Thin-walled parts are widely used in various industrial sectors, which have the characteristics of light weight, material saving and compact structure. However, thin-walled parts are difficult to process. This paper analyzes the technical problems that exist in the processing of thin-walled parts, such as easy deformation, part dimensional accuracy, positional accuracy and surface roughness not easily guaranteed, in order to provide a basis and reference for better milling of thin-walled parts.
Aluminum alloy monolithic structural parts have the characteristics of thin-walled, lightweight, high strength and corrosion resistance, which can effectively meet the requirements of aircraft high-speed, high mobility of the parts. These parts are currently produced by a large number of CNC milling processing methods, but due to the complex shape of the thin-walled structure, the relative stiffness is low, so the processing process is poor.
General processing of such parts, in order to ensure the accuracy of the process, generally used in the final finishing after the light cut without feed several times, which undoubtedly increases the working hours, reducing productivity, but also easy to cause the processing surface roughness due to the tool back tool surface and the chip tumor between the workpiece. The following is a study of the causes and control methods of deformation during milling.
1. The cause of deformation
Thin-walled parts are due to their relatively complex structure, thin walls, and small mass, while high accuracy requirements, rigidity and strength requirements, which leads to its susceptibility to cutting forces, cutting vibration and clamping forces, and cutting heat. When choosing the blank, try to use the raw material that has eliminated the internal stress.
2. Clamping conditions of the workpiece
Rigidity of thin-walled structural parts, clamping is a more important factor causing processing deformation. Thin-walled parts of the CNC milling, clamping program of the advantages and disadvantages, will directly affect the accuracy of processing, surface quality, labor productivity and production costs. In the development of thin-walled parts clamping program, should first be based on the structural characteristics of the parts and processing technology requirements, the processing of force and deformation analysis and calculation, to find the most vulnerable to deformation of the weakest part; at the same time, we should pay special attention to positioning and clamping methods, clamping force selection, so that the workpiece is subject to a comprehensive force and moment as small as possible, so as to improve the rigidity of the parts process, reduce the clamping deformation of the parts and cutting vibration, and ultimately achieve the purpose of improving the geometric accuracy of the workpiece. Finally achieve the purpose of improving the geometric accuracy of the workpiece.
2.1 Machining residual stress
Parts of the machining process are due to the tool on the machined surface of the extrusion, the tool before the surface and chips, after the surface and the friction between the machined surface and other comprehensive action, so that the internal surface of the parts produce new processing residual stresses. Residual stress is an unstable stress state, when the part is subjected to external forces, external forces and residual stress interaction, so that some of its local plastic deformation, redistribution of stress within the cross-section, when the external force removed, the entire part due to the role of internal residual stress deformation, this cutting process caused by the redistribution of residual stress deformation of the workpiece, an important impact on the quality of processing.
3. Ways and methods to reduce the deformation of thin-walled parts
3.1 improve the process rigidity of thin-walled parts
Thin-walled parts CNC milling, increase the stiffness and strength of thin-walled parts, can effectively enhance the stress resistance of thin-walled parts, thereby reducing the processing of clamping deformation and processing deformation. Ways to enhance the strength of thin-walled parts are: ① using pouring liquid, pouring stone grinding, etc., filling the inside of the processed parts with some easy to remove substances, so as to increase the wall thickness of the parts and improve the stiffness; ② using materials with high elastic modulus, can effectively enhance the stiffness of the parts, so as to avoid force deformation; ③ because the process stiffness of thin-walled parts and processing methods, so enhance the effective between the tooling and workpiece machining accuracy and surface finish can improve the contact stiffness, thus enhancing the stiffness of the material.
3.2 Optimize tooling strategy and machining sequence
The processing sequence and the walking strategy of CNC milling of thin-walled parts have a direct impact on the structure of the parts, and the following quality control measures should be done in order to avoid material deformation. First of all, designing a reasonable machining sequence can effectively reduce machining deformation. The overall principle of selecting a good machining sequence is to ensure the workpiece is convenient, reliable positioning and facilitate the workpiece clamping, as the processing proceeds, to minimize the reduction of its own stiffness and process stiffness, so that the processing process is in a better state of rigidity to reduce processing deformation.
Secondly, the choice of tools, processing, tool materials and Cao Bureau structure has a key impact on cutting, so the choice of tools, should meet the requirements related to high hardness, wear resistance and economy, as well as the need to have heat resistance and good mechanical stability at high temperatures. For thin-walled materials, it is necessary to choose the right tool material according to the processing conditions and to ensure that the tool meets the requirements of the cutting rate and the dimensional structure of the machine tool. At present, carbide has become the mainstream of tool materials, in order to manufacture precision tools with complex structures, high hardness tool materials with good cutting performance and strong wear resistance should be selected. The tool structure needs to be selected according to the structure of the parts, because of the poor rigidity of the parts, so the tool should meet the requirements of cutting force and cutting accuracy, so as to ensure the quality of parts processing.
3.3 Develop a reasonable process route
The process flow of CNC milling of thin-walled parts and the setting of process parameters have an important impact on the deformation of the parts. In order to effectively control the processing deformation, the stable processing of the fixture should be ensured during the machining process, so as to reduce the cutting force and clamping deformation as much as possible. The clamping force of the fixture must be calculated according to the maximum cutting volume, so as to determine the value of the clamping force. In the machining process, the roughing-finishing process should be used for machining, because roughing leaves a large cutting margin, so the heat treatment process needs to be carried out effectively to eliminate the residual stress of the part, so as to improve the stability of the part. Thin-walled materials should be suspended in the machining process with reasonable cutting forces, reasonable clamping solutions and cooling methods, so as to effectively control the processing factors of the material and avoid material deformation caused by the machining process.
Post time: Feb-22-2023
