The CNC machining center is suitable for the processing of various types of parts. The commonly processed materials are aluminum parts, iron parts and steel parts. Due to the large thermal expansion coefficient of the aluminum parts, the thin-wall processing process is easy to deform.

(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. For the blanks with fat ears and large ears, due to the large margin, the deformation after processing is also large. If the excess part of the blank is pre-processed and the remaining amount of each part is reduced, not only can the processing deformation of the subsequent process be reduced, but also a part of the internal stress can be released by placing it for a period of time after pre-processing.

(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. Proper selection of the tool is essential to reduce the machining deformation of the part.

① Reasonable selection of tool geometry parameters.

Rake angle: Under the condition of maintaining the strength of the blade, the rake angle should be properly selected. On the one hand, the sharp cutting edge can be ground, and the cutting deformation can be reduced to make the chip evacuation smooth, thereby reducing the cutting force and cutting temperature. Never use negative rake tools.

Back angle: The size of the back angle has a direct impact on the wear of the flank and the quality of the processed surface. Cutting thickness is an important condition for choosing the clearance angle. During rough milling, due to the large feed, heavy cutting load, and large heat generation, the tool requires good heat dissipation conditions, so the back angle should be selected to be smaller. When fine milling, the cutting edge is required to be sharp, to reduce the friction between the flank face and the processed surface, and to reduce the elastic deformation. Therefore, the back angle should be selected to be larger.

Helix angle: In order to make milling stable and reduce the milling force, the helix angle should be selected as large as possible.

Main declination angle: Appropriately reducing the main declination angle can improve the heat dissipation conditions and make the average temperature of the processing area drop.

②Improve the tool structure. Reduce the number of teeth of the milling cutter and increase the chip space. Due to the greater plasticity of the aluminum parts, the larger the cutting deformation during processing, and the larger the chip-retaining space, the chip-receiving flute bottom radius should be large and the number of cutter teeth should be small. For example, milling cutters of φ20mm or less use two cutter teeth; milling cutters of φ30 ～ φ60mm use three cutter teeth to avoid deformation of thin-walled aluminum parts caused by chip clogging.

Fine grinding of teeth: The roughness value of the cutting edge of the teeth should be less than Ra = 0.4um. Before using a new knife, you should use a fine whetstone to lightly grind a few times in front of and behind the teeth to eliminate the burrs and slight jagged lines that remain when sharpening the teeth. In this way, not only can the cutting heat be reduced but also the cutting deformation is relatively small.

Strictly control the tool wear standard: after the tool wears, the surface roughness value of the workpiece increases, the cutting temperature rises, and the deformation of the workpiece increases accordingly. Therefore, in addition to choosing a tool material with good wear resistance, the tool wear standard should not be greater than 0.2 mm, 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.

③ Improve the clamping method of the workpiece. For thin-wall aluminum parts with poor rigidity, the following clamping methods can be used to reduce deformation:

For thin-walled bushing parts, if a three-jaw self-centering chuck or spring chuck is used to clamp in the radial direction, the workpiece will inevitably deform once loosened after processing. At this time, the method of compacting the axial end face with better rigidity should be used. Position the inner hole of the part, make a threaded mandrel, and insert it into the inner hole of the part. Use a cover plate to press the end surface and tighten it with the nut. When machining the outer circle, clamping deformation can be avoided, and satisfactory machining accuracy can be obtained.

When processing thin-walled and thin-plate workpieces, it is best to choose a vacuum chuck to obtain a uniformly distributed clamping force, and then use a smaller amount of cutting to process, which can well prevent deformation of the workpiece.

In addition, you can also use the padding method. 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 clamping and cutting. For example, pouring urea melt containing 3% to 6% potassium nitrate into the work piece, after processing, immersing the work piece in water or alcohol, the filler can be dissolved and poured out.

④ Arrange the process reasonably. During 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, the CNC high-speed cutting processing process can be generally divided into: roughing-semi-finishing-angle processing-finishing and other procedures. For parts with high accuracy requirements, it is sometimes necessary to perform secondary semi-finishing and then finishing.

After rough machining, the parts can be cooled naturally to eliminate the internal stress generated by rough machining and reduce deformation. The remaining amount after roughing should be greater than the amount of deformation, generally 1 ~ 2mm. When finishing, the finishing surface of the parts should maintain a uniform machining allowance, generally 0.2 to 0.5mm, so that the tool is in a stable state during the machining process, which can reduce cutting deformation and obtain good surface processing quality. Ensure the accuracy of the product.

The main factor that affects the processing accuracy and surface quality of aluminum parts is that such parts are prone to deformation during processing. There are many reasons for the deformation of aluminum parts processing, which are related to the material, part shape, production conditions, etc. There are mainly the following aspects: the deformation caused by the internal stress of the blank, the deformation caused by the cutting force and cutting heat, and the deformation caused by the clamping force. This requires the operator to have certain operating experience and skills.