CLADDING TECHNOLOGY SHANXI CO., LTDTIG Overlay Welding Process for Copper Alloy Molds of Xiaoli Sedan
Literature Overview
This study note examines the TIG (gas tungsten arc welding) overlay welding process applied to copper alloy molds used in the Xiaoli sedan body-in-white manufacturing process. Copper alloy molds in automotive stamping operations are subjected to extreme thermal cycling, mechanical impact, and wear, making surface restoration through overlay welding a critical maintenance technology. The literature describes process development work aimed at extending mold life through effective TIG cladding of wear-resistant copper alloy layers.
Process Parameters and Technical Challenges
TIG overlay welding on copper alloy substrates presents unique challenges due to the high thermal conductivity of copper, which tends to dissipate heat rapidly and make it difficult to achieve adequate fusion and bonding. The literature identifies the following key process parameters:
| Parameter | Typical Value | Rationale |
|---|---|---|
| Arc current | 120-180 A | Sufficient heat input for copper fusion |
| Arc voltage | 12-16 V | Maintains stable arc on copper |
| Travel speed | 200-400 mm/min | Controls dilution and bead width |
| Shielding gas | Pure Ar or Ar/He mix | Adequate protection for copper alloy |
| Wire diameter | 1.6-2.4 mm | Matching consumable size to deposit rate |
| Pulse frequency | 50-100 Hz (if pulsed) | Controls heat input per pulse |
The primary technical challenge is managing the dilution rate between the copper alloy substrate and the overlay material. When applying a hardfacing copper alloy layer on a base copper alloy mold, the dilution affects the final hardness and wear resistance of the overlay. The literature reports that dilution rates between 20% and 40% produce optimal mechanical properties for stamping mold applications.
Microstructural Analysis and Property Evaluation
The metallurgical quality of TIG overlay welds on copper alloys is assessed through several methods. Metallographic examination reveals the grain structure of the overlay layer, which typically shows columnar grains growing from the fusion line. The grain orientation and size directly affect the hardness distribution and crack resistance of the overlay.
| Test Method | Acceptance Criteria | Purpose |
|---|---|---|
| Microhardness (HV) | Gradient from base to surface | Verify hardness profile |
| Bond strength (shear) | >80% of base metal shear strength | Ensure metallurgical bond |
| Dilution analysis (optical emission) | 20-40% base metal in overlay | Control composition |
| Wear test (pin-on-disk) | Specific wear rate <0.5 mm3/N·m | Validate wear resistance |
| Thermal fatigue (100 cycles) | No cracks at fusion line | Ensure thermal cycling durability |
Engineering Practice and Quality Control
In automotive stamping operations, mold maintenance through overlay welding must meet strict quality requirements. The overlay layer must provide uniform hardness across the entire stamped area, maintain dimensional accuracy within tight tolerances, and survive thousands of stamping cycles without failure. The literature describes a systematic approach to quality control that includes pre-weld cleaning, interpass temperature monitoring, and post-weld machining verification.
A critical aspect of TIG overlay on copper molds is the control of hot cracking susceptibility. Copper alloys are particularly prone to solidification cracking due to their narrow freezing range and low solubility of impurities. The literature recommends limiting sulfur and phosphorus content in both the substrate and consumable materials to below 0.01% to minimize hot cracking risk.
Study Reflections
This literature provides valuable insight into the practical application of TIG overlay welding in a high-volume manufacturing environment. The challenges described — thermal management, dilution control, and crack prevention — are directly analogous to those encountered in clad plate and weld overlay pressure vessel fabrication. The systematic approach to process development and quality control described here is transferable to our own qualification procedures under NB/T 47014 and ASME IX. The emphasis on microstructural control as the key to achieving desired overlay properties reinforces the importance of metallurgical understanding in all overlay welding applications.