How to prevent bending defects in automatic pipe bending machines

To prevent or mitigate bending defects in automatic pipe bending machines and achieve satisfactory bending quality, corresponding countermeasures should be taken during the bending process. Firstly, within the limits allowed by the product design structure, the bending radius of the pipe fittings should be designed to be as large as possible. Secondly, when purchasing equipment, automatic pipe bending machines with side-assisted pushing and tail-end jacking mechanisms should be selected.

In general, for the common defects mentioned above, targeted measures should be taken, and specific methods can be implemented as follows:

(1) For pipe fittings on automatic pipe bending machines that suffer from severe flattening on the outer side of the arc, the clamping die (wheel) can be designed with an anti-deformation groove to reduce or eliminate the flattening during pipe bending when performing mandrel-less bending. For mandrel-driven bending, when the mandrel diameter is too small or severely worn, a suitable mandrel should be replaced. The single-sided gap between the mandrel and the inner wall of the pipe should not exceed 0.5mm, and the lead-in amount when installing the mandrel should be appropriate. In addition, when installing the mold, it is necessary to ensure that the pipe groove axis of each component is on the same horizontal plane.

(2) Thinning of the outer arc during small-radius pipe bending is determined by the characteristics of the bending process and is unavoidable. However, measures should be taken to overcome excessive thinning. A commonly used and effective method is to use an automatic pipe bending machine with a side-mounted assist device or a tail-mounted jacking device, or both. In this way, the assist or jacking mechanism pushes the pipe forward, offsetting some of the resistance during pipe bending, improving the stress distribution on the pipe cross-section, and causing the neutral layer to shift outward, thereby reducing the thinning of the outer pipe wall. The assist and jacking speeds should be determined according to the actual bending situation to match the bending speed. At the same time, the advance of the mandrel installation should be checked to ensure it is appropriate. If it is not, necessary adjustments should be made.

(3) For cases of cracks on the outer side of the pipe’s arc, the cause should be carefully analyzed. First, ensure that the pipe has a good heat treatment condition. The weld seam of the welded steel pipe should not be directly opposite the clamping die and bending wheel die. After eliminating factors related to the pipe, check whether the pressure of the clamping die is too high and adjust it to an appropriate pressure. For newly used mandrels, check whether their diameter is too large. If the diameter is too large, necessary grinding should be performed, and good lubrication between the mandrel and the inner wall of the pipe should be ensured to reduce bending resistance and friction between the inner wall of the pipe and the mandrel. At the same time, appropriate measures should be taken to avoid machine tool vibration, etc.

(4) For wrinkles on the inner side of the arc, corresponding measures should be taken according to the wrinkle position. If the wrinkles are at the front tangent point, the mandrel position should be adjusted forward to make the mandrel advance appropriately so as to achieve reasonable support for the pipe during bending. If the wrinkles are at the rear tangent point, anti-wrinkle blocks should be installed and the anti-wrinkle blocks should be installed in the correct position so that they can fit well with the bending die. The pressure of the clamping die (wheel) should also be adjusted to make the pressure appropriate. If the inner side of the arc is full of wrinkles, in addition to adjusting the clamping die (wheel) to make the pressure appropriate, the diameter of the mandrel and the pitch between each section of the ball joint mandrel should also be checked. If the diameter is too small or the wear is severe, the mandrel should be replaced.

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