Engineered Cutting Tools for Precision Bearing Seat Channel Machining

A bearing seat and a squirrel cage are assembled to form a monolithic bearing seat. Given the structural characteristics and the machining challenges, a specialized tool with a ribbed pad was designed. Trial production was conducted using a simulated part to validate the tool design and cutting parameters. This method effectively addressed the machining difficulties associated with the deep and narrow cavities of the monolithic bearing seat, resulting in a qualified part.

 

Introduction 01

In the central transmission unit of an aircraft engine, the bearing seat is a critical load-bearing component that provides rigid support for the safe and stable operation of the engine’s rotor bearings. To reduce vibrations, a squirrel cage with elastic support is often assembled onto the bearing seat. As engine performance continues to improve, lightweight design has become an important area of research. Consequently, one engine model employs a monolithic bearing seat that integrates both the bearing seat and the squirrel cage, as illustrated in Figure 1. While many researchers have conducted extensive studies on the machining of individual bearing seats or squirrel cages, there have been no reports on the machining of monolithic bearing seats that combine both components. In response to this gap, this paper proposes a machining method specifically designed for deep and narrow cavities, which takes into account the unique structural characteristics of monolithic bearing seats.

 

Part Structure Analysis 02

The structural characteristics and machining difficulties of the integral bearing seat are as follows.

- The component is constructed from martensitic stainless steel, which is known for its high hardness, high tensile strength, and low thermal conductivity, making it a challenging material to cut.

- This innovative thin-walled part features a deep, narrow cavity situated between the cage bars and the bearing seat. Eighty cage grooves are evenly distributed around the circumference of the thin wall, and these grooves require a surface roughness of Ra = 0.8 μm.

- The narrow cavity is only 9 mm wide at its narrowest point and extends 82 mm deep. Additionally, the cavity has an undercut structure at its exit, meaning it is smaller at the edges and larger on the inside. This design results in limited tool accessibility, rendering conventional grooving tools ineffective for machining this deep, narrow cavity.

- The cavity includes multiple mating surfaces with tolerance grades of IT6 and IT7, necessitating high dimensional accuracy and imposing stringent requirements on turning stability and measurement.

 

Trial production process plan 03

Due to challenges related to poor tool accessibility and the difficulty of measuring dimensions in the deep and narrow cavity of the integral bearing seat, we propose a process plan. This plan involves designing a special tool and using simulations to verify the tool’s effectiveness and the measurement method.

 

3.1 Design of special tool

When processing deep and narrow cavities—whether during rough turning, semi-finishing, or finishing—addressing the accessibility and rigidity of the turning tool is essential. Thus, the structural design of the turning tool becomes the focal point of research. Key aspects of the tool’s structural design include the overhang length of the tool bar, the type of cross-section, the method of blade attachment, the shape of the front cutting face, geometric angles, the design of the tool tip, and the type of chip breaker groove. This paper presents the design of two specialized tools, considering factors such as tool accessibility, manufacturing cost, cutting performance, rigidity, and tool life.

 

(1) Integral high-speed steel turning tool
The blade and the tool holder are made of the same material as a whole, as shown in Figure 2, with the following characteristics.

1) The tool holder consists of a blade and an overhang. The overhang has a thickness of 8 mm and a length of approximately 85 mm. The cross-sectional dimensions of the blade are 25 mm × 25 mm.

The length of the overhang is about 3.4 times the height of the blade (H), which is 1 to 1.5 times greater than that of standard turning operations. This indicates that the tool holder’s overhang may be excessively long, and its rigidity should be verified or simulated.

The front face of the tool features a flat surface with a chamfered edge. It has a rake angle ranging from 5° to 9° and a back angle between 10° and 15°. Additionally, the chip breaker is designed as a linear arc.

The tool is manufactured from high-speed steel using processes such as wire electrospark cutting and grinding.

(2) Welded carbide turning tool

The carbide blade is brazed onto a tile-type tool holder that features reinforcement ribs, as illustrated in Figure 3. The main features are as follows:

- The tool holder comprises two parts: a blade and a tile section. The tile section has an arc-shaped cross-section, while the blade section has a square cross-section measuring 25 mm by 25 mm.
- The arc radius of the tile section is specifically designed to accommodate the structure of deep and narrow cavities in the workpiece. This design ensures that the arc is unconfined by surrounding space, providing ample arc length to meet the tool’s rigidity requirements.
- Reinforcement ribs are incorporated at the rear end of the tile section to further enhance tool rigidity and effectively reduce tool vibration.
- An arc-shaped chip groove is designed beneath the tile section to aid in chip removal and prevent chip accumulation that could scratch the machined surface of the workpiece.
- A water outlet is integrated into the tool holder to deliver cutting fluid directly to the cutting edge, improving the cooling effect during operation.
- The blade is made of YW-type carbide, with a flat front cutting edge that features chamfered edges. The front angle is designed to be 5° to 9°, while the back angle ranges from 10° to 15°. The chip breaker has a straight arc design.

- The blade is brazed onto the handle, allowing for multiple replacements to accommodate different cutting conditions.

- The handle is constructed from 45 steel and tempered, ensuring good cutting performance at a low cost.

 

3.2 Tool Force Simulation

To reduce the number and costs associated with tool trial production, we simulated the stress and strain conditions experienced by the tools using the 3D numerical simulation software ANSYS. By applying the same cutting force to two different tool designs, we conducted the simulation analysis, as illustrated in Figure 4. The results indicate that the maximum strain experienced by the welded carbide turning tool is approximately 88% lower than that of the conventional tool. This finding demonstrates that the welded carbide turning tool exhibits greater rigidity and stability. The actual tool is displayed in Figure 5.

 

3.3 Simulator Design

To assess the feasibility and effectiveness of a specialized tooling solution and to identify optimal cutting parameters, it is crucial to design and manufacture a simulator for trial production before commencing formal part machining. Given the structural characteristics of the integral bearing seat, the deep, narrow cavity is divided into two components: a cage and a bearing seat. The simulated part is designed as a split structure comprising the cage and the bearing seat. Roughing and semi-finishing operations are performed on each component separately, leaving appropriate machining allowances. Subsequently, these parts are assembled into a combined, integrated structure with the deep, narrow cavity, as illustrated in Figure 6.

The main advantages of this split structure are as follows:

1) Separating the deep, narrow cavity into individual parts significantly reduces 5 axes machining difficulties. Performing roughing and semi-finishing on the separate cage and bearing seat is much less challenging than machining the deep, narrow cavity as a single unit.

2) It effectively validates machining strategies, tool accessibility, and cutting performance. The disassembly of the combined structure allows for the measurement of critical dimensions within the inner cavity, effectively confirming the accuracy of custom-made measuring tools.

3) Compared to trial production with integral forgings, this split simulated part considerably shortens machining cycles and reduces costs.

Machining Example 04

Based on the research conducted, we initially employed a split simulation to assess the feasibility and rationality of the dedicated tooling, while also exploring the optimal cutting parameters. The aluminum machined parts simulation is illustrated in Figure 7. The final machined one-piece bearing seat is displayed in Figure 8. After testing, all surface finishes, dimensions, and geometric tolerances conformed to the drawing specifications.

 

Conclusion 05

1) A rational process plan was developed to address the structural characteristics and machining challenges of the integral bearing seat. This plan successfully tackled the difficulties associated with machining deep and narrow cavities, resulting in the production of qualified finished parts.

2) By using ANSYS simulation software and conducting split-body simulations, we were able to verify and optimize tooling and cutting parameters. This approach minimized the number of tool trials needed, reduced the trial production cycle, and lowered associated costs.

3) The ribbed pad-type welded carbide turning tool is effective for machining deep and narrow cavities, offering a viable process solution for similar structural parts.

 

 

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We specialize in precision custom-made CNC turning and milling machining auto spare parts for the aerospace industry. To expand our international market, Anebon primarily supplies overseas customers with top-quality mechanical parts, milled components, and CNC turning services.