Stretch forming process:
Stretch forming process is a dieless punch system. The die is also called as form block or tool. The stretch forming consists of gripper mechanism which is supported by hydraulic unit of holding the sheet metal. The system having set of gripper is used to stretch the sheet metal. The die depends on the final require shape of product. when the die is support on the rotating table as shown in figure. First, the sheet metal is stretched to its yield point by tension process and then wrapped over the die shape. The metal is stretched by using two gripper mechanisms which is support by a hydraulic system. Then the die become forward at same time the gripper mechanisms are turned through turn table. These forms of shape die on sheet metal.
The die movement may be upward, downward or slid ways depends on machine type. The dies are stretched the sheet material such as zinc alloy, wood and steel. During the stretch forming process the lubrication required. In this stretch forming, all the types of fiber can be stretched, but inside of stretched metal less than compare to outside. When the process, the deformation is restricted on the area with in the tool. Some failure occurs through localized necking.
The sheet metal is consist of tensile load, there is less tendency to spring back. But that is reduced when compare to other forming process. And allowances must be made dimensional changes occurred. During stretch forming process the length of sheet metal increased at same time width decreased.
The stretching forming classified depends on the conventional die system.
- The sheet metal is stretched the form block move to form shape.
- The gripper is stretched first and then wrapped around the form block. This method mostly avoids friction and die made up out of inexpensive metal.
- The tooling lost reduced
- Spring back will be less
- Low friction
- It is fast as compare to drawing
- Tearing and wrinkling of metal is less
The stretch forming produce either simple shape components the cylindrical cups, or more complicated press shape can be obtain.
- Windows frames
- Automobile door panels
- Cylindrical cups
- More complicate press shape
- Aircraft wing- skin panels
- The process suitable for low volume production in air craft industry.