CLADDING TECHNOLOGY SHANXI CO., LTDCladding Process and Economic Analysis for Large Cover Insert Molds
Literature Overview
This 2009 paper by He Bolin, Yu Yingxia, Zhang Jianxin, and Wei Xingbao, published in Mechanical Design and Manufacturing, presents a comprehensive study of the cladding process for insert molds used in large automotive cover panels. Funded by the Ministry of Machinery Industry Education Department Science and Technology Fund (95251214) and the Provincial-Ministerial Joint Key Laboratory of Vehicle Equipment, the research was conducted jointly by East China Jiaotong University and Luoyang First Tractor and Construction Machinery Company. The work combines metallurgical process optimization with economic analysis, making it particularly relevant for production engineers responsible for cost-effective tooling solutions.
Core Technical Points
Application Background
Large cover insert molds are used in the stamping of automotive body panels such as doors, hoods, and fenders. These molds are subject to severe wear at the insert areas where the sheet metal is directly formed. The inserts are typically made of hardened tool steel, but their service life is limited by abrasive wear from the sheet metal and by galling under high contact pressure. Cladding with a wear-resistant overlay layer is a cost-effective solution to extend insert life.
| Component | Material | Service Life (without cladding) | Service Life (with cladding) |
|---|---|---|---|
| Insert mold | H13 (48-52 HRC) | 50,000-80,000 strokes | 150,000-250,000 strokes |
| Overlay layer | Cr-Ni-Mo alloy | - | - |
| Base plate | 45 steel | - | - |
Cladding Process Selection
Several cladding processes were evaluated for applicability to large cover insert molds:
| Process | Advantages | Limitations | Applicability |
|---|---|---|---|
| SAW overlay | High deposition rate, good for large areas | Limited to flat or gently curved surfaces | Primary process for flat inserts |
| GMAW overlay | Flexible, good for complex shapes | Lower deposition rate than SAW | Secondary process for curved areas |
| Oxy-acetylene | Low equipment cost | Poor quality, high distortion | Not recommended for precision molds |
| Hardfacing (manual) | Flexible, repairable | Inconsistent quality, labor-intensive | Emergency repair only |
The recommended process is a combination of SAW for flat areas and GMAW for curved or hard-to-reach areas, with manual hardfacing reserved for in-service repairs.
Process Parameters for SAW Overlay
| Parameter | Value | Notes |
|---|---|---|
| Wire diameter | 1.2 mm or 1.6 mm | 1.6 mm for thicker overlay |
| Current | 250-400 A | Depends on wire diameter |
| Voltage | 24-30 V | Stable arc |
| Travel speed | 20-40 cm/min | Balance deposition and quality |
| Flux type | HJ431 or equivalent | Low hydrogen flux |
| Preheat temperature | 150-200°C | Reduce cracking risk |
| Overlay thickness | 3-5 mm | Optimal for wear life |
| Number of passes | 2-3 | Transition + wear layers |
Microstructure and Properties of Clad Layer
| Property | Specification | Measured Value |
|---|---|---|
| Hardness | 50-55 HRC | 51-54 HRC |
| Wear resistance | > 2× base material | 2.5-3.0× base material |
| Dilution | < 30% | 20-28% |
| Cracking | None permitted | 0% cracking |
| Surface roughness | Ra < 1.6 μm | Ra 0.8-1.4 μm |
Economic Analysis
The economic evaluation is a critical aspect of this paper, as it demonstrates the financial justification for cladding investment:
| Cost Item | Without Cladding | With Cladding |
|---|---|---|
| Insert replacement cost (per cycle) | 100% | 30% |
| Downtime per replacement (hours) | 8-12 | 2-3 |
| Production loss per replacement | 50,000-80,000 CNY | 15,000-25,000 CNY |
| Cladding cost per insert | - | 5,000-8,000 CNY |
| Number of replacements per year | 12-15 | 4-5 |
| Annual total cost | 750,000-1,200,000 CNY | 250,000-400,000 CNY |
| Annual savings | - | 500,000-800,000 CNY |
| ROI (return on investment) | - | 60-80% |
The economic analysis clearly demonstrates that cladding provides a significant return on investment, with payback periods of less than 6 months in most cases.
Quality Control and Inspection
| Inspection Item | Method | Frequency | Acceptance Criteria |
|---|---|---|---|
| Surface appearance | Visual | 100% | No cracks, no porosity |
| Hardness | Rockwell C | 5 points per insert | 50-55 HRC |
| Dilution | Metallographic | 1 per batch | < 30% |
| Dimensional accuracy | CMM | 1 per insert | ±0.05 mm |
| Surface roughness | Roughness tester | 1 per insert | Ra < 1.6 μm |
Engineering Practice Integration
The cladding process described in this paper has been successfully implemented in automotive stamping production lines. The key to success is maintaining precise dimensional control after cladding, which requires careful machining of the clad layer to achieve the final mold geometry. The overlay thickness should be designed to allow for 0.5-1.0 mm of post-cladding machining while still providing adequate wear life.
Common Issues and Solutions
| Issue | Root Cause | Solution |
|---|---|---|
| Excessive distortion | High heat input, asymmetric welding | Reduce heat input, use symmetric sequence |
| Poor dimensional accuracy | Inconsistent overlay thickness | Use multi-wire SAW for uniform deposition |
| Cracking at overlay/base interface | High carbon in base, inadequate preheat | Increase preheat, use transition layer |
| Surface roughness after machining | Coarse microstructure | Optimize cooling rate, consider post-weld tempering |
Key Questions and Reflections
An important question raised by this work is the long-term stability of the cladding layer under repeated stamping cycles. The authors suggest that the cladding layer should be periodically inspected for wear and re-clad when the remaining thickness falls below 1.0 mm. This predictive maintenance approach can prevent unexpected mold failures and production interruptions.
Another reflection concerns the environmental impact. Cladding extends the service life of inserts by 2-3 times, which significantly reduces the consumption of tool steel and the associated environmental burden from steel production. This makes cladding not only economically attractive but also environmentally responsible.
Study Insights and Implications
This paper provides a comprehensive framework for implementing cladding solutions on large cover insert molds, combining metallurgical optimization with economic justification. The economic analysis is particularly valuable for engineers who need to present business cases to management for cladding investments. The key takeaway is that cladding is not merely a technical solution but a strategic cost-reduction and productivity-enhancement tool that should be considered for all high-wear stamping applications.