Aerospace heavy-duty metal forming requires hydraulic presses with capacities of 10,000 tons or more to bend, form, bond, or straighten aluminum, titanium, and exotic alloys into fuselages, spars, and airframes. Specialized production floor machines – stretch forming presses, hot stretch straighteners, contour rolls, superplastic forming presses, diffusion bonding presses, powdered metal compaction presses – manufacture parts to custom aerospace specifications applying process-specific pressures and temperatures.
These customized machines require precise controls and processes to reliably achieve the specified final product. So, partnering with a manufacturer with deep expertise in metal forming is essential for success.
“A custom-engineered machine and control solution is often required when precise control of position, axis synchronization, force, and heat-and-force is essential for the forging/forming process,” says Bill Goodwin, vice president of Sales and Engineering at Erie Press Systems, a company that manufactures custom-engineered hydraulic presses for metal forming, stretch forming, composite compression molding, cold extrusion, and forging. The Park Ohio subsidiary is part of Ajax-CECO-Erie Press. Drawing on Erie Press’ decades of experience in aerospace applications, Goodwin reviews some essential custom metal forming equipment.
Stretch forming has several advantages compared to pure bending and other types of metal forming. Stretch wrap forming machines stretch the metal to its elastic limit, then wrap the part around a forming die, increasing the metal’s yield strength and resulting in a stronger part. Stretch forming machines keep metal under constant tension throughout the process, minimizing canning or buckling imperfections.
Stretch forming machines also perform tasks in one step, saving time and money. For some parts, stretch forming enables production runs that would otherwise be impossible.
Sheet stretch forming machines are designed to meet all tonnage, length, and width specifications, Goodwin adds. Historically, these machines have been used in stretch forming aluminum fuselage, wing, and engine cowl panels. The process has evolved into forming exterior panels for other aerospace and commercial rocket applications. Additionally, specially adapted, high-tonnage stretch forming machines can manufacture main structural support spars for large commercial aircraft. Heavy cross-section beam material is gripped in specially designed jaws, stretched to its yield point, and bent over a die that follows the plane’s curvature.
Extrusion stretch forming was developed within the aircraft industry to bend and form complex aluminum, titanium, and stainless-steel structural components that are challenging to work with using other processes. Due to highly accurate and repeatable part production, extrusion stretch forming machines have also gained wide acceptance in structural applications in other industries.
“Aluminum tends to wrinkle if bent. However, the stretch forming process can eliminate those defects because the first step is stretching the part to yield, and then bending it so you can bend extrusions without wrinkling,” Goodwin says.
High production rate stretch forming uses aluminum stretch forming (ASF) machines, with CNC-controlled AC servo motor technology combined with high-resolution load cells and rigidly guided, low friction components to optimize speed and accuracy. ASF machines are ideal for stretch-forming extrusions with profiles up to 90° total bend angles.
ASF machines use two vertically mounted jaw carriage assemblies to apply full stretching and forming force on the part against a stationary die. Jaw assemblies automatically center and clamp the piece, program tangency tracking, engage a support mandrel into hollow extrusions, and provide an inertia suppression system to prevent machine damage if a part breaks during forming.
Read more: Aerospace metal forming