Investment Casting of Precious Metals: Materials and Methods

Aim of this work is the analysis of the materials and parameters related to the investment casting process,mainly focusing on peculiarities and criticisms of the casting of precious metals in jewelry production.Precious metals casting is traditionally and historically targeted to overcoming limitations in terms of geometries and final quality of the cast part. Moreover, an increasing interest rises concerning the use of new technologies and the industrializations of typical handcraft skills. New materials are therefore introduced into the process, in order to be able to get thin and intricate shapes, hollow parts and innovative design features. This is leading to a substantial rearranging of the process, with a constant innovation regarding technologies and medication of traditional materials. Considering the whole process, nvestment casting is dealing with a wide range of materials, from metallic, polymeric and ceramic classes. All these materials cannot be considered as single identities, but their synergetic behavior has to be studied, not just meaning that all of them contribute to the final quality of the cast part, but taking into account possible mutual interdependencies. The research work has been divided in a preliminary analysis of the process, in order to deepen the knowledge about material features, and in a extended study on the application of competences deriving from other sectors to the specific one. In fact it’s almost impossible to find sector boundaries between jewelry and fashion accessories both in terms of process and in terms of market. Therefore the analysis of the state of the art has been widened to other processes and applications, in particular focusing on fashion accessories and eyewear component production. Market analysis clearly show a high interest of jewelry towards innovative processes/materials, often deriving from completely different fields of application. For this reason, an analysis of the investment casting process applied in the automotive and biomedical sectors can give valuable hints for the jewelry production optimization. Particular attention has also been paid to fluid dynamic analysis of the casting system, considering metal flow into the flask and following cooling and solidification. For this purpose, computational fluid dynamic has been applied to the process. Material analysis, needed for both the simulation and for a complete understanding of the process, has been carried out. Physical and thermal properties of metals and investment materials have been analyzed in order to get a proper database for casting simulation. Waxes and resins have been tested both in terms of thermal, mechanical and chemical characteristic, in order to understand their respective roles into the process and try to optimize them. Following the analysis, process implementation has been performed in order to apply information deriving from experimental tests to the process. Many parameters can be taken into account when optimizing precious metal casting; in order to focus the research activity, some limitation in terms of process have been applied. Casting trails were conducted using a static vacuum casting machine on sterling silver and 18 kt. Gold alloys, referring to traditional investment casting process.