Sheet Metal — validation & limitations

What it calculates

• Bend allowance, bend deduction and flat blank length to DIN 6935 (K-factor neutral-axis arc method), with the standard's own k = 0.65 + 0.5·lg(r/s) correlation offered as a one-click K
• Feasibility judged against the minimum inside bend radius for the ACTUAL material and temper you selected — not a fixed R/t rule
• Flat pattern layout for boxes and pans with corner relief (closed / open corner options)
• Springback angle, final radius and required over-bend on the same panel as the bend itself (Gardiner elastic–perfectly-plastic relation, with validity warnings)
• Punching and blanking force (F = P · t · τ, τ = 0.8·UTS) with press tonnage, stripping force, cut energy and punch compressive stress computed on the TRUE punched area for circles, rectangles and obrounds
• Deep drawing punch force and blank-holder force, with the required blank compared against the blank you intend to cut
• Blank development for plain AND flanged cylindrical cups, rectangular pans (graded on the corner quarter-cups that actually govern), conical shells and tubes
• Multi-stage draw sequence with intermediate annealing, single-sourced to the same limiting draw ratio the feasibility check uses
• Forming limit diagram (FLD) to the Keeler-Brazier / NADDRG model, with an explicit warning when the selected alloy sits outside the low-carbon-steel data the correlation was fitted on
• Built-in material library (mild steel, stainless 304, aluminium 6061-T6 and 5052-H32, DP 980, copper, brass) with E, Sy, UTS and n; custom material entry

Standards this tool applies

• DIN 6935 — K-factor flat-pattern bend allowance with the DIN 6935 k-correlation offered as an opt-in K suggestion, plus springback (Gardiner), punching force, deep drawing and forming-limit-diagram (FLD) assessment in a single ten-tab tool. Only the k-correlation and minimum-radius context relate to DIN 6935; the other tabs are not DIN 6935 methods.

Validation evidence — independent reference cases (0)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

No independent reference case is registered for this tool yet. Its engine is covered by the regression suite, but no published worked example has been reproduced end to end.

Limitations

Not checked by this tool

• Bend: hole-to-bend and edge distances, bend relief — Not checked; keep holes clear of the bend zone per your press-brake practice
• Bend: press-brake bending force and V-die opening — Not computed; take the tonnage from the press-brake maker's bending chart
• Bend: minimum radius along the rolling direction or for thick sheet / plate — The table is the across-grain value for thin sheet; a bend along the grain or in plate needs a larger radius — confirm with the supplier
• Draw: material anisotropy (r-value) and earing — The limiting draw ratio is shop guidance independent of r-value; confirm with supplier data and trials
• Draw: local wall thinning along the cup — Not computed; use forming simulation or trials
• Punch: buckling of a slender punch — Punch stress is printed, not graded; check the punch as a column with /buckling at its free length
• Punch: minimum pierce diameter (D ≥ t) — Not checked; keep the hole diameter at least the sheet thickness (about 2t for stainless and high-strength sheet) or the punch breaks
• Draw: total drawing load against the press capacity — The draw forces are printed, not graded against a press; check their sum (punch + holder) against the press rating with margin