Today, five drawing processes of pipe material are introduced.
1. empty sinking
Empty sinking refers to the production mode of no mandrel placed in the tube blank during drawing, which is one of the most commonly used drawing methods in pipe material production. This kind of technology can be used for the common pipe material which only controls the outer diameter and the size accuracy is not very high, but it is not suitable for the high-precision pipe material which needs to control the inner diameter.
2. Fixed short mandrel drawing
When drawing with fixed short mandrel, the inner mandrel of the pipe material is built-in, its metal deformation is more uniform than that of the empty drawing, and its inner diameter dimension accuracy and inner surface quality are higher than that of the empty drawing. However, in order to produce high-precision pipe material with small inner diameter dimension deviation, it is difficult to meet the requirements of the standard by using ordinary short mandrel drawing method.
3. Long mandrel drawing
The deformation characteristics of long mandrel drawing and fixed short mandrel drawing are similar. The difference is that when the long mandrel is drawn, the mandrel is pulled out from the die hole along with the pipe material, and the friction between the mandrel and the pipe material is in the same direction as the drawing force. The long mandrel drawing process is beneficial to reduce the drawing force, increase the pass deformation, and process the pipe material with low plasticity and thin wall.
4. Swaying core pulling
At present, the floating core drawing is an advanced production method for pipe material production. Its deformation characteristics are similar to that of fixed short core rod drawing, and it is mostly used for long pipe material drum drawing. During drawing, the core head is in a free state, and it is stable in the deformation area depending on its own special shape, so as to realize the reduction of pipe material blank diameter and wall. In the straight line drawing, the drawing process of moving core and fixed end core is similar, and there is no obvious advantage. This method is not suitable for the production of large-scale pipe material. At the same time, due to the uneven material, unstable drawing force, unstable processing equipment, and the influence of environment and lubrication conditions, the stability of the core head is not easy to control, and the size accuracy of the controlled pipe material is not high, so this method is only suitable for the mass production of ordinary pipe material.
5. Expanding and drawing
The method of expanding diameter is to produce large-scale pipe material with small-scale tube blank. After expanding diameter of pipe material increases, length and wall thickness decrease. This method can be used to control the inner diameter accuracy of pipe material. Expanding method is divided into drawing expanding and pressing expanding.
Drawing expanding can be divided into tube drawing and core rod drawing. Special device is needed to fix the pipe material blank when pulling the core rod, and the vibration of the core rod in the drawing process will affect the dimensional accuracy of the pipe material. When drawing the tube, there is the problem of how to put the core into the tube blank and how to start the tube blank in advance.
The drawing expanding method is suitable for the production of thin-walled long pipe material with small cross-section. The press in expanding is suitable for the pipe material with large diameter and short length. If the pipe is too long, it is easy to lose stability, thus increasing the deviation of the inner diameter. Generally, the press in expanding is carried out on the hydraulic drawing machine, while the hydraulic drawing machine with good stability has relatively high price and is not easy to promote.
When the pipe material is produced by expanding method, the outer wall of the tube is always in the state of free deformation, the inner wall is in the state of high stress processing, and the stress gradually decreases from the inside to the outside. After drawing, the inner wall of the tube is in the state of free recovery. The high stress state results in a large amount of elastic recovery after drawing and a large size change of the inner diameter. Therefore, the size accuracy of the inner diameter is not easy to control.