Research on CNC milling process of thin-walled parts

Provide CNC Machining service with rich experiecnces.CNC machining technology as an important component of industrial production, along with the industrial market material supply, parts and components production mode of continuous adjustment, in the process of CNC machining, the need to optimize the processing source system, to ensure that the properties of parts and components in line with the actual application of production requirements.

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

If the processing process does not take into account the rigidity or strength of the parts, in the high-speed rotation of the cutting process, it is very easy 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, and gradually enhance the production accuracy of thin-walled parts.

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

The current situation of thin-walled parts

Thin-walled parts have been widely used in various fields of industrial development, but due to the complex internal structure of the parts, it is easy to appear in the process of CNC milling processing of various problems, which not only hinders the development of the entire 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, light weight, 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, handling 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 are easily deformed, and there are a series of problems such as uneven thickness of the thin wall, inappropriate size, etc., which is 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, in order to ensure the accuracy of CNC milling process, the general processing plant adopts fine machining in the final processing of thin-walled parts, and then several times without feed light cutting, although it can improve the quality of thin-walled parts, but the consumption increases, wasting time and reducing 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.

In order to solve the processing difficulties faced by the factory at this stage and the deformation of thin-walled parts during CNC milling, the manufacture of high-quality and high-efficiency thin-walled parts has become the main direction of research.

Thin-walled parts CNC milling machining process problems and causes

1. Thin-walled parts CNC milling processing link problems

In the CNC milling process of thin-walled parts, fine processing is generally used in order to obtain high-quality thin-walled parts.

Due to the relatively fragile structure of the thin-walled parts themselves, in order to obtain high-precision, high-quality parts, it is necessary to analyze the internal structure, 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 point of difference, so that the cutting rate exceeds the thin-walled parts of the outer surface layer of the load-bearing capacity, resulting in deformation of thin-walled parts.

At the same time, the production of milling tools may also be due to a long time of processing overheating problems, thin-walled parts of their own external surface of the thermal load-bearing efficiency is relatively low, the thermal limit value of the stress effect is higher than the blade or thin-walled parts of the load-bearing limit value, it is very easy to produce thermal deformation.

Later processing and adjustment process, should be in-depth analysis of CNC milling processing problems, combined with the operation process, improve the thin-walled parts production and processing procedures.

2. Reasons for problems arising from CNC milling of thin-walled parts

Due to the complexity of the internal structure of thin-walled parts, it is easy to have various problems when 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 bearing performance of the parts themselves, resulting in parts production during the production of broken or microdeformation.

From the point of view of the parts production situation, the following problems may arise during the application of technical processes:

(1) cutting heat problems. High-speed rotary tools or cutting, etc. will produce thermal values, 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 problem. Wear and tear of the tool over a long period of time can cause damage to the surface of thin-walled parts. Milling tool is a continuous consumption product, long time running mode, the internal structure may be broken, once the tool surface gap, the impact on the parts is fatal.

(3) Operational problems. Thin-walled parts clamping process, non-standardized operation will lead to deformation of the parts. Thin-walled parts with thin internal materials and high fragility, if the fixture clamping process does not follow the physical properties of the parts themselves, the deformation problem will arise.

(4) Improper tool lowering method problem. Improper tool lowering method or parameter setting will lead to deformation of the parts. If there is an error in the way of lowering the tool, it will destroy the thin-walled parts.

For example, in the production process, if the position of the lower cutter at the end of the parts, it is very easy to produce due to the speed or reverse order of the cutting method between the existence of errors in the quality of parts unqualified.

Application of CNC milling machining process for thin-walled parts

1. Process based on mechanical characteristics of parts

The influencing factors of parts processing include mechanical stiffness coefficient, geometric accuracy coefficient, tool vibration coefficient, tool wear coefficient, workpiece thermal deformation coefficient and so on.

When carrying out CNC milling processing for thin-walled parts, the main consideration is the thermal influence that the tool may cause 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, aerospace aluminum alloy material corresponding to the modulus of elasticity of 70 to 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 processing, especially large-scale thin-walled parts.

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

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, auxiliary equipment for processing. During the clamping period, the parameters should be defined in accordance with 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 process, fully exclude the residual stress inside the parts, for the implementation of the later finishing process to provide basic protection.

2. Process flow based on production tooling and machining sequence

When CNC cutting of thin-walled parts, tool selection, elasticity and plasticity changes in the tool production process, and part materials are highly correlated.

If you want to reduce the heat generated by the friction between the cutting tool and the material itself, you need to analyze the thermal deformation problems that may exist in the production process according to the machining of different parts of the workpiece or the force situation, and then combined with the actual production indicators, as far as possible, to control the residual stress that may exist in the current process 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 parts 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, 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, the CNC milling tool in the 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 existence of more differences between the problem, and may even make the processing accuracy is reduced.

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

For example, in the processing process of a large area of the belly plate, you can use the process of circular knife walking on the belly plate level by level of circular processing, and then combined with the workpiece in the processing process 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 in accordance with 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 can be under the established CNC milling machining process, on top of the theoretical basis of the maintenance, 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 in the production of parts and components.

3. Process flow based on 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 produced 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, 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 index, and analyze the relationship between the current processing design and the actual processing results, to determine whether it is consistent with the pre-predicted benchmarks, combined with productivity, cost and other controllability factors for synchronous drive control, in the CNC machining process of the programming program and production conditions to find a balance between the further clarification of the tool selection, machining path, cutting speed and Feed parameters, etc., to improve production efficiency and reduce the wear rate of tool operation.

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 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, defining the workpiece positioning form and clamping form, to minimize the workpiece production process due to changes in the external stresses and deformation, thereby improving the machining accuracy of thin-walled parts.

Conclusion

In summary, thin-walled parts in the aerospace field is more and more widely used, more and more strong applicability, its special working environment for thin-walled parts machining accuracy requirements are also more and more high. Carrying out research on thin-walled parts cutting process optimization has important theoretical significance and practical value.

On the basis of ensuring the smooth processing of thin-walled parts, the deformation phenomenon of CNC milling is scientifically managed, focusing on the adjustment of parts