Specialized Fixture Solutions for Thin-Walled Component Machining

To address the challenges of deformation, high precision requirements, and the complexity of processing thin-walled parts, we propose a method that focuses on fixture design and processing technology tailored to these parts. By creating a lightweight, high-strength frame-type fixture, and incorporating a spring-adjustable elastic support system along with an axial clamping method, we enhance the rigidity and stability of the components, thereby reducing processing deformation.

 

PART 1 Introduction

In modern manufacturing, thin-walled parts are commonly utilized in aerospace, automobile manufacturing, and precision instruments due to their lightweight and high strength. These parts are typically shell components with complex shapes and precise dimensions. During processing, the low thickness and poor rigidity of thin-walled parts make them susceptible to the effects of cutting forces, clamping forces, and cutting heat. As a result, these parts can experience shape and size distortions, such as becoming elliptical or tapering in the middle while being larger at both ends. These issues significantly hinder improvements in production efficiency and product quality.

Moreover, the processing of thin-walled parts usually involves multiple stages, including roughing, semi-finishing, and finishing. Each of these stages requires strict control over processing parameters and quality to ensure the accuracy and surface finish of the final product. Therefore, researching and developing efficient and precise fixture designs and processing technologies is crucial.

Currently, researchers and companies around the world have conducted extensive studies on the processing of thin-walled parts. Traditional fixtures often utilize rigid connections, which cannot effectively accommodate the deformation characteristics of these parts.

In recent years, advancements in materials science and manufacturing technology have led to the emergence of new types of fixtures, such as elastic and floating fixtures. These fixtures can better accommodate the deformation of parts and reduce stress and distortion during processing by incorporating elastic elements or floating mechanisms. However, the design of the parameters for these fixtures often relies heavily on experience and lacks systematic theoretical guidance and optimization methods. Additionally, the selection and optimization of processing technologies frequently depend on trial and error, which results in low processing efficiency and high costs.

To address these challenges, this study proposes a fixture design and processing technology method tailored to the needs of thin-walled parts. This approach aims to enhance processing accuracy and surface quality while reducing production costs. Among the innovative aspects of this research is the introduction of a lightweight, high-strength frame-type tooling fixture that combines an adjustable spring elastic support system with an axial clamping method. This design effectively improves the rigidity and stability of the parts and minimizes processing deformation. Furthermore, the study emphasizes the use of precise processing techniques and cutting parameters, along with meticulous control of multiple processes, to ensure the dimensional accuracy and surface quality of the components.

 

PART 2 Design of fixtures and processing technology for thin-walled parts

2.1 Processing requirements for thin-walled parts and fixture design

The company has an annual demand of approximately 1,000 thin-walled parts. These parts are tubular structures made from an aviation aluminum alloy, featuring complex shapes and precise size requirements. The initial specifications of each part include an outer diameter of φ190mm, a length of (517±0.1)mm, and a shell wall thickness of about 1mm. Specific locations on the parts undergo grooving and punching treatments, while the inner hole requires multiple machining processes, including rough turning, semi-finishing turning, and finishing.

During manufacturing, it is essential to maintain a roundness error of the outer circle of less than 0.02mm and a coaxiality error of the inner hole of less than 0.02mm. Overall, the design of the thin-walled control chamber part is complex and presents challenges due to its thin profile, susceptibility to deformation, high precision requirements, and stringent standards for processing accuracy and surface quality. As a result, there are several production difficulties to address, as illustrated in Figure 1.

 

One of the main challenges in processing thin-walled parts is their tendency to deform easily. With a wall thickness of only 1 mm and low rigidity, these parts are susceptible to deformation caused by cutting forces, clamping pressures, and temperature fluctuations. This deformation can adversely affect the part’s dimensional accuracy and geometric tolerance. To address this issue, it is essential to design specialized fixtures and tooling that enhance the rigidity and stability of the parts.

Another critical requirement in the processing of thin-walled parts is high precision. Both the outer roundness error and the inner hole coaxiality error must be maintained within 0.02 mm. Achieving this level of accuracy necessitates the use of high-precision machine tools, cutting tools, and measuring instruments, as well as strict control over various parameters and quality throughout the processing process.

Additionally, thin-walled control chamber parts often feature complex shapes and size requirements, which may include grooving and punching at specific locations. These features must be meticulously managed during processing to ensure the parts function correctly and assemble properly.

The demands of mass production further complicate the situation, requiring that the processing be efficient and stable. Appropriate cutting parameters and cutting fluids must be selected to minimize surface roughness and scratches, thereby improving the surface quality and corrosion resistance of the parts. Furthermore, managing tool wear and ensuring timely replacement are crucial factors that influence processing quality and efficiency, necessitating an emphasis on tool management and maintenance.

 

In view of the above difficulties and needs, the following design scheme for the fixture is proposed.

1) The main structure of the fixture features a frame made from lightweight, high-strength aluminum alloy. This design not only minimizes the weight of the fixture but also ensures adequate rigidity and strength while reducing vibration and deformation during CNC processing.

2) A spring-based adjustable elastic support system is integrated into the spherical inner support section of the fixture. This system automatically adjusts the inner support force based on the varying processing states and gaps of the parts, ensuring close contact between the fixture and the parts. This helps prevent processing deformation caused by any hollow gaps.

3) Adjustable bolts are positioned on the top and sides of the fixture, utilizing axial compression to ensure that the parts do not deform due to applied force during processing.

4) Multiple concentric rings are installed on the inner circle of the fixture to provide radial support, enhancing the rigidity of the parts and further reducing deformation.

5) A coolant circulation channel surrounds the fixture and is connected to an external cooling system. During the turning process, a specialized cutting fluid is used to cool the cutting area locally. Additionally, the coolant circulation channel regulates the temperature of the entire processing area, maintaining a constant temperature around the workpiece and effectively reducing deformation due to temperature fluctuations.

6) The designed fixture aligns with the turning tool and the cutting path. The tool, made from carbide material, minimizes cutting force and heat generation. Furthermore, the positioning of the fixture components and the clamping method are optimized to support the turning operation, focusing primarily on axial cutting.

 

2.2 Processing technology design for thin-walled products

(1) Clamping and turning.

To ensure the stability and accuracy of the workpiece during processing, utilize a stable clamping method such as one-support-one-top or two-top clamping. Additionally, employ fixtures like chucks, positioning rings, and nuts to precisely position the workpiece. This will help maintain processing accuracy and coaxiality. Tool positioning and turning are illustrated in Figure 2.

 

In Figure 2, one end of the aluminum alloy tube is supported, while the other end is fixed at the center. The turning process begins with machining the outer diameter to φ182.5mm until the length reaches 300mm. Following this step, a section with a diameter of 179.5mm is turned to a length of 19.8mm, ensuring that both the outer diameter and length meet the design specifications.

Next, we utilize back-tool turning to create a step from φ182.5mm to φ188mm, with a tolerance ranging from -0.1mm to 0mm. The step must be precisely 20.5mm in length. During back-tool turning, the tool’s total length must be maintained at 518mm, using the chuck side as the reference. The tool’s zero point is set at a positive offset of 3mm to ensure accurate processing.

The outer diameter is turned down to φ169mm at the chuck end and φ166mm at the center end. The 300mm-long end is then inserted into the tooling, using the φ188mm positioning hole for alignment, secured by a nut cover. The inner diameters are turned to φ169.5mm and φ166.5mm, ensuring sharp corners at both ends to facilitate later docking or assembly processes. The total length is turned to 518mm, with the other end reduced to 23.5mm.

During the entire turning process, it is crucial to maintain an adequate supply of cutting fluid and to manage chip discharge effectively to prevent overheating of the workpiece and avoid chip blockage.

 

(2) Material preparation and preliminary processing

Based on the company’s requirements for use and the processing performance of thin-walled products, aviation-grade aluminum alloy materials have been selected. Aluminum alloy tubes with specifications of φ190mm × 525mm are prepared. First, a sawing machine is used to accurately cut the aluminum tubes to meet the needs of subsequent processing.

 

(3) Inner hole and fine turning processing

To ensure accurate aluminium CNC machining, a specially designed rough turning inner hole tool is employed. The left end face is connected to the machine tool spindle, with a positioning ring used to establish the processing center. The workpiece is secured using a right-end nut.

On the left side of the tooling, a positioning step is turned, and a groove is cut into the outer circle to accommodate an O-ring. The dimensions of the O-ring are tightly controlled, ranging from φ169.5 to φ169.8 mm to ensure proper sealing and fit. Similarly, a groove is cut on the right side of the tooling for another O-ring measuring φ166.5 to φ166.8 mm. The left end face of the tooling serves as the positioning reference, while the O-rings on both ends are utilized for centering. The end cover on the right end face is secured with a nut to prevent any movement of the workpiece during processing.

The two-top clamping method is implemented along with reverse tool turning technology, which reduces the diameter from φ188 mm to φ183 mm for precise size transition. The left flat end face is turned down by 0.25 mm, and the outer circle is sized to φ182 mm (with a tolerance of -0.1 to 0 mm), ensuring a length of 500 mm. The positive tool flat end face is also reduced by 0.25 mm to achieve a length of 517.5 mm. The outer circle is turned to φ179 mm, while the length is set to 19.8 mm, as illustrated in Figure 3a.

Next, the positioning ring is used again to establish the center, positioning the left end face, and tightening the nut on the right end face. The inner hole is semi-finished to φ171 mm and φ168 mm, maintaining sharp corners to prepare for subsequent finishing. The locating ring is again employed to determine the center, and the lower end face is positioned with the upper end face nut tightened.

Using special tooling, the inner hole is milled to create lightening grooves, reducing the weight of the workpiece and improving material utilization. The right end face is then turned down by 0.25 mm to φ170 mm, while the left end face is turned by 0.25 mm to φ175 mm, ensuring a total length of (517 ± 0.1) mm. The outer circle is semi-finished to φ181 mm (with a tolerance of -0.1 to 0 mm) and φ178 mm (with the same tolerance), as shown in Figure 3b.

Finishing includes a 2 mm × 45° chamfer, an inner hole diameter of φ(172 + 0.1) mm, and a turning diameter of φ(169 ± 0.1) mm with a 1 mm × 45° chamfer, as depicted in Figure 3c. The outer circle is finished to φ(180 ± 0.1) mm with a step down to φ177 mm (tolerance of -0.043 to 0.143 mm), as shown in Figure 3d.

Lastly, a four-axis chuck is used to clamp one end with a top, and the position is accurately aligned through a pin hole to ensure precise workpiece positioning during milling and drilling operations.

 

 

 

PART 3 Testing the application effect of thin-walled parts fixtures

To verify that the fixtures developed during the research can effectively reduce part deformation while enhancing processing efficiency and quality, test cutting was conducted on the actual production line. This process produced five thin-walled parts. The outer radii of these parts were then thoroughly measured using a high-precision three-dimensional coordinate measuring machine. The results are presented in Table 1.

 

As shown in Table 1, the measurements of both the outer diameter and inner diameter for all parts match the nominal values exactly, with no deviations. This indicates that the dimensional accuracy of the parts is well-controlled and that they have not undergone any deformation under the fixture and processing flow designed by the institute. Additionally, all outer and inner diameter measurements fall within the specified tolerances. This accuracy is attributed to the fixture’s ability to minimize part deformation by reducing vibrations during processing and ensuring precise positioning of the parts. Furthermore, the processing time and qualification rate for 1,000 thin-walled parts were evaluated, with the results illustrated in Figure 4.

 

According to Figure 4a, producing 1,000 qualified thin-walled parts using the fixture and process on the original production line takes approximately 1,896 hours. In contrast, after implementing improvements from our research, the same quantity of parts can now be produced in about 1,562 hours. This enhancement not only increases production efficiency but also significantly shortens the production cycle, saving valuable time and resources for the company.

Further analysis of the data in Figure 4 reveals that the original production line had a qualified rate of only 85.3% for producing 1,000 thin-walled CNC lathe parts. However, after the research improvements, the qualified rate rose to an impressive 96.4%. This increase not only lowers the scrap rate and production costs but also boosts the market competitiveness of the products and enhances customer trust in the company. As a result, these changes can lead to greater benefits for the organization.

Additionally, the annual order volume of thin-walled parts for the manufacturer in 2022 and 2023 has been compiled, and the results are presented in Figure 5.

 

As illustrated in Figure 5, the enhancements made to the fixtures and production processes for thin-walled parts in 2023 have led to an increase in monthly orders compared to 2022. The total number of orders for thin-walled parts in 2022 was 661, while in 2023, it rose to 1,037. This growth not only demonstrates the effectiveness of the research and improvements implemented, but also highlights the strong market demand for high-quality thin-walled parts.

Additionally, these process improvements have not only enhanced product quality and increased the competitiveness of the company in the market, but they have also resulted in more orders and revenue. This, in turn, provides significant support for the company’s long-term development and expansion in the market.

 

PART 4 Conclusion

To address the issues of deformation, high precision requirements, and the complexity of processing thin-walled parts, this study presents a fixture design and processing technology tailored to the needs of thin-walled components. The data analysis demonstrates that the improved fixtures and processes have significantly enhanced both production efficiency and quality. Specifically, the time required to produce 1,000 qualified thin-walled parts was reduced from 1,896 hours to 1,562 hours, resulting in a production efficiency increase of approximately 21.4%. Additionally, the qualified rate of parts improved from 85.3% to 96.4%, while the scrap rate decreased significantly, leading to lower production costs and increased market competitiveness for the company.

Furthermore, following the implementation of these improvements, the annual order volume for thin-walled parts rose from 661 in 2022 to 1,037 in 2023, representing a growth of about 56.9%. This confirms the effectiveness of the enhancements and underscores the strong market demand for high-quality thin-walled parts. Although the newly designed fixtures and processing methods effectively reduce vibration during machining, maintain the parts’ positioning accuracy, and minimize deformation, the production process remains relatively complex. Future research will focus on developing more advanced composite processing machine tools to minimize the need for part conversions between machines, streamline the production process, and further reduce costs.

 

 

 

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