How does Peak current and Base current affect the properties of weldments?

The current levels are only two of the parameters determining weld quality. To understand parameters function, the period can be broken down into several parts:

1. Ramp up rate increase stiffens the arc, reducing the arc column size and increasing the propelling force throwing molten drops detached from the electrode,
2. Overshoot, an instantaneous current increase above the peak current level, necessary to overcome the influence of inductance, variable with cable length,
3. Peak current level directly controls penetration: the higher the peak current, the deeper the penetration,
4. Peak Time or Peak Duration influences the width of the bead shape,
5. Tail-out drop time, speed of change and shape controls energy addition to the molten droplet, directly influencing puddle fluidity and penetration,
6. Sudden current drop down to background level, reduces the tendency for fine droplet spatter,
7. Background Current, the low-level current needed to maintain the arc,
8. Frequency or Repetition Rate shapes the weld bead by narrowing the arc cone with increased frequency.

Effective control of gas shielded arc welding fume

HSE inspectors have noted that, although Local Exhaust Ventilation (LEV) was often available for controlling exposure to inert gas shielded welding fume, it frequently remained unused, due, partly to claims by welders that the LEV was responsible for removing shielding gas and thereby compromising the quality of the weld. However, there appeared to be few data to substantiate the welders’ claims. HSE commissioned this research project to establish whether efficient welding fume capture could be achieved using LEV whilst, at the same time, maintaining weld metal integrity. The objectives of this research project were to be met in three phases:

• Phase 1 was to provide the information necessary to develop an experimental plan.

• Phase 2 was to determine the maximum cross flow velocity of air that could be tolerated before the onset of weld metal porosity during gas shielded arc welding using parameters defined in Phase 1.

• Phase 3 was to measure capture efficiencies for a range of different LEV hoods positioned at various distances and orientations to the welding arc, whilst monitoring weld metal integrity. An on-gun extraction system was also evaluated. This report gives a brief summary of the work carried out in phase 1 and 2, and details the work carried out in phase 3

The report shows that when using standard welding parameters, satisfactory fume extraction is possible without compromising the weld integrity. The results are confirmed for a number of welding positions and with various extraction hoods in different positions. The results for the on-gun extraction equipment are evaluated against those observed for the stand-alone fume extraction equipment.

This report and the work it describes were funded by the Health and Safety Executive (HSE). The on-gun evaluation study was part funded by Nederman and Abicor-Binzel. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.