Development of Vibration Damping Steel Sheets for Automobile Oil Pans 930023
Recently, Vibration Damping Steel Sheet (VDSS) has been increasingly used for automobile parts such as dash boards and partition panels. VDSS is also used in oil pans, but the rquirements in this application are much stricter than those in other auto applications. The material must remain sound (show no wall break) and not delaminate during deep drawing press forming. In service, it must be oil tight at the welded drain nut and must maintain good adhesion characteristics at high temperatures of 60-120°C. The VDSS with a thermoplastic resin core used to date in oil pans provides poor baking durability and heat durability in high temperature service. For use in oil pans, the authors therefore developed a new VDSS material comprising two extra deep drawing class steel skin sheets (of ultra low carbon steel) and a thermosetting polyester resin core layer containing metal powder.
The shear adhesion strength (SAS) of the thermoplastic resin VDSS was less than half the initial SAS after post-coating baking at 160∼200 °C, because the melting point of the resin was lower than the baking temperature. However, the SAS of the new thermosetting resin VDSS does not decrease from the initial SAS.
It is generally thought that higher SAS values give better deep drawing press formability in VDSS, but the limit formability of VDSS decreased at SAS values higher than 17MPa, because higher SAS values create a higher press forming load. The optimum SAS of VDSS is 8.4∼14.5MPa for both types of resin.
When thermosetting resin VDSS is welded, the time required for elimination of the resin layer under the welding electrode tip is 2∼3 times longer than that of thermoplastic resin VDSS in resistance welding and the projection welding used as a by-pass method. Thermosetting resin VDSS has the defects of ringed cut-off in resistance welding and an imperfect welding nugget in projection welding of the drain nut because of the long elimination time of the resin. The newly developed VDSS with a thermosetting resin core containing metal powder has the same weldability as thermoplastic resin VDSS. In addition, the frequency response function (inertance) of an oil pan of the newly developed VDSS was found to be 1OdB lower than that of an ordinary steel sheet.