Machining method of titanium alloy pipe fittings
Titanium alloy pipe fittings with their own light weight, compact structure and other advantages in this modern society, especially in the field of aviation now has a deep foothold, and in the future development, it is bound to have its place. However, in terms of the current processing technology and processing methods, because of the low rigidity of pipe fittings, the problem of workpiece deformation in processing engineering still limits the large-scale development of pipe fittings, especially some traditional processing methods, which are now facing elimination, CNC processing is an inevitable development trend of workpiece processing in the future.
Classification and characteristics of Titanium Alloy Pipe fittings
The shape of the common pipe fittings in our life is generally circular, shell and flat. The structural dimensions of these parts are generally far greater than their thickness. When the ratio of their structural dimensions or curvature radius to their own thickness is greater than 20, we call such parts pipe fittings. Pipe fittings can be divided according to the most basic material attributes, generally titanium alloy, plastic and some composite materials. The pipe fittings processed from these different materials have different properties, which can meet the needs of various markets. This paper mainly analyzes the high-precision processing methods of thin-walled titanium alloy parts. Pipe fittings are almost made up of thin plates and stiffeners, which is the reason why the pipe fittings are light in weight. According to the structural use, pipe fittings can be divided into beam type, joint type, wall plate type and rib type. These different types of parts have their own unique shapes and complete their own functions. However, the characteristics of the pipe fittings make the production process more difficult, because The pipe fittings have low stiffness, so in the process of processing, it is easy to have deformation and other situations, resulting in the production of pipe fittings do not meet the standards. Therefore, it can be seen that it is necessary to analyze the processing methods of pipe fittings and optimize their processing technology, which is of great significance to promote the development of pipe fittings processing industry.
Factors affecting the machining accuracy of titanium alloy high-precision pipe fittings
In the actual machining process of pipe fittings, there are countless factors that affect the machining accuracy of titanium alloy high-precision pipe fittings. Generally speaking, the attributes of workpieces, cutting tools, machine tools all affect the machining accuracy of pipe fittings. For example, if the rigidity of the workpiece itself is insufficient, the possible deformation in the process of processing will lead to a large loss of accuracy. Therefore, in the process of processing, reduce or avoid the deformation of the workpiece as much as possible, which is the most effective way to improve the processing accuracy of pipe fittings.
Influence of clamping factors on deformation of parts
Clamping technology is one of the core technologies of the whole pipe fittings processing technology. No matter what processing method is adopted, the quality of clamping technology will directly determine the processing quality of pipe fittings. For the machining of pipe fittings, the quality of the parts to be machined is determined by the clamping scheme, the position of the clamping point and the clamping force. If improper clamping point position or clamping force is adopted, it may lead to different degrees of deformation of parts, and also affect the machining accuracy of parts to a great extent. Especially in the machining of pipe fittings on machine tools, the importance of clamping technology is embodied incisively and vividly. Among them, 30% – 50% of the machining errors are from clamping technology. In addition, in the process of pipe fittings processing, the fluctuation effect between tightening force and cutting force will produce coupling effect, resulting in the redistribution of machining residual stress and initial residual stress inside the parts, which will also affect the machining quality of parts. Therefore, the clamping problem of pipe fittings can not be ignored. It is of great significance to improve the clamping technology of pipe fittings to prevent the deformation of parts in the process of processing.
Effect of cutting force and heat on deformation of parts
The processing parameters of pipe fittings directly reflect the relationship between pipe fittings and processing props. In the process of pipe fittings processing, due to the low elastic modulus of titanium alloy pipe fittings, the machined parts will have a large rebound on the surface, which will directly lead to the increase of the contact area between the machined surface and the back face of the cutter, and the machining quality of pipe fittings The quantity has a great impact on the machining accuracy of the parts, and at the same time, it will reduce the tool durability. On the other hand, if the cutting force is too large and exceeds the elastic limit of the material, it will lead to plastic deformation of the part. Moreover, the existence of cutting heat is also one of the key factors affecting the machining quality of parts. The cutting heat is generated by the friction between chips and the front cutter face, the machined surface and the back cutter face of the workpiece. A large amount of cutting heat will lead to the uneven temperature of various parts of the workpiece, and will also aggravate the deformation of the parts, thus leading to the decline of the machining accuracy of the parts. At the same time, the surface quality of the parts cannot be very good Good guarantee.
Effect of residual stress on deformation
There are two main components of residual stress in pipe fittings. One part is the initial residual stress produced in the initial forming process of pipe fittings. There are many reasons for the generation of this part of residual stress. Among them, for large-area splicing pipe fittings, the influence of residual stress is more obvious in the process of machining. The second part is the residual stress of the machined surface, which is mainly the result of the comprehensive influence of various factors such as the mechanical and thermal effects of the tool on the surface metal of the workpiece and the elastic recovery of the inner metal. In the processing of pipe fittings, it is very likely to break the balance of residual stress in the blank. At this time, the internal stress balance of the parts is broken, resulting in the redistribution of stress, resulting in the deformation of the parts.
Processing technology and optimization of titanium alloy high precision pipe fittings
Considering from the structure of workpiece
When designing the structure of the workpiece, we should not only consider the performance of the workpiece, but also consider the adaptability of this structure to the processing process. Different workpiece structures correspond to different processing methods. In order to ensure the processing accuracy of pipe fittings, the design of the workpiece structure is particularly important. Generally speaking, the application of pipe fittings made of titanium alloy plate has higher precision requirements and use requirements. The deformation of parts will not only cause difficulties in the installation process, but also may not complete the work required by the design of parts. Therefore, in order to avoid the deformation of the workpiece in the process of processing, first, we can consider to design the workpiece as a symmetrical structure, which makes the release of internal force of each part of the workpiece in the process of processing synchronous, to avoid the uneven distribution of internal force. Second, in the design of the thin plate, the thickness of the whole thin plate should be consistent as much as possible, and at some corners of the workpiece, because of the processing or heat treatment, the phenomenon of stress concentration may occur. The transition of the structure of the circular arc of the corner design can be carried out to reduce the deformation of the workpiece.
Consideration from workpiece clamping
The pipe fittings have thin thickness and low rigidity, that is to say, the ability of the workpiece to resist the elastic deformation is weak. Therefore, in the processing of the workpiece, the clamping will also affect the deformation of the workpiece to a large extent. Clamping is mainly used to fix the workpiece. It is used to locate the workpiece and ensure the stability of the workpiece in processing, as shown in Figure 3. Unreasonable clamping position and clamping force will reduce the machining accuracy. Therefore, when selecting the clamping position, try to ensure that each clamping position is symmetrical, and the selection of clamping force can be adjusted according to the rigidity of the workpiece. When the rigidity of the workpiece is high, the larger clamping force can be selected, but pay special attention to that when the rigidity of the workpiece is low, it must be selected Choose appropriate clamping force, otherwise it is easy to cause workpiece deformation in the process of processing.
Consideration from heat treatment
The general heat treatment of workpieces is completed by quenching and artificial aging treatment, and the timing of heat treatment of workpieces is very important to reduce the deformation of workpieces. Because in the process of heat treatment, because of the change of temperature, the temperature stress and phase transformation stress will be produced in the workpiece, which is the main cause of workpiece deformation. At the same time, heat treatment can not destroy the mechanical properties of the workpiece, so it is generally considered to arrange the time of heat treatment before rough processing of the blank. In a word, the time of heat treatment should be rationalized as much as possible, which can not only ensure the mechanical properties of the workpiece, but also reduce the deformation caused by the heat treatment of the workpiece.
Considering the process method and cutting fluid
In the process arrangement of workpiece processing, the first step is to arrange the working procedure according to the different composition and structure of different kinds of workpieces. Among them, it should be paid special attention to analyze the parts easy to deform in the processing of the workpiece, and consider whether the deformation of the workpiece can be reduced through the adjustment of some working procedures. Secondly, in the rough machining of the workpiece, it is necessary to reserve a large cutting allowance at the beginning, and do a good job in the positioning of the reference plane. With the processing of the workpiece, it is necessary to pay attention to the correction of the reference plane at all times, because the reduction of the allowance in the machining process will inevitably lead to the change of the reference plane. The choice of cutting fluid is mainly based on the nature of machining and the selection of machining tools. The reasonable use of cutting fluid is based on different technological arrangements and the use of tools, which is helpful to improve the efficiency of workpiece machining.
Elimination of residual stress of pipe fittings
The initial residual stress of the pipe fittings is generally determined by the heating factors of the blank materials, and the machining residual stress is generally reflected after the machining of the pipe fittings, so the research on the residual stress is worthy of attention, how to predict the influence of the residual stress and how to eliminate the influence of the residual stress on the machining quality of the parts.
Although the source of the residual stress in The pipe fittings has been known, its influence on the deformation of the pipe fittings can not be accurately determined, because the deformation of the pipe fittings caused by the residual stress of the pipe fittings is generally the result of the joint action of the heating factors and the mechanical factors. At present, the control of residual stress is to establish the finite element model of pipe fittings by using the current popular finite element analysis method, and predict the influence of residual stress by using the numerical analysis method. In addition, this method can not only simulate the deformation correction results of pipe fittings, but also predict the springback.
At present, the methods to eliminate the residual stress include pre drawing, vibration aging, aging annealing and cryogenic treatment. Among these methods, cryogenic treatment is the most successful one. Cryogenic treatment can effectively reduce the residual stress in The pipe fittings, at the same time, it can improve the hardness and strength of the parts, improve the wear resistance of the parts, and improve the service life of the parts. In addition, the cryogenic treatment can ensure the dimensional accuracy of the parts and improve the internal stress distribution in the parts. In order to reduce the influence of machining residual stress on the deformation of parts, it is necessary to reduce the cutting heat.
Generally speaking, there are many factors that lead to the deformation of pipe fittings in the processing, and these factors have primary and secondary differences. How to distinguish the key influencing factors and control them effectively, and how to optimize and improve the processing technology of pipe fittings is an effective means to control the processing deformation of pipe fittings. This paper analyzes the causes of pipe fittings machining deformation, and summarizes the current control methods of pipe fittings machining deformation. It can be seen that by changing the traditional processing methods and optimizing the processing technology, the workpiece deformation can be reduced to a certain extent and the stability and usability of the products can be guaranteed. However, the machining quality of pipe fittings can be improved only by considering all the influencing factors, using the finite element method and numerical simulation to further predict and control the deformation of pipe fittings.
Source: China Titanium Pipe Fittings Manufacturer: www.titaniuminfogroup.com