Powder Spreading System for Metal-Powder-Supported Overlay Forming

Literature Overview

This paper, published in Machinery Design and Hydraulics (2017, Vol. 45, No. 13, pp. 15-18) by Jiang Xiangsheng, Xu Yan, Zhou Jianping, and Shan Xuehai from Xinjiang University, presents the design and development of a powder spreading system for GMAW overlay forming based on metal powder support. The authors introduce the spreading principle, system composition, hardware and software architecture, control strategies, layered algorithm for software, and experimental verification of spreading precision.

Core Technical Content

Concept and Significance of Powder-Supported Overlay Forming

The concept of metal powder-supported overlay forming represents a hybrid approach that combines additive manufacturing principles with conventional arc welding. In this method, metal powder is first spread onto the substrate to form a support layer, and then GMAW arc welding is applied to fuse and build up the overlay. This approach offers several advantages over direct welding:

1. Reduced dilution: The pre-deposited powder acts as a controlled alloy reservoir, allowing for more precise control of the final overlay composition.
2. Improved geometry control: The powder layer provides a defined starting geometry, reducing the need for complex torch positioning.
3. Enhanced coating uniformity: The spreading system ensures consistent powder distribution, which translates to more uniform overlay properties.
4. Applicability to complex geometries: The powder can conform to irregular substrate shapes before welding, enabling overlay of complex component geometries.

System Architecture

The system employs a layered algorithm in the software, which is analogous to the layer-by-layer approach in additive manufacturing. Each layer is defined by a set of parameters including powder thickness, welding parameters, and travel path. The software system manages the sequencing of operations: powder spreading, parameter setting, welding execution, and layer verification.

Powder Spreading Principle

The spreading mechanism is designed to deposit metal powder with controlled thickness and uniformity. The powder particles must have appropriate size distribution (typically 45-150 μm for GMAW overlay applications) to ensure good flowability and layer compaction. The spreading head must maintain consistent standoff distance from the substrate to achieve uniform layer thickness. Surface preparation of the substrate (cleaning, degreasing, and possibly roughening) is critical for ensuring powder adhesion before welding.

Control Strategy and Software Architecture

The control system employs a hierarchical approach:

1. Upper level: Process planning and layer definition, where the engineer specifies the desired overlay geometry, powder material, and welding parameters.
2. Middle level: Motion control and process parameter coordination, where the software generates G-code or equivalent motion commands and synchronizes powder feeding with torch movement.
3. Lower level: Real-time parameter monitoring and adjustment, where sensors provide feedback on welding current, voltage, torch height, and powder flow rate.

The layered algorithm is particularly important for multi-layer overlay builds, where each subsequent layer must be deposited on a properly cooled and verified previous layer. Interlayer cooling time, surface temperature monitoring, and layer thickness verification are all managed by this algorithm.

Experimental Verification of Spreading Precision

The authors conducted experiments to verify the spreading precision of the system. Key metrics include:

• Layer thickness uniformity: Deviation from target thickness across the build area
• Powder coverage: Percentage of substrate area covered by powder
• Edge definition: Sharpness of powder layer boundaries
• Repeatability: Consistency of spreading results across multiple trials

While the paper does not provide extensive quantitative data in the abstract, the verification experiments confirm that the system can achieve the required spreading precision for subsequent welding operations.

Engineering Practice Integration

The powder-supported overlay forming approach is particularly relevant for several industrial applications:

1. Repair of worn components: In mining, cement, and power generation industries, components such as mill liners, fan blades, and pump impellers experience severe wear. The powder-supported method allows for precise rebuild of worn surfaces with controlled overlay composition.
2. Surface engineering for corrosion resistance: In chemical processing and offshore environments, corrosion-resistant overlays can be applied to carbon steel substrates using this method, providing a cost-effective alternative to full alloy fabrication.
3. High-temperature component repair: Turbine blades, exhaust components, and heat exchanger tubes can be repaired with the overlay alloy composition tailored to the specific service temperature and environment.

For pipe fitting and piping applications, this technology could be applied to:

• Overlay repair of corroded pipe internals
• Application of high-temperature alloy cladding on carbon steel pipe spools
• Surface hardening of valve seats and gland areas
• Repair of heat-affected zones in thick-walled pipe components

Key Reflections

The development of powder spreading systems for overlay forming represents a significant step toward flexible, on-demand surface engineering. The traditional approach of pre-fabricated overlay plates or cladding strips is limited by geometry and composition flexibility. The powder-supported method allows for virtually any overlay composition to be applied to any accessible surface geometry.

However, several challenges remain for industrial implementation:

1. Powder handling and safety: Metal powder handling requires careful attention to explosion prevention, dust control, and material segregation.
2. Process optimization: The interaction between powder layer properties (thickness, density, composition) and welding parameters requires extensive experimentation for each application.
3. Quality assurance: Non-destructive testing methods for verifying overlay quality (thickness, bonding, composition) must be adapted for this process.
4. Economic evaluation: The productivity advantage of this method must be demonstrated against conventional overlay welding methods for each specific application.

The software architecture described in this paper is particularly noteworthy. The layered algorithm approach provides a systematic framework for process planning that can be extended to include in-situ monitoring and adaptive control. Future developments should focus on integrating real-time process monitoring (such as arc voltage analysis, thermal imaging, and acoustic emission) with the control system to enable closed-loop quality assurance.

Study Insights and Implications

This paper documents an important step in the evolution of overlay welding technology toward more flexible, precise, and automated approaches. The powder-supported method bridges the gap between conventional welding and additive manufacturing, offering a practical pathway for industrial adoption. For engineers working on pipe fitting and piping surface engineering, this technology opens new possibilities for in-situ repair and overlay application that were previously impractical. The key to successful implementation will be the development of validated process windows and quality assurance protocols specific to each application scenario.