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FORMING.TXT
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1989-04-09
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Stainless steels have higher strength and are more abrasive than many of the
ordinary steels. The stainless alloys also work harden more rapidly than
conventional plain carbon steels. However the stainless steels can still be
worked and formed on the same basic machines and tooling as used for the plain
carbon steels.
The following guidelines are of assistance in regard to the forming of the
stainless steels.
Bending:
The smallest radius that can be formed without cracking is called the "minimum
bend radius". This radius increases as the thickness of the material
increases. Typical bend radii data are shown in the following table:
Thickness (T) Bend Radius Angle of Bend
Alloy Temper Range R/T Degrees
301 Annealed 3/8" max. 0 180
302 Over 3/8" 1/2 180
─┐
304│
310│ All of these grades behave in similar fashion and are
316│ subject to the above guidelines.
321│
347│
─┘
301 1/4 hard All 1/2 180
1/2 hard 0.050 max. 1/2 180
Over .050" 1 180
3/4 hard 0.050 max. 1 180
Over .050" 1 90
Full hard 0.050 max. 1-1/2 180
Over .050" 1-1/2 90
302 1/4 hard 0.050 max. 1/2 180
and Over .050" 1/2 90
304 1/2 hard 0.050 max. 1 180
.050 to .187 1 90
316 1/4 hard 0.050 max. 1 180
.050 to .187 1 90
Flaring:
When tubing is flared the edge of the tube undergoes considerable stretching.
The amount of flare (diameter) is limited by the diameter of the tubing. It
is difficult to successfully flare any of the harder temper conditions of
stainless steel, such as 1/4 hard. Flaring should be done on annealed tubing
with a yield strength not exceeding 95,000 psi.
Tubing edges should be thoroughly deburred before flaring.
The following table relates tubing diameter to flare diameter and applies
generally to all of the stainless steels with less than 95,000 psi yield
strength as ready to be flared.
Tube Dia.-Inches Flare Dia.-Inches
1/8 0.234
3/16 0.312
1/4 0.359
5/16 0.421
3/8 0.484
1/2 0.656
5/8 0.781
3/4 0.937
1.0 1.187
1-1/4 1.300
1-1/2 1.721
1-3/4 2.106
2.0 2.356
Bending of Tubing:
Large bend radii, as would be expected, are easier to form than small radii.
Large diameter tubing has a greater differential in stretch between the inner
and outer bend radii and thus has a greater propensity to thin, or flatten,
in bending. Thin wall tubes tend to wrinkle upon bending. The most difficult
bends are on large diameter, thin wall tubing. All but the easiest of bends
require precautions to avoid collapsing of the tube. Internal support and
often external guidance, or support, is needed. Internal support can be as
simple as sand, or sealed rubber tubing to avoid collapse. In production
operations an internal mandrel is used.
Some flattening (reduction of the actual tube diameter) will occur during
bending. This is dependent upon the diameter and wall thickness of the tubing
and the bend radius - the greater the radius the less the flattening.
Flattening for a bend radius of approximately 2 times the tube diameter, for
a 1" to 2" diameter tube, is 2.5 to 3 % of the original tube diameter.
Suitability of Stainless Steel to Forming:
The following table presents a general guide to the common forming techniques
as they relate to the stainless steels.
KEY: 1 - Excellent, 2 - Good, 3 - Fair, 4 - Not Recommended
Forming Operation
Press Deep Roll
Alloy Blank Pierce Brake Draw Spinning Form Coining
201 ------ 2 3 2 2 3 2 3
202 ------ 2 2 1 1 3 1 2
301 ------ 2 3 2 2 3 2 3
302 ------ 2 2 1 1 3 1 2
303 & Se -- 2 2 4 4 4 4 3
304 ------ 2 2 1 1 2 1 2
309 & S --- 2 2 1 2 3 2 2
310 & S --- 2 2 1 2 2 1 2
316 ------ 2 2 1 2 2 1 2
321, 347 -- 2 2 1 2 2 2 2
403, 410 -- 1 2 1 1 1 1 1
416 & Se -- 2 2 3 4 4 4 4
420 ------ 2 3 3 3 4 3 3
430 ------ 1 2 1 2 1 1 1
440 ------ 3 3 3 3 4 3 4