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Stretch Forming / Metal Curving

Stretch Forming

People 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.

Benefits of Stretch Forming by Linetec

• Stretch forming by Linetec alleviates the worry and hassle of multiple points of contact.
• Linetec's ability to offer stretch forming provides our customers with:
• Convenience and time savings with finishing and curving services on one campus
• Full finishing capabilities: liquid paint, powder coat, anodize
• Reduced freight costs. No freight costs between curving and finishing facilities.
• Damage-free material when delivered on Linetec route truck
• Our partner, Southern Stretch Forming, has over 20 years of curving experience
• Ability to finish curved material with the rest of the project, ensuring color consistency
• Full coating warranty benefits for material finished after curving
• Inventory services available for high-usage profiles
• Shortened lead time

Stretch Form Capabilities

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 [email protected] 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

Stretch Form Guidelines

Half-Circle or Eyebrow Openings

Determine at what points the curve begins and ends. These points are called the tangent points (or straight-line points). Measure the distance between these points ideally with a laser measurer. This distance is called the chord. If the opening is a complete half-circle (180°), this distance will also be the diameter, and half of this measurement is your radius.

From the exact center of the chord, measure straight up to the top of the arc. Do not include any straight leg. This distance is called the rise (or height). If the rise is one half of the chord, then you have a complete half circle or 180°. See “Notes” below for a comment on inside vs. outside measurements.

If straight legs are required, measure from the tangent point (where the curve ends) down to the lowest point needed

Gothic Shapes

Hang a plumb bob from the point of the Gothic opening.

Determine at what point along the side that the curve begins. This tangent point acts as the top of an arc that begins at the top of the pointed opening and extends through this tangent point and continues as an imaginary line until it intersects with the plumb line coming straight down from the upper point. This distance on the plumb line between these points is the chord.

The distance from the center of the chord (on the plumb line) measured horizontally to the beginning of the curve (or tangent point) is the rise.

If there are straight legs, measure from the tangent point (where the curve ends) straight down to the bottom of the piece.

Additional Notes

• The rise, the chord and straight legs (if needed) are the only measurements Southern Stretch Forming needs to determine the arc length and provide you with a quote. We can also work with the chord and radius if your drawing provides this information.
• The above procedure gives us the outside dimensions so we will deduct the width of the material you are using to determine the inside radius. If using an inside dimension, use inside dimensions throughout, i.e. be consistent and advise which you are using.
• We will assume standard cut-length material (24’) unless you tell us otherwise
• A template is needed for compound curves (having more than one radius) and will likely require a custom die