There are many reasons for the deformation of CNC aluminum parts, which are related to materials, part shapes and production conditions. There are mainly the following aspects: deformation caused by internal stress of the blank, deformation caused by cutting force, cutting heat, and deformation caused by clamping force.
First, the process measures to reduce processing deformation
Improve the cutting ability of the tool
The material and geometric parameters of the tool have an important influence on the cutting force and the cutting heat. The correct selection of the tool is essential for reducing the deformation of the part.
(1) Reasonable selection of tool geometry parameters.
1 Front angle: Under the condition of maintaining the strength of the cutting edge, the front angle is appropriately selected. On the one hand, the sharp cutting edge can be ground, and the cutting deformation can be reduced, the chip removal can be smoothed, and the cutting force and the cutting temperature can be reduced. Never use a negative rake cutter.
2 Back angle: The size of the back angle has a direct influence on the flank wear and the quality of the machined surface. Cutting thickness is an important condition for selecting the back angle. In rough milling, due to the large feed rate, the cutting load is heavy, the heat generation is large, and the heat dissipation condition of the tool is required. Therefore, the back angle should be selected to be smaller. When finishing milling, the edge is required to be sharp, the friction between the flank and the machined surface is reduced, and the elastic deformation is reduced. Therefore, the back angle should be selected to be larger.
3 helix angle: In order to make the milling smooth and reduce the milling force, the helix angle should be as large as possible.
4 lead angle: Properly reducing the lead angle can improve the heat dissipation condition 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 the aluminum material, the cutting deformation during processing is large, and a large space for chipping is required. Therefore, the bottom radius of the chip groove should be large, and the number of teeth of the milling cutter is small.
2 fine grinding teeth. The roughness value of the cutting edge of the cutter is less than Ra = 0.4 um. Before using a new knife, you should use a fine stone to grind a few times in front of and behind the teeth to eliminate residual burrs and slight zigzag when sharpening the teeth. In this way, not only the cutting heat can be reduced but also the cutting deformation is relatively small.
3 Strictly control the wear standard of the tool. After the tool wears, the surface roughness of the workpiece increases, the cutting temperature increases, and the workpiece deformation increases. Therefore, in addition to the choice of tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it will easily lead to built-up edge. When cutting, the temperature of the workpiece should not exceed 100 °C to prevent deformation.
Method for improving workpiece clamping
For thin-walled aluminum workpieces with poor rigidity, the following clamping methods can be used to reduce distortion:
1 For thin-walled bushing parts, if the three-claw self-centering chuck or the collet chuck is used for clamping from the radial direction, once the workpiece is loosened after machining, the workpiece is inevitably deformed. In this case, a method of compacting the axial end face with better rigidity should be utilized. Positioning the inner hole of the part, make a threaded threading mandrel, and insert the inner hole of the part, and press the end face with a cover plate and then tighten it with the nut. When the outer circle is machined, the clamping deformation can be avoided, and satisfactory machining accuracy can be obtained.
2 When processing thin-walled thin-plate workpieces, it is best to use vacuum suction cups to obtain a uniform distribution of clamping force, and then to process with a small amount of cutting, which can prevent deformation of the workpiece well.
In addition, a packing method can also be used. In order to increase the process rigidity of the thin-walled workpiece, the medium can be filled inside the workpiece to reduce the deformation of the workpiece during the clamping and cutting process. For example, a urea melt containing 3% to 6% of potassium nitrate is poured into the workpiece, and after the processing, the workpiece is immersed in water or alcohol, and the filler can be dissolved and poured out.
In high-speed cutting, due to large machining allowance and intermittent cutting, the milling process often produces vibration, which affects machining accuracy and surface roughness. Therefore, the numerical control high-speed machining process can be generally divided into: roughing-semi-finishing-clearing-finishing-finishing. For parts with high precision requirements, it is sometimes necessary to perform secondary semi-finishing before finishing. After roughing, the parts can be naturally cooled, eliminating internal stresses caused by roughing and reducing distortion. The margin left after roughing should be greater than the amount of deformation, typically 1 to 2 mm. When finishing, the finished surface of the part should maintain a uniform machining allowance, generally 0.2~0.5mm, so that the tool is in a stable state during the machining process, which can greatly reduce the cutting deformation and obtain good surface processing quality. Product accuracy.
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