kernelcad-sheet-metal

name: kernelcad-sheet-metal description: Folded sheet-metal parts — sheetMetal(profile, opts), .bend(edge, angle, radius), .flattenPattern(). Use when building L-brackets, U-channels, service panels, or any part fabricated from a flat blank + folds.

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.

Slice-1 limits

• Bend axis derived from { atX } / { atY } EdgeQuery or { face: 'top' }. Other selectors emit feature.bend.edge-not-linear.
• radius >= 0.5 * thickness recommended; tighter bends emit feature.kernel-failed.
• flattenPattern() supports at most 2 bends in the chain; 3+ emits feature.flattenPattern.multi-bend-unsupported.
• Sketch profiles must be polylines (path().moveTo / lineTo / close). Arcs in the profile are not supported by flattenPattern() in slice 1.
• The lowering pipeline (slice 1) omits the curved bend section in favor of a sharp-corner fuse — agents see the rotation but not the radiused inside corner. The K-factor math still holds for flat-pattern recovery.

MCP introspection

• flatten_pattern — returns the unfolded Region as JSON (outer ring + bend lines + holes).
• inspect({ of: 'bend-table' }) — lists every bend with its K-factor bend allowance, axis line, and parent sheetMetal opts.

Sheet-metal diagnostic codes

• feature.sheetMetal.kfactor-invalid (error) — kFactor not in [0, 1] or non-finite. Hint: pass a value in [0, 1]; typical 0.33-0.45.
• feature.bend.edge-not-linear (error) — resolved bend axis cannot be derived from the selector. Hint: pick a straight perimeter edge; slice-1 supports { atX: <n> }, { atY: <n> }, or { face: 'top' }.
• feature.flattenPattern.multi-bend-unsupported (error) — chain has 3+ bends. Hint: flatten an upstream Shape with <= 2 bends, or wait for slice 2.

Verification gates

After authoring a sheet-metal part, run before reporting done:

Related skills

• kernelcad-authoring — path() + Sketch shape this skill operates on; rotate / translate the bracket after folding.
• kernelcad-features — fillet / chamfer / hole apply to the folded result; remember the slice-1 sharp-corner approximation when placing features on the inside corner.
• kernelcad-params — thickness, kFactor, angle, radius all accept Editable<number>; wire to params for fab-iteration.
• kernelcad-mcp — flatten_pattern and inspect({ of: 'bend-table' }) are the inspection surface for downstream CAM / nesting tools.