CLADDING TECHNOLOGY SHANXI CO., LTDEdge Overlay Welding of Japanese Automotive Molds
Literature Overview
This 2000 study by Ren Xueyan from Zhengzhou Nissan Motor Co., Ltd., published in Welding Technology, examines the overlay welding practices used for the sharpening and repair of edge tools in Japanese automotive mold manufacturing. The work provides a valuable perspective on the industrial application of overlay welding in the automotive stamping industry, where mold edges must maintain precise geometry and hardness throughout their service life. The study reflects the advanced manufacturing practices of Japanese automotive companies, which have long been leaders in tool and die technology.
Core Technical Points
Application Context and Requirements
Automotive stamping molds are subjected to severe plastic deformation during the forming of sheet metal components. The mold edges, which are in direct contact with the sheet metal, experience high contact stresses, friction, and temperature cycling. Over time, the mold edges become worn, rounded, or damaged, requiring periodic sharpening and repair. Overlay welding is used to restore the edge geometry and hardness, extending the service life of the mold and reducing the need for complete mold replacement.
The overlay material must meet several critical requirements: it must be compatible with the mold steel substrate, provide sufficient hardness to resist wear, maintain toughness to resist chipping and cracking, and be amenable to subsequent grinding and sharpening operations. Typical mold steels include H13 (4Cr5MoSiV1), D2 (Cr12MoV), and SKD11, all of which are high-carbon, high-chromium tool steels with a hardness of 45–55 HRC in the as-tempered condition.
Overlay Welding Processes
The study discusses several overlay welding processes used for mold edge repair:
| Process | Typical Application | Hardness (HV) | Dilution | Advantages | Limitations |
|---|---|---|---|---|---|
| TIG (GTAW) | Precision edge repair | 800–1000 | Low (5–15%) | High quality, low distortion | Low deposition rate |
| MIG (GMAW) | Larger area repair | 700–900 | Moderate (10–25%) | High deposition rate | Higher dilution, more spatter |
| Flux-cored (FCAW) | Heavy buildup | 700–900 | Moderate (15–30%) | High deposition rate, outdoor use | Flux residue, higher porosity risk |
| Oxy-fuel | Quick field repair | 600–800 | High (25–40%) | Equipment simplicity | Low quality, high dilution |
Microstructural Control
The overlay layer on mold edges typically consists of a martensitic structure with retained austenite, similar to the base mold steel but with higher carbon and alloy content. The hardness of the overlay is achieved through the formation of fine carbides (M₇C₃, M₂₃C₆) and the high carbon content of the martensitic matrix. The retained austenite provides a degree of toughness and can transform to martensite during subsequent grinding or heat treatment, further increasing the hardness.
The dilution ratio is a critical parameter in mold edge overlay welding. Excessive dilution with the low-carbon substrate reduces the hardness of the overlay and may lead to a soft zone at the interface. Conversely, too low a dilution ratio can result in cracking due to the high carbon content and brittleness of the overlay. The optimal dilution ratio for mold edge overlays is typically 15–25%, which provides a good balance of hardness and toughness.
Heat Treatment Considerations
After overlay welding, the mold edges are typically subjected to a heat treatment cycle to restore the hardness and relieve residual stresses. The heat treatment parameters depend on the overlay material and the desired final hardness. A typical cycle for H13-based overlays is:
- Austenitizing at 1050–1100°C for 1–2 hours
- Quenching in air or oil to achieve a martensitic structure
- Tempering at 500–550°C for 2–4 hours to achieve a hardness of 48–52 HRC
This heat treatment cycle must be carefully controlled to avoid cracking or distortion of the mold. The cooling rate during quenching should be moderate to minimize thermal stresses, and the tempering temperature should be optimized to achieve the desired hardness-toughness balance.
Process Analysis and Standards Considerations
The study is relevant to standards governing the welding of tool and die components, such as AWS D1.2 (Structural Welding Code) and ISO 14274 (Welding Consumables for Hardfacing). These standards provide guidelines for welding procedure qualification, welder qualification, and inspection requirements.
Key Defects and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Cracking | High carbon content, rapid cooling | Preheating, low heat input, post-weld heat treatment |
| Excessive dilution | High heat input, wrong filler selection | Reduce heat input, use higher carbon filler |
| Porosity | Gas inclusion, moisture in flux | Dry flux, proper shielding gas, clean base metal |
| Lack of fusion | Insufficient heat input, poor technique | Increase heat input, proper welding technique |
| Distortion | Thermal stress, asymmetric welding | Symmetric welding, preheating, post-weld stress relief |
Integration with Engineering Practice
In the automotive mold manufacturing industry, overlay welding is a routine maintenance operation that is performed on a regular basis to extend the service life of mold edges. The study highlights the importance of process standardization and quality control in ensuring consistent results. Each mold edge repair should be documented in a welding log, including the welding process, parameters, filler material, and post-weld heat treatment.
The study also emphasizes the importance of welder skill and experience in achieving high-quality overlay welds on mold edges. The geometry of the mold edge, the accessibility of the weld joint, and the need for precision all require a high level of welder proficiency. Training and certification programs should be in place to ensure that welders are qualified to perform overlay welding on mold edges.
The practical recommendation is to develop a standardized welding procedure for each mold edge repair application, specifying the welding process, parameters, filler material, preheating temperature, and post-weld heat treatment. This procedure should be qualified in accordance with the relevant standards and documented in a welding procedure specification (WPS). The WPS should be reviewed and updated periodically to incorporate lessons learned from field experience and to reflect any changes in materials or processes.
Study Insights and Implications
This study provides a practical perspective on the application of overlay welding in the automotive mold manufacturing industry. The findings demonstrate that overlay welding is a viable and cost-effective method for repairing and restoring mold edges, provided that the process is carefully controlled and the welder is skilled and experienced. The study also highlights the importance of post-weld heat treatment in achieving the desired hardness and relieving residual stresses.
The practical implication is that mold manufacturers should invest in training and qualification of welders, development of standardized welding procedures, and implementation of quality control systems to ensure consistent results. The study also underscores the importance of understanding the metallurgical behavior of the overlay material and its interaction with the substrate, as this directly influences the service performance of the repaired mold edge.