Page 618 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Design and material utilization C HAPTER 18.1

Table 18.1-3 Body-in-white cost analysis presented by Dieffenbach 14

Steel Aluminium Steel Aluminium Composite
unibody unibody spaceframe spaceframe monocoque
Body-in-white cost analysis: key design inputs for selected case study alternatives

Geometry
Overall vehicle
mass (kg) 315 188 302 188 235
Mass as % of steel unibody 100% 60% 96% 60% 75%

Spot joints (#) 3250 3400 1000 n/a
Seam joints (cm) n/a n/a 4000 6000
Piece count
Total piece count (#) 204 224 137 137 41
Count as % of steel unibody 100% 110% 67% 67% 20%

Number of stampings 187 207 40 40 n/a
Number of castings n/a n/a 30 30 n/a
Number of roll/ n/a n/a 50 n/a n/a
hydroformings

Number of extrusions n/a n/a n/a 50 n/a
Number of mouldings n/a n/a n/a n/a 7
Number of foam cores n/a n/a n/a n/a 34
Panels (inners/outers) 17 17 17 17 17

Materials
Material prices ($/kg) $0.77–0.92 $3.00–3.50 $0.77–2.20 $2.00–3.00 $3.13
3
Material density (g/cm ) 7.85 2.70 7.85 2.70 1.59
Stamping Casting Hydro-forming Extrusion Moulding
Body-in-white cost analysis: key fabrication input for selected case study alternatives
Range of cycle times (s) 8–12 50–60 30–40 3–10 600–1200

Range of labourers/fab’n line 4–6 2 2 2 2
Range of machine costs ($M) $1.3–7.5 $0.8–1.5 $1.0–2.0 $1.0–2.0 $0.5–1.0
Range of tool set costs ($M) $0.2–6.0 $0.1–0.2 $0.1–0.5 $3k–7k $0.1–$1.2

influence. Thus the trends shown in Table 18.1-3 are higher volumes the steel unibody shows the lowest cost.
mirrored in these studies with steel characterized by high The aluminium spaceframes or unibody do not show
investment cost, lower material and faster production a cost advantage although the aluminium spaceframe
rate. Conversely moulded plastic has a lower investment competes fairly well (a 15 per cent cost penalty) and
cost, higher material cost and slower production rate. The compares with the steel unibody at high volumes. For
composite monocoque has the lowest cost up to about outer panel assembly sets compression moulded SMC has
30 000 vehicles per year; from 30 000 to 60 000 vehicles the lowest cost for volumes up to about 100 000 sets per
per year the steel spaceframe shows the lowest cost. For year above which steel has the lowest costs.

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