Bending Fundamentals 105

against the grain

Bending with the line of the bend perpendicular to the line of the grain direction. Bending against the grain requires greater force but leads to a lower risk of material defects.

air bending

A bending method in which the workpiece does not touch the bottom of the die. Air bending requires relatively low tonnage and precise movement of the slide.

bed plate

The foundation for a press brake. The bed plate is located at the bottom of the machine.

bend allowance

The length of the arc along a bent portion of a workpiece. Bend allowance is an important factor in determining how long a workpiece must be to accommodate the planned bend.

bend angle

The measurement, in degrees, of the desired angle between two flanges. The bend angle is dependent on the shape of the tooling and the amount of force applied by the press brake.

bend clearance

The amount of space between the upper and lower die. Appropriate bend clearance ensures that the part is formed accurately.

bend radius

The distance from the center point of an imaginary circle at the center of the bend to the inside of the material. The bend radius determines how likely a material is to crack or experience springback.

bend sequence

The order of operations for a workpiece that requires more than one bend. Bend sequence must be carefully planned and adhered to so that defects can be avoided.

bending

A forming operation that shapes a workpiece by straining it into a desired angle. Bending often creates parts with simple shapes and minor contours.

bottom bending

A bending method in which the workpiece makes full contact with the bottom of the die. Bottom bending requires relatively high tonnage and can result in large volumes of consistently accurate parts.

coining

A bending method in which the workpiece makes full contact with the bottom of the die and is then compressed by additional forces. Coining requires extremely high tonnage and is only used to make highly precise parts.

compression

A pushing or pressing force that is directed toward the center of an object and attempts to squeeze it. The interior of a bent workpiece experiences compression.

compressive strength

The ability of a material to resist forces that attempt to squeeze or crush it. Compressive strength is the amount of compressive stress a material can withstand before fracturing.

cracking

The breaking of a workpiece. Cracking occurs when the pressure applied to the material far exceeds its tensile or compressive strength.

deform

To change or distort an object’s shape. Deforming an object results in the object taking on a shape that is different from its original.

deformation

A change in the size or shape of an object as a result of stress. Deformation intentionally changes the shape of a workpiece in bending operations.

dies

A tooling component of press brakes with two halves that attach to the slide and bed plate. A die makes contact with the workpiece to perform bending operations.

elastic deformation

A temporary change in the shape of an object or material due to stress. When a material experiences elastic deformation, it returns to its original shape once the stress is removed.

elastic limit

The maximum amount of stress a material can withstand before it experiences plastic deformation. A material’s elastic limit, sometimes called yield strength, must be exceeded to permanently change the shape of the workpiece.

flange

A portion of a bent workpiece from one bend to the end of the workpiece. Every bend will have at least two flanges.

flange length

The distance from where the upper die tooling contacts the workpiece to the end of the workpiece. Every bent part has at least two flange lengths.

folding machines

A machine that uses three beams to clamp and bend metal. Folding machines creates precise and consistent bends but is less suited than a press brake to complete a variety of bending operations.

forming

A general category of metalworking processes that shape metal. Types of forming include rolling, extruding, drawing, and bending.

gooseneck punch

An upper die tooling component that has a portion cut away so that other bends that have already taken place on a workpiece do not collide with the tooling. A gooseneck punch is typically used if there is a sequence of bends to be made.

grain direction

The layout or arrangement of molecules that make up a material. Grain direction is an important factor in making sure bent parts are accurate, consistent, and free from defects.

mechanical force

A stress that attempts to bend, stretch, break, or indent a material. Mechanical forces include compressive, shear, and tensile stress.

neutral axis

An area on a workpiece that does not experience tension or compression. The neutral axis is located approximately halfway through the material’s thickness.

outside bend radius

The distance from the center point of an imaginary circle at the center of the bend to the outside of the material. The outside bend radius is equal to the bend radius plus the material’s thickness.

overbending

A method used in bending to account for springback. Overbending bends the metal past the desired angle so that after the workpiece experiences springback, the result is the desired bend shape.

parallel

Extending in the same direction and equidistant at all points. You are bending with the grain when the bend line and the grain direction are parallel.

perpendicular

A line that forms an angle of 90 degrees with another line. You are bending against the grain when the bend line and the grain direction are perpendicular.

plastic deformation

A permanent change in the shape of an object or material due to stress. Plastic deformation occurs after a material’s yield point has been exceeded.

press brake

A type of press with an open frame and wide, narrow bed. A press brake is often used for a variety of bending operations.

presses

A machine with a stationary base and an upper slide that repeatedly moves up and down. Presses shapes or cuts metal to create useful parts for a range of industries.

profound radius bend

A bend in which the bend radius is over 10 times the material thickness. Profound radius bends have the greatest amount of springback.

punch

A tooling component that pushes into the workpiece. The punch is a component of the upper half of the die that is used in most bending operations.

radius bend

A bend in which the bend radius is within the range of 63% to 1000% of the material thickness. Radius bends are common because they are less prone to cracking, springback, and other bend defects.

ram

The portion of a press brake that moves up and down during operation. The ram, sometimes called a slide, provides the required force to complete stamping operations.

sharp bend

A bend in which the bend radius is less than 63% of the material thickness. A sharp bend is often at risk for cracking because the inside bend radius is so small.

sheet metal

Flat metal stock. The sheet metal used in press brakes can vary in thicknesses ranging from 0.023 inches (0.584 mm) to 0.500 inches (12.700 mm).

slide

The portion of a press brake that moves up and down during operation. The slide, sometimes called a ram, provides the required force to complete stamping operations.

springback

The tendency of a material to return to its original shape once stress has been removed. Springback is often corrected in bending operations with overbending.

strain

The physical change in an object’s shape when it is under stress. Strain exists while the object is under stress but can also exist once the force has been removed.

strength

A material’s ability to resist forces that attempt to break or deform it. A material exhibits tensile, compressive, or shear strength, depending on the deforming force.

stress

A force that attempts to deform an object. Common forms of stress include compressive, shear, and tensile.

stress fracture

Hair-like cracks that appear on the surface of the workpiece if the tensile or compressive strength of the material has been exceeded. A stress fracture in a material means the part becomes waste and must be re-made.

tensile strength

The ability of a material to resist forces that attempt to pull it apart or stretch it. Tensile strength is the amount of tensile stress a material can withstand before fracturing.

tension

A pulling force that is directed away from an object and attempts to move, stretch, or elongate it. The exterior of a bent workpiece experiences tension.

test bend

A bend completed on a sample workpiece to determine the effectiveness of a bending operation. A test bend is most often performed when the bend radius is small or in other situations where cracking is likely.

tonnage

The amount of force a press brake must generate to complete a given operation. Tonnage must be applied correctly to accurately create parts that meet specifications.

tooling

Assorted tools used in various manufacturing processes. Tooling used on press brakes includes dies.

with the grain

Bending with the line of the bend parallel to the line of the grain direction. Bending with the grain requires less force but leads to a greater risk of material defects.

workpiece

A part that is being worked on during manufacturing. The workpiece on a press brake is often a piece of sheet metal.

wrinkling

Unwanted waves in the bent material. Wrinkling often results when the workpiece does not have appropriate clearance or support.

yield point

The point at which a material is permanently deformed. The yield point of a workpiece must be exceeded by the forces of the press brake to maintain the desired shape.

yield strength

The maximum amount of stress a material can withstand before it experiences plastic deformation. A material’s yield strength, sometimes called elastic limit, must be exceeded to permanently change the shape of the workpiece.