Page 3 - Summer 2014 World of Welding
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hiwt@welding.org                                       HOBART INSTITUTE OF WELDING TECHNOLOGY



            FAILED WELD? WHOSE FAULT IS IT?

            SKILLED OR UNSKILLED?



            By André A. Odermatt, President
            Hobart Institute of Welding Technology

                                                               importance   of  these
            Who is to blame for a bad                          “distinct  level”   variables
            weld? An  unskilled welder                         and  can either  set them
            tends  to  find  all  kind  of                     himself  or make  sure that
            reasons for having produced                        they are set properly by the
            a bad weld;  often  it  is a bad                   person responsible  for the
            electrode  or wire, or the                         welding operation.
            welding machine, or the guy
            who did the fit-up, or anything                    The primary  adjustable
            else except him. An unskilled                      variables are used to control
            welder may not even know                           the welding process after the
            why his/her  weld does not                         preselected  variables  have
            pass  the  required  tests.  Arc                   been established.   They
            welding is arguably the best                       control the formation of the
            and fastest process to reliably                    puddle itself  by affecting
            join metals. However, it has many variables that all have to be   such things as penetration,
            set properly to achieve a good weld.               bead width, bead height,
                                                               arc stability, deposition rate
            Based on their ability to be used as controls, welding variables   and weld soundness.  The
            can be divided into three distinct groups  or classes.  These   primary  welding  variables
            are; preselected “distinct level” variables, primary adjustable   are arc voltage, welding
            variables, and secondary adjustable variables.     current and travel speed.        Lack of fusion
                                                               Because  they  can be easily
                                                               measured   and  continually
                                                               adjusted over a wide range, they can effectively be used as
                                                               controls.    Discrete  values  can  be  assigned  to  the  primary
                                                               adjustable variables and these values can be accurately reset
                                                               time after time. A properly trained welder becomes skilled in
                                                               setting and controlling these primary variables.

                                                               The secondary adjustable variables can also be changed
                                                               continuously over a wide range of values. However, they are
                                                               sometimes  more  difficult  to  measure  accurately.  Therefore,
                                                               it is not easy to employ them as controls since, for the most

                             Porosity in the weld              part; they cannot be assigned exact values.  This is especially
                                                               true for semiautomatic welding operations. Often they do not
            Preselected  “distinct  level”  variables  are those which can   directly affect puddle formation. Instead, they usually cause a
            only be changed in large steps or intervals and are therefore   change in a primary variable which in turn causes the desired
            unfavorable as controls. For the MIG welding process, these   change in bead formation. Secondary adjustable variables are
            variables are such things as; wire size, wire type, gas type, gas   such things as stick out, nozzle angle, and wire feed speed. A
            flow rate, etc. Preselected variables are set according to the   properly trained welder becomes skilled in controlling these
            type of material to be welded, the thickness of the material,   secondary variables.
            joint design, fit-up, welding position, deposition rate required
            and mechanical properties required. Although, they are also   In summary, a skilled welder knows why a weld is bad and
            affected by other welding characteristics, these requirements   assumes full responsibility and does not play the blame game!
            are  the  major  considerations  in  determining  the  proper
            selection of preselected variables. A skilled welder knows the    Adapted from Hobart Welding Process Manual EW 300


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