Aluminum is the most widely used metal material among non-ferrous metals, and its application range is still expanding. There are many kinds of aluminum products produced by aluminum materials. According to statistics, there are more than 700,000 kinds of aluminum products, and various industries such as construction and decoration, transportation, and aerospace have different needs. Today, I will introduce you to the processing technology of aluminum parts and how to avoid processing deformation.
The Advantages and Characteristics of Aluminum Parts
Low density. The density of aluminum is about 2.7g/cm3. Its density is only 1/3 of iron or copper.
High plasticity. Aluminum parts have good ductility and can be made into various products through pressure processing methods such as extrusion and stretching.
Corrosion resistance. Aluminum parts are made of highly negatively charged metal. A protective oxide film will be formed on the surface under natural conditions or anodizing oxidation. Aluminum parts have much better corrosion resistance than steel.
The strength of pure aluminum parts which are easy to be strengthened is not high, but its strength can be improved by anodizing oxidation
Easy surface treatment can further improve or change the surface properties of the aluminum anodizing process is quite mature, and stable operation has been widely used in the processing of aluminum parts.
Good electrical conductivity and easy to recycle.
Aluminum Parts Machining Technology
Use material aluminum pellets. The extrusion machine and the mold are used for one-time molding, which is suitable for cylindrical products or product shapes that are difficult to achieve by the stretching process, such as oval, square, and rectangular products. (Picture 1 is a machine, picture 2 is aluminum pellets, and the picture is 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, and the vertical gap between the upper die punch and the lower die tungsten steel to the bottom dead center is The top thickness of the product. (example 4)
Advantages: shorter die opening period, lower development cost than drawing die.
Disadvantages: the production process is long, the product size fluctuates greatly in the process, and the labor cost is high.
Using material aluminum skin. The continuous mold machine and the mold are used for multiple deformations to meet the requirements of the shape, suitable for non-columnar bodies (products with curved aluminum materials). (Picture 5 is a machine, picture 6 is a mold, picture 7 is a product)
Advantages: More complex and multiple-deformed products have stable dimensional control during the production process, and the product surface is smoother.
Disadvantages: high mold cost, relatively long development cycle, high requirements for machine selection, and accuracy.
Surface Treatment of Aluminum Parts
Sandblasting (Shot Blasting)
The process of using the impact of high-speed sand flow to clean and roughen the metal surface.
The surface treatment of cnc aluminum parts in this way can make the surface of the workpiece obtain a certain degree of cleanliness and different roughness, and improve the mechanical properties of the workpiece surface, thus improving the fatigue resistance of the workpiece and increasing the gap between it and the coating. The adhesion force extends the durability of the coating film and is also conducive to the leveling and decoration of the coating. We often see this process in various products of Apple.
The use of mechanical, chemical, or electrical chemical effects to reduce the surface roughness of the workpiece to obtain a bright, smooth surface processing method. The polishing process is mainly divided into mechanical polishing, chemical polishing, and electrolytic polishing. The aluminum parts can be close to the mirror effect of stainless steel after mechanical polishing + electrolytic polishing. This process gives people a sense of high-end simplicity and a stylish future.
Metal wire drawing is the manufacturing process of repeatedly scraping aluminum plates out of lines with sandpaper. Wire drawing can be divided into straight wire drawing, chaotic wire drawing, swirl drawing, and thread drawing. The metal wire drawing process can clearly show every minute wire mark so that the metal matte shine with fine hair luster and the product has a sense of fashion and technology.
The diamond knives are reinforced on the high-speed rotating (generally 20,000 rpm) spindle of the fine-engraving machine to cut the machined parts, and a local highlight area is generated on the surface of the machined parts. The brightness of the cutting highlights is affected by the speed of the milling drill bit. The faster the drill speed, the brighter the cutting highlights, otherwise, the darker it is and the tool marks are likely to occur. High-gloss and high-gloss cutting are particularly used in mobile phones, such as iphone5. In recent years, some high-end TV metal frames have adopted high-gloss milling technology, coupled with anodizing and drawing processes, making the TV as a whole full of fashion and technological sharpness.
Anodizing refers to the electrical chemical oxidation of metals or alloys. Aluminum and its alloys form an oxide film on the aluminum parts (anode) due to the action of the applied current under the corresponding electrolyte and specific process conditions. Anodizing can not only solve the defects of aluminum parts’ surface hardness and wear resistance, but also prolong the service life of aluminum parts and enhance their aesthetics. It has become an indispensable part of aluminum parts surface treatment and is currently the most widely used and very successful process.
Double Colors Anode
Two-color anodizing refers to anodizing a product and assigning different colors to a specific area. The two-color anodizing process is rarely used in the TV industry because of its complicated process and high cost. But the contrast between the two colors can better reflect the unique appearance of the high-end aluminum parts products in CNC machining services.
Process measures and operation techniques to reduce aluminum parts deformation.
There are many reasons for the machining deformation of aluminum parts, which are related to the shape production conditions of material machined parts and so on. 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 Machining Deformation
Reduce the internal stress of the machin tool
Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre-processing is also an effective process method. For the blank with fat heads and big ears, due to the large margin, the deformation after processing is also large. If the excess machined parts of the blank are pre-processed and the margin of each part is reduced, not only can the processing deformation of the subsequent process be reduced, but also an aluminum part of the internal stress can be released after pre-processed for a period of time.
Improve the cutting ability of the tool
The material and geometric parameters of the tool have an important influence on the cutting force and cutting heat. The correct selection of the tool is essential to reduce the deformation of the aluminum parts.
1) Reasonably choose the tool geometry parameters
①The rake angle: Under the condition of maintaining the strength of the cutting edge, the rake angle should be appropriately selected to be larger. On the one hand, it can grind a sharp cutting edge, and on the other hand, it can reduce cutting deformation and smooth chip removal, thereby reducing cutting force and cutting temperature. Never use negative rake angle tools.
②Clear angle: In the CNC machining service, the size of the relief angle has a direct impact on the wear of the flank surface and the quality of the surface of the machined part. Cutting thickness is an important condition for selecting the relief angle. During rough milling parts, due to the large feed rate, heavy cutting load, and large heat generation, good heat dissipation conditions of the tool are required. Therefore, the relief angle should be selected smaller. When finishing milling parts, the cutting edge is required to be sharp, reduce the friction between the flank face and the surface of the machined part, and reduce the elastic deformation. Therefore, the relief angle should be selected larger.
③Helix angle: In order to make the CNC milling parts smooth and reduce the milling force, the helix angle should be selected as large as possible.
④ Entering angle: Appropriately reducing the entering angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
2)Improving tool structure
①Reduce the number of teeth of the milling cutter and increase the chip space. Due to the large plasticity of the aluminum parts material, the large cutting deformation during processing requires a large chip space, so the bottom radius of the chip pocket should be larger and the number of milling cutter teeth should be small.
②Fine grinding of the teeth. The roughness value of the cutting edge of the tooth should be less than Ra=0.4um. Before using a new knife, you should lightly sharpen the front and back of the teeth with a fine oil stone to eliminate the remaining burrs and slight serrations when sharpening the teeth. In this way, not only the cutting head can be reduced but also the cutting deformation is relatively small.
③Strictly 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 deformation of the workpiece increases. Therefore, in addition to the selection of tool materials with good wear resistance, the tool wear standard should not be greater 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°C to prevent deformation.
Improving the clamping method of the workpiece
For thin-walled aluminum parts with poor rigidity, the following clamping method can be used to reduce deformation:
①For thin-walled bushing machined parts if a three-jaw self-centering chuck or spring chuck is used to clamp from the radial direction, once it is released after processing, the workpiece will inevitably be deformed. At this time, the method of pressing the axial end face with better rigidity should be used. To locate the inner hole of the part, make a self-made thread through the mandrel, sleeve it into the inner hole of the aluminum parts, press the end face with a cover plate on it, and then tighten it with a machined nut. The clamping deformation can be avoided when the outer circle is processed, thereby obtaining satisfactory processing accuracy.
②When processing thin-walled and thin-plate aluminum parts, 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 well prevent the aluminum parts from deformation.
In addition, a packing method can also be used. In order to increase the processing rigidity of thin-walled aluminum parts, the medium can be filled inside the machined parts to reduce the deformation of the aluminum parts during clamping and cutting. For example, pour a urea melt containing 3% to 6% potassium nitrate into the workpiece, and after processing, immerse the aluminum parts in water or alcohol to dissolve the filler and pour it out.
Reasonable arrangement of process
During high-speed cutting, due to the large CNC machining allowance and intermittent cutting, the milling parts process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into rough machining-semi-finish machining-clear corner machining-finishing, and other processes. For the aluminum parts with high precision requirements, it is sometimes necessary to perform secondary semi-finishing and then finishing. After rough machining, the aluminum parts can be cooled naturally to eliminate internal stress caused by rough machining and reduce deformation. The margin-left after rough machining should be greater than the amount of deformation, generally 1 to 2 mm. During finishing, the finishing surface of the aluminum parts should maintain a uniform machining allowance, generally, 0.2-0.5mm is appropriate, so that the tool is in a stable state during the machining process, which can greatly reduce cutting deformation, obtain good surface machining quality, and ensure The accuracy of the aluminum parts.
The Operation Technique of Reducing the Machining Deformation
1. For CNC machining parts with a large machining allowance, in order to have better heat dissipation conditions during the machining process and avoid heat concentration, symmetrical machining should be used during machining. If there is a 90mm thick sheet that needs to be processed to 60mm if one side is milled and the other side is milled immediately, and the final size is processed once, the flatness will reach 5mm; if repeated feed symmetrical processing is used, each side is processed twice. The final size can guarantee a flatness of 0.3mm.
2. If there are multiple cavities on the sheet metal part, it is not advisable to use a cavity-by-cavity sequential processing method during processing, as this will easily cause uneven stress and deformation of the metal parts. Multi-layer processing is adopted, and each layer is processed to all cavities at the same time as much as possible, and then the next layer is processed to make the machined parts evenly stressed and reduce deformation.
3. Reduce cutting force and cutting heat by changing the cutting amount. Among the three elements of cutting amount, the amount of back-cutting has a great influence on 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 durability of the tool. If you reduce the number of knives backed, the production efficiency will be greatly reduced. However, high-speed milling in CNC machining can overcome this problem. While reducing the amount of back-grabbing, as long as the feed is correspondingly increased and the speed of the machine tool is increased, the cutting force can be reduced while ensuring processing efficiency.
4. The order of the knife should also be paid attention to. Rough machining parts emphasize the improvement of machining efficiency and the pursuit of removal rate per unit time. Generally, upside milling can be used. That is to remove the excess material on the surface of the blank with the fastest speed and the shortest time, and basically form the geometric contour required for finishing. The emphasis on finishing is high precision and high quality, and down milling should be used. Because the cutting thickness of the cutter teeth gradually decreases from the maximum to zero during down milling, the degree of work hardening is greatly reduced, while reducing the degree of deformation of the metal parts.
5. The deformation of thin-walled workpieces due to clamping during processing is difficult to avoid even for finishing. In order to reduce the deformation of the workpiece to the minimum, you can loosen the compression piece before the final size is reached in the finishing process so that the metal parts can be restored to their original shape freely, and then slightly compressed, subject to the rigid clamping of the metal parts (completely By hand), so you can get the ideal processing effect. In short, the point of action of the clamping force is best on the supporting surface, and the clamping force should act in the direction of good rigidity of the metal parts. Under the premise of ensuring that the machined parts do not loosen, the smaller the clamping force, the better.
6. When machining parts with cavities, try not to let the milling cutter plunge directly into the part like a drill bit, resulting in an insufficient chip holding space of the milling cutter, unsmooth chip removal, overheating, expansion, and collapse of the machined part. Unfavorable phenomena such as knives and broken knives. First, drill the hole with a drill of the same size as the milling cutter or one size larger, and then mill it with the milling cutter. Alternatively, the CAM software can be used to produce the spiral cutting program.