Processing technology of aluminum products
What is aluminum?
Aluminum is the most widely used non-ferrous metal material, and its application scope is expanding. There are more than 700000 kinds of aluminum products produced by using aluminum materials. There are different demands in all walks of life, from the construction and decoration industry to the transportation industry and aerospace industry. Today, I’d like to introduce the processing technology of aluminum products and how to avoid deformation.
- 1. Low density. The density of aluminum is about 2.7g/cm3. Its density is only one third of that of iron or copper.
- 2. High plasticity. Aluminum has good ductility and can be made into various products by extrusion, stretching and other pressure processing means.
- 3. Corrosion resistant. Aluminum is a metal with strong negative charge. Under natural conditions or anodic oxidation, protective oxide film will be formed on the surface of aluminum, which has much better corrosion resistance than steel.
- 4. Easy to strengthen. The strength of pure aluminum is not high, but it can be improved by anodizing.
- 5. Easy surface treatment. Surface treatment can further improve or change the surface properties of aluminum. Aluminum anodizing process is quite mature, stable operation, and has been widely used in the processing of aluminum products.
- 6. Good conductivity, easy to recycle.
Processing technology of aluminum products
Stamping of aluminum products
1. Cold flushing
Use material aluminum particles. The extrusion machine and die are used for one-time forming, which is suitable for cylindrical products or products with difficult drawing process, such as ellipse, square and rectangular products（ As shown in Figure 1, table, figure 2 aluminum particles, and figure 3 products)
The tonnage of the machine used is related to the cross-sectional area of the product. The gap between the upper die punch and the lower die tungsten steel is the wall thickness of the product. The vertical clearance from the upper die punch and the lower die tungsten steel to the bottom dead point is the top thickness of the product.
Advantages: the opening period is short, and the development cost is relatively low compared with the drawing die.
Disadvantages: the production process is long, the product size fluctuates greatly in the process, and the labor cost is high.
2. Stretch
Use material aluminum skin. Continuous die machine and die are used to make it meet the needs of shape by many deformation, and it is suitable for non cylindrical body (aluminum products with bending)（ As shown in Fig. 5 machine table, Figure 6 mold and Figure 7 products)
Advantages: the complex and multiple deformation products are stable in size control during the production process, and the surface of the products is smooth and smooth.
Disadvantages: high cost of die, relatively long development cycle, high requirements for selection and precision of machine table.
Surface treatment of aluminum products
1. Sand blasting
The process of cleaning and coarsening metal surface by the impact of high-speed sand flow.
The surface treatment of aluminum parts by this method can make the surface of workpiece obtain certain cleanliness and different roughness, and improve the mechanical properties of the workpiece surface. Therefore, it improves the fatigue resistance of the workpiece, increases the adhesion between it and the coating, prolongs the durability of the film, and also benefits the leveling and decoration of the coating. We often see the process in Apple’s products.
2. Polishing
The surface roughness of workpiece is reduced by mechanical, chemical or electrochemical action to obtain a bright and flat surface processing method. Polishing process is mainly divided into mechanical polishing, chemical polishing, electrolytic polishing. Aluminum parts can be close to the stainless steel mirror effect after mechanical polishing + electrolytic polishing. This process gives people a high-end simple and fashionable future feeling.
3. Wire drawing
Metal drawing is a process of repeatedly scraping aluminum plate out of line with sandpaper. The drawing can be divided into straight thread drawing, random drawing, spinning thread drawing and thread drawing. Metal drawing technology can clearly show every fine micro wire mark, so that the metal matte is covered with fine hair luster, and the products are also equipped with fashion and technology sense.
4. High gloss cutting
Diamond knife is reinforced by a precision Carver to cut parts on the spindle of high speed rotary (generally 20000 RPM), and local highlight area is produced on the surface of the product. The brightness of cutting highlights is affected by the speed of milling bit, the brighter the high light of the bit speed is, and the darker the other is, the more likely the cutter pattern will be produced. High light and high-light cutting is especially used in mobile phones, such as iphone5. In recent years, some high-end TV metal frames adopt high-end milling technology, and the anodizing and wire drawing technology make the TV set full of fashion and technology sharpness.
5. Anodizing
Anodizing refers to the electrochemical oxidation of metal or alloy. Aluminum and its alloy form a layer of oxide film on aluminum products (anodes) under the corresponding electrolyte and specific process conditions due to the action of external current. Anodizing can not only solve the defects of aluminum surface hardness, wear resistance, etc., but also prolong the service life of aluminum and enhance the aesthetic degree. It has become an indispensable part of aluminum surface treatment, and is the most widely used and very successful technology.
6. Two color anode
Two color anode is to anodize a product and give different colors to a specific area. The double color anodizing technology is less applied in the television industry, because of the complex technology and high cost; But through the contrast between two colors, it can reflect the high-end and unique appearance of the product.
The technological measures and operation skills of reducing the deformation of aluminum processing
There are many reasons for the deformation of aluminum parts, which are related to the material, shape and production conditions. There are mainly the following aspects: the deformation caused by the internal stress of the blank, the deformation caused by cutting force and cutting heat, and the deformation caused by clamping force.
Technological measures to reduce machining deformation
1. Reduce the internal stress of wool culture
The internal stress of the blank can be partly eliminated by natural or artificial aging and vibration treatment. Pre processing is also an effective method. For the roughcast with fat head and big ear, because of the large allowance, the deformation after processing is also large. If the surplus parts of the blank are machined in advance and the allowance of each part is reduced, not only the processing deformation of the later process can be reduced, but also the internal stress can be released after a period of time.
2. Improving the cutting ability of cutting tools
The material and geometric parameters of cutting tool have important influence on cutting force and cutting heat. The correct selection of cutting tool is very important to reduce the deformation of parts.
1) Reasonable selection of tool geometry parameters.
- ① Rake angle: under the condition of maintaining the strength of the cutting edge, the rake angle should be appropriately larger. On the one hand, it can grind out a sharp edge, on the other hand, it can reduce the cutting deformation, make chip removal smooth, and then reduce the cutting force and cutting temperature. Do not use negative rake tool.
- ② Rake angle: the size of rake angle has a direct impact on the wear of flank and the quality of machined surface. The cutting thickness is an important condition to select the back angle. In rough milling, due to the large feed rate, heavy cutting load and high calorific value, the tool heat dissipation condition is required to be good, so the back angle should be smaller. In finish milling, the cutting edge should be sharp to reduce the friction between the flank and the machined surface and the elastic deformation. Therefore, the rake angle should be larger.
- ③ Helix angle: in order to make milling smooth and reduce milling force, the helix angle should be 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, increase the chip space. Due to the large plasticity of aluminum material and the large cutting deformation in machining, a larger chip holding space is needed, so the bottom radius of chip holding groove should be larger and the number of milling cutter teeth should be less.
- ② Fine grinding of cutter teeth. The roughness of the cutting edge is less than RA = 0.4um. Before using a new knife, you should use a fine oilstone to gently grind the front and back of the knife teeth to eliminate the residual burr and slight serration. In this way, not only the cutting heat can be reduced, but also the cutting deformation is relatively small.
- ③ Strictly control the tool wear standard. After tool wear, the surface roughness of the workpiece increases, the cutting temperature rises, and the deformation of the workpiece increases. Therefore, in addition to choosing the tool material with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to produce chip buildup. When cutting, the temperature of workpiece should not exceed 100 ℃ to prevent deformation.
3. Improving the clamping method of 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 used to clamp from the radial direction, once it is loosened after processing, the workpiece will inevitably be deformed. At this time, the axial end compression method with better rigidity should be used. A self-made threaded through shaft is positioned by the inner hole of the part, which is inserted into the inner hole of the part. A cover plate is used to press the end face, and then the nut is used to back up. When machining the outer circle, the clamping deformation can be avoided, and the satisfactory machining accuracy can be obtained.
- ② When machining thin-walled thin-walled workpiece, it is better to select vacuum chuck to obtain evenly distributed clamping force, and then to process with small cutting parameters to prevent workpiece deformation.
- In addition, packing method can be used. In order to increase the process rigidity of thin-walled workpiece, the medium can be filled in the workpiece to reduce the deformation of workpiece during clamping and cutting. For example, the urea melt containing 3% – 6% potassium nitrate is poured into the workpiece. After processing, the workpiece is immersed in water or alcohol, and the filler can be dissolved and poured out.
4. Arrange working procedure reasonably
In high-speed cutting, due to large machining allowance and intermittent cutting, vibration often occurs in the milling process, which affects the machining accuracy and surface roughness. Therefore, the NC High-speed machining process can be generally divided into: rough machining semi finishing corner cleaning finishing and other processes. For parts with high precision, sometimes it is necessary to carry out secondary semi finishing, 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 1-2mm. When finishing, the surface of parts should keep uniform machining allowance, generally 0.2 ~ 0.5mm, so that the tool is in a stable state in the process of processing, which can greatly reduce the cutting deformation, obtain good surface processing quality, and ensure the accuracy of products.
Operation skills of reducing machining deformation
In addition to the above reasons, in the actual operation, the operation method is also very important.
- 1. For the parts with large machining allowance, in order to have better heat dissipation conditions and avoid heat concentration, symmetrical machining should be adopted. If a 90mm thick sheet needs to be machined to 60mm, if one side is milled and the other side is milled immediately and processed to the final size at one time, the flatness can reach 5mm; If repeated feed symmetrical processing is adopted, each side is processed twice to the final dimension, the flatness can reach 0.3mm.
- 2. If there are multiple cavities on the plate parts, it is not suitable to use the sequential processing method of one cavity and one cavity, which will easily lead to uneven stress and deformation of the parts. Each layer is processed to all cavities at the same time, and then the next layer is processed to make the parts uniformly stressed and reduce deformation.
- 3. The cutting force and heat can be reduced by changing the 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, the cutting force of one-time cutting will not only deform the parts, but also affect the rigidity of the machine tool spindle and reduce the tool life. If we reduce the amount of back cutting, the production efficiency will be greatly reduced. However, in NC machining, high-speed milling can overcome this problem. At the same time, as long as the feed is increased and the machine speed is increased, the cutting force can be reduced and the machining efficiency can be ensured.
- 4. We should also 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 to cut off the surplus material on the surface of the blank with the fastest speed and the shortest time, and basically form the required geometric profile for finishing. The finishing machining emphasizes high precision and high quality, so it is better to use the parallel milling. Because the cutting thickness of the cutter teeth gradually decreases from the maximum to zero, the work hardening degree is greatly reduced, and the deformation degree of the parts is reduced at the same time.
- 5. The deformation of thin-walled workpiece during machining is unavoidable even in finishing because of clamping. In order to reduce the deformation of the workpiece to the minimum, the pressing part can be loosened before the finishing process is about to reach the final size, so that the workpiece can be freely restored to its original state, and then the workpiece can be slightly pressed, subject to the rigid clamping of the workpiece (completely depending on the handle), so that the ideal processing effect can be obtained. In a word, the point of action of clamping force is best on the supporting surface, and the clamping force should act in the direction of good rigidity of the workpiece. On the premise of ensuring that the workpiece is not loose, the smaller the clamping force is, the better.
- 6. When machining parts with cavity, try not to let the milling cutter directly plunge into the parts like a drill bit, which leads to insufficient chip space and unsmooth chip removal, resulting in overheating, expansion, tool collapse, tool breaking and other adverse phenomena. First, drill the hole with a drill of the same size or size as the milling cutter, and then mill it with the milling cutter. Alternatively, CAM software can be used to produce spiral cutting program.
Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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