Aluminum alloy is the most widely used non-ferrous metal structural material in industry. There are aluminum alloy workpieces in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industries. In order to reduce weight in aircraft structures, a large number of thin-walled parts made of aluminum alloy materials are used. Due to the large thermal expansion coefficient of aluminum alloy parts, thin-walled parts are easily deformed during processing. Especially when free forging blanks are used, the margin is large and the deformation problem is more prominent.

1. Causes of cutting deformation of aluminum alloy workpieces

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

2. Process measures to reduce workpiece deformation

(1) Reduce the internal stress of the blank

The blank can be partially eliminated by aging and vibration treatment or pre-processing The internal stress of the blank workpiece has a large margin, so the deformation is also large. If the excess part of the blank is removed in advance to reduce the margin of each part, it can not only reduce the deformation in subsequent processes, but also leave it for a period of time to release part of the internal stress.

(2) Reasonable selection of tool geometric parameters

Rake angle: Under the condition of maintaining the strength of the blade, choose a larger rake angle. On the one hand, it can grind a sharp edge, and on the other hand, the rake angle can be sharpened. It can reduce cutting deformation and smooth chip removal, thus reducing cutting force and cutting temperature.

Relief angle: The size of the relief angle has a direct impact on flank wear and surface quality. During rough milling, due to the large feed rate, heavy cutting load, and high heat generation, the tool requires good heat dissipation conditions, so the relief angle should be smaller. During fine milling, the cutting edge is required to be sharp to reduce the friction between the flank surface and the surface and reduce elastic deformation, so the relief angle should be larger.

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

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

(3) Improve the tool structure

Reduce the number of milling cutter teeth and increase the chip space. Since the aluminum alloy material has greater plasticity and greater cutting deformation, it requires a larger chip-holding space. Therefore, it is better to have a larger chip-containing groove bottom radius and a smaller number of milling cutter teeth.

(4) Precision grinding of the blade teeth

Before using a new knife, you should use a fine oilstone to gently grind the front and back of the blade teeth a few times to eliminate the need for sharpening the blade teeth. Residual burrs and slight jagged marks. This not only reduces cutting heat but also reduces cutting deformation.

(5) Strictly control the wear standard of the tool

After the tool is worn, the surface roughness value of the workpiece increases, and the deformation of the workpiece increases as the cutting temperature rises. Therefore, in addition to selecting tool materials with good wear resistance, the degree of tool wear should also be strictly controlled, otherwise built-up edge will easily occur. The temperature of the workpiece cannot be too high during cutting to prevent deformation.

(6) Improve the clamping method of workpieces

For thin-walled aluminum alloy workpieces with poor rigidity, if you use a three-jaw self-centering chuck for thin-walled bushing parts Or the spring chuck clamps radially, and the workpiece will inevitably deform once it is released. Locate the inner hole of the part and insert a self-made threaded mandrel into the inner hole of the part. Use a cover plate to press the end face and tighten it with a nut. The outer circle can avoid clamping deformation and obtain satisfactory accuracy.

(7) Selection of cutting oil

Due to the low hardness and poor machinability of aluminum alloy, the cooling, lubrication, penetration and cleaning performance of the cutting oil are higher. Requirements, in addition, certain anti-corrosion properties are needed to prevent the workpiece from turning black. Commonly used cutting oils can form high-melting-point sulfides on the metal surface during the cutting process, and are not easily damaged at high temperatures. They have good lubrication and have a certain effect. Cooling effect, generally used in cutting, drilling, reaming and tapping processes.