Practical MIG Welding: Achieving Correct Gas Flow
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Achieving Correct Gas Flow
04.35
| 00:00 | The role of shielding gas is to protect the molten weld pool and arc from contaminants in the air that would otherwise cause a reaction in the weld pool, leading to an ugly, porous weld with greatly reduced strength. |
| 00:11 | Achieving the correct gas flow in MIG welding is paramount when we are looking to produce a strong weld. |
| 00:16 | The idea is to have enough gas to flood the weld pool but not so much that we're wasting gas and money in the process. |
| 00:23 | Picking up a new gas cylinder and paying for it is a burden that we have to endure as motorsport fabricators so by optimising our gas flow, we can produce more welds before having to swap our cylinders out and in turn, save money in the process. |
| 00:37 | Running around 10 litres per minute is a great starting point for most indoor MIG welding operations but we may still need to vary the flow from this value. |
| 00:45 | So, how do we figure out the correct amount of gas flow for the situation that we're in? Like many forms of shielded gas welding, we need to adjust for our surroundings. |
| 00:54 | So, even though we can't see the shielding gas, we need to understand that it can be affected by the ambient airflow through our workspace. |
| 01:02 | A slight breeze for example could easily blow away the shielding gas and introduce a reaction with the atmospheric air seen as small bubbles, what we call porosity, or a discolouring of the weld. |
| 01:13 | By closing a door, creating a windblock or simply increasing the flow of shielding gas, this can be overcome but keep in mind that using too much gas will be counterproductive as the turbulence of the gas can cause inclusions of atmospheric contaminants into the gas stream. |
| 01:29 | We also need to look at the condition of our consumables such as the gas nozzle and contact tip holder to make sure that there aren't any obstructions to the gas flow path. |
| 01:39 | This is because over time, the weld spatter can stick to the nozzle and block the gas from flowing smoothly onto the workpiece. |
| 01:45 | The inclusion of atmospheric air in the reaction that happens in the molten weld pool is easy to see. |
| 01:51 | The amount of spatter will increase, the weld pool will begin to deform and we'll see small air bubbles and a brown haze of smoke being emitted from the weld area. |
| 02:00 | These are all signs that there's a lack of gas from either an inadequate flow rate or an obstruction in the gas path. |
| 02:06 | It's almost certain that you'll experience this at several points while MIG welding when you accidentally forget to open the gas bottle prior to starting to weld. |
| 02:14 | This will give you a more extreme example of what happens when we don't have sufficient gas flow. |
| 02:19 | If the flow rate at the cylinder looks fine, then we might need to purge the gas system by either using a setting on the machine or removing the drive roller tension to disable the wire feed system and then fitting a flow gauge onto the end of the nozzle to ensure it's running at the same rate as our gas cylinder. |
| 02:34 | If the flow rate indicated on the cylinder's regulator doesn't match the flow rate we have at the gas nozzle, then we may have to diagnose a leak or obstruction in the system. |
| 02:43 | This is a pretty rare occurrence but it's something to keep in mind if our weld seems to be developing porosity for no other obvious reason. |
| 02:51 | When we achieve the correct gas coverage, typically between 10 and 20 litres per minute depending on the situation, our weld will be completely shielded from the contaminants in the atmosphere and will have a consistent shiny appearance. |
| 03:03 | Outside corner joints will require slightly more gas than inside fillet welds as argon is heavier than air and tends to fall away if it doesn't have a corner to pull into. |
| 03:12 | Most of us won't be changing our flow rates every time we change position though, it's a matter of constantly watching our weld as we move along the joint and assessing if there are any gas flow problems. |
| 03:22 | As a guide, this 10 to 20 litres per minute gas flow rate should cover most operations but may need to be increased if we have a breeze running through the workshop or we're forced to weld outside. |
| 03:33 | Increasing flow in increments of 2 litres per minute should allow us to maintain strong shielding gas coverage but remember it's always going to be better to attempt to eliminate or block ambient airflow around the weld area rather than trying to use increased gas flow as a band aid. |
| 03:48 | Let's summarise what we've learned in this module before we move on. |
| 03:51 | Shielding gas is essential in MIG welding to protect the weld pool from atmospheric contaminants and maintaining proper gas flow is vital to preventing issues such as porosity and discoloured welds. |
| 04:02 | Achieving the right gas flow rate is crucial for producing strong welds and saving money on gas cylinders. |
| 04:08 | Typically a great starting point for indoor MIG welding is around 10 litres per minute but this may need to be adjusted based on environmental factors like air circulation. |
| 04:17 | Obstructions in the gas flow path like spatter on the nozzle should be regularly checked and cleared. |
| 04:22 | The ideal gas flow rate generally falls between 10 and 20 litres per minute, depending on the situation, with outside corner joints potentially requiring more. |
