Optimization of Impeller Milling Process Based on CNC Technology

Together with the rapid development of high-end manufacturing, impellers, as important components in various fluid machinery, feature complex structures and high precision requirements, posing enormous challenges to machining processes. Traditional processes have been strained to meet impellers’ overall requirements for form and position accuracy, surface quality, and efficiency. CNC-based milling techniques, with high accuracy, high automation, and satisfactory repeatability, have been widely applied in impeller manufacturing.

Introduction

Impellers find a vital application in aerospace, ship propulsion, power generation, petrochemicals, and other fields, carrying out the mission of core energy conversion and fluid control. They are typically equipped with complex features such as free-form surfaces, thin-walled slender structures, and deep cavity flow channels, making them readily prone to issues like tool interference, deformation vibration, and heat concentration during machining. CNC milling technology has been an important approach to solving the above problems. However, only using empirically determined process parameters can no longer meet the comprehensive requirements of high precision, low energy consumption, and green manufacturing.

Meanwhile, the current manufacturing sector is faced with energy efficiency challenges under the “double carbon” goals, and carbon emissions and resource waste during the machining process are increasingly prominent. How to prolong tool life, reduce energy consumption, and lower carbon emissions based on the presupposition of guaranteeing machining efficiency and precision has turned into the eternal pursuit of CNC impeller machining optimization. This paper comprehensively expounds the impact of impeller structures on processes, proposes the parameter optimization approach of green manufacturing, and further enhances the overall performance of CNC technology for machining complex parts.

Influence of Impeller Structural Characteristics on CNC Milling

The typical geometric shape of impellers involves spatial free-form surfaces, blades with varying thickness, and deep flow channels. The structural characteristics directly affect machining stability and path planning methods:

• Complex Surfaces and Small Spacing: The tight space between blades and radical curvature changes impose extremely high requirements on the continuity and accuracy of tool paths.
• Thin-Walled and Long Cantilever Structures: Prone to deformation and chatter in machining, leading to geometric error and surface defects.
• Widespread Use of Difficult-to-Machine Materials:  Titanium alloys, nickel-based superalloys, etc., are widely used in aviation impellers with large cutting force and big heat-affected zones, which further add to tool wear.
• Extremely High Surface Quality Requirements: Some applications require surface roughness Ra < 0.4 μm, demanding precision tools and optimized parameters to be coordinated.

These structure features compel the process system to synchronize optimize in path planning, fixture design, thermal deformation control, tool layout, etc., for the overall machining quality and efficiency assurance.

Optimization Paths for CNC Milling Processes

Although impeller structures are developing in the direction of complicated surfaces, high precision, and light weight, traditional milling processes have not met the different requirements of modern manufacturing for efficiency, product quality, and environmental sustainability. Therefore, process optimization centered on the CNC milling operation, especially tool path planning, cutting parameter control, and intelligent tool system design, has been a critical link to improve the impeller production level.

Tool Path Optimization Strategies

Impeller blades have arbitrary free-form surface geometries, and tool path generation for CNC milling directly affects surface quality, machining efficiency, and machine safety. Today, advanced CAM systems combined with five-axis technology can achieve multi-dimensional path optimization and interference avoidance. Among them, composite path approaches are particularly efficient:

• The contour + equal residual path composite strategy suitable for areas of smooth geometry on the outer boundary of blades, which helps to improve path coverage, reduce repeated cutting and tool idle strokes, and balance surface finish and productivity.
• Spiral interpolation and progressive cutting paths are widely used in deep cavity areas, effectively eliminating tool cutting shock and machining vibration, with special suitability for stable machining of narrow curved surface areas at the impeller root.
• Dynamic five-axis paths can continuously adjust the direction of the tool axis during machining, maximize the avoidance of tool holder interference, balance the tool loads, provide smooth transition between surfaces, and improve overall machining stability.

Besides, through path simulation and dynamic interference check systems, the path feasibility and risk points can be predicted in advance of machining, and high-precision and high-safety intelligent CNC milling can be realized.

Cutting Parameter Regulation and Energy Conservation & Emission Reduction

CNC milling cutting parameters have a great impact on tool life, machining efficiency, and energy consumption levels. For the purpose of fine-grained management, a zoned parameter design approach is generally taken, determining spindle speed, feed rate, and feed per tooth based on the structural characteristics and processing difficulty of various parts. For instance:

Meanwhile, for the needs of green manufacturing energy saving and emission reduction, an energy consumption-carbon emission-tool life model is presented. A predictive relationship between tool wear (with maximum flank wear width VBmax as the life criterion) and machining time is established by neural networks, and a carbon emission equation is built by combining the power-time-carbon emission factor model of machine tool operation:C=P×t×EF

where C is carbon emission, P is cutting power, t is machining time, and EF is the carbon emission factor per unit energy consumption. This model quantifies the environmental impact of different parameter combinations.

Besides, targeting “maximizing tool life and reducing carbon emissions” with the NSGA-II multi-objective optimization algorithm, a Pareto optimal solution set is obtained. Afterward, the TOPSIS decision method is applied to filter the optimum process combination, providing scientific and efficient technical support for green impeller manufacturing.

Tool System and Intelligent Monitoring

Tool system optimization is also necessary for successful machining of complex impeller shapes. In tool selection, coated cemented carbide tools (e.g., TiAlN coating) or PCBN tools are usually used to enhance wear resistance and tool life. For different area characteristics:

• Ball-end end mills are used for finishing free-form surfaces of blades for natural curvature transition and surface finish.
• R-angle tools are typically used in machining impeller roots to reduce stress concentration and improve structural fatigue life.

Besides, the integration of intelligent monitoring systems for achieving real-time tooling status and machining process perception has been one of the important features of smart manufacturing. By integrating vibration sensors, spindle power monitors, and temperature rise sensing modules, online identification of abnormal tool wear and operating condition change can be achieved. Meanwhile, on-machine measurement and automatic tool compensation correction ensure machining accuracy and quality stability.

In collaboration with digital twin models imitating the entire machining process, it achieves tool path verification, parameter setting verification, and equipment response simulation in the virtual environment, pre-judgment, early warning, and optimization adjustment are achieved before actual machining, significantly enhancing the reliability and intelligence level of CNC milling.

Optimization Practice Case

Case Background

The case focuses on a titanium alloy compressor impeller, a key component in aero-engines. It significantly impacts engine performance but poses high machining difficulties.

Situation Before Optimization

Traditionally, this impeller used to be machined on a three-axis machine with basically fixed process parameters. It took 14 hours to machine one impeller, with a surface roughness of 0.8 microns (rough surface). An average tool could machine only 3 impellers, and machining of one impeller generated approximately 8.6 kg of carbon emissions.

Changes After Optimization

Then the group added a sophisticated five-axis machine, applied the NSGA-II intelligent optimization method, and modeled and controlled carbon emissions. The results were remarkable:

• Machining time per impeller was shortened to 8 hours.
• The surface became smoother, with roughness reduced to 0.35 microns.
• Tool life was extended to machine 7 impellers.
• Carbon emissions per impeller were reduced to 5.2 kg.

The key technologies achieving these results included:

• Intelligent optimization of machining paths.
• Predicting tool wear through power changes.
• Real-time judgment of tool status.
• Establishing an energy consumption model during machining.

Conclusion

As the important components of high-performance equipment, the manufacturing level of impeller directly affects the efficiency and lifespan of the entire equipment. The optimization of the CNC-based technology milling process should be systematically considered from multiple perspectives, including structural characteristics, machining paths, tooling performance, and green manufacturing. Through integrating CAM path planning, intelligent parameter optimization, tool wear prediction, and carbon emission modeling, it not only significantly improves machining quality and efficiency but also evidently extends tool life and reduces carbon emissions, providing strong support for intelligent and green manufacturing. In the future, with the deep integration of CNC machining with artificial intelligence and green technologies, impeller machining processes will move further in the direction of intelligence, green, and high precision.