1. Field of the Present Invention
The present invention relates to a coil spring end forming apparatus and a coil spring end forming method. More specifically, the present invention relates to a coil spring end forming apparatus and a coil spring end forming method for forming a pigtail portion at the end of a coil spring.
2. Description of the Related Art
In a suspension device of an automobile, a combination of a coil spring as a spring device and a shock absorber inserted into the inner side coil spring is widely used. In such suspension device, a direction of an input from a tire is not always matched with the axis of the shock absorber. Each time there is a vibration input from the tire to the shock absorber, a lateral load acts on the shock absorber. The lateral load acts between a piston and a cylinder of the shock absorber to cause sliding resistance. The riding comfort of the automobile can be deteriorated and the life of the shock absorber can be shortened.
As a method for solving the above problems, there are a method for mounting a coil spring so as to be offset with respect to the axis of a shock absorber and a method for forming pigtail portions having a pigtail shape at both ends of a coil spring and offsetting the axes of the pigtail portions with respect to the axis of a large-diameter portion of the coil spring.
When a pigtail portion is formed at the end of a coil spring, there is widely used a pigtail forming apparatus which forms, at the end of a semi-formed spring in a cylindrical coil shape, a pigtail portion as a conical winding portion whose diameter is gradually reduced toward its edge.
The pigtail forming apparatus typically has a forming jig driven rotatably and rotated while holding the open end of a cylindrical coil spring, a first engaging structure for fixing the end of the cylindrical coil spring onto the forming jig while a pigtail portion is formed on the cylindrical coil spring, and a second engaging structure for engaging and restricting a pigtail portion forming start point of the cylindrical coil spring (Patent Document 1).
In the pigtail forming apparatus, the end of the cylindrical coil spring is held by the first engaging structure and the pigtail portion forming start point is held by the second engaging structure. Then, with the end of the coil spring being held by the first engaging structure and the pigtail portion forming start portion being held by the second engaging structure, the forming jig is rotated to form the pigtail portion.
There is proposed another pigtail forming apparatus having clamp means for releasably clamping the open end of a cylindrical winding portion of a semi-formed spring; a platform on which the semi-formed spring is placed horizontally and which can be moved toward or away from the clamp means and can be moved up or down; a first engaging structure disposed on the platform and performing position regulation in the radius direction of the end winding portion of the semi-formed spring; a second engaging structure for regulating axial movement of the semi-formed spring with respect to the platform; rotating means for forcibly rotating the clamp means in the winding direction of the semi-formed spring; a first moving means for forcibly moving up the platform in such a manner that the center axis of the cylindrical winding portion is moved toward the rotation center of the clamp means in the state that the open end of the cylindrical winding portion positioned on the upper side of the semi-formed spring placed on the platform is clamped by the clamp means; and a second moving means for forcefully moving the platform along the center axis direction of the semi-formed spring (Patent Document 2).    [Patent Document 1] Japanese Patent Application Laid-Open (JP-A) No. 2005-349447    [Patent Document 2] Japanese Patent Application Laid-Open (JP-A) No. 2003-290860