CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of CNC Weld Overlay Machine for Continuous Casting Rolls
Literature Overview
This research publication in Welding Technology (2009), supported by the China University of Mining and Technology Science Research Foundation (Project No. 206B008), documents the development of a computer numerically controlled (CNC) weld overlay machining system for continuous casting rolls by Hao Feng and Gao Ding from the School of Mechanical and Electrical Engineering, China University of Mining and Technology, in collaboration with Fu Ping'an from Zhengzhou Coal Mine Machinery Group Co., Ltd. The work represents a significant advancement in the automation and precision of overlay welding for critical industrial components.
Core Technical Content
Continuous casting rolls are among the most critical components in steel and non-ferrous metal production facilities. They must maintain extremely precise surface geometry and dimensional accuracy to ensure consistent product quality. The working surface of a casting roll is subjected to severe thermal and mechanical loading during operation, requiring periodic overlay repair and resurfacing. The traditional manual or semi-automatic approach to roll cladding introduces variability in layer thickness, surface quality, and geometric accuracy that can compromise casting product quality.
CNC System Architecture
The CNC weld overlay system integrates the following functional modules:
| Module | Function | Technology |
|---|---|---|
| Numerical control system | Program execution, coordinate control | CNC controller with G-code interpreter |
| Welding power source | Arc generation and energy delivery | DC or AC welding power supply |
| Consumable feed system | Electrode or wire feeding | Motor-driven feed mechanism |
| Shielding gas system | Atmosphere protection | Gas flow control and delivery |
| Workpiece rotation | Roll positioning and rotation | Servo-driven rotary table |
| Weld head positioning | Arc trajectory control | Multi-axis positioning system |
| Monitoring system | Process parameter and quality monitoring | Sensors and data acquisition |
The CNC system enables precise control of the welding trajectory, maintaining constant arc length, consistent deposition rate, and uniform layer thickness across the entire roll surface. The system can execute complex multi-pass welding sequences with automatic pass sequencing, parameter adjustment between passes, and real-time monitoring of welding conditions.
Process Parameters and Performance
The CNC overlay system achieves the following performance characteristics:
- Layer thickness uniformity: ±0.05 mm across the roll surface
- Surface roughness: Ra 6.3-12.5 μm (as-welded), improvable to Ra 1.6-3.2 μm by grinding
- Deposition rate: 1.5-3.0 kg/h depending on consumable and parameter settings
- Dilution rate: 10-20% (controlled by process parameters)
- Overlay hardness: 50-60 HRC (adjustable by consumable selection)
- Geometric accuracy: ±0.1 mm diameter tolerance after machining
The system supports multiple welding processes including submerged arc welding (SAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW), allowing flexibility in consumable selection based on the specific roll application and performance requirements.
Defect Prevention and Quality Assurance
The CNC approach significantly reduces the occurrence of common overlay welding defects through automated process control:
- Thickness variation: Eliminated through precise arc trajectory control and constant deposition rate monitoring
- Porosity: Reduced through consistent shielding gas flow and stable arc conditions
- Cracking: Minimized through controlled heat input and systematic pass sequencing
- Surface irregularities: Reduced through consistent arc length and travel speed
- Interpass contamination: Minimized through automated interpass cleaning (if equipped) or controlled interpass intervals
Quality assurance is enhanced through in-process monitoring of welding parameters (current, voltage, travel speed, arc length) and post-weld inspection using ultrasonic testing (UT) for subsurface defects, magnetic particle inspection (MT) for surface defects, and dimensional measurement for geometric accuracy.
Engineering Practice Integration
At Zhengzhou Coal Mine Machinery Group, the deployment of the CNC overlay system resulted in measurable improvements in continuous casting roll manufacturing quality and productivity:
- Productivity increase: 40-60% reduction in overlay welding cycle time compared to manual methods
- Quality improvement: Reduction in post-weld machining allowance from 1.5-2.0 mm to 0.5-1.0 mm per side
- Consistency: Elimination of operator-dependent variability in layer quality
- Material savings: Reduced overlay material consumption through precise deposition control
- Operator productivity: Welders can monitor multiple machines simultaneously
The system is particularly valuable for high-volume production environments where consistent quality and rapid turnaround are essential. The CNC programming allows rapid adaptation to different roll sizes, overlay thicknesses, and consumable types through simple parameter changes without the need for physical setup modifications.
A significant advantage of the CNC approach is the ability to implement intelligent welding strategies that optimize the overlay process for specific applications. For example, the system can automatically adjust welding parameters based on the roll diameter, the required overlay thickness, and the selected consumable type. Advanced implementations can incorporate real-time feedback from sensors to compensate for process variations and maintain consistent quality throughout the welding operation.
Key Reflections and Study Insights
This research represents a paradigm shift from manual craftsmanship to automated precision in overlay welding. The CNC approach does not eliminate the need for skilled engineers and welders but rather elevates their role from manual operation to process design, programming, and quality oversight. This transition is consistent with the broader trend in manufacturing toward automation and digitalization, where human expertise is applied to system design and optimization rather than repetitive manual tasks.
The development of CNC overlay systems also highlights the importance of process standardization and documentation. Automated systems require well-defined process parameters and procedures, which in turn drive the formalization of welding knowledge that was previously embedded in individual operator experience. This knowledge codification is valuable for training, quality control, and continuous improvement initiatives.
The research underscores a fundamental principle in engineering: that the quality of the final product is determined not only by the intrinsic properties of the materials but also by the precision and consistency of the manufacturing process. In the context of continuous casting rolls, where surface geometry directly impacts product quality, the CNC approach provides the process control necessary to achieve the dimensional and surface quality requirements of modern steelmaking.