Abstract
A new type of air permeable mold which can be applied to the various manufacturing fields, has been developed. The mold is made by a mixture of mullite powder, iron powder and ethyl silicate and then sintering it in an air atmosphere at around 900°C for a few hours. The mold has a porosity between 20-30 vol%, as well as an adequate permeability to air. The sintered layer of the mold is found to consist of the ceramic powder being firmly bonded by the oxidized iron powder. Furthermore, a compressive strength of 100 MPa at the maximum is obtained although there are many pores within the layer. The dimensional change of the mold can be suppressed to a value smaller than 0.2% linear expansion, though it is manufactured by sintering process. In addition to the above mentioned features of the mold, a fine complicatedshaped surface of the mold can be manufactured very easily by casting the mixture on to the master model. In this paper, the production procedure and characteristics of the mold are described, as well as the application to the vacuum forming of plastic sheet as one of several usages of the mold. In addition to the advantage that the proposed mold can eliminate drilling holes for air evacuation, it gives a good forming capability of fine-complicated shape due to uniform evacuation through the well distributed fine pores in the mold.
