Page 200 - CITS - Welder - Trade Theory
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WELDER - CITS



           Following table gives gas and gas mixtures recommended for the welding applications.

            Sl No   Metals        Recommended             Advantages
                                  Shielded Gas
                                  Argon                   Easier ignition, better cleaning Improved weld
                                  Helium                  Quality.
               1    Aluminium
                                  Argon-Helium            Possibility of higher welding speed.
                                                          Compared to pure helium, better weld quality.
                    Magnesium     Helium                  Penetration easier to obtain.
               2    0-1.5 mm      Argon                   Excellent cleaning, pool easier to control.
                    > 1.5 mm
                    Mild Steel    Argon                   Increasing operating flexibility. (possibility of overheating).
                    0-3 mm
                                                          Helium addition improves penetration of thick work pieces.
               3    > 3 mm        Argon-Helium            Argon generally preferred. Lower electrode wear, easier
                    According to                          ignition, lower gas flow.
                    preparation   Argon                   Control of weld pool easier, especially for positional
                    TIG spot                              welding.
                    Stainless     Argon                   Welding of thin work pieces, good (easier) control of
               4    Steel                                 penetration.
                                  Argon-helium            Higher arc power, higher welding speed on thick sheets.

                    Copper –Ni    Argon                   Easier to control pool, penetration and bead shape on
                    Cupro –Ni                             thinner sections
                    Inconel       Argon-Helium            Higher arc energy is useful for thick materials having high
               5
                    Copper alloys                         thermal conductivity.
                                  Helium                  High thermal power, useful for welding thick materials.



           Pulsed TIG welding and application. Square wave

           concept and wave balancing

           Objectives : At the end of this lesson you shall be able to
           •  describe the pulse TIG welding
           •   explain the pulse TIG application.



           Pulsed TIG welding
           In the pulsed-current mode, the welding current rapidly alternates between two levels. The higher current state
           is known as the pulse current, while the lower current level is called the background current. During the period
           of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the
           weld area is allowed to cool and solidify. Pulsed-current GTAW has a number of advantages, including lower
           heat input and consequently a reduction in distortion and war page in thin work pieces. In addition, it allows
           for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar
           method, manual programmed GTAW, allows the operator to program a specific rate and magnitude of current
           variations, making it useful for specialized applications.
           Advantages of pulsation are:
           •  Low heat input
           •  Low porosity formation
           •  Resistance hot cracking

           •  Added life to electrode
           •  Low distortion


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                                         CITS : C G & M - Welder - Lesson 61-76
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