Although castings have been found to be cost-effective already during the 1950's, their usage in critical aircraft structures was limited due to the imposition of a margin of safety. In those early days of casting technology poor controls over the material composition and casting processes resulted in parts with entrapped gas or inclusions.
Lack of process control produced castings with shrinkage, cold-shuts, and hot-tears. Many parts had coarse, non-uniform microstructure and chemical segregation. These defects caused high variabilities in the mechanical properties of castings.
This led to the introduction of an added margin of safety for castings, or a casting factor, that is still widely-used today in the design of cast components despite the advancements and achievements that have been made. in casting technology alongside the increased reliability and quality of cast parts.
This is true especially for titanium investment castings as the melting process used is very advanced and hot isostatic pressing as well as appropriate heat treatment lead to near-wrought properties, including fatigue resistance and ductility.
TITAL® has performed a determination of the coefficients of variation on TiAl6V4 castings on more than 250 representative casting parts.
This included the investigation of the influence of chemistry, weld repair, as well as the level of discontinuities with regard to the variability of static properties.
The critical process parameters and their control have been summarized and frozen. The same applies to the hot isostatic pressing and heat treatment parameters, as well as to the casting process.
Consequently, Airbus Germany approved TITAL® to manufacture titanium cast parts with Casting Factor 1.0 for the A380 aircraft, resulting in significant savings in weight, time and cost for the customer.