A crash box is an energy-absorbing structural component mounted between a vehicle’s bumper beam and the main body. It is designed to deform in a controlled manner during low- to moderate-speed impacts, reducing crash forces transmitted to the chassis and lowering repair costs by localizing damage to a replaceable module.

// Crash-box with beam cutout and mounting holes
// A crash box is an energy-absorbing structural component mounted between a vehicle’s bumper beam and the main body. It is designed to deform in a controlled manner during low- to moderate-speed impacts, reducing crash forces transmitted to the chassis and lowering repair costs by localizing damage to a replaceable module.
// Categories: Automotive

@settings(defaultLengthUnit = mm)

// -----------------------------
// Parameters
// -----------------------------

// Hole parameters (for mounting/fastening to the bumper beam)
mountHoleRadius = 16
mountHoleOffsetFromTop = 150
mountHoleSpacing = 200

// Beam/cutout parameters
beamCutoutDepth = 300

// Crash-box overall dimensions
crashBoxExtrudeLength = -1200
crashBoxOuterWidth = 400

// -----------------------------
// Crash box: square tube profile and extrusion
// -----------------------------


sketchCrashBox = startSketchOn(XY)
profileCrashBoxOuter = startProfile(
       sketchCrashBox,
       at = [
         -crashBoxOuterWidth / 2,
         -crashBoxOuterWidth / 2
       ],
     )
  |> angledLine(angle = 0deg, length = crashBoxOuterWidth, tag = $rectangleSegmentA001)
  |> angledLine(angle = segAng(rectangleSegmentA001) + 90deg, length = crashBoxOuterWidth, tag = $seg03)
  |> angledLine(angle = segAng(rectangleSegmentA001), length = -segLen(rectangleSegmentA001), tag = $seg01)
  |> line(endAbsolute = [profileStartX(%), profileStartY(%)], tag = $seg02)
  |> close()

// Create a solid crash box from the square profile
crashBoxSolid = extrude(profileCrashBoxOuter, length = crashBoxExtrudeLength)

// Optional exterior edge softening
filletCrashBoxCorners = fillet(
  crashBoxSolid,
  tags = [
    getCommonEdge(faces = [seg01, seg02]),
    getCommonEdge(faces = [rectangleSegmentA001, seg02]),
    getCommonEdge(faces = [rectangleSegmentA001, seg03]),
    getCommonEdge(faces = [seg03, seg01])
  ],
  radius = 60,
)

// Shell the crash box from both ends to create a constant wall thickness
crashBoxShelled = shell(crashBoxSolid, faces = [END, START], thickness = 20)

// -----------------------------
// Bumper beam surrogate: used to cut a mating pocket in the crash box
// -----------------------------


sketchBeam = startSketchOn(-YZ)
profileBeam = startProfile(sketchBeam, at = [-870.13, 0])
  |> angledLine(angle = 0deg, length = 1744.11, tag = $rectangleSegmentA002)
  |> angledLine(angle = segAng(rectangleSegmentA002) - 90deg, length = beamCutoutDepth)
  |> angledLine(angle = segAng(rectangleSegmentA002), length = -segLen(rectangleSegmentA002), tag = $seg04)
  |> line(endAbsolute = [profileStartX(%), profileStartY(%)])
  |> close()

// Extrude the beam surrogate symmetrically, tagging start/end faces for fillets
beamSolid = extrude(
  profileBeam,
  length = 250,
  symmetric = true,
  tagStart = $capStart001,
  tagEnd = $capEnd001,
)

// Ease the beam pocket edges for a better fit
filletBeamEnds = fillet(
  beamSolid,
  tags = [
    getCommonEdge(faces = [seg04, capStart001]),
    getCommonEdge(faces = [seg04, capEnd001])
  ],
  radius = 80,
)

// -----------------------------
// Subtract the beam volume from the crash box to form the mating pocket
// -----------------------------


crashBoxWithPocket = subtract(crashBoxSolid, tools = beamSolid)

// -----------------------------
// Mounting holes: through-holes from front to back of crash box
// -----------------------------

// Sketch on one side face (seg02) and pierce through to opposite face (seg03)
sketchHoles = startSketchOn(crashBoxWithPocket, face = seg02)
profileHoleLeft = circle(
  sketchHoles,
  center = [
    -mountHoleSpacing / 2,
    -mountHoleOffsetFromTop
  ],
  radius = mountHoleRadius,
)
profileHoleRight = circle(
  sketchHoles,
  center = [
    mountHoleSpacing / 2,
    -mountHoleOffsetFromTop
  ],
  radius = mountHoleRadius,
)

// Create cylindrical cutters to the opposite wall; keep as new bodies to subtract
holeCutters = extrude([profileHoleLeft, profileHoleRight], to = seg03, method = NEW)

// Apply the hole cut to the crash box with pocket
crashBoxFinal = subtract(crashBoxWithPocket, tools = holeCutters)

// -----------------------------
// Appearance
// -----------------------------


appearance(crashBoxFinal, color = "#00aaff")


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crash-box