Capps Manufacturing is one of an elite few sheet metal fabricators in the world specializing in sheet metal stretch forming. Sheet metal stretch forming is exceptional for producing complex shapes. Compared to drawn or rolled parts, stretch formed aircraft parts offer better shape control and surface quality.
What Is Stretch Forming?
Stretch forming is a metal forming process that shapes pieces of sheet metal into large, contoured aircraft parts by simultaneously stretching and bending them over a die. There are a wide range of applications for using stretch formed parts in the aerospace industry.
The Stretch Forming Process
The stretch forming process involves applying both plastic and elastic deformation to a metal blank. It begins by placing the blank on a die table and securing it with hydraulic holding jaws. The stretch press grips the piece of sheet metal securely along its edges using gripping jaws which are attached to a carriage that’s pulled by pneumatic or hydraulic force, stretching the sheet.
The tooling used in this process is a solid, contoured stretch form block, called a form die. A ram-driven punch stretches the material over the die to produce the desired shape. When the workpiece is unloaded, it retains the plastic deformation.
Stretch Forming Equipment
Stretch forming equipment excels at producing complex shapes in metal sheets, plates or extrusions. The hydraulic system for stretch forming equipment consists of a power unit and a ram. With some stretch forming equipment, there are separate cylinders operating each arm.
Types of Stretch Forming Equipment
Stretch forming equipment is generally categorized into two types: longitudinal (vertical) and transverse (horizontal).
Longitudinal Stretch Forming Equipment
Longitudinal equipment stretches the workpiece along its length. Stretch presses are most often oriented vertically with the form die resting on a press table. A hydraulic ram then raises the form die into the sheet of metal. This increases tensile forces, causing the sheet to plastically deform into the desired shape.
Transverse Stretch Forming Equipment
Transverse stretch forming equipment, or horizontal stretch presses, stretch the workpiece along its width. In this case, the form die is mounted sideways on a stationary press table. Then, the gripping jaws pull the sheet sideways (horizontally) around the form die.
Advanced Features for Modern Stretch Forming
Stretch forming equipment can be connected to a computer and may include features like computer numeric control (CNC) and a built-in console. In the case of CNC machines, the operator programs the jaw radius instead of manually adjusting locking screws for each jaw assembly. There is also software made specifically for stretch forming equipment.
