Based on the classification of thin-walled parts and their own characteristics, this paper analyzes the reasons why thin-walled parts are widely used and the problem of deformation during processing, and then optimizes their processing methods and process arrangements. Reduce the deformation of the workpiece during processing.
Thin-walled parts rely on their own advantages such as light weight and compact structure in this modern society, especially in the current aviation field, and have a firm foothold, and in the future development, it will certainly have its place. However, in view of the current processing technology and processing method, because of the low rigidity of the thin-walled parts, the problem of deformation of the workpiece in the processing engineering still limits one of the reasons for the large-scale development of thin-walled parts, especially some Traditional machining methods are now being eliminated, and CNC machining is an inevitable development trend for workpiece machining in the future.
1. Classification and characteristics of thin-walled parts
The shapes of thin-walled parts common in life are generally circular, shell and flat. The structural dimensions of these parts are generally much larger than their thickness, and when the ratio of their structural dimensions or radius of curvature to their thickness is greater than 20 At that time, we called such parts thin-walled parts. Thin-walled parts can be divided according to the most basic material properties. Generally, there are titanium alloys, plastics, and some composite materials. The thin-walled parts processed from these different materials have different properties and can meet the needs of various markets. Analysis of high-precision machining methods for thin-walled titanium alloy parts. Thin-walled parts are almost always composed of thin plates and ribs, which is why the thin-walled parts are light in weight. By manufacturing thin-walled parts of different specifications, they can be used for various purposes. According to structural purposes, thin-walled parts can be divided into beams, joints, wall panels and ribs. These different types of parts have their own unique shapes and complete their functions. However, the characteristics of such thin-walled parts make the production process more difficult, because the thin-wall has a lower rigidity, so it is easy to deform during the processing process, resulting in the production of thin-walled parts that do not meet the standards. From this, it can be seen that the analysis of the processing method of thin-walled parts and the optimization of its processing technology are very necessary, which is of great significance for the development of the thin-walled parts processing industry.
2. Factors affecting the machining accuracy of titanium alloy high-precision thin-walled parts
In the actual processing of thin-walled parts, there are countless factors that affect the precision of titanium alloy high-precision thin-walled parts. Among them, the main influencing factors can be seen in Figure 1. In general, the properties of the workpiece, tools, and machine tools Will affect the processing accuracy of thin-walled parts. For example, if the workpiece itself has insufficient rigidity, the deformation that may occur during processing will cause a large loss of accuracy. Therefore, in the processing process, as far as possible to reduce or avoid deformation of the workpiece, this is to improve the thin wall The most efficient method for machining parts.
- Influence of clamping factors on part deformation
Clamping process is one of the core processes of the whole thin-walled parts processing technology. No matter what processing method is adopted, the quality of the clamping process will directly determine the processing quality of the thin-walled parts. For the processing of thin-walled parts, the clamping scheme, clamping point position and clamping force determine the quality of the processed parts. If an inappropriate clamping point position or clamping force is used, the parts may be deformed to varying degrees, and the machining accuracy of the parts will also be affected to a large extent. Especially when processing thin-walled parts on the machine tool, the importance of the clamping process is fully reflected. Among them, 30% to 50% of the processing errors are derived from the clamping process. In addition, during the processing of thin-walled parts, the fluctuation effect of the force between the? A tightening force and the cutting force will produce a coupling effect, resulting in the redistribution of the processing residual stress and the initial residual stress inside the part, which will also affect the processing quality of the part. To influence. Therefore, the clamping problem of thin-walled parts is still not to be ignored. It is of great significance to improve the clamping technology of thin-walled parts to prevent the deformation of parts during processing.
- Influence of cutting force and cutting heat on part deformation
The processing parameters of the thin-walled parts directly reflect the relationship between the thin-walled parts and the processing props. During the processing of the thin-walled parts, due to the low elastic modulus of the titanium alloy thin-walled parts, the surface of the processed parts will be Large springback occurs, which will directly lead to an increase in the contact area between the processed surface and the flank of the tool, which will have a very large impact on the processing quality of thin-walled parts, resulting in a sharp decline in the machining accuracy of the parts. At the same time, It will also reduce tool durability. On the other hand, if the cutting force is too large and exceeds the elastic limit of the material, it will cause plastic deformation of the part. Moreover, the existence of cutting heat is also one of the keys that affects the processing quality of parts. Cutting heat is generated by the friction between the swarf and the rake face, the processed surface of the workpiece and the rake face, and a large amount of cutting heat will cause various parts of the workpiece Uneven temperature will also aggravate the deformation of the parts, resulting in a decrease in the machining accuracy of the parts, and at the same time, the surface quality of the parts cannot be well guaranteed.
- Effect of residual stress on deformation
Residual stress in thin-walled parts has two main components. One part is the initial residual stress generated in the initial forming process of thin-walled parts. This part of the residual stress has various causes. Among them, for large-area splicing and synthesis of thin-walled parts, the residual stress is affected by the processing process. more obvious. The second part is the residual stress of the processed surface. This part of the residual stress is mainly the result of the combined effects of various factors such as the mechanical action, thermal action and elastic recovery of the inner metal of the tool on the surface metal of the workpiece. In the processing of thin-walled parts, it is very likely to break the balance of residual stress in the part blank. At this time, the stress balance inside the part is broken, resulting in stress redistribution, which causes deformation of the part.
3. Processing technology and optimization of titanium alloy high-precision thin-walled parts
- Considering the structure of the workpiece
When designing the structure of the workpiece, not only the performance of the workpiece should be considered, but also the adaptability of this structure to the processing process should be considered. Different workpiece structures correspond to different processing methods. In order to ensure the processing of thin-walled parts The accuracy is particularly important for the design of the workpiece structure. Generally speaking, the application of thin-walled parts processed from titanium alloy plates has high precision requirements and use requirements. The deformation of the parts will not only cause difficulties in installation and other processes, and may not complete the design parts. What needs to be done. Therefore, in order to avoid the deformation of the workpiece during the machining process, first, it may be considered to design the workpiece to be a symmetrical structure. This structure makes the release of the internal force of each part of the workpiece in the machining process synchronous, and avoids the distribution of internal force Unequal situation. Second, in the design of the thin plate, as far as possible to ensure that the thickness of the entire thin plate is consistent, and at some corners of the workpiece, due to processing or heat treatment, stress concentration may occur, and the corner design can be transitioned to a circular arc structure. , Thereby reducing the deformation of the workpiece.
- Considering the clamping of the workpiece
The thin-walled parts themselves are thinner and only have lower stiffness, that is, the workpiece has a weaker ability to resist elastic deformation. Therefore, in the processing of the workpiece, the clamping will also affect the workpiece to a large extent. Deformed. The clamping is mainly used to fix the workpiece. The clamping is used to position the workpiece and ensure the stability of the workpiece during processing, as shown in Figure 3. Unreasonable clamping position and clamping force will reduce the processing accuracy, so when choosing the clamping position, try to ensure that each clamping position is in a symmetrical relationship, and the selection of clamping force can be adjusted according to the rigidity of the workpiece. When the rigidity of the workpiece is high, you can choose a larger clamping force, but pay special attention to it, but when the rigidity of the workpiece is low, you must choose the appropriate clamping force, otherwise it will easily cause the workpiece to deform during the processing. 3.3 From the aspect of heat treatment
The general heat treatment of the workpiece is completed by quenching and artificial aging treatment, and the timing of heat treatment of the workpiece is very important for reducing the deformation of the workpiece. Because when the workpiece is heat-treated, the workpiece will have temperature stress and phase transformation stress inside the workpiece due to its own temperature change, which is the main reason for the deformation of the workpiece. At the same time, heat treatment can not destroy the mechanical properties of the workpiece, so generally, the timing of heat treatment can be considered before rough machining of the blank. In short, as far as possible to rationalize the timing of heat treatment, so as to not only ensure the mechanical properties of the workpiece, but also reduce the deformation caused by the workpiece heat treatment.
- Considered from the process method and cutting fluid
In the process arrangement of workpiece processing, first of all, according to the different composition of different types of workpieces, the process arrangement is arranged. Among them, special attention should be paid to analyze the parts of the workpiece that are easily deformed during processing to consider whether it can Through the adjustment of some processes, the deformation of the workpiece is reduced. Secondly, when roughing the workpiece, it is necessary to reserve a large cutting margin at the beginning and do the work of positioning the reference plane. As the machining of the workpiece progresses, it is necessary to always pay attention to the correction of the reference plane because of the processing The reduction of the margin in the process will inevitably bring about changes in the datum. The choice of cutting fluid is mainly based on the nature of the processing and the processing tool. The reasonable use of cutting fluid according to different process arrangements and tool usage helps to improve the efficiency of workpiece processing.
- Removal of residual stress of thin-walled parts
The initial residual stress of thin-walled parts is generally determined by the heating factor of the blank material, and the processing residual stress is generally reflected after the processing of the thin-walled parts, so the study of residual stress is worth paying attention to, how to predict The influence of residual stress and how to eliminate the influence of residual stress on the processing quality of parts.
Although the source of residual stress in thin-walled parts is known, its influence on the deformation of thin-walled parts cannot be accurately determined, because the residual stress of thin-walled parts causes the deformation of thin-walled parts is generally caused by the combination of heating factors and mechanical forces. The result of action. At present, the control of residual stress is generally to use the currently popular finite element analysis method to establish a finite element model of thin-walled parts, and use numerical analysis to predict the effect of residual stress. In addition, this method can not only simulate the results of deformation correction of thin-walled parts, but also predict springback.
At present, the methods to eliminate the residual stress of the workpiece blank include pre-stretching, vibration aging, aging annealing and cryogenic treatment. Among these methods, cryogenic treatment is the most successful. Cryogenic treatment can effectively reduce the residual stress in thin-walled parts. At the same time, the treatment can also increase the hardness and strength of the parts, improve the wear resistance of the workpiece, and increase the service life of the parts. In addition, the cryogenic treatment can also ensure the dimensional accuracy of the parts and improve the internal stress distribution in the parts. And to reduce the influence of machining residual stress on the machining deformation of parts, it is still necessary to reduce the cutting heat.
In general, there are many factors that cause the deformation of thin-walled parts during processing, and these factors are divided into major and secondary. How to distinguish the key influencing factors and effectively control them, and improve the thin-walled parts through optimization The processing method is an effective means to control the deformation of thin-walled parts. This paper analyzes the reasons for the deformation of thin-walled parts and summarizes the current control methods for the deformation of thin-walled parts. It can be seen that by changing the traditional processing methods and optimizing the processing technology, it can help the processing of the workpiece to a certain extent, which can reduce the deformation of the workpiece to ensure the stability and usability of the produced product. However, only the comprehensive consideration of all influencing factors, through the finite element analysis method, and the use of numerical simulation to further predict and control the deformation of thin-walled parts, can improve the processing quality of thin-walled parts.