Six ways to avoid parts deformation in aluminium alloy processing, collect spare

Six ways to avoid parts deformation in aluminium alloy processing, collect spare!

Aluminum alloy is an important industrial raw material. Because of its relatively small hardness and large coefficient of thermal expansion, it is easy to deform in the mechanical processing of thin-walled and thin-plate parts. In addition to improving the performance of cutting tools and eliminating the internal stress of materials by aging treatment in advance, some measures can be taken to reduce the deformation of materials as far as possible from the point of view of processing technology.

For aluminium alloy parts with large processing margin, in order to create better heat dissipation conditions and reduce thermal deformation, excessive heat concentration must be avoided as far as possible, and symmetrical processing can be adopted. For example, there is a 90 mm thick aluminium alloy sheet, which needs to be milling to 60 mm thick. If one side is milling and the other side is turned over immediately after milling, the flatness of the milled aluminium alloy sheet will be caused because each side is processed to the final dimension at one time and the continuous processing margin is large. Only 5 mm. If the symmetrical processing method of two-sided repeated feeding is adopted, each side is processed at least twice until the final size is reached, which is conducive to heat dissipation and flatness can be controlled at 0.3 mm.

_1. Layered multi-processing method

When there are many cavities on aluminum alloy plate parts to be processed, if one cavity is processed sequentially, the wall of the cavity will be easily wrapped up and deformed due to uneven force. The best solution is to adopt layered multi-processing method, that is, to process all the cavity at the same time, but not in one processing, but in several layers, one by one processing to the required size. In this way, the force on the part will be more uniform, and the probability of deformation will be smaller.

_2. Appropriate selection of cutting parameters

Choosing appropriate cutting parameters can effectively reduce the cutting force and heat in the cutting process. In the process of machining, the excessive cutting force of the primary tool will be caused by the excessive cutting parameters, which will easily cause the deformation of the parts, and will affect the rigidity of the spindle of the machine tool and the durability of the tool. Among all the factors of cutting parameters, the most important factor affecting the cutting force is the knife feed back. It is said that reducing the back feed is beneficial to ensure that the parts do not deform, but at the same time it will reduce the processing efficiency. High-speed milling in NC machining can solve this problem. It can reduce cutting force and ensure processing efficiency only by increasing feed and speed of machine tool while reducing back feed.

_3. Improving the Cutting Ability of Cutting Tools

Material and geometric parameters of cutting tools have an important influence on cutting force and heat. Correct selection of cutting tools is very important to reduce machining deformation of parts.

Rational selection of tool geometry parameters.

Front Angle: Under the condition of keeping the edge strength, the front angle should be selected appropriately larger. On the one hand, it can grind a sharp edge, on the other hand, it can reduce cutting deformation, make chip removal smoothly, and then reduce cutting force and cutting temperature. Never use negative rake tool.

Back angle: The size of the back angle has a direct impact on the wear of the flank and the quality of the machined surface. Cutting thickness is an important condition for choosing rear angle. In rough milling, because of the large feed, heavy cutting load and high heat output, the cutter is required to have good heat dissipation conditions, so the back angle should be selected smaller. In finishing milling, sharp edges are required to reduce friction between the flank and the machined surface and reduce elastic deformation. Therefore, a larger rear angle should be chosen.

Helix angle: In order to make the milling smooth and reduce the milling force, the helix angle should be as large as possible.

Principal deviation angle: Appropriate reduction of the main deviation angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.

Improve tool structure.

Reduce the number of milling cutter teeth, increase chip space. Because of the large plasticity of aluminium alloy material and the large cutting deformation in processing, it needs larger chip space, so it is better to have larger radius of chip groove bottom and fewer teeth of milling cutter. For example, two cutter teeth are used for milling cutters less than 20 mm and three cutter teeth for milling cutters between 30 mm and 60 mm are better to avoid the deformation of thin-walled aluminum alloy parts caused by chip blockage.

Precision grinding of cutter teeth: The roughness of cutting edge of cutter teeth is less than Ra=0.4um. Before using a new knife, a few gentle rubbings should be made on the front and back of the knife teeth with fine asphalt to eliminate the burrs and slight serrated marks remaining when grinding the knife teeth. In this way, not only cutting heat can be reduced, but also cutting deformation is relatively small.

Strict control of tool wear standards: after tool wear, the workpiece surface roughness increases, cutting temperature increases, and workpiece deformation increases. Therefore, in addition to choosing tool materials with good wear resistance, the tool wear standard should not be greater than 0.2 mm, otherwise it is easy to produce chip tumors. When cutting, the temperature of the workpiece should not exceed 100 C in order to prevent deformation.

_4. Knife-walking sequence is exquisite

Rough and finish machining should adopt different cutting sequence. Rough machining requires cutting the superfluous material on the surface of the blank at the fastest cutting speed and in the shortest time to form the required geometric contour for finish machining. Therefore, the emphasis is on the processing efficiency, and the material removal rate per unit time should be used in reverse milling. Finishing requires higher machining accuracy and surface quality. It emphasizes processing quality and should use forward milling. As the cutting thickness of the cutter teeth decreases gradually from the maximum to zero, the hardening phenomenon will be greatly reduced, and the deformation of the parts will also be restrained to a certain extent.

_5. Second Compression of Thin-walled Parts

When processing Thin-walled Aluminium Alloy parts, the clamping force is also an important cause of deformation, which is unavoidable even if the processing accuracy is improved. In order to reduce the deformation of workpiece caused by clamping, the compacted parts can be loosened before finishing reaches the final size, release the compaction force, and make the parts free to return to their original state, and then re-compact slightly. The action point of secondary compaction is best on the supporting surface, and the clamping force should be applied in the direction of good rigidity of the workpiece. The magnitude of the clamping force should be based on the rigidity of the workpiece without loosening, which has a higher requirement for the operator's experience and feel. The compaction deformation of the parts processed in this way is small.

_6. Drilling before milling

When machining parts with cavity, if the milling cutter is directly inserted downward into the parts, the chip removal will not be smooth because of the insufficient chip space of the milling cutter, which will lead to the accumulation of a large amount of cutting heat, expansion and deformation of the parts, and may even cause accidents such as tool collapse and tool breakage. The best way is to drill before milling, that is, to drill the hole with a bit of size no less than the milling cutter, and then use the milling cutter into the hole to start milling, which can effectively solve the problems mentioned above.