The K-factor describes the relationship between the neutral axis and the thickness of a sheet of metal. As a metal sheet is bent, the material on the outside of the curve expands while the material on the inside contracts. As a result, the neutral axis shifts from its original position at fifty per cent of a material thickness towards the inside face of the bend. Still, no further changes occur in this region where compression and expansion meet. Elongation happens during bending because the neutral axis moves, but the length stays the same. The thickness, inner bend radius, and forming method affect how much the neutral axis moves.
You can calculate the new location of the neutral axis by multiplying the thickness of the material by the standard K-factor value of 0.446. Essentially, we are trying to fit the length measurement from a bigger radius onto a smaller one. By squeezing the same amount of material into a smaller radius, we have elongation rather than the previously assumed additional length.
Think about using a material thickness of 0.060 inches. To get 0.0268 in, we multiply by such a K-factor of 0.446. So from the inside of the curve, the axis has rotated by 0.0268 inches. 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 figure out how much the arc should bend.
It is important to remember that the K-factor varies depending on the type of material, the forming method, and the connection between the bend radius and the material thickness. These subsequently affect the overall amount of elongation and the necessary bend deductions.
SOLIDWORKS sheet metal equipment is quite simple; it is not often well understood. The K-Factor is one of the most potent constants of bending in sheet metal. The result approximates the stretch that works even if you don't know the exact nature of the material being bent. Since you do not even know the precise method or machine that will be employed to bend the sheet, this allowance can serve as a stand-in.
Table of Contents
Why Is K-Factor Important?
The k-factor is arguably the most crucial mathematical constant for high-precision sheet metal production. It's the starting point for figuring out how much leeway to give for bending and how much to deduct from there. Finally, a mathematical multiplier is used to find the newly relocated neutral axis of the bend.
After the k-factor is determined, the entire amount of elongation within a specific bend can be predicted. For example, a precision part's flat layout, outside setback, bend allowance, and bend deduction can all be determined using the k-factor.
How Do You Define the Neutrality Axis?
It is necessary to have a good grasp of a few fundamental terms, the first of which is the neutral axis, to comprehend the k-factor. When the material is flat and unstressed, a theoretical region called the neutral axis exists at this halfway point. Put another way; the neutral axis is not a fixed point; it moves inward as the curve is curved. The arc's bending unaffected the length of the putative neutral axis line.
When a material is bent, compressive forces act on the region between the pivot point and the inner surface. In contrast, tensile forces act on the region between the centre line and the outer surface. It is the plane through which tension and compression are equal and distinct that we call the neutral axis. The interior bend radius, bending angle and forming method all influence where the neutral axis lies.
The flat section must be less than the sum of the produced piece's exterior dimensions behaviour on the part of the neutral axis.
What Exactly Is the Function of K-Factor?
We'll cover the various k-factor definitions in upcoming columns. In any case, the standard definition of the k-factor is available in several places. The one that comes up next was written by a professor at Bangladesh's Ahsanullah Science and Technology University and comes from the school's Mechanical but also Production Engineering Department.
Just dividing the sheet's thickness by the position of the centre line yields the k-factor, a constant. The region inside the sheet that is the neutral axis is not affected by compression on the inside or expansion on the outside. When anything is bent, the length of the neutral axis doesn't alter in any way.
Yet, the neutral axis shifts inward by a certain amount—the k-factor indicates how much. During forming, the neutral axis of the part moves from a position at exactly half the layer thickness to the new location at exactly half the material thickness or less. The bend allowance is the linear radius around the curve's arc at the neutral axis.
Let's pretend the thickness of your material is One millimetre. The neutral axis of the material is centred on fifty per cent of thickness, or 0.5 mm, when it is in a balanced state. When the material is bent, the neutral axis moves inward to a new location at a distance of 0.446 mm from the curved surface. The letter t denotes this rotation of the neutral axis in Figure 2. The k-factor is found by dividing time by the thickness of the material: The formula for the k-factor is t/Mt.
The k-factor is just a multiplier that provides a precise estimate of the new position of the neutral axis. The k-factor can be calculated from the bend allowance. Knowing the k-factor will help you to calculate the allowable bending radius for a given angle.
When working with sheet metal, the k-factor is essential for precision. Without consulting a table, you may calculate the bending deduction for a wide range of angles. Although bend calculation charts for bend allowance and bend deductions have historically been notoriously inaccurate, modern bending deduction charts are now relatively accurate. Most of the time, they would only apply to the specific factory where they were developed. It's also worth noting that many of these diagrams are still in circulation.
A perfect k-factor does not exist. For instance, it ignores all of the internal tensions and stresses that occur in a material when it is bent. The tension and yield strengths, the forming technique, the tooling, and other factors all play a role in determining the k-factor.
A chart showing the range of possible k-factors, from 0.50 to 0.33, is shown in Figure 3. The k-factor may also be quite small. The average k-factor value offered in practical contexts is 0.4468.
There is a good reason why k-factors greater than 0.50 are seldom used in the real world. To avoid failure, the stress concentration of the bend must be less than the strain from the outside. The neutral axis is in the centre of the sheet when there is no load on it. But when you put the metal under some pressure, you'll see what happens. Under tension, the granular linkages are stretched, tugged, and sometimes break, causing the grains to separate.
If you stretch something in one way, it will shrink in the other. This is an example of Poisson's Ratio in action. The reason that the outer region of a bend's cross-section is larger than the inner part is explained by Poisson's Ratio. Leaving the curve, your sphere of influence will grow larger while your interior will contract.
Check out Austgens METAL ASSEMBLY
What Is the Minimum Bend Radius?
Parts built with an interior bend radius significantly tighter than necessary are a prevalent issue in the sheet metal or plate industries. Press brakes are vulnerable to this problem, as they can lead to cracking on the bend's outer surface.
Too much force from the bending causes plastic deformation if the bend is too acute. Damage from the issue will show up as cracks on the surface, affecting how much the material can bend. The neutral axis moves closer to the inside surface of a bend as the inside bend radius decreases.
Based on data from Machinery's Handbook, this general k-factor chart provides typical k-factor values for various uses. By "thickness," we mean the depth or breadth of a piece of material. In most bending situations, a k-factor of 0.4468 is employed.
The term "minimum bend radius," which appears on many drawings, and its various interpretations, is a major contributor to this. When they see "minimum bend radius," many people automatically grab the punch with the sharpest tip.
As opposed to the punch's radius, the material determines the minimum bend radius. Therefore, the minimum inside bend radius is possible in the air without bottoming and coining material.
A severe bend would result from air forming with a punch radius smaller than the minimum floating radius. In addition, part-to-part material variances exacerbate the normal angle deviation, leading to dimensional flaws in the workpiece as the material's inherent variations become more apparent.
There are two distinct variants of the minimum bend radius. However, they both have the same effect on the k-factor. The transition between a sharp and a minimum radius in an air form represents the first form of such a minimum radius. When this happens, the material's imperfections are accentuated, and a crease forms at the bend's centre because the pressure of form is greater than the pressure to puncture. The k-factor shifts when the punch nose breaks through the material and further compresses that inner area of the bend.
The second method for calculating the minimal inside bend radius involves dividing the bend radius by the thickness of the material. The tensile strain on the material's surface increases as the Ratio of the inner radius to the thickness decreases. As soon as the proportion
If the sheet metal is bent with its grain or rolling direction, the problem becomes even more severe. Sharp punch-nose radii, when compared to the thickness of the material, cause the grains in the material to extend significantly further than they would have if the diameter were equal to the thickness. Poisson's Ratio is at work once more. When this occurs, the neutral axis shifts towards the material's interior while its thickness increases at the exterior.
In this context, the term "minimum bend range for material thickness" describes the second type of minimum bend radius. Common units are 2Mt, 3Mt, 4Mt, etc., where Mt is the material thickness. Charts detailing the smallest bend radii required for various alloys and tempers are available from most material suppliers.
What is the source of the data used for the minimum radius charts? They involve other components, such as flexibility, that enhance our k-factor gumbo. A material's flexibility, or its capacity for plastic deformation, can be gauged via a tensile test. Reduced area, often known as tensile reduction of area, is a metric used to assess flexibility. Given the material thickness, the minimum bend radius can be roughly estimated from the tensile reduction value.
If your material is at least 0.25 inches thick, you can use this formula to determine the minimum bend radius: (50/tensile area reduction %) - 1) Mt. You may utilize this calculation to determine the smallest radius you can bend material thinner than 0.25 inches: The formula is: [(50/Tensile decrease of area %) - 1] Mt 0.1
To solve these equations, the % must be entered as a full number, not a decimal. Hence, if your 0.5-inch-thick material has a 10% reduction percentage, you would substitute 10 for 0.10 in the equation.
(50/Tensile area decrease %) minus 1. × Mt
[(50/10) – 1] × 0.5 = 2
The inside edge of a curve becomes "convex" due to compression inside the bend.
A minimum inside bend radius of two times the overall material thickness is required here. It's important to remember that this is only a rough estimate. As with any metal, research is needed to determine the minimum radius of curvature for steel or aluminium plate. Information from your material provider is essential, but so is knowing whether you're working against or for the grain when calculating your k-factor.
Check out Metal Fabrication Welding Aluminium
What’s Grain Direction?
Grain runs through the middle of the sheet because it forms in the direction of rolling at the mill. If you look closely at a brand-new sheet of metal, you'll be able to tell which way the lines are going. The particles take on an extended shape when rolled into a sheet.
The grain pattern of a piece of wood is not the same as the surface finish, which is achieved through sanding or other mechanical processes. Yet, whenever the finish grain is perpendicular to the natural grain, cracking is more likely to occur due to finish surface scratches.
The grains' inherent orientation makes for angle and, possibly, interior radius fluctuation. Anisotropy refers to the material's reliance on orientation, which plays a crucial role in manufacturing accurate components.
Metal becomes anisotropic when bent perpendicular to the grain, altering the angle and radius. Therefore, predicting the k-factor and the bend tolerances with any degree of precision requires considering the metal's anisotropy.
When you bend anything with the grain, you're shifting the neutral axis inward, altering the k-factor. Also, the probability of cracking on the outer radius increases as the neutral axis approaches the inner surface of the bend.
The grain can be bent with less force than it can be bent crosswise, but the result is a weaker bend. As a result, the particles are more easily torn apart, which might cause cracking on the outer radius. Sharp bending can amplify this effect. So, it is safe to assume that a bigger inside bend radius is required if you are bending with the grain.
How Thick and Tough Should the Material Be?
The next two components are the thickness and hardness of the material. The neutral axis is displaced inward as the thickness of the material grows thinner about the inner radius.
Along with decreasing in value, the k-factor also decreases as the difficulty increases. More stretching effort is needed to achieve a given angle with materials that are harder to work with. This results in a larger tension region outside the neutral axis and a smaller region inside. The interior radius must be a multiple of the thickness of the material if it is particularly hard. Poisson's Ratio is at work here once more.
Check out Exactly what is the sheet metal working procedure.
How to Compute K-Factor?
There is no easy way to determine the K-Factor before the first bend, as it depends on the quality of a metal and its thickness. The K-Factor is typically between 0.5 and 1.0. Determine the Bend Allowance from bending a material sample to obtain the K-Factor. The K-Factor can then be calculated by plugging the Bend Allowance into the formula.
To start, get some sample blanks ready that are all the same size. For a uniform bent, the blanks ought to measure at least a foot long, and they should be a few inches deep so that they may be propped up against the backstops. Take a 14-gauge,.075", 4-inch-wide, the 12-inch-long piece as an illustration. We won't be factoring in the whole length of the work. To aid in this endeavour, prepare as least three samples and use the average of their respective measurements.
Make a 90° twist in the middle of the metal and set up the press braking with the appropriate equipment for working with this thickness of metal. Here, that signifies a turn just at the 2" mark.
When you've bent all sample pieces, you should meticulously record their flange lengths. Don't forget to tally all the measurements and average them out. It would be best if you aimed for a length greater than 50 per cent of the original. For this particular example, the typical flange length is 2.735 inches.
The second is to calculate the new interior radius after bending. You can obtain close to the right measurement with a set of radius gauges, but an optical comparator would give you the most precise reading. In this case, we use an inside radius of.105 as an illustration.
We can calculate the Bending Tolerance once you've provided us with the necessary dimensions. Start by subtracting the thickness inside and radius of the material from the flange length to get the leg length. Hence, in this case, the leg length is found to be 1.893 by subtracting 2.073 from 2.105 and 0.075.
To calculate the Bend Allowance, take the beginning length and add twice the leg length. 4 – 1.893 * 2 = .214.
To calculate the K-Factor, enter the Bend Allowance, Bend Angle, Inside Radius, and Layer Thickness into the following equation. To give an illustration, consider
K = d/180 c. b. a. pi c. b. m. t. - d/frac. i. r. m. t.
Define the K-Factor graph.
K-Factors can be smaller or bigger than 0.5, but for most materials and thicknesses, you'll find it falls somewhere in that range. To get you started, I've provided a K-Factor Chart with some standard values for steel, aluminium, and stainless steel that should work well for general fabrication.
Conclusion
The K-factor describes how the neutral axis of a metal sheet relates to its thickness. The K-factor varies with the properties of the material, the forming technique, and the relationship between the bend radius and the thickness of the material. The new position of the neutral axis can be determined by multiplying the material's thickness by the typical K-factor value of 0.446. The outcome is a close approximation of the stretch that is effective even if the exact nature of the material being bent is unknown. When it comes to fabricating metal sheets with a high level of accuracy, the k-factor is an essential mathematical constant.
A mathematical multiplier is used to determine the new location of the neutral axis of the bend by dividing the thickness of the sheet by the location of the centre line. We refer to the plane in which tension and compression are equal and distinct as the neutral axis. When something is bent, the neutral axis' length does not change because of internal compression or external expansion. When bending a material, the k-factor can be used as a multiplier to get a good idea of where the neutral axis will end up. The linear radius around the arc of the curve at the neutral axis can be used to determine the bend allowance, which is then used to determine the radius of the curve.
Because tension and yield strengths, forming technique, tooling, and other variables all contribute to the k-factor, there is no such thing as a perfect k-factor. Typically, 0.4468 is the k-factor value that is suggested in real life. Since the localised stress of the bend must be less than the external strain, K-factors greater than 0.50 are rarely used in practise. It's largely due to the fact that the material itself establishes the "minimum bend radius," a term that has become ubiquitous in the industry. Poisson's Ratio, which states that the outer region of a bend's cross section is larger than the inner part, provides an explanation for this phenomenon.
A severe bend would result from air forming with a punch radius smaller than the minimum floating radius, but the minimum inside bend radius is possible in air without bottoming and coining material. There are two distinct forms of the k-factor that both have the same effect on the imperfections of the material, but they are distinguished by their minimum bend radius. The first example of such a minimum radius is the change from a sharp to a minimum radius in an air form. The second approach to finding the smallest possible inside bend radius divides the bend radius by the material's thickness. Most material suppliers have charts showing the minimum bend radii required for various alloys and tempers.
Data used to create minimum radius charts comes from other components, such as flexibility, which can be measured with a tensile test. The following formula can be used to calculate the minimum bend radius for material at least 0.25 inches thick: Using the formula: (50/tensile area reduction%) - 1) Mt. For steel and aluminium plate, the inside bend radius must be at least two times the total material thickness, and the k-factor and bend tolerances must be calculated using a whole number, not a decimal. Finding out whether the grain is working with or against the material is crucial for determining the k-factor. The anisotropy of a material describes its dependence on orientation, which is essential for producing precision parts. When metal is bent in a longitudinal direction, less force is required to achieve the same degree of deformation than when bending it across its grain.
This is amplified by sharp bending. The K-Factor ranges from 0.5 to 1.0, reflecting the thickness and hardness of the material being evaluated. As the challenge grows, the neutral axis moves outward, creating a larger tension region beyond it and a smaller one within it. Sample blanks used in determining the K-Factor should be at least a foot long and a few inches deep so that they can be supported by the backstops. As an example, determine the Bending Tolerance, Bend Allowance, Bend Angle, Inside Radius, and Layer Thickness of a 14-gauge,.075", 4-inch-wide, 12-inch-long piece. To determine the K-Factor, take the flange length, deduct the material's inner radius and thickness, and add twice the leg length. For most materials and thicknesses, the K-Factor graph is between 0 and 1, though it can be smaller or larger. For general fabrication, a K-Factor Chart with some typical values for steel, aluminium, and stainless steel should do the trick.
Content Summary
- The K-factor describes the relationship between the neutral axis and the thickness of a sheet of metal.
- You can calculate the new location of the neutral axis by multiplying the thickness of the material by the standard K-factor value of 0.446.
- It is important to remember that the K-factor varies depending on the type of material, the forming method, and the connection between the bend radius and the material thickness.
- The K-Factor is one of the most potent constants of bending in sheet metal.
- The k-factor is arguably the most crucial mathematical constant for high-precision sheet metal production.
- Finally, a mathematical multiplier is used to find the newly relocated neutral axis of the bend.
- Just dividing the sheet's thickness by the position of the centre line yields the k-factor, a constant.
- The region inside the sheet that is the neutral axis is not affected by compression on the inside or expansion on the outside.
- Yet, the neutral axis shifts inward by a certain amount—the k-factor indicates how much.
- During forming, the neutral axis of the part moves from a position at exactly half the layer thickness to the new location at exactly half the material thickness or less.
- The bend allowance is the linear radius around the curve's arc at the neutral axis.
- The neutral axis of the material is centred on fifty per cent of thickness, or 0.5 mm, when it is in a balanced state.
- When the material is bent, the neutral axis moves inward to a new location at a distance of 0.446 mm from the curved surface.
- The formula for the k-factor is t/Mt.The k-factor is just a multiplier that provides a precise estimate of the new position of the neutral axis.
- The k-factor can be calculated from the bend allowance.
- Knowing the k-factor will help you to calculate the allowable bending radius for a given angle.
- There is a good reason why k-factors greater than 0.50 are seldom used in the real world.
- The reason that the outer region of a bend's cross-section is larger than the inner part is explained by Poisson's Ratio.
- Parts built with an interior bend radius significantly tighter than necessary are a prevalent issue in the sheet metal or plate industries.
- The neutral axis moves closer to the inside surface of a bend as the inside bend radius decreases.
- As opposed to the punch's radius, the material determines the minimum bend radius.
- The k-factor shifts when the punch nose breaks through the material and further compresses that inner area of the bend.
- The second method for calculating the minimal inside bend radius involves dividing the bend radius by the thickness of the material.
- In this context, the term "minimum bend range for material thickness" describes the second type of minimum bend radius.
- Given the material thickness, the minimum bend radius can be roughly estimated from the tensile reduction value.
- Hence, if your 0.5-inch-thick material has a 10% reduction percentage, you would substitute 10 for 0.10 in the equation.(50/Tensile area decrease%) minus 1.
- A minimum inside bend radius of two times the overall material thickness is required here.
- As with any metal, research is needed to determine the minimum radius of curvature for steel or aluminium plate.
- Metal becomes anisotropic when bent perpendicular to the grain, altering the angle and radius.
- Therefore, predicting the k-factor and the bend tolerances with any degree of precision requires considering the metal's anisotropy.
- The next two components are the thickness and hardness of the material.
- The neutral axis is displaced inward as the thickness of the material grows thinner about the inner radius.
- There is no easy way to determine the K-Factor before the first bend, as it depends on the quality of a metal and its thickness.
- Determine the Bend Allowance from bending a material sample to obtain the K-Factor.
- We can calculate the Bending Tolerance once you've provided us with the necessary dimensions.
- Start by subtracting the thickness inside and radius of the material from the flange length to get the leg length.
- 4 – 1.893 * 2 = .214.To calculate the K-Factor, enter the Bend Allowance, Bend Angle, Inside Radius, and Layer Thickness into the following equation.
FAQs About Weldings
The K-factor depends on many variables, including the material, the type of bending operation (coining, bottoming, air-bending, etc.), the tools, etc. and is typically between 0.3 and 0.5.
The K factor is defined as the ratio between the material thickness (T) and the neutral fibre axis (t), i.e. the part of the material that bends without being compressed nor elongated.
In general, the greater the temperature difference between the hot and cold areas of fluid, the greater the thermal driving head and the resulting flow rate.
The meter base K-factor is used in the flow computer's calculation of the quantity of liquid delivered, so it must be considered during the testing of a meter. The proving K-factor (PKF) is used to calculate the correct meter factor based on the pulses it receives while a known amount of liquid passes through the SVP.
The relationship between the pressure in the pipe and the flow rate is proportional. That is, the higher the pressure, the higher the flow rate. The flow rate is equal to the velocity multiplied by the cross-section. For any section of the pipe, the pressure comes from only one end.