Improvement of single-machine automation of aviation cylinder parts
By analyzing the processing of cylindrical parts during the vertical-horizontal conversion process, we can identify the challenges encountered in production. From this analysis, we will develop an automation improvement plan for individual machines. This plan will also implement relevant controls to ensure process stability based on specific processing requirements, ultimately leading to automated operation of single machines. Furthermore, this improvement plan can be adapted for use with other parts as well.
1. Introduction
Cylinder parts are extensively used in aviation products, primarily in actuation systems such as propulsion systems for various doors and landing gear systems. The strict angular relationships and positional requirements between the inner hole and outer contour, as well as among different hole systems, pose challenges in machining. Our company specializes in machining these cylinder parts.
With the opening of the aviation market, customer orders are increasing, lead times are shrinking, and product prices are becoming more competitive. These trends are putting greater pressure on production and delivery. To reduce manufacturing costs and enhance our competitiveness, we need to optimize our cylinder manufacturing process to improve efficiency.
In line with our long-term goals, we ultimately aim to implement unmanned intelligent manufacturing. Currently, we are focusing on single-machine automation improvements to lay the groundwork for future development.
2. Cylinder Part Process Analysis
We are planning to improve the cylinder part, which is a key component for an international subcontractor and has a relatively high cost. In 2023, our delivery performance was poor, with a contract fulfillment rate of only 78.2%. Despite receiving numerous complaints from customers, the company continues to experience backorders. If we do not address these ongoing backorders, it will adversely affect the company’s reputation with customers.
In 2024, orders for this part have increased by 20% compared to 2023. If we fail to enhance the processing efficiency for this part, it will not only negatively impact our delivery performance but also affect orders for other components, jeopardizing the company’s future development. To meet delivery targets and improve the company’s image, it is crucial to resolve the low processing efficiency and ensure timely delivery of this part.
The part’s appearance is illustrated in Figure 1. The manufacturing process involves the following steps: material preparation, rough turning, rough milling, heat treatment, deep hole machining, fine turning, fine milling, vertical-to-horizontal conversion, honing, and surface treatment. The low yield for this part is primarily due to the lengthy processing time during the vertical-to-horizontal conversion phase, which represents a bottleneck in its production.
This cylindrical component is machined using a vertical-horizontal conversion process. Currently, the processing time for each piece is 50 minutes, which is inefficient and strains production capacity, significantly affecting the output of the vertical-horizontal conversion equipment.
Figure 2 illustrates the processing requirements for this conversion process. It primarily consists of several steps: fixture installation, part installation, part alignment, establishing the machining coordinate system, rough boring, fine boring, hole diameter measurement, rough milling of six small slots, fine milling of six small slots, and part disassembly.
The total processing time required to complete all these steps is outlined in Table 1, which amounts to 50 minutes.
3 Process Analysis
The following four factors contribute to long processing times for parts:
- The fixture does not provide angular control, necessitating individual alignment of each part.
- There is limited clamping of parts, which requires the establishment of a coordinate system for each component.
- The clamping mechanism relies on screw clamps, which is inefficient.
- The keyway milling cutter is excessively long and lacks adequate strength.
Figure 3 illustrates the influencing factors, while Figure 4 shows the slot milling cutter.
The analysis reveals that most of the issues stem from the fixture, along with problems related to improper tool selection. After evaluating these challenges, we implemented targeted improvements, leading to enhancements in both the fixture and tool design. The requirements for manufacturing a specialized fixture include the following:
- The fixture must have pin holes with fixed angular orientation and position to ensure axial positioning of the part without the need for realignment after clamping.
- A double V-shaped positioning system is required to prevent any radial deviation of the part after it is clamped.
- The fixture should incorporate a pneumatic clamp to facilitate rapid part clamping.
- A pressure-retaining structure is needed to ensure stable clamping, even if there is a loss of air pressure during machining.
4. Single-machine Automation Solution Design
To ensure both interchangeability and stability in vertical and horizontal machining processes, we optimized the machining method.
1. We implemented small holes for positioning, which constrains the axial dimensions and angular orientation of the parts. This approach tightens the tolerances for both the hole diameter and positioning dimensions.
2. A double V-shaped positioning system was designed for radial positioning, which reduces the tolerance on the outer diameter of the parts and enhances radial positioning accuracy.
These process controls are essential for maintaining product quality consistency before transitioning the parts from vertical to horizontal machining. They play a crucial role in improving the efficiency of single-machine automation. Achieving stable interchangeability requires keeping the parts within the specified accuracy range. The details of the process optimization are shown in Table 2.
An analysis of the fixture requirements for part clamping informed the specific design of the fixture structure and its functionality. The newly developed automated fixture addressed these challenges and operated automatically. The design of the fixture was tailored to integrate the cylindrical part structure with the processing requirements of the vertical-horizontal conversion process. After several iterations, a design solution was ultimately chosen that effectively balanced automation with multi-station operation. The reasons for selecting the three solutions are as follows.
1) Solution 1: The part is positioned using its end face to restrict axial dimensions and the flat surface of the ear to establish its angular relationship. A double V-shaped fixture was designed to allow for radial positioning of the part, as shown in Solution 1 in Figure 5. However, this solution was not adopted because both the flat surface and the V-shaped fixture could simultaneously restrict the Z-direction dimension of the part, leading to over-positioning.
2) Solution 2: To position the part, a small hole was used to restrict both axial dimensions and angular orientation. A double V-shaped fixture was created for radial positioning of the part, as illustrated in Figure 6. Although a four-station fixture was initially designed, it was ultimately discarded due to its excessive weight of 70 kg.
3) Solution 3: To accurately position the part, we utilize small holes that restrict both the axial dimension and the angular orientation. The double V-shaped fixture is specifically designed to ensure radial positioning of the part. As illustrated in Figure 7, Solution 3 features a dual-station fixture that guarantees both axial and radial positioning. This design reduces repeatable clamping errors and allows for the use of interchangeable parts. Our company also employs this automated fixture design for similar components, specifically cylinders A and B, as depicted in Figures 8 and 9.
The slot milling cutter was optimized, with a diameter of 23 (+0.02, -0.02) mm and a cutting edge length of 2 mm. This enhanced tool rigidity and increased back cutting depth were achieved. The new milling cutter solution is shown in Figure 10.
5. Automated fixture inspection and effect verification
After the fixture is installed, it is necessary to confirm its performance and status, ensuring that it meets the required functions for automated operation. Several factors that need to be inspected include the following.
(1) Please verify the automatic clamping and release functions of the fixture. The new fixture should feature pneumatic clamping and release mechanisms to address the issue of the original fixture taking an excessive amount of time to clamp. The condition of the part after clamping is illustrated in Figure 11, while Figure 12 shows the condition of the part after it has been released.
(2) Ensure to verify the orientation function of the parts after clamping. During the design process, requirements were established for controlling the angles of the parts. After clamping, proper angular positioning can be achieved, which eliminates the necessity of aligning each part during processing. The orientation of the parts after clamping is shown in Figure 13.
(3) After clamping the part, verify the runout of the busbar. The runout must be less than 0.03 mm to meet the positional accuracy requirements for this cylindrical part. Additionally, check the runout of both the top surface and the side surfaces. To comply with process requirements, the runout for these surfaces should be less than 0.015 mm. The verification of the runout of the top surface of the part is shown in Figure 14, and the verification of the runout of the side surface of the part is shown in Figure 15.
(4) To ensure successful single-machine automation, it is crucial to verify the repeatability of the parts after clamping. Consistent repeatability is key to guaranteeing the processing quality of the turning components. During the process adjustment, the size of the positioning holes was compressed to 24.38 ± 0 mm, with a tolerance of 0.04 mm. Upon verification, the repeatability of the parts was controlled within 0.015 mm, achieving stable interchangeability after clamping. The results of the repeatability verification are illustrated in Figure 16.
(5) Verify the safety of the fixture. The fixture protection is illustrated in Figure 17. The fixture switch operates in a rotary manner. General misoperations or collisions will not activate the release switch, thus ensuring the safety of the clamped parts. Additionally, the fixture is powered by compressed air. To prevent the fixture from loosening its grip on the part when the air supply is cut off, a one-way valve is installed at the air inlet of the fixture. This one-way valve maintains the stability of the air source; even in the event of an air cutoff, it ensures that the fixture can continue to clamp the part securely and reliably.
After the implementation, the machining time for the part was reduced to 25 minutes. For detailed statistics on machining time, see Table 3. Additionally, the exceptional interchangeability between the fixture and the part allowed for automated operations, requiring only a single calibration for continuous batches. The design and implementation of the tooling and processes in this project enabled the process personnel to master the core technology of single-machine automation, offering valuable guidance for future improvements on other parts.
6 Conclusion
The successful implementation of single-machine automation for cylindrical parts depends on several key factors:
1) During project planning, a detailed analysis of the CNC machining process for the part uncovered issues with the old fixture. These included its inability to determine angular orientation, lengthy alignment times, the requirement to establish a separate coordinate system, and time-consuming disassembly. This analysis helped identify areas for future improvement.
2) A comprehensive examination of the high stability requirements for automated fixtures allowed us to gain effective control over key positioning dimensions, ensuring stable interchangeability.
3) In the design phase, all relevant factors and their potential impacts were thoroughly assessed, leading to the selection of an appropriate solution.
The successful implementation of this solution for cylindrical parts has established a solid theoretical foundation and provided practical guidance for subsequent improvements in single-machine automation for similar components. Based on this success, our company has gone on to design and manufacture automated fixtures for other parts, resulting in significant efficiency gains.
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