The common roll bending machine has two forms 3-roll and 4-roll, and their working principle is that three points form a circle. Compared with the 3 roll bending machine, the 4 roll bending machine has two side rolls and one lower roll, so here we are the four-roller bending machine to explain the principle and analyze the process.
The 4 roll bending machine has many advantages such as convenient centering, small remaining straight sides, pre-bending without other auxiliary equipment, high production efficiency, etc., and it occupies an increasingly important position in profile and sheet metal/plat roll forming.
Four steps in the roll bending process of the 4-roll bending machine
In order to prevent the metal sheet/plate or profile from being skewed during bending and causing the parts to be scrapped after roll bending, it is necessary to center the edge of the profile before bending to ensure that the end face of the metal sheet/steel plate or profile and the generatrix of the side roll are parallel to each other. It is a major feature of the four-roll bending machine to align directly on the equipment without the need for other auxiliary tools. As shown in Figure 1, the alignment is carried out directly on the four-roll bending machine.
The main three steps of metal sheet/profile alignment are as follows:
(1) The lower roll rises to clamp the profile;
(2) The left and right side rolls rise to the calculated position;
(3) The top roller rotates to drive the metal sheet/profile to feed until the left end surface of the workpiece contacts and aligns with the busbar of the left side roll to complete the centering.
During roll bending, because there is a certain distance between the driving roll and the side roll in the horizontal direction, there will be a section of material at the end of the profile that is not in contact with the side roll and remains in a straight state, which is called the remaining straight edge/unbent flat end. The existence of remaining straight edges will not only waste materials but also easily cause greater weld stress, resulting in equipment quality problems. On a four-roll bending machine, the asymmetric distribution of the position of each roller can be used to pre-bend the end of the part without using other equipment or molds, as shown in the figure.
The main steps of profile/steel plate pre-bending are as follows:
(1) On the basis of centering, the left roll drops to the corresponding position;
(2) The top roll reverses to drive the profile/steel plate to move in reverse to the left end of the profile/steel plate with a corresponding margin;
(3) The right side roll rises to the corresponding position, and at the same time, the top roll rotates positively to drive the profile/steel plate to move forward for pre-bending.
Continuous roll bending
As shown in the figure, continuous roll bending is the main process of roll bending. During this process, it is necessary to strictly control the speed and position of the top roll and the feed rate of the side rolls. According to the thickness of the roll-bending profile/steel plate web, two methods of one-time forming and multi-pass forming can be selected.
The main steps of continuous roll bending are as follows
(1) On the basis of pre-bending, the right roller descends to the corresponding position, and the left side roll rises to the corresponding position;
(2) The top roll rotates forward to drive the profile/steel plate feed to complete continuous bending.
After completing the continuous roll bending process of the profile/steel plate, return each roll to its original position.