The white dashed line on the part shown above represents the neutral axis which is the theoretical point in the material that does not change during the course of forming. Bend allowance is nothing more than the amount of material that is used for the bent portion of the sheet metal. To calculate r which is the radius of the arc on the neutral axis we can use the following equation. Working with an included bend angle of 60 degrees, a material thickness of 0. The bend angle a in degrees, inside bend radius r in m, kfactor k. Online calculator of sheet metal bend deduction and flat. There should have a bending radius for sheet metal bending, it should not be too large or too small, and should be chosen appropriately. Inside radius is generally equal to the radius of the bending tool. The tables below show bend radii and minimum bend sizes for materials and tooling combinations stocked by protocase. For example, if the thickness of the sheet is 1 mm, the minimum bend radius should be 1 mm. Sheet metal bend allowance explained with formula and. Cut a sample sheet and measure its total flat length and sheet thickness in mm. The minimum radius of bend of a sheet of material is the sharpest curve, or bend, to which the sheet can be bent without critically weakening the metal at the bend.
A seam is a method of joining two pieces of sheet metal together, figure 5. The bend allowance and bend deduction are two measures that relate the bent length of a piece of sheet metal to the flat length. Often bend allowances are calculated for a sheet metal part and. The force pressed on the sheet metal during bending is different, the counterforce is also different. Minimum bend radius calculator in sheet metal or plate. The acute bend actually produces a small flat across the inside of the bend rather than a true radius, figure 3. When bending steel, no material is lost and no material is gained. C50 steel, ultimate tensile strength can be taken as.
The amount of bending spring back is generally expressed in terms of angle. The leg lengths are the part of the flange which is outside of the bend radius. Kfactor calculator for sheet metal bending smlease design. Sheet metal bending design tips, bend allowance, k. The primary focus in this article is on sheet metal forming operations, such as the one shown. For a sheet metal stock with inch thickness, determine the minimum tool radius for both the steel and aluminum alloys that will not tear the material. However, you can use v grooving machine to groove first, and then bend. This bend allowance formula is used to determine the flat pattern length when a. Bend radius as a rule, inside bend radius should be equal to material thickness. Bending is a commonly used sheet metal shaping process in various sheet metal industrial products tekiner 2004. Bend radius throughout the sheet metal design is kept constant to take the advantage of using the same tool during manufacturing. The basics of applying bend functions the fabricator.
Sheet metal unfold rule equations ketiv technologies. Bending is a manufacturing process that produces a vshape, ushape, or channel shape. S 4mpa of the sheet metal by using the formula of bending. And by having t and the sheet thickness t we can calculate the kfactor as follow. We go beyond the general rules of sheet metal bending, as our customers want tight bend radii for sheet metal parts. Sheet metal calculator bend allowance equations and. But in some cases for material like crca you can manufacture parts with inner radius equal to 60 percent of sheet thickness check out more in details about sheet metal design guidelines here. Online bend deduction calculator microform precision. Pdf bend allowance and developed length calculation for. Calculating bend allowance, bend deduction, and kfactor. How to use this kfactor calculator in sheet metal reverse engineering approach step1. Tight bend radius gradual bend radius kfactor effectively 50%t max. If the radius of bend is too small, stresses and strains weaken the metal and may result in cracking.
The formula for calculating sheet metal bending allowance is please refer to the above picture. Bending is defined as the plastic deformation of sheet metal along a straight line. Here again, a minimum bend radius is not necessarily the same thing as a sharp bend. Recommended inside bend radius for sheet metal parts should be equal to material thickness. A sharp bend will always be less than a minimum bend radius but, a minimum bend radius does not need to be sharp minimum bend radius. Making a radius bending fixture for sheetmetal youtube. The bend allowance added to the flange lengths is equal to the total flat length of the part. Due to this tension and compression, the length of the sheet metal piece increases. The bending angle will be affected by material, plate thickness, pressure, bending radius etc. Actual dimensions can only be found by making the bend and measuring the results. That means you subtract the negative bd again, the same as adding when doing the flatblank calculation. Open sheet metal bend allowance calculator sheet metal bend allowance equations. Design for manufacturability sheet metal guidelines bends for the ease of manufacturing, multiple bends on the same plane should occur in the same direction. A minimum radius of bend is specified for each type of aircraft sheet metal.
Material to the inside of this line ought to compress whereas the material on the outside of it should expand. As this happens you gain a small amount of total length in your part. It is very difficult to calculate the bending spring back accurately. Bending is one of the most common sheet metal fabrication operations. It explains how setback, bend allowance, bend radius, and sight lines work when bending. In sheet metal design, the kfactor is used to calculate how much sheet metal one needs to leave for the bend in order to achieve particular final dimensions, especially for between the straight sides next the bend. A radius that is larger than the thickness of the material has no aesthetical issues. Understanding the bend allowance and consequently the bend deduction of a part is a crucial first step to understanding how sheet metal parts are fabricated. Pdf the study of design constants in sheet metal forming. Due to this elastic recovery, it is necessary to over bend the sheet a precise amount to achieve the desired bend radius and bend angle.
Now lets see how we can obtain these values for a specific sheet. For most applications with stainless steel or aluminum, you can get away with a zero radius bend on anything under 0. V l2 rt bend allowances for cincinnati incorporated. For gaging, remember to use only one leg and onehalf of the bend allowance to approximate the distance. The force must exceed the materials yield strength to achieve a plastic deformation. When bending a piece of sheet metal, the residual stresses in the material will cause the sheet to springback slightly after the bending operation. The bend allowance formula takes into account the geometries of bending and. Figure 2 illustrates the sheet that is bent with the bend angle of 90 degrees. Bend relief when a bend is made close to an edge the material may tear unless bend relief is given. As i mentioned in my last post you need to do some tests to calculate these values for a specific sheet. Sheet metal operations 3 nageswara rao posinasetti february 6. The following illustration shows the equation calculation for determining the bend allowance when forming sheet metal. Therefore, the bend allowance added to the flange lengths is equal to the total flat.
Please note the bending of sample part is done in the same manner as we are planning for production. Use the known kfactor and the known inner bending radius to calculate the bending radius. Since the inside compression can not exceed the outside tension, the kfactor can never exceed. To calculate the neutral axis distance from the inner face t we can subtract inside bend radius from r. The neutral line is located at a distance t from the inside of the bend radius. Thus the smallest radius of any bend in a sheet should be at least equal to the thickness of the sheet. Lower the bend radius, higher is the strain in this zone. When a piece of sheet metal goes through the process of bending, its upper layer with inside radius is compressed and the lower layer with outside radius is stretched. Understanding the bend deduction and consequently the bend allowance of a part is a crucial first step to understanding how sheet metal parts are fabricated. Bends that are in the same plane need to be designed in the same direction to avoid part re orientation, to save both money and time. In my previous post i talked about kfactor, bend allowance and bend deduction and what they mean in sheet metal design. This calculator predicts what the minimum bend radius should be to avoid chacking or orange peeling on the outside radius of the bend.
I have already learned about the following formulas. Other standard bend radii available, some of which will add additional cost to your part, include. A physicsbased model for calculating bend allowance and developed length for a strain hardening sheet metal formed by pressbrake bending. The smallest width of bending is 8 to 10 times the material thickness and the minimum inside corner radius of the bend is 1. Ron covell shows how easy it is to build a radius bending attachment that mounts to a workbench. How to select a vdie opening for press brake bending. If the bending radius is too small, it will cause cracking at the bend position. Pdf version a printable pdf version of this information is available here. With this free online tool we quickly get the sheet metal bend deduction, and therefore the sheet metal blank initial flat length, from the finished part measurements you only have to insert interior angle, flange lengths, k factor, inside radius, and material thickness. Sheet metal design guidelines design for manufacturing. For this layout example, use the minimum radius chart in figure 4125 to choose the correct bend radius for the alloy, temper, and the metal thickness. When the radius is less than recommended, this can cause material flow problems in soft material and fracturing in hard material.
Keeping the bend radius consistent will also make parts more costeffective. The bend deduction, sometimes called the bend compensation, describes how much the outside of the sheet has been stretched. Bend the sheet to 90 degrees and measure length a and b. Press brake bending basics a guide to sheet metal bending. Calculate the setback and then subtract it from the sum of two outside dimensions as. But to make this happen, you need to make sure every factor in the equation is what it should be, and this includes the inside bend radius. The procedure for bending sheet metal in a folding machine is as follows. This k factor is derived from the bend allowance formula. In low carbon steel sheet metal, the minimum radius of a bend should be onehalf the material thickness or 0. Bend allowances, outside setbacks, bend deductionsif you can calculate all of these with precision, you have a much better chance of bending a good part on the first try. An example of a manually operated folding machine is shown in fig. When folding sheet metal, if the resulting radius is less than the thickness we are bending, then the extra material must go somewhere and can cause an undesirable deformation. Bend deduction explained with formula and calculator. Therefore, the bend deduction equals the difference between the mold line lengths and the total flat length.
The bending tool has a radius of 30 mm which means that our inside bend radius r is 30 mm. Ideally it should be equal to sheet metal thickness. Length of tube consumed in a bend clrcenter line radius x dob degree of bend x. We recommend a minimum bend radius of 1t for all sheet metal parts. This page also includes a link to a online sheet metal bend allowance calculator. It is possible to choose other bends if you require, but additional lead time and tooling charges may apply.
Avoid large sheet metal parts with small bent flanges. Bending a known length of sheet metal is easy, but to calculate the bend. Design for manufacturability sheet metal guidelines. When the sheet metal is put through the process of bending the metal around the bend is deformed and stretched. Use this document to choose values that are both manufacturable and meet your needs. Sheet metal bend brakes are used to bend material into the parts desired geometry. A bending operation is employed to fabricate parts such as braces, brackets, supports, hinges, angles, frames, channel and other non. It is most economical to use a single bend radius throughout the design, but if necessary, you can utilize multiple radii. In other words the kfactor you calculate now will take into account any small inaccuracies in the bend radius measurement and compensate for it. Bending of sheet metal the international journal of engineering. Most sheet metal materials will conform to the calculations. Bending and forming tools sheet metal operations bending. Calculate the bending force required for a c50 steel 1.