CLADDING TECHNOLOGY SHANXI CO., LTDComputer Control System for Automatic TIG Welding of Aluminium Alloy Sheets
Literature Overview
The paper by Liu Huijie, Zhang Jiuhai, and Lu Shixiong, published in China Welding in 1996, describes the development of a computer-based control system for automatic TIG welding of aluminium alloy sheets. Aluminium alloys present unique welding challenges due to their high thermal conductivity, low melting point, and susceptibility to oxidation and porosity. The authors address these challenges through a dedicated control architecture that enables precise regulation of welding parameters and real-time monitoring of the welding process.
Core Technical Content
The control system described in this paper integrates a microprocessor-based controller with current and voltage sensors, encoder feedback for travel speed, and gas flow monitoring. The system allows operators to program welding parameters including current waveform, pulse frequency, gas flow rate, and travel speed, and to store these parameters for repeatable production runs. The computer interface provides real-time display of welding variables and alarms for parameter deviations.
For aluminium alloy welding, the system implements a square-wave pulsing strategy where the current alternates between a high peak current for penetration and a low trailing current for arc stability. The peak-to-base current ratio and the duty cycle are programmable, allowing the operator to optimize the thermal input for different aluminium alloy thicknesses and compositions.
Technical Parameter Analysis
| Parameter | Typical Value for Al Alloys | Control Function |
|---|---|---|
| Peak current | 80-200 A | Governs penetration depth |
| Base current | 20-50 A | Maintains arc during off-phase |
| Pulse frequency | 1-20 Hz | Controls thermal cycle frequency |
| Travel speed | 200-600 mm/min | Depends on thickness and alloy |
| Shielding gas flow | 12-25 L/min | Prevents oxide formation |
| Tungsten electrode | 2.4-4.0 mm | Arc stability and heat input |
| Preheating | 100-200 degrees C | Reduces porosity in thick sections |
The control system also incorporates a gas purge function that activates before and after the welding arc to prevent oxide formation at the start and end of the weld. This is critical for aluminium alloys, where even brief exposure to atmospheric oxygen during the welding cycle can introduce oxide inclusions that degrade the mechanical properties of the weld.
Engineering Practice Implications
In the fabrication of aluminium alloy pressure vessels and heat exchangers, automatic TIG welding with computer control is essential for achieving the consistency and repeatability required by codes such as ASME VIII Division 1 and NB/T 47002. The control system described in this paper provides the foundation for modern robotic TIG welding cells that are now standard in aerospace and automotive aluminium fabrication.
The use of computer control also enables the implementation of advanced welding strategies such as multi-pass welding with programmed interpass temperature control. For thick aluminium alloy sections, the system can be programmed to adjust the welding parameters based on the number of passes completed, ensuring that the thermal input remains within acceptable limits for the entire weld build-up.
Key Reflections and Study Insights
This paper represents an important milestone in the transition from manual welding operations to automated, computer-controlled welding systems. The integration of microprocessor control with welding power sources and motion systems laid the groundwork for the modern welding automation industry. From a metallurgical perspective, the ability to precisely control the thermal cycle through computer programming has a direct impact on the microstructure and mechanical properties of the weld, particularly for heat-sensitive aluminium alloys such as 2024 and 7075.
One reflection from studying this work is that the quality of automatic welding is only as good as the quality of the parameter programming. A well-designed control system is useless if the underlying welding parameters are not properly optimized through welding procedure qualification. This underscores the importance of the interaction between welding engineering, process control, and materials science in achieving high-quality automatic welds. The principles established in this 1996 paper continue to be relevant today, as modern control systems still rely on the same fundamental sensor feedback and parameter control loops, albeit with faster processing and more sophisticated algorithms.