In the aircraft structure, in order to reduce its own weight, a large number of thin-walled parts made of aluminum alloy materials are used, but the thermal expansion coefficient of aluminum alloy parts is relatively large, and thin-walled aluminum alloys are easily deformed when processed, especially When the free forging blank is used, the processing workload is large, so its deformation problem is more serious. analyzes the reasons and solutions for the deformation of aluminum alloy processing, hoping to help the staff.
1. Reasons for processing deformation
There are many reasons for the deformation of aluminum alloy processing, which are related to the material, the shape of the parts, and the production conditions. There are mainly the following aspects: deformation caused by internal stress of the blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.
2. Process 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 blank with fat head and big ears, due to the large margin, the deformation after processing is also large. If the excess part of the blank is pre-processed and the margin of each part is reduced, not only can the processing deformation of the subsequent process be reduced, but also a part of the internal stress can be released after pre-processed for a period of time.
(2) Improve the cutting ability of the tool. The material and geometric parameters of the tool have an important influence on the cutting force and cutting heat. The correct selection of the tool is very important to reduce the deformation of the part.
① Reasonably choose the geometric parameters of the tool. Rake angle: Under the condition of maintaining the strength of the cutting edge, choose a larger rake angle. On the one hand, it can grind a sharp edge, and on the other hand, it can reduce cutting deformation and smooth chip removal, thereby reducing cutting force and cutting temperature. Never use negative rake angle tools.
Relief angle: The size of the relief angle has a direct impact on the wear of the flank surface and the quality of the machined surface. Cutting thickness is an important condition for selecting the relief angle. During rough milling, due to the large feed rate, heavy cutting load, and large heat generation, good heat dissipation conditions of the tool are required. Therefore, the relief angle should be selected smaller. When finishing milling, the cutting edge is required to be sharp, to reduce the friction between the flank face and the machined surface, and to reduce the elastic deformation. Therefore, the relief angle should be selected larger.
Helix angle: In order to make the milling smooth and reduce the milling force, the helix angle should be selected as large as possible.
Entering angle: Appropriately reducing the entering angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
②Improve the tool structure. Reduce the number of milling cutter teeth and increase the chip space. As aluminum alloy material has greater plasticity, larger cutting deformation during machining, and larger chip holding space, so the bottom radius of the chip pocket should be larger and the number of milling cutter teeth should be smaller. For example, milling cutters below φ20mm use two teeth; milling cutters with φ30—φ60mm are better to use three teeth to avoid deformation of thin-walled aluminum alloy parts caused by chip clogging.
Fine grinding teeth: the roughness value of the cutting edge of the teeth should be less than Ra=0.4um. Before using a new knife, you should lightly grind the front and back of the teeth with a fine oil stone to eliminate the residual burrs and slight serrations when sharpening the teeth. In this way, not only the cutting heat can be reduced, but also the cutting deformation is relatively small.
Strictly control the wear standard of the tool: After the tool wears, the surface roughness value of the workpiece increases, the cutting temperature rises, and the deformation of the workpiece increases. Therefore, in addition to the selection of tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to produce built-up edge. When cutting, the temperature of the workpiece should generally not exceed 100°C to prevent deformation.
③Improve the clamping method of the workpiece. For thin-walled aluminum alloy workpieces with poor rigidity, the following clamping methods can be used to reduce deformation:
For thin-walled bushing parts, if a three-jaw self-centering chuck or spring chuck is used to clamp from the radial direction, once it is released after processing, the workpiece will inevitably be deformed. At this time, the method of pressing the axial end face with better rigidity should be used. Use the inner hole of the part to locate, make a self-made threaded mandrel, sleeve it into the inner hole of the part, and use a cover plate to press the end face on it, and then tighten it with a nut. When machining the outer circle, clamping deformation can be avoided, so that satisfactory machining accuracy can be obtained.
When processing thin-walled and thin-plate workpieces, try to use vacuum suction cups to obtain evenly distributed clamping force, and then process with a smaller cutting amount, which can well prevent workpiece deformation.
In addition, a packing method can also be used. In order to increase the process rigidity of thin-walled workpieces, medium can be filled inside the workpiece to reduce the deformation of the workpiece during clamping and cutting. For example, pour the urea melt containing 3%-6% potassium nitrate into the workpiece, and after processing, immerse the workpiece in water or alcohol to dissolve the filler and pour it out.
④ Arrange the procedures reasonably. During high-speed cutting, due to the large machining allowance and intermittent cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into: rough machining-semi-finish machining-clear corner machining-finishing and other processes. For parts with high precision requirements, it is sometimes necessary to perform secondary semi-finishing and then finishing. After rough machining, the parts can be cooled naturally to eliminate internal stress caused by rough machining and reduce deformation. The margin left after rough machining should be greater than the amount of deformation, generally 1-2mm. During finishing, the finishing surface of the part should maintain a uniform machining allowance, generally 0.2-0.5mm is appropriate, so that the tool is in a stable state during the machining process, which can greatly reduce the cutting deformation and obtain a good surface machining quality. Ensure the accuracy of the product.
Aluminum alloy cutting is relatively rare, and special aluminum alloy milling cutters are needed to cut. When cutting aluminum alloy carbide drill bits , you must pay attention to the cutting parameters and processing technology to avoid deformation and other failures. Noble reminds that different carbide drill bits are used for cutting of different materials, so be careful not to choose the wrong carbide drill bits when choosing aluminum alloy carbide drill bits .
