Processing of aluminum alloy materials, thin-walled parts, due to the thermal expansion coefficient of aluminum alloy parts larger, thin-walled process is easy to deformation. Especially in the use of free forging rough, the processing margin, deformation is more prominent.
The reason for processing deformation of aluminum alloy parts
Aluminum alloy parts for many reasons for deformation, and material, parts shape, production conditions, cutting fluid performance and so have a relationship. Mainly the following aspects: rough deformation caused by the blank, cutting force, cutting heat caused by deformation, clamping force caused by deformation.
To reduce the aluminum alloy parts processing of deformation of the process measures
(1) reduce the internal stress of the blank
With natural or artificial aging and vibration treatment, can be part of the blank to eliminate the internal stress. Pre-processing is also an effective process. On the fat head of the rough, due to the margin, so after processing deformation is also large. If the excess part of the blank is machined in advance, the margin of each part is reduced, not only the processing deformation of the subsequent process can be reduced, but also a part of the internal stress can be released after being pre-processed for a period of time.
(2) to improve the tool structure.
Reduce the number of milling cutter teeth, increase the chip space. Due to the large plasticity of the aluminum alloy material, the cutting deformation is larger in the process, and the larger chip space is needed. Therefore, the radius of the chip bottom should be larger and the number of milling cutter is less. For example, φ20mm below the cutter with two knife teeth; φ30-φ60mm milling cutter with three knife teeth is better to avoid the blockage of the chip caused by thin-walled aluminum alloy parts deformation.
The roughness value of the cutting edge is less than Ra = 0.4um. Before using the new knife, you should use fine stone in the knife before the teeth, gently grinding a few times to eliminate the blade when the teeth of the remaining burrs and slightly sawtooth. In this way, not only can reduce the cutting heat and cutting deformation is relatively small.
Strict control of the tool wear standards: After the tool wear, the workpiece surface roughness value increases, the cutting temperature increases, the workpiece deformation increases. Therefore, in addition to the use of good wear resistance of the tool material, the tool wear standards should not be greater than 0.2mm, or prone to BUE. Cutting, the workpiece temperature is generally not more than 100 ℃, to prevent deformation.
(3) to improve the workpiece clamping method.
For less rigid thin-walled aluminum alloy workpieces, the following clamping method can be used to reduce deformation:
For thin-walled bushing parts, if the three-jaw self-centering chuck or spring chuck from the radial clamping, after processing once released, the workpiece must be deformed. At this point, should be used to improve the rigidity of the axial end of the method of compression. To the parts of the hole positioning, made a threaded thread through the mandrel, into the parts of the hole, with a cover on the end of its face and then tighten the nut tight. Machining the outer circumference can avoid clamping deformation, so as to obtain satisfactory machining accuracy.
For thin-walled sheet workpieces, it is best to use a vacuum chuck to obtain a uniform distribution of clamping force, and then a smaller amount of cutting to the processing, can be very good to prevent deformation of the workpiece.
In addition, you can also use the packing method. In order to increase the rigidity of the thin-walled workpiece, the medium can be filled with the medium to reduce the workpiece during the clamping and cutting process. For example, a urea melt containing 3% to 6% potassium nitrate is poured into the workpiece, and after processing, the workpiece can be immersed in water or alcohol.
(4) reasonable arrangements for the process.
High-speed cutting, due to large processing margin and intermittent cutting, so the milling process often produce vibration, affecting the processing accuracy and surface roughness. Therefore, the NC high-speed machining process can be divided into; rough processing - semi-finishing - Qing angle processing - finishing and other processes. For parts with high precision requirements, it is sometimes necessary to perform secondary semi-finishing and then finish the finishing. After roughing, the parts can be naturally cooled to eliminate the internal stress generated by roughing and reduce the deformation. Roughing after the remaining margin should be greater than the amount of deformation, usually 1-2mm. Finishing, the parts of the finished surface to maintain a uniform processing margin, generally 0.2-0.5mm is appropriate, so that the tool in the processing process in a stable state, can greatly reduce the cutting deformation, access to good surface processing quality, to ensure that Product accuracy.