Brass CNC bending

CuZn37 in the soft temper bends to a tight radius; the same alloy in a harder temper will crack. Brass is prone to orange-peel on the outside of a tight bend, which becomes visible after polishing or plating. Springback is moderate and varies with temper.

The commercial consequence is that brass 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 brass 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. Lead-bearing CuZn39Pb2 machines and shears more freely but is restricted in some markets under RoHS and REACH, so the grade has to be chosen against the destination market, not only the drawing. 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 where the bend line crosses a decorative etched face; handling and tooling marks will show through the finish.

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.

• Trim and edging
• Electrical brackets
• Decorative angles
• Instrument bezels

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 brass the practical constraint is alloy restriction and tarnish: the grade has to satisfy the destination market's substance rules, and the surface needs protection if it must stay bright. Brass is usually a volume material by nature, so the process decision is often already made by the part family; the real choice is the alloy and the temper, and whether the destination market permits the lead content.

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 brass, 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.