Page 55 - Plastics Engineering

38 General Roperties of Plastics

Table 1.10
The energy required to manufacture and process a range of materials at typical design thickness

Design Energy Jlm2 x lo6
Material thickness 0
-mm
Magnesium 1.9
Aluminium sheet 1.3
Zinc die casting 1.3
Aluminium casting 1.3
Steel 0.8
Acetal 2.0
Modified PPO 2.0
S MC 3.3
Rgid polyurethane foam 5.3
Wycurbmate 2.0
Acrylic 2.0
Nylon 6 1.8
Nylon 66 1.8
LOPE 2.7
HDPE 2.4
Polystyrene 2.0
RRlM polyurethane 3.2
Polypropylene 2.5
ABS 1.9
PVC 2.0
Feedstodc Fuel 0 Process

where 83 is a constant, which will be the same for all materials. Therefore we
can define a cost factor, Cf, where
Cf = (5) (1.14)

which should be minimised in order to achieve the best combination of price
and performance. Alternatively we may take the reciprocal of Cf to get a
Df = (g) (1.15)
desirability factor, Df ,

and this may be compared to Df given by equation (1.5).

Selection for Stiffness at Minimum Cost
Using equation (1.7) and an analysis similar to above it may be shown that on
Df = (s) (1.16)
the basis of stiffness and cost, the desirability factor, Df, is given by