Stretch forming is performed on a stretch press, in which a piece of sheet metal is securely gripped along its edges by gripping jaws. The gripping jaws are each attached to a carriage that is pulled by pneumatic or hydraulic force to stretch the sheet. The tooling used in this process is a stretch form block, called a form die, which is a solid contoured piece against which the sheet metal will be pressed. The most common stretch presses are oriented vertically, in which the form die rests on a press table that can be raised into the sheet by a hydraulic ram. As the form die is driven into the sheet, which is gripped tightly at its edges, the tensile forces increase and the sheet plastically deforms into a new shape. Horizontal stretch presses mount the form die sideways on a stationary press table, while the gripping jaws pull the sheet horizontally around the form die.
Stretch formed parts are typically large and possess large radius bends. The shapes that can be produced vary from a simple curved surface to complex non-uniform cross sections. Stretch forming is capable of shaping parts with very high accuracy and smooth surfaces. Ductile materials are preferable, the most commonly used being aluminum, steel, and titanium. Typical stretch formed parts are large curved panels such as door panels in cars or wing panels on aircraft. Other stretch formed parts can be found in window frames, boat hulls, architectural shapes and enclosures.
In the automotive industry in particular, stretch forming dies are used to shape body panels. The blank is clamped over the die cavity and the punch is brought down to press the work piece. Because the blank is clamped around its edges, the material stretches and thins as it is formed. In the aerospace industry the process can be slightly different. Instead of using both a punch and die, the material is clamped and stretched over the forming die to produce aircraft skins. An old craft, a modern process: People have been bending metal for centuries, but stretch forming is a relatively new process born from the aeronautic industry’s need to maintain precise dimensions throughout a curve while limiting, or even eliminating, wrinkling inside the arc. Heat and press: Most metals can be stretch formed, although aluminum is by far the most common. In simplest terms, stretch forming is a way of bending metal into a desired shape—usually curved—by heat treating it then pressing it over a die. Stretchforming – Process for Lineal Shapes| |
Loading: Both ends of the part are inserted in gripper jaws, themselves mounted on swing-arm.| |
Pre-Stretching: The part is stretched to its yield point.| |
Wrapping: The part is wrapped around the form die while the stretch force is continuously maintained.| |
Release: When the wrapping is completed, the stretch force is released and the gripper jaws are opened.|
Don’t try this at home: As with other ways of curving metal, stretch forming is both difficult and delicate, requiring advanced technology, experienced management and skilled, highly trained metal workers. Our standards: At Southern Stretch Forming, our customers know they can count on the right equipment, mature management and knowledgeable workers to realize their projects. Southern Stretch Forming is committed to an ethic that has guided our business from the beginning: customer service means customer satisfaction. Our credo is simple: until the customer is satisfied, the job isn’t done.
STRETCH FORMING makes possible the shape of the modern world. Stretch forming turns a straight aluminum extrusion into a vital component of contemporary structures: a hotel skylight, a contoured sign, a mall archway or a skyscraper’s glass and metal facing. Like many modern technologies, stretch forming may not be a household word, but without it, our houses and buildings and cities would look very different. Stretch forming frees architects, designers and builders to realize forms as graceful as they are sturdy and functional. From the delicate barrel vaulting of a solarium to the bold contours of a superstore sign, stretch forming makes possible all sorts of shapes – including the shape of tomorrow. Southern stretch forming and fabrication-texas
| Stretch-draw forming is the process of cold forming sheet stock over a forming block by a mating die of the desired shape while the workpiece is held in tension. The workpiece material is extended just beyond the yield point to retain the desired shape. Bar, rolled, and extruded stock may also be used.Process Characteristics | Uses flexible low cost tooling| | Produces large parts at a reduced weight|
| Reduces material thickness by 5% to 7%|
| Increases yield stress up to 10%|
| Requires less forming pressure|