Zhuojin Pipe Fitting Co., LtdApplication of SIEMENS 840D System in NAXOS Reducer Grinding Machine Renovation
Literature Overview
This paper by Liu Changjie and Wang Yang, published in Manufacturing Technology & Machine Tools in 2006, describes the application of the SIEMENS 840D CNC system in the renovation of a NAXOS eccentric reducer grinding machine at Tianrun Crankshaft Co., Ltd. The renovation involves replacing the original control system with a modern CNC system to improve machining accuracy, production efficiency, and product quality. The paper covers the selection of the control system, the design of the servo drive configuration, the integration of PLC control logic, and the practical results of the renovation.
Renovation Objectives and Challenges
The original NAXOS eccentric reducer grinding machine, while capable of producing eccentric reducers for engine crankshafts, suffered from limitations in control precision, program flexibility, and diagnostic capability. The renovation aimed to address these limitations while preserving the mechanical structure and grinding wheel configuration of the original machine.
Renovation Requirements
| Requirement | Original System Limitation | Target Improvement |
|---|---|---|
| Machining accuracy | Limited by analog control precision | Sub-micron positioning accuracy |
| Program flexibility | Limited to fixed cycle programs | Full CNC programming capability |
| Diagnostic capability | Basic fault indication | Comprehensive diagnostic and alarm system |
| Production efficiency | Manual cycle adjustment | Optimized cycle with automatic compensation |
| Operator interface | Basic panel controls | Graphical HMI with program editing |
SIEMENS 840D System Configuration
The SIEMENS 840D system was selected for its robust servo control capabilities, extensive PLC programming environment, and proven track record in machine tool applications. The system configuration includes:
- CNC controller: SIEMENS 840D sl with integrated PLC
- Servo drives: SIEMENS SINAMICS drives for all axes
- Positioning system: High-resolution encoders for closed-loop control
- HMI: SIEMENS OP series operator panel
- Communication: Industrial Ethernet for network connectivity
System Architecture
The control architecture follows a modular design where the CNC controller manages the motion control and PLC functions, while the servo drives handle the power amplification and motor control. The system supports multi-axis simultaneous interpolation, which is essential for the complex grinding paths required for eccentric reducer profiles.
The step drive configuration mentioned in the paper refers to the use of stepper motors or servo motors with precise stepping control for the grinding wheel feed axes. The system supports both continuous and indexed motion modes, allowing for flexible grinding cycle programming.
Process Integration and Programming
The renovation required careful integration of the CNC system with the existing mechanical structure of the grinding machine. Key integration points include:
- Grinding wheel axis control: The form grinding wheel must be precisely controlled to achieve the required eccentric reducer profile. The 840D system supports complex tool path programming with high interpolation accuracy.
- Workpiece rotation control: The eccentric reducer workpiece must rotate synchronously with the grinding wheel to achieve the correct profile. The system supports coupling between axes with high precision.
- Feed rate control: Variable feed rates are required to optimize the grinding process, with higher feed rates for rough grinding and lower feed rates for finish grinding.
- Coolant and chuck control: PLC logic manages the auxiliary functions including coolant pumps, workpiece chucking, and safety interlocks.
Process Cycle Optimization
| Process Step | Original Cycle | Optimized Cycle | Improvement |
|---|---|---|---|
| Workpiece loading | Manual | Semi-automatic | Reduced handling time |
| Rough grinding | Fixed cycle | Adaptive cycle | Material removal optimization |
| Finish grinding | Fixed cycle | Adaptive cycle | Surface finish improvement |
| Workpiece unloading | Manual | Semi-automatic | Reduced handling time |
| Tool compensation | Manual | Automatic | Consistent dimensional accuracy |
| Quality inspection | Offline | In-process | Real-time quality feedback |
Results and Performance Evaluation
The renovation achieved significant improvements in machining performance and product quality. The key results include:
- Dimensional accuracy: Improved from ±0.05 mm to ±0.01 mm for critical dimensions
- Surface finish: Improved from Ra 1.6 μm to Ra 0.4 μm on finished surfaces
- Cycle time: Reduced by approximately 30% through optimized process parameters
- Operator productivity: Increased due to reduced manual intervention and improved HMI
- Maintenance: Reduced unplanned downtime through improved diagnostic capabilities
Transferable Lessons for Pipe Fitting Manufacturing
The principles demonstrated in this renovation are directly applicable to the modernization of pipe fitting manufacturing equipment:
- CNC system upgrade: Replacing legacy control systems with modern CNC systems can dramatically improve machining accuracy and flexibility for pipe fitting production, particularly for operations such as boring, drilling, and threading of flanges and fittings.
- PLC integration: Integrating PLC control for auxiliary functions (coolant, chucking, safety interlocks) can improve process reliability and reduce operator error in fitting manufacturing.
- Process optimization: CNC systems enable data-driven process optimization through cycle analysis, tool wear monitoring, and adaptive control, which can improve both quality and efficiency in fitting production.
- Machine tool renovation: Rather than purchasing new equipment, renovating existing machines with modern control systems can provide significant performance improvements at a fraction of the cost of new equipment, which is particularly relevant for specialized pipe fitting manufacturing equipment.
Study Insights and Implications
This paper demonstrates the value of CNC system renovation as a cost-effective approach to improving manufacturing capability. The systematic approach of identifying performance limitations, selecting an appropriate control system, integrating the new system with the existing machine, and optimizing the process parameters provides a replicable methodology for equipment modernization projects. For engineers involved in pipe fitting and welding manufacturing, the lessons of CNC system selection, integration, and process optimization are essential for maintaining competitive manufacturing capabilities in an increasingly demanding market environment. The paper also highlights the importance of considering the full system architecture, including servo drives, positioning systems, and operator interfaces, when planning equipment modernization projects.