Zhuojin Pipe Fitting Co., LtdCNC Overlay Welding Machine for Continuous Casting Rolls
Literature Overview
The paper by Hao Feng, Gao Ding, and Fu Ping'an, published in Welding Technology (2009, Vol. 38, No. 10, pp. 29–32), describes the development of a CNC overlay welding machine specifically designed for continuous casting (CC) rolls. The machine integrates the SINUMERIK 801 CNC system with a dual-microprocessor digital control system for submerged arc welding (SAW), achieving high automation and consistent overlay quality. This work is funded by the China University of Mining and Technology Research Fund (206B008).
Technical Background
Continuous casting rolls are critical components in steelmaking, responsible for shaping and cooling the molten steel strand. They are subjected to:
- Thermal cycling: Repeated heating from ~1500 °C (molten steel) to ~100 °C (water cooling).
- Mechanical loading: Contact pressure from the solidifying shell.
- Thermal shock: Rapid temperature changes at the roll surface.
The roll surface must therefore exhibit excellent thermal fatigue resistance, wear resistance, and surface integrity. Overlay welding is the standard method for applying a protective layer to the roll surface, but manual or semi-automatic welding often results in inconsistent overlay thickness and quality.
Machine Design and Architecture
Mechanical Structure
The machine is built upon an existing welding machine platform with the following key components:
- Rotary table: Supports the roll and provides rotation for circumferential welding.
- Linear traverse: Moves the torch along the roll axis for multi-pass coverage.
- Welding head: Houses the SAW torch with flux supply and wire feed mechanism.
- Roll support system: Adjustable supports for different roll diameters and lengths.
Control System Integration
The control architecture is the core innovation of this machine:
| System | Function | Key Features |
|---|---|---|
| SINUMERIK 801 | CNC control | G-code programming, position control, speed control |
| Dual-MCU SAW controller | Welding parameter control | Current, voltage, wire feed speed, arc length |
| Communication interface | Data exchange between CNC and SAW controller | Synchronized motion and welding |
The dual-microprocessor SAW controller manages:
- Current control: Regulates welding current to maintain stable arc.
- Wire feed speed: Synchronized with the traverse speed for uniform deposition.
- Arc length regulation: Maintains constant arc length for consistent bead profile.
- Flux supply control: Ensures adequate flux coverage for SAW.
Process Parameters
The typical welding parameters for CC roll overlay are:
| Parameter | Range |
|---|---|
| Welding current | 400–600 A |
| Arc voltage | 28–35 V |
| Wire feed speed | 8–12 m/min |
| Travel speed | 200–400 mm/min |
| Flux type | Basic or fluorite-apatite |
| Wire diameter | 1.6–2.0 mm |
| Preheating temperature | 150–250 °C |
Quality Control Features
The CNC system enables precise control of several quality-critical parameters:
- Overlay thickness uniformity: The CNC-controlled traverse and rotation ensure consistent overlap between passes, achieving thickness uniformity within ±0.1 mm.
- Heat input control: The synchronized wire feed and travel speed maintain constant heat input, minimizing distortion.
- Interpass temperature monitoring: An infrared pyrometer integrated with the CNC system monitors the surface temperature and pauses welding if the interpass temperature exceeds the set limit.
- Bead profile control: The dual-MCU controller adjusts the arc length and current to maintain a consistent bead profile, critical for subsequent machining.
Performance Comparison
| Parameter | Manual/Semi-Auto | CNC Machine |
|---|---|---|
| Thickness uniformity | ±0.3–0.5 mm | ±0.1 mm |
| Welding time per roll | 8–12 hours | 4–6 hours |
| Operator skill requirement | High | Low |
| Defect rate | 5–8% | <1% |
| Consistency between rolls | Variable | Excellent |
The CNC machine reduces welding time by approximately 50% while significantly improving quality consistency. The lower defect rate is attributed to the elimination of operator variability in travel speed, wire feed, and arc length control.
Engineering Practice Implications
This machine design has several important implications for industrial practice:
- Scalability: The modular control architecture (CNC + dual-MCU) can be adapted to different roll sizes and welding processes (SAW, FCAW, GMAW) by changing the welding head and adjusting the control parameters.
- Integration with production: The G-code programming capability allows easy integration with production planning systems, enabling batch production of rolls with different overlay specifications.
- Operator training: The high automation level reduces the skill requirements for operators, making the technology more accessible to smaller shops.
- Data logging: The CNC system can log welding parameters for each roll, providing traceability for quality assurance and continuous improvement.
Study Insights
This paper represents a significant step in the automation of overlay welding for heavy industrial components. The integration of CNC motion control with a specialized welding controller is a practical solution that does not require a full robotic system, making it economically viable for small and medium-sized manufacturers. The dual-microprocessor approach for SAW control is particularly elegant, as it isolates the fast control loop (arc length, current) from the slower motion control loop, ensuring both stability and precision. For engineers evaluating automation options for roll repair, this design provides a proven reference architecture that balances cost, complexity, and performance.