Process Enhancement：Utilizing Adhesives and Putties to Eliminate Thin-Walled Part Rejection

Are you struggling with deformation and vibration issues when machining thin-walled parts? Don’t worry! Here’s a practical solution: use adhesive instead of traditional clamping, along with rubber putty for additional support. Real-world machining examples show that this combination effectively addresses the long-standing problems of clamping and springback deformation. It also enhances part rigidity and eliminates machining vibration with the rubber putty, ensuring consistently high precision and a superior surface finish.

 

1. Introduction

Thin-walled parts are commonly utilized in the aerospace and marine industries. However, because of their low rigidity and strength, these parts are susceptible to deformation and vibration during machining, making it challenging to ensure machining quality. The clamping method used is a critical factor that affects the quality of machining for thin-walled parts. Traditional radial clamping methods, such as self-centering chucks or single-acting chucks, can lead to clamping deformation. Even when employing axial clamping instead of radial clamping, the part may still spring back after machining due to the clamping force. When combined with cutting forces and the rigidity of the machining system, this results in resonance, which can cause significant vibration marks on the machined surface. As a result, both dimensional accuracy and surface quality cannot be guaranteed.

This article presents a solution to the deformation problem encountered in the machining of high-precision thin-walled parts. By using a specific processing example, it introduces a method that combines adhesive fastening with rubber putty-assisted support to effectively address these challenges.

 

2. Problems in Part Machining

The thin-walled shell component displayed in Figure 1 has an inner hole stop size of φ224.5 mm and a wall thickness of 2.75 mm. The manufacturing process includes the following steps: rough machining, aging treatment, semi-finishing, and finishing.

- Rough Machining: In this initial stage, significant amounts of material are removed, leaving a 2 mm allowance on each surface after machining.

- Aging Treatment: This step is designed to enhance the material’s strength and machinability while vrelieving internal stresses.

- Semi-Finishing: During semi-finishing, parts with less stringent precision requirements are machined to their near-final dimensions, with a remaining allowance of 0.2 mm for the high-precision inner hole stop.

- Finishing: The final stage focuses on achieving the precise dimensions of the inner hole stop.

 

However, while finishing the inner hole stop, problems arise due to the component’s weak rigidity and low strength. These challenges include:

- Springback occurs after machining due to clamping forces, making it difficult to ensure dimensional accuracy.
- Severe vibrations happen during the machining process, compromising surface quality.

 

3. Solutions

The machining of CNC auto parts involves addressing two main issues: clamping force and rigidity.

First, it’s crucial to manage the clamping force. To prevent any shifting of the part during machining, the clamping force should be kept relatively low and positioned far from the machining surface. This allows for free cutting and helps avoid springback deformation both before and after machining.

Second, to improve rigidity, auxiliary supports are necessary. These supports must not only enhance rigidity and eliminate vibrations but also apply force conveniently to the machining area. Since hard contact with metal materials is not acceptable, a specific strategy was developed: the use of adhesive instead of traditional clamping methods. This ensures that the part can cut freely without any displacement. Rubber putty acts as the auxiliary support, meeting the necessary support requirements.

The clamping device consists of several components: a base (see Figure 2), a support ring (see Figure 3), adhesive, rubber putty, shims, pressure plates, screws, threaded rods, and nuts. The base is designed to position the workpiece accurately, with the boss surface, step surface, and bottom surface all perpendicular to each other. The boss surface fits with the inner hole surface of the workpiece, while the step surface contacts the bottom surface of the workpiece for proper positioning. A central through hole connects to the machine tool table via a threaded rod, ensuring the workpiece is correctly positioned.

Adhesive is applied in a ring around the contact area between the bottom surface of the workpiece and the stepped surface of the base, utilizing bonding force instead of traditional clamping force. The support rings and rubber putty are used to support the machined parts of the workpiece. The inner diameter of the support ring is approximately 20 mm larger than the outer diameter of the workpiece, and the outer diameter of the support ring is about 100 mm larger than the inner diameter. The thickness of the support ring is roughly equal to the depth of the machined surface of the workpiece.

During use, rubber putty is filled between the outer diameter of the machined part of the workpiece and the inner diameter of the support ring, providing support and enhancing rigidity. The flexibility of the rubber putty also effectively minimizes vibrations. Additionally, shims, pressure plates, screws, bolts, and nuts facilitate the clamping process. Clamping is illustrated in Figure 4, and the specific implementation process follows.

 

 

- Secure the base to the workbench using screws to ensure it remains stable and does not shift.

- Place two shims symmetrically on either side of the base, ensuring their height is close to the lower edge of the part being machined. Next, position a support ring on top of the shims, making sure it fits over the workpiece with approximately a 10mm gap. Secure the shims and support ring in place with screws and a clamping plate.

- Place the part on the base, ensuring that the inner hole of the part aligns with the boss on the base for proper positioning.

- Apply adhesive around the contact area between the part and the base to secure them together.

- Fill the gap between the support ring and the workpiece with putty.

- Once everything is prepared, begin machining. After machining the first piece, remove the putty and adhesive; the workpiece can then be taken out. Repeat steps 3 to 6 for all subsequent machining processes.

 

4. Processing Results

After using this processing solution, the product dimensions remain stable, the surface roughness is Ra ≤ 0.8μm, and the product qualification rate reaches 100%, ensuring on-time delivery.

 

5. Conclusion

This paper addresses the challenge of deformation during the processing of high-precision thin-walled brass machined parts by introducing a solution that combines adhesive fastening with rubber putty-assisted support. Adhesive fastening replaces traditional mechanical clamping methods, effectively resolving issues related to part clamping and springback deformation. Meanwhile, rubber putty support enhances the rigidity of the part and eliminates cutting vibrations. Verification through actual processing demonstrates that this approach meets the required standards for machining accuracy and surface quality. It offers a novel method for processing similar weakly rigid thin-walled parts and holds significant potential for application and promotion.

 

 

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