Proper Gas Flow
Adjusting for proper gas flow is not an exact science, though general guidelines are published all over the web and are available with a click of a button. Gas is expensive and too much is a waste, and can even cause issues with turbulence and gas coverage over the weld, leading to the same problem experienced with too little gas flow: welding porosity.
Whether it is for MIG or for TIG welding, adjusting gas flow can be done fairly simply. One thing to keep in mind is that the same gas flow rate may not always work, if any one condition is changed. Changing the joint type, location of the part to be welded, or just changing the cup size can affect gas coverage on a weld, so knowing how to compensate is important, despite what the charts and graphs say.
To make a proper adjustment to the gas flow rate, set the gas flow to a point where the gas can be heard flowing through the torch head in a slow hiss without having to strain to hear it. Then start a series of test welds. Each weld should be just long enough to see clearly the gas coverage, with sufficient distance between the start and the end of the weld, to see a regular pattern of gas coverage. Between each weld, turn the gas flow down little by little, repeating the weld until you see welding porosity begin to form in the weld. When the porosity begins to form, increase the flow just until the welding porosity disappears. Then, simply add about 1 cfh or .5 lpm to give a measure of insurance against drafts and changes in welding conditions.