either tubing piece 22 or 24, is inserted between a first side member 14 of base member assembly 12 and a clarrping yoke 16. The tubing piece is then secured using a pair of clarrping yoke fasteners 18. A second piece of tubing, the piece remaining of tubing piece 22 or 24, is then clanped between the second side member 14 and a second clarrping yoke 16, using a second set of clarrping yoke fasteners 18. The tube welding fixture and heat shield assembly 10 is now fully installed onto the tubing pieces 22 and 24. The welding fixture assembly 10 can be adjusted to allow better access during the welding process by loosening the clamping yoke fasteners 18 and rotating the assembly 10 to the desired location and re-tightening the yoke fasteners 18.

The spacing between the side members 14, which determines the length of the bottom member 26, depends on the type of welding apparatus to be used. In general, this spacing is minimized to enable a smaller overall fixture assembly 10. However, larger welding assemblies and specialized applications may require greater spacing. This also applies to the spacing between the upper surface of the bottom member 26 and the center of the cylindrical clarrping bore 29, or equivalently, the top of the side members 14.

A preferred side member 14 spacing, when working with 0.50 inch outer diameter tubing and an orbital type welding apparatus, has been found to be approximately 1.50 inches between the inner walls. A preferred spacing between the upper side of the bottom member 26 and the top of the side members 14, when working with 0.50 inch tubing is approximately 2.00 inches.

Other preferred dimensions when working with 0.50 inch tubing include an overall tube welding fixture assembly 10 width of approximately 1.25 inches, a side member 14 and bottom member 26 thickness of 0.375 inches and a clarrping yoke 16 height of 0.375 inches. For this assembly, .25-20NC machine bolts are preferred with through holes in the clamping yokes 16, and .25-20NC threads in the side members 14.

To provide heat protection when welding, the tube welding fixture and heat shield assembly 10 is made from heat conducting material such as aluminum, copper, or other heat conducting metal. Aluminum has proved inexpensive and easy to work with and is generally preferable. The tight fit of the clamped tubing 22 and 24 through side members 14 and clarrping yokes 16, respectively, acts to create a heat shield which prevents heat from being conducted along the tubing pieces 22 and 24 and thereby damaging adjacent valves, seals and assemblies. The highly heat conductive material of the tube welding and heat shield assembly 10 additionally acts to absorb excess heat from the welding operation and to dissipate the heat throughout the entire assembly 10. The side members 14 further act as cooling fins and may be fitted with grooves, fins, and holes for improved heat dissipation, if desired.

Referring now to FIGS. 4-7, a second alternative embodiment of a tube welding fixture having the features of the present invention and generally including the features described in the previous embodiment is described. The tube welding fixture and heat shield assembly 30 includes a generally U-shaped base member assembly 32 having two generally rectangular side members 34 and 36 preferably extending perpendicularly upwardly from a generally rectangular bottom member 46. The upper ends of each side member 34 and 36 are flat with a semi-cylindrical cut therein as shown in FIG. 5 and FIG. 6, and as described in the previous embodiment above. Side member 36 is removably mounted to bottom member 46 of base member assembly 32 through the use of a fastener 44 such as, for example, a machine screw, wing-nut, ball-detent fastener or the like. A pair of alignment pins 42 are fixed in the side member 36 for engagement into matching alignment holes in the bottom member 46. These alignment pins 42 are preferably made from steel, but other equivalent materials of similar qualities may be employed as well. The alignment pins are preferably press fit into the side member 36 and slip fitted into bottom member 46 by means of tight fitting bores (not shown) .

Clamping yokes 38 are removably attached to the upper surface of side members 34 and 36. The clarrping yokes 38 are each fitted with a flat lower section having semi-cylindrical cuts therein. These semi- cylindrical cuts correspond to the semi-cylindrical cuts in the side members 34 and 36 to create a cylindrical hole or clarrping bore having a diameter slightly smaller than the outer diameter of the tubing to be engaged. When attached, the clamping yokes 38 act to coπpressively engage the tubing (not shown) as described in the previous embodiment. Each clamping yoke 38 is removably joined to the upper end of each side member 34 and 36 using any convenient mechanical fastener, such as, machine screws, wing-nuts, pin-detent fasteners or the like. Preferably, similar fasteners are used for attaching the clarrping yokes 38 to the side members 34 and 36 as are used for attaching the side member 36 to the bottom member 46.

In a typical application, a first piece of tubing (not shown) is inserted between the fixed side member 34 of base member assembly 32 and a clamping yoke 38. The tubing is secured by tightening the clarrping yoke fasteners 40. A second piece of tubing (not shown) is then inserted between the removable side member 36 and a second clarrping yoke 38, and secured using a second set of clarrping yoke fasteners 40. The removable side member 36 may then be loosely attached to the bottom member 46 using fastener 44. The tubing end pieces may then be precisely aligned in an end-to-end butted fashion by engaging the alignment pins 42 into the alignment pin holes in the bottom member 46 of the base member assembly 32. The side member 36 is then secured to the bottom member 46 by fully engaging the fastener 44. Alternatively, a slight gap may be left between the side member 36 and the base member 46 prior to clamping on the tubing pieces (not shown) . The ends of the tubing pieces (not shown) can then be brought into intimate contact by further tightening of fastener 44. The tube welding fixture and heat shield 30 is now installed onto the tubing pieces but may be further adjusted to allow better access for the welder or assembler. This may be accomplished by loosening the clarrping yoke fasteners 40 and rotating the entire tube welding fixture assembly 30 to a desired orientation and re-tightening the fasteners 40.

Referring now to FIGS. 8-10, a third alternative embodiment of a tube welding fixture and heat shield having the features of the present invention and generally including the features described in the previous embodiments is described. In this embodiment, tube welding fixture and heat shield assembly 50 includes an L-shaped side member 52 having a flat upper surface with a semi-cylindrical cut therein. The axis of the semi-cylindrical cut is aligned parallel to the "L" of the L-shaped side member 52. A clamping yoke 54 of the same design and function as described in the previous embodiments is used in conjunction with the side member 52 to engage and secure tubing pieces 58 and 62.

Attachment holes 60 are provided in the side member 52 for attachment to a base plate 64 or other fixed supporting means, such as an aircraft frame member or similar structural support. Preferably, attachment holes 60 are 0.25 inch diameter holes located in the lower section of base member 52, however, other attachment holes of various sizes and locations may be preferable depending on installation requirements and availability. Fasteners 66 may be used to attach the fastener 50 to the base plate 64 or aircraft frame member.

The tube welding fixture and heat shield 50 has similar advantages as the previously described embodiments and can often be installed in even more restrictive space environments. Since the spacing between a pair of these tube welding fixtures 50 can be adjusted, greater installation flexibility is allowed on the tubing pieces. A further advantage, is the ability to use the tube welding fixture and heat shield 50, either alone or in pairs on a work bench (not shown) . The fixtures 50 may be used in conjunction with base plate 64 or attached directly to the work bench. Additional fixtures 50 may be used to act as a heat shield and increase heat dissipation as necessary.

Although several embodiments of the invention have been described, it is to be understood that the invention is not to be limited to those descriptions. Various changes and alterations may be made to the design and arrangement of the individual components without departing from the spirit and scope of the invention as understood by one with skill in the art.

Claims

What is Claimed is:

1. A tube clarrping apparatus for holding and axially aligning cylindrical tubing pieces in end-to-end butted relation comprising: a generally U-shaped base member having a lower member and a pair of side members extending from the lower member, each of the side members having a substantially flat upper surface with a semi-cylindrical cut therein, the semi-cylindrical cuts being of substantially the same diameter as the outer diameter of the tubing pieces to be held; a pair of substantially similar clarrping yokes, each having a lower surface and an upper surface, each of the lower surfaces of the yokes being essentially flat and having a semi-cylindrical cut therein, the semi-cylindrical cuts of the clamping yokes being of substantially the same diameter as the outer diameter of the tubing pieces to be held, each of the lower surfaces of the yokes being removably seatable against the upper surfaces of the side members such that the semi- cylindrical cuts of both the side members and the clamping yokes are correspondingly aligned, thereby together creating a generally cylindrical clarrping bore for holding the tubing pieces; and fasteners for removably attaching each clamping yoke to each of the flat upper surfaces of the side sections; wherein the apparatus, when installed onto tubing pieces with an outer diameter essentially equivalent to the clarrping bore, securely holds the tubing ends in close proximity and in radial alignment.

2. The tube clamping apparatus as described in claim 1 wherein the generally U shaped base member and the clamping yokes are made from heat conducting materials .

3. The tube claping apparatus as described in claim 1 wherein the generally U shaped base member and the clarrping yokes substantially comprise aluminum.

4. The tube clarrping apparatus as described in claim 1 wherein the generally U shaped base member and the clamping yokes substantially comprise copper.

5. The tube clarrping apparatus as described in claim 1 wherein the base member is sized to allow for an orbital style welding head to fit within the side members and weld the clamped tubing pieces .

6. The tube clamping apparatus as described in claim 1 wherein the fasteners used to attach the clamping yokes to the base member comprise machine screws .

7. The tube clarrping apparatus as described in claim 6 wherein the side members further comprise internally threaded bores for removably attaching the clarrping yokes.

8. An apparatus for holding and axially aligning a first piece of cylindrical tubing and a second piece of cylindrical tubing in end-to-end butted relation for use during welding and assembly comprising: a generally U-shaped base member made from a heat conducting material, said base member having a substantially rectangular lower member with a pair of substantially similar side members extending from the lower section, each of the side members having a substantially flat upper surface which has a centrally disposed half cylinder cut therein, the cylindrical cuts extending across the narrower width of the upper surface of each side member and being of substantially the same diameter as the outer diameter of the tubing piece to be held; a pair of substantially similar rectangular clamping yokes made from heat conducting material and having a lower surface and an upper surface, each of the lower surfaces of the yokes being essentially flat with a centrally disposed semi-cylindrical cut therein, the cylindrical cuts extending across the narrower width of the lower surface and being of substantially the same diameter as the outer diameter of the tubing section to be held, each of the lower surfaces being removably seatable against the flat upper surfaces of the side members wherein the half cylindrical cuts of both the side members and the clarrping yokes are correspondingly aligned, thereby together creating a generally cylindrical clarrping bore for holding the tubing pieces; and fasteners for removably attaching the clamping yokes to the upper surfaces of the side members.

9. The apparatus for holding tubing as described in claim 8 wherein at least one side member is removably attached to the base member.

10. The apparatus for holding tubing as described in claim 9 wherein the at least one side member is removably attached to the base member using at least one machine screw.

11. The apparatus for holding tubing as described in claim 9 further comprising a pair of alignment pins for axially aligning the held tubing sections when attaching the removable side member.

12. The apparatus for holding tubing as described in claim 11 wherein the alignment pins are steel pins which are fixed in the removable side member and insertable into the base member.

13. The apparatus for holding tubing as described in claim 8 -wherein the fasteners comprise bolts .

14. The apparatus for holding tubing as described in claim 8 wherein the half cylindrical cuts have a smaller diameter about one axis to ensure a corrpressive fit when the clamping yokes are attached to the side members over a piece of cylindrical tubing.

15. A tube clarrping apparatus for holding cylindrical tubing sections during welding and assembly, comprising: a first clamping member, said clamping member having a substantially rectangular lower member and a substantially rectangular upper member that form an L shape, the lower member having a plurality of holes for attachment to supporting structure, the upper member having a flat upper surface with a centrally disposed, substantially half cylindrical cut extending across the narrow width; a second clamping member opposed to the first clamping member and adapted to be moved toward and away from the first clamping member, the second clamping member being substantially rectangular and having a lower surface and an upper surface, the lower surface being essentially flat and having a centrally disposed, substantially half cylindrical cut which extends across the narrow width of the lower surface and which may be aligned with the substantially half cylindrical cut in the first clarrping member to form a cylindrical bore; and fasteners for removably attaching the first clamping member to the second clamping member wherein a cylindrical tubing section may be clanped between the first and second clarrping members in preparation for welding and assembly.

16. The tube clamping apparatus as described in claim 15 wherein the clarrping members further comprise heat conducting material

17. The tube clarrping apparatus as described in claim 16 wherein the clamping members are comprised of aluminum.

18. The tube clamping apparatus as described in claim 16 wherein the clamping members are comprised of copper.

19. The tube clamping apparatus as described in claim 15 wherein the fasteners comprise machine screws.

20. The tube clarrping apparatus as described in claim 15 wherein the half cylindrical cuts have a smaller diameter about one axis to ensure a corrpressive fit when the clarrping members are clamped over a cylindrical tubing section.