1. Field of the Invention
This invention relates to a bending machine for preforming bending process on a long work such as a pipe or a bar at various places along the longitudinal direction of the work.
2. Description of the Prior Art
Among conventional bending machines, there is one having the following structure. That is, the bending machine comprises a bend arm mounted on a base frame for turning movement, a bend die disposed coaxially with the center axis of turn of the bending arm and a clamp die provided on the bend arm in order to clamp the work to the bend die. In this machine, the bend arm is pushed, at a point thereof off the center axis of turn, by a drive mechanism and is turned relative to the base frame. The work is bent on the model of the bend die by the turn of the bend arm. The bending machine of this type is exemplified by U.S. Pat. No. 4,552,006.
It is a feature of the bending machine having the bend arm thereof pushed by the drive mechanism that the machine can perform appropriate bending processes on the long work at various places one after another along the longitudinal direction of the work even though spacing between places to be processed is small. This point is explained in details. The bending process is first performed on the work at a first place. Then the work is shifted forwards and a second place of it is positioned between the bend die and the clamp die. In this case, in order to make the direction of bending at the second place be different from that at the first place, for example, by 90.degree., the work is turned by 90.degree. about the center axis of that portion of the work which is not yet processed, i.e., positioned in the backward of the bend die. As the result of this turn of the work, the portion of the work in the forward of the already bent first place is pendant in front of the bend arm. In this situation, the bending process is performed at the second place.
When the bending process is performed in the above mentioned manner, the bending machine having its bend arm pushed by the drive mechanism leaves such a large space in the forward of the bend arm as extending up to a position close by the bend die. Accordingly, even though the first place is close by the second place, the portion of the work in the forward of the first place can be hung in front of the bend arm without any hindrance. Consequently, even though the spacing between places to be processed is small, the bending process can be appropriately performed.
On the other hand, when the work is to be bent by 180.degree., it has to be turned by an angle larger than 180.degree. since the work has a tendency to spring back. In this case, it is impossible to turn the bend arm by an angle larger then 180.degree. by pushing it by a linearly expanding and contracting drive means such as a hydraulic cylinder since there appears than a dead point in the turning movement of the bend arm. For this reason, it is necessary to use, as a drive mechanism for the bend arm, a special drive apparatus, i.e., one comprising a pair of cranks provided separately from each other and adapted to be synchronously turned and a drive link with the forward end thereof connected to the bend arm and the intermediate portion and the backward end thereof connected to the respective cranks. The drive mechanism of this type, however, occupies a large area. Accordingly, it occupies a large space within the base frame and restricts the installation of other various mechanisms to be provided on the base frame.