The bending process for pipes and profiles holds a crucial position in various industries such as metal structures, agricultural machinery, construction equipment, transportation, boilers, chemical engineering, and power machinery. It encompasses a wide range of metals, including commonly used steel, copper, and aluminum, as well as various alloys and other metals. Apart from their extensive use in gas and liquid pipelines, pipes and profiles are also frequently employed in metal structures.
Although the nature and characteristics of deformation in pipes, profiles, and sheet metal bending are similar, there are significant differences in terms of process methods, challenges to overcome, product defects and preventive measures, and the use of bending tools and equipment.
The 5 key factors in the bending process for pipes and profiles
- Applying appropriate external forces or torque to ensure that improper loading does not lead to distortion or localized collapse of the cross-sectional shape.
- Employing suitable methods or taking necessary measures to prevent distortion of the cross-sectional shape within the bending deformation zone.
- Utilizing simple and practical bending tools and equipment.
- Ensuring a certain level of productivity.
- Commonly used bending methods for pipes and profiles in production include: compression bending, roll bending, stretch bending, push bending, rotary bending, and other methods.
Compression Bending Method
In compression bending, the working surface of the die matches the shape of the bent pipe or profile to establish optimal contact, preventing damage to the pipe or profile during bending. Throughout the bending process, air cushions support the two movable arms, ensuring the workpiece remains in a suitable bending and stress condition. This bending method is suitable for components with large curvature radii. To prevent distortion of the cross-sectional shape during bending, two mandrels can be placed inside the pipe. The mandrels, which are straight, gradually exit during the compression bending process without hindering the bending deformation.
Roll Bending Method for Pipes and Profiles
The roll bending method and working principle for pipes and profiles are identical to those used for sheet metal bending, with the difference lying in the fact that the rolling rollers for pipes and profiles have working surfaces that match the shape of the bent cross-section.
Stretch Bending Principle
Stretch bending is suitable for components with large curvature radii. When bending profiles, the working surface of the fixed die should be designed with a groove that matches the shape of the raw material’s cross-section to prevent rotation and distortion of the section. Due to the difficulties in maintaining the shape of the cross-section during bending, stretch bending is not commonly used for pipes, especially in the bending forming of thin-walled tubes.
Rotary Bending Principle
Rotary bending with a revolving die can only shape parts with a constant curvature radius, while rotary bending with a fixed die can shape parts with varying curvature radii. To prevent distortion of the cross-sectional shape in the bending deformation zone, mandrels are placed in the straight sections of the bent tube. During the bending process, the tube progresses continuously while the mandrels remain stationary. The shape and position of the mandrels are crucial, as they greatly influence bending deformation, friction resistance, and the quality of the bent tube.
Push Bending Principle
The intended bent tube is placed inside a guiding sleeve. Under the action of the thrust force from the convex die, the workpiece passes through the hole in the concave die and is bent into the shape shown in the diagram. The ends of the bent tube are prone to collapse during the bending process, so a mandrel is placed inside the tube, which is pushed out together with the bent tube by the convex die. To obtain a smooth end of the bent tube, the end of the raw tube should be shaped into the inclined surface
shown in the diagram. This method is suitable for producing bends without straight sections and with small bending radii.
Other bending methods include resistance local heating bending, induction heating without tool bending, vibration bending, and various other forms.