Reduce aluminum processing deformation of the process measures and operating skills!
There are many reasons for the machining deformation of aluminum parts, which are related to material quality, parts shape, production conditions and so on. There are mainly the following aspects: deformation caused by internal stress of the blank, deformation caused by cutting force, cutting heat, clamping force.
Technological measures to reduce machining deformation
1. Reduce the internal stress of the blank
Natural or artificial aging and vibration treatment can partly eliminate the internal stress of the blank. Pre-processing is also an effective process method. To the blank of FAT head big ear, because the allowance is big, so the deformation after processing is also big. If the spare part of the blank is preprocessed and the allowance of each part is reduced, not only the deformation of the later working procedure can be reduced, but also some internal stress can be released after the blank is preprocessed and left for a period of time.
2. Improve the cutting ability of the tool
The material and geometric parameters of the cutting tool have important influence on cutting force and cutting heat.
1) reasonable selection of geometric parameters of cutting tools.
1 Rake Angle: under the condition of keeping the strength of the cutting edge, the rake angle should be chosen bigger, on the one hand, the sharp cutting edge can be ground, on the other hand, the cutting deformation can be reduced, the chips can be removed smoothly, and then the cutting force and cutting temperature can be reduced. Do not use a negative rake angle tool.
2 The 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 selecting back angle. Rough milling, due to large feed, heavy cutting load, heat, requires good tool cooling conditions, therefore, the rear angle should be selected smaller. When finishing milling, the cutting edge should be sharp, the friction between the flank and the machined surface should be reduced, and the elastic deformation should be reduced.
3 Helix Angle: In order to make milling smooth and reduce milling force, the Helix Angle should be selected as large as possible.
4 Main declination: reducing the main declination properly can improve the heat dissipation condition and decrease the average temperature of the processing zone.
2) improve tool construction.
1. Reduce the number of teeth of milling cutter and increase the space of chip capacity. Because the material of aluminum is plastic, the machining deformation is big and the chip-holding space is big, so the bottom radius of chip-holding groove should be bigger and the number of milling cutter teeth should be less.
2. Finish grinding the cutter teeth. The roughness of the cutting edge is less than RA = 0.4 um. Before using a new knife, you should use a fine stone in the teeth before, after gently grinding a few times, in order to eliminate the tooth edge sharpening residual burr and slight serration. In this way, not only can reduce cutting heat and cutting deformation is relatively small.
3. Strictly control the wear standard of cutting tools. After the tool is worn, the workpiece Surface roughness value increases, the cutting temperature increases, the workpiece deformation increases. Therefore, in addition to the selection of good wear-resistant cutting tool materials, cutting tool wear standards should not be greater than 0.2 mm, otherwise prone to chipping. When cutting, the temperature of the workpiece should not exceed 100 °C to prevent deformation.
3. Improve the clamping method of the 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 clamped from the radial direction, the workpiece will inevitably deform once it is loosened after processing. At this point, we should make use of the better rigidity of the axial end compression method. Positioning the inner hole of the part, a self-made threaded Mandrel is inserted into the inner hole of the part, and a cover plate is used to compress the end surface and then a nut back is used to tighten it. When the outer circle is processed, the clamping deformation can be avoided and the satisfactory machining precision can be obtained.
2 When machining thin-wall thin-plate workpiece, it is best to choose vacuum sucker to obtain uniform clamping force, and then to reduce the amount of cutting to prevent the deformation of the workpiece.
In addition, a tamponade method can be used. In order to increase the technological rigidity of thin-walled workpiece, medium can be filled in the workpiece to reduce the deformation of the workpiece during clamping and cutting. For example, a urea melt containing 3% to 6% potassium nitrate is poured into the workpiece. After processing, the filling can be dissolved and poured out by immersing the workpiece in water or alcohol.
4. Organize your work
High speed cutting, due to large machining allowance and intermittent cutting, milling process often produce vibration, affect the accuracy and Surface roughness. Therefore, CNC high-speed cutting process can be generally divided into: Rough machining-semi-precision machining-clear Angle machining-finish machining and other processes. For high precision parts, sometimes need to be twice semi-precision machining, and then finish machining. After rough machining, the parts can be cooled naturally to eliminate the internal stress and reduce the deformation. The allowance left after rough machining should be greater than the deformation, generally 1 ~ 2 mm. When finishing, the finishing surface of the part should be kept uniform machining allowance, generally 0.2 ~ 0.5 mm is suitable, so that the cutter is in a stable state in the process of machining, which can greatly reduce the cutting deformation and obtain a good surface machining quality, ensure the accuracy of the product.
Operation Skills of reducing machining deformation
In addition to the above-mentioned reasons, the operation method is very important in the actual operation of aluminum parts in the process of deformation.
1. The parts with large machining allowance should be processed symmetrically in order to have better heat dissipation condition and avoid heat concentration. If a piece of 90mm thick sheet metal needs to be machined to 60mm, if one side is milled immediately and the other side is machined to the final dimension once, the flatness will reach 5mm; if repeated feed is used, each side will be machined to the final dimension twice, the flatness is guaranteed to be 0.3 mm.
2. If there are several cavities on the plate parts, the sequential processing method of one cavity and one cavity should not be used when machining, which will cause the deformation of the parts. Adopt multi-layer processing, each layer as far as possible at the same time processing to all the cavity, and then processing the next level, so that parts uniform stress, reduce deformation.
3. Reduce cutting force and heat by changing the amount of cutting. Among the three factors of cutting parameters, the cutting force is greatly influenced by the amount of cutting tool. If the machining allowance is too large and the cutting force is too large, it will not only deform the parts, but also affect the machine tool spindle rigidity and reduce the durability of the tool. If reduce back to eat knife quantity, will make the production efficiency big discount. However, in the numerical control processing is high-speed milling, can overcome this problem. At the same time, as long as the corresponding increase in feed, increase the speed of the machine, you can reduce the cutting force, while ensuring processing efficiency.
4, also pay attention to the sequence of tool. The emphasis of rough machining is to improve the efficiency of processing, the pursuit of the removal rate within the unit time, generally can be used reverse milling. That is to the fastest speed, the shortest time to cut off the surface of the surplus materials roughcast, the basic form of finishing required by the geometric contour. And the emphasis of finishing is high-precision high-quality, suitable for the use of shun milling. Because the cutting thickness of the cutter teeth decreases from maximum to zero gradually, the degree of work hardening is greatly reduced, and the degree of deformation of the part is reduced.
5, thin-walled workpiece in processing because of clamping deformation, even finish machining is also difficult to avoid. In order to minimize the deformation of the work-piece, you can loosen the workpiece before it reaches the final dimension in finishing, so that the work-piece is free to return to its original state, and then press it slightly, depending on whether the work-piece can be clamped just by hand, in this way, the desired processing effect can be obtained. In a word, the action point of the clamping force should be on the supporting surface. The clamping force should be acted on the direction of the rigidity of the workpiece.
6, in the processing of parts with cavity, machining cavity, do not let milling cutter like drill directly into the parts, resulting in milling cutter chip space is not enough, not smooth chip removal, causes the parts to overheat, the expansion as well as collapses the knife, the broken knife and so on disadvantageous phenomenon. First with the milling cutter with the same size or larger drill down the hole, and then milling cutter. Alternatively, you can use CAM software to produce a spiral cutter procedure.
The main factor affecting the machining precision and surface quality of aluminum parts is that the deformation is easy to occur in the machining process, which requires the operator to have certain operating experience and skills.
