Antenna panel forming machine for Vertex Communications, Kilgore, Texas: (1994)
H. Tezcan (H. E Tezcan & Associates/T Square, Inc.) Researched, Procured, Overhauled and sold a used longitudinal stretch forming machine (Sheridan Gray) to Vertex Communications (now part of General Dynamics) for their antenna panel skin production. The company was outsourcing the most critical process of their production and was looking for an alternative to bring this process in house. Besides our involvement with the procurement of the stretch forming machine we also assisted Vertex Manufacturing department in improving their antenna panel forming fixtures and dies. The overhauled used machine which was previously used by an aircraft parts manufacturer cost Vertex a fraction of what a new custom designed machine would have cost. We also designed and constructed a new larger and more agile set of grip jaws to accommodate a wider range of panel forming sizes.
The introduction of this ‘in-house’ stretch forming machine and process helped Vertex to fully control the quality of the panel surfaces (by drastically improving the surface tolerances to better than 0.005” RMS), reduced and standardized the cost of panel forming and considerably improvement their overall antenna panel products in a very short period of time.
What is Sheet Stretch Forming?
The basic principle of this technology is to stretch the material above the elastic limit in order to reach the plastic mode so that permanent elongation with less spring back is obtained.
The sheet to be formed is stretched around a tool through a traction force applied on the sheet. This force induces a traction stress in excess of the yield point of the material.
To apply this traction force, the sheet is held at both ends in gripper jaws. The latter are mounted on stretching heads which ensure positioning and stretching of the sheet.
The kinematics generated by the machine to the set of jaws allows bringing the part in a direction tangential to the tool throughout the forming operation.
Stretch forming is widespread in the aerospace industry. It allows the manufacture of large parts, most often made of aluminum, with lower tooling costs than those of the drawing tools, as a single run is required to form the part, on a single die.
On the work piece:
- gives very low and homogeneous residual stresses,
- greatly reduces spring back,
- allows without deformation, machining or assembling operations,
- increases hardness by about 2 %,
- allows the production of long sheets
- allows a final normalized metallurgical state of the product after completion of the forming phases.
On the press and the tool:
- allows simple and fast tools changeover,
- finished product matching the shape of the tool,
- cheap form tools (1 form instead of 1 die + 1 punch) : about one-third of conventional tools,
- Maximum Die Table Force 1200 Tons
- Sheet Jaw Tension Force 1500 Tons
- Sheet Length Capability 480″ (720″ with extensions)
- Curvable Jaws Handle over 100″
- Jaws Rotates, Oscillates, & Swings to match tengency pull-off from the die
- Jaws move inboard and outboard
Watch a 3d Video animation of Sheet Stretch Forming Press in Action (courtesy of Cyril Bath Co.):
Pictures of the Vertex stretch forming machine installation: