Sheet metal Fold (SheetMetalFoldCmd): fold the base panel along a sketch line (followed when the sketch changes) or two points on its face; angle, bend radius and K-factor from the rule; the bend zone (BA = θ(R + K·T)) comes out of the existing sheet so the flat pattern keeps its size; the line at the bend's centre, start, end or on the mould line; the side holding a picked point stays (default the larger), flip folds down; flanges on the moving part ride along

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/cmd/sheet.rs

@@ -22,6 +22,11 @@ pub static COMMANDS: &[CommandSpec] = &[
         .at("SHEET METAL", "CREATE")
         .icon("hem")
         .params("edges: [[x,y,z] on sheet edges]; length (to the outer face); gap? (inner radius, default: rule); flip?; body?"),
+    CommandSpec::new("SheetMetalFoldCmd", "Fold", fold).at("SHEET METAL", "CREATE").icon("fold").params(
+        "line: sketch + curve (a sketch line on the sheet's base face; followed when the sketch changes) or points: [[x,y,z], [x,y,z]]; \
+         angle? (default 90 deg); radius? (default: rule); position?: centerline|start|end|mould (where the line sits in the bend, default centerline); \
+         fixed?: [x,y,z] on the side that stays (default: the larger side); flip? (fold the other way); body?",
+    ),
     CommandSpec::new("FusionSheetmetalUnfoldCommand", "Unfold", unfold).at("SHEET METAL", "MODIFY").icon("unfold").params("body? (default: the last sheet body) — all bends"),
     CommandSpec::new("sheet.refold", "Refold", refold).at("SHEET METAL", "MODIFY").icon("refold").params("body? (default: the last unfolded sheet)"),
     CommandSpec::new("ConvertToSheetMetalCmd", "Convert to Sheet Metal", convert)
@@ -133,6 +138,48 @@ fn hem(s: &mut Session, p: &Value) -> Result<Value> {
     )
 }
 
+fn fold(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "SheetMetalFoldCmd";
+    let (sketch, curve, a, b) = match p.get("points") {
+        Some(v) => {
+            let pts = v.as_array().map(|a| a.iter().filter_map(vec3).collect::<Vec<Vec3>>()).unwrap_or_default();
+            let [a, b] = pts[..] else { return Err(bad(cmd, "`points` must be two points [x, y, z]")) };
+            (None, None, a, b)
+        }
+        None => {
+            let sk = sketch_id(s, p.get("sketch"), cmd, "sketch")?;
+            let c = str_(p, "curve").ok_or_else(|| bad(cmd, "give `sketch` + `curve` (a sketch line) or `points`"))?.to_string();
+            let st = s.model.state();
+            let ss = st.sketch(sk).ok_or_else(|| bad(cmd, "no such sketch"))?;
+            let ci = ss.sketch.curve_index(&c).ok_or_else(|| bad(cmd, format!("no curve `{c}` in the sketch")))?;
+            let (a, b) = match ss.sketch.segs(ci).as_slice() {
+                [solvecraft_geom::Seg2::Line { a, b }] => (ss.plane.to_world(*a), ss.plane.to_world(*b)),
+                _ => return Err(bad(cmd, "the fold line must be a sketch line")),
+            };
+            (Some(sk), Some(c), a, b)
+        }
+    };
+    if a.dist(b) < 1e-9 {
+        return Err(bad(cmd, "the fold line has no length"));
+    }
+    let angle = expr(p, "angle").unwrap_or_else(|| "90 deg".into());
+    check_expr(s, &angle, Kind::Angle, cmd, "angle")?;
+    let radius = expr(p, "radius");
+    if let Some(r) = &radius {
+        check_expr(s, r, Kind::Length, cmd, "radius")?;
+    }
+    let position = str_(p, "position").unwrap_or("centerline").to_ascii_lowercase();
+    if !matches!(position.as_str(), "centerline" | "start" | "end" | "mould" | "mold") {
+        return Err(bad(cmd, "`position` must be centerline, start, end or mould"));
+    }
+    let fixed = match p.get("fixed") {
+        Some(v) => Some(vec3(v).ok_or_else(|| bad(cmd, "`fixed` must be a point [x, y, z]"))?),
+        None => None,
+    };
+    let body = str_(p, "body").map(str::to_string);
+    add_feature(s, p, FeatureKind::SheetFold { sketch, curve, a, b, angle, radius, position, flip: bool_(p, "flip").unwrap_or(false), fixed, body })
+}
+
 fn unfold(s: &mut Session, p: &Value) -> Result<Value> {
     add_feature(s, p, FeatureKind::SheetUnfold { body: str_(p, "body").map(str::to_string), refold: false })
 }

crates/engine/src/cmd/sheet_tests.rs

@@ -141,3 +141,95 @@ fn unfold_cut_refold_and_convert() {
     run(&mut t, "PrimitiveCylinder", json!({"radius": 10, "height": 30, "body_name": "Rod"}));
     assert!(t.execute("ConvertToSheetMetalCmd", &json!({"body": "Rod", "face": [0, 0, 30]})).is_err());
 }
+
+/// A sketch line across a 100 x 60 plate's top face at x = 40.
+fn fold_line(s: &mut Session) {
+    run(s, "SketchCreate", json!({"plane": "XY", "offset": 2.5, "name": "FoldLine"}));
+    run(s, "DrawPolyline", json!({"points": [[40, 0], [40, 60]], "ids": ["fl"]}));
+    run(s, "SketchStop", json!({}));
+}
+
+fn bbox(s: &mut Session) -> Value {
+    run(s, "MeasureCommand", json!({}))["bodies"][0]["bbox"].clone()
+}
+
+#[test]
+fn fold_takes_the_bend_out_of_the_flat_sheet() {
+    let (t, r, k) = (2.5, 2.5, 0.44);
+    let ba = FRAC_PI_2 * (r + k * t);
+    let mut s = Session::default();
+    base(&mut s, 100.0, 60.0);
+    fold_line(&mut s);
+    run(&mut s, "SheetMetalFoldCmd", json!({"sketch": "FoldLine", "curve": "fl"}));
+    // The flat pattern keeps its size; the bend's centre line is the sketch line.
+    let f = flat(&mut s);
+    assert!((f["flat_size_mm"][0].as_f64().unwrap_or(0.0) - 100.0).abs() < 1e-6, "{f}");
+    assert!((f["flat_size_mm"][1].as_f64().unwrap_or(0.0) - 60.0).abs() < 1e-6, "{f}");
+    assert!((f["bends"][0]["allowance"].as_f64().unwrap_or(0.0) - ba).abs() < 1e-9, "{f}");
+    // Folded: the zone's flat volume BA·T·w becomes the bend's θ·T·(R + T/2)·w.
+    let want = 15000.0 - ba * t * 60.0 + FRAC_PI_2 * t * (r + t / 2.0) * 60.0;
+    assert!(rel(volume(&mut s), want) < 1e-4, "{} {want}", volume(&mut s));
+    // The smaller side (x < 40) stands up: outer face at the zone start less R + T, leg 40 − BA/2
+    // tall above the bend.
+    let b = bbox(&mut s);
+    assert!((b["min"][0].as_f64().unwrap_or(0.0) - (40.0 + ba / 2.0 - r - t)).abs() < 1e-6, "{b}");
+    assert!((b["max"][2].as_f64().unwrap_or(0.0) - (t + r + 40.0 - ba / 2.0)).abs() < 1e-6, "{b}");
+    assert!((b["max"][0].as_f64().unwrap_or(0.0) - 100.0).abs() < 1e-6, "{b}");
+}
+
+#[test]
+fn fold_positions_fixed_side_and_flip() {
+    let (t, r, k) = (2.5, 2.5, 0.44);
+    let ba = FRAC_PI_2 * (r + k * t);
+    let case = |p: Value| {
+        let mut s = Session::default();
+        base(&mut s, 100.0, 60.0);
+        fold_line(&mut s);
+        let mut q = json!({"sketch": "FoldLine", "curve": "fl"});
+        for (k, v) in p.as_object().into_iter().flatten() {
+            q[k] = v.clone();
+        }
+        run(&mut s, "SheetMetalFoldCmd", q);
+        bbox(&mut s)
+    };
+    let x0 = |b: &Value| b["min"][0].as_f64().unwrap_or(f64::NAN);
+    // Start: the bend starts at the line (on the fixed side), so the folded outer face is R + T
+    // short of it. End: the bend ends there. Mould: the outer face lands on the line.
+    assert!((x0(&case(json!({"position": "start"}))) - (40.0 - r - t)).abs() < 1e-6);
+    assert!((x0(&case(json!({"position": "end"}))) - (40.0 + ba - r - t)).abs() < 1e-6);
+    assert!((x0(&case(json!({"position": "mould"}))) - 40.0).abs() < 1e-6);
+    // Keep the small side: the large one (x > 40) stands up instead.
+    let b = case(json!({"fixed": [10, 30, 2.5]}));
+    assert!((b["max"][0].as_f64().unwrap_or(0.0) - (40.0 - ba / 2.0 + r + t)).abs() < 1e-6, "{b}");
+    assert!((b["max"][2].as_f64().unwrap_or(0.0) - (t + r + 60.0 - ba / 2.0)).abs() < 1e-6, "{b}");
+    // Flipped: folds down, below the sheet.
+    let b = case(json!({"flip": true}));
+    assert!((b["min"][2].as_f64().unwrap_or(0.0) + (r + 40.0 - ba / 2.0)).abs() < 1e-6, "{b}");
+    // A 45° fold: the leg leans.
+    let b = case(json!({"angle": "45 deg"}));
+    assert!(b["max"][2].as_f64().unwrap_or(0.0) < t + r + 40.0 - ba / 2.0);
+}
+
+#[test]
+fn fold_carries_flanges_on_the_moving_side() {
+    let mut s = Session::default();
+    base(&mut s, 100.0, 60.0);
+    // A flange on the left edge, then a fold between it and the rest.
+    run(&mut s, "FusionSheetMetalFlangeCommand", json!({"edges": [[0, 30, 2.5]], "height": 20}));
+    let v0 = volume(&mut s);
+    fold_line(&mut s);
+    run(&mut s, "SheetMetalFoldCmd", json!({"sketch": "FoldLine", "curve": "fl", "fixed": [90, 30, 2.5]}));
+    // The flange rode along: it is above the plate now, nothing left at z < 0.
+    let b = bbox(&mut s);
+    assert!(b["min"][2].as_f64().unwrap_or(-1.0) > -1e-6, "{b}");
+    let ba = FRAC_PI_2 * (2.5 + 0.44 * 2.5);
+    let want = v0 - ba * 2.5 * 60.0 + FRAC_PI_2 * 2.5 * (2.5 + 1.25) * 60.0;
+    assert!(rel(volume(&mut s), want) < 1e-4, "{} {want}", volume(&mut s));
+    assert!(flat(&mut s)["bends"].as_array().map(Vec::len) == Some(2));
+    // Errors: off the sheet, through the flange's bend.
+    let mut e = Session::default();
+    base(&mut e, 100.0, 60.0);
+    assert!(e.execute("SheetMetalFoldCmd", &json!({"points": [[40, 0, 30], [40, 60, 30]]})).is_err());
+    assert!(e.execute("SheetMetalFoldCmd", &json!({"points": [[40, 0, 2.5], [40, 60, 2.5]], "position": "sideways"})).is_err());
+    assert!(e.execute("SheetMetalFoldCmd", &json!({"points": [[0.5, 0, 2.5], [0.5, 60, 2.5]]})).is_err(), "no material past the bend");
+}