Stainless steel CNC bending

304 needs roughly 1.5 times the tonnage of mild steel at the same thickness, and springback is higher, so overbend is set from a trial part. Tooling should be polished or coated for visible surfaces, and protective film has to be removed before bending, not after, or it stretches and leaves adhesive marks.

The commercial consequence is that stainless 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 stainless 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. Stainless must be cut with high-pressure nitrogen to keep the edge oxide-free; that is the difference between a weldable edge and one that has to be pickled. The route is quoted as one sequence so the customer does not have to coordinate a cutter, a former, a welder and a coater.

A press brake is the wrong choice for very long, thin stainless panels that would need a special crowning setup; a folder or a roll-formed profile may hold the face better.

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.

• Cabin and door panels
• Hygienic enclosures
• Trim sections
• Railway interior panels

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 stainless the practical constraint is contamination: carbon steel tooling, brushes and blast media transfer free iron, so stainless work is kept on dedicated tooling and its own handling. Stainless raises the stakes on the decision: tool wear, gas cost and slower forming mean the volume needed to justify a tool is higher than for CRCA, and the wrong early choice is expensive to reverse once a die has been cut.

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 stainless 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.