Steel sheet coated with a self-lubricating resin consisting of polyvinylbutyral resin with added polyolefin wax was found to have excellent press formability.
The self-lubricating property is affected by the degree of cross-linking in the base resin which forms the film and is obtained by baking in the range of 120∼180°C.
The effect of the properties of the base resin on press formability was therefore studied using polyvinyl butyral resin.
The maximum drawing height of the specimens increased when the specimen temperature during press forming was near the glass transition temperature Tg of the base resin.
This was attributed to the fact that the coefficient of friction μ of the base resin reached its minimum value near Tg because the decreaing tensile strength and increasing elongation of the resin at this temperature permitted easier deformation.
