The pipe bending machine bending head is equipped with important parts such as the pipe bending die and the spindle. Pipe clamping is achieved through the clamping cylinder and clamping screw. Tube rotates with the bending die. In the case of bending a larger diameter tube, while the bending radius is small, and the tube wall is thin, wiper die and ball mandrel should be used.
When the tube is bent, the material inside its centerline is compressed, and when bent to a certain angle, the material will be pushed back and over the tangent point due to the high material compression force, and if this area of the tube wall is not supported by the bending die, wrinkles will form. Even if later flattened by the mandrel and the bending die, the wrinkles can not be eliminated. And when the bend is over, a large wrinkle will form on the tube. The use of an wiper die increases the support in this area and allows the tube wall to thicken evenly after compression without wrinkles.
The shape of the wiper die is very important. The slot through which the tube slides should be slightly larger than the outer diameter of the tube, the value can be 10% of the wall thickness, and it should also be polished carefully to prevent the tube from scratching.
The front end of the wiper die should be made very thin, reaching to the cutting point of the bending die, supported by the bending die, and fixed to form a closed cavity. In order to reduce the resistance when bending, the wiper die should be installed with a small taper. The pressure of the press die should be adjusted properly. When installing and adjusting the wiper die, it is better to use the “adjusting mandrel” and do it with the clamping die clamped.
During the bending process, the wiper die should be coated with a moderate amount of lubricant. However, too much or too thick lubricant can also create wrinkles in this area. While using the wiper die, the ball mandrel is often used at the same time. The wiper die is used to prevent the tube from wrinkling when bending; while the ball mandrel keeps the tube from collapsing after leaving the mandrel support point, which supports the tube.
When bending thin-walled, large diameter, small radius tube, in order to avoid wrinkles, the following points should be noted.
- Reduce the resistance between the mandrel and the inner wall of the tube during bending. Before bending, the tube inner cavity should be clean.
- The machine body and spindle should have enough rigidity.
- The mandrel rod should be rigid enough to eliminate the trembling and stretching produced by the rod as much as possible.
- The radial clearance between the mandrel and the inner diameter of the tube should not be greater than 10% of the wall thickness.
- Clamping die, pressure die, mandrel, wiper die should be properly adjusted, especially the pressure die pressure should be more carefully selected and adjusted. Bending large diameter pipe, clamping die clamping is also a prominent problem. The straight distance between the two bends should be as longer as possible, so that the clamping die can be made wider to increase the clamping force, which can ensure smooth bending. If the clamping die is too narrow, there is not enough clamping force when bending, the pipe will slip, so that the bending can not be carried out.
- Choose the right amount of lubricant.