CLADDING TECHNOLOGY SHANXI CO., LTDAutomatic Control Method for Grinding Roll Open-Arc Weld Overlay System
Literature Overview and Research Motivation
This paper, published in the Journal of Welding in 2008, presents an automatic control method for a grinding roll open-arc weld overlay system. The research was conducted by Li Zhenying, Dai Liping, Hou Ming, and He Qiong from Beijing Information Science and Technology University. The work addresses a critical practical challenge: achieving consistent and high-quality overlay layers on grinding rolls through automated control of the open-arc welding process.
Grinding rolls are large cylindrical components used in rolling mills to reduce the thickness of steel slabs. The overlay layer on grinding rolls must withstand extreme conditions, including high temperatures, heavy mechanical loads, and abrasive wear from the steel being rolled. The open-arc welding process is commonly used for overlaying grinding rolls because of its high deposition rate and good penetration, but achieving consistent overlay quality requires precise control of multiple process parameters.
Core Technical Analysis
Control System Architecture
The automatic control system for the grinding roll open-arc weld overlay system typically includes the following components:
- Position control system: Controls the position of the welding torch relative to the grinding roll surface to ensure consistent weld bead geometry.
- Travel speed control system: Controls the welding speed to maintain the desired heat input and deposition rate.
- Wire feed control system: Controls the wire feed speed to maintain the desired current and arc length.
- Current and voltage control system: Controls the welding current and voltage to maintain the desired arc characteristics.
- Cooling system control: Controls the cooling water flow to prevent excessive heating of the grinding roll.
Control Algorithm Design
The control algorithm for the grinding roll open-arc weld overlay system typically employs a combination of feedback and feedforward control strategies:
- Arc length control: A feedback control loop maintains the arc length at the desired setpoint by adjusting the wire feed speed based on the measured welding voltage. The control law is typically a PID (proportional-integral-derivative) controller with tuning parameters optimized for the specific welding process.
- Travel speed control: A feedforward control system adjusts the travel speed based on the grinding roll diameter and the desired weld bead width. The travel speed is also adjusted in real time based on feedback from the welding current and voltage sensors to compensate for variations in the grinding roll surface condition.
- Multi-pass coordination: For multi-pass overlay welding, the control system coordinates the welding sequence and parameters for each pass to ensure uniform overlay thickness and microstructure. The control system also manages the interpass temperature to prevent excessive heating of the grinding roll.
- Defect detection and correction: The control system includes real-time monitoring of the welding process to detect and correct potential defects such as porosity, lack of fusion, and undercut. The monitoring system uses sensors to measure the welding current, voltage, arc length, and wire feed speed, and applies corrective actions when deviations from the setpoints are detected.
Process Parameter Optimization
The automatic control system is designed to operate within an optimized process parameter window:
| Parameter | Setpoint | Control Tolerance | Measurement Method |
|---|---|---|---|
| Welding current | 300–500 A | ±10 A | Current sensor |
| Welding voltage | 28–35 V | ±1 V | Voltage sensor |
| Wire feed speed | 3–8 m/min | ±0.2 m/min | Encoder on wire feed motor |
| Travel speed | 200–600 mm/min | ±10 mm/min | Encoder on travel drive |
| Arc length | 2–5 mm | ±0.5 mm | Inferred from voltage |
| Interpass temperature | <200 °C | ±20 °C | Thermocouple on roll surface |
Engineering Practice and Implementation
Grinding Roll Overlay Requirements
Grinding rolls require overlay layers with specific performance characteristics:
- Hardness: 40–55 HRC to provide adequate wear resistance while maintaining sufficient toughness to resist cracking.
- Thickness: 3–10 mm depending on the roll diameter and expected service life.
- Uniformity: The overlay thickness should be uniform around the roll circumference to prevent imbalance during operation.
- Bond strength: The overlay layer must be metallurgically bonded to the grinding roll substrate with no defects at the interface.
Implementation Challenges
The implementation of the automatic control system for grinding roll open-arc weld overlay faces several challenges:
- Large workpiece size: Grinding rolls can have diameters of 1–2 meters and lengths of 2–4 meters, making it challenging to maintain consistent torch position and welding parameters over the entire roll surface.
- Variable surface condition: The grinding roll surface may have variations in flatness, roughness, and residual stress from previous operations, which can affect the welding process and require real-time compensation.
- Thermal management: The large heat input required for overlay welding can cause significant thermal distortion of the grinding roll, which must be minimized through careful control of the welding sequence and cooling.
- Multi-pass coordination: Multi-pass overlay welding requires careful coordination of the welding sequence and parameters for each pass to ensure uniform overlay thickness and microstructure.
Study Insights and Independent Reflection
This research demonstrates the critical importance of automated control in achieving consistent and high-quality overlay layers on large components such as grinding rolls. The manual welding of grinding roll overlay layers is labor-intensive, time-consuming, and prone to inconsistencies, making automated control an essential requirement for modern manufacturing.
One key insight is that the automatic control system must not only maintain the welding parameters at their setpoints but also adapt to variations in the workpiece condition and welding environment. This adaptive capability is essential for achieving consistent overlay quality in production environments where conditions are not always ideal.
Another important insight is the integration of multiple control loops to manage the various aspects of the welding process. The control system must coordinate the position, travel speed, wire feed, current, voltage, and cooling systems to achieve the desired overlay quality. This integration requires careful system design and tuning to ensure stable and responsive control.