Thin-Walled Casing Fusion Welding with Pulsating Current
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Solution Overview
Problem
The challenge in welding thin-walled cylindrical casings lies in achieving high-quality fusion welding due to the random formation of contact points, leading to overheating and ejection of metal, as well as uneven thermal stresses causing distortion or burn-through, especially when the joining edges are not precisely aligned in terms of thickness and circumference.
Innovation Solution
A method involving plastic deformation of microprotrusions on the end faces with rollers to create a dense, fine-grained structure, followed by spot welding and continuous main welding with controlled heat removal, ensuring a wide fusion zone and minimizing radial deformations, while using shielding gases to maintain the quality of the weld seam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If continuous melting welding is used on thin-walled parts, then welding speed is improved, but the heating zone becomes insufficiently wide leading to poor weld quality
Solution Approach 1:
The patent applies periodic action by using pulsating current instead of continuous current for welding thin-walled parts. The current is supplied in pulses with specific parameters (frequency 50-200 Hz, duty cycle 20-80%), which allows controlled heating and cooling cycles. This periodic heating creates a wider effective heating zone while maintaining high welding speed, resolving the contradiction between speed and weld quality.
2Manufacturing precision
If mechanical processing is used to prepare edges of thin-walled parts, then alignment precision is improved, but surface roughness becomes commensurate with wall thickness making high-quality welding impossible
Solution Approach 1:
The patent changes the surface roughness parameter by applying pulsating current during welding. The thermal cycles created by pulsed current modify the surface morphology, reducing the harmful effect of roughness created by mechanical processing. This allows the use of mechanically processed edges without compromising weld quality, resolving the contradiction between alignment precision and surface roughness.
3Ease of manufacture
If welding current is applied at random contact points, then welding process simplicity is maintained, but metal overheats and is ejected from the welding zone
Solution Approach 1:
The patent implements feedback control by using pulsating current with controlled parameters. The periodic nature of the current allows the metal to heat and cool in a controlled manner, preventing overheating and ejection. The feedback mechanism is inherent in the pulsed current system where each pulse duration and amplitude can be optimized to prevent metal ejection while maintaining process simplicity.
4Device complexity
If thin-walled parts are welded without special preparation, then manufacturing complexity is reduced, but uneven thermal stresses cause distortion or burn-through
Solution Approach 1:
The patent uses periodic action through pulsating current to weld thin-walled parts without special preparation. The pulsed current creates controlled thermal cycles that reduce uneven thermal stresses, preventing distortion and burn-through. This allows welding of unprepared thin-walled parts while maintaining dimensional stability, resolving the contradiction between manufacturing complexity and dimensional stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances the quality of the weld seam by creating a dense, defect-free structure, improving the reliability and effectiveness of the welding process, particularly for thin-walled casings, by ensuring precise alignment and controlled heat management.
Implementation Method 1
under the action of the welding current flowing at the contact points, the metal of the contact points rapidly overheats
Implementation Method 2
supplying pulsating current to the welding area with a frequency of 50-200 Hz and a duty cycle of 20-80%
Implementation Method 3
joint fusion welding in a medium of protective gases with the addition of halogen reagents in the welding zone
Data Source
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AI summary
The method for connecting thin-walled casings by fusion welding comprises the following: preparation of the end faces to be connected of the casings, abutting arrangement on centring devices and common melting of the end faces to be connected while an arrangement gap sufficient for carrying out the welding is temporarily maintained between the surfaces lying against one another of the end faces. On each of the casings to be connected, deforming of the micro-projections on the surface to be welded of the end faces is carried out by plastic deformation along with upsetting of the material. On the end face, the metal to be deformed is moved to the side of the inner surface of the casing and an inner, annular bead strip is formed thereupon. The casings to be connected are arranged in a device that carries out centring with respect to the outer diameter. Then, initially at the circumference in the plane of the connection, spot welding thereof is carried out. Subsequently, main welding is carried out right through, thereby forming a fusion zone of a width between 4 d and 6 d, where d is the thickness of the wall of the casing to be welded in mm, and the heat removal in the parts to be welded begins at a distance that does not exceed 8 d from the centre line of the connection.