1, reduce the internal stress of the blank

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. For larger blanks, due to the large margin, so the deformation after processing is also large. If pre-processing off the excess part of the blank, reduce the allowance of each part, not only can reduce the processing deformation of the subsequent process, and pre-processing after placing for a period of time, but also can release part of the internal stress.

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, and the correct selection of the tool is essential to reduce the deformation of the part machining.

(1) Reasonable selection of tool geometry parameters.

① Front angle: under the condition of maintaining the strength of the cutting edge, the front angle is appropriately chosen to be larger, on the one hand, you can grind a sharp edge, and on the other hand, you can reduce the cutting deformation, so that the chip removal is smooth, which in turn reduces the cutting force and cutting temperature. Never use negative front angle tools.

② rear angle: the size of the rear angle has a direct impact on the wear of the rear cutter face and machining surface quality. Cutting thickness is an important condition for selecting the back angle. Rough milling, due to the large feed, heavy cutting load, heat generation, the requirements of the tool heat dissipation conditions, therefore, the rear angle should be selected smaller. Precision milling, the requirements of sharp edges, reduce the friction between the rear face and the machined surface, reduce elastic deformation, therefore, the rear angle should be selected larger.

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

④ Main deflection angle: appropriately reducing the main deflection angle can improve the heat dissipation conditions, so that the average temperature of the machining area decreases.

(2) Improve the tool structure.

① Reduce the number of teeth of the milling cutter and increase the chip space. Due to the aluminium material plasticity is large, cutting deformation in the processing is large, need to be larger chip space, so the bottom radius of the chip slot should be larger, the number of teeth of the milling cutter is less good.

Precision grinding of cutter teeth. Roughness of the cutting edge of the teeth of the cutter should be less than Ra = 0.4 um. Before using a new knife, you should use a fine oil stone in front of the teeth of the cutter, the back of a few gently grinding to eliminate the edge of the teeth of the teeth of the residual burrs and slight sawtooth pattern. In this way, not only can reduce the cutting heat and cutting deformation is relatively small.

③Strictly control the standard of tool wear. After the tool wear, the surface roughness of the workpiece increases, the cutting temperature rises, and the deformation of the workpiece increases. Therefore, in addition to the selection of wear-resistant tool materials, tool wear standard should not be greater than 0.2mm, otherwise it is easy to produce chip tumour. When cutting, the temperature of the workpiece should generally not exceed 100 ℃, in order to prevent deformation.

3, improve the workpiece clamping method

For the less rigid thin-walled aluminium workpiece, 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 collet is used to clamp from the radial direction, the workpiece is bound to deform once it is loosened after processing. At this point, you should use the more rigid axial end face compression method. Positioned in the hole of the part, a self-made threaded through the heart of the shaft, set into the hole of the part, with a cover plate on the end of the compression face and then backed with a nut tight. Processing of the outer circle can be avoided clamping deformation, thus obtaining satisfactory machining accuracy.

(2) for thin-walled sheet workpiece processing, it is best to use the vacuum suction cup, in order to obtain a uniform distribution of clamping force, and then a smaller amount of cutting to process, can be very good to prevent deformation of the workpiece.

(3) Use of filling method. In order to increase the rigidity of the process of thin-walled workpieces, can be filled with media inside the workpiece to reduce the clamping and cutting process of the workpiece up to deformation. For example, to the workpiece filled with 3% to 6% potassium nitrate urea melt, after processing, the workpiece will be immersed in water or alcohol, you can dissolve the filler poured.

4, reasonable arrangement of work processes

High-speed cutting, due to large machining allowances as well as intermittent cutting, so the milling process tends to produce vibration, affecting the machining accuracy and surface roughness. Therefore, CNC high-speed cutting machining process can generally be divided into: roughing - semi-finishing - clear angle machining - finishing and other processes. For parts with high accuracy requirements, it is sometimes necessary to carry out a second semi-finishing process, followed by finishing. After rough machining, the parts can be naturally cooled to eliminate the internal stresses generated by rough machining and reduce deformation. The margin left after rough machining should be larger than the deformation, generally 1 ~ 2mm. finishing, parts finishing surface to maintain a uniform machining margin, generally 0.2 ~ 0.5mm is appropriate, so that the tool in the machining process is in a smooth state, you can greatly reduce the cutting deformation, to obtain a good surface finish quality, to ensure the accuracy of the product.