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How To Prevent Deformation Of CNC Machining Aluminium Alloy Parts
Mar 22, 2018

Due to the large coefficient of thermal expansion of aluminum alloy parts, it is easily deformed during thin-wall machining. Especially when free forging blanks are used, the machining allowance is large, and the problem of deformation is even more pronounced.

First, the cause of processing deformation

There are many reasons for deformation of CNC Machining Aluminium Alloy Parts, which are related to the material, part shape, production conditions, cutting fluid performance, and so on. There are mainly the following aspects: the deformation caused by the internal stress of the blank, the cutting force, the deformation caused by the cutting heat, and the deformation caused by the clamping force.

Second, reduce the deformation of the processing measures

1, reduce the internal stress of the blank

With natural or artificial aging and vibration treatment, the internal stress of the blank can be partially eliminated. Pre-processing is also an effective process. For rough heads, there is a large amount of residue, so the deformation after processing is also large. If the excess part of the blank is processed in advance and the remaining amount of each part is reduced, not only the processing distortion in the subsequent process can be reduced, but also a part of the internal stress can be released after being placed in advance for a period of time.

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. Selecting the correct tool is crucial to reduce the machining distortion of the part.

Reasonable choice of tool

Under the condition of maintaining the blade edge strength, the rake angle is appropriately selected to be larger. On the one hand, the sharp edge can be ground, and the cutting deformation can be reduced to make the evacuation smoothly, thereby reducing the cutting force and the cutting temperature. Never use a negative rake tool.

The size of the relief angle has a direct effect on the flank wear and the quality of the machined surface. Cutting thickness is an important condition for selecting the relief angle. During roughing, due to the large feed, heavy cutting load, and large heat output, the tool requires good heat dissipation conditions. Therefore, the back angle should be selected smaller. When finishing milling, sharp edges are required to reduce the friction between the flank and the machining surface and reduce the elastic deformation. Therefore, the relief angle should be larger.

Helix angle: To make the milling smooth and reduce the milling force, the helix angle should be chosen as large as possible.

Main declination angle: Properly reducing the main declination angle can improve the heat dissipation conditions and reduce the average temperature in the processing area.

improve the workpiece clamping method

For thin-walled bushing parts, if the clamp is clamped in the radial direction with a three-jaw self-centering chuck or collet chuck, the workpiece will inevitably deform once released. At this point, the method of compacting the axial end face with good rigidity should be used. Positioning the hole in the part, make a threading through mandrel and insert it into the inner hole of the part. Press the end face with a cover plate and tighten it with the nut. When the outer circle is processed, the clamping deformation can be avoided so that a satisfactory machining accuracy can be obtained.

Reasonable arrangement process

In high-speed cutting, due to the large machining allowance and intermittent cutting, the milling process often generates vibrations that affect the machining accuracy and surface roughness. Therefore, CNC high-speed cutting process can be divided into: roughing-semi-finishing-clearing-finishing. For parts with high precision requirements, secondary semi-finishing may be necessary before finishing. After rough machining, the parts can be naturally cooled, eliminating the internal stress generated by rough machining and reducing the deformation. The remaining amount after roughing should be greater than the amount of deformation, generally 1-2mm. During finishing, the part finish machining surface 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 distortion and obtain a good surface machining quality. The accuracy of the product.