Bending of metal is an important process in metal fabrication operations, an application of which are I-beams in structural steel construction. When metal sheets are bent, the top surface contracts and the bottom surface stretches. The neutral radius is the internal border between these two phases inside the metal. This border exactly divides the thickness of the metal while the metal is flat, but it moves when the metal is bent. The K-factor and Y-factor of sheet metal are two measures of its ductility and flexibility, respectively, during bending. What are these measures and how do they assist fabricators in the metal bending process? This blog will look to delve deeper in this topic and also provide an overview of types of metal bending.
Types of Metal Bending
Minimum radius, perfect radius, sharp radius, and sharp bends are the four fundamental categories of metal bending in light metal fabrication operations. The metal is manipulated until its radius is the shortest it can be without creases being formed, and this is known as the minimum radius bend. Using this number, the sharpest and most precise of bends can be located. Perfect bends have radii that range from the minimum to 125% of the material’s thickness. To generate a radius bend, the deviation must be greater than 125% of the metal’s thickness. At the other extreme of the spectrum are 90-degree angles. These appear when the metal is bent beyond its bending radius, creating a sharp crease.
What are K and Y Factors?
The K-factor describes the relationship between the neutral axis and the thickness of a sheet of metal. A metal sheet is bent by compressing the inner area and expanding the outside using heat induction bending services. The neutral axis shifts from its initial position at 50% of the material thickness towards the inner surface of the bend, but no further changes take place in this region where compression and expansion meet. Elongation happens during bending because the neutral axis moves, but its length remains constant. The thickness, inner bend radius, and forming process all have a role in how much the neutral axis moves. On standard charts, the K-factor is found by dividing the neutral radius by the thickness of the material, and it ranges from 0.3 to 0.5.
The Y-Factor is a derivative of the more standard K-Factor. It is calculated by reducing the K-Factor by 0.5, then multiplying that result by pi. The Y-factor is comparable to the K-factor but more accurately accounts for the stresses present in the material being examined.
How is K-factor determined?
Measuring multiple different metals will provide data points required to calculate the K-factor. It is necessary to know the interior radius along with the outside dimensions and the pre- and post-bent dimensions. Gauge pins, radius gauges, or an optical comparator may be used to determine these values. The BA, or bend allowance can be calculated using this data. Sheet elongation may be determined with the bend allowance. Readings of the included angle, which is 180 degrees, and the complimentary bend angle, which is Ir minus the included angle should be taken. Discovering the material’s thickness, Mt, allows one to compute the K-factor for bending sheet metal. The K-factor may be calculated by dividing 180 by the product of BA and the ratio of Ir to Mt, and by the difference between the product of pi, Mt, and the corresponding bend angle. This formula may be written mathematically as:
K-factor = 180 x BA ( x Complementary Bend Angle x Mt) – (Ir x Mt)
The degree to which a metal is stretched while bending is a vital metric to be considered when designing large scale infrastructure like bridges, airports, offices etc. It is here that K and Y factors play a role by making metal bending more precise without damaging the material during steel fabrication. K and Y factors may be mathematically complex concepts; however, fabricators swear by them when it comes to bending a length of flat sheet metal!