14. Mechanisation. and Welding Fixture

Transcription

1 14. Mechanisation and Welding Fixture

2 14. Mechanisation and Welding Fixtures 197 As the production costs of the metal-working industry are nowadays mainly determined by the costs of labour, many factories are compelled to rationalise their manufacturing methods by partially and fully mechanised production processes. In the field of welding engineering where a consistently good quality with a maximum productivity is a must, automation aspects are conse-quently taken into account. Designation manual welding m partially mechanised welding t fully mechanised welding v automatic welding a br-er14-01e.cdr Figure 14.1 examples gas-shielded arc welding TIG GMAW torch-/ workpiece control manually manually movement/ working cycles filler wire feeding manually mechanically mechanically mechanically workpiece handling manually manually manually mechanically mechanically mechanically The levels of mechanisation in welding are stipulated in DIN 1910, part 1. Distinctions are made with regard to the type of torch control and to filler addition and to the type of process sequence, as, e.g., the transport of parts to the welding point. Figure 14.1 explains the four levels of mechanisation. Figure shows manual welding, in this case: manual electrode welding. The control of the electrode and/or the arc is carried out manually. The filler metal (the consumable electrode) is also fed manually to the welding point. br-er14-02e.cdr ISF 2002 Manual Welding (Manual Electrode Welding) Figure 14.2

3 14. Mechanisation and Welding Fixtures 198 In partially mechanised welding, e.g. gas-shielded metal-arc welding, the arc manipulation is carried out manually, the filler metal addition, however, is executed mechanically by means of a wire feed motor, Figure br-er14-03e.cdr Figure 14.3 Partially Mechanised Welding (Gas-Shielded Metal-Arc Welding) In fully mechanised welding, Figure 14.4, an automatic equipment mechanism carries out the welding advance and thus the torch control. Wire feeding is realised by means of wire feed units. The workpieces must be positioned manually in accordance with the direction of the moving machine support. In automatic welding, besides the process sequences described above, the work-pieces are mechanically positioned at the welding point and, after welding, automatically trans-ported to the next working station. Figure14. 5 shows an example of automatic welding (assembly line in the car industry). br-er14-04e.cdr Figure 14.4 Fully Mechanised Welding (Gas-Shielded Metal-Arc Welding)

4 14. Mechanisation and Welding Fixtures 199 br-er14-05e.cdr Figure 14.5 Automatic Welding (Assembly Line) Apart from the actual welding device, that is, the welding power source, the filler metal feeding unit and the simple torch control units, there is a variety of auxiliary devices available which facilitate or make the welding process at all possible. Figure 14.6 shows a survey of the most important assisting devices. assembly line welding robot machine carrier linear travelling mechanism track-mounted welding robots spindle / sliding head turntable turn-/ tilt table dollies assembly devices br-er14-06e.cdr Before welding, the parts are normally aligned and then tack-welded. Figure 14.7 depicts a simple tack-welding jig for pipe clamping. The lower part of the device has the shape of a prism. This allows to clamp pipes with different diameters. Devices, however, may be Figure 14.6 significantly more complex. Figure 14.8 shows an example of an assembly equipment used in car body manufacturing. This type of device allows to fix complex parts at several points. Thus a defined position of any weld seam is reproducible.

5 14. Mechanisation and Welding Fixtures 200 In apparatus engineering and tank construction it is often necessary to rotate the components, e.g., when welding circumferential seams. The equipment should be as versatile as possible and suit several tank diameters. Figure 14.9 shows three types of turning rolls which fulfil the demands. Figure bottom: the rollers are adjustable; Figure middle: the rollers automatically adapt to the tank diameter; Figure top: the roller spacing may be varied by a scissor-like arrangement. In general, dollies are motor-driven. This provides also an effortless movement of heavy components, Figure br-er14-07e.cdr Figure 14.7 br-er14-08e.cdr Figure 14.8 Simple Tack Welding Jig for Welding Circumferential Welds 1 portal with 2 industrial robots IR 400, equipped with tool change system 2 resting transformer welding tongs 3 depot of welding tongs 4 clamping tool 5 copper back-up bar for car roof welding 6 transformer welding tongs for car roof welding 7 driverless transport system 8 component support frame 9 swivelled support for component support frames 10 resting transformer welding tongs for car boot A work piece positioner, e.g. a turn-tilt-table, is part of the standard equipment of a robot working station. Figure shows a diagrammatic representation of a turn-tilt-table. Rotations around the tilting axis of approx. 135 are possible while the turn-table can be turned by 365. Those types of turn-tables are designed for working parts with weights of just a few kilograms right up to several hundred tons.

6 14. Mechanisation and Welding Fixtures 201 br-er14-09e.cdr set of rollers 1 set of rollers 2 br-er14-10e.cdr Turning Rolls Turning Rolls Figure 14.9 Figure rotational axis table top gear segment table support tilting axis support A turn-tilt-table with hydraulic adjustment of the tilting and vertical motion as well as chucking grooves for the part fixture is depicted in Figure br-er14-11e.cdr Figure 14.11

7 14. Mechanisation and Welding Fixtures 202 In robot technology the types of turn-tilt-tables - as shown in Figure are gaining importance. Positioners with orbital design have a decisive advantage because the component, when turning around the tilting axis, remains approx. equally distant to the welding robot. br-er14-12e.cdr Turn-Tilt-Table With Hydraulic Adjustment Other types of workpiece Figure positioners are shown in Figure the double column turn-tilt-table and the spindle and sliding holder turn-tilt-table. Those types of positioners are used for special component geometries and allow welding of any seam in the flat and in the horizontal position. single-column turn-tilt-table table top table support tilting axis support rotational axis br-er14-13e.cdr Turn-Tilt-Tables orbital turn-tilt-table table top table support tilting axis support rotational axis ISF 2002 In the field of welding, special units are designed for Figure special tasks. Figure shows a pipe-flange-welding machine. This machine allows the welding of flanges to a pipe. The weld head has to be guided to follow the seam contour.

8 14. Mechanisation and Welding Fixtures 203 tilting axis rotational axis table top support table support br-er14-14e.cdr ISF 2002 Double-Column Turn-Tilt-Table Figure table tops spindle holder sliding holder bed way br-er14-15e.cdr ISF 2002 Spindle / Sliding Holder Turntable Figure br-er14-16e.cdr Figure 14.16

9 14. Mechanisation and Welding Fixtures 204 Plain plates or rounded tanks are clamped by means of longitudinal jigs for the welding of a longitudinal seam, Figure The design and the gripping power are very dependent of the thickness of the plates to be welded. br-er14-17e.cdr Figure welding, Figure This device is designed for the application on-site and provides, besides the supply of the filler metal, also the welding speed as well as the feeding and suction of the welding flux. A simple example of a special welding machine is the tractor travelling carriage for submerged-arc For the guidance of a welding head and/or welding device, machine supports may be used. Figure shows different types of machine supports for welding and cutting. Apart from the translatory and rotary principal axes they are often also equipped with additional axes to allow precise positioning. br-er14-18e.cdr Tractor for Submerged-Arc Welding Figure 14.18

10 14. Mechanisation and Welding Fixtures 205 To increase levels of mechanisation of welding processes robots are frequently applied. Robots are handling devices which are equipped with more than three user-programmable axes. Figure describes kinematic chains which can be realised by different combinations of translatory and rotary axes. a b c d br-er14-19e.cdr boom pillar Figure travelling mechanism auxiliary piloting system case main piloting system case e cross piloting system case auxiliary piloting system case The most common design of a track-mounted welding robot is shown in Figure The robot designation cartesian robot cylinder coordinated robot spherical coordinated robot horizontal knuckle arm robot vertical knuckle arm robot depicted here is a hinged- arrangement arm robot with six axes. The axes are divided into three principal and three addi- kinematic schedule x z y z C R C B R C z D C B A tional axes or hand axes. The wire feed unit and the operating space spool carriers for the wire br-er14-20e.cdr ISF 2002 electrodes are often fixed on Kinematic Chains the robot. This allows a compact welding design. Figure 14.20

11 14. Mechanisation and Welding Fixtures 206 Varying lever lengths permit the design of robots with different operating ranges. Figure shows the operating range of a robot. In the unrestricted operating range the component may be reached with the torch in any position. The restricted operating range allows the torch to reach the component only certain positions. In the case of a suspended arrangement the robot fixing device is shortened thus allowing a compact design. br-er14-21e.cdr Figure Robot Motions For the completion of a robot welding station workpiece positioners are necessary. Figure shows positioner devices where also several axes may be combined. These axes may either turn to certain defined positions or be guided by the robot control and moved synchronically with the internal axes. The complexity and versatility of the axis positions increases with the number of axes which participate in the movement. br-er14-22e.cdr Figure 14.22

12 14. Mechanisation and Welding Fixtures 207 br-er14-23e.cdr Figure Movement by means of a linear travelling mechanism increases the operating range of the robot, Figure This may be done in ease of stationary as well as suspended arrangement, where there is a possibility to move to fixed end positions or to stay in a synchronised motion with the other movement axes. br-er14-24e.cdr Figure 14.24