Aluminum product processing technology

Aluminum is the most widely used non-ferrous metal material, and its application range is still expanding. More than 700,000 kinds of aluminum products are produced using aluminum materials. According to statistics, there are more than 700,000 kinds of aluminum products, and various industries, such as the construction and decoration industry, transportation industry, aerospace industry, etc., have different needs. Today, Xiaobian will introduce the processing technology of aluminum products and how to avoid processing deformation. CNC machining part 

The advantages and characteristics of aluminum are as follows:

1. Low density. The density of aluminum is about 2.7 g/cm3. Its density is only 1/3 that of iron or copper.
2. High plasticity. Aluminum is flexible and can be made into various products by pressure processing methods such as extrusion and stretching.
3. Corrosion resistance. Aluminum is a highly negatively charged metal, and a protective oxide film will be formed on the surface under natural conditions or anodizing. It has much better corrosion resistance than steel.
4, easy to strengthen. Pure aluminum is not very strong, but it can be increased by anodizing.
5. Easy surface treatment. Surface treatments can further enhance or alter the surface properties of aluminum. The aluminum anodizing process is quite mature and stable and widely used to process aluminum products.
6. Good conductivity and easy to recycle.

Processing technology of aluminum products

Punching of aluminum products
1. Cold punch
Use material aluminum pellets. The extrusion machine and die are used for one-time molding and are suitable for cylindrical products or product shapes that are difficult to achieve by stretching processes, such as oval, square, and rectangular products.
The tonnage of the machine used is related to the cross-sectional area of ​​the product. The product's wall thickness is the gap between the upper die punch and the lower die tungsten steel. When the upper die punch and the lower die tungsten steel are pressed together, the vertical gap to the bottom dead center is For the top thickness of the product. aluminum part

Advantages: The mold opening cycle is short, and the development cost is lower than that of the drawing mold.
Disadvantages: The production process is long, the product size fluctuates significantly, and the labor cost is high.
2. Stretching
Use material aluminum skin. It is suitable for deforming non-cylindrical bodies (aluminum products with curved products), often using continuous die machines and molds to meet the shape requirements.
Advantages: more complex and multiple deformation products have stable dimensional control in the production process, and the product surface is smoother.
Disadvantages: high mold cost, relatively long development cycle, and high machine selection and precision requirements.

Surface treatment of aluminum products

1. Sandblasting (shot peening)
The process of cleaning and roughening metal surfaces using the impact of high-speed sand flow.
The surface treatment of aluminum parts in this method can obtain a certain degree of cleanliness and different roughness on the surface of the workpiece so that the mechanical properties of the surface of the workpiece are improved, thus improving the fatigue resistance of the workpiece and increasing the gap between it and the coating. The adhesion of the coating prolongs the durability of the coating film and is also conducive to the leveling and decoration of the coating. We see in this process that Apple's products are o2. Polishing
They use mechanical, chemical, or electrochemical action to reduce the surface roughness of the workpiece and obtain a bright, flat surface processing method. The polishing process is divided into mechanical, chemical, and electrolytic polishing. After mechanical polishing + electrolytic polishing, the aluminum parts can be close to the mirror effect of stainless steel. This process gives people a sense of high-end simplicity and a fashionable future.
3. Drawing
Metal wire drawing is the manufacturing process of repeatedly scraping an aluminum sheet out of lines with sandpaper. Drawing can be divided into straight, random, spiral, and thread. The metal wire drawing process can clearly show every tiny silk mark, so the refined hair luster appears in the metal matte, and the product has a sense of fashion and technology.
4. High gloss cutting
Using the engraving machine, the diamond knife is reinforced on the main shaft of the engraving machine, rotating at a high speed (generally 20,000 rpm) to cut the parts, and a local highlight area is generated on the product's surface. The brightness of the cutting highlights is affected by the speed of the milling drill. The faster the drill speed, the brighter the cutting highlights, and vice versa, the darker and more accessible to produce cutting lines. High-gloss and high-gloss cutting are mainly used in mobile phones like iPhones. Some high-end TV metal frames have recently adopted a high-gloss milling process. In addition, anodizing and wire drawing processes make the TV set full of fashion and technology.
5. Anodizing
Anodic oxidation refers to the electrochemical oxidation of metals or alloys. Under the corresponding electrolyte and specific process conditions, aluminum and its alloys form an oxide film on the aluminum product (anode) due to the action of an applied current. Anodizing can not only solve the defects of aluminum surface hardness and wear resistance but also prolong the service life of aluminum and enhance the aesthetics. It has become an indispensable part of aluminum surface treatment and is currently the most widely used and very successful. craft
6. Two-color anode
Two-color anodizing refers to anodizing on one product and imparting different colors to specific areas. The two-color anodizing process is rarely used in the TV industry because the process is complicated and costs high. Still, the contrast between the two colors can

better reflect the high-end and unique appearance of the product.

Process measures and operation skills to reduce deformation of aluminum processing
There are many reasons for the deformation of aluminum parts, which are related to the material, shape of the part, and production conditions. There are mainly the following aspects: deformation caused by internal stress of blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.
Process measures to reduce processing deformation
1. Reduce the internal stress of the hair culture
Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre-processing is also an effective process method. Due to the large allowance, the deformation after processing is also significant for the blank with a fat head and big ears. Suppose the excess part of the blank is pre-processed, and the allowance of each part is reduced. In that case, it can reduce the processing deformation of the subsequent process and release some of the internal stress after pre-processing for some time.
2. Improve the cutting ability of the tool
The material and geometric parameters of the tool have an essential influence on the cutting force and cutting heat. The correct selection of the tool is necessary to reduce the machining deformation of the part.
1) Reasonable selection of tool geometric parameters.
①Rake angle: Under the condition of maintaining the strength of the blade, the rake angle is 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 tools with a negative rake angle.
②Relief angle: The size of the relief angle directly impacts the flank's wear and the machined surface's quality. The cutting thickness is an essential condition for selecting the clearance angle. The tool requires good heat dissipation during rough milling due to the significant feed rate, heavy cutting load, and extensive heat generation. Therefore, the clearance angle should be selected to be smaller. When fine milling, the cutting edge must be sharp, the friction between the flank face and the machined surface is reduced, and the elastic deformation is reduced. Therefore, the clearance angle should be more significant.
③ Helix angle: The helix angle should be as large as possible to smooth and reduce the milling force.
④Main declination angle: Properly reducing the central declination angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
2) Improve the tool structure.
①Reduce the number of teeth of the milling cutter and increase the chip space. Due to the enormous plasticity of the aluminum material and the large cutting deformation during processing, ample chip space is required, so the bottom radius of the chip groove should be significant, and the number of milling cutter teeth should be small.
② Finely grind the teeth. The roughness value of the cutting edge of the cutter teeth should be less than Ra=0.4um. Before using a new knife, you should use a fine oil stone to lightly sharpen the front and back of the knife teeth a few times to eliminate the burrs and slight serrations left when sharpening the teeth. This way, the cutting heat can be reduced, and the cutting deformation is relatively small.
③ Strictly control the wear standard of the tool. After the tool is worn, the surface roughness value of the workpiece increases, the cutting temperature rises, and the workpiece deformation increases. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not be more excellent than 0.2mm. Otherwise, it is easy to produce a built-up edge. When cutting, the temperature of the workpiece should generally not exceed 100 ℃ to prevent deformation.
3. Improve the clamping method of the workpiece
For thin-walled aluminum workpieces with poor rigidity, the following clamping methods can be used to reduce deformation:
①For thin-walled bushing parts, if the three-jaw self-centering chuck or spring chuck is used for radial clamping, the workpiece will inevitably deform once it is released after processing. The method of pressing the axial end face with better rigidity should be used. Position the inner hole of the part, make a threaded mandrel, insert it into the inner hole, press the end face with a cover plate on it, and then tighten it with a nut. Clamping deformation can be avoided when machining the outer circle to obtain satisfactory accuracy.
② When processing thin-walled and thin-plate workpieces, it is best to use vacuum suction cups to obtain evenly distributed clamping force and then process with a small amount of cutting, which can prevent workpiece deformation.
In addition, the packing method can also be used. To increase the processing rigidity of thin-walled workpieces, a medium can be filled inside the workpiece to reduce the deformation of the workpiece during clamping and cutting. For example, urea melt containing 3% to 6% potassium nitrate is poured into the workpiece. After processing, the workpiece can be immersed in water or alcohol, and the filler can be dissolved and poured out.
4. Reasonable arrangement of processes
During high-speed cutting, due to the large machining allowance and interrupted cutting, the milling process often generates vibration, which affects the machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into roughing-semi-finishing-corner-clearing-finishing and other methods. It is sometimes necessary for parts with high precision requirements to perform secondary semi-finishing and finish. After rough machining, the parts can be cooled naturally, eliminating the internal stress caused by rough machining and reducing deformation. The allowance left after rough machining should be greater than the deformation, generally 1 to 2 mm. During finishing, the finishing surface of the parts should maintain a uniform machining allowance, generally 0.2 ~ 0.5mm, so that the tool is stable during the machining process, which can significantly reduce cutting deformation, obtain good surface machining quality and ensure Product accuracy.

Operational skills to reduce machining distortion

In addition to the above reasons, the parts of aluminum parts are deformed during processing. The operation method is also critical in actual operation.
1. For parts with large machining allowance, to provide them with better heat dissipation conditions during the machining process and avoid heat concentration, symmetrical machining should be adopted during machining. If a 90mm thick sheet needs to be processed to 60mm if one side is milled and the other side is milled immediately, and the final size is processed at one time, the flatness will reach 5mm; if it is processed symmetrically with repeated feeding, each side is processed twice to The final dimension can guarantee a flatness of 0.3mm. stamping part
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 during processing, which will quickly cause the parts to be deformed due to uneven stress. Multi-layer processing is adopted, and each layer is processed to all the cavities at the same time, and then the next layer is processed to make the parts evenly stressed and reduce deformation.
3. Reduce the cutting force and cutting heat by changing the cutting amount. Among the three elements of cutting amount, the amount of back-engagement greatly influences the cutting force. If the machining allowance is too large, the cutting force of one pass is too large, which will not only deform the parts but also affect the rigidity of the machine tool spindle and reduce the tool's durability—the number of knives to be eaten. If the back is reduced, the production efficiency will be significantly reduced. However, high-speed milling is used in CNC machining, which can overcome this problem. While reducing the amount of back-cutting, as long as the feed is increased accordingly and the speed of the machine tool is increased, the cutting force can be reduced, and the processing efficiency can be ensured simultaneously.
4. The order of knife moves should also be paid attention to. Rough machining emphasizes improving efficiency and pursuing the removal rate per unit of time. Generally, up-cut milling can be used. That is, the excess material on the surface of the blank is removed at the fastest speed and the shortest time, and the geometric contour required for finishing is formed. While finishing emphasizes high precision and high quality, it is advisable to use down milling. Because the cutting thickness of the cutter teeth gradually decreases from the maximum to zero during down milling, the degree of work hardening is significantly reduced, and the degree of deformation of the part is also reduced.
5. Thin-walled workpieces are deformed due to clamping during processing; even finishing is unavoidable. To reduce the deformation of the workpiece to a minimum, you can loosen the pressing piece before completing the final size so that the workpiece can freely return to its original state and then slightly press it, as long as the workpiece can be clamped (entirely). According to the hand feel), the ideal processing effect can be obtained this way. In other words, the action point of the clamping force is preferably on the supporting surface, and the clamping force should be applied in the direction of good workpiece rigidity. To ensure that the workpiece is not loose, the smaller the clamping force, the better.
6. When machining parts with a cavity, try not to let the milling cutter plunge directly into the part like a drill when machining the cavity, resulting in insufficient space for the milling cutter to accommodate chips and poor chip removal, resulting in overheating, expansion, and collapse of the parts—knives, brokenness, and other unfavorable phenomena. First, drill the hole with a drive the same size as the milling cutter or one more significant size, then mill it with the milling cutter. Alternatively, CAM software can be used to produce spiral rundown programs.