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Technological measures for reducing deformation in processing aluminum parts

2023-01-06(1345)Views

There are many reasons for processing deformation of aluminum parts, which are related to material, part shape, production conditions, etc. There are mainly the following aspects: deformation caused by internal stress of blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.
1、 Technological measures to reduce processing deformation
1. Reduce the internal stress of the blank
Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre-processing is also an effective process method. For the rough of fat head and big ears, due to the large margin, the deformation after processing is also large. If the surplus parts of the blank are processed in advance and the allowance of each part is reduced, not only can the processing deformation of the subsequent processes be reduced, but also a part of the internal stress can be released after the pre-processing is placed for a period of time.

2. Improve the cutting ability of the tool
The material and geometric parameters of the tool have an important impact on the cutting force and cutting heat. The correct selection of the tool is crucial to reduce the machining deformation of the part.
1) Reasonable selection of tool geometric parameters.
① Front angle: under the condition of maintaining the strength of the cutting edge, the front angle should be appropriately larger. On the one hand, it can grind the sharp edge, and on the other hand, it can reduce the cutting deformation, make the chip removal smooth, and then reduce the cutting force and cutting temperature. Never use negative rake tools.
② Back angle: The size of the back angle has a direct impact on the wear of the back tool surface and the quality of the machined surface. Cutting thickness is an important condition for selecting back angle. During rough milling, due to the large feed rate, heavy cutting load and large heat generation, the tool heat dissipation condition is required to be good, so the back angle should be smaller. During finishing milling, the cutting edge is required to be sharp to reduce the friction between the back face and the machined surface and reduce the elastic deformation. Therefore, the back angle should be larger.
③ Helical angle: In order to make milling smooth and reduce milling force, the spiral angle should be selected as large as possible.
④ Main deflection angle: properly reducing the main deflection angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.

2) Improve tool structure.
① Reduce the number of milling cutter teeth and increase the chip holding space. Due to the large plasticity of aluminum parts and the large cutting deformation during machining, large chip holding space is required, so the radius of the chip holding groove bottom should be larger and the number of milling cutter teeth should be smaller.
② Finish grinding cutter teeth. The roughness value of the cutting edge of the cutter tooth should be less than Ra=0.4um. Before using a new knife, gently grind the front and back of the knife tooth with a fine oilstone to remove the remaining burrs and slight serrations when grinding the knife tooth. In this way, not only cutting heat can be reduced, but also cutting deformation is relatively small.
③ Strictly control the tool wear standard. After tool wear, the workpiece surface roughness value increases, the cutting temperature increases, and the workpiece deformation increases. Therefore, in addition to selecting the tool material with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to produce chips. During cutting, the temperature of the workpiece should not exceed 100 ℃ to prevent deformation.

3. Improve the clamping method of workpiece
For thin-walled aluminum parts with poor rigidity, the following clamping methods can be used to reduce deformation:
① For thin-walled bushing parts, if the three-jaw self-centering chuck or spring chuck is used to clamp radially, the workpiece will inevitably deform once it is loosened after processing. At this time, the method of axial end compression with good rigidity should be used. Position with the inner hole of the part, make a threaded mandrel, insert it into the inner hole of the part, press the end face with a cover plate and then back it with a nut. The clamping deformation can be avoided when machining the outer circle, so as to obtain satisfactory machining accuracy.
② When processing thin-walled thin plate workpiece, it is best to select vacuum chuck to obtain evenly distributed clamping force, and then use small cutting amount to process, which can effectively prevent workpiece deformation.
In addition, packing method can also be used. In order to increase the technological rigidity of the thin-walled workpiece, media can be filled in the workpiece to reduce the deformation of the workpiece during clamping and cutting. For example, the molten urea containing 3%~6% potassium nitrate is poured into the workpiece. After processing, the workpiece is immersed in water or alcohol, and the filler can be dissolved and poured out.

4. Reasonably arrange the process
During high-speed cutting, due to large machining allowance and intermittent cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, the NC high-speed machining process can generally be divided into: rough machining - semi-finish machining - corner cleaning - finish machining and other processes. For parts with high accuracy requirements, it is sometimes necessary to carry out secondary semi-finishing and then finish machining. After rough machining, the parts can be naturally cooled to eliminate the internal stress generated by rough machining and reduce deformation. The allowance left after rough machining shall be greater than the deformation, generally 1~2mm. During finishing, the finished surface of the part shall be kept with uniform machining allowance, generally 0.2~0.5mm, so that the tool is in a stable state during the processing, which can greatly reduce cutting deformation, obtain good surface processing quality and ensure the accuracy of the product.

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