CRCA / mild steel CNC bending

Mild steel springback is lower than stainless or aluminium, but it is not zero, and it changes with yield strength. A CR4 grade at the top of the yield range needs more overbend than a CR1 at the bottom. Thickness variation across a coil also moves the neutral axis, so flat length should be validated on the first part rather than trusted from a table.

The commercial consequence is that CRCA is priced on its own material line, not blended into a steel rate. Material grade, thickness, tolerance and finish are quoted separately from conversion, so a change of specification is visible in the price.

Ganesh quotes to the drawing first and to ISO 2768 general tolerances where the drawing is silent. For CRCA CNC bending, the practical starting points are in the table below. They are starting points, not a guarantee: the part geometry, thickness and fixturing decide what can actually be held, and the quotation states the tolerance offered.

Flat length is calculated from bend allowance, not outside dimensions; a K-factor taken from a table rather than the actual material and die is the most common cause of a part that is 1 mm short across a box. Hot-rolled IS 2062 E250 plate above 6 mm is cut and formed, not pressed, on Ganesh's route: the 12 kW fibre laser cuts to 20 mm and the 200 T brake forms to 10 mm. The route is quoted as one sequence so the customer does not have to coordinate a cutter, a former, a welder and a coater.

Press brake bending is the wrong route when the part needs a closed hem, a coining operation or a bend line that intersects a large cut-out. Those belong on a press with a dedicated tool.

A manufacturability review before quotation is the cheapest place to find this out. Send the drawing, material, finish and annual quantity and the review comes back in writing.

• Enclosure and cabinet bodies
• Rack frames
• Canopy doors and panels
• Chassis sections

Use press brake bending for almost every formed sheet part, including production parts, because the brake stores a program per part and needs no tool beyond standard punches and dies. A dedicated forming tool only makes sense when the geometry needs a feature a brake cannot produce: a coining operation, a closed hem, a very short flange on a high-volume part, or a form that must be identical across a million cycles. For CRCA the practical constraint is rust: cut, formed and coated parts should not sit unprotected in a humid shop, and the route is sequenced so pretreatment follows fabrication within the same production window. CRCA is also the easiest material to change late: a grade swap from CR1 to CR4, or a 0.2 mm thickness change, can be made without retooling in many cases, which keeps the decision reversible while volumes are still uncertain.

Give the inside radius, the bend angle and its tolerance, the bend line dimensions and whether they are to the outside or the inside of the form. State the flat pattern expectation if the customer owns it, and the bend sequence if the part is boxed and the order matters. Mark the cosmetic faces. On a 4,450 mm panel, say whether the full length is a single bend or a stepped form.

Angular tolerance is checked with a protractor or against a fixture, and linear dimensions against the drawing. The stored program is the setup record. First article approval covers the first part off the program, not the drawing review.

Cost splits into setup, handling and stroke time. Setup is amortised across the batch, which is why 50 parts cost more per part than 500 off the same program. The number of bends, the part size and whether a second operator is needed to handle a long panel all move the price more than the tonnage does. On CRCA / mild steel, material is quoted as its own line at the prevailing rate for the grade and thickness, so a change of specification is visible rather than hidden in a blended rate.