BMW and
Hitchiner engineers
worked together to respond to this unexpected challenge, doing a joint
study to choose and test an alternate alloy with higher hardness and
improved required wear resistance. The
development team chose and validated a European alloy -- a 30Cr-MoV9 tool
steel -- to
meet the performance requirements of the lever arm. A plasma
nitriding treatment produces hard, wear resistance surface layers on the
casting.
There
was one negative factor with the new alloy -- lower yield. The
30CR-MoV9 steel has lower fluidity which required higher casting
temperatures for good fill. Higher temperatures required longer
solidification time, which increased the casting time and produced fewer
daily casting cycles. |