Research on Machining Process of Aeroengine Turbine

Liang Songshan, China Southern Aviation Industry Group Co., Ltd.

A specific type of turbine component plays a critical role in the engine's turbine section. The material used is GH2132, and the finished part is ring-shaped with an outer diameter of 674.8 mm, an inner diameter of 605.5 mm, a total length of 221.8 mm, and an average wall thickness of approximately 2.8 mm. Inside the ring, there are three groups of grooves, each containing between 23 to 27 slots. These grooves have a width ranging from 18 to 25 mm and a depth of about 2 to 6 mm. Due to the large size and complex geometry, the machining and inspection processes are quite challenging. More than 30 machining steps are involved, which increases the risk of clamping deformation and machining distortion. Additionally, tool vibration and chipping are common, especially during groove processing. For many years, the grooves have been machined using traditional milling techniques, which are labor-intensive, time-consuming, and prone to errors, leading to out-of-tolerance parts that affect overall quality. As production volumes increase, it becomes essential to enhance processing capacity and streamline operations. Converting the turbine groove machining process to CNC milling is considered the most effective solution to these challenges. This paper explores the CNC milling process for turbine grooves, covering aspects such as process design, feed mode optimization, feed rate adjustment, equipment selection, and improved measurement methods.

1. CNC Milling Process Design

Through a comprehensive analysis of existing product specifications and the capabilities of CNC milling equipment, a new process was developed for machining the turbine grooves, as illustrated in Figure 1.

2. Technical Solution for CNC Milling

(1) Equipment Selection: Several factors impact the production schedule, primarily during the roughing and finishing stages. The capability of the roughing process limits the efficiency of the milling stage. After optimizing the turbine program, the process was shifted directly to the milling stage. However, the three sets of grooves for parts 740, 760, and 780 cannot be processed using standard CNC machines. By analyzing dimensional data and conducting process demonstrations, a specialized five-axis machining center was selected, equipped with a CNC indexing rotary table and an angle head, based on a vertical machining center. (2) Feed Method Improvement: During the 530 milling process, an elliptical shape of approximately 0.15 mm was observed, making it difficult to position the groove accurately. The flatness of the rib ring at the groove location and the spacing between ribs also showed large tolerances, affecting the positioning of G54, G55, and G66. In addition, continuous tool additions were required. Based on this analysis, the 530 process size is 44±0.2 mm, and the fifth-stage groove direction ranges from f558 to f623 mm, which creates a large section causing significant stress accumulation. Stress release during subsequent steps leads to poor flatness on the bearing surface, affecting the accuracy of the groove ribs and the relative plane of the ring. The number of empty cuts in this step is excessive, resulting in wasted resources and increased labor hours. The proposed solution includes replacing the 80° external circular cutter with a straight insertion tool and using a 6 mm wide groove cutter with R0.8 mm instead of an R3 mm round groove cutter (see Figure 2).

Figure 2

(3) Feed Rate Adjustment: It was found that the original feed rate of the machining program was too high, contributing to part deformation. The solution involves reducing the feed rate from 0.2 mm/r to 0.1 mm/r. (4) Tooling Design Improvements: When using the spacer clamping method, several issues were identified. First, eight supporting blocks under the clamps caused vibration during the machining of thin-walled turbine components, especially when processing the S3 group grooves, leading to visible vibration marks. Second, the design flaws made the supporting blocks prone to loosening or sliding during disassembly, reducing operational efficiency. Lastly, the fixture had poor compatibility when machining other parts. An improved tooling design was implemented: special tooling was created, integrating the eight separate blocks into a single annular block. The middle section is made of aluminum alloy, while the contact surfaces are composed of two wear-resistant steel plates connected by screws. Eight screw pressing plates are located on the part’s side, and a thick positioning ring is included in the ring structure. This design effectively reduces vibration and ensures compatibility with other parts.

Figure 4 Turbine Groove Profile

For more detailed information, please download the attachment or refer to *Metal Processing (Cold Processing)*, Issue 15, 2013.

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