Canadian aerospace metal forming: A survey of equipment and processes
by Del Williams, Technical Writer
Partnering with a metal forming professional provides aerospace manufacturers with the specialized equipment and expertise required to customize the process.
Within Canadian aerospace manufacturing, a wide variety of heavy-duty metal forming, hydraulic presses with capacities of 10,000 tons or more are required to bend, form, bond, or straighten aluminum, Titanium, and alloys into structures and components such as fuselages, spars, and airframes.
On the production floor, specialized machines such as stretch forming presses, hot stretch straighteners, contour rolls, superplastic forming presses, diffusion bonding presses, and powdered metal compaction presses are often required to manufacture to custom aerospace specifications under process-specific applications of pressure and temperature.
Because these machines are customized and require precise controls and processes to reliably achieve the specified final product, partnering with a manufacturer with deep expertise in such metal forming is frequently 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 aerospace applications. The company was acquired by Park Ohio and is now a part of the largest forging equipment supplier in North America: Ajax-CECO-Erie Press.
Drawing on Erie Press’s decades of experience in Canadian aerospace applications, Goodwin surveys some of the essential equipment utilized in custom metal forming.
Stretch Forming Machines:
When applicable, stretch wrap forming methods provide several unique advantages over pure bending and other types of metal forming. Stretch wrap forming machines operate by stretching the metal to its elastic limit, then wrapping the part around a forming die. This process increases the metal’s yield strength and results in a stronger part. Since stretch forming machines also keep the metal under constant tension throughout the process, they minimize imperfections such as “cans” or “buckles.”
Sheet Stretch Forming:
According to Goodwin, stretch forming machines for sheets are designed to meet all tonnage, length, and width specifications. Historically, these machines have been widely used in stretch forming aluminum fuselage, wing, and engine cowl panels. Still, the process has now evolved to forming exterior panels on a high-speed locomotive, recreational vehicles, and buses, as well as proprietary aerospace and commercial rocket applications.
Extrusion Stretch Forming:
Extrusion stretch forming machines were developed within the aircraft industry to bend and form complex aluminum, Titanium, and stainless steel structural components that have been challenging to work with using other manufacturing processes. Due to highly accurate and repeatable part production, extrusion stretch forming machines have also gained wide acceptance in structural applications within high-speed locomotive, rail, transit, and automotive industries.
High Production Rate Stretch Forming:
Aluminum Stretch Forming (ASF) machines have been developed to service the automotive industry’s high production requirements. CNC-controlled AC servo motor technology combines with high-resolution load cells and rigidly guided, low friction components to optimize the speed and accuracy for high production rate stretch forming of extrusions.
Hot Stretch Straightener:
This forming machine press is utilized to resistively heat, stretch, and straighten long extruded tubes, or flat plates, because the cooling process after the heated extrusion cycle tends to introduce curvature. When using the hot stretch straightener, the pressure is gradually reduced as the long, extruded metal component cools. This maintains a tensile load on the part, maintaining part straightness during the cooling process.
Contour Roll Forming:
Specially designed for stringers and frames, contour roll forming machines bend and twist on three planes and allow for theoretically unlimited lengths. These multi-axis bending machines are utilized to manufacture rounded, structural aircraft parts, such as those used around a fuselage. Generally, a straight piece is run through the machine, and it is bent and curved to the desired shape.
Super Plastic Forming – Diffusion Bonding Hot Presses:
Superplastic forming (SPF) was developed as an advanced forming process for making complicated and large parts and structures, such as vehicle and airplane components, difficult to manufacture by the traditional forming process. Commonly used materials to form superplastic formed parts are Titanium, aluminum, stainless steel, and magnesium alloys. The superplastic forming process requires high heat. When Titanium and stainless steel reach temperatures between 1400 and 1850 degrees Fahrenheit (about 1000 to 1100 for aluminum), these metals become incredibly malleable.
When in a superplastic state, pressure from inert gasses (mainly argon) forms the metals. As a result, superplastic forming proves especially useful for producing complex shapes out of difficult to shape materials. Created to manufacture engine blades, a variety of applications now employ the use of superplastic forming.
Isothermal forging is a hot working process that attempts to maintain the workpiece at its maximum elevated temperature throughout the entire operation. This is achieved by heating the die to or slightly below the starting work piece’s temperature. As forces exerted by the die form the work, cooling the workpiece between the mold work interface is eliminated, and thus, the flow characteristics of the metal are greatly improved.
Powder Compaction Presses:
Sometimes, aerospace manufacturers will take a special blend of metals to achieve certain material properties and turn them into a hybrid powder. After hydraulic presses compact the powder to a specific force, the powder is heated and forged to create a special hybrid piece.
“With powder compaction, aerospace manufacturers spin a powdered material at thousands of RPMs while heating it to specified temperatures. The process produces two different metals: a lower-cost metal at its base and a very high-cost metal at its skin. The process then compacts the two layers of powder together and uses this as a raw material to forge into a final multilayered piece,” explains Goodwin.
The Future of Canadian Aerospace Metal Forming
With all the demands placed on aerospace manufacturers for lighter, stronger materials and greater efficiency, innovation must be a priority even within metal forming.
“In the next 5 to 10 years, instead of hydraulic drives, we expect electric presses driven by geared servo motors and larger roller screws to become increasingly important to aerospace manufacturers for any application that is sensitive to oil leaks or where precise control is required. So, we are developing the technology today,” concludes Goodwin.
Teaming up with a partner can provide a wide range of specialized, high-tonnage machinery, that can future-proof an aerospace manufacturer’s operations heading into a post-pandemic economy.