WT1-c13 - 13. Special Processes 2003 13. Special Processes...

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2003 13. Special Processes
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13. Special Processes 175 Apart from the welding processes explained earlier there is also a multitude of special welding processes. One of them is stud welding. Figure 13.1 depicts different stud shapes. Depending on the application, the studs are equipped with ei- ther internal or ex- ternal screw threads; also studs with pointed tips or with corrugated shanks are used. In arc stud welding , a distinction is basically made between three process varia- tions . Figure 13.2. depicts the three variations – the differences lie in the kind of arc ignition and in the cycle of motions during the welding process. Figure 13.1 Figure 13.2
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13. Special Processes 176 The switching arrangement of an arc stud welding unit is shown in Figure 13.3. Besides a power source which produces high currents for a short-time, a control as well as a lifting device are necessary. In drawn-arc stud welding the stud is first mounted onto the plate, Figure 13.4. The arc is ignited by lifting the stud and melts the entire stud diameter in a short time. When stud and base plate are fused, the stud is dipped into the molten weld pool while the ceramic ferrule is forming the weld. After the solidification of the liquid weld pool the ceramic ferrule is knocked off. Figure 13.3 Figure 13.4
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13. Special Processes 177 Figure 13.5 illustrates tip ignition stud welding . The tip melts away immediately after touching the plate and allows the arc to be ignited. The lifting of the stud is dis- pensed with. When the stud base is molten, the stud is positioned onto the partly molten workpiece. Studs with diameters of up to 22 mm can be used. Welding currents of more than 1000 A are necessary. The arc stud welding process allows to join different materials, see Fig- ure 13.6. Problematic are the different melting points and the heat dissipation of the individual materials. Aluminium studs, for example, may not be welded onto steel. The relatively high welding currents in the arc stud welding process cause the somewhat troublesome side- effects of the arc blow . Figure 13.7 depicts different arrangements of current contact points and cable runs and illustrates the developing arc deflection (B,C,E).
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WT1-c13 - 13. Special Processes 2003 13. Special Processes...

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