kernelcad-sheet-metal

kernelCAD — sheet metal

Build folded sheet-metal parts (L-brackets, U-channels, service panels) from a closed Sketch + thickness + K-factor. Bend along a linear axis line; recover the flat blank as a Region for laser / CNC consumption.

// L-bracket: 100 x 60 x 2 mm, one 90 degree fold along x=50.
const s = path().moveTo(0, 0).lineTo(100, 0).lineTo(100, 60).lineTo(0, 60).close();
const blank = sheetMetal(s, { thickness: 2, kFactor: 0.38 });
const bracket = blank.bend({ atX: 50 }, 90, 3);
return bracket;

// Recover the flat blank as a Region.
const flat = bracket.flattenPattern();
console.log(flat.outer);     // [[0,0], [100,0], [100,60], [0,60]]
console.log(flat.bendLines); // [{ start: [50,0], end: [50,60], angle: 90, radius: 3, ordinal: 0 }]

API

// Top-level constructor — captures kind:sheetMetal record.
sheetMetal(profile: Sketch, opts: {
  thickness: Editable<number>;   // mm, > 0
  kFactor: Editable<number>;     // unitless, in [0, 1]
  faceLabels?: FaceLabelsMap;
}): Shape;

// Shape methods — chain on a sheetMetal-rooted Shape.
shape.bend(
  edgeRef: EdgeSelector | string,  // slice-1: { atX: n } | { atY: n } | { face: 'top' }
  angle: Editable<number>,         // degrees, signed (positive = fold +normal)
  radius: Editable<number>,        // mm, inner bend radius
): Shape;

shape.flattenPattern(): Region;    // derived view — no FeatureRecord

Bend-allowance math (K-factor approximation)

BA = (pi * |angle_deg| / 180) * (kFactor * thickness + radius)

• BA = developed length of the neutral axis through the bend arc.
• kFactor = neutral-axis offset ratio. Typical values: 0.33-0.45 (mild steel / aluminum).
• Slice 1 supports the K-factor formula only.

How a bend folds

• The bend line is in FLAT-BLANK coordinates for every bend of a chain: .bend({ atX: 25 }, 90, 2).bend({ atX: 75 }, 90, 2) is a U-channel, even though the second line has moved by the time it folds.
• The strip of width BA centred on the line becomes the arc (inner radius = radius); the flange beyond it keeps its flat length, so the flat pattern is exactly the blank (flange lengths + bend allowances).
• The SHORTER side of the blank across the line folds (a tie folds the +X / +Y side). A web with a bend near each end stays on the bench.
• Holes and cutouts drilled in the flat blank before .bend() ride along with their flange: sheetMetal(...).holes({ byNormal: 'Z' }, ...).bend(...).
• Parallel bend lines whose zones overlap fail with feature.invalid-args.