Although this will take some practice to master,your MIG welding will be most successful if you learn how to change voltage and amperage according to the needs of the moment, and of the weld that you are making.The depth,width,and shape of the weld will vary as you change these two electrical characteristics of your welding machine,and as you will discover,different metals, angles,and projects all have an optimal width and shape of weld to produce the strongest bond possible.
Even the direction in which you move the welding gun while making a weld can have a strong impact on the final characteristics of the join.If you point the welding gun slightly forward,pushing the weld pool ahead of the gun (the push method),then the weld will end up being wider and shallower; conversely,the drag technique,in which the gun leads ahead of the welding pool, creates a narrower,deeper weld that penetrates closer to the far side of the metal.
Keeping the gun perfectly perpendicular to the surface that is,neither pushing nor dragging will produce a weld bead that is intermediate in both width and depth between the two extremes.The exact balance of width and depth for each technique depends on the metal you are welding,the shielding gas you are using, the length of the arc,and so on,you so may need to experiment to find the ideal position for a specific welding job.
Voltage and amperage to control weld characteristics
Your MIG welder should include controls allowing you to change both voltage and amperage.In simple terms,voltage determines whether your weld bead is flush to the surface of the metal, or raised in a rounded ridge along the surface. Again,which shape is most desirable depends on the job you are doing. Low voltages produce raised beads and high voltages tend to flatten the bead.
Amperage is controlled chiefly through the speed of the wire feed in MIG welding.The faster the wire feed,the higher the amperage, and the more material will be deposited in the weld.If you need an ample weld bead with large amounts of filler metal,then use a high amperage,created by increasing wire feed speed towards the maximum your unit allows.
Conversely,if you need a fine bead that does not overlap into surrounding areas very much, lower the wire feed speed and amperage to create a bead with fairly small amounts of filler metal in it.Balancing all of these factors shielding gas,pushing or dragging,voltage,and amperage is a crucial part of developing your skill in welding.
As with all welding, you are well advised to practice with scrap metal before attempting an actual weld on a valuable object.Vary all factors to see how they affect the finished shape, depth, and width of the weld bead.