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We all know that in the aviation field, in order to reduce the weight of the aviation parts themselves, a large number of aluminum alloy materials will be used. However, in the precision machining of aluminum alloy, due to the relatively large expansion coefficient of the material, deformation is easy to occur in the process of thin-wall processing, especially when free forging blanks are used, the machining allowance is large, and the problem of deformation is more prominent. . So next, the editor of Xiehe CNC processing factory will briefly introduce the skills of precision machining of aluminum alloy in CNC processing.

1. Causes of processing deformation

There are actually many reasons for the deformation of aluminum alloy parts, which are related to the material, the shape of the part, and various production conditions, such as the performance of the cutting fluid. To sum up, it roughly includes the following points, that is, the internal stress deformation of the blank, cutting force, cutting heat and deformation caused by clamping.

2. Technological measures should be formulated to reduce processing deformation

1. To reduce the internal stress of the blank

We can use natural or artificial aging and vibration treatment, which can partially eliminate the internal stress of the blank. Pre-processing is also an effective process method. Compared with the larger blank, due to the large allowance, the deformation after processing is also large. If we pre-process the excess part of the blank and reduce the margin of each part, it can not only reduce the processing deformation in the subsequent process, but also release part of the internal stress after pre-processing for a period of time.

2. It can improve the cutting ability of the tool

The material and geometric parameters of the cutting tool have an important influence on the cutting force and cutting heat. The correct selection of the cutting tool is very important to reduce the machining deformation of the part.

①Reasonably choose the geometric parameters of the cutting tool

Rake angle: Under the condition of maintaining the strength of the blade, a larger rake angle can be selected properly. On the one hand, it can grind out a sharp edge, and can also reduce cutting deformation, make chip removal smoother, and reduce cutting force and cutting heat. Never use tools with negative rake angles.

Relief angle: The size of the relief angle has a direct impact on the flank wear and the quality of the machined surface. Cutting thickness is an important condition for selecting relief angle. During rough milling, due to the large amount of feed, 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 finishing milling, the cutting edge is required to be sharp, to reduce the friction between the flank and the machined surface, and to reduce elastic deformation. Therefore, the relief angle should be selected larger.

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

Leading angle: Appropriately reducing the leading angle can effectively improve heat dissipation conditions and reduce the average temperature of the processing area.

② Improve tool structure

Reduce the number of milling cutter teeth and increase the chip space. Due to the high plasticity of the aluminum alloy material, the cutting deformation is large during processing, and a large chip space is required. Therefore, the radius of the bottom of the chip groove should be large and the number of teeth of the milling cutter should be small. For example, milling cutters below φ20mm use two teeth; milling cutters between φ30-φ60mm use three teeth to avoid deformation of thin-walled aluminum alloy parts due to chip clogging.

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

Strictly control the tool wear standard: After the tool is worn, 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 exceed 0.2mm, otherwise built-up edge will easily occur. When cutting, the temperature of the workpiece should generally not exceed 100°C to prevent deformation.

③Improve the clamping method of the workpiece

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

For thin-walled bushing parts, if the three-jaw self-centering chuck or collet is used to clamp radially, the workpiece will inevitably be deformed once it is released after processing. At this time, the method of compressing the axial end face with better rigidity should be used. Locate with the inner hole of the part, make a self-made threaded mandrel, insert it into the inner hole of the part, press the end face with a cover plate and tighten it with a nut. Clamping deformation can be avoided when machining the outer circle, so as to obtain satisfactory machining accuracy.

When processing thin-walled and thin-plate workpieces, it is best to use vacuum suction cups to obtain evenly distributed clamping force, and then process with a small amount of cutting, which can well prevent deformation of the workpiece.

In addition, the packing method can also be used. In order to increase the process rigidity of the thin-walled workpiece, the inside of the workpiece can be filled with medium to reduce the deformation of the workpiece during clamping and cutting. For example, pour urea melt containing 3%-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 process reasonably

During high-speed cutting, due to the large machining allowance and intermittent cutting, vibrations are often generated during the milling process, which affects the machining accuracy and surface roughness. Therefore, the CNC high-speed cutting process can generally be divided into; rough machining - semi-finishing - corner cleaning - finishing and other processes. For parts with high precision requirements, sometimes it is necessary to perform secondary semi-finishing and then finish machining. After rough machining, the parts can be cooled naturally to eliminate the internal stress generated by rough machining and reduce deformation. The margin left after rough machining should be greater than the deformation, generally 1-2mm. When finishing, the surface of the finished 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, which can greatly reduce cutting deformation, obtain good surface processing quality, and ensure The precision of the product.

The above content is the precision machining skills of aluminum alloy for cnc processing introduced by Xiehe cnc processing factory. I hope it can be helpful to you. If you want to know more about cnc processing, or customers who want to do cnc processing, please call Xiehe cnc processing factory, we will serve you wholeheartedly.