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Bending metal

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NUFCBernie21/10/2020 19:56:16
46 forum posts
7 photos

Does this sound right?

I started with 1.2 mm thick steel x 61mm depth.

I bent it in my Sealey 760 metal bender to start practising ready to make the chassis rails.

The top and bottom flanges are to be 12.5 mm wide and i bent at a line of 13.5 to allow for a 2mm radius.

Now measuring the total top to bottom and the 12.5mm widths (which were 13.5) it comes to 64.5, its grown, glad i got plenty of scrap.

Malc

JasonB21/10/2020 19:59:50
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You need to measure the neutral point which is just less than half way through the thickness of the metal if I remember right. The outside dimension increases and internal decreases.

NUFCBernie21/10/2020 20:04:14
46 forum posts
7 photos

i thought overall it would be about the same, but 4mm increase...wow

JasonB21/10/2020 20:28:09
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Yes thats about it. Assuming this is what you measured as 13.5mm flanges and a 37.5mm leg to give the 64mm overall then if you measure the green lines which I have drawn mid way you get 10.8 + 3.3 (1/4 circle) + 32.1 + 3.3 + 10.8 which totals 60.3. thinking again the neutral point is just beyond half way not below so that would make it abit longer and give your 61mm starting width

bending.jpg

Dave Halford21/10/2020 20:33:37
1011 forum posts
9 photos

The Zeus book has the bending data in it.

If the distance between the flanges is correct then it's fine. If you are measuring the outside then doesn't part of the bent section get measured twice?

Joseph Noci 121/10/2020 20:41:59
778 forum posts
984 photos

Sheet metal bending is not so simple! The neutral axis is never a fixed axis - it depends on the material thickness, the bend radius and whether the elastic limit of the material is exceeded in the bend. There are tables that can help you with this, but unless you know exactly the sheet material grade, its temper, etc, ....

The safest way for the home shop is to bend a trial piece - say a piece of material 50mm wide, 200mm long, scribe a bend at 50mm from one end, into the brake long end first, bend tight on the line, and then lay the long end flat on the table, short end upright, and measure the height with a vernier. The delta from 50mm allows you to calculate the bend allowance, which will give you the end points of each bend. The sums from then follow reasonably easily...

There are some good references that can help - use google.

Your description of the bends and total lengths was a little unclear to me ...Maybe a photo to help?

Joe

NUFCBernie21/10/2020 20:59:29
46 forum posts
7 photos

Thank you Jason thats a great pic and helpful.

Thank Joseph as i think you hit the nail about home practise until its right, this is what i have done.

To get my req piece size of 12.5 x 50 x 12.5 mm i ended up with a 72mm strip, bending it a 11mm in from the edge with the tightest radius the bender could accommodate

img_4302.jpg

Edited By NUFCBernie on 21/10/2020 20:59:57

Edited By NUFCBernie on 21/10/2020 21:00:50

Paul Lousick21/10/2020 23:45:12
1576 forum posts
594 photos

Bending to a specified length is probably the leaste accurate of the fabrication & machining processes.

The neutral axis for thin sheet metal is approximately in the middle of the sheet but for thicker plate moves closer to the inside edge of the bend. (depends on material properties of the bent part). An approximate position for the neutral axis for 20mm plate is about 1/3 of the distance from the inside edge. (Metal stretches more easily than it compresses)

If you are not accurately calculating the bend dimensions with a formula and the correct metal properties, do a test bend first. Material does not have to be very wide, just the same thickness and type.

Some of the better 3D CAD systems (I use Solidworks) have a sheet metal function that calculates the position of the bend line of the metal sheet in the flat position prior to bending.

Paul

Edited By Paul Lousick on 21/10/2020 23:49:10

NUFCBernie22/10/2020 07:47:43
46 forum posts
7 photos

You really do need to know your materials in this game and not just a piece of steel covers all

Thanks for that Paul, i gave Jason's diagram a real good go over until i was fully conversant in how it all comes together and i really feel i have a much better grasp on metal bending, thanks to all.

Gary Wooding22/10/2020 10:57:32
767 forum posts
196 photos
Posted by Paul Lousick on 21/10/2020 23:45:12:

Some of the better 3D CAD systems (I use Solidworks) have a sheet metal function that calculates the position of the bend line of the metal sheet in the flat position prior to bending.

Edited By Paul Lousick on 21/10/2020 23:49:10

Fusion 360 (even the personal version) has a very powerful sheet metal facility.

Gary Wooding22/10/2020 11:00:42
767 forum posts
196 photos
Posted by Paul Lousick on 21/10/2020 23:45:12:

Some of the better 3D CAD systems (I use Solidworks) have a sheet metal function that calculates the position of the bend line of the metal sheet in the flat position prior to bending.

Edited By Paul Lousick on 21/10/2020 23:49:10

Fusion 360 (even the personal version) has a very powerful sheet metal facility.

Andrew Johnston22/10/2020 11:02:26
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5718 forum posts
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Paul is correct; the neutral axis is not usually at the midpoint of the material, but is closer to the inside of the bend. I normally do sheet metal design using the sheetmetal function in Alibre CAD where the K-factor is 0.33 by default, ie, the neutral axis is one third of the material thickness from the inside of the bend. Assuming that a box and pan folder is being used the other important factor is the bend line, ie, the start of the bend. This is where the material is clamped. Based on previous work if I made the part shown I'd expect overall dimensions to be within 0.1 to 0.2mm.

For large bend radii, as in this wheel rim, assuming that the neutral axis is at half material thickness is valid:

bending_rolls.jpg

The length of material needed to get the final wheel diameter was based on the diameter at half material thickness. After rolling and welding the final wheel diameter was about 15 thou off the target of 14.5".

Andrew

NUFCBernie22/10/2020 11:23:47
46 forum posts
7 photos
Posted by Andrew Johnston on 22/10/2020 11:02:26:

Paul is correct; the neutral axis is not usually at the midpoint of the material, but is closer to the inside of the bend. I normally do sheet metal design using the sheetmetal function in Alibre CAD where the K-factor is 0.33 by default, ie, the neutral axis is one third of the material thickness from the inside of the bend. Assuming that a box and pan folder is being used the other important factor is the bend line, ie, the start of the bend. This is where the material is clamped. Based on previous work if I made the part shown I'd expect overall dimensions to be within 0.1 to 0.2mm.

For large bend radii, as in this wheel rim, assuming that the neutral axis is at half material thickness is valid:

The length of material needed to get the final wheel diameter was based on the diameter at half material thickness. After rolling and welding the final wheel diameter was about 15 thou off the target of 14.5".

Andrew

wow, impressed, all my years of being a commercial vehicle mechanic are lost here , the closest i got to accuracy was a torque wrench :-D

Loving all this new info though

NUFCBernie22/10/2020 12:50:04
46 forum posts
7 photos

I had forgot about fusions sheet metal , cheers gary, that was sooo easy, although it came up with 69.7mm and i double checked the settings, the only bit i am not sure of is what the k setting should be, i put 33

 

Edited By NUFCBernie on 22/10/2020 12:50:18

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