Research on Machining Technology and Method of Thin-Wall Sleeve
Thin-walled sleeves have always been difficult to form in machining. This is mainly because they are prone to deformation during machining, and the size and shape tolerances are difficult to meet the requirements. However, the thin-walled sleeve is a necessary structural part of various machines, which requires the machining technology to overcome the thin-walled sleeve. This article is to solve the problem of thin-walled sleeve machining and analyze its technology and methods.
Factors affecting the quality of thin-walled sleeves
Modern processing technology is constantly advancing, and thin-walled sleeve processing technology has become increasingly mature, and it has now become one of the important symbols of the high-tech industry. Thin-walled sleeve machining technology in the military. It has been applied in many fields such as aerospace. Aerospace urgently needs lightweight parts, and the thin-walled sleeve just meets the requirements of light weight, and can save materials and has a compact structure, but because it is difficult to process, and it is easy to deform the sleeve during processing, so that its processing accuracy It is difficult to be guaranteed, which will directly affect the quality of the pipe sleeve.
For thin-walled sleeves, the accuracy of the machining process is an important problem to be solved in the field of machining, which is one of the important problems faced by precision machining. The thin-walled sleeve has its own advantages, such as its light weight, but its structure is more complex and the strength is not high, which brings difficulties to its processing. Therefore, it is necessary to grasp the factors that affect the quality of thin-walled sleeves and conduct in-depth analysis on them, so as to propose effective process improvement measures.
The main factors affecting the quality of thin-walled sleeves are shown in Figure 1. Physical factors, force effects, thermal deformation of the process system, and process route arrangement will all affect the quality of thin-walled sleeve processing. Among them, the physical factors mainly include errors from machining principles, machine tool accuracy, tool accuracy, fixture accuracy and the internal stress of the sleeve itself; the force acting factors mainly come from clamping force and cutting force; also include machine tool thermal deformation, tool thermal deformation, and The thermal deformation factors of the process system including the thermal deformation of the sleeve; in terms of the process route, whether it is the cutting method, the milling method or the heat treatment arrangement, it will have an important impact on the machining accuracy of the thin-walled sleeve; in addition to the above influencing factors, the tool is broken And machine failure will also affect the quality of thin-walled sleeves. Through analysis, it can be known that by setting the relevant process routes reasonably, and scientifically planning the arrangement of tool parameters, and optimizing the tool path, the processing deformation of the sleeve can be controlled as much as possible.
Fig.1 Factors affecting the quality of thin-walled pipe sleeves
Analysis of processing technology and method of thin-walled pipe sleeve
The clamping of the sleeve will have a significant impact on the processing of the pipe sleeve, which is determined by the strength of the sleeve itself. If a traditional three-jaw chuck, vise or pressure plate is used, it can cause stress concentration, which will cause greater deformation at the three points where the clamping force is located. Considering the pressure formula P=F/S, it is conceivable to increase the area of the contact surface between the thin-walled sleeve and the clamping device, that is, under the same pressure, through the increase of the force area, it is effectively reduced The pressure, at the same time, makes the force more uniform, which improves the deformation caused by clamping to the greatest extent. The specific method is that when machining thin-walled sleeves, the orientation and clamping device of each sleeve should be carefully considered. Most of the clamping devices can be handled with special fixtures, such as auxiliary bearings, expansion sleeves or construction rings. In addition, the thin-walled annular sleeve can also be applied to the axial clamping device, not the radial clamping device, and through this part of the improved optimization method, the deformation problem of the parts can be solved in a targeted manner. If you want to improve the machining accuracy, you also need to consider from the perspective of the sleeve. One of the methods is to increase the hardness of the parts. In this regard, the more common method is to temporarily increase the wall thickness of the sleeve during processing. For this type of operation, some special materials should be used to pour the vacancies of the pre-processed sleeve, such as injecting paraffin or rosin into it. After this process is over, such pour materials should be removed. Among them, the annular thin-walled sleeve can use the jacket and the cushion cover to complete the clamping work, as shown in Figure 2.
Fig.2 Clamping method of annular thin-walled sleeve
When other conditions are fixed, the length of man-hours required for the machining of the sleeve is mainly related to the tool path. How to select the tool path reasonably can greatly improve the processing efficiency. For the cavity parts, the path of the knife is divided into the line cutting method and the ring cutting method. Compared with the two, the ring cutting method makes the cutting force of the sleeve more uniform, and can also release the stress, thereby promoting The machining accuracy of the sleeve. If there is a symmetrical cavity on the sleeve, it is best not to process one cavity and then process another cavity, and to adopt a layered symmetrical ring cutting method, so that the product quality can be controlled. In the process of finishing, usually the inner cavity has been roughed. If you want to process the outer wall at this time, it is a kind of thin and long sleeve. At this time, the single-side down milling method should be used, because the cutting thickness of this method is larger than that of up-cut milling, the cutting is short and thick, and the deformation will be relatively small. At this time, the sleeve is under unilateral force. The texture consistency of the cutting is better, the cutting vibration is relatively small, and the accuracy of the processed sleeve is better than that of the two-way milling line cutting method.
During metal cutting, due to the cutting force, the cut parts are deformed. The cutting amount is closely related to the cutting force. The smaller the cutting amount, the smaller the cutting force and the smaller the deformation, but this will increase the processing time, so The appropriate cutting amount should be selected to ensure the processing accuracy of the thin-walled sleeve under the premise of ensuring the processing time. The principle of metal cutting gives three elements of the cutting amount, which are the amount of back-cutting, the amount of feed and the cutting speed. Because the deformation of the thin-walled sleeve caused by the force in the radial direction is more significant, the back component of cutting is taken as the research object. Through practice and theoretical analysis, it can be known that when the cutting method and conditions are fixed, the cutting force coefficient and correction coefficient will be fixed, and the cutting force will increase with the increase of the amount of back tool and feed. For thin-walled sleeves, the amount of back-grabbing can be reduced by increasing the amount of feed to a certain extent, the machining allowance can be reasonably allocated, and the number of passes and cutting force can be controlled. In the finishing process, the back-cutting amount is usually 0.2~0.5mm. The feed amount will be 0.1~0.2mm/r, or a smaller back-cutting amount to control the cutting force at a time. High-speed cutting can be used to improve the quality of the machined surface during fine turning, but the vibration of the workpiece should be controlled by controlling the angle of the tool, auxiliary support and other factors to improve the machining accuracy of the sleeve.
In the processing of thin-walled sleeves, the geometric angle of the tool has a significant influence on the cutting force. The distribution of the cutting force in the axial and radial directions, as well as the thermal deformation caused by cutting or the roughness of the sleeve are very important. influences. The size of the tool rake angle is a key factor that affects the sharpness of the tool. Generally, the larger the rake angle, the sharper the tool, and it will reduce the cutting force, effectively reducing the friction between the tool and the sleeve and reducing thermal deformation. . However, if the current angle is too large, the wedge angle of the tool will be reduced and its strength will decrease, which will reduce the durability of the tool. For example, when processing 40Cr, if a cemented carbide tool is used, the rake angle is usually 5°~16°. If rough turning is required, the rake angle is 5°~8°, which is effective To improve the durability of the tool, if the precision turning is performed, the rake angle will be 8°~16°, which will increase the sharpness of the tool.
There will be friction between the tool and the workpiece, which mainly depends on the size of the tool clearance angle, which directly affects the degree of friction between the rear surface of the tool and the workpiece. Generally, the larger the clearance angle, the smaller the friction, and the resulting cutting heat will also decrease. However, if the relief angle continues to increase, the strength of the tool will be weakened. In the process of cutting thin-walled sleeves, the relief angle is generally selected according to the characteristics of finishing and rough turning. If it is a finishing turning, the relief angle is selected. For slightly larger tools, if rough turning, choose a tool with a smaller relief angle. For example, when cutting a sleeve made of 40Cr material, a cemented carbide tool is used. In order to effectively ensure the rigidity of the tool during the rough turning process, the clearance angle is selected at 5°~8°. The angle is selected from 8°~12°, which can effectively reduce the friction between the tool and the workpiece, thereby improving the surface quality of the processing plane.
The distribution of cutting force is determined by the entering angle, which is very important for the cutting of thin-walled sleeves. If the entering angle increases, the radial cutting force will decrease, and the axial cutting force will increase. On the contrary, the radial direction cutting force will decrease axially. Therefore, thin-walled sleeves should choose tools with large entering angles. By increasing the entering angle, the cutting force in the radial direction can be effectively controlled. The deflection angle of the tool pair directly affects the surface roughness of the sleeve, and it also has an important impact on the strength of the tool. If the secondary deflection angle is too small, it will increase the friction with the processed surface and cause vibration. Therefore, when cutting thin-walled sleeves, the secondary deflection angle is usually 8°~15°. When rough turning, the secondary deflection angle should be large, and the fine turning can be small. Effectively improve the durability of the tool while ensuring the roughness of the machined surface.
The following takes the processing of a thin-walled sleeve of an annular inner cylinder as an example for analysis, and the sleeve diagram is shown in Figure 3. The sleeve is 391mm long and has a minimum wall thickness of about 2mm, which is a typical thin-walled pipe fitting. Leakage is easy to occur during turning. Reasonably use the above analysis content to formulate the process as shown in Figure 4.
Fig.3 Annular inner cylinder thin-walled sleeve diagram
Fig.4 Process flow chart
In order to reduce the cutting force of the sleeve, it is necessary to ensure the machining allowance. Therefore, in the process 2, the outer skin can be removed by rough turning to make the sleeve round and the frame position is turned out. In process 4, a radial drilling machine is used and an extended drill pipe is used to ensure coaxiality. When performing semi-finishing and finishing turning, two clampings are used, which is equivalent to alternating front and back turning, so that the force is more uniform. When turning the outer circle, use a 90° offset tool for cutting and the feed amount should be as small as possible. The finishing turning feed is less than 0.2mm, which can effectively reduce the internal stress of cutting.
Thin-walled sleeves are difficult to process, but through analysis of the causes of their deformation, combined with processing experience, and theoretical analysis, the quality and accuracy of the pipe sleeve can be guaranteed through the optimization of the process plan. When clamping, the contact area between the sleeve and the clamping device should be increased as much as possible to control the uneven force, and a more reasonable milling method can be selected according to the shape of the workpiece, and a reasonable cutting amount can be selected to control The role of cutting force. The tool angle is also an important factor to be considered in the processing of thin-walled sleeves. The rake angle, back angle, main deflection angle and secondary deflection angle of the tool should be selected according to the different finishing, roughing and processing materials, so as to ensure Increase the service life of the tool under the premise of the requirement of sleeve accuracy.
Source: China Pipe Sleeve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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