Sheet Metal Mould Casting - A Novel Alternative to Production of Sand Castings

摘要

A new casting process based on sheet metal and loose unbounded sand, named as Sheet Metal Mould Casting (SMMC), is proposed in the present work. In the first step, the surface of a casting to be produced is divided into two or more parts depending on the complexity of the casting in such a manner that each part of the surface can be produced of a sheet metal by sheet metal working. Each part is produced from sheet metal by cutting to required dimensions and subsequently by forming with die and punch. The gating system and risers are also produced from the sheet metal. These parts are assembled to produce a sheet metal mould. The whole assembly is embedded in loose unbounded sand contained in a mould box and compacted. The subsequent steps are similar to conventional sand casting.A few steel castings were produced successfully by the above process. However, it was found that the sheet metal does not bond with the sections of the castings at the outer surface, whereas proper bonding occurred at the internal (core) surfaces. Therefore, either suitable measures are to be taken to ensure bonding of sheet metal to casting by controlling pouring temperature etc. or the unbounded sheet metal at outer surfaces are to be removed and recycled as scrap. The process offers several advantages. Since no binders are used in the moulding sand, no pollution in the moulding / core making shop and pouring area arising out of binder, cost of binder can be saved, easy shake out of casting and easy removal of core sand, less chances of sand fusion over casting in case of steel and iron castings, sand mixing / mulling are not needed, sand is reusable, therefore no sand disposal or sand reclamation required, moisture/ binder - related casting defects are eliminated. Other major advantages include, no cores are required since holes / recesses in casting are parts of sheet metal mould, all metals can be cast by SMMC process, no parting line defects such as mismatch / fins, no chances of sand drop and sand inclusion during filling of mould,close tolerance casting. The process also offers possibility of producing bi-metallic casting with a thin wear / corrosion - resistant outer layer of different alloy. On the other hand, there are a few disadvantages and limitations of the casting process. The process is feasible only for mass production, suitable for small and medium size castings only, uneconomic for complex shaped castings, overall high installation cost associated with making and assembly of sheet metal mould, chances of misrun defect in absence of proper venting, risk of mould collapse since no binder in sand mould and chances of improper bonding of sheet metal mould with body of casting. Initial trials show that, many sand castings in general and simple shaped iron and steel castings in particular, can be produced commercially by this process.