WELDING-Wire
      M.I.G.(Metal Inert Gas) - Points to Remember
                                                                 

                                                                 

      1. Mig (GMAW) welding is often referred to
         by the manufacturer's trade name as Micro-wire,
         Aircomatic, Sigma, and Millermatic Welding.
                                                                 

      2. Mig welding is faster than stick electrode
         welding and is much easier to learn.
                                                                 

      3. Spray transfer type of welding is particu-
         larly adapted for welding heavy gage metals.
                                                                 

      4. Short circuiting transfer welding is best
         for welding light gage metals.
                                                                 

      5. For optimum efficiency, DCRP current is  
         required for Mig welding.          
                                                                 

      6. For  Mig  welding, a constant  potentiaI
         power supply with a nearly flat volt-ampere char-  
         acteristic produces the best results.
                                                                 

      7. As a general rule, an air-cooled gun  is   
         satisfactory  when  welding  with  amperage
         around 200 and a water-cooled gun for welding    
         heavy metals requiring higher amperages.
                                                                 

      8. The use of CO2 as a shielding gas is most
         effective and less expensive when welding steel.     
                                                                 

      9. Argon or a mixture of argon and oxygen   
         will produce the most effective results in welding
         aluminum and stainless steel.
                                                                 

     10. The rate of gas flow for welding most 
         metals is approximately 35 cu ft/hr. However,     
         this rate may have to be varied somewhat, de-   
         pending on the type, electrode size, and thick-     
         ness of metal.                                        
                                                                 

                                                                  
                                                                  
                                                                  
                                                                  
                                                                  
     11. The effectiveness of the shielding gas is
         often governed by the distance of the gun from     
         the workpiece. Generally the gas nozzle should           
         not be spaced more than 2" from the workpiece.
                                                                 

     12. The use of correct diameter wire electrode               
         is necessary for good welds. Check recommen-             
         dations for correct electrode diameters.
                                                                 

     13. The correct current for welding must often
         be determined by trial. Check recommendations
         for starting current.
                                                                 

     14. Be sure the wire feed is set for the amper-
         age which is to be used for welding.
                                                                 

     15. For most Mig welding applications, the
         wire stick-out should be about 3/8" to 3/4".
                                                                 

     16. Keep the gun properly positioned to insure
         uniform weld with proper penetration.
                                                                 

     17. Cold laps will occur if the arc does not
         melt the base metal sufficiently.
                                                                 

     18. Check the weld for surface porosity. Sur-
         face porosity is usually caused by improper gas
         shielding.
                                                                 

     19. Do not remove the gun from the weld area
         until the puddle has solidified, otherwise cracks
         may develop.
                                                                 

     20. Remember, insufficient or excessive pene-
         tration  is the  result of failure to  control  heat
         input.             


