Arc Length Control Effects on Aluminum Alloy Double-Pulse MIG Welding

Literature Overview

This paper by Shi Yan, Han Yongquan, Liu Rui, and Du Maohua from Inner Mongolia University of Technology (2011, Welding Technology, Vol. 40, No. 1, pp. 11-13) investigates the effects of arc length control on double-pulse MIG welding of 2.5 mm thin aluminum alloy plate (1060 grade). The study used a Fronius TPS2700 digital inverter welding power source and a Hannover welding quality analyzer to monitor and analyse the welding electrical signals. The authors examined how low-energy pulse arc length correction (AL1) and high-energy pulse arc length correction (AL2) parameters affect welding process stability and weld quality.

Core Technical Findings

The key finding is that for thin aluminum alloy double-pulse MIG welding, the low-energy and high-energy pulse arc length corrections must be adjusted separately, and the arc length control parameters should be set slightly higher than those used for thick plate welding to achieve stable welding and good quality.

Double-Pulse MIG Welding Principle

Double-pulse MIG welding employs two types of pulses within each welding cycle:

Low-energy pulse (pulse 1): Maintains the arc, keeps the wire in contact with the molten pool, and prevents short circuits.
High-energy pulse (pulse 2): Provides the primary heat input for melting and penetration.

The separation of these two functions allows for better control of the welding process, particularly for thin plates where excessive heat input can cause burn-through.

Arc Length Correction Parameters

Parameter	Function	Effect on Welding
AL1 (Low-energy pulse arc length correction)	Controls arc length during low-energy pulse	Affects arc stability and wire feeding
AL2 (High-energy pulse arc length correction)	Controls arc length during high-energy pulse	Affects penetration and weld geometry

The authors found that:

AL1 and AL2 must be adjusted independently for optimal results.
For thin plate welding (2.5 mm), slightly higher arc length control parameters than those used for thick plate welding are required.
Proper adjustment of both parameters leads to stable welding processes and good weld quality.

Process Analysis and Parameter Optimisation

The double-pulse MIG welding process for thin aluminum alloy requires careful parameter selection to balance penetration, stability, and defect avoidance. The following parameter windows are suggested:

Parameter	Typical Range	Critical Consideration
Low-energy pulse current	80-120 A	Must maintain arc without excessive heat
High-energy pulse current	180-250 A	Provides penetration without burn-through
Low-energy pulse time	1-3 ms	Short enough to prevent excessive melting
High-energy pulse time	2-5 ms	Long enough for penetration
Pulse frequency	50-200 Hz	Affects weld bead appearance
Wire feed speed	3-6 m/min	Matched to pulse parameters
Shielding gas	Pure Ar or Ar/He mix	Prevents porosity and oxidation

Arc Length Control Strategy

The arc length control strategy for double-pulse MIG welding involves:

Independent adjustment: AL1 and AL2 are adjusted separately to optimise the respective pulse functions.
Slightly higher parameters for thin plate: The arc length correction values should be set slightly higher than for thick plate welding to accommodate the different heat input requirements.
Iterative optimisation: The parameters should be adjusted iteratively based on welding quality observations and electrical signal analysis.

Engineering Practice Implications

For production welding of thin aluminum alloy plates, the following considerations are critical:

Burn-through prevention: The low-energy pulse must be carefully controlled to avoid excessive heat input that could cause burn-through.
Porosity prevention: Proper shielding gas coverage is essential, particularly for thin plates where gas flow can be disrupted by wind or workpiece geometry.
Weld bead appearance: The pulse frequency and current settings affect the weld bead appearance, which is important for cosmetic applications.

Quality Control Measures

For ensuring weld quality in double-pulse MIG welding, the following measures are recommended:

Visual inspection: Check for burn-through, porosity, and undercut.
NDT: Use ultrasonic testing (UT) or radiographic testing (RT) to detect internal defects.
Mechanical testing: Perform tensile and impact tests on weld coupons to verify mechanical properties.
Electrical signal monitoring: Use a welding quality analyzer to monitor and optimise the welding parameters in real time.

Study Insights and Reflections

This study highlights the importance of arc length control in double-pulse MIG welding, particularly for thin aluminum alloy plates. The finding that AL1 and AL2 must be adjusted independently is a critical insight for process optimisation. The recommendation to use slightly higher arc length control parameters for thin plate welding is counterintuitive but is supported by the experimental results.

The use of a welding quality analyzer for electrical signal monitoring is a valuable diagnostic tool. By analysing the current and voltage waveforms, engineers can identify process instabilities and optimise parameters without relying solely on visual inspection of the weld.

One limitation of the study is the focus on a single aluminum alloy grade (1060). The findings may not be directly applicable to other aluminum alloys with different thermal properties, such as 6061 or 5083. Future work should investigate the applicability of the arc length control strategy to other aluminum alloys and plate thicknesses.

In conclusion, this study provides valuable practical guidance for engineers implementing double-pulse MIG welding for thin aluminum alloy plates. The key takeaway is that careful, independent adjustment of the low-energy and high-energy pulse arc length corrections is essential for achieving stable welding and good weld quality.