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Mechanical processing which factors will cause the workpiece deformation
Dec 21, 2017

In particular, the structure of large parts should be more reasonable. Before processing, the defects such as hardness and porosity should be strictly controlled to ensure the quality of the blank and reduce the deformation of the workpiece.

1.Deformation of the workpiece during clamping

When the workpiece is clamped, the correct clamping point should be selected first, and then the appropriate clamping force is selected according to the position of the clamping point. Therefore, as far as possible, the clamping point and the supporting point should be consistent so that the clamping force will act on the support. The clamping point should be near the machining surface as far as possible, and the location of clamping deformation is not easy to be selected by force.

When there are several clamping forces acting on the workpiece, the order of clamping force should be considered. For the contact force between workpiece and support, the clamping force should not be too large. For balancing the cutting force, the clamping force should be applied at last.

Secondly, the contact area between the workpiece and the fixture should be increased or the axial clamping force should be adopted. Increasing the rigidity of parts is an effective way to solve the clamping deformation. However, due to the shape and structure characteristics of thin-walled parts, it has low rigidity. In this way, the deformation can be produced under the action of clamping force.

The increase of the contact area between the workpiece and the fixture can effectively reduce the deformation of the workpiece clamping. As in Milling Thin-walled Parts, the extensive use of the elastic pressing force is to increase the contact area of the parts; in outer diameter and thin cover turning, either by opening or the use of a simple transition ring, elastic core shaft, the whole arc claw, is used by large workpiece contact area when the clamping. This method is helpful to load the clamping force and avoid the deformation of the parts. Axial clamping force is also widely used in production. Design and manufacture of special fixture can make clamping force on the end face, and solve the bending deformation of workpiece caused by thin wall and poor rigidity.

2.Deformation of workpiece during machining

In the process of cutting, due to the effect of the cutting force, the elastic deformation to the direction of force is produced, which is the phenomenon that we often say. To deal with such deformation should take corresponding measures to the tool, the precision machining requirements of cutting tools sharp, one can reduce the friction of the tool and the workpiece forming resistance, heat dissipating capacity. On the other hand can improve the cutting workpiece, thereby reducing the residual stress on the workpiece.

For example, when milling large part of thin-walled parts, using single edge milling method, tool parameters choose larger main angle and larger front angle, so as to reduce cutting resistance. Because this cutting tool is easy to cut and reduces the deformation of thin wall parts, it is widely used in production.

In turning thin walled parts, a reasonable tool angle is critical for cutting force, turning deformation and surface micro quality. The size of the front angle of the cutter determines the sharpness of the cutting deformation and the front angle of the tool. The front corner is large, and the cutting deformation and friction force are reduced. But the front angle is too large, which will reduce the wedge angle of the tool, reduce the strength of the cutter, reduce the heat dissipation of the cutter and accelerate the wear. Therefore, when the thin-walled parts of steel parts are generally turning, the front angle is taken from 6 to 30 degrees with high speed cutting tools, and the front angle is taken from 5 to 20 degrees with hard alloy cutting tools.

The rear angle of the cutter is large, the friction force is small, and the cutting force decreases accordingly, but the back angle too large will also weaken the tool strength. When turning thin walled parts, the cutting angles of high-speed steel turning tools are 6 to 12 degrees, the carbide tools are used, and the rear corners take 4 to 12 degrees. When the car is picked up, the larger rear corners are taken, and the smaller rear corners are smaller when the rough car is used. When the inner and outer circle of the car's thin wall parts are taken, the main angle of the main body is taken. The correct choice of cutting tools is a necessary condition for the deformation of the workpiece.

The heat produced by the friction of the tool and the workpiece in the processing will also make the workpiece deformed, so high speed machining is chosen in many times.  In high-speed machining, because the chip is removed in a relatively short period of time, most of the cutting heat by cutting away, reducing the thermal deformation of the workpiece; secondly, in high speed machining, the cutting material softening part decreases, also can reduce the deformation of parts processing, is beneficial to ensure the parts size, shape accuracy. In addition, the cutting fluid is mainly used to reduce the friction in the cutting process and to reduce the cutting temperature. The rational use of cutting fluid plays an important role in improving the tool's durability, surface quality and machining precision. Therefore, in order to prevent the deformation of parts, it is necessary to reasonably use the full cutting fluid.

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