Research on Five-axis Machining and UG Programming Application of Titanium Alloy Impellers

Titanium alloy impellers are widely used in high-tech fields such as aerospace, ship propulsion, and chemical turbines due to their superior mechanical properties of high strength, low density, and corrosion resistance. However, titanium alloy materials are difficult to machine, especially in the manufacturing of impellers with complex structures. Traditional three-axis machining methods can no longer meet the requirements of precision and efficiency. Five-axis simultaneous machining technology as a high-level processing method has the capacity to machine titanium alloy impellers efficiently and accurately.

Technical Challenges in Machining Titanium Alloy Impellers

Titanium alloy impellers have important application values in high-end fields such as aerospace, energy power, and advanced manufacturing. Particularly, α+β titanium alloys like Ti-6Al-4V have been the preferred materials for producing impellers due to their high specific strength, corrosion resistance, and fatigue strength. However, due to their special physical and mechanical properties combined with complex geometric shapes and high precision requirements, CNC machining of titanium alloy impellers is troubled with technical challenges. Its essential difficulties are discussed systematically from the points of material properties, structure characteristics, precision demand, and trajectory planning as follows.

Special Material Properties Lead to Intensified Heat Concentration and Tool Wear

Titanium alloys themselves have the characteristics of low thermal conductivity, high strength, and strong chemical activity. In machining, a lot of cutting heat is accumulated in the tool-workpiece contact area, and it is not easy to be removed or diffused by the workpiece, which readily forms a “heat accumulation” effect, causing the tool rake face temperature to increase dramatically, thereby accelerating wear and oxidation or even edge chipping. At the same time, titanium alloys also have strong “affinity to tools”, and chips are easily adhered to the tool surface to form built-up edges, damaging the cutting edge form and causing cutting vibration and surface roughness instability. All these material characteristics significantly limit tool life and continuous and stable high-efficiency machining. For this reason, machining methods such as low feed, low cutting depth, and high cutting speed are typically applied in machining, and they are (combined) with efficient cooling systems such as high-pressure cooling or minimum quantity lubrication in order to weaken the phenomenon of heat concentration.

Complex Geometric Structures Increase the Difficulty of Path Planning and Interference Avoidance

Titanium alloy impellers are typically machined in an integral manner, with multiple thin-walled, high-curvature, and large-torsion spatial free-form surface blades, with close proximity to each other and small machining areas. There are two primary challenges of this setup: one is that spatial interference between the tool and workpiece or fixture is readily induced in machining, which requires the tool path planning to consider fully the change of the five-axis attitude and the clamping boundary; the other is that due to the thin and long blades, the stiffness is low, and vibration, deformation, or even chatter are prone to occur in the cutting process, not only affecting the dimension accuracy but also degrading the surface integrity. Therefore, it is necessary to rely on a five-axis simultaneous high-dynamic machining platform and high-precision CAM programming system for precision control of the machining path, tool attitude, and feed strategy in order to implement compliant contour machining. 

Strict Machining Precision and Surface Quality Control Requirements

In high-reliability applications such as aero-engines, titanium alloy impellers need to meet very strict manufacturing tolerances and surface quality requirements. The overall requirements are that the contour size tolerance is not greater than ±0.01 mm, the surface roughness Ra of the key blade area should be controlled below 0.4 μm, and even some functional surfaces need to reach Ra ≤ 0.2 μm. Due to the fact that titanium alloys possess simple deformation and a large elastic recovery coefficient, it tends to springback after machining, and it is difficult to control the forming precision; at the same time, traditional machining techniques (difficult to) balance precision and efficiency, trimming allowance is minimal, and it requires very high tool accuracy and equipment movement accuracy. Therefore, there is a necessity to use composite technologies such as five-axis simultaneous machining, precision grinding, plasma finishing, or laser-assisted machining integrally in order to achieve formulating with high quality without loss of machining efficiency.

Tool Path Design and Tool Change Strategies Highly Depend on System Integration

Facing the complexity of the blade structure of titanium alloy impellers, it is generally impossible to prevent interference and the tool change is frequent by relying solely on conventional three-axis path design, which results in machining interruption, position error accumulation, and low efficiency. Therefore, the application of a five-axis CAM system with interference check functions has become an unstoppable trend. This system not only needs to fit the path to 3D surface information of impeller blades but also to optimize the tool axis direction and feed rhythm dynamically to ensure balanced cutting force, rational machining attitude, and smooth path. In addition, to improve efficiency, the types of tools should be minimized and tool life schedule logic be optimized, and the path-tool-cooling systemic connection should be realized by the automatic tool changer system (ATC) integration, so that the stability of the entire process and continuity of machining rhythm can be ensured.

Application Advantages of Five-axis Simultaneous Technology in Machining Titanium Alloy Impellers

In the production of titanium alloy impellers, faced with complex 3D free-form surfaces, multi-angle structures, and high-precision requirements, the traditional three-axis machining methods have been difficult to (compete). Five-axis simultaneous machining technology, with its breakthrough in the spatial motion degrees of freedom, has been the key to complete the machining of titanium alloy impellers with precision and efficiency. It not only is able to optimize tool attitude and improve cutting efficiency but significantly improve surface quality and overall machining reliability. The following article interprets its main advantages from several aspects.

Completing Complex Contour Machining in One-time Clamping, Significantly Improving Positioning Accuracy

The structure of the titanium alloy impeller usually has complex spatial shapes such as multi-blades, hollow, and inclination. When using traditional three-axis machining, a number of segmented clampings are generally required to encompass all machining surfaces, which not only wastes time but also leads to accumulative error due to repositioning. Five-axis simultaneous machining can realize the free motion of the tool in different directions so that the entire impeller from the base, hub to each blade can be continuously machined in single clamping. This “single setting, worldwide machining” function greatly improves the clamping precision and process stability, avoids dimensional deviation and positioning error caused by multiple clamping, and provides a basic assurance for the consistency and reproducibility of aviation-level titanium alloy impellers.

Dynamically Adjusting Tool Attitude to Improve Blade Surface Quality

Impeller blades normally possess a thin-walled, high-curvature shape, and deformation, vibration modes, or surface defects will occur unless care is taken in the machining process. The five-axis simultaneous machine possesses the ability to vary the tool attitude dynamically with respect to the changing normals of the various areas of the blade in such a way that the tool is continuously in cutting engagement with the workpiece surface at the optimum angle. This not only reduces the lateral pushing of the cutting force on the blade but also reduces cutting vibration and thermal impact, thereby effectively suppressing surface defects such as micro-cracks, scratches, and abrasions, and maintaining the surface roughness stably below Ra 0.4 μm, and even within Ra 0.2 μm. This advantage is highly suited to aviation, energy, and other applications that subject the impeller surface to extreme demands.

Improving Machining Efficiency and Shortening the Overall Manufacturing Cycle

In terms of machining efficiency, five-axis simultaneous machining realizes continuous and high-speed machining of complex surfaces by optimizing feed path and tool attitude, significantly reducing the empty travel time and tool changing quantity. Compared with the redundant movements such as tool retreat, rotation, and re-machining frequent in three-axis machining, five-axis can achieve interference-free continuous machining through reasonable path design, thereby improving the machine tool output per unit time. Additionally, five-axis machining can also improve the cutting speed and feeding amount without affecting the machining quality, thereby reducing the entire machining cycle. Especially in mass production of titanium alloy impellers, this efficiency advantage is translated into significant (production capacity improvement) and cost saving.

Expanding the Machining Space and Solving the Dilemma of Interference in Extreme Areas

Titanium alloy’s impeller blade gaps are narrow and the curvature change is large, and there are numerous areas where it is difficult to achieve effective cutting on the three-axis platform, which is often limited by the tool shank or machine tool structure interference. The five-axis simultaneous is not troubled to avoid obstacles by tilting and rotating the worktable or the tool spindle, realizing free cutting and feeding in any direction, and is especially able to handle extreme curvature surfaces, root transition areas, and closed areas close to the hub. This kind of multi-axis coordinated machining capability enables all structural parts of the impeller to realize high-quality formation under safe conditions, effectively avoiding machining blind spots and interference dead angles, and improving the yield and integrity of the overall product.

Application Process of UG Programming in Five-axis Machining of Titanium Alloy Impellers

As a typical difficult-to-machine part with complex structure and high surface freedom, the titanium alloy impeller has very high requirements for the accuracy, reasonability, and reliability of the simulation of the five-axis simultaneous machining path. UG (Siemens NX), a comprehensive CAD/CAM/CAE system, its mature five-axis machining module and powerful geometric modeling capabilities provide a complete solution for efficient programming of titanium alloy impellers. The following is its typical application process in detail:

3D Modeling and Workpiece Preparation: Constructing an Accurate Geometric Foundation

The foundation of five-axis machining path planning is complete and precise geometric modeling. In actual engineering applications, the impeller design model is first imported into UG, or the solid model is created according to the impeller parameters through the NX modeling module. On the basis of this, the blank geometry required for machining is ascertained, and the clamping reference, part coordinate system (WCS), machining coordinate system (MCS), and other data are established accurately to ensure the continuity between programming accuracy and machine tool positioning. In the meantime, with the assistance of UG’s feature recognition function, the impeller is divided into characteristic zones such as the hub, blades, blade tip edges, and flow passages, providing ordered support for subsequent strategy decision and area path planning. Accurate geometric preparation is the basic guarantee to ensure path calculation efficiency and avoid interference risk.

Machining Strategy Selection and Tool Path Planning: Targeted Strategy Matching Surface Structure

Impeller machining has many complex surfaces and transition areas, and it requires the selection of reasonable five-axis strategies according to the region characteristics. In UG five-axis module, Normal Projection Milling is generally used for the blade surface, which can make the tool attitude close to the surface normal, improving the machining surface consistency and smoothness. For the transitional flow channel from the blade root to the hub, Streamline or Helical Multi-Axis Milling can be used, which can optimize the path density distribution, improve the machining evenness, and suppress the local heat concentration. In the hub area, the use of Z-Level Profile 5X is more beneficial to control the height progression and machining allowance. In programming, the tool attitude control parameters’ lead angles and tilt angles must also be properly set to prevent the tool from interfering in the small clearance area or the root cutting angle from failing. In the meantime, the tool entry and exit strategy is well planned, e.g., ramp in or helical tool entry, which can effectively reduce the tool entry shock and extend the tool life.

Tool Path Simulation and G-code Output: Ensuring Path Safety and Code Adaptation

After the multi-axis path generation, dynamic visual analysis of tool behavior and machine tool movement status can be performed by the Machine Simulation module in UG, analyzing problems such as the interference of tool shanks, collision of rapid movement route, and range of motion exceeding the limit. By integrating the machine tool model and the controller model, the motion logic of the physical device can be simulated in a way that the path planning can be ensured to be executable on the physical device. After the simulation is confirmed to be correct, combined with the post-processor template of the destination machine tool control system (e.g., FANUC, Siemens, Heidenhain, etc.), the related NC code (G code) is generated in Post Builder. In order to ensure the consistency of post-processing accuracy and tool path generation, it is recommended to use low-speed cutting in path verification of the first piece trial cutting, and combine coordinate measuring equipment (CMM) or profiler for dimension feedback correction to enhance the reliability and stability of five-axis machining even more.

Key Process Parameters and Optimization Strategies

In order to improve the machining efficiency and tool life of titanium alloy impellers, reasonable process parameters are necessary. The recommended process parameters for turning Ti-6Al-4V titanium alloy impellers are as follows:

Additionally, adopting a multi-stage rough machining and finish machining layered control strategy decreases the tool load and improves the machining stability.

Conclusion

Five-axis machining and UG programming of titanium alloy impellers have greatly improved the efficiency and quality of titanium alloy impeller manufacturing. Five-axis machining technology can properly solve the machining problems of multi-angle and curvature, and UG, as a powerful programming platform, provides flexible path planning, path optimization, and machining simulation functions. In the future, through the development of new technologies such as intelligent CAM, digital twin simulation, and AI path optimization, titanium alloy impeller machining will be guided towards an intelligent and efficient direction.