Welcome to bending aircraft metal. This video is part of the digital project of the Vancouver Community College PID or Provincial Instructor Diploma Program in the spring of 2012. This video will show us how to bend sheet metal. Well, Maybe not this kind of bending, but we're going to go through the basic procedures and requirements for bending a piece of aluminum over 90 degrees on a bending break. What are some of the important pieces of information that we need to know before we actually start to bend a piece of metal? First thing we need to know is what direction does the grain in the aluminum actually run?
Aluminum has grain in it, and it's actually quite visible if you get down close and have a look at it. The other nice part of a piece of aircraft aluminum is when they put the information on the sheet, they print the information along the grain line of the material. So you've got a pretty good idea as to exactly where the grain is.
The other important piece of information that you need to know is the thickness of the material. That's very important. The third piece of information that you probably need to know is you need to know over what sort of a radius you're going to bend this piece of sheet metal. We don't bend sheet metal over tight, like knife edge type of bending brakes.
We have a bending brake that has a nose bar on it that has a built in radius. You can see that the nose bar, in this case, has a 1 8th. radius on it. So the important things to know are grain direction, nose bar radius, and material thickness. When you get a drawing of a piece of material that they want you to bend up, they'll give you specifications.
In this case, six inches on one leg, eight inches on the other leg. And those dimensions are from the end of the piece of metal to the flat on the opposing side. We can see that we have a 1 8th radius that we're going to bend the material around and we'll be using 040 or 40 thou aluminum. We're going to make it about 6 inches wide. So that's the other dimension that might want to know about.
But the main one that we're concerned with are the two legs that need to be bent and around what sort of radius we're going to use. The best way to figure out what the actual material is in that area where we're bending it around the radius is to use a bend allowance chart. The bend allowance chart shows us the actual material that will be used up in the bend.
You can see here that bend allowance represents that material between the two black lines on the piece of aluminum. So what you need to know is your bending radius and your material thickness to figure out on the chart the bend allowance. Bend allowance usually has two numbers.
It gives you a big number, in this case 0.224, to bend around a 90 degree angle. And it'll also give you another number that you can multiply by the number of degrees that you're bending. Setback is a formula that we use in order to figure out the actual final developed length of each of the flat legs on the 90 degree bend. Again, the two most important key features that we need to know are what is our radius that we're bending the material around and what is the thickness of the material. So setback, Sb, is actually equal to the bend radius plus the thickness of the material.
So in this case, it's 1 8th, 0.125, plus 040. So our total setback is 0.165. So to find the developed length of one of the legs, we take the length that the drawing shows, and we subtract setback. So in this case, it's 6 inches minus 0.165, which equals 5.86.
So you can see here our original length was 6 inches. We take off the thickness of the material. We take off the radius of the bend. And what we're left with is the final developed length of 5.835.
That setback. So we would do the exact same thing with the other leg. The next thing we're going to look at is called the developed length.
So what we're going to look at here will be the actual total length of the material that we're going to cut. You'd think if one leg was 6 inches and one leg was... 8 inches, that the whole piece of material would end up being about 14 inches long. But actually, in having the radius in our bend, we actually end up saving some material. So we have the two individual flat sections, and we have the bend allowance.
There's our bend allowance, BA, and we have leg 1 and leg 2. So leg 1 is the desired length, or the drawing length, of 6 minus... 0.165. The other leg is 8 minus 0.165. And by the bend allowance chart, we found out that our bend allowance is 0.224.
So the total length is is the sum of length 1 plus length 2 plus our bend allowance. So in this case it's 5.835 plus 7.835 plus 0.224. Giving us a total of 13.894.
See, we saved some material. Didn't have to use the whole 14 inches. And with that length, when we cut it exactly to 13.894, when we put it in the bending break and bend it, we'll end up with exactly a leg 6 inches long and a leg that's 8 inches long. Are we ready to start bending? I don't know.
I think there's a few more things that we might have to do. How about another airplane to finish the page? The next thing we're going to look at is this thing called a sight line. The sight line is a tool that we have that shows us when we have put just the right amount of material into the brake in order to start the bend right at the edge of the bend allowance.
The Bend sight line allows us to get our eyes directly above the bending brake, looking down onto the piece of material, and know that we can start bending the material at just the right spot. The first thing we want to do is to get our eyes that we need to know when we have or we want to lay down a sight line is that we need to have that sight line exactly one radius away from the actual edge of our bend allowance so from the edge of the flat We want to go in until we have the edge of our bend allowance, which is showing here as the red dotted lines. We have our two flats, flat 1 and flat 2. And we know exactly what those demands are.
dimensions are because we just figured those dimensions out using our setback. So in this case, flat 2 is our 8 inch long flat and we know that the actual dimension of flat 2 is point 835 inches from its end. From the 7.835, that takes us to the edge of the bend allowance. So now what we need to do is we need to add 1 eighth of an inch, or.125 from that point.
And we need to make a mark. on both sides of the sheet and have a line that goes in between the two of them. That line is now our sight line. The sight line is there to show us that that's the point that we want directly flush with the end of the bending brake when we put the piece of material into the brake. One of the very important things to remember is, and what I always do, is put an arrow on the side that you're sliding in to the brake.
Because if you happen to accidentally spin it around and put the wrong side in, the bend is not going to work out. So make sure you slide the correct side into the brake. It's a very important skill. We're almost there.
Getting close to putting that piece of material into the brake. Okay, so here's our brake. See, it says the brake. Got a handle there for crunching down to hold our piece of material.
We've got the arm that comes out the front. That actually is what we use to bend the piece of material. Here's the bending arm.
That rotates up 90 or more degrees. And we have our piece of material that we put into the bending break. Now, we have a couple lines on our piece of material.
The most important line being our sight line. That's the red mark on the piece of material there. So, when we have our sight line, we slide it down.
slide it in, we slide the piece of material into the bar until our eye is directly above the bending break bar and we look straight down onto that sight line and make sure that it touches flush to the end of that bending break. That way we know that the bend allowance line starts right where the material is going to start to be bent around that bend radius. Well, they look happy.
I think we're getting close. Hey, we mean getting bent. Once you get that piece of material in exactly where you want it into the bending break, we can grab that bending arm and start bending our material up to 90 degrees.
Now aluminum is kind of springy, and so... we actually have to bend it a little bit past the 90 degree mark usually about 10% past as you bend more and more material you'll get a feel for what is just about perfect for getting that 90 degree bend you The material tends to spring back and try to go back to its original shape. So, when we bend it, we need to just add a little bit extra to make sure that we get the perfect 90 degree bend. We've got that 90 degree bend, we've got the 1 8th radius in there, we've got the 8 inch leg, we've got the 6 inch leg, and when we measure it all out, whammo, it's right on the numbers.
I hope this information has been helpful to you. The next time you're bending a piece of aircraft aluminum, I hope you'll remember the different steps that we went through. The first three most important pieces of information are The thickness of the material, the radius of the bend that we're actually going to bend it around. We want to keep in mind the actual grain direction on the piece of material. With that, it gives us the starting information to build all those steps for bending aircraft sheet metal.
Hope you've learned something. And remember, those guys that are bending the aircraft metal, they do a great job.