Ehsan Khan,
International Expert – W&C (ALTEC – Middle East & India),
Air Liquide India
1. Parameter Optimisation– Procedures which are not well designed will cause spatters. Parameters like Amperage, voltage and electrical stick out are crucial when processes are being established.
a) Amperage:
Amperage in GMAW is determined by your wire feed speed. An amperage that is too high will cause spatter. Efforts to be put in to reach an optimum mode transfer, globular will cause excess spatter, while short circuit mode is obtained at low amperage at times it’s good to have but for many it will not only reduce the productivity but will also jeopardise penetration & bead aspect also. Spray generally is mode of choice but it has limitations for low thickness jobs.
Based on the job and quality requirements one has to optimise his current (WFS) setting.
b) Voltage:
Alongwith the current your voltage should also be tuned in, if your voltage is too low your spatter levels will increase. Increase your voltage until spatter decreases. It will also change your weld bead width.
c) Contact tip to work distance (CTWD) or Electric Stick Out (ESO):
Contact tip to work distance is the distance from your contact tip to the work piece. When mig welding you want to be around 15 ~20 mm. A bit more for high amperage. Excessive stick out will increase spatter somewhat, but it will create bigger problems (porosity due to lack of shielding gas and lack of penetration). Also it will affect the heat input .
2. Work angle too steep – Regardless of which drag or push you prefer make sure your drag (pull) or push work angle does not exceed about 15 degrees. At times there is no choice if accessibility is a problem. But when you can control it, do not exceed 15 degrees. Steep angles generate a lot of spatter.
3. Surface Contaminants – Rust, oil, paint and other surface contaminants will create spatter. Clean surfaces as best as possible prior to welding.
4. Erratic Feeding – when the wire feeder cannot feed wire at a constant speed there will be fluctuations in amperage that will drastically affect the arc causing a lot of spatter. Make sure you don’t have any feeding issues. Please check your Tip as well as tension/pressure setting at wire feeder.
5. Quality of Consumables – Variations in wire diameter, copper coating, cast, helix and chemistry should be within the allowance limit. In robotic applications and other situations in which wire consistency is critical, please do not take the chance to buy cheap wires. A single spool or drum may be consistent, but across several spools, drums or lots there may be variations in wire diameter, copper coating, and chemistry.
6. Shielding Gas –
a) Selection of shielding gas is very important. As straight spray transfer is not possible higher than 18% CO2, you may never get the desired result even after meeting all other parameters. 100% CO2 may feel cheaper to you cheaper but it will increase your overall weld cost by changing the weld bead, spatters and spatter cleaning activities will eat away your efficiency. There is a range of shielding gases available, please check which mix and which ratio is fit to your application.
b) Impurities present into shielding gases can be very critical for some applications, e.g. H2O, O2, N2 etc. can spoil all your other efforts in your welding process. Additionally mixing tolerance is another important aspect of gas quality.
c) Improper or inadequate cylinder preparation can be an issue as internal cylinder wall rusts, dusts etc can travel along with the high pressure gas to your weld puddle leading to inclusions etc.
