Abstract
In order to spot-weld VDSS without providing a shunting curcuit, electro-conductive property is needed to the core damping material. The method to give electro-conductivity is addition of metal particles into the resin which has diameter nearly equal to the resin thickness to ensure direct contacts between skin sheets.
As particles were increased or resin thickness became thinner under the same particle content, the resistance between skin sheets was reduced. Nickel particle exhibited the best conductivity of all which were tested.
In the case of the small amount of Nickel particle, pin-hole defects were observed and these defects were peculiar to the welding of VDSS because welding current was concentrated to an specific Nickel particle with relatively low electrical resistance. The defect was caused by growing the melting area by joule heating to the outer surface of skin sheet.
Decreasing the voltage between skin sheets is effective to prevent pin-hole defect formation. From the practical point of view, it is needed that decreasing the resistance between skin sheets or controlling the welding voltage.
As for the resistance, it was showed that initial resistance between skin sheets was useful for the virtual index in material production. Using a sufficient conductive VDSS, time to exclusion of resin was quite short, and weld defect was not observed.
