Grain direction in bending sheet metal
Grain direction in bending sheet metal
(OP)
Has anybody heard of bending sheet stock (.063 5052-H32 Aluminum)with grain direction on the diagonal? Local sheet metal shop (not an aircraft shop) experienced cracking on folding up a simple bracket. The bracket is like an upside down 6"long x 4"wide x 2"high box but has integral attaching flanges on the two 4" ends. I say with a zero bend radius (not 2-3t) and no concern for grain direction they were asking for cracks and failure even with this material.
I have never ever heard of a spec calling for diagonal grain direction.
What say you??
I have never ever heard of a spec calling for diagonal grain direction.
What say you??





RE: Grain direction in bending sheet metal
I agree with a very sharp bend radius you would probably experience cracking.
Have a look at this site:-
http://ar
regards
desertfox
RE: Grain direction in bending sheet metal
RE: Grain direction in bending sheet metal
RE: Grain direction in bending sheet metal
RE: Grain direction in bending sheet metal
You will experience cracking problems if the bends are coined with a zero inside radius.
B.E.
RE: Grain direction in bending sheet metal
My ref handbook calls for a minimum 0.12-BR for 0.063 thick 5052-H34 (close to H32). This may be tweeked downward (maybe 0.09-BR) if bent 90+/-10 to the sheet grain... and the following is observed...
NOTE: grain is the rolling direction which elongates grains in the same direction. When bent transverse to the grain, long edges of grain boundaries are exposed to high strain with high potential for crack initiation.
Scratches and sharp/burred edges contribute to crack initiation when bending to severe radii. Polishing and radiusing the sheet metal edges and blending-out scratches or surface roughness will virtually eliminate cracking when bent over a SMOOTH radius. CAUTION: burrs, gouges, nicks, chips, scratches, roughness, corrosion, etc on the sheet-metal brake edge radius also need to be eliminated.
OLD sheet-metal guy trick...
Form a 0.032 thick sheet of "O" aluminum sheet [or annealed CRES 3XXX sheet] TIGHLY around the "sharp" edge of the brake (usually sharp edges on brakes are actually a very small polished radius [R~0.016]... or the "point" is squared-off [truncated]).
Lightly oil the outer surface of the bent sheet... and form ANOTHER layer of 0.032 OVER the base sheet. Repeat this "stack forming process", until the total thickness of the stack is "equal-to, or slightly higher than" the required Bend Radius. Form the production part around the sheet metal stack. This "back pocket trick" allows use of a single "sharp-edge" brake blade...for precision bending of "tin sheet metal [~0.080+/+ depending on sheet metal yield strength BR rqrmnts.
CAUTION: There are limitations to this "trick"... and every time the radius stack thickness is increased, then small adjustments to the fixed-blade-edge position, relative to the forming flange of the brake (the rotating surface that forces the sheet metal to bend around the "fixed-blade-edge" of the brake) need to be accomplished by the metal tech, to avoid binding.
NOTE: an acft manufacturer I used-to work for had a special v-knife-brake die for forming the trailing edges of the RH/LH elevator and rudder skin trailing edges [same part all (3) places]. Somehow it got slightly bent... and all the parts coming off the tool had a barely perceptable bowed trailing edge which was determined to be aero- & structure- wise acceptable "as-is"... but when You knew what to look for it was really annoyingly apparent.
Regards, Wil Taylor
RE: Grain direction in bending sheet metal
Great comments and I still stand my ground that the old school is best. Use 2-3t BR and bends that you want to survive to be transverse to rolling/grain direction. I had to teach these guys that the world uses inside BR (not outside) in callouts on dwgs. For example set-back calcs would be little confused if one used outside BR.
Wil, as you and I both know the T-18 is a great sheet-metal learning exercise. Thorp knew the rules and used them to the nth degree!! Thanks to all.
Regards,John Cragin