Research on improving the processing precision of thin-walled parts（2）
Third, measures to improve the processing accuracy of thin-walled parts
1. Using special fixtures
For thin-walled parts, the appropriate special fixtures can be used in the process to replace the traditional universal fixtures, which can change the force characteristics of the parts, including the force application point, the force direction and the clamping force, thus reducing the clamping force. Causes deformation of the part. The direction of the clamping force of the clamp should be such that the deformation of the workpiece is as small as possible, and the clamping force should be applied to the part with good stiffness, and the clamping force should be suitable . For example, in the cutting process of thin-walled sleeve parts, the radial clamping force of the three-jaw chuck is changed to the axial force by a special fixture, which can greatly improve the strength of the force and reduce the deformation of the clamping force. In the case of workpieces requiring radial clamping, a soft clamping mechanism such as deer skin can be used to increase the contact area of the clamping, so that the best clamping effect can be achieved under the same unit area pressure.
2. Compensation cutting
In the processing of thin-walled parts, under the action of the cutting force, the workpiece will produce under-cut deformation, that is, in the turning, the drum-shaped structure is formed, and during the milling process, the protruding surface is formed, so special special can be used in the cutting process. Processing method. For example, in the turning, the undercut compensation is performed by the artificial adjustment of the relative position of the tool or the workpiece, and the milling precision is controlled by the high-speed machining technology to control the machining precision. In many modern machining, CNC machine tools are used for machining. The actual machining process can be simulated by a certain experiment or computer software to measure the deformation of each part of the part. The large feed is used in the small deformation, and the deformation is large. The position adopts a small feed amount. During the programming process, the feed amount is changed locally to realize the tool yaw, so that the tool can compensate the deformation according to the degree of deformation in the original trajectory, compensate the deformation caused by the deformation, and improve the part. Processing accuracy .
3. Choose the right tool
The contact and friction between the tool and the workpiece are the main reasons for the cutting force and the heat of cutting. Therefore, the cutting force can be greatly reduced by using the appropriate tool material and the appropriate tool angle. Generally, the size of the rake angle of the tool is the main factor affecting the sharpness of the tool. The larger the rake angle, the smaller the cutting deformation and friction. When the rake angle is increased by one degree, the cutting temperature and cutting force will be reduced by 10%, and the vibration amplitude of the tool will be Greatly reduced, helping to improve processing accuracy and quality. However, if the rake angle is too large, the wedge angle of the tool will be reduced, the strength of the tool will be reduced, and the heat dissipation of the tool is not favorable, so that the tool is easy to wear. Therefore, if the tool durability is allowed, the reasonable tool material is selected to make the tool expansion coefficient small, and the larger tool rake angle and back angle are used to help reduce the deformation and thermal deformation of the workpiece.
4. Choose the right amount of cutting
During the machining process, the interaction between the tool and the workpiece causes the deformation and plastic deformation of the cutting layer metal to generate a certain amount of heat, and the friction between the chip and the tool generates heat. Throughout various influencing factors, the cutting speed has the greatest influence on the cutting heat. In the low speed machining, as the cutting speed increases, the cutting temperature increases significantly, which not only makes the workpiece deformation obviously, but also causes the sharp wear of the tool and affects the machining accuracy. However, as the temperature continues to rise, the heat generated by the cutting decreases, resulting in so-called high-speed machining. In high-speed machining, due to the faster cutting speed, the heat is taken away by the chips in time, and the workpiece has less thermal deformation. However, the hot deformation of the spindle during high-speed machining will lead to the elongation of the high-speed spindle of the machine tool. Therefore, it is necessary to select a suitable cutting speed to optimize the overall effect of the two. From the processing point of view, according to the selected equipment and actual working conditions, selecting the appropriate cutting speed can greatly reduce the cutting heat and cutting force and improve the processing quality. In addition, the feed rate also has a certain influence on the cutting heat. During the machining process, the heat in the cutting zone mainly accumulates in the chips, so continuous feed and high-speed feed should be used. Continuous feed can prevent the tool from staying at a certain position, so as to avoid local overheating of the workpiece. During the high-speed feed process, with constant chip breaking, the heat is carried away by the chips and is not transferred to the workpiece, and the workpiece is substantially unaffected by the heat of cutting, thus avoiding thermal deformation.
5. Reasonable choice of machine tools
In the processing process, the stability of the processing equipment directly affects the machining accuracy of the parts. Therefore, selecting a machine tool with good machining performance, high rigidity and good thermal stability is the primary condition for improving the accuracy of the parts. During the use of the machine tool, it is necessary to pay attention to the method of heat dissipation, ventilation or intermittent processing to make the machine work in a thermal equilibrium state as much as possible, so that the machine tool is not affected by the temperature.
6. Conduct reasonable process design
The part process design mainly includes: the division of the process, the determination of the processing sequence, and the determination of the feed route. The focus of the thin-walled part processing process should focus on the structural characteristics of the part. The roughing and finishing are used to divide the process, that is, roughing and then finishing. This processing method facilitates the insertion of aging treatments of thin-walled parts during the machining process, corrects the process and adjusts the clamping force, so that the residual stress of the parts is released and the deformation is minimized. In the processing sequence arrangement, the reference surface and the main surface should be processed first, and then roughed and then finished. The feed route should be arranged reasonably for the knives, tool changes and motion superpositions, not only to meet the requirements of the tool's trajectory, but also to ensure that the tool wear is minimal and the workpiece deformation is minimal. The process design of the part is a very complicated problem, and the reasonable design helps to improve the machining accuracy of the part.
7. Select the appropriate cutting fluid
A large amount of cutting heat is formed during the machining process, and can be processed by the coolant method in addition to being carried away by the chips. Different coolants can be used depending on the material of the part and the material of the tool. For example, when finishing with a high speed steel tool, an aqueous solution can be used, and a water-insoluble cutting fluid is used for machining cast iron . At the same time, different processing methods should choose different cutting fluids, for example, in the finishing process, choose high concentration emulsion or oily cutting fluid. Milling is interrupted cutting, the cutting depth of each tooth continues to change, the vibration and impact force in the machining is large, and a large amount of cutting heat is generated. Therefore, in high-speed milling, a cutting fluid with good cooling property and certain lubricating performance is required. .
Fourth, the conclusion
In this paper, the causes of deformation of thin-walled parts are analyzed, and the basic way to reduce the deformation of thin-walled parts is proposed. The weights of various factors can be fully considered in the processing of thin-walled parts, and each relevant link can be handled reasonably. The basic structural characteristics, accuracy requirements, cost performance and other multi-angles, reasonable control of the amount of deformation, improve the machining accuracy of the parts.
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