Aluminum is the most widely used and widely used metal material in non-ferrous metals, and its scope of application is constantly expanding. According to statistics, there are more than 7 million aluminum products. Construction, decoration, transportation, aerospace and many other industries have aluminum alloy parts.
The advantages and characteristics of aluminum are as follows
- Low density, aluminum has a density of about 2.7 grams per cubic centimeter, and its density is only 1/3 of that of iron or copper.
- High plasticity, aluminum has good ductility and can be processed by a variety of processes.
- Corrosion resistance, aluminum is a strongly negatively charged metal, which can form a protective oxide film on the surface through natural oxidation and anodization, and has excellent corrosion resistance.
- Easy to strengthen, pure aluminum is not very strong, but can be improved by anodizing.
- Surface treatment is easy, and surface treatment can further improve or change the surface properties of aluminum. The aluminum anode treatment process is quite mature and stable, and is widely used in the processing of aluminum products.
- good conductivity.
Technical measures to reduce processing deformation
1). Reduce internal pressure
Vibration treatment can eliminate internal stress, and pretreatment of blanks can reduce the possibility of part deformation.
2). 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. In order to reduce the machining deformation of the part, it is very important to select the correct tool.
1. Reasonably select the geometric parameters of the tool.
- (1) Bevel angle: Under the condition of maintaining the strength of the cutting edge, a larger bevel angle can be selected. On the one hand, sharp edges can be ground, and on the other hand, cutting deformation can be reduced.
- (2) Clearance angle: The size of the relief angle directly affects the wear of the relief surface and the quality of the machined surface. The cutting thickness is an important condition for choosing the safety angle. During rough machining, due to the high feed speed, heavy cutting load and high heat generation, good heat dissipation conditions of the tool are required. Therefore, it is necessary to reduce the clearance angle. When milling is done, reduce the friction between the cutting edge and the machined surface, and sharpen the edge to reduce elastic deformation.
- (3) Helix angle: In order to smooth milling and reduce cutting force, the helix angle should be as large as possible.
- (4) Main deflection angle: By appropriately reducing the main deflection angle, the heat dissipation conditions can be improved and the average temperature of the processing area can be reduced.
2. Improve the structure of the tool.
- (1) Reduce the number of cutting teeth and increase the blade space. Due to the large plasticity of aluminum parts and the large cutting deformation during processing, due to the need for a larger blade holding space, the radius of the bottom of the blade holding groove is increased, and the number of milling teeth is reduced.
- (2) Grinding and finishing of tool teeth. The roughness of the tool tip is less than or equal to Ra = 0.4 um. Before using a new knife, lightly grind the front and back of the teeth with a fine calculus to remove residual burrs and light grinding from grinding the teeth. Therefore, not only cutting heat, but also cutting deformation can be reduced.
- (3) Strictly control the tool wear standard. After the tool wears, the surface roughness of the workpiece increases, the cutting temperature increases, and the deformation of the workpiece increases. Therefore, in addition to selecting a tool material with excellent wear resistance, the tool wear standard cannot exceed 0.2mm, and blade accumulation can be easily carried out. When cutting, the temperature of the workpiece should not exceed 100°C to prevent deformation.
3. Improve the workpiece clamping method
In thin-walled aluminum workpieces with poor rigidity, the following clamping methods can be used to reduce deformation.
- (1) In the thin bushing part, if a three-jaw self-centering chuck or a spring chuck is used to tighten radially, it will deform after being loosened after machining. In this case I use the stiffness of the good shaft end pressing method. Found in the hole inside the part, the home made screw spindle put it into the hole inside the part. Use the cover to press the end face and tighten the nut. During the processing of the outer ring, clamping deformation can be avoided and good processing accuracy can be obtained.
- (2) When machining thin-walled workpieces, select a vacuum suction cup to obtain a clamping force for uniform adsorption, and it is best to prevent machining deformation by machining with a small amount of cutting. Alternatively, wrapping methods can be used. In order to improve the machining rigidity of thin-walled workpieces, in the workpiece, in order to reduce the deformation of the workpiece during fastening and cutting, a medium can be filled. For example, a urea melt containing 3% to 6% potassium nitrate is poured into the workpiece, and after processing, the workpiece is immersed in water or alcohol, and injected by dissolving the filler.
4. Reasonable arrangement procedures
In high-speed cutting, due to large machining allowance and intermittent cutting, milling often produces vibration, which affects machining accuracy and surface roughness. Therefore, NC high-speed machining steps are generally divided into roughing, semi-finishing, corner cleaning, finishing, and the like. For high precision parts, it is necessary to perform secondary semi-finishing and finish machining. After roughing, the deformation can be reduced by removing the internal stress caused by roughing by natural cooling. The allowance after roughing is usually greater than 1 to 2 mm of deformation. When finishing, in order to maintain a stable state during the processing, the finishing surface of 0.2~0.5mm is generally processed uniformly, which greatly reduces cutting deformation, obtains good surface processing quality, and ensures product accuracy. CNC Aluminum Machining
5. Operation technology for reducing processing deformation
In addition to the above reasons, the method of operation is also very important in practice.
For parts with large machining allowance, in order to provide better heat dissipation conditions and avoid heat concentration during machining, symmetrical machining is adopted.
When there are multiple cavities in the plate part, one cavity and one cavity successive treatment method must be adopted in the processing process, which is likely to cause partial uneven stress and deformation. With multi-layer processing, after each layer is processed into all cavities at the same time as possible, the next layer is processed to uniformly reduce the deformation of stress.
Cutting force and cutting heat can be reduced by changing cutting parameters. Among the three elements of cutting parameters, back-pull has a greater 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. Reducing the number of back knives will greatly reduce production efficiency. However, in nc cutting, high speed milling can overcome this problem. While reducing back pull, as long as the feed is increased and the speed of the machine tool is increased, the cutting force can be reduced and the machining efficiency can be ensured.
Please pay attention to the cutting order. Rough machining emphasizes improving machining efficiency and pursuing cutting speed per unit time. In general, reverse milling can be used. That is, the extra material of the blank surface, essentially forming the geometry needed to finish, cut at the fastest speed and in the shortest time possible. While emphasizing high precision and high quality, it is appropriate to adopt forward forming. Since the cutting thickness of the tool teeth gradually decreases from the maximum to zero during the down milling process, the degree of work hardening is greatly reduced, and the degree of deformation of the part is reduced.
It is difficult to avoid deformation of thin-walled workpieces due to tightening during finishing. Before finishing the minimum amount, in order to minimize the deformation of the workpiece, by loosening the pressing part, let the workpiece return freely to its original state, and then press slightly, by grasping the workpiece (completely manually) to obtain the desired machining result. In short, the point of application of the tightening force must be the bearing surface. The clamping force causes the stiffness of the workpiece to act in a good direction. On the premise of ensuring that the workpiece is not loose, the smaller the clamping force, the better.
When machining parts with a cavity, when machining the cavity, do not rush directly into the milling cutter like a drill bit, there is a lack of chip space in the milling machine, chip discharge, overheating, parts expansion, tool damage and other adverse effects. First, drill the hole with a drill that is the same size as the milling cutter, then use the milling machine to mill the tool hole.
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