Aluminum is the most widely used and widely used metal material in non-ferrous metals, and its application range is still expanding. There are many kinds of aluminum products produced with aluminum materials. According to statistics, there are more than 700000 kinds of aluminum products. From the construction and decoration industry to the transportation industry, aerospace and other industries have different needs. Today, we will introduce how to avoid the deformation of aluminum products.
The advantages and characteristics of aluminum are as follows:
- Low density. The density of aluminum is about 2.7 g / cm3. Its density is only 1 / 3 of that of iron or copper.
- High plasticity. Aluminum has good ductility and can be made into various articles by pressing, stretching and other pressure processing means.
- Corrosion resistance. Aluminum is a metal with strong negative electricity. Under natural conditions or anodic oxidation, a protective oxide film will be formed on the surface, which has much better corrosion resistance than steel.
- Easy to strengthen. The strength of pure aluminum is not high, but it can be improved by anodizing.
- Easy surface treatment. Surface treatment can further improve or change the surface properties of aluminum. Aluminum anodizing process is quite mature and stable, and has been widely used in the processing of aluminum products.
- Good conductivity and easy recovery.
Technological measures to reduce machining deformation
1. Reduce the internal stress of wool culture
Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre processing is also an effective process. As for the blank with fat head and big ears, the deformation after processing is also large due to the large margin. If the surplus parts of the blank are processed in advance and the surplus of each part is reduced, not only the processing deformation of the subsequent process can be reduced, but also the internal stress can be released after being processed in advance and placed for a period of time.
2. Improve the cutting ability of the tool
The material and geometric parameters of the tool have an important impact 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) Reasonably select the geometric parameters of the tool.
① Rake angle: under the condition of maintaining the strength of the cutting edge, the rake angle can be 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 negative rake angle tools.
② Relief angle: the size of relief angle has a direct impact on the wear of relief surface and the quality of machined surface. The cutting thickness is an important condition for selecting the relief angle. During rough milling, due to large feed rate, heavy cutting load and large heat generation, it is required that the heat dissipation condition of the tool is good. Therefore, the clearance angle should be smaller. When finishing milling, the edge shall be sharp to reduce the friction between the flank and the machining surface and reduce the elastic deformation. Therefore, the relief angle shall be larger.
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 deflection angle: properly reducing the main deflection angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
(2) Improve the tool structure.
① Reduce the number of milling cutter teeth and increase the chip space. Due to the large plasticity of aluminum parts and the large cutting deformation during machining, a large chip holding space is required, so the radius of the chip holding groove bottom should be large and the number of milling cutter teeth should be small.
② Finish grinding the cutter teeth. The roughness value of the cutting edge of the cutter tooth shall be less than RA = 0.4um. Before using a new knife, gently grind the front and back of the knife teeth with a fine oil stone to eliminate the burrs and slight serrations left when grinding the knife teeth. In this way, not only the cutting heat but also the cutting deformation can be reduced.
③ Strictly control the tool wear standard. After the tool wear, the surface roughness of the workpiece increases, the cutting temperature increases, and the workpiece deformation increases. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to generate chip accumulation. During cutting, the temperature of the workpiece shall not exceed 100 ℃ to prevent deformation.
3. Improve the clamping method of workpieces
For thin-walled aluminum workpieces with poor rigidity, the following clamping methods can be adopted to reduce deformation:
① For thin-walled bushing parts, if the three claw self centering chuck or spring chuck is used to clamp them from the radial direction, the workpiece will be deformed once it is loosened after processing. At this time, the axial end face pressing method with better rigidity should be used. Locate with the inner hole of the part, self-made a threaded spindle, and put it into the inner hole of the part. Use a cover plate to press the end face and then tighten the nut. The clamping deformation can be avoided when machining the outer circle, so as to obtain satisfactory machining accuracy.
② When processing thin-walled thin-walled workpieces, it is best to select vacuum suction cups to obtain evenly distributed clamping force, and then process them with small cutting amount to prevent workpiece deformation.
Alternatively, the packing method may be used. In order to increase the process rigidity of thin-walled workpieces, media can be filled in the workpieces to reduce the deformation of workpieces during clamping and cutting. For example, the urea melt containing 3% ~ 6% potassium nitrate is poured into the workpiece, and after processing, the workpiece is immersed in water or alcohol, and the filler can be dissolved and poured out.
4. Reasonably arrange procedures
In high-speed cutting, because of the large machining allowance and intermittent cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, the NC High-speed machining process can generally be divided into: rough machining semi finishing corner cleaning finishing and other processes. For parts with high precision requirements, it is sometimes necessary to perform secondary semi finishing and then finish machining. After rough machining, the parts can be cooled naturally to eliminate the internal stress generated by rough machining and reduce the deformation. The allowance left after rough machining shall be greater than the deformation, generally 1-2mm. During finishing, uniform machining allowance shall be kept on the finished surface of parts, generally 0.2-0.5mm, so as to keep the tool in a stable state during the machining process, greatly reduce the cutting deformation, obtain good surface processing quality and ensure the accuracy of products.
Operation skills for reducing machining deformation
In addition to the above reasons, the operation method is also very important in the actual operation.
- For parts with large machining allowance, in order to provide better heat dissipation conditions and avoid heat concentration during machining, symmetrical machining should be adopted.
- If there are multiple cavities on the plate part, the sequential processing method of one cavity and one cavity should not be adopted during processing, which is easy to cause uneven stress of the part and deformation. The multi-layer processing is adopted, and each layer is processed to all cavities at the same time as possible, and then the next layer is processed, so that the parts are uniformly stressed and the deformation is reduced.
- Cutting force and cutting heat can be reduced by changing cutting parameters. Among the three elements of cutting parameters, the back draft has a great influence on the cutting force. If the machining allowance is too large and the cutting force of the tool is too large, it will not only deform the parts, but also affect the rigidity of the machine tool spindle and reduce the durability of the tool. If you reduce the amount of back knives, the production efficiency will be greatly reduced. However, high-speed milling can overcome this problem in NC machining. While reducing the back draft, as long as the feed is correspondingly increased and the rotation speed of the machine tool is increased, the cutting force can be reduced and the machining efficiency can be ensured.
- Pay attention to the order of cutting. Rough machining emphasizes the improvement of machining efficiency and the pursuit of cutting rate per unit time. Generally, reverse milling can be used. That is, the excess material on the surface of the blank is cut off at the fastest speed and in the shortest time to basically form the geometric profile required for finishing. While finishing emphasizes high precision and high quality, it is appropriate to adopt forward milling. Because the cutting thickness of the cutter teeth gradually decreases from the maximum to zero during down milling, the work hardening degree is greatly reduced and the deformation degree of the parts is reduced.
- It is difficult to avoid the deformation of thin-walled workpieces due to clamping during machining, even when finishing. In order to reduce the deformation of the workpiece to the minimum, before the finishing machining reaches the final size, loosen the pressing part to make the workpiece freely return to the original state, and then slightly press it, subject to the workpiece being clamped (completely by hand), so as to obtain the ideal processing effect. In short, the action point of the clamping force should be on the bearing surface. The clamping force should act on the direction with good rigidity of the workpiece. On the premise of ensuring that the workpiece is not loose, the smaller the clamping force, the better.
- When processing parts with cavities, try not to let the milling cutter directly plunge into the parts like a drill bit when processing the cavities, resulting in insufficient chip space for the milling cutter, unsmooth chip discharge, overheating, expansion of the parts, tool breakage, and other adverse phenomena. First drill the cutter hole with a drill of the same size or larger than the milling cutter, and then mill with a milling cutter. Alternatively, the spiral cutting program can be produced with CAM software.