CLADDING TECHNOLOGY SHANXI CO., LTDStrip Cladding Controller Technology and Process Optimization
Technical Overview and System Architecture
Strip cladding (also known as weld overlay using a strip electrode) is a highly efficient method for depositing corrosion-resistant or wear-resistant layers on large flat surfaces. The process uses a continuous strip of alloy material as the electrode, which is fed into the arc and melted to form the overlay. A strip cladding controller is the critical equipment that governs the welding parameters, strip feed rate, and torch movement to ensure consistent overlay quality across potentially large production runs.
The controller system typically integrates several subsystems: a power supply unit (DC or AC), a strip feed mechanism with speed control, a torch position control system (X-Y or X-Y-Z axes), a wire feed regulator, and a monitoring and recording system. Modern controllers incorporate programmable logic controllers (PLCs) or dedicated welding controllers that allow parameter storage, recipe management, and real-time process monitoring.
Key Process Parameters and Control Strategy
The strip cladding process involves several interrelated parameters that must be precisely controlled to achieve uniform overlay thickness, consistent metallurgical quality, and minimal defects. The controller's primary function is to maintain these parameters within tight tolerances throughout the welding operation.
| Parameter | Typical Range | Control Method | Tolerance |
|---|---|---|---|
| Welding current | 300–600 A (DC) | Power supply feedback | ±5% |
| Arc voltage | 18–28 V | Arc voltage regulation | ±0.5 V |
| Strip feed speed | 0.5–2.0 m/min | Servo motor control | ±2% |
| Travel speed | 300–800 mm/min | Torch movement servo | ±3% |
| Strip diameter | 6–16 mm | Pre-set (fixed) | — |
| Torch angle | 5–15° from vertical | Mechanical positioner | ±1° |
| Gas flow rate | 15–25 L/min | Flow controller | ±1 L/min |
The relationship between strip feed speed and travel speed is critical. The deposition rate is directly proportional to the feed speed and inversely proportional to the travel speed. The controller must maintain a consistent ratio to ensure uniform overlay thickness. A common rule of thumb is that for a 10 mm strip at 400 A, the feed speed should be approximately 0.8 m/min at a travel speed of 500 mm/min, producing an overlay thickness of approximately 1.5 mm per pass.
Defect Prevention and Process Monitoring
The strip cladding controller must incorporate defect detection and prevention features to maintain production quality. Common defects in strip cladding include:
| Defect Type | Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Porosity | Moisture in flux/gas | Visual, UT | Ensure dry gas, proper shielding |
| Undercut | Excessive current/speed ratio | Visual, profilometry | Adjust current-speed ratio |
| Lack of fusion | Insufficient heat input | UT, MT | Increase current or reduce speed |
| Cracking | High residual stress, H pickup | MT, visual | Reduce travel speed, add preheat |
| Uneven thickness | Feed speed variation | Profilometry, laser scan | Verify servo calibration |
| Arc blow | Magnetic field interference | Visual | Reduce current, add shims |
Modern controllers integrate real-time monitoring of arc voltage, current, and travel speed, with automatic alarm and shutdown functions if parameters deviate beyond set limits. Some advanced systems incorporate laser thickness gauges or optical pyrometers that provide feedback on overlay thickness and temperature, enabling closed-loop control of the welding parameters.
The controller should also manage the welding sequence for multi-pass overlay operations. The interpass temperature must be monitored and controlled to prevent excessive softening of the previous pass. A typical interpass temperature limit for stainless steel overlay is 250°C, while for nickel-based alloys it may be as low as 150°C. The controller should incorporate temperature monitoring (via thermocouples or infrared sensors) and automatically pause the welding cycle if the interpass temperature exceeds the limit.
Engineering Practice and Operational Considerations
In practice, the strip cladding controller must be configured and calibrated for each specific application. This involves:
- Material qualification: Testing the overlay material and process parameters on coupon specimens to establish baseline properties (hardness, corrosion resistance, bond strength).
- Parameter optimization: Adjusting current, voltage, feed speed, and travel speed to achieve the target overlay thickness and quality.
- Torch calibration: Ensuring the torch position, angle, and nozzle clearance are set correctly for the specific strip diameter and welding geometry.
- Gas system verification: Confirming that the shielding gas supply is clean, dry, and at the correct pressure and flow rate.
- Joint preparation: Verifying that the base material surface is clean, flat, and free of defects that could propagate into the overlay.
A practical challenge in strip cladding is maintaining consistent torch-to-workpiece distance throughout the welding operation, especially on large plates with potential warpage. The controller should incorporate either mechanical height control (via a floating torch mount) or optical height sensing to maintain a constant arc length. Variations in torch height of even 1–2 mm can significantly affect arc stability, heat input, and overlay quality.
Another important consideration is the end-of-weld and restart behavior. At the end of each pass, the controller must ramp down the current gradually to prevent crater cracking. At the start of each new pass, the controller should ramp up the current to ensure proper strike and avoid cold lap defects. These transient behaviors are critical for producing high-quality overlays on large production runs.
Standards and Quality Requirements
Strip cladding operations must comply with relevant standards depending on the application. For pressure vessel applications, NB/T 47014 (Welding procedure qualification) and GB/T 150 (Pressure vessel design and fabrication) govern the qualification and acceptance criteria. For general industrial applications, AWS D3.2M (Specification for Welding Procedures for Surface Cladding) provides the framework for procedure qualification and performance qualification.
The qualification process requires testing of the qualified welding procedure on coupon specimens that simulate the production geometry. The tests typically include:
- Hardness testing: Minimum and maximum hardness limits defined by the specification.
- Bond strength testing: Shear or peel test to verify overlay-substrate adhesion.
- Corrosion testing: Immersion test or electrochemical test to verify corrosion resistance.
- Metallographic examination: Verification of microstructure and absence of defects.
- Chemical analysis: Verification of overlay composition within specification limits.
Summary
The strip cladding controller is the central piece of equipment that determines the quality and consistency of strip cladding operations. Its proper configuration, calibration, and operation are essential for producing overlays that meet the required specifications for thickness, metallurgical quality, and mechanical properties. Engineers responsible for strip cladding programs must understand the interrelationships between welding parameters, overlay quality, and the controller's control algorithms. The integration of real-time monitoring and feedback control systems represents the current state of the art in strip cladding technology, enabling the production of high-quality overlays with reduced operator dependence and improved process consistency. A thorough understanding of the controller's capabilities and limitations, combined with rigorous qualification and quality control procedures, is the foundation of a successful strip cladding program.