CLADDING TECHNOLOGY SHANXI CO., LTDFour-Degree-of-Freedom Microcomputer Control System for Internal Overlay Welding of Bent Pipes
Literature Overview
This research, conducted by Wei Lun, Cui Shusen, and Yin Dianxiang from the Harbin Welding Research Institute (1993), presents the development of a four-degree-of-freedom microcomputer control system for internal overlay welding of bent pipes. Published in the Welding journal, this study represents an early and pioneering effort in the automation of internal overlay welding for complex geometries, addressing a significant challenge in the fabrication of piping systems for chemical, petrochemical, and power generation industries.
Core Technical Content
Internal overlay welding of bent pipes presents unique challenges due to the curvature of the pipe, the restricted access for welding equipment, and the need for precise torch positioning to ensure uniform overlay coverage. The four-degree-of-freedom control system developed in this study enables precise positioning of the welding torch along the curved internal surface of the pipe.
Key Technical Parameters
| Parameter | Description |
|---|---|
| System Configuration | Four degrees of freedom (4-DOF) |
| Control Method | Microcomputer-based (early digital control) |
| Application | Internal overlay welding of bent pipes |
| Pipe Geometry | Curved/bent pipe sections |
| Welding Process | Arc welding (likely GTAW or GMAW) |
| Research Institution | Harbin Welding Research Institute |
Four Degrees of Freedom Analysis
The four degrees of freedom in this system correspond to the independent motions required to position the welding torch along the curved internal surface of a bent pipe:
| Degree of Freedom | Motion Type | Function |
|---|---|---|
| DOF 1 | Axial translation | Movement along pipe axis |
| DOF 2 | Radial translation | Adjustment of torch standoff from pipe wall |
| DOF 3 | Angular rotation | Rotation around pipe axis |
| DOF 4 | Curvature compensation | Adjustment for pipe bend radius |
System Architecture
The microcomputer control system integrates several key subsystems:
- Positioning control: Servo motors drive each degree of freedom with encoder feedback for precise positioning.
- Welding parameter control: Current, voltage, travel speed, and gas flow are controlled by the microcomputer based on programmed sequences.
- Sensor feedback: Current sensors, voltage sensors, and potentially optical sensors provide real-time feedback for adaptive control.
- Trajectory planning: The microcomputer calculates the optimal torch path along the curved pipe surface based on the pipe geometry parameters.
Engineering Practice Integration
The application of this system is particularly relevant for the fabrication of piping systems in:
- Chemical processing plants requiring corrosion-resistant internal linings
- Power generation facilities with overlay welded steam piping
- Petrochemical installations with special alloy internal surfaces
- Marine applications requiring internal corrosion protection
Defect Analysis and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Uneven overlay thickness | Poor torch positioning | 4-DOF control ensures consistent standoff |
| Incomplete fusion | Insufficient heat input | Adaptive current control based on position |
| Porosity | Inadequate gas shielding | Optimized gas flow rate and nozzle design |
| Weld spatter | Excessive arc energy | Parameter optimization for each DOF position |
| Overlap deficiency | Torch misalignment | Real-time feedback correction |
Process Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Welding current | 80-200 A | Depends on process (GTAW/GMAW) |
| Travel speed | 30-100 mm/min | Adjusted for pipe curvature |
| Shielding gas flow | 10-20 L/min | Argon or mixed gas |
| Torch standoff | 3-8 mm | Critical for arc stability |
| Pipe bend radius | >5D | Minimum for system operation |
Study Insights and Implications
This 1993 research represents a significant milestone in the automation of internal overlay welding. The development of a four-degree-of-freedom control system demonstrates the feasibility of automating complex welding operations that were previously performed manually. The microcomputer-based control approach was innovative for its time, enabling programmable welding sequences and adaptive parameter control.
The key insight from this research is that the automation of internal overlay welding requires not only precise positioning control but also the ability to adapt welding parameters to the changing geometry along the weld path. The four degrees of freedom provide the necessary flexibility to maintain optimal welding conditions throughout the entire weld length, even on curved pipe sections.
For modern engineering practice, this research is foundational. Contemporary internal overlay welding systems incorporate advanced sensor technologies, machine vision, and real-time process monitoring that build upon the fundamental principles established in this early work. The evolution from microcomputer control to modern CNC systems with integrated process monitoring represents a continuous improvement trajectory that began with innovations like the one described in this study.
The study also highlights the importance of system integration in automated welding. The success of the four-degree-of-freedom system depends not only on the mechanical design and control algorithms but also on the careful integration of welding parameters, gas shielding, and torch design. This holistic approach to welding automation remains relevant in contemporary engineering practice.