The K-Factor: What Is It?

The K-factor describes the relationship between the neutral axis and the thickness of a sheet of metal. When bending metal, the centre of the curve contracts while the edge of the bend widens. The neutral axis shifts from its initial position at 50 percent 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.

You may calculate the new location of the neutral axis by multiplying the thickness of the material by the standard default K-factor value of 0.446. The length measured (the length of the neutral axis at 50% of the material thickness) is being distorted such that it fits on a smaller radius. We have elongation or surplus material since the same overall length is being measured across a smaller radius.

Think about using a 0.060-inch thick sheet. To achieve 0.0268 inches, we multiply by K = 0.446. From the inner surface of the bend, the axis has moved from 0.030 in. (half the material thickness) to 0.0268 in. In other words, there was an inward shift of 0.0032 inches in the axis. That’s where we’ll get the data we need to solve for the curve in the road.

It is important to remember that the K-factor varies depending on the kind of material, the forming technique, and the connection between the bend radius and the material thickness. The overall amount of elongation and the necessary bend deductions are subsequently affected by these factors.

SOLIDWORKS Although sheet metal tools aren’t too complicated to use, they aren’t often well understood. The K-Factor, a strong bend constant, is used in sheet metal. In the end, it lets you approximate the stretch without understanding the exact nature of the material you’re working with. When you don’t know the precise method or machine that will be used to bend the sheet, this allowance might serve as a stand-in. Let’s go through K-Factor and how it relates to your sheet metal work.

There wasn’t any malice in the beginning. A reader wrote in to enquire about the k-factor and radius of curvature calculations. We briefed him on the practical applications of the k-factor and directed him to the standard k-factor tables. The reader expressed gratitude for my reply but expressed interest in learning more. How are the k-factor values determined if no chart is available?

Following a chain of logical deductions, We realised that we needed to consider not only k-factor calculations, but also Y-factors, minimum radii, kinetic friction, and grain directions, all of which are essential to understanding the sweet, subtle, complicated gumbo that is the science of bending, in order to provide a comprehensive answer. So, let’s start preparing dinner.

Melbourne steel fabrication

What Are the Ingredients in K-Factor?

We discussed a few of the things that may be found in a k-factor gumbo. Some of the variables I’ll cover next month are die width, coefficient of friction, y-factors, and, of course, bending technique (air bending, bottoming, or coining). In addition, I will explain a second kind of K-factor (this one with the “K” capitalized).

Then, I’ll show you how to compute a bend from scratch, which will be comparable to figuring out the k-factor by hand. As a result of this investigation, it should be clear that, indeed, a k-factor value of 0.4468 produces a delicious gumbo. For regular usage, it comes quite near to ideal. However, a k-factor specifically computed for the application allows you to go even closer, and the gumbo will taste even better as a result.

How to Calculate K-Factor?

There is no easy method to determine the K-Factor before the first bend, since it depends on the quality of the metal and its thickness. The K-Factor is usually between 0 and.5 or thereabouts. To get the K-Factor, bend a small piece and extrapolate the Bend Allowance from it. In order to calculate the K-Factor, the Bend Allowance is substituted into the aforementioned formula.

Get started by making sure your sample blanks are of the same size. To get a nice, even bend out of the blanks, you’ll want to make sure they’re at least a foot long, and you’ll also want to make sure they’re at least a few inches deep so you can set them Take a 14-gauge,.075″, 4-inch-wide, 12-inch-long piece as an example. We won’t be factoring in the whole duration of the work. Taking the average of the readings from at least three different samples will be a big help.

Place a 90° bend in the middle of the metal and set up your press brake with the appropriate equipment for working with this thickness of metal. Our example calls for a turn at the 2″ mark.

After you have bent your samples, you should measure their flange lengths precisely. Keeping track of lengths and averaging them out might help you find the optimal solution. You should aim for a length that’s more than 50 percent of the original. In this case, we use a typical flange length of 2.735 inches as an example.

The second is to calculate the new interior radius after bending. Even if a set of radius gauges will bring you close, an optical comparator will give you the most precise result. In this case, we use an inner radius of.105 as an illustration.

You’ve got your dimensions, now let’s figure out the Bending Tolerance. To achieve this, first calculate the leg length by deducting the flange length from the thickness of the material and the inner radius. (Remember that the leg length is measured from the tangent point, therefore this equation only applies to right angles.) The resulting leg length in our case is 1.893 (2.073-0.105-0.075).

The Bend Allowance is calculated by reducing the total length by twice the leg length. 4 – 1.893 * 2 = .214.

In order to calculate the K-Factor, you will need to plug in the Bend Allowance (BA), the Bend Angle (B), the Inside Radius (IR), and the Material Thickness (MT) into the following equation: (K). To provide an illustration, consider

K = dfrac180 cdot BApi cdot B cdot MT – dfracIRMT

What Is a K-Factor Chart?

Standard materials and thicknesses will have a K-Factor between 0 and.5, while K-Factors may be less or bigger depending on the circumstances. I’ve included a K-Factor Chart that has some decent baseline values for general fabrication across steel, aluminium, and stainless steel to get you started.

Why Does the K-Factor Matter?

When working with precision sheet metal, the k-factor is one of the most important mathematical constants to keep in mind. This number will be used as a baseline to calculate the bend allowance and, ultimately, the bend deduction. After the neutral axis of the bend has been shifted, a mathematical multiplier is applied to determine its new position.

The k-factor provides a rough estimate of the amount of elongation that will occur at a given curve. Precision formed parts have their outer setback, bend deduction, bend allowance, and flat layout calculated with the help of a k-factor.

What Is the Neutral Axis?

Learning the k-factor requires first understanding the neutral axis and other such foundational concepts. Located at 50% of the material’s thickness, the neutral axis is a theoretical plane that is both flat and stress-free. As the curve bends inward, the neutral axis does the same. The theoretical length of the line of the neutral axis is the same both before and after the turn.

The area between the neutral axis and the exterior surface of a curved body is subjected to tensile forces, while the area between the neutral axis and the interior surface is subjected to compressive forces during bending. We refer to the plane through which both tension and compression are equal and distinct as the neutral axis. Forming method, interior bend radius, and bend angle all play a role in determining where the neutral axis lies.

Because of the behaviour of the neutral axis, the total outer dimensions of the product must be less than the flat section.

How Does K-Factor Work?

We’ll delve into the various interpretations of the k-factor in subsequent columns. However, it is worth noting that the usual k-factor definition can be found in a variety of sources. The one below is a piece written by a professor of mechanical and production engineering at Bangladesh’s Ahsanullah University of Science and Technology.

A constant known as the k-factor can be determined by dividing the sheet thickness by the orientation of the neutral axis. With a sheet’s neutral axis, the area around it is unaffected by compression or expansion. The bending process has no effect on the length of the neutral axis.

In order to quantify how far the neutral axis rotates inwards, we use the k-factor. This lengthening of the component occurs because the neutral axis shifts during the forming process from its original position at exactly half the material thickness to a new location at exactly half the material thickness or less. The straight line distance around the curve’s centerline is what’s used to determine the bend allowance.

Let’s say your stuff is only 1 mm thick. Halfway through its thickness, or about 0.5 mm, is where the neutral axis of the material lies when laid flat. The neutral axis shifts inward as the material is bent, landing at a new position 0.4461 mm from the inwardly curved surface. According to Figure 2, we denote this change in the neutral axis with the letter t. To calculate the k-factor, divide the time period (t) by the material thickness (Mt): formula: k = t / Mt

Multiplying by the k-factor yields an accurate approximation of the new neutral axis’s location. From the bend radius, the k-factor can be determined. The k-factor can be used to determine the maximum bend radius for a given bend angle.

In order to design precise sheet metal products, the k-factor is indispensable. It is possible to determine the bend deduction for a variety of angles without resorting to a table. Both bend allowance and deduction calculation charts have a history of inaccuracy, but modern bend deduction charts are more reliable. Typically, they were only effective in their original manufacturing environments. Even today, there are still a great deal of these graphs available.

The k-factor has some serious flaws that prevent it from being used universally. By way of illustration, it pays no attention to the internal stresses and strains that develop in a material when it is bent. The tensile and yield strengths of the material, as well as the forming method (air forming, bottoming, or coining), play a role in establishing the k-factor.

Figure 3 is a bar chart showing a variety of k-factors, from 0.50 down to as low as 0.33. Further reduction of the k-factor is possible. Typically, a k-factor of 0.4468 is provided in real-world situations.

There is good reason why k-factors greater than 0.50 have never been used in practise. The tensile stress exerted from without the bend must be higher than the compressive stress exerted within the bend. The centre of the sheet is where the neutral axis is located if there is no load on it. Simply apply pressure and see what happens to the metal. Tensile forces cause grains to become dislodged because the granular linkages are strained, tugged, and sometimes even break.

Poisson’s Ratio is illustrated by this fact: when a material is stretched, its length in the opposite direction decreases. Poisson’s ratio explains why the area outside of a curve is greater than the area inside of it. There appears to be much more space on the outside of a curve than on the inside.

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What Is the Minimum Bend Radius?

Manufacturers in the sheet metal and plate industries often encounter difficulties due to inside bend radii that are too small. The outer surface of the bend in the press brake could crack as a result.

When subjected to the high tension created by a sharp bend, material starts to deform plastically. External cracks indicate a flaw and reduce the material’s pliability. The neutral axis is brought closer to the inner surface of the curve as the inner bend radius decreases.

This general k-factor chart provides typical k-factor values for a variety of uses, and it is based on data from Machinery’s Handbook. A substance’s thickness is referred to as its “thickness.” The most common k-factor for bending tasks is 0.4468.

The term “minimum bend radius,” which appears on numerous design types, is largely to blame for this. Many people, upon reading the phrase “minimum bend radius,” reach for the punch with the pointiest end.

The minimum bend radius is set not by the punch’s radius but by the material itself. You can’t get an inner bend radius smaller than this in air without bottoming or coining it.

If the punch radius used in an air form is smaller than the minimum floated radius, a crease will form in the inner centre of the bend. Material variations between components can amplify any normal in-angle deviation, which can lead to dimensional errors in the workpiece. (Just type “how an air bend becomes sharp” into the search box at www.thefab ricator.com to read up on sharp bends.)

The k-factor is unaffected by either of the two alternatives for the minimum bend radius. In air, the first form of a minimal radius is the transition between a “sharp” and “minimum” radius. This causes a crease to form in the exact centre of the bend, and it also highlights any natural differences between the materials involved. If the force required to form is greater than the force required to puncture, then this will occur. The additional compression of the inner region of the bend caused by the punch nose penetrating the material causes a change in the k-factor.

The minimum bend radius on the inside can also be determined by dividing the bend radius by the material’s thickness. As the inner radius to thickness ratio decreases, the tensile strain at the surface of the material increases. The probability that the ratio

More serious issues arise when the bend line goes against the grain or rolling direction of the sheet metal. If the radius of the bend is much smaller than the thickness of the metal being worked with, the grains of the material will expand at a much faster rate. Here we have yet another illustration of Poisson’s Ratio in operation. When the thickness of the material exceeds a certain threshold, the neutral axis is compelled to move inward.

As a result, this secondary minimum bend radius is typically referred to as the “minimum bend radius for material thickness.” When referring to material thickness, the standard units are 2, 3, 4, etc. Minimum bend radii for a variety of alloys and tempers are typically listed on bend radius charts provided by most raw material producers and distributors.

To what extent do the minimum radius charts reflect actual conditions? They add new ingredients to our k-factor stew, some of which are ductile. A tensile test can tell you how plastically deformable a metal is. Reduction in area under tension is a measure of ductility. Using the tensile reduction value and the thickness of the material, you can get a rough estimate of the minimum bend radius.

The following formula can be used to calculate the minimum bend radius for material 0.25 inches in thickness or greater: You can reduce Mount Everest by [(50/Tensile decrease of area%) -1]. For materials thinner than 0.25 inches, the following formula can be used to calculate the minimum practical bending radius: Mt = 0.1 [(50/Tensile reduction in area%) – 1]

In these calculations, % is a whole number, not a decimal. In the above example, if your half-inch thick material had a 10% reduction percentage, you would replace 0.10 with 10.

Reducing the tensile area by a factor of fifty minus one yields a value of mt.

[(50/10) – 1] × 0.5 = 2

The “convex” shape of a bend’s interior is caused by compression.

The minimum acceptable radius for an inside bend in this situation is twice the material thickness. Remember that this is only a ballpark figure derived from some averages. The minimum bend radius for steel or aluminium plate needs more investigation. Without knowing your suppliers and whether you’re going with or against the grain, your k-factor gumbo will be missing a key ingredient.

Check out Metal Fabrication Welding Aluminium

What Is Grain Direction?

Since the grain forms along the direction of rolling at the mill, it extends the entire length of the sheet. The lines on a brand-new metal sheet will be oriented in a specific way, revealing this information. Individual sheet particles grow longer along the rolling axis as a result of the manufacturing process.

Unlike sanding and other mechanical processes, changing the grain direction does not result in a smooth surface. Nonetheless, surface scratches are more likely to cause cracking when the finish grain is perpendicular to the natural grain.

These factors may cause shifts in both the angle and the inner radius, due to the directional nature of the grains. As the term “anisotropy” suggests, orientation is essential to the material and plays a significant role in the production of precision parts.

Metals show anisotropy when they are bent at right angles to the grain, changing both their angle and radius. Taking into account the metal’s anisotropic properties is crucial for obtaining accurate k-factor and bend allowance estimates.

By bringing the neutral axis inward when bending with the grain, the k-factor can be changed. Outside cracking is more likely as the neutral axis gets closer to the inside surface of the bend.

A bend that is made with the grain is weaker than one that is made across the grain, but it is easier to achieve. Since it’s easier for the particles to pull apart, this could lead to cracking on the surface’s periphery. This could be exacerbated by particularly sharp bending. This suggests that a larger inside bend radius is needed when bending with the grain.

What Should Be the Material Thickness and Hardness?

The material’s thickness and hardness are additional factors to consider. The neutral axis is pushed further inward as the material’s thickness increases in relation to its inner radius. (This is assuming a die opening that is in direct proportion to the material thickness. The impact of die width on k-factor will be covered in next month’s article.

The k-factor goes down as the difficulty goes up. Materials with a higher stiffness require more effort to stretch. As a result, the area of tension increases further from the neutral axis and decreases closer to it. If the material is exceptionally tough, the radius inside must be a multiple of its thickness. Poisson’s Ratio has found yet another application here.

Check out Exactly what is the sheet metal working procedure?

Conclusion

The K-factor characterises how the neutral axis of a metal sheet varies with its thickness. When a material is bent, the neutral axis moves inward towards the curved surface while maintaining the same overall length as before the bend. Multiplying the material thickness by the default K-factor of 0.446 yields the new position of the neutral axis. Remember that the K-factor changes depending on the type of material, the forming method, and the relationship between the bend radius and the thickness of the material. The reader wanted to know how to determine the k-factor and the radius of curvature.

Die width, friction, y-factors, and bending method were all mentioned as potential k-factor gumbo ingredients. One can determine the K-Factor by bending a sample piece and extrapolating the Bend Allowance; typically, this number lies between 0 and.5. The most crucial information includes the length, width, thickness, bending tolerance, bending allowance, bending angle, inside radius, and material type of the sample blanks. If you know the length of the flange and the inner radius of the bend, you can figure out the bend allowance, and if you know the length of the legs, you can figure out the bend angle. The K-Factor is then determined by solving the following equation for the bend Allowance, Bend Angle, and Inside Radius: (K).

When fabricating precise sheet metal, the k-factor is a crucial mathematical constant. Used for determining the outer setback, bend deduction, bend allowance, and flat layout, it provides a rough estimate of the amount of elongation that will occur at a given curve. There is no tension or stress along the neutral axis, a hypothetical flat plane. The neutral axis’ location is affected by the forming technique, the interior bend radius, and the bend angle. The product’s total external dimensions must be smaller than its flat cross-section.

To calculate the k-factor, divide the sheet thickness by the orientation of the neutral axis. The bend radius can be calculated for any angle without having to consult a table. Nonetheless, it is not suitable for widespread implementation due to a number of significant shortcomings. The k-factor is determined by the material’s tensile and yield strengths, as well as the forming technique (air forming, bottoming, or coining). As can be seen in Figure 3, k-factors range from 0.50 to as low as 0.33.

When referring to bending tasks, the most common k-factor is 0.4468. When working with air, the minimum bend radius is determined not by the punch’s radius but by the material itself. Both options for the minimum bend radius have the same effect on the k-factor, but a crease will form in the inner centre of a bend if the punch radius used in an air form is smaller than the minimum floated radius. When the bend radius is divided by the thickness of the material, the smallest possible inside bend radius is obtained. Sometimes called the “minimum bend radius for material thickness,” this secondary minimum bend radius is essential for bending materials of varying thicknesses. Most raw material manufacturers and distributors provide bend radius charts that detail the minimum bending radii for a wide range of alloys and tempers.

For materials thicker than 0.25 inches, the minimum bend radius can be estimated using minimum radius charts, but these charts are only approximations based on averages. Accurate manufacturing relies heavily on the material’s inherent grain direction. Compression causes the interior of a bend to take on a “convex” shape, and an inside bend needs to have at least twice the material thickness as a radius to be considered acceptable. When metals are bent perpendicular to the grain, they exhibit anisotropy, which allows for precise calculations of the k-factor and the bend allowance. As the degree of difficulty increases, the k-factor decreases, meaning that a larger inside bend radius is required when bending with the grain.

The neutral axis is displaced inward as the material thickens in relation to its inner radius, so the material’s thickness and hardness are also relevant factors. Here, Poisson’s Ratio is used for the second time in as many uses.

Content Summary

• The K-factor describes the relationship between the neutral axis and the thickness of a sheet of metal.
• It is important to remember that the K-factor varies depending on the kind of material, the forming technique, and the connection between the bend radius and the material thickness.
• The K-Factor, a strong bend constant, is used in sheet metal.
• A reader wrote in to enquire about the k-factor and radius of curvature calculations.
• Following a chain of logical deductions, We realised that we needed to consider not only k-factor calculations, but also Y-factors, minimum radii, kinetic friction, and grain directions, all of which are essential to understanding the sweet, subtle, complicated gumbo that is the science of bending, in order to provide a comprehensive answer.
• In addition, I will explain a second kind of K-factor (this one with the “K” capitalized).Then, I’ll show you how to compute a bend from scratch, which will be comparable to figuring out the k-factor by hand.
• As a result of this investigation, it should be clear that, indeed, a k-factor value of 0.4468 produces a delicious gumbo.
• There is no easy method to determine the K-Factor before the first bend, since it depends on the quality of the metal and its thickness.
• Get started by making sure your sample blanks are of the same size.
• After you have bent your samples, you should measure their flange lengths precisely.
• When working with precision sheet metal, the k-factor is one of the most important mathematical constants to keep in mind.
• Precision formed parts have their outer setback, bend deduction, bend allowance, and flat layout calculated with the help of a k-factor.
• A constant known as the k-factor can be determined by dividing the sheet thickness by the orientation of the neutral axis.
• This lengthening of the component occurs because the neutral axis shifts during the forming process from its original position at exactly half the material thickness to a new location at exactly half the material thickness or less.
• The neutral axis shifts inward as the material is bent, landing at a new position 0.4461 mm from the inwardly curved surface.
• From the bend radius, the k-factor can be determined.
• The k-factor can be used to determine the maximum bend radius for a given bend angle.
• In order to design precise sheet metal products, the k-factor is indispensable.
• Typically, a k-factor of 0.4468 is provided in real-world situations.
• There is good reason why k-factors greater than 0.50 have never been used in practise.
• Poisson’s ratio explains why the area outside of a curve is greater than the area inside of it.
• Manufacturers in the sheet metal and plate industries often encounter difficulties due to inside bend radii that are too small.
• The neutral axis is brought closer to the inner surface of the curve as the inner bend radius decreases.
• The most common k-factor for bending tasks is 0.4468.The term “minimum bend radius,” which appears on numerous design types, is largely to blame for this.
• If the punch radius used in an air form is smaller than the minimum floated radius, a crease will form in the inner centre of the bend.
• In air, the first form of a minimal radius is the transition between a “sharp” and “minimum” radius.
• The additional compression of the inner region of the bend caused by the punch nose penetrating the material causes a change in the k-factor.
• The minimum bend radius on the inside can also be determined by dividing the bend radius by the material’s thickness.
• As the inner radius to thickness ratio decreases, the tensile strain at the surface of the material increases.
• Here we have yet another illustration of Poisson’s Ratio in operation.
• Using the tensile reduction value and the thickness of the material, you can get a rough estimate of the minimum bend radius.
• Without knowing your suppliers and whether you’re going with or against the grain, your k-factor gumbo will be missing a key ingredient.
• Metals show anisotropy when they are bent at right angles to the grain, changing both their angle and radius.
• Taking into account the metal’s anisotropic properties is crucial for obtaining accurate k-factor and bend allowance estimates.
• By bringing the neutral axis inward when bending with the grain, the k-factor can be changed.
• Outside cracking is more likely as the neutral axis gets closer to the inside surface of the bend.
• This suggests that a larger inside bend radius is needed when bending with the grain.
• The neutral axis is pushed further inward as the material’s thickness increases in relation to its inner radius. 
• This is assuming a die opening that is in direct proportion to the material thickness.
• If the material is exceptionally tough, the radius inside must be a multiple of its thickness.

FAQs About Metal

What Is a Good K-Factor?

From discussions with other entrepreneurs, investors, and growth hackers, I’ve learnt the following: for a consumer internet product, a sustainable viral factor of 0.15 to 0.25 is good, 0.4 is great, and around 0.7 is outstanding.

What Is a Normal K-Factor?

The K-factor is usually somewhere between 0.3 and 0.5.

How Do You Calculate K-Factor Referral?

How to calculate the k-factor? The most common formula is k-factor = i*c, where i is an average number of invitations sent by one user, c is an average conversion from received invitation into registration.

What Does a High K-Factor Mean?

K factor is soil erodibility factor which represents both susceptibility of soil to erosion and the rate of runoff, as measured under the standard unit plot condition. Soils high in clay have low K values, about 0.05 to 0.15, because they resistant to detachment.

What Is Transport K-Factor?

The K factor, defined as the proportion of annual average daily traffic occurring in an hour, has traditionally been a critical factor in highway planning and design. The standard practice is to design roadways to the 30th or 100th highest hourly volume of the year.