There are many reasons for the deformation of aluminum parts during processing, which are related to material, part shape, production conditions, etc. There are mainly the following aspects: deformation caused by internal stress in the blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.

Technological measures to reduce processing deformation

1. Reduce internal stress of Mao Pei

The use of 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 rough parts with fat heads and big ears, due to the large margin, the deformation after processing is also large. If the excess parts of the blank are pre processed and the surplus of each part is reduced, not only can the deformation of subsequent processes be reduced, but also a portion of internal stress can be released after being left for a period of time after pre processing.

2. Improving the cutting ability of cutting tools

The material and geometric parameters of the cutting tool have an important impact on cutting force and cutting heat. The correct selection of the cutting tool is crucial for reducing part machining deformation.

(1) Reasonably select the geometric parameters of the cutting tool.

① Front corner: Under the condition of maintaining the strength of the cutting edge, the front corner should be appropriately selected to be larger. On the one hand, it can grind out sharp edges, and on the other hand, it can reduce cutting deformation, ensure smooth chip removal, and thereby reduce cutting force and cutting temperature. Do not use negative rake tools.

② Back angle: The size of the back angle has a direct impact on the wear of the back tool surface and the quality of the machined surface. Cutting thickness is an important condition for selecting the back angle. During rough milling, due to the large feed rate, heavy cutting load, and high heat generation, it is required that the tool has good heat dissipation conditions. Therefore, the back angle should be selected to be smaller. When precision milling, it is required to have a sharp edge to reduce friction between the rear cutting surface and the machining surface, and to reduce elastic deformation. Therefore, a larger rear angle should be selected.

③ Spiral angle: To ensure smooth milling and reduce milling force, the spiral angle should be chosen as large as possible.

④ Principal deviation angle: Reducing the principal deviation angle appropriately can improve heat dissipation conditions and reduce the average temperature of the processing area.

(2) Improve tool structure.

① Reduce the number of milling cutter teeth and increase the chip holding space. Due to the high plasticity of aluminum materials and the large cutting deformation during processing, a larger chip holding space is required. Therefore, it is better to have a larger bottom radius of the chip holding groove and fewer milling cutter teeth.

② Refine the cutting teeth. The roughness value of the cutting edge of the cutting tooth should be less than Ra=0.4um. Before using a new knife, a fine oilstone should be used to gently grind the front and back of the blade teeth a few times to eliminate the remaining burrs and slight serrations when grinding the blade teeth. This not only reduces cutting heat but also reduces cutting deformation.

③ Strictly control the wear standards of cutting tools. After tool wear, the surface roughness value of the workpiece increases, the cutting temperature increases, and the deformation of the workpiece increases accordingly. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to generate chip buildup. During cutting, the temperature of the workpiece should generally not exceed 100 ℃ to prevent deformation.

3. Improving the clamping method of workpieces

For thin-walled aluminum parts with poor rigidity, the following clamping methods can be used to reduce deformation:

① For thin-walled bushing parts, if a three jaw self centering chuck or spring chuck is used to clamp radially, once loosened after processing, the workpiece will inevitably deform. At this point, a method of compressing the axial end face with good rigidity should be used. Using the internal hole of the component for positioning, create a threaded threaded mandrel and insert it into the internal hole of the component. Use a cover plate to compress the end face and then tighten it with a nut. When machining the outer circle, clamping deformation can be avoided, thus achieving satisfactory machining accuracy.

② When processing thin-walled thin plate workpieces, it is best to use vacuum suction cups to obtain evenly distributed clamping force, and then use smaller cutting amounts to process, which can effectively prevent workpiece deformation.

In addition, the packing method can also be used. To increase the process rigidity of thin-walled workpieces, media can be filled inside the workpiece to reduce large deformation during clamping and cutting processes. For example, by pouring molten urea containing 3% to 6% potassium nitrate into the workpiece, and after processing, immersing the workpiece in water or alcohol, the filler can be dissolved and poured out.

4. Reasonably arrange the process

During high-speed cutting, due to large machining allowance and intermittent cutting, vibration often occurs during the milling process, which affects machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into processes such as rough machining, semi precision machining, corner cleaning machining, and precision machining. For parts with high precision requirements, sometimes secondary semi precision machining is required before precision machining. After rough machining, the parts can naturally cool, eliminate internal stress generated by rough machining, and reduce deformation. The margin left after rough machining should be greater than the deformation, usually 1-2mm. During precision machining, the surface of the parts should maintain a uniform machining allowance, generally ranging from 0.2 to 0.5mm, to keep the cutting tool in a stable state during the machining process, which can greatly reduce cutting deformation, achieve good surface machining quality, and ensure product accuracy.

Article source: Packaging Home

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