It is recommended Ar/He blend with 30%-50% helium is welded in 0.8-3mm stainless steel sheet and can raise arc temperature to 18000K (pure argon only 12000K) and contribute 40% to penetration depth. Boeing Company’s 2022 report showed that He75%+Ar25% blended welding aviation aluminum (6mm thickness), the welding speed as high as 1.2m/min (60% better than pure argon), reduced porosity from 0.8% to 0.12%. However, the cost of helium needs to be sufficiently controlled, and the current market price of helium is approximately 32/m3(Argon 5/m³), and with each 10% rise in the composition ratio, the cost of a single-meter weld increases by $0.18.
For reflective materials, ideal helium welding gas ratios can improve energy absorption. In laser welding of copper, the He50%+N₂50% gas mixture increases the beam absorption rate from 7% to 23%, and the weld tensile strength to 320MPa (260MPa for welding under pure nitrogen). Weld tests of the Tesla 4680 battery housing proved that the He40%+Ar60% gas mixture reduced the weld defect rate from 1.2% to 0.3%, and reduced the protective gas flow rate from 25L/min to 18L/min, saving $48,000 in gas costs each year. However, it is necessary to pay attention to the purity requirements of helium. According to ISO 14175, the purity of weld-grade helium should be ≥99.996% and the impurity oxygen content should be < 10ppm, otherwise the thickness of titanium alloy weld oxide layer will increase by 0.3μm.
In thick plate welding scenarios, the high heat input characteristics of helium welding gas significantly increase efficiency. Marine steel plate (25mm thickness) submerged arc welding, He20%+Ar60%+CO₂20% of the terene mixture enhances the melting rate of 12kg/h, compared to the normal Ar+CO₂ mixture by 55%. After Hyundai Heavy Industries adopted this ratio, the welding deformation was reduced by 37%, and the welding working time of each VLCC tanker was reduced by 800 hours. However, the current parameter has to be matched. With every 10% increase in the content of helium in the mixture, the voltage needs to be increased by 2-3V for the stability of the arc. For offshore engineering platform building, the weld path width differs by up to ±1.5mm (the allowed deviation is ±0.8mm) as the voltage is not controlled.
The precision welding sector has to balance the protective effect and the cost. The welding of the molybdenum alloy parts in semiconductor devices (0.1mm thickness) uses He95%+H₂5% gas mixture, which can control the width of heat affected zone between 0.05mm (pure argon is 0.12mm), and vacuum chamber welding of ASML lithography machine adopts this plan, and the air tightness arrives at the standard rate between 88% to 99.7%. But the hydrogen added should be strictly controlled, and research has shown that hydrogen embrittlement of the weld will take place when over 8% H₂ is added, and the impact toughness of 316L stainless steel will decrease by 23%. According to Apple supply chain firms’ comments, He80%+Ar20% mixture in the M2 chip heat sink welding achieves the difference of welding diameter ≤5μm (specification ±10μm), but helium usage takes up 62% of the whole cost of welding and the rate of use needs to be optimized from 35% to 68% by the gas recovery system.
Environmental aspects also affect the selection of the mixture. When welding plateau areas (3000m or higher than sea level), the helium content in helium welding gas should be increased to more than 60% to compensate for the arc diffusion caused by the low atmospheric pressure. The data of Qinghai-Tibet Railway project show that He60%+Ar40% mixture maintains the weld of X80 pipeline steel at 245J (plain standard ≥200J), while the pure argon welding drops to 182J. But the wire feed speed must be modified in synchronism. For every 10% change of the gas ratio, the wire feed speed of the ER70S-6 wire must be modified by 0.5m/min correspondingly, or it is easy to produce unfused defects (incidence rate up to 7%).
In cost saving, dynamic gas distribution technology can be used. After the intelligent mixing system is installed in a car body-in-white manufacturing line, the actual-time helium consumption of helium welding gas drops by 22%. The mixing ratio error is compressed from ±3% to ±0.7% after welding parameter learning algorithm (500 sets of current/voltage waveform data acquisition). With the application of this technology, the welding gas cost in one body is reduced from 18.5 to 14.2, and the yearly capacity of 500,000 vehicles is conserved by 2.1 million. But one has to take care of the investment on the equipment, the acquisition price of dynamic gas distribution system is around 75,000, and the investment cycle for the return on investment must be 2.3 years (based on 8 hours/day production).