Remanufacturing System Based on Fully Automatic MIG Surfacing via Robot

Literature Overview

This 2005 study published in the Journal of Central South University, authored by Zhu Sheng, Guo Yingchun, and Yang Pei from the National Key Laboratory for Remanufacturing, presents a fully automated robotic MIG surfacing system for component remanufacturing. The work was supported by multiple national research programs including the National Natural Science Foundation of China (Grants 50075086 and 50235030), the National Basic Research Foundation of China (Grant 413270103), and the Ministry of Education Outstanding Teachers Project (2000476). Robotic MIG surfacing represents a significant advancement in the remanufacturing sector, enabling the restoration of worn or damaged components to their original or improved specifications through automated overlay welding.

System Architecture and Configuration

The fully automatic robotic MIG surfacing system integrates several critical subsystems that work in concert to achieve consistent overlay quality across complex component geometries:

Overlay Process Strategy

The robotic MIG surfacing process for remanufacturing follows a systematic multi-layer multi-pass approach that must account for the geometry of the worn component, the required overlay thickness, and the desired metallurgical properties of the final surface:

1. Surface preparation: The worn component is machined to remove damaged material and provide a clean, properly contoured base for overlay deposition. Surface roughness should be controlled to Ra ≤ 6.3 μm for optimal bonding.
2. First layer (bonding layer): A thin layer (typically 1.5 to 3.0 mm) of transition alloy is deposited to ensure metallurgical compatibility between the base material and subsequent overlay layers. This layer is critical for preventing cracking and ensuring adequate bond strength.
3. Intermediate layers: Multiple layers of the target overlay alloy are deposited with appropriate interpass temperatures (typically 150 to 300 °C depending on the alloy system) to manage residual stress and prevent cracking.
4. Final layer (working layer): The topmost layer is deposited with the specified surface finish requirements, often requiring a single-pass wide bead or a precisely controlled multi-pass sequence.
5. Post-weld machining: The overlay surface is machined to final dimensions and surface finish specifications (typically Ra 0.8 to 3.2 μm for bearing surfaces).

Process Quality Control

Quality assurance in robotic MIG surfacing is critical for remanufacturing applications where the overlay layer must withstand severe service conditions. The following quality control measures are essential:

• Weld procedure qualification (WPQ): Each overlay welding procedure must be qualified in accordance with applicable standards such as ASME Section IX, AWS D10.9, or NB/T 47014, with qualification tests including macrograph examination, microstructure analysis, hardness mapping, and mechanical property testing.
• In-process monitoring: Arc voltage and current monitoring provide real-time feedback on arc stability and wire feed consistency. Deviations beyond ±5% of set parameters should trigger automatic process interruption.
• Post-weld inspection: Non-destructive testing (NDT) including magnetic particle testing (MT) for surface cracks, ultrasonic testing (UT) for subsurface defects, and dye penetrant testing (PT) for surface discontinuities should be performed on all production overlays.
• Dilution analysis: Chemical analysis of the overlay layers (typically at depths of 0.5 mm, 1.0 mm, and 1.5 mm from the surface) verifies that the alloy composition meets specification requirements and that dilution from the base material is within acceptable limits.

Engineering Practice Cases

Robotic MIG surfacing has found extensive application in several industrial sectors:

Key Reflections and Technical Challenges

Several technical challenges inherent to robotic MIG surfacing deserve careful attention from practicing engineers:

1. Thermal management: Multi-layer deposition generates significant cumulative heat input, which can lead to excessive grain growth, softening of the base material, and distortion of the component. Interpass temperature control using thermocouples and/or infrared pyrometers is essential.
2. Geometric complexity: Components with complex 3D geometries require sophisticated robot path planning to maintain consistent arc length, wire stick-out, and travel speed. Adaptive control algorithms that adjust robot motion based on real-time sensor feedback are increasingly important.
3. Hydrogen-induced cracking: Low-alloy steel base materials overlaid with high-alloy weld metals are susceptible to hydrogen-induced cracking (HIC). Preheating to 200-400 °C, controlled cooling rates (typically < 150 °C/h for susceptible materials), and post-weld heat treatment are standard mitigation measures.
4. Overlay layer defects: Common defects include lack of fusion at the base/overlay interface, porosity from hydrogen absorption, hot cracking in the overlay layer, and undercut at the bead edges. Each defect type requires specific root cause analysis and corrective action.

Study Conclusions

This research establishes a comprehensive framework for fully automated robotic MIG surfacing that integrates robot control, welding process monitoring, and quality assurance into a unified remanufacturing system. The systematic approach to multi-layer overlay deposition, combined with in-process monitoring and post-weld verification, provides a reliable methodology for restoring worn components to serviceable condition. For engineers involved in cladding and overlay operations, this study underscores the importance of process standardization, qualification, and documentation in achieving consistent, code-compliant overlay welds in production environments.