The development and manufacturing capabilities of a cast titanium configuration is relatively new, going back approximately ten years. Although there are thousands of foundries in the United States producing cast parts from various other metals, there are presently only six companies that have accomplished the difficult task of casting in titanium. The reason so few companies have ventured to work successfully with titanium is because of the special handling requirements which are vastly different from other metals.
Ti Squared Technologies, Inc. has developed and perfected the various techniques and methodologies which have overcome the many difficulties in working with this volatile element which include its reactivity to various elements, rapid contamination rate, inherent solvent properties, and its lack of fluidity.
Molten titanium is very reactive to liquids, gases, and solids. Therefore, Ti Squared Technologies employs consumable vacuum arc melting which we have found to be the only suitable commercial method of producing titanium castings.
Elevated temperatures of titanium contribute to its rapid contamination by oxygen and nitrogen as well as causing severe damage to its ductility by small percentages of such contaminants. Therefore, the melting of titanium at Ti Squared Technologies is done with the absence of air.
Liquid titanium is an extremely effective solvent creating difficulties in containing the molten metal within a crucible during the melting operation. Ti Squared has overcome this challenge by using a method called skull melting. A water-cooled copper crucible is utilized to extract heat so rapidly from the liquid metal that it solidifies before its solvent reaction can take effect. This provides a thin film of solid titanium between the molten titanium and the copper crucible, creating a protective barrier which minimizes the solvent capabilities of titanium.
Titanium’s very narrow range of liquids to solids creates a significant fluidity problem. Ti Squared Technologies has found that by cutting the power after enough molten titanium has accumulated in the crucible, quickly withdrawing the electrode, and tilting the pot all within a few seconds prevents the pool from solidifying. Then a process for assisting the pressure during fill can be used within the furnace vacuum chamber during the pouring of the melt. The additional “g” force during the casting operation helps to overcome the lack of fluidity. The pressure assists in filling mold cavities with metal densities vastly superior to those from conventional static casting and promotes complete fill-out of even the most difficult titanium alloys such as gamma titanium. Mold materials such as sand, silica shell, or low refractory ceramic are unsatisfactory for titanium since titanium melts above or near the melting point of these materials and will violently react with them. Ceramic materials such as yttria and graphite mold system have been used in titanium casting and configurations with close tolerances and excellent surface finishes are obtainable.