Curved, finished and complete – What you should know about architectural stretch forming

Henry Ford Int MI

Henry Ford Museum in Greenfield Village, Dearborn, Michigan, built in 1929, was renovated with large, arched top windows using stretch-formed, finished aluminum framing members 
Credit: Courtesy of Wausau Window and Wall Systems

Stretch forming was invented during the 1940s with the rise of the aerospace industry for the curving of aluminum aircraft parts to reduce weight, and thereby, fuel consumption. It expanded into car components and eventually, into the architectural industry. Architects and designers pursued new opportunities to create curved facades and building components.

The process of stretch forming is more of an art, than a science. It takes years of experience to become a skilled craftsperson that can stretch form consistent, successful, curved aluminum components for architectural projects.

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Stretch forming is a metal bending process in which a lineal shape, such as an aluminum extrusion, is stretched and bent simultaneously over a form, called a die.

Stretch forming is a metal bending process in which a lineal shape, such as an aluminum extrusion, is stretched and bent simultaneously over a form, called a die. Each form is built to the required radius. These forms may be customized for a special curvature and used only once, or re-used for more popular, repeating arcs.

Opportunities with stretch forming

Stretch forming capabilities typically include portions of circles, including half-circles and eyebrows, ellipses and arched shapes. These shapes can be formed with straight leg sections at one or both ends of the curve. This method of curving eliminates several conventional fabrication and welding steps.

The variety of shapes and cross-sections that can be stretch-formed is almost unlimited – from muntin bars and panning for windows, cladding and spirals for handrails, large mullions for building envelopes to serpentine shapes for canopies. Stretch forming allows architects, designers and builders to realize forms as graceful as they are sturdy and functional.

In most cases, the stretch-formed aluminum component’s curvature is so highly precise that even intricate multi-components and snap-together curtain wall components can be formed from metal without loss of section properties or original design function.

To achieve this level of precision, the basic stretch-forming machine has two arms or carriage beams that hold multiple-positioning gripping jaws. Both ends of the extrusion are inserted into the gripper jaws and stretched to their yield point. The jaws are attached to hydraulic tension cylinders that stretch the extrusion. The arms swing by rotating on large, machined pins with bearings that allow the extrusion to wrap around and against the form. This produces perfectly contoured products, while limiting or even eliminating wrinkling inside the arc. When the wrapping is completed, the stretch force is released and the gripper jaws are opened.

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It takes years of experience to become a skilled craftsperson that can stretch form consistent, successful, curved aluminum components for architectural projects.

Stretch forming maintains close and consistent tolerances with excellent repeatability, and alignments of complex profiles and compound curves. There should be no visible surface marring, distortion or ripples. These benefits inherent in the stretch forming process yield a smooth and even surface. Each component must meet the project’s specifications and warranty conditions.

Structural vs. non-structural application

Aluminum has proven to be a suitable, reliable material for load-bearing structures for more than 100 years. However, the application of the parts being curved dictates the process used.

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Vancouver’s PARQ Resort and Casino features a 23,000-square-foot façade with curved corners and curtainwall details made possible with stretch-formed aluminum framing members finished in clear anodize.
Credit: Courtesy of Gamma North Corporation

After being pushed through an extrusion press, extrusions are cut and placed into a tempering oven to harden and give them structural integrity. When they are fully hardened to a T5 or T6 temper, they are too hard to curve. If the parts to be curved have been fully tempered, they will need to be annealed before curving. To do this, the part is placed in a large oven and heated to a peak temperature range of 700 to 800 degrees Fahrenheit for two to three hours.

Annealing makes the extrusion soft again—enabling it to be curved. Metal that is annealed cannot be hardened again. Once it is softened, it will remain soft. In applications where the parts are expected to carry a structural load or have another structural application, annealing generally is not an acceptable practice.

PARQ-Vancouver-all-stretchforming-(8WEBFor structural or load-bearing applications, the best practice is to have extrusions tempered to a soft state of T1, T4 or to a T52 state. Material tempered to a T1 or T4 can be bent without annealing, and can be tempered after the curving process to a T5 or T6 that is typical in structural applications. T52 is a very stable temper and can be curved without annealing, and it maintains its properties after curving without the need for additional tempering.

Painted or anodized finishes

Similar to the curving process, the end-use application of the part will determine the best practice for how curved parts should be finished. If an extrusion has been painted or anodized, and has been tempered to a T5 or T6 hardness before being curved, the parts will need to be annealed. The high heat associated with the annealing process likely will cause painted finishes to burn and anodized finishes to discolor or craze. For this reason, when parts require annealing, it is best to finish them after the curving process has been completed.

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Orlando International Airport’s new South Intermodal Terminal Facility showcases a segmented barrel vault skylight featuring aluminum framing that has been stretch formed, thermally improved and finished in Bright Silver 70% PVDF architectural coatings.
Credit: Greater Orlando Aviation Authority

For extrusions tempered to a T1, T4 or T52 hardness, parts can be finished before curving. However, some marring or slight damage to the finished surface should be expected due to the parts being stretched across the form’s hard surface during the curving process. Depending on the tightness of the radius, anodic coatings also may craze or discolor as a result of being curved. If the T1 or T4 tempered extrusions require oven-aged tempering after curving, the high heat will likely damage the coating.

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The stretch forming process yields a smooth and even surface with each component meeting the project’s specifications and warranty conditions.

Regardless of the effect the curving process has on the finish, nearly all manufacturer and applicator warranties are voided when extrusions or brake metal are finished prior to curving. To obtain the best finish quality and to keep parts fully warranted, it is best to finish after curving—regardless of the temper of the extrusion. The American Architectural Manufacturers Association (AAMA) publishes industry-accepted specification standards for anodize and paint finishing of architectural aluminum components.

Thermally improved curves

Rolled-TB-Extrusion-web136At least one U.S. finishing and service provider also offers thermal improvement services for curved and radius, finished aluminum extrusions backed with an industry-leading warranty. The thermal improvement processes may be specified as either a full pour-and-debridge of radius material, both structural and non-structural, or a fully crimped thermal strut system. The service provider places no restrictions to the degree of curvature, and finishes may be specified in liquid paint, powder coat or anodize.

Installing the thermal barrier in the metal after it has been curved helps minimize stress on the thermal barrier and ensures performance as specified. Choosing the thermal strut system provides the additional design flexibility of dual finishing, where the interior and exterior surfaces may be finished in different colors and formulations.

Ensure that aluminum products’ thermal improvement options strictly comply with its material suppliers’ standards and AAMA’s quality assurance processing guidelines. For optimal quality and convenience, some finishers provide a single-source solution where stretch forming, thermal improvement and finishing are synchronized and retain the full warranty. When available, utilizing the finisher’s trucks also can reduce material handling and packaging to minimize the opportunity for damage, while saving costs and time.

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The basic stretch-forming machine has two arms or carriage beams that hold multiple-positioning gripping jaws. Photos courtesy of Southern Stretch Forming

 

Will it bend? Understanding stretch forming aluminum

big-8800-1Choosing a single partner to curve and finisher your architectural aluminum products offers a more efficient process with a higher quality result. At Linetec, our paint and anodize finishing options are both possible in combination with stretch forming services. Not only does this provide you with a single point of contact, it saves time and costs, and ensures a full warranty on the finished, curved materials.

What is stretch forming?

curved-metal-rack-698X400Stretch forming shapes aluminum sheets and extrusion profiles into simple or complex contoured curves with tensile and bending forces. The material is kept under constant tension, while wrapping it around a form, or die, to produce the desired arc.

Born from the aerospace industry, stretch forming maintains precise dimensions throughout a curve and produces perfectly contoured products while limiting, or even eliminating, wrinkling inside the arc.

Yale Peabody Closeup CTWhat shapes and sizes are possible?

Half circles (180 degrees) and eyebrow (usually 135 degrees) curves are the most popular requests that Linetec receives. These curves may be coupled with straight legs to create a larger opening as a window or door frame. Gothic arches also are common, especially for historic retrofit projects.

Larger arc lengths typically are specified on more modern facilities. Linetec can accommodate a maximum arc length of 260 inches. Those exceeding 260 inches can be reviewed and discussed. We can curved material up to 10 inches in width.

We can advise on accurate measurements to confirm the material dimensions meet your project’s requirements. A template will be needed for compound curves, which have more than one radius, and usually require a custom die.

Can thermal improvements be made to curved aluminum framing members?

Rolled-TB-Extrusion-web136At Linetec, not only can we coordinate the curving of your material and finish it in your choice of paint or anodize, we also can thermally improve the aluminum framing. We offer either a fully crimped, insulating, thermal, polyamide strut system or a three-step, pour-and-debridge process.

Both options separate the inside and outside aluminum framing members of a window, door, skylight, storefront or curtainwall system to reduce the amount of heat transfer, therefore saving energy and increasing occupant comfort.

Installing the thermal barrier in the metal after it has been curved helps minimize stress on the thermal barrier and ensures performance as specified.

What else can affect lead times, costs and warranties?

In addition to maintaining strict, factory-controlled standards by a single point of contact, relying on Linetec for your stretch forming, finishing and thermal improvement services also saves you time and money. You don’t need to coordinate between multiple suppliers’ facilities for logistics and freight. Which also minimizes handling and decreases the chances of your materials being damaged during loading and transport.

Nearly all manufacturer and applicator warranties require that the aluminum sheets and extrusions are finished after curving. When customers ship us their aluminum, Linetec alleviates this worry and performs all the services in the proper sequence and in the same place to retain the full finish warranty.

To learn more about how Linetec can support your next project with our stretch forming, finishing and thermal improvement services, please contact our regional sales managers, email sales@linetec.com or call 888-717-1472.

Stretch Forming by Linetec curves and finishes architectural aluminum products in one location

curved-metal-rackStretch Forming by Linetec allows our customers to have their metal building components curved and finished in one location. Half-circles, eyebrows and Gothic arches are popular architectural applications.

Customers can ship their aluminum to Linetec for bending and finishing to retain the full finish warranty.

Utilizing Linetec’s dedicated fleet of trucks saves customers shipping costs and transit time, as well as reduces material handling and packaging to minimize the opportunity for damage.
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Linetec’s full scope of bending capabilities includes annealing and tempering to soften and harden aluminum. Born from the aerospace industry, stretch forming maintains precise dimensions throughout a curve. The extrusion is kept under constant tension, while wrapping it around a form, or die. This produces perfectly contoured products, while limiting or even eliminating wrinkling inside the arc.

McDonalds interior dispay2 Jay&Kay mfgIn addition to stretch forming, Linetec offers a broad choice of paint, anodize and powder coat, plus field repair and restoration, thermal improvement and other support for finished aluminum products. For more information about Stretch Forming by Linetec, finishing and other services, please call 888-717-1472, email sales@linetec.com or visit www.linetec.com.

Stretch Forming by Linetec Wins USGlass 2014 Readers Choice Awards

USGlass awardJan 2015—USGlass magazine, the magazine of record for architectural glass industry leaders, announced that Linetec has won a 2014 Readers Choice Award. The products were featured in the December 2014 issue.

The products were selected through a survey of USGlass readers, who voted for their favorites in a variety of categories. Stretch forming from Linetec was selected as a winner in the Architectural Metal Products category.

Stretch Forming by Linetec is designed to allow architectural product manufacturers to have their metal building components curved and finished in one location. Stretch forming is the newest service Linetec has added to benefit customers seeking not only paint, anodize and powder coat, but also field repair and restoration, thermal improvement and other support for finished aluminum products.

curved metal rack“Stretch Forming by Linetec alleviates the worry and hassle of multiple points of contact
and brings tremendous value,” says Rick Marshall, Linetec’s president. “Customers can ship us their aluminum for bending and then, have it finished in the same place to retain the full finish warranty. This saves shipping costs and transit time, as well as reduces material handling and packaging to minimize the opportunity for damage.”

USGlass magazine’s Readers Choice Awards are unique in that they are selected by our readers, recognizing their top picks for architectural glazing products,” says USGlass editor Ellen Rogers. “Linetec is more than deserving of this award and we are excited to recognize them with this achievement.”

For more information about Stretch Forming by Linetec, finishing and other services, please call 888-717-1472, email sales@linetec.com or visit http://www.linetec.com.

USGlass magazine serves the entire architectural glass and glazing industry. It is the only industry publication that is audited by BPA Worldwide and has a circulation of more than 40,000 subscribers.

Specify Aluminum Stretch Forming with Confidence

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Stretch forming is a very accurate and precise method for curving metal extrusions. The level of precision is so high that, in most cases, even intricate multi-components and snap-together curtainwall components can be formed without loss of section properties or original design function. Stretch forming capabilities include portions of circles including half-circles and eyebrows, ellipses and arched shapes. These shapes can be formed with straight leg sections at one or both ends of the curve. This method of curving eliminates several conventional fabrication and welding steps.

Stretch forming is a metal forming process in which the extrusion or part is kept under constant tension while stretched and bent simultaneously over a die in order to form contoured parts. The variety of shapes and cross sections that can be stretch formed is almost unlimited. Window systems, skylights, storefronts, signs, flashings, curtainwalls, walkway enclosures, and hand railings can be accurately and precisely formed to the desired shapes.

stretch1The basic machine design has two arms or carriage beams that hold multiple-positioning gripping jaws. The jaws are attached to hydraulic tension cylinders that provide the stretch of the extrusion. The arms swing by rotating on large machined pins with bearings, thus allowing the extrusion to wrap around and against the forming die. This produces perfectly contoured products, while limiting or even eliminating wrinkling inside the arc.

Close and consistent tolerances, no surface marring, no distortion or ripples, and no surface misalignment of complex profiles are important benefits inherent in stretch forming (given understandable tightness of radius limitations on some shapes). A smooth and even surface results from the stretch forming process.

Structural or Load-Bearing Application vs. Non-Structural Application

Aluminum has proven itself as a suitable material for load bearing structures for more than 100 years. However, the application of the parts being curved dictates how the curving process will need to be carried out.

After being pushed through an extrusion press, extrusions are generally cut and then placed into a tempering oven to harden and give them their structural integrity. When extrusions are fully tempered to a T5 of T6 temper they are difficult to curve. If a customer desires to curve parts that have been fully tempered the parts will need to be annealed prior to curving. When a part is annealed it is placed in a large oven and heated to a very high temperature for a specific period of time. Annealing makes the extrusion soft again, enabling it to be curved. Once an extrusion is annealed, it cannot cost-effectively be re-tempered. In applications where the parts are expected to carry a structural load, or are desired to have another structural application, annealing is generally not an acceptable practice.

For structural or load-bearing applications, best practice is to have extrusions tempered to a soft state T1, T4 or to a T52 state. Material tempered to a T1 or T4 temper can be bent without annealing, and can then be tempered (hardened) after the curving process to a T5 or T6 temper typical in structural applications. T52 is a very stable temper and can be curved without annealing, and it maintains its properties after curving without the need for tempering.

Stretch Formings’ Effect on Finishing

Crazing of the anodized surface

Crazing of the anodized surface

Similar to the curving process, the end application of the part will determine the best practice for how curved parts should be finished.

If an extrusion has been painted or anodized, and has been tempered to a T5 or T6 hardness, the parts will need to be annealed. Because of the high heat associated with the annealing process, paint finishes will likely burn and anodize finishes will likely discolor or craze (crack). For this reason, when parts require annealing it is best to finish after the curving process has been completed.

For extrusions that have been tempered to a T1, T4, or T52 hardness, parts can be finished prior to curving. However, customers should expect some marring or slight damage to the finished surface due to the parts being “stretched” across a hard die surface during the curving process. Again, depending on the tightness of the radius anodic coatings may also craze or discolor as a result of being curved.

If the T1 or T4 tempered extrusions require oven-aged tempering after curving, the high heat will likely damage the coating.

McDonalds interior dispay2 Jay&Kay mfgRegardless of the effect the curving process has on the finish, all manufacturer and applicator warranties are generally voided when extrusions or brake metal are finished prior to curving. To obtain the best finish quality and keep parts fully warranted, it is best to finish after curving regardless of the temper of the extrusion.

It should also be noted that on parts that require a poured thermal break, it is also best practice to have extrusions thermally broken after curving so there is no cracking of the thermal break, and the manufacturer’s warranties stay intact.

 Request a Quote

Learn more about Linetec’s capabilities on our website or contact us at sales@linetec.com or 888-717-1472.

Visit Linetec at the AIA Expo Chicago

Please join us June 26-28 in Chicago for the American Institute of Architects (AIA) Expo. Among the exciting developments we’ll be showcasing in booth #4634 are:

curvedsqtubeStretch Forming by Linetec 

Whether its half-circles, eyebrows or Gothic arches, we can curve and finish your architectural aluminum products in one location to save time and retain the full finish warranty.

colorsampleguide3-3Linetec Color Select & Spec

Debuting at AIA, our new online color matching tool lets you choose an interactive “chip” from eight color families and order painted aluminum samples directly to your door.

 

Terra Cotta color finish 

Mimicking the look and feel of natural terra cotta wall panels, we now offer an economical alternative in a durable, painted 70% PVDF coating.

Linetec-ICU-From-Nurse's-StationAntimicrobial  coatings

For high-touch surfaces in hospitals and other important projects, choose our painted coatings infused with antimicrobial protection to inhibit the growth of stain and odor causing bacteria.

 

EMU Close Up-low resCopper Anodize finishes 

From distinctive, new construction projects to historic renovation projects, you can depend on our proprietary copper anodize to retain its bright copper color for many years to come.

 

LInetec Guide Spec3-Part Spec 

Ensure your finish delivers the look and performance you expect using the first-known, non-propriety “Section 05 0513 Shop Applied Coatings for Metal 3-part Guide Specification.”

 

AIA CES logoAIA/CES credits 

Earn up to 2.25 Learning Units with our AIA-approved online and in-person continuing education programs and new 15-minute, in-booth AIA Expo Chat.

 

As one of the nation’s largest paint and anodize finishers, our assortment of durable finishes may be requested as liquid coatings, powder coatings or as eco-friendly anodize for such products as aluminum windows, wall systems, doors, hardware and other architectural metal components. Learn more at www.Linetec.com and at AIA Expo booth #4634.

 

Stretch Forming by Linetec

Stretch Forming by LinetecPeople have been bending and curving metal for centuries, but stretch forming, born from the aerospace industry, maintains precise dimensions throughout a curve and produces perfectly contoured products while limiting, or even eliminating, wrinkling inside the arc.

Stretch forming is the process of forming sheets and profiles by the combined application of tensile and bending forces. Stretch forming keeps the extrusion under constant tension while wrapping it around a form, or die, to make parts into simple or complex contoured curves.

To deliver these stretch forming services, Linetec has teamed with Southern Stretch Forming, headquartered in Texas. The company will provide a full scope of bending capabilities on Linetec’s campus in Wausau, Wis., including annealing and tempering to soften and harden aluminum.

STRETCH FORM CAPABILITIESStretch Forming by Linetec

Linetec and Southern Stretch Forming will work together, striving to meet every need of our customer. However, there may be some cases that an extrusions configuration are not suitable for curving/stretch forming. Below are some broad overview capabilities, if your needs are outside of these capabilities contact us directly at sales@linetec.com for assistance.

    • Maximum arc length of 260 inches (larger lengths reviewed on individual basis
    • Curved shapes up to 10 inches in width
    • Full annealing and tempering
    • Ability to manufacture and stretch form brake metal
    • Custom die/tooling
    • Thermal improvement services on curved metal, both thermal strut and poured thermal barriers

Request a Quote document

For more information on Linetec and our stretch forming services, visit our website, www.linetec.com.