Shielding gas Optimization of the TIG welding process

Related Vendors

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Translating technical jargon into welder's language: meaningful analysis methods of shielding gas flows are now finding practical application in the industry for the first time.

On average, about 50 percent of the effort in TIG welding is devoted to downstream inspection and rework. For higher quality requirements, the share of these steps quickly rises to two-thirds of the production process, as tighter inspection cycles and more elaborate repair welding may be required. However, the effort can be significantly reduced by selecting the parameters of the shielding gas. These factors, however, can usually only be evaluated based on their effects. A correction is then possible at most for the next workpiece, which may necessitate an adjustment of the other process variables. While schlieren methods can help identify suitable shielding gas parameters early on, these precise imaging techniques have so far only been used in academic research and have barely been translatable to industrial practice. Gesellschaft für Wolfram Industrie  has built a bridge over this seemingly insurmountable gap between industry and research: By combining schlieren and sensory measurements, they offer developments and consultations in their Swiss welding lab to optimize the TIG welding process specifically for industrial applications.

If the electrode oxidizes, for example, because the shielding gas flow is set too low, then the component will also oxidize. This is because TIG welding takes place in a closed system where interactions occur between the individual components: the tungsten electrode, the weld seam, and the shielding gas. This brings several challenges, as depending on the application area, a porous or otherwise defective weld seam on the component can have fatal consequences. Additionally, the welding process, i.e., the joining of components, often occurs relatively late within the value chain. Therefore, quality defects that arise at this point can painfully slow down the entire production.

However, gas shielding is an influential factor that cannot be determined intuitively. Recommendations are mostly general and can significantly deviate from the configurations actually needed in a specific application. Difficulties such as electrode wear, ignition problems, or material defects are often caused by either a gas flow that is too high, subject to strong turbulence, or a flow rate that is too low, which in turn makes the gas shielding more susceptible to air turbulence and drafts in the workplace. With an unsuitable configuration of the shielding gas supply, the TIG welding process quickly becomes a costly endeavor.

Complex rework and production downtimes

One of the biggest cost factors arises from rework needed to compensate for quality defects that occur during the welding process. This includes repair welding to remove peripheral oxidations and improve surface quality. Additionally, non-destructive material testing is performed, where the weld seam is tested for porosity down to the micro level. While oxidation is caused by the titular oxygen, porosity in the metal usually results from nitrogen or hydrogen. Both can typically be traced back to improperly configured gas shielding and can be eliminated through process improvement.

With increasing automation in production, machine availability becomes increasingly important. To be economically viable, complex and costly welding cells, orbital systems, and automation in general rely on high utilization rates. However, the tungsten electrode used can thwart this: Turbulent gas flows can cause even high-quality electrodes to oxidize, significantly increasing not only the quality of the weld seam but also manufacturing costs. Incorrectly or suboptimally set gas quantities and times often necessitate frequent replacement of wear parts and associated equipment downtime, which significantly restricts productivity. However, even small adjustments can achieve significant improvements.

More doesn't help much

The third cost factor lies in the consumption of the shielding gas itself. The premise "more is better" offers no benefit in shielding gas welding. On the contrary, many problems actually originate from an excessively high gas flow. Besides improving weld quality, reducing unnecessary gas consumption directly impacts production costs. Especially when using mixed gases with a high proportion of helium, significant additional costs can quickly arise. By optimizing the gas supply specifically for the respective application, savings of up to several hundred euros per production day can be achieved.

Although there are measurement methods to tailor gas shielding to specific conditions, these are currently almost exclusively used in academic research. For the industry, this means that the effects of individual parameters can only be observed in practice through their often negative outcomes. Adding to the challenge is the fact that the gas itself is invisible to the naked eye. Indications of improperly adjusted shielding gas flow are initially visible to the welder as discoloration and wear on the tungsten electrode. More problematic quality defects in the workpiece itself, such as porosity, are typically only discovered during in-process or subsequent volumetric material testing. Thus, optimization of the parameters can affect the next workpiece at the earliest—provided it does not require entirely different process conditions.

New link between academia and industry

To avoid the laborious trial-and-error principle, Gesellschaft für Wolfram Industrie operates a welding lab at their location in Switzerland. There, welding experts can accurately replicate, measure, and optimize the environmental conditions of any TIG welding application. Two approaches from scientific research have been adapted for industrial use: Firstly, schlieren methods, an imaging technique from fluid mechanics, are used to create high-resolution images of gas and heat flows around the burning arc. Secondly, Gesellschaft für Wolfram Industrie  employs sensory measurements that capture parameters such as the stagnation pressure, speed, and chemical composition of the shielding gas. Combined with precise positional data, this allows for a three-dimensional measurement of the gas shielding, optimizing it for each industrial application while considering all environmental conditions and influencing factors.