How to improve the process quality of CNC machining of thin-wall

Table of Contents

With the development of the modern manufacturing industry, thin-walled parts have been widely used in aviation, automobile, and high-precision equipment due to their lightweight, high strength, and energy saving. However, due to their special structure, there are many technical difficulties in CNC machining, which require scientific and effective strategies to optimize and solve.

Brief Introduction of CNC Machining Technology for Thin-walled Parts

 

Thin-walled parts are widely used in mechanical manufacturing, electronic engineering, and other industrial fields. Their main feature is that the wall thickness of some parts is relatively small compared with other dimensions of the parts. The main purpose of this construction form is to reduce weight, save materials, improve efficiency, or meet specific design requirements.

1. Characteristics analysis

 

Thin-walled parts have unique structural characteristics that present multiple challenges during machining. First, they have low rigidity, and their physical properties make them prone to deformation under any form of external pressure. In addition, friction and heat during machining can also affect the parts, causing thermal deformation. This thermal deformation not only affects the size and shape of the parts but may also affect their physical properties. Finally, due to their weak structure, these parts are prone to unnecessary vibrations during cutting, which can seriously affect the accuracy and effectiveness of machining.

2. Choose the right tool

 

The choice of tool is particularly important for CNC machining of thin-walled parts. Due to the unique structure of such parts, it is necessary to select tools with appropriate tip radius and cutting angle to ensure that the force generated during cutting is evenly distributed and reduces the pressure on the parts. In addition, the use of specially designed tools can effectively reduce the generation of friction and heat, thereby reducing the risk of thermal deformation.

3. Processing strategy

 

For thin-walled parts, it is necessary to process them in stages, such as rough machining to remove most of the excess material, and then semi-finishing and finishing. This step-by-step processing method can effectively reduce the pressure on the parts and ensure their stability during the processing. In addition, it is necessary to carefully select and adjust cutting parameters such as cutting speed, feed rate, and cutting depth to ensure the stability and efficiency of processing.

Process quality issues in CNC machining of thin-walled parts

 

1. Easy to deform during processing

 

The unique structure of thin-walled parts makes them extremely sensitive to external stress, and even small external pressure can cause deformation. During CNC machining, the superposition of cutting force and clamping force makes this deformation more obvious. Thermal expansion caused by heat accumulation and internal stress released after material removal are the main causes of deformation. This deformation can lead to inaccurate dimensions, shape deviations, and even damage to the workpiece.

2. Rough surface easily causes scratches

 

The surface roughness of thin-walled parts directly affects the performance, life, and assembly accuracy of the parts. During the machining process, due to the inherent low rigidity and easy vibration of thin-walled parts, unstable cutting may occur even under the best cutting conditions. This instability leads to high-frequency vibration, which in turn causes periodic rough textures or scratches on the workpiece surface.

3. Easy to be damaged during processing

 

The risk of damage is relatively high during the processing of thin-walled parts. This is closely related to their weak structure. Excessive cutting force or uneven force distribution may cause damage or breakage of parts. In addition, the clamping method also plays a key role. Excessive clamping force or improper clamping method may cause deformation or damage to parts.

4. Size and shape are prone to deviation

 

Machining thin-walled parts face technical challenges in meeting the required accuracy and shape. Machine tools are the core of CNC machining. The imbalance of the spindle, the slight offset of the slide, and the wear of other mechanical parts may cause part size deviations.

During the machining process, the tool is subjected to continuous friction and pressure, which causes tool wear and the cutting effect gradually decreases, which in turn affects the size and shape of the workpiece. Worn tools not only cause dimensional deviations but may also cause the surface quality of the workpiece to deteriorate or cause tool marks.

Improvement strategy for the quality of CNC machining of thin-walled parts

 

To solve the problems of thin-walled parts being easily deformed, scratched, damaged, and having size and shape deviations during CNC machining, improvements can be made by comprehensively adopting simulation technology, optimizing workpiece clamping methods, scientifically setting cutting angles, adopting the best tool path form, and optimizing process flow.

1. Use simulation technology

 

With the rapid development of science and technology, simulation technology is becoming more and more mature and widely used. By using simulation technology to simulate the CNC machining of thin-walled parts, we can effectively predict the cutting force, vibration, and thermal deformation problems that may occur during machining, thereby optimizing cutting parameters, tool selection, and machining paths. This method not only improves machining quality and efficiency but also reduces errors in the actual machining process, saving time and cost.

2. Optimize the workpiece clamping method

 

When machining thin-walled parts, choosing the right clamping method is crucial. This can be achieved by using technologies such as internal positioning fixtures or magnetic chuck adsorption to significantly improve machining quality. In actual operation, we need to design the best support and clamping force according to the special strength of the workpiece.

Due to the low rigidity of thin-walled parts, proper support must be provided when clamping. This support not only enhances the processing strength of the workpiece but also prevents damage to the workpiece due to excessive clamping force. Therefore, when clamping these parts, we should carefully evaluate and adjust the clamping force to ensure that the parts will not deform during processing.

For workpieces with greater rigidity, to achieve a better clamping effect, we need to increase the clamping force accordingly. In addition, when selecting a fixture, the process requirements and material properties of thin-walled parts must be considered to ensure that the selected auxiliary fixture can effectively meet the processing needs.

3. Scientifically set the cutting angle

 

The cutting angle is closely related to the processing quality of thin-walled parts. If the cutting angle is set improperly, the processing quality of thin-walled parts will be reduced, and the accuracy cannot meet the requirements, thus affecting subsequent applications. Therefore, when processing thin-walled parts, it is very important to choose a reasonable cutting angle.

First, if there is a hole in the workpiece, the cutting angle should be set slightly smaller, ensuring that the angle does not exceed 5°. This can effectively prevent the tool from vibrating significantly when it contacts the workpiece, thereby reducing errors during the machining process.

Secondly, when the surface contour of the part needs to be processed, try to use a tangential or arc-shaped feed method. This feed method can reduce various unnecessary textures on the surface of the part, thereby improving the surface quality.

During the cutting process, the best main and secondary rake angles should also be determined. Specifically, the main rake angle should be set between 93° and 97°, while the secondary rake angle should be kept between 8° and 12°. This can effectively reduce tool wear and ensure tool life and cutting effect during processing.

By reasonably setting the cutting angle and feed method, the processing quality and precision of thin-walled parts can be significantly improved, providing a strong guarantee for their stability and reliability in practical applications.

4. Use the best cutting pattern

 

When machining thin-walled parts, turning is the research direction. To ensure the quality and precision of the parts, it is necessary to set the optimal tool path and calculate the optimal cutting amount according to the different materials and product sizes, to provide a basis for the movement of the tool and the feed amount of the material.

After calculating the cutting amount, the reasonable spindle speed, back-cutting amount, and feed amount should be set on this basis. Taking aluminum alloy materials as an example, the specific values can be referred to in Table 1 and Table 2 (the actual cutting parameters need to be selected and adjusted according to the specific aluminum alloy material, processing requirements, tool type, and other factors).

Table 1. External turning back cutting depth selection table (end face cutting depth is halved)

 

Table 2  Aluminum material cutting parameters

 

When designing the cutting pattern, it is necessary to determine the optimal path of the tool. Specifically, there are 3 points to note:

(1) As far as the roughing process is concerned, the traditional tool path should be replaced by a better step roughing method so that the workpiece can move stably in the horizontal and vertical directions, and the excess material can be removed according to the shape and specifications of the part, thereby improving the cutting quality of the part.

(2) In most cases, symmetrical machining has a relatively better effect, as shown in Fig 2. It can effectively prevent deformation during the cutting process and can therefore be used as the preferred tool path.

(3) Different feed types have different effects on surface quality. Therefore, the feed type can be adjusted to remove tool marks and improve the surface quality of parts, as shown in Figures 3 and 4.

 

Fig 2 Symmetrical machining of tool paths

 

 

Fig 3 Effect picture with knife marks

 

Fig 4  Effect without knife marks

 

5. Optimize process flow

 

First, we need to strengthen the structural analysis of parts, accurately grasp the characteristics of parts, find out the possible deformation problems, and then use relevant technologies and theories to design a set of processing technologies suitable for parts. Then use experimental analysis to verify the effect of the process, find out the shortcomings and deficiencies, and then optimize it to obtain a better process.

At the same time, when processing thin-walled parts, special pressure monitoring instruments should be used to monitor the stress conditions of parts and continuously adjust the processing orientation of parts so that the tool can better contact with the parts and avoid violent vibrations during the processing process, to ensure that the quality of the parts can meet the requirements.

6. Introducing adaptive processing technology

 

Adaptive machining technology is an intelligent machining method based on real-time monitoring and feedback. During the machining of thin-walled parts, the forces between the tool and the workpiece will change as the machining progresses. By monitoring the cutting force, temperature, and vibration through sensors and control systems, the system can dynamically adjust cutting parameters such as feed rate and spindle speed.

This real-time adjustment can not only reduce errors in machining but also reduce the possibility of material deformation during machining, ensuring the stability and consistency of machining quality. Especially when machining complex structures and high-precision parts, adaptive technology can significantly improve efficiency and precision.

7. Use vibration-damping devices and smart tool holders

 

Thin-walled parts are susceptible to vibration during machining, which can lead to reduced machining accuracy and poor surface quality. To this end, vibration reduction devices can be used or smart tool holders with active control functions can be used. These tool holders have built-in sensors and control systems that can detect vibrations in real time and suppress them by adjusting the internal damping structure.

In addition, vibration-reducing supports can be used or passive vibration-reducing materials can be installed during machining to further improve machining stability. This can reduce friction and vibration between the tool and the workpiece, ensuring the final machining effect.

8. Apply advanced material coating tools

 

To improve the performance and life of the tool, tools with advanced coatings, such as nanocoatings and diamond coatings, can be used. These coatings can significantly reduce the generation of friction and heat, improve the wear resistance of the tool, and thus improve the quality of the machined surface. When processing high-strength alloys or composite materials, coated tools can not only reduce the impact of cutting heat but also effectively reduce the frequency of tool wear and improve production efficiency. In addition, the use of appropriate tool coatings can also make the processing process smoother and reduce the risk of tool marks on the surface of the part.

9. Environmental control and constant temperature processing

 

When processing thin-walled parts, temperature fluctuations will cause thermal expansion of the workpiece and the machine tool, affecting the processing accuracy. Therefore, to ensure dimensional stability, a constant temperature processing environment control can be used. Introducing a constant temperature system in the processing workshop to keep the temperature around the machine tool and the workpiece stable can reduce the error caused by thermal deformation.

In addition, in temperature-sensitive processing tasks, coolant can be used in combination with a constant temperature process to prevent a sudden temperature rise during the processing process. This strategy not only improves processing accuracy but also reduces scrap rate and improves product quality.

10. Composite processing technology

 

Composite machining is a process that combines multiple machining methods, such as turning and milling, laser-assisted machining, etc. This type of process can complete multiple machining tasks at one time, reduce the number of times parts are transferred between different machine tools, and reduce positioning errors. In the machining of thin-walled parts, laser-assisted machining can reduce the hardness of the material through local heating, and reduce cutting forces and deformation risks. In addition, composite machining can significantly shorten processing time, improve production efficiency, and ensure the overall quality and consistency of parts.

Conclusion

 

The technical challenges in CNC machining of thin-walled parts are the key factors restricting its widespread application. By adopting a series of improvement strategies, including using simulation technology, optimizing workpiece clamping methods, scientifically setting cutting angles, adopting the best tool path form, and optimizing process flow, the technical problems in CNC machining of thin-walled parts can be solved and the quality of CNC machining of thin-walled parts can be efficiently improved.