Aluminum is a lively metal, and aluminum is the most abundant metal element in the earth's crust. The development of the three important industries of aviation, construction, and automobiles requires the material properties to have the unique properties of aluminum and its alloys, which greatly facilitates the production and application of this new metal aluminum.
Due to the large thermal expansion coefficient of aluminum alloy parts, it is easy to deform during thin-wall processing. Especially when the free forging blank is used, the machining allowance is large, and the deformation problem is more prominent.
There are many reasons for the deformation of CNC aluminum alloy parts, which are related to the material, the shape of the part, the production conditions, and the performance of the cutting fluid.
During CNC machining, what should I do if the material of aluminum parts is easily deformed? The reasons for the deformation mainly include the following aspects: deformation caused by the internal stress of the blank, deformation caused by cutting force, deformation caused by cutting heat, and deformation caused by clamping force.
Therefore, in the process of processing, measures to reduce processing deformation are particularly important. There are mainly the following aspects: reduce the internal stress of the blank, improve the cutting ability of the tool, reasonably select the geometric parameters of the tool, improve the tool structure, improve the clamping method of the workpiece, and arrange the processes reasonably
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, due to the large allowance, the deformation after processing is also large.
If the excess part of the blank is pre-processed and the allowance of each part is reduced, it can not only reduce the processing deformation of the subsequent process but also release a part of the internal stress after pre-processing 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 machining deformation of the part.
(1) Reasonable selection of tool geometric parameters.
Rake angle: Under the condition of maintaining the strength of the blade, the rake angle is appropriately selected to be larger, on the one hand, it can grind a 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 tools with a negative rake angle.
Relief angle: The size of the relief angle has a direct impact on the wear of the flank and the quality of the machined surface. The cutting thickness is an important condition for selecting the relief angle.
During rough milling, the medium-dry feed is large, the cutting load is heavy, and the heat generation is large, which requires good heat dissipation conditions of the tool. Therefore, the clearance angle should be selected to be smaller. When fine milling, the cutting edge is required to be sharp, the friction between the flank face and the machined surface is reduced, and the elastic deformation is reduced. Therefore, the clearance angle should be larger.
Helix angle: In order to make the milling smooth and reduce the milling force, the helix angle should be as large as possible.
Main declination angle: Properly reducing the main declination angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
(2) Improve the tool structure.
Reduce the number of milling cutter teeth and increase the chip space. Due to the large plasticity of the aluminum material and the large cutting deformation during processing, a large chip space is required, so the bottom radius of the chip groove should be large and the number of milling cutter teeth should be small.
Finely ground teeth. The roughness value of the cutting edge of the cutter teeth should be less than Ra=0.4um. Before using a new knife, you should use a fine oil stone to lightly sharpen the front and back of the knife teeth a few times to eliminate the burrs and slight serrations left when sharpening the teeth. In this way, not only can the cutting heat be reduced, but also the cutting deformation is relatively small.
Strictly control the wear standard of the tool. After the tool is worn, the surface roughness value of the workpiece increases, the cutting temperature rises, and the workpiece deformation 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 a built-up edge. When cutting, the temperature of the workpiece should generally not exceed 100 ℃ to prevent deformation.
3. Improve the clamping method of the workpiece
For thin-walled aluminum workpieces with poor dry 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 for radial clamping, once it is released after processing, the workpiece will inevitably deform. At this time, the method of pressing the axial end face with better rigidity should be used.
(3)Position 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 on it, and then tighten it with a nut. When machining the outer circle, clamping deformation can be avoided, so as to obtain satisfactory machining accuracy.
(2) When processing thin-walled and thin-plate workpieces, it is best to use vacuum suction cups to obtain evenly distributed clamping force, and then process with a small amount of cutting, which can well prevent workpiece deformation.
In addition, the field filling method can also be used, in order to increase the technological rigidity of the workpiece, the material can be filled inside the workpiece to reduce the deformation of the workpiece during clamping and cutting.
For example, pour urea melt containing 3%~6% potassium nitrate into the workpiece, and after processing, immerse the workpiece in water or sprinkling essence, and then the filler can be dissolved and poured out.
4. Reasonable arrangement of processes
During high-speed cutting, due to the large machining allowance and interrupted cutting, the milling process often generates vibration, which affects the machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into roughing, half finishing, clearing corners, and finishing.
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, eliminating the internal stress caused by rough machining and reducing deformation. The allowance left after rough machining should be greater than the deformation, generally 1~2mm.
When finishing, the finishing surface of the parts should maintain a uniform machining allowance, generally 0.2~0.5mm, so that the tool can be in a stable state during the machining process, which can greatly reduce cutting deformation, obtain good surface machining quality, and ensure Product accuracy.
The above introduces the solutions for the easy deformation of aluminum parts during CNC machining. If you have any questions about the above problems or need to customize CNC aluminum parts, please contact us.
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