METHOD FOR FORMING PATTERN

PURPOSE:To improve the accuracy of product shape by forming a core part with lost foam pattern, coating the surface with shape holding layer and further, forming the lost foam pattern having the same shape as the produce at outside thereof. CONSTITUTION:The lost foam pattern 1 having the same shape as a hollow part in the product is formed and facing agent is coated on this surface to form shape holding layer 2. Successively, the pattern 1 is set in a metallic mold 3 and space having the same shape as the product is formed at between the shape holding layer 2 and the inner face of the metallic mold 3, and the lost from pattern 4 is formed in the space. Successively, the pattern 5 is set in a flask 7 and after packing sand, the flask is vibrated and the sand is hardened under reducing pressure. As the pattern 5 does not has hollow part, the deformation caused by uniform force of the sand 8 is prevented. By pouring the molten metal into the pattern 4, the product is obtd. and the core pattern is gradually softened and taken out. As the pattern 5 does not deform, the accuracy of the product shape is improved.