CLADDING TECHNOLOGY SHANXI CO., LTDNew Alloy Cladding Technology for Blanking Die Cutting Edges
Literature Overview
This study introduces a novel alloy cladding technology specifically developed for the cutting edges of blanking dies in precision sheet metal forming. The technology combines hot-wire gas tungsten arc welding (HW-TIG) with a proprietary tungsten-cobalt-chromium alloy wire to achieve a high-hardness, low-dilution overlay that significantly extends die life. The study addresses the challenges of cladding narrow cutting edges (width <3 mm) where conventional processes suffer from excessive heat input, distortion, and poor wetting.
Technical Challenges and Process Innovation
Blanking die cutting edges present unique challenges for cladding operations. The edge width is typically 1.5–3 mm, the required hardness is 800–1000 HV30, and the allowable distortion is less than 0.05 mm. Conventional processes such as SMAW and oxy-acetylene hardfacing introduce excessive heat, causing substrate softening and edge distortion. The authors developed a HW-TIG process that uses a 1.2 mm tungsten-cobalt wire fed at a controlled rate while a non-consumable tungsten electrode provides the arc heat.
| Parameter | Conventional TIG | HW-TIG (This Study) | Advantage |
|---|---|---|---|
| Wire diameter | N/A (non-consumable) | 1.2 mm consumable | Continuous deposition |
| Heat input | 0.3–0.8 kJ/mm | 0.5–1.2 kJ/mm | Higher deposition rate |
| Dilution rate | 30–50% | 8–15% | Better alloy retention |
| Overlay hardness | 350–450 HV30 | 850–950 HV30 | Superior wear resistance |
| Distortion | 0.1–0.3 mm | <0.05 mm | Dimensional accuracy |
| Deposition rate | 0.5–1.0 g/min | 5.0–8.0 g/min | 8× productivity |
The key innovation is the use of a tungsten-cobalt wire (composition: 60% Co, 25% W, 8% Cr, 7% C) which has a melting point of approximately 1480°C, significantly higher than conventional cobalt-based wires. This high melting point ensures that the wire acts as both a heat sink and a filler material, resulting in a more controlled heat input and reduced dilution.
Microstructural and Mechanical Properties
The HW-TIG overlay microstructure consisted of a complex mixture of WC, Co3W, and Co7W6 carbides dispersed in a cobalt-chromium matrix. The carbide phase fraction was approximately 35–40%, which was higher than typical PTA overlays (20–25%) due to the lower dilution rate. The overlay hardness was measured at 880–930 HV30, with a depth of uniform hardness extending to 1.2–1.5 mm.
The bond strength between the overlay and the H13 substrate was tested using a micro-scratch method, yielding a critical load of 45 N, which corresponds to a bond strength of approximately 280 MPa. This was well above the minimum requirement of 200 MPa specified in most tooling standards. The overlay exhibited good resistance to thermal cycling, maintaining hardness above 800 HV30 after 500 thermal cycles between 25°C and 350°C.
Process Optimization and Quality Control
The authors conducted a systematic process optimization using a Taguchi L18 orthogonal array to identify the optimal combination of welding parameters. The key findings were:
- Wire feed speed was the most influential parameter, affecting hardness and dilution rate.
- Arc current had a significant effect on penetration depth and bond strength.
- Travel speed primarily influenced overlay width and deposition rate.
- Shielding gas flow rate had minimal effect on hardness but was critical for preventing oxidation.
The optimal parameter set was: arc current 120 A, arc voltage 22 V, wire feed speed 6.0 m/min, travel speed 250 mm/min, shielding gas (Ar) 12 L/min. These parameters produced a single-pass overlay of 1.5 mm width and 1.2 mm height with uniform hardness and no visible defects.
Quality control procedures included:
- Visual inspection for surface defects (cracks, porosity, undercut)
- Hardness mapping at 0.5 mm intervals across the overlay cross-section
- Metallographic examination of the substrate-overlay interface
- Magnetic particle testing (MT) for detection of surface cracks in the overlay
- Ultrasonic testing (UT) for detection of internal lack of fusion
Study Insights and Reflections
This study demonstrates the potential of HW-TIG as a superior process for narrow-edge cladding applications. The low dilution rate is particularly valuable for maintaining the alloying composition of wear-resistant overlays, which is critical for achieving the target hardness and carbide distribution. However, the study has limitations: the testing was conducted on flat specimens, and the transition from flat to curved geometries (as found in actual die profiles) requires additional process qualification. The authors also did not address the issue of overlay repair after wear, which is a practical concern in production environments. In my assessment, the HW-TIG process should be complemented with a final grinding and sharpening step to achieve the required edge geometry, and the grinding parameters must be carefully controlled to avoid thermal damage to the overlay. The economic analysis presented in the study is compelling: despite the higher equipment and consumable costs, the extended die life results in a net cost reduction of 60–70% per stroke.