CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Welding Performance of Middle Groove Based on Plasma Cladding
Literature Overview and Technical Background
The middle groove (or center groove) configuration in weld overlay applications presents unique challenges related to dilution control, geometric constraints, and mechanical property optimization. The literature reviewed here investigates the welding performance of middle groove configurations using plasma transferred arc (PTA) cladding, with a focus on the effects of groove geometry, process parameters, and consumable selection on the resulting weld quality. This study is particularly relevant to applications where a defined groove geometry is required for overlay attachment, such as in the cladding of turbine blades, pump impellers, and pressure vessel internals.
Middle Groove Configuration and Geometry
The middle groove configuration involves depositing overlay material into a pre-machined groove in the base material surface, creating a defined interface between the base and overlay. This configuration differs from surface cladding in several important ways:
| Feature | Middle Groove Cladding | Surface Cladding |
|---|---|---|
| Interface geometry | Defined groove with machined walls | Flat surface |
| Dilution control | Groove geometry influences dilution | Primarily depends on process parameters |
| Bond strength | Mechanical interlock + metallurgical bond | Primarily metallurgical bond |
| Geometric accuracy | Groove dimensions must be controlled | Less critical |
| Stress concentration | Groove root can be a stress concentrator | Lower stress concentration |
The groove geometry parameters studied in the literature include:
- Groove width: 6, 8, 10 mm
- Groove depth: 3, 5, 7 mm
- Groove angle: 60°, 75°, 90° (included angle)
- Groove root radius: 1.0, 2.0 mm
Plasma Transferred Arc (PTA) Process Characteristics
PTA cladding is particularly well-suited for middle groove applications due to its high energy density, precise heat input control, and low dilution capability. The key process parameters and their effects are summarized below:
| Process Parameter | Typical Range | Effect on Dilution | Effect on Weld Quality |
|---|---|---|---|
| Arc current | 100-300 A | Higher current → higher dilution | Higher current → wider bead |
| Powder feed rate | 200-600 g/min | Higher feed rate → lower dilution | Higher feed rate → more porosity risk |
| Travel speed | 100-400 mm/min | Higher speed → lower dilution | Higher speed → thinner bead |
| Shielding gas flow | 15-30 L/min | Minimal effect | Higher flow → better shielding |
| Powder standoff distance | 5-15 mm | Affects powder trajectory | Optimal at 8-12 mm |
| Arc-to-powder distance | 3-8 mm | Affects powder melting efficiency | Optimal at 5-7 mm |
The literature identifies a critical relationship between the powder feed rate and arc current that determines the dilution level. For middle groove cladding, the optimal powder-to-current ratio (PCR) is typically 1.5-3.0 g/min/A, compared to 1.0-2.0 for surface cladding. The higher PCR in groove cladding is necessary to fill the groove volume while maintaining acceptable dilution levels.
Dilution Analysis and Control
Dilution is the most critical factor in middle groove cladding, as it directly affects the chemical composition and properties of the overlay layer. The literature presents a comprehensive dilution analysis for different groove geometries and process parameters:
| Groove Configuration | PCR | Dilution (%) | Overlay Hardness (HV) | Notes |
|---|---|---|---|---|
| 8 × 5 mm, 90° | 2.0 | 18-22 | 280-320 | Moderate dilution |
| 8 × 5 mm, 90° | 2.5 | 12-16 | 320-360 | Improved dilution control |
| 8 × 5 mm, 90° | 3.0 | 8-12 | 360-400 | Low dilution, risk of porosity |
| 6 × 3 mm, 60° | 2.0 | 22-28 | 260-300 | Higher dilution (narrower groove) |
| 10 × 7 mm, 75° | 2.0 | 15-19 | 290-330 | Lower dilution (wider groove) |
The findings demonstrate that groove geometry has a significant effect on dilution. Narrower grooves exhibit higher dilution because the base material walls are closer to the weld pool, promoting greater heat transfer into the base. Deeper grooves also tend to exhibit higher dilution due to the increased volume of base metal that must be melted to fill the groove.