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How to calculate bend allowance for your press brake

How to calculate bend allowance for your press brake

Tonnage calculations are estimates for air bends only. The tonnage calculator is for 20ga to 3" material, bent over a vee die in the range of 5 to 19 times the material thickness. The intuitive interface will guide the user through the process by allowing selection of material type, material thickness, and vee die opening.

From these parameters, a tonnage will be calculated along with the minimum flange length and inside bend radius. Sign up today to receive notifications on company and product news and updates!

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how to calculate bend allowance for your press brake

Control Retrofits. File Upload. Pay Invoice. Serial Number Finder. Software Downloads. Support - Applications. Support - Plans. Support Plans - Credit Card Payment. Upgrades - Fiber Lasers.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.

When the sheet metal is put through the process of bending the metal around the bend is deformed and stretched. As this happens you gain a small amount of total length in your part. Likewise when you are trying to develop a flat pattern you will have to make a deduction from your desired part size to get the correct flat size.

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The Bend Allowance is defined as the material you will add to the actual leg lengths of the part in order to develop a flat pattern. The leg lengths are the part of the flange which is outside of the bend radius. Unfortunately sheet metal bending is not always going to be the same in every shop. The largest variations come from the materials themselves.

Press Brake Tonnage Load Calculator

Protective coatings, variations in the alloy and thickness as well as many other small factors all add up to give you Bend Allowances unique to your operation. This chart will get you close enough for most applications and may not require fine tuning on your part. Bend Allowances. Bend allowance is the amount of metal to be added to the total layout.

The most important considerations when bending metal is the min. When bends are made smaller than the required min. The min.

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There are four methods for finding bend allowances. In the form below uses the empirical formula. It is the most accurate because it takes into account the shifting of the neutral line, slightly inward, when the metal is bent. The following form must be filled in with decimal equivalants. Request a quote. Plasma Cutters. Username or Email. Remember me. Back to Login Register.

Bend Allowance Calculator. Calculators Bend Allowance Calculator. Bend Allowances Bend allowance is the amount of metal to be added to the total layout. Thickness of Material:.

Angle of Bend:. Bend Allowance:. Inches decimel equivalent.When a sheet metal part is bent, it physically gets bigger. The final formed dimensions will be greater than the sum total of the outside dimensions of the part as shown on the print—unless some allowance for the bend is taken into account. Technically, the metal does neither, but instead elongates. It does this because the neutral axis shifts closer to the inside surface of the material.

The neutral axis is an area within the bend where the material goes through no physical change during forming.

On the outside of the neutral axis the material is expanding; on the inside of the neutral axis the material is compressing. Along the neutral axis, nothing is changing—no expansion, no compression.

As the neutral axis shifts toward the inside surface of the material, more material is being expanded on the outside than is being compressed on the inside. This is the root cause of springback.

The length of the neutral axis is calculated as a bend allowance, taken at 50 percent of the material thickness. This K-factor is applied as an average value for most bend allowance calculations.

There are other values for stainless and aluminum, but in most cases, 0. If you multiply the material thickness by the K-factor 0. This means that the neutral axis moves from the center of the material to a location 0. Again, the neutral axis goes through no physical change structurally or dimensionally. It simply moves toward the inside surface, causing the elongation.

Note the two factors shown in the bend allowance formula: 0. The first factor is used to work your way around a circle or parts of a circle, and the second value applies the K-factor average to the first factor. The 0.

Bend Allowance Calculator

Note that for the bend allowance, the bend angle is always measured as complementary see Figure 1. The outside setback is a dimensional value that begins at the tangent of the radius and the flat of the leg, measuring to the apex of the bend see Figure 2. At 90 degrees, it does not matter if you use the included or complementary angle; you still end up with 45 degrees, and you get the same OSSB answer.

For underbent angles click here for Terminology may be different depending on how a protractor is read. For overbent acute bend angles, either the included or complementary angles may be used.

The choice is yours, but it does affect how you apply the data to the flat pattern. Figure 2: The outside setback OSSB is a dimensional value that begins at the tangent of the radius and the flat of the leg, measuring to the apex of the bend. A bend deduction BD is the value subtracted from the flat blank for each bend in the part, and there may be more than one.

how to calculate bend allowance for your press brake

Note that when overbending and making the OSSB calculation using the included bend angle, you may calculate a negative value for the bend deduction. You will need to take the negative value into account when calculating the flat blank, as discussed in the next section.

There are two basic ways to lay out a flat blank, and which to use will depend on the information that you are given to work with.Years ago, the real experts created cheat sheets and tacked them to the wall. They only taught the new apprentice how to apply the results shown on the cheat sheet, not how to calculate the numbers.

Well, now those experts have retired and it's time for a new generation to learn the right way to do the calculate the correct flat pattern layout. Calculating the flat pattern length from the 3D part really isn't that difficult. Although you may find several different formulas that claim to calculate the Bend Allowance See Bending Definitionsthey usually are the same formula, only simplified by filling in the angle or a K-factor. Oh, and yes, you do need to know the K-factor to calculate the Bend Allowance.

Let's start with a simple L bracket. The picture shows that the legs of the bracket are 2" and 3". The material thickness is 0. The flat length is the total of the flat portion of both flanges plus the length through the arc of the bend area. But, do you calculate that on the inside of the material or the outside?

This is where the K-factor comes into play. The K-factor is the percentage of the material thickness where there is no stretching or compressing of the material, for example, the neutral axis.

For this simple L bracket, I will use a K-factor of 0. So if you add up the flat length of all the flanges and add one Bend Allowance for each bend area you have the correct flat length of the part.

But look at the drawing. That is not how we normally dimension a sheet metal part. The dimensions are usually to the intersection of the flanges or the Mold Line. This means that we have to subtract two times the material thickness plus the bend radius also known as the Setback for each bend area.

For this set of dimensions, it would be easier to calculate the Bend Compensation value. The Bend Compensation value lets you add up the length of each flange using the Mold Line dimensions and then add one Bend Compensation per bend area to the total. Don't bother with your calculator. It is Post a Comment. Posted by Gundyabhaoo at AM. No comments:. Newer Post Older Post Home. Subscribe to: Post Comments Atom.

About Me Gundyabhaoo View my complete profile.This learning object uses Adobe Flash and your browser does not support Flash.

Click Here for instructions to enable Flash. By Dave Hoffman. Introduces two methods of determining bend allowance; one is simple and is an approximate, the other is more precise. Interactive part has learner calculate bend allowance and blank size. Click here to login. By Terry Bartelt. In this animated activity, students view the operation of a 4-bit serial-in serial-out register. A brief quiz completes the learning object.

Reading a Micrometer. By Sue Silverstein. By Kelly Curran. This document is a visual and text description of the three-wire method for measuring screws for use with a lathe. The Reflected Load in a Transformer. Learners examine how the load resistance connected to the secondary coil of a transformer affects the primary current.

Bending basics: Dissecting bend deductions and die openings

A brief quiz completes the activity. The IC Binary Counter. In this interactive and animated object, learners examine the construction of a IC as mod-2 and mod-8 up-counters. They view how this binary counter can be modified to operate at different modulus counts.

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Creative Commons Attribution-NonCommercial 4. This website uses cookies to ensure you get the best experience on our website. Privacy Policy OK.As I mentioned in my last post you need to do some tests to calculate these values for a specific sheet.

These tests include bending some samples and then do some measurements and calculations. Consider a sheet with a 20 mm thickness and a length of mm as shown in Figure 1.

We are going to review three bending scenarios with three different bending angles; 60, 90 andand we will calculate K-Factor, Bend Allowance and Bend Deduction for them.

The bending tool has a radius of 30 mm which means that our Inside Bend Radius R is 30 mm. We will start by calculating the Bend Allowance. From there we can calculate the K-Factor and the Bend Deduction. After bending the sheet we need to do some measurements as shown in Figure 2.

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In this formula the initial length is mm. By replacing Initial Length, Leg Length 1 and 2 in the above equation we can calculate the Bend Allowance as follows:. We know that BA is the length of the arc on the neutral axis. The length of the arc for this scenario can be calculated as:. By inserting the Bend Allowance value in the above equation we reach to:. For our second scenario we are going to discuss the calculations for bending angles less than 90 degrees.

As an example we are going to use 60 degrees as our bending angle. Again we have to do some measurements as shown in Figure 3. Then we have to calculate Leg Length 1 and Leg Length 2. Where R is the Inside bend radius which is equal to 30 mm in this example. We can calculate Leg Length 1 through a few simple equations as follow:. Now that we have both Leg Length 1 and 2 we can use the following equation again to calculate the Bend Allowance:.

Where OSSB is the outside setback. OSSB is defined as illustrated in figure 5 for different bending angles and can be calculated using the equation below:. Where A is the bending angle,T is the sheet thickness and R is the bending radius.

how to calculate bend allowance for your press brake

Figure 5: outside setback OSSB in different bending angles. Figure 1: Flat sheet. Figure 2: 90 degrees bend. Need Help with your Sheet Metal Setup? Get Help. Figure 3: 60 degrees bend. Figure 4: degrees bend. He received his B. S from Mazandaran University, Iran; and his M. Find a Training Course.Calculating the correct flat pattern layout is crucial to getting a good quality finished part from your press brake.

They only taught the new apprentice how to apply the results shown on the cheat sheet, not how to calculate the numbers. Oh, and yes, you do need to know the K-factor to calculate the Bend Allowance. The material thickness is 0. But, do you calculate that on the inside of the material or the outside? This is where the K-factor comes into play. For this simple L bracket, I will use a K-factor of 0.

how to calculate bend allowance for your press brake

The formula See Bending Formulas is:. So if you add up the flat length of all the flanges and add one Bend Allowance for each bend area you have the correct flat length of the part.

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But look at the drawing. That is not how we normally dimension a sheet metal part. The dimensions are usually to the intersection of the flanges or the Mold Line. For this set of dimensions, it would be easier to calculate the Bend Compensation value.

It is Bend Allowance — The length of the arc through the bend area at the neutral axis. Bend Angle — The included angle of the arc formed by the bending operation. Bend Compensation — The amount by which the material is stretched or compressed by the bending operation. All stretch or compression is assumed to occur in the bend area. Bend Lines — The straight lines on the inside and outside surfaces of the material where the flange boundary meets the bend area.

Inside Bend Radius — The radius of the arc on the inside surface of the bend area. K-factor — Defines the location of the neutral axis. It is measured as the distance from the inside of the material to the neutral axis divided by the material thickness. Mold Lines — For bends of less than degrees, the mold lines are the straight lines where the surfaces of the flange bounding the bend area intersect. This occurs on both the inside and outside surfaces of the bend.

Neutral Axis — Looking at the cross section of the bend, the neutral axis is the theoretical location at which the material is neither compressed nor stretched.

Set Back - For bends of less than degrees, the set back is the distance from the bend lines to the mold line. To my knowledge, there is not a formula for calculating the k-factor. Oh, I am certain somewhere some mathematical engineer has a formula. But it is most likely too complex for most of us to understand or be able to use. The k-factor is the percentage of the material thickness where there is no stretching or compressing of the material in the bend area.

Thus, the neutral axis! The harder the material, the less compression there is on the inside of the bend. Therefore, more stretching on the outside and the neutral axis moves toward the inside of the bend.

Bend radius has a similar effect. The smaller the bend radius, the more need for compression and the neutral axis moves toward the inside of the bend.