Development of Positioner for Overlay Welding Technology in Engineering Machinery Component Repair

Literature Overview

This engineering development work by Zhang Jianxin, Zhang Guosheng, Liu Junying, and Jiang Boping from the Tianjin Engineering Machinery Research Institute, published in Mechanical and Electrical Engineering (2013, Vol. 30, No. 3, pp. 284-287), addresses the design and development of a specialized positioner for overlay welding repair of rotating components in engineering machinery. The project was funded by the National Science and Technology Support Program (Grant No. 2011BAF11B08) as part of the "Key Technologies and Equipment for Remanufacturing of Engineering Machinery Parts" research program. The classification code TG439.2 identifies this as a study on welding equipment and automation.

Core Technical Objectives and Design Requirements

The positioner was developed to address specific challenges in overlay welding repair of rotating engineering machinery components, such as slewing rings, gear rings, and bearing housings. These components typically have complex geometries, large dimensions, and require overlay welding at various spatial orientations. The design requirements are summarized as follows:

Requirement	Specification	Rationale
Workpiece clamping	Flexible, adaptable to various shapes	Accommodate different component geometries
Rotation	360° continuous rotation	Access all circumferential weld positions
Tilting	±90° or greater	Access vertical and overhead weld positions
Speed control	Variable speed (stepless)	Optimize welding parameters for different sections
Control modes	Independent and linked control	Flexibility for different welding configurations
Interlock	Safety interlock between modes	Prevent operator injury and equipment damage

Positioner Structure and Transmission Design

The positioner design incorporates the following structural features:

Main rotating axis: A heavy-duty spindle capable of supporting large workpieces (typical capacity: 500-2000 kg) with high precision and minimal runout.
Tilting mechanism: A robust tilting axis allowing the workpiece to be positioned at various angles, enabling welding in all spatial orientations.
Clamping system: A flexible clamping arrangement that can accommodate cylindrical, ring-shaped, and irregular workpieces without excessive deformation.
Drive system: Variable frequency drive (VFD) motors providing stepless speed control from low speeds (for precise positioning) to higher speeds (for efficient workpiece handling).

The transmission design employs a combination of gear reduction and VFD control to achieve the following:

Stepless speed control: The VFD allows continuous adjustment of spindle speed, enabling optimization of welding travel speed without mechanical gear changes.
Start/stop control: Smooth acceleration and deceleration to prevent workpiece movement during welding.
Forward/reverse control: Bidirectional rotation for access to weld positions in both directions.

Control System Architecture

The electrical control system implements two operational modes with safety interlock:

Control Mode	Description	Application
Independent control	Positioner operates independently from welding equipment	Manual welding, inspection, positioning
Linked control	Positioner speed synchronized with welding travel	Automated or semi-automated overlay welding
Interlock	Modes are mutually exclusive	Prevents simultaneous operation that could cause damage

The VFD-based speed control provides the following advantages:

Energy efficiency: VFDs reduce energy consumption by 20-40% compared to fixed-speed drives.
Precise speed control: Resolution of ±0.1 rpm, enabling consistent welding parameters.
Soft start/stop: Reduces mechanical shock and extends equipment life.
Overload protection: Built-in protection against excessive loading.

Engineering Application and Performance Validation

The positioner was successfully applied in the "Key Technologies and Equipment for Remanufacturing of Engineering Machinery Parts" research project at the Tianjin Engineering Machinery Research Institute. The application context includes:

Slewing ring repair: Overlay welding of worn bearing surfaces on large slewing rings used in excavators and cranes.
Gear ring refurbishment: Restoration of worn gear teeth and bearing surfaces on large gear rings.
Bearing housing repair: Overlay welding of worn journal surfaces and sealing surfaces.

The performance benefits demonstrated include:

Metric	Before Positioner	With Positioner	Improvement
Welding flexibility	Limited to accessible positions	All positions accessible	Significant
Automation level	Manual positioning	Semi-automated	Moderate to high
Welding efficiency	Low (frequent repositioning)	High (continuous operation)	30-50%
Weld quality consistency	Variable	Consistent	Improved
Operator fatigue	High	Reduced	Significant

Quality Control and Welding Process Integration

The positioner enables improved quality control through the following mechanisms:

Consistent welding parameters: Steady rotation speed ensures consistent heat input and travel speed, reducing variability in weld quality.
Reduced operator error: Automated positioning reduces the likelihood of human error in workpiece orientation.
Improved accessibility: All weld positions can be accessed without manual repositioning, ensuring complete coverage.
Non-destructive testing facilitation: The positioner can also be used to rotate components for NDT inspection (MT, PT, UT) after welding.

The welding process parameters for overlay repair on the positioner typically include:

Parameter	Range	Notes
Welding process	SMAW, FCAW, or TIG	Depends on component and overlay type
Current	100-300 A	Depends on process and electrode
Voltage	20-35 V	Depends on process
Travel speed	50-150 mm/min	Depends on overlay thickness
Rotation speed	0.5-5 rpm	Synchronized with travel speed
Preheat	100-300°C	Reduces cracking susceptibility
Interpass temperature	≤300°C	Controls microstructure

Key Questions and Reflections

Several questions arise from this engineering development:

Scalability: The positioner is designed for a specific size range of components. How easily can the design be scaled for larger or smaller components? Modular design principles could address this.
Integration with robotic welding: While the positioner supports linked control, full integration with robotic welding systems would require additional coordination between the positioner and robot controller.
Wear and maintenance: The positioner itself is subject to wear, particularly the clamping mechanisms and drive components. Maintenance intervals and wear monitoring should be established.
Safety considerations: The interlock system is critical for safety, but additional safety features such as emergency stop, overload protection, and anti-collision systems should be considered for industrial deployment.

Study Insights and Implications

This engineering development demonstrates the practical value of purpose-built equipment in improving the efficiency and quality of overlay welding repair operations. The integration of VFD-based speed control and flexible clamping mechanisms addresses specific challenges in rotating component repair that generic positioners cannot adequately handle. For engineers involved in remanufacturing and component repair, this work highlights the importance of matching equipment design to specific application requirements. The successful application in a national research program validates the technology and provides a foundation for further development, including integration with automated welding systems and expansion to other component types. The work also underscores the role of equipment innovation in enabling advanced welding technologies to be deployed in practical industrial settings.