July 16, 2024 | Processing
Cut-to-length sounds like a simple operation: uncoil, level, shear. What actually decides press yield are the items nobody puts on the quotation.
The most visible, and the most over-specified. Tighter is not better — a requirement beyond the line's capability either cannot be met or doubles the cost. Work backwards from the assembly allowance: if the part has clearance, there is no reason to hold the sheet to a limit.
The length and width are right but the sheet is a parallelogram — and the press feeds crooked, pilot pins miss. Almost never discussed on the quote, and the classic reason a "correctly sized" blank will not fit.
Shearing always leaves a burr. Too much and it scores the die, cuts hands, and shows as a ridge along the edge after painting. Whether deburring is included, and to what level, changes cost significantly — settle it at order stage.
Watch edge wave and centre buckle. Insufficient levelling leaves the sheet crowned or wavy, which feeds badly and locates poorly. Thin sheet is far more sensitive — 0.3 mm is much harder to level than 1.0 mm.
The most overlooked of the five. If stress is not released during levelling, the part will spring back, twist or lift at the corners after stamping or bending — correct in the die, wrong on the bench. That is not a material failure; it is a processing one.
A crude but reliable check: lay the blank on a surface plate. The smaller and more even the corner gaps, the better the stress was released.
Do not stop at "to national standard". Break it into acceptance items: length and diagonal tolerance, burr limit, flatness, whether deburring is included, and packing. Written down, you have a basis when something goes wrong. Left vague, both sides end up splitting the loss.
