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Thin-walled parts CNC milling machining process investigation

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Thin-walled parts are the current CNC milling process in the heavy difficulties, which has lightweight, thin-walled features, and will increase the instability of basic production.

Suppose the processing process does not take into account the rigidity or strength of the parts, in the high-speed rotation of the cutting process. In that case, it is straightforward to produce deformation problems due to uneven force, resulting in parts in the production and processing of precision errors, resulting in surface unevenness or burr chamfering problems, seriously increasing the gap between the parts design and parts production.

Later processing adjustment process, the need for thin-walled parts of the CNC machining process for gradual adjustment, through technical design and planning, gradually enhancing the production accuracy of thin-walled parts.

Analyzing the causes of problems in the processing of thin-walled parts, taking corresponding targeted measures to reduce the amount of deformation in the processing of thin-walled parts, improve the quality of workpiece processing, and shorten the working time have an important reference role.

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The current situation of thin-walled parts

 

Thin-walled parts are widely used in various fields, but due to the complexity of the internal structure of the parts, a variety of problems are prone to occur in the process of CNC milling. However, the complexity of the internal structure of the parts is prone to various problems during the CNC milling process, which not only hinders the development of the whole thin-walled parts processing industry but also restricts the development of other fields related to the application of thin-walled parts.

For example, in today’s aerospace field, the application of thin-walled parts requires high standards, so attention needs to be paid to the maturity, development and further improvement of CNC milling processing technology to meet the needs of the times. Aluminum alloy integral structure parts have the characteristics of thin-wall, lightweight, high strength, and strong corrosion resistance, and it is because of these advantages that they can meet the higher requirements of the parts under the high-speed and high-performance operation of the aircraft, so thin-walled parts have gradually appeared in the field of aerospace and have been more and more widely used.

At this stage, people generally use CNC milling processing technology for the processing, processing, and production of thin-walled parts. However, due to the complex structure of thin-walled parts, the stiffness is relatively low, resulting in the thin-walled parts in the process of CNC milling machining being easily deformed, and a series of problems such as uneven thickness of the thin wall, inappropriate size, etc., which are greater than or lower than the expected target, so that the overall quality of thin-walled parts decreases, resulting in the overall accuracy does not meet the requirements of the aerospace field.

Nowadays, to ensure the accuracy of the CNC milling process, the general processing plant adopts fine machining in the final processing of thin-walled parts and then performs no-feed light cutting many times, which improves the quality of thin-walled parts but increases the consumption, wastes time, and reduces the productivity.

In addition, it is also easy to make the machined surface of thin-walled parts not smooth due to the residual fine slag in the center of the tool gap. To solve the machining difficulties faced by factories at this stage and the deformation of thin-walled parts during CNC milling, manufacturing high-quality and efficient thin-walled parts has become the main direction of research.

Problems and reasons in the CNC milling machining process of thin-walled parts

1. Problems

 
 

In the CNC milling process of thin-walled parts, fine processing is generally used to obtain high-quality thin-walled parts. Due to the relatively fragile structure of the thin-walled parts themselves, to obtain high-precision, high-quality parts, it is necessary to analyze the internal structure, and set the cutting force or tool selection process, to ensure that the manipulation process will not have any impact on the parts themselves.

This process may cause a relatively high error rate or breakage rate, for example, the cutting force parameter design inaccuracy leads to the actual production and processing of thin-walled parts in the process of the existence of the specified parameters of the difference, so that the cutting rate exceeds the thin-walled parts of the outer surface layer of the load-bearing capacity, leading to deformation of thin-walled parts.

At the same time, the production of milling tools may also be due to long processing overheating problems, thin-walled parts of their outer surface of the thermal load-bearing efficiency is relatively low, the thermal limit value of the stress generated by the effect of higher than the blade or thin-walled parts of the load-bearing limit value, very easy to produce thermal deformation. Later processing and adjustment process should be an in-depth analysis of CNC milling processing problems, combined with the operation process, to improve the thin-walled parts production and processing procedures.

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2. Causes

 

Due to the complexity of the internal structure of thin-walled parts, various problems can easily occur during processing. CNC milling process, thin-walled parts may produce a relatively large number of problems, the main reason is that there are differences between the machining process and the load-bearing properties of the parts themselves, resulting in parts production during the production of broken or micro deformation. From the point of view of the parts production situation, the following problems may arise during the application of technical processes:

(1)Cutting heat

 

High-speed rotary tools or cutting, etc. will produce thermal values and will have an impact on the internal material or structure of thin-walled parts, which in turn produces deformation problems. Thin-walled parts of the material structure and special shape, so that thin-walled parts because of the impact of processing heat corresponding deformation.

(2)Stress Load

 

Wear and tear of the tool over a long period can cause damage to the surface of thin-walled parts. A milling tool is a continuous consumption product, with a long time operation mode, the internal structure may be broken, and once the tool surface gap, the impact on the parts is fatal.

(3)Unstandardized operation

 

Thin-walled parts clamping process and non-standardized operation will lead to deformation of the parts. Thin-walled parts of the internal material are thin, and high vulnerability, if the fixture clamping process does not follow the physical properties of the parts themselves, it will produce deformation problems.

(4)Improper tool lowering method

 

Improper tool setting or parameter setting can lead to deformation of the part. If there is an error in the way of cutting, it will destroy the thin-walled parts. For example, in the production process, if the position of the lower cutter is at the end of the part, it is very easy to produce due to the rotational speed or reverse order of the cutting method of the error between the parts of substandard quality problems.

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Application of machining processes

 

1. mechanical characterization of parts

 

The influencing factors of parts machining include mechanical stiffness coefficient, geometric accuracy coefficient, tool vibration coefficient, tool wear coefficient, and thermal deformation coefficient of the workpiece. When CNC milling for thin-walled parts, the main consideration is the thermal influence that the tool may have on the parts processing.

At the same time, in the cutting process of the tool, the mechanical properties it presents may also cause the part rebound phenomenon, triggering the problem of letting the tool, reducing the accuracy of parts processing. Generally speaking, aviation aluminum alloy material corresponds to the modulus of elasticity of 70 ~ 73 MPa, the value is smaller than the modulus of elasticity of steel material, yield strength is relatively large, it is easy to produce rebound in the machining process, especially large-scale thin-walled parts.

The actual machining process may produce cutting rebound parameters that are relatively large, and should be adjusted for different types of parts of thin-walled parameters, reasonable setting of CNC milling processing parameters, and the basis of the setup process to minimize the processing of deformation problems in production.

At the same time, the machining process should be based on the control of processing deformation, to achieve the adjustment of different cutting force parameters or clamping process, and auxiliary equipment for processing. During the clamping period, the parameters should be defined by the cutting amount, when the cutting amount is large, it is necessary to introduce roughing process ideas, cut the amount of excision level by level to reduce the processing, and reserve the corresponding operating margin for the later finishing process.

After the completion of rough machining, the thin-walled parts need to be heat-treated, fully eliminating the residual stress inside the parts, to provide a basic guarantee for the implementation of the later finishing process.

2. production tooling and machining sequences

 

When CNC cutting thin-walled parts, tool selection, elastic-plastic changes in the tool production process, and part material are all highly relevant. If you want to reduce the cutting tool and the material itself because of the heat generated by friction, according to the processing of different parts of the workpiece or the force situation, analyze the possible thermal deformation of the production process, and then combine with the actual production indicators, as far as possible, the current process of processing the possible existence of the residual stress is controlled within a reasonable range.

For example, when processing aluminum alloy thin-walled parts, generally need to limit the residual stress thickness value within 0.1 mm, if such thickness value exceeds its limit value, its part’s residual stress will not be able to exclude all, it is very easy to produce deformation problems under the action of the later external force. At the same time, for parts processing, according to the requirements of the finishing process, you need to reduce the thickness of parts by level. When the thickness of the parts is reduced by more than 2 mm, the effect of residual stress in the cutting process of parts processing needs to be analyzed.

In addition, CNC milling tools in process of tool walking, the residual stress of the parts themselves may also affect the accuracy of tool walking, or in the cutting process to produce the phenomenon of polythermal, so that the CNC milling process in the implementation of the process of the existing more differences in the problem, and may even reduce the machining accuracy.

In the actual processing process, the differences that may exist in the CNC milling process should be analyzed for different cutting amounts or tools, parts stress state, etc., select the corresponding processing mode, such as small cutting processing mode and hierarchical processing mode, etc., and by the process of tool walking, to ensure the stability of the CNC milling process of stress generation and elimination.

For example, in the processing process of a large area of the belly plate, you can use the process of a circular knife walking on the belly plate level by level of circular processing and then combining with the workpiece in the processing of force changes, analyze whether it is in line with the smoothness and reliability of the processing process, and then enhance the effectiveness of the use of the workpiece.

In this process, the tool should be avoided as much as possible in the process of sharp stops or sharp turns, as far as possible to ensure that the corner area of the arc transition, such as through the control of the feed rate, cut in and cut out of the articulation operation, etc., to enhance the smoothness of the cutting.

When operating by the normative process, it should be combined with the processing of possible deformation problems, to determine whether the quality of the workpiece and its efficiency in the existing CNC milling process, maintenance of the theoretical basis, and gradually through the process to determine the production mechanism, increase the accuracy between the design and the actual production, to avoid the problem of deformation of the parts in the production process.

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3. milling parameters

 

In the process of CNC milling, the cutting parameters of thin-walled parts need to be analyzed, and the cutting parameters will affect the accuracy of thin-walled parts, so in the process of CNC milling, the cutting parameters should be carefully selected.

In the process of CNC milling, the cutting force effect generated by the tool and the cutting heat generated by the tool acting on the surface of the thin-walled parts are relatively high. To further improve the cutting accuracy, it is necessary to adjust the tool processing material, part material, and CNC system, and effectively prevent the processing error problem caused by external constraints.

CNC milling dosage should be set according to the existing processing index, and the relationship between the current processing design and the actual processing effect, be to determine whether it is consistent with the pre-predicted benchmarks, combined with productivity, cost, and other aspects of controllability factors for synchronous drive control.

In the CNC machining process between the programming program and production conditions to find a balance point, further clarification of tool selection, machining path, cutting speed and feed parameters, etc., to improve production efficiency and reduce the wear rate of the tool operation process.

In addition to the selection of cutting parameters, an important influence to be considered is the workpiece clamping program, as it can easily lead to the deformation of thin-walled parts in the machining process.

Tool in the clamping process, the staff should be combined with the production structure of thin-walled parts, analyze the milling tool machining process of the force change points and thermal deformation factors, combined with the weak position of the parts themselves, define the form of positioning of the workpiece and the clamping form, to minimize the deformation of the workpiece production process due to changes in the external stresses, to improve the accuracy of the processing of thin-walled parts.

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Conclusion

 

To summarize, thin-walled parts are more and more widely used and applicable in the aerospace field, and their special working environment requires higher and higher machining accuracy of thin-walled parts. It is of great theoretical significance and practical value to research the subject of cutting process optimization of thin-walled parts.

Based on ensuring the smooth processing of thin-walled parts, the phenomenon of CNC milling deformation is scientifically managed, focusing on adjusting the parts processing route, integrating the knife program, increasing the rigidity of the process operation, scientifically selecting the CNC milling processing parameters, reducing the possibility of CNC milling deformation through effective measures, and more comprehensively improving the specific dimensions of the thin-walled parts and the processing results.

In the subsequent development, the state should increase technology, and policy support, strengthen the basic production and refinement of production adjustment and control, in-depth analysis of China’s technology production and foreign technology production gap, and do a good job of detailed control and adjustment, comprehensively improve the quality of China’s industrial production.

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