milling technology

How to avoid machining deformation of aluminum parts?

Titanium cavity milling and spiral interpolation milling

There are many reasons for the deformation of machined aluminum parts, which are related to the aluminum material, the shape of the part, and the CNC machinery and equipment. There are mainly the following aspects: blank internal stress, cutting force, deformation caused by cutting heat, and deformation caused by clamping force.

Process measures to reduce processing deformation
1. Reduce the internal stress of the blank. 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 large blanks, the deformation after processing is also large due to the large margin. If pre-milling the excess part of the large blank. It can not only reduce the processing deformation in the subsequent process, but also can release a part of the internal stress after pre-processing.
2. Improve the cutting ability of the tool and the material of the tool. Geometric parameters have an important influence on cutting force and cutting heat. The correct choice of tools is essential to reduce the deformation of parts.

1) Reasonably choose the geometric parameters of the milling tool.
① The rake angle: Under the condition of maintaining the strength of the blade, the rake angle should be appropriately larger. On the one hand, it can grind sharp cutting edges, and on the other hand, it can reduce cutting deformation, make chip removal smooth, and then reduce cutting force and cutting temperature. Never use negative rake angle tools.
② Relief angle: The size of the relief angle has a direct effect on the wear of the flank surface and the quality of the machined surface. Cutting thickness is an important condition for selecting the relief angle. During rough milling, due to the large feed rate, heavy cutting load and large heat generation, good heat dissipation conditions of the tool are required. Therefore, the clearance angle should be smaller. When finishing milling, the cutting edge is required to be sharp to reduce the friction between the flank face and the machined surface and reduce the elastic deformation. Therefore, the relief angle should be larger.
③ Helix angle: In order to make the milling 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.

Method to prevent deformation of machined aluminum parts

Method to prevent deformation of machined aluminum parts

2) Improve the milling tool structure.
① Reduce the number of milling cutter teeth and increase the chip space. Due to the large plasticity of aluminum materials, large cutting deformation during processing, and larger chip-capacity space is required, so the bottom radius of the chip-accepting flute should be larger and the number of milling cutter teeth should be smaller.
② Fine grinding of milling cutter 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 grind the front and back of the teeth with a fine oil stone to eliminate the residual burrs and slight serrations when sharpening the teeth. In this way, not only can the cutting heat be reduced, but also the cutting deformation is relatively small.
③ Strictly control the wear standard of milling tools. 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 built-up edge. When cutting, the temperature of the workpiece should generally not exceed 100°C to prevent deformation.

Filling method to prevent deformation of machined large aluminum parts

Filling method to prevent deformation of machined large aluminum parts

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:
① For thin-walled aluminum bushing 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 clamping method of the axial end face with better rigidity should be used. To locate the inner hole of the part, make a self-made threaded through mandrel, sleeve it into the inner hole of the part, press the end face with a cover plate and then tighten it with a nut. The clamping deformation can be avoided when the outer circle is processed, thereby obtaining satisfactory processing accuracy.
② When processing thin-walled and thin-plate aluminum workpieces, it is best to use vacuum suction cups to obtain evenly distributed clamping force, and then process with a smaller cutting thickness (quantity), which can well prevent workpiece deformation. In addition, an internal filling method can also be used. In order to increase the process rigidity of thin-walled workpieces, medium can be filled inside the workpiece to reduce the deformation of the workpiece during clamping and cutting. For example, pour a urea melt containing 3% to 6% potassium nitrate into the workpiece. After processing, immerse the workpiece in water or alcohol to dissolve the filling and pour it out.

4. Arrange the procedures reasonably. During high-speed cutting, due to the large machining allowance and continuous cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness.
Therefore, the machining process of CNC high-speed cutting can generally be divided into: roughing – Semi-finishing – Clear corner processing – Finishing and other processes. For parts with high precision requirements, sometimes it is necessary to perform a second semi-finish machining and then finish machining. After rough machining, the 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 part 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. It can greatly reduce cutting deformation, obtain good surface processing quality, and ensure product accuracy.

In addition to the above-mentioned reasons, the operation method of aluminum parts is also very important in actual operation.

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