Brake Press Forming Problem

[FabproHelp]

Hey can anybody help me with some forming issues. We are trying to form some 1/2 plate and no matter what we do it cracks. The only thing that seems to work is grinding out the stress point before forming. Is there a specific way to avoid the cracking all together? If anybody can help I would greatly appreciate it. Pictures will be coming soon.

 

[mcgyvr]

Forming/die radius?
Angle?
alloy?

http://www.thefabricator.com/article/bending/bending-basics-the-fundamentals-of-heavy-bending

 

[FabproHelp]

Sorry I wasn't sure if I was in the right forum. We are using A36 1/2" Plate. Forming a 90 degree bend. I am attaching forming pictures of the die, punch, and the parts. The two parts are the same. One is cracked and the other had the stress riser ground away before we had formed.

http://files.engineering.com/getfil...6f-baba-f74ee97b505b&file=20160118_093307.jpg

http://files.engineering.com/getfil...8c-be1c-7e03088cd88a&file=20160118_093319.jpg

http://files.engineering.com/getfil...dc-9f38-a09a3795c42f&file=20160118_093329.jpg

http://files.engineering.com/getfil...eb-8c0a-873cf5c813cd&file=20160118_093338.jpg

http://files.engineering.com/getfil...9c-b6b4-302448a21e0c&file=20160118_093411.jpg

http://files.engineering.com/getfil...db-9955-5b994dc94c25&file=20160118_093437.jpg

 

[hendersdc]

A larger bend radius will work better. You are currently at 1/2 material thickness, try bumping it up to 1/2" from 1/4". You may need to move the mounting hole on the short flange to accommodate the larger radius.

 

[FabproHelp]

Your saying use a 1/2 radius punch instead? Wouldn't that only change the inside bend radius?

 

[hendersdc]

The inside radius will be increased, the radius of the outside of your bend is determined by adding the material thickness to the inside radius. So if you have a 1/4" radius bend and a 1/2" thick material your outer radius is 3/4". If you increase the inner radius to 1/2" your outer radius is now 1". Your lower tool on the press break is just a basic "V" shape and will work with different radii and material thicknesses. Depending how wide the "V" is you may need to swap it out for a wider one if the points at which it contacts your sheet metal won't be out past the ends of the bend once you change to a larger radius, otherwise you won't get a full 90 degree bend no mater how hard you press.

 

[FabproHelp]

Thank you hendersondc, you wouldn't believe how many different issues you have resolved. So, hypothetically, I have every type of punch and die. What would the ideal choices be for 1/2" A36 plate formed to 90 degrees?

 

[hendersdc]

Glad to help! The link that mcgyvr posted is a good starting point to understand all the considerations that go into determining bend radius. That said, the design will not always allow for as large a radius as would be ideal. For example, a radius of 3X material thickness would be great from a ease of manufacturing and material strength standpoint in your application but this will add significantly to the size of your bracket. If the resulting strength of the finished part is already satisfactory, you can just increase the radius until you can successfully bend the part without failures.

 

[berkshire]

FabproHelp,
Mcgyvr has given you the best start, you are trying to form at too tight an inside radius. The guidelines I have used, are, that except for very soft metals plate, should have a " Minimum" inside radius of the thickness if the metal. As you well know changing the inside radius will affect the developed length of your part and will require a new flat pattern. If you absolutely have to bend at that radius then I would suggest hot forming the part. Heat to cherry red with a blowtorch then bend. Your dies looked like they were part of an expensive set, either use an older set of dies or use protective disposable steel shims to protect your dies.
B.E.

You are judged not by what you know, but by what you can do.

 

[dhengr]

FabproHelp:
Increase the inside radius of the bend. Grind the two rough edges as you did, parallel to the plane of the plate, and grind a slight radius on the corners of those edges, rather than leaving very sharp corners. Finally, cut the blanks from the piece of plate in such a way that the rolling grain of the material runs across the bend, rather than along the bend. Finally, heat the plate.