What is the diameter changes principle in the pipe, tube drawing process?

In the process of pipe drawing, the pore diameter changes in the following specific laws:

Relationship with drawing pass

· General trend: With the increase of drawing passes, the diameter of the pipe decreases gradually. After each drawing, the pipe will undergo plastic deformation under the action of the mold, and the aperture will be reduced according to a certain reduction amount to gradually reach the target size.

· Rate of change: Generally in the first few draws, the rate of reduction of the aperture is relatively large. Because the size of the pipe at this time is different largely than the original size, the compression effect of the mold on the pipe is obvious, and the pipe can produce a large amount of deformation. With the advance of the drawing pass, the diameter of the pipe gradually approaches the final size, and the rate of the diameter reduction is gradually reduced to avoid excessive deformation or defects of the pipe.

Relationship with material properties

· Malleable materials: such as pure copper, pure aluminum, etc., the pore size changes relatively evenly during the drawing process. These materials can better adapt to the shape change of the mold, under the action of drawing force, can be more smoothly through the mold, the aperture is gradually reduced according to the design law, and it is not easy to appear local deformation is too large or too small.

· High strength, poor ductility materials: such as high carbon steel, some high strength alloy steel, etc., the aperture change may appear uneven when drawing. Due to the large deformation resistance of the material, under the action of the mold, a large stress may be generated on the surface or inside the pipe, resulting in a faster reduction of the aperture in some parts, and a slower reduction in other parts, and even defects such as cracks may occur, affecting the regularity of the change of the aperture.

The relationship with drawing process parameters

· Drawing speed: Within a certain range, drawing speed has an effect on the change of aperture. When the drawing speed is low, the friction time between the pipe and the die is relatively long, the aperture is relatively stable, but the production efficiency is low. With the increase of the drawing speed, the deformation time of the pipe in the mold is shortened, if the speed is too fast, it may lead to local overheating of the pipe, so that the mechanical properties of the material change, and then affect the uniformity of the aperture change, and even the aperture deviation may exceed the tolerance range.

· Lubrication conditions: Good lubrication can reduce the friction between the pipe and the die, so that the force of the pipe in the drawing process is more uniform, and the change of the aperture is more uniform and stable. If the lubrication is insufficient, the increase of friction will increase the deformation resistance of the pipe in the mold, which may lead to uneven reduction of the aperture, but also increase the wear of the mold, further affecting the accuracy of the aperture.

The relationship with the mold structure

· Cone Angle of the mold: The cone Angle of the mold entrance determines the initial deformation Angle of the pipe when it enters the mold. When the cone Angle is large, the deformation of the pipe in the early stage of entering the mold is more severe, and the speed of the aperture is relatively fast, but it may cause the surface of the pipe to be subjected to greater pressure and friction, and it is easy to appear scratches and other defects. When the cone Angle is small, the deformation of the pipe is relatively moderate, and the speed of aperture reduction is slow, but it is conducive to ensuring the surface quality and dimensional accuracy of the pipe.

· Sizing zone length: the sizing zone of the die plays the role of sizing and calibrating the final aperture of the pipe. When the length of the sizing zone is longer, the radial deformation of the pipe can be better limited, so that the diameter of the pipe after passing through the sizing zone is more stable and accurate. However, too long sizing area will increase the friction between the pipe and the die, resulting in an increase in drawing force, which may affect the surface quality of the pipe. If the sizing area is too short, it is difficult to ensure the accuracy of the diameter of the pipe, and the aperture fluctuation may occur.