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NEUTRAL AXIS.
When sheet metal is subject to bending, the external fibers of the bend angle are stretched, while the internal fibers are compressed. As a consequence, the fibers on the outside are going to become longer, while the fibers on the inside are going to be shorter. Between these two opposite stresses, there is a "neutral" area where longitudinal stress is zero. This is the neutral axis, also called neutral PLANE or neutral FIBER. Here, fibers are deformed without elongation or compression. It is thanks to this characteristic, that it is possible to perform sheet metal bending.
BA – BEND ALLOWANCE.
Bend allowance is the length of the neutral fiber, measured along the whole arc created by the bend. Bend allowance is an extremely important parameter when calculating the extra length of bent sheet metal. We will focus on how to determine bend allowance in the next articles.
B< – BEND ANGLE.
Bend angle is the angle resulting from sheet metal deformation. It is the value of the bend expressed in degrees. Its dimension is determined by the customer's request and it depends on certain factors related to the properties of the material, such as its thickness, plasticity and alloys. The most common bend angle is the right angle (90°), also called "square bend". When the bend is less than 90° it is an acute angle, and it is formed using 30°, 45° and 60° tools. When the bend is between 90° and 180° it is an obtuse angle, and it is usually formed by air bending.
BD – BEND DEDUCTION.
In a few words, bend deduction is the quantity of material you will have to remove from the total length of the flanges in order to arrive at the correct length. Bending, indeed, elongates the material, increasing its initial length. We will soon focus on the formula to calculate bend deduction.
K FACTOR.
Factor K is a variable depending on the ratio between the thickness of the material and the location of the neutral axis, that is to say, between material thickness (MT) and offset of neutral axis (t), which we are going to talk about below. Formula: k=t:MT
f - FLANGE.
Flange is the total length of sheet metal on the outside of the bend, from edge to apex.
IR – INSIDE RADIUS.
Internal bend radius.
ISSB – INSIDE SETBACK.
Distance between the inside tangent points (where the metal stops bending) and the apex of the inside mold lines.
LEG.
Legs are the flat lengths of the workpiece, the parts that are not deformed.
MT – MATERIAL THICKNESS.
The thickness of the material to be bent. This value is very important because it determines other parameters, such as K Factor and the amount of force to be applied in the bending operation.
OR – OUTSIDE RADIUS.
External bend radius.
OSSB – OUTSIDE SETBACK.
Distance between the outside tangent points (where the metal starts to bend) and the apex of the outside mold lines.
t – OFFSET OF NEUTRAL AXIS.
The distance between the inside arc of the bend and the neutral axis. In other words, the location of neutral fiber inside the material. Neutral axis is not always in the center between the tensile and compressive stresses, it is usually closer to the inside radius.