Fracture Free Forming
Fracture Free Forming
(OP)
Good morning: I have a problem that requires expertise not available locally. We are experiencing moderate to severe fracturing of 0.250 inch 5052-H32 plate during forming. We are using a CNC press brake with a .375R forming die. We have successfully formed this plate hundreds of times in the past. In discussing with our plate supplier we are told that they cannot guarantee fracture free forming because there are no N values in the ASTM B209-14 Table 2. That seems disingenuous and a free way to absolve themselves of liability. Can someone familiar with that particular Specification explain what the absence of a recommended Bend Diameter Factor N really means? Does it truly mean that these materials cannot be formed?
Thanks in advance.
Greg M
Thanks in advance.
Greg M





RE: Fracture Free Forming
RE: Fracture Free Forming
RE: Fracture Free Forming
Either they changed a process in order to save money so they don't want to go back, or something changed that is not under good control and they can't go back.
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P.E. Metallurgy, Plymouth Tube
RE: Fracture Free Forming
Would still like some guidance on the B209-14 spec though.
RE: Fracture Free Forming
I was once in a company where someone "improved" the life of some furnace tubes by turning down the temperature and increasing the processing time to compensate, but that someone told no one about it, and it went undetected for about 3 years, since that part of the process was only affecting a portion of our typical product, which already had lousy yield. We then got a product where most of product required that process and we got abysmal yields. Big panic ensued, as the product was for a corporate sister division, Paymentec (the credit card chip guys). Months of tiger-teams followed, but it was an obscure article in an IBM Systems Journal from more than 15 yrs prior that had the data showing that a mere 50C drop from 1100C could totally and completely discombobulate the process.
In any case, you need to do your due diligence:
> try to find old material that can be formed to make sure your internal process hasn't gone funky
> try to find out if someone decided to make the process "better" without telling anyone, or worse yet, it improves the process for other products, but not yours.
TTFN (ta ta for now)
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RE: Fracture Free Forming
RE: Fracture Free Forming
We have made arrangements for Montana State University Materials Science faculty to perform the investigation for us. As much as I'd love to be able to use an independent lab for this, we don't have the budget so we'll take the free help.
I left this part out of the original post, but the plate's origin is China. Given my long experience with Chinese manufacturers and their quality groups, I suspect that the material certs supplied with the plate are worth just about the cost of the paper. We have a sample of US plate and we're waiting for the brake operator to return from vacation. I did say we're small.
I'm still looking for an interpretation of B209-14. Anyone?
RE: Fracture Free Forming
I have the latest copy of ASME SB 209 material specification. The section on bend testing is 12.0
The ... for missing N values in Table 2 means the value is not specified. It does not mean it prohibits bending. You will need to determine the pin diameter based on trial and error or agreement between the supplier and Purchaser.
RE: Fracture Free Forming
FWIW, the standard data sheet from Alcoa for 5052 shows a min. bend radius of 1.5t for 1/4" thicknesses, i.e. you should be able to make a crack free 90 deg. bend.
RE: Fracture Free Forming
We are using a 1.5T die, no problems for more than a year then boom. Obviously we did something magical for a year and the heat lot had nothing to do with our magic disappearing, as all magic does eventually...
Thanks all! It'll be interesting to see what the materials folks find.
RE: Fracture Free Forming
You never mentioned the total bend angle You are forming to.
An [aerospace] formability chart that I have for various aluminum alloys indicates that the min bend radius [BR] for 5052-H34 0.190"-thick sheet [no data for -H32] is BR0.50". This implies that a much larger BR for -H34 0.250-thick plate is required. Extrapolating 0.25 thick leads me to believe a safe BR for this material should probably NLT BR0.66"... far from BR0.375 [BR0.38] You have been using.
On the-other-hand, the chart indicates that min BR for 5052-O sheet 0.190" thick is only BR0.19"... hence would extrapolates to a min BR0.25 [+] for 0.250-thick -O stock plate.
Quite frankly I simply cannot conceive of how You have been getting away with such a tight BR for -H32 plate.
NOTE. Three concepts to be very aware-of when bending thick stock to extreme tight BR are:
(a) ALWAYS bend ACROSS the sheet/plate grain [rolling direction] whenever possible... NEVER bend along the grain. Maximum material ductility is almost always in the 'L' direction... not the 'LT' [across the plate] orientation. Yes, I stated that correctly...
(b) Ensure that the plate stock is well supported during the bend process. One side must be rigidly/flat-clamped; and the other side must be free to move/slide as the 'break-tool' rotates that free edge in a sweeping motion. Applying light lubrication to the under-side of the [unclamped] plate edge being bent [sweeping/sliding] MAY help it slide smoothly [minimize friction] during the sweeping motion around the BR and against the break face. A light lube on the side formed-around the brake radius might also help.
(c) 'Hot-bend-forming' is also a way to further reduce BR and make a successful bend. I'm unsure what temperature/time -H32/0.250"-thick would require to substantially tighten the BR. this is tricky and could involve high temp SFLs, etc.
NOTE.
IF you see 'Luders-lines' [Luders-Bands, etc] form along [parallel to] the outer [tensile strain] side of the bend, You can guarantee You're right at the formability limit for that particular raw stock.
https://en.wikipedia.org/wiki/L%C3%BCders_band
https://www.google.com/search?q=luders+lines+alumi...
Regards, Wil Taylor
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RE: Fracture Free Forming
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P.E. Metallurgy, Plymouth Tube
RE: Fracture Free Forming