德國原版焊接技術(shù)資料(12)

1、 Figure 1 Principle of one-sided resistance spot welding 1 Figure 3 Modern inverter power source Foto: EWMFigure 2 Principle of TIG spot weldingSpot technology, fast, low-voltage Spot welding with tungsten shielding gasby Heinz Lorenz, Mündersbach, GermanyIntroductionIn mechanical engineering,

2、switch cabinetconstruction, car construction, as well as in various other sectors, such as the manufacture of household appliances, including refrigerators, washing machines etc., there are many welding tasks in which thin panels need to be welded on one side using a spot welding technique. These we

3、lds can also beperformed using resistance spot welding. If the point to be welded is only accessible from one side, theelectrodes are aligned with one another on one side of the workpiece in this process, and the metal sheets lie on a copper base, Figure 1 1. However, accessibility is often so restr

4、icted that it is not even possible toinsert the copper base underneath, and therefore resistance welding cannot be performed. For many years, variations of the arc welding process have therefore been used for one-sided spot welding on thin metal, such as MIG/MAG, TIG (Figure 2 andmore recently the p

5、lasma process. Especially fortungsten shielding gas spot welding, there have been recent developments in terms of the power sources, controls and torches, which make this process easier to use and which improve the quality of the spots.Advantages of arc spot weldingThe surface formation produced on

6、the welding points is one argument against the use of one-sidedresistance spot welding. To position and fix the metal sheets sufficiently well on the copper base, a higher pressure needs to be used that can causeimpressions in the heated surface of the metal sheet. Resistance welding systems also ne

7、ed to beavailable, which is not the case at every site. Arc spot welding machines, on the other hand, can also beused for seam welding and therefore provide universal usage.In comparison to MIG/MAG spot welding, tungsten shielding gas welding offers the advantage of improved spot surfaces. As the we

8、lding can be performed without filler material and is only melted onto the parent material, the welded points produced are particularly flat and smooth. This is a significant benefit, especially on visible areas. In addition, the heat feeding is very low thanks to the short welding times, and this r

9、esults in very low thermal stress and low distortion on the workpieces.Systems for tungsten shielding gas spot welding Standard inverter power sources (Figure 3 can be used for TIG and spot welding, fitted with special torches (Figure 4.A spot/pulse remote control (Figure 5 ensures high quality, rep

10、roducible results thanks to the adjustable spot welding time and the optimum preset pulse parameters.Welding with current pulses offers the advantage that deeper fusion penetration is produced during thepulse phase, and a certain level of cooling is achieved early on in the longer lasting base curre

11、nt phase, which permits good fusion penetration and low heatloading of the material. Figure 8 View of the surface using TIG-spot weldingFigure 4 spotArc-spot welding torch, water cooledFigure 5 Remote control for TIG spot welding Foto: EWM Figure 6 Spot welding nozzle for different groove shapesFigu

12、re 7 Tack welding with spotArc-spot welding machineThe torches are especially important here as well. These have feet or specially shaped ends on the shielding gas nozzle, which can be placed on thesurface of the metal sheet during welding. They permit to maintain a constant distance between the tor

13、ch andworkpiece, and thus also a constant arc length, which contributes to reproducibility of the welding results. At the same time, the gas nozzle attached can be used to exert force onto the surface, which presses the parts being joined against one another. Thiscontributes to the high quality of t

14、he welding points and to the workpieces keeping their correctdimensions. These special shielding gas nozzles are available for butt welds, fillet welds and corner joints (box welds. Figure 6 shows various gas nozzle shapes for tungsten shielding gas spots.ApplicationsThe process can be used for tack

15、ing (Figure 7, andfor joint welding steel sheets and CrNi alloys up to a thickness of around 2.5 mm. Metal sheets of different thickness can also be welded on top of one another. As this is a one-sided process, it is also possible to weld on hollow components, such as round or square pipes.In arc spot welding, the arc melts through the upper sheet and the lower sheet is melted onto it. Thisproduces flat, fine-textured welding points (Figure 8 which require little or no finishing work, even in visible areas.Literature:1 Killing, R. and H. Loren