GB2385817A

GB2385817A - Welding jig

Info

Publication number: GB2385817A
Application number: GB0204630A
Authority: GB
Inventors: Peter John Kitching
Original assignee: Henry Smith
Current assignee: Henry Smith
Priority date: 2002-02-27
Filing date: 2002-02-27
Publication date: 2003-09-03
Also published as: GB0204630D0

Abstract

A jig for welding frame members of a building comprises a baseplate 21 having a tailstock 27 and headstock 23 movable together and apart thereon. The tailstock 27 and headstock 23 have rotatable support arms 29, 30 and a clamp (46 - 48, figs 4 and 8) for a beam to be welded, the arms preferably being offset to place the beam substantially on the rotational axis. A robot welder 40 preferably runs on a track parallel to the rotational axis. A central support 33 may be provided to prevent sagging of the beam.

Description

Device for Fabrication of Frame Members This invention relates to the fabrication of frame members of a building, particularly steel framework consisting of'H'section beams.

Steel framed structures are a preferred method of construction for large covered spaces such as industrial buildings, shopping malls, sport centres and the like. Such a frame can be erected rapidly and inexpensively. The frame members are fabricated off-site from standard'H'section steel joists, and are bolted together to form the structure. It is of course of great importance that the individual sections are accurately manufactured, so that the structure can be assembled efficiently.

Computer programs are used to speed up the design process, and to perform the required stress analysis. In particular such a program can usually suggest the use of smaller material sections provided that adequate reinforcement is provided in regions of high load. Thus the theoretical computer design may be considerably lighter and cheaper than traditional methods using larger material sections. A problem which arises however is that of fabricating the individual sections to the required degree of precision, and with good quality control.

A typical fabricated section is the roof girder. This comprises a long'H'section beam, typically 300-900 mm deep and up to 25 m long. Such a girder is bolted to an upright at an angle to define the pitch of the roof. At the junction a haunch or gusset is welded to the underside of the girder, and an end plate added. The end plate is drilled to correspond with bolt holes in the upright.

In order to use the lightest possible section, high quality and precise welding is required. However such large beams pose a considerable manipulation problem and welding is not always possible in the desired orientation. Ideally welding should be from above and along a freely accessible seam. Frequently however welding from underneath is often inevitable because of the physical difficulty of turning a partially

complete fabrication, and the risk of introducing bending stress and deformation as the beam is turned.

What is required is a means of beam manipulation which is capable of providing adequate support during welding, yet allows free access to the welder at the most suitable welding orientation.

According to the invention, there is provided a welding jig for structural steel beams and comprising a bed, a headstock and a tailstock on the bed and movable towards and away from each other, the headstock and tailstock each having an arm mounted for rotation in unison about a common axis, the arms extending toward one another and each having a generally horizontal support surface adapted to receive one respective end of a beam, the arms further including clamps to fix a beam thereto whereby the beam can be rotated about said axis.

Such an arrangement permits rotation of the beam to any desired angle for welding.

Preferably the arms include bearing members thereon whereby the beam can be shifted axially relative to the headstock so as to adjust the position thereof. Such an arrangement ensures that the beam can be displaced in order to give welding access to an otherwise obscured region. The bearing members typically comprise rollers, but ball bearings are a suitable alternative.

The clamps preferably consist of opposed jaws having a horizontal opening and closing axis perpendicular to said common axis, and preferably each of said jaws includes a generally vertical clamping member. Such an arrangement is particularly suitable for clamping the web and flange of an'H'section beam.

The jig may further include an intermediate support to counter sagging of long beams, such support also being on the bed and consisting of a base and an annular frame rotatable thereon about said common axis, a beam passing through the annular frame on supports provided at the inner side thereof. In the preferred embodiment, the annular frame opens to permit a beam to be lowered onto a support thereof. Preferably this

support is vertically adjustable in order to counter sagging of the beam to the desired degree; the support may comprise a fluid ram and a screw threaded stop.

The bed preferably includes a rack thereon whereby the tailstock may be driven towards or away from the headstock. By releasing only the headstock clamp the beam may be shifted relative thereto by movement of the tailstock. Similarly the beam may be shifted relative to the tailstock by releasing only the tailstock clamp.

In the preferred embodiment, the headstock and tailstock arms are offset from the common axis so as to permit the approximate centreline of the beam to be positioned on the common axis.

In the preferred embodiment a robot welder is provided on a track running parallel to said common axis, the welder having a manipulator adapted to traverse a welding head along a seam to be welded. Preferably the robot welder includes contact sensing means whereby it can learn about the shape and form of the beam prior to welding. Such an arrangement ensures that the welding head can closely follow deviations and minor defects of the beam.

The robot welder may be mounted on the bed.

Other features of the invention will be apparent from the following description in which :- Fig. 1 is a scrap elevation of a partial steel frame.

Fig. 2 is an enlarged isometric view of the end of a roof beam with haunch.

Fig. 3 is a horizontal elevation of a jig according to the invention.

Fig. 4 is a cross-section on line 4-4 of Fig. 3.

Fig. 5 is a cross-section on line 5-5 of Fig. 3.

Fig. 6 is a cross-section on line 6-6 of Fig. 3.

Fig. 7 is an enlarged end elevation of the headstock.

Fig. 8 is a cross-section on line 8-8 of Fig. 7.

With reference to the drawings Fig. 1 illustrates part of a portal steel frame for a building structure, and comprising an upright 11 to which is bolted a roof girder 12 having a haunch 13 welded to the underside thereof.

Fig. 2 shows the end of the girder 12 and haunch 13 in more detail. The haunch, which may be cut from a standard'H'beam section is welded to one flange of the'H'beam girder 12 by intermittent or continuous welds 14. An end plate 15 is welded to the end of the girder and haunch to stiffen the fabrication and provide a convenient bolting surface for flush fitting to the upright 11. Both holes 16 are drilled in the end plate as illustrated.

In practice, the haunches 13 and end plates 15 are held in a frame and tack welded to the girder 12 and to each other. The fabrication is then transferred to the welding jig of the present invention, which is illustrated in Figs. 3-8.

A typical beam may be 25 m long and have a web depth of 300-900 mm. Although very stiff, such a beam exhibits considerable distortion when lifted, or when not adequately supported.

The jig comprises a massive bedplate 21, typically of concrete and incorporating longitudinally extending slideways and guideways, e. g. of steel. At one end of the bedplate 21 is a headstock 22 comprising a fixed frame 23 having a faceplate 24 rotatable thereon about a generally horizontal axis 25. At the other end of the bedplate a tailstock 26 comprises a movable frame 27 having a faceplate 28 rotatable thereon

about axis 25. The movable frame 27 is mounted on e. g. rollers and can slide towards and away from the headstock 22. The frame 27 is for example supported on spaced rails with a guide track therebetween so as to remain in precise alignment with the headstock during movement thereof. Conventional means (not shown) are provided to lock the tailstock in a desired position against fore and aft movement, for example a series of holes in the guide track into which a pin mounted on the tailstock can selectively engage.

Each faceplate 24,28 includes an axially protruding arm 29,30 offset from the axis 25 and providing a pair of horizontally aligned support surfaces defined by rollers 31. The rollers are mounted for free rotation with respect to the arms 29,30 in any suitable manner. An array of ball bearings may be used as an alternative where freedom of movement in two mutually perpendicular directions is desired, for example for ease of centreing a girder in the jig.

As illustrated, a long girder 32 having tack welded haunches and end plates may be lowered onto the rollers 31 from above after the tailstock has been positioned at a suitable distance from the headstock.

In order to compensate for sagging of the girder, one or more central supports 33 may be provided, each comprising a support frame 34 movable along the slideway of the bed 21 and an annulus 35 mounted thereon by rollers 36. The external surface of the annulus 35 is circular, and is arranged concentric with the axis 25. Within the annulus one or more hydraulic and screw jacks 37 may be adjusted to lift the beam to an approximately straight condition. Additional jacks or clamps (not illustrated) may be provided to engage the one or both flanges (as illustrated) and web so as to retain the girder 32 within the annulus 35 in a predetermined position.

The annulus is divided along the horizontal diameter thereof to permit a girder to be lowered onto the jack 37. An eye bolt 38 is provided for lifting and lowering the upper half. Conventional location and fastening means are provided to retain the two parts of the annulus 35 in register for unrestricted rotation about the axis 25.

A robotic welder 40 is mounted on a carriage 41 for movement longitudinally of the bedplate 21 on a suitable guideway thereof. The welder is of conventional form and has a manipulator 42 to the end of which is mounted a MIG welding torch.

The guideway of the robotic welder 40 is carefully positioned and aligned with respect to that of the tailstock and central support 33.

Each arm 29,30 includes a clamping device 45 adapted to secure the girder thereon. As best illustrated in Figs. 7 and 8, this device 45 comprises opposed jaws 46,47 connected by a lead screw 48 with opposite handed threads, and a handwheel 49. The jaws are slidable on the respective arm 29,30 in a conventional manner and are secured thereto by suitable interengaging slideways (not shown).

Mounted on each jaw 46,47 are two clamp screws 50 which can engage both sides of the lower flange, as illustrated, in order to lock this flange against the rollers 31.

Datum faces 51,52 are provided on the outer face of each faceplate 24,28, as illustrated in order to provide a reference for the robotic welder 40.

The device is used in the following manner. The girder, haunches and end plates are first tack welded in a suitable fixed jig so as to ensure that each part is precisely located with respect to another, and that distortion of the components is so far as possible taken into account. Such a jig may be of conventional kind, and sufficiently massive to ensure that precise location is maintained during the tack welding stage. The tack welding stage is performed with the beam in the same orientation as illustrated in Fig.

3.

The part fabricated girder is then transported by overhead crane to the jig of the invention, and lowered onto the arms 29,30. The rollers 31 facilitate movement of the girder to the left and right. When lowered onto the arms, the girder has the same orientation as when tack welded, and accordingly the introduction of additional stresses is avoided.

Once in the desired lateral condition the lead screws 48 are closed so that the jaws 46,47 lightly grip the web of the girder. The sag of the girder is counteracted by the screw jack 37, and the clamp screws 50 are tightened. Suitable girder supports (not shown) are provided in the annulus 35 to hold the girder against sideways or upwards movement (as viewed). The girder is now precisely located with respect to the faceplates 24,28 and bedplate 21.

In a known fashion, the welder can be caused to traverse the length of the girder and record position data with respect to one or more of the datum faces 51,52. Having recorded this data, the welder is caused to seam weld from above in those places which are accessible.

The face plates are adapted for rotation in unison by means of suitable stepper motors in order to allow all necessary seams of the girder to be welded from above. In this way weld quality can be closely controlled, and in practice most welds can be made by a generally horizontal traverse of the welding torch.

Rotation solely by a motor of the headstock may be sufficient for certain stiff beam sections since the resistance to rotation is relatively small.

The jaws 46,47, clamp screws 50, and the clamping/supporting arrangement of the central support 33 ensure that the girder is retained in a known condition with respect to the datums, even when upended (as viewed). Accordingly welding can be accurate and precise.

At any stage during the seam welding operation, the clamps and jaws may be slackened to permit lateral movement of the girder on the rollers 31 in the orientation shown in Fig. 3. Such movement, which may be in the range 0-500 mm, allows access to areas which might otherwise be obscured by the clamps and jaws themselves. No distortion is introduced by this lateral movement since the girder remains fully supported at all times. After movement the jaws and clamps may be re-tightened, to permit seam

welding to continue. It will be appreciated that the girder may include many minor welded fitments, for example for the attachment of roof spars and the like, all of which may be tack welded during an initial fabrication stage, and seam welded on the jig of the present invention.

The offset of the arms 29,30 is intended to accommodate the largest beam section likely to be welded. Less deep sections can be placed approximately on the axis 25 by the use of packing pieces clamped thereto and supported on the rollers 31.

The various clamps, jacks and jaws may be activated mechanically or automatically (for example by the use of hydraulic or electrical actuators), and means may be provided on one or both faceplates 24,28 to nudge the girder laterally to a new location.

Claims

1. A welding jig for structural steel beams and comprising a bed, and a headstock and a tailstock on the bed, the headstock and tailstock being relatively movable towards and away from each other, the headstock and tailstock each having an arm mounted for rotation in unison about a common axis, the arms extending toward one another and each having a generally horizontal support surface adapted to receive one respective end of a beam, the arms further including clamps to fix a beam thereto whereby the beam can be rotated about said axis.

2. A jig according to claim 1 wherein said arms include bearing members thereon whereby the beam can be shifted axially relative to the headstock so as to adjust the position thereof.

3. A jig according to claim 2 wherein said bearing members comprise rollers.

4. A jig according to any preceding claim wherein said clamps consist of opposed jaws having a horizontal opening and closing axis perpendicular to said common axis.

5. A jig according to claim 4 wherein each of said jaws includes a generally vertical clamping member.

6. A jig according to any preceding claim and further including an intermediate support to counter sagging of long beams, such support being on the bed and consisting of a base and an annular frame rotatable thereon about said common axis, in use a beam passing through the annular frame on supports provided at the inner side thereof.

7. A jig according to claim 6 wherein said annular frame opens to permit a beam to be lowered onto a support thereof.

8. A jig according to claim 7 wherein said support is vertically adjustable in order to counter sagging of the beam to the desired degree.

9. A jig according to claim 8 wherein said support comprises a fluid ram and a screw threaded stop for abutment with a beam.

10. A jig according to any preceding claim and further including a rack thereon whereby the tailstock may be driven towards or away from the headstock.

11. A jig according to any preceding claim wherein the headstock and tailstock arms are offset from the common axis so as to permit the approximate centreline of the beam to be positioned on the common axis in use.

12. A jig according to any preceding claim and further including a robot welder provided on a track running parallel to said common axis, the welder having a manipulator adapted to traverse a welding head along a seam to be welded on a beam.

13. A jig according to claim 12 wherein said robot welder includes contact sensing means whereby it can in use learn about the shape and form of the beam prior to welding.

14. A welding jig substantially as described herein with reference to the accompanying drawings.