Cutting and Forming Operations
What this domain tests
Cutting questions test process selection, kerf, and cut quality; forming questions test bend calculations, minimum radii, springback, and how the material behaves.
Cutting processes
- Oxy-fuel cutting burns steel with an oxygen jet after preheat; it suits carbon steel, not aluminum or stainless without powder injection. Kerf is typically 1.5-3 mm, and drag lines show travel speed.
- Plasma cuts conductive metals including stainless and aluminum. Quality depends on amperage, standoff, travel speed, and dry air; dross on the bottom signals too slow or too much standoff.
- Laser gives a narrow kerf and small HAZ on thin material.
- Waterjet cuts cold, with no HAZ, and handles thick plate and non-metals.
- Shear gives straight cuts only, with a burr and edge distortion on thick plate. Band saw and abrasive saw are for stock; abrasive cutting leaves a hardened edge.
Kerf matters: on a CAM nest, the tool path is offset by half the kerf so the finished part meets the dimension.
Forming
Press brake bending is air bending or bottoming. The neutral axis does not stretch, and its position is the K-factor, roughly 0.33 to 0.5 of thickness. Bend allowance is the arc length at the neutral axis: BA = (pi/180) x bend angle x (inside radius + K x thickness). Bend deduction is twice the setback minus BA, and flat length equals the sum of outside dimensions minus the bend deduction.
- Minimum bend radius: about 1T for mild steel, more for stainless, and much more for 6061-T6, which may need annealing or a different alloy.
- Springback rises with yield strength and radius-to-thickness ratio; overbend or use a compensating die.
- Bend across the rolling direction, not with it, to reduce cracking.
- Rolling: pre-bend the ends to avoid flat spots.
Worked example
3 mm plate, 90 degree bend, inside radius 3 mm, K = 0.4. BA = 1.5708 x (3 + 0.4 x 3) = 1.5708 x 4.2 = 6.6 mm. Setback = (3 + 3) x tan 45 = 6 mm, so BD = 2 x 6 - 6.6 = 5.4 mm. For outside dimensions of 50 mm and 30 mm, flat length = 80 - 5.4 = 74.6 mm.
Traps
- Laying out from outside dimensions without bend deduction.
- Trying oxy-fuel on stainless or aluminum.
- Bending 6061-T6 to a mild-steel radius.
- Ignoring kerf on a finished part.
- Forgetting springback on high-strength steel.