During the past few years the titanium and aluminum investment casting specialist TITAL located in Bestwig, Germany, has convinced many of its aerospace customers to use near-net-shape castings. At Airbus alone 40 machined parts have been converted into near-net-shaped castings in the last four years. A critical factor when making the machined versus casting decision is the fly-to-buy ratio.
This is the ratio between the material inventory (purchased) and the material used (finished and built into the aircraft). Using a near-net-shape casting for production saves material and therefore is considerably more cost effective. Furthermore, castings are perfectly suited for optimizing the topology which also saves additional weight. Using near-net-shape castings makes a lot of sense especially for titanium alloys. When compared to aluminium, titanium is relatively expensive, and is very difficult to machine making it a cost intensive material.
Approximately 95% of the material is removed when machining parts from solid material and thus a lot of waste is produced. With castings, only the material that is required for the shape of the casting is needed. “Proportionately it is much more efficient and cheaper”, explains Key Account Manager Thomas Stephan. The more expensive the material, the sooner a conversion to near-net-shape production pays off.
When using a near-net-shape casting any subsequent machining of the functional areas where the casting is in direct contact to other parts is greatly reduced. Very exact tolerances can be achieved and material waste is reduced to a minimum. Thomas Stephan: “Generally this is not more than 1 to 2 mm that has to be removed when finishing the functional areas mechanically.”
Another advantage to castings versus machining solid material is the ability to achieve very complex design geometries. This is next to impossible and very expensive when machining from wrought titanium. Even free formed surfaces can be easily accomplished with the casting process. “Historically these same surfaces could only be achieved by machine scanning, an expensive and time consuming process”, says Stephan. An example of this is the very complex Sponsen Peak for the A400M military carrier. This part was originally machined from solid material and is now in production as a near-net-shape casting.
As most of the developers think, design and develop parts in terms of the machining technology, TITAL offers expert seminars dealing with investment castings. The seminars take place at TITAL’s Bestwig site but on occasion also on the customer’s premises. “For professionals this is so complex that the best way to communicate this is in a workshop atmosphere”, explains Philipp Jerusalem, Director of Sales and Marketing at TITAL. Philipp Jerusalem also sees the trend that more and more developers are turning to casting solutions as a result of these events.
At first glance the tooling investment (moulds made out of metal where the wax pattern is produced which is finally used for producing the casting form) counteracts the conversion to an investment casting. “However the fixed costs are usually overestimated compared to the savings so depending on the delivery quantity, the conversion will pay off within one year”, explains Philipp Jerusalem. The investment level in tooling for the casting depends on the complexity of the component. Especially for titanium castings the costs are amortized right from the start. “Because”, adds Jerusalem”, “the material loss when producing investment casting is close to zero.”