Power Generation Case Study


The project background

Fabwell undertook this project for a UK-based company that specialises in the manufacture of gas path components - primarily rotating blades and stationary nozzle guide vanes for the aerospace and industrial gas turbine industries. The customer consists of three manufacturing facilities covering precision casting, blade machining and nozzle guide vanes. The customer produce turbine blades through a process called investment casting. Investment casting (or lost wax casting) is a multi-step process that delivers accurately cast and economical products. It can be used for low quantity, complex components. The tooling cost is lower than that of die casting or gravity casting, with the trade-off in higher part unit cost. The materials used range from aluminium, steel, stainless steel to titanium.


Fabwell sought to develop a suitable investment container or fixture to hold, convey and safely pour molten metal in order to cast a new, large turbine blade out of nickel-cobalt super alloy. The ceramic mould is placed upright in the container, and is then back filled with vermiculite, helping the mould to be held securely and safely. This material also acts as a thermal insulator to help achieve the correct temperature of the mould prior to pouring, and aid in the correct cooling rate after pouring. It is heated in a rotary hearth furnace up to 1150°C for approximately 20 hours, before being removed and transported to the pouring area, where the investment container is placed and the molten metal poured into the mould. It is left to cool in a controlled environment, before the mould is removed from the investment container  and ceramic/vermiculite is broken off from the casting. The investment container is reloaded and put through another cycle. The life expectancy of the investment container is expected to be 3 years, but this is dependent on the number of cycles.

The technological baseline and status at the start of the project

The customer had recently produced a new design turbine blade that was much larger than anything they had developed before. However, they did not have suitable sized investment containers to cater for this. Hence, with no off-the-shelf solution readily available, a bespoke programme of development had to be undertaken.

Work done

Fabwell embarked on a comprehensive research and development programme to address the technological issues. The project commenced with a feasibility study where Fabwell sought to gain a better understanding of the casting process and the stages involved; the new turbine blade design and it complex geometry; the pour temperature and pour weight of the molten metal; the material properties and behaviour  etc., before a suitable design, development and implementation strategy could be identified (BEIS guidelines paragraphs 27b, 31g and 36).


Using the knowledge obtained as a foundation and following a critical assessment, a technical scoping exercise was conducted for the creation of the investment container fixtures along with the creation of a project plan as to how it would be achieved. Due to the complex shape of the container, an iterative design exercise had to be conducted. As part of this process, a number of simulations on CAD software were run including stress analysis. In parallel, several possible materials were explored to determine which would be best for this application. Following numerous trials, 253MA stainless steel was chosen as the material that would best meet the requirements.


Different welding techniques to create the main body of the investment container were explored with  tungsten inert gas shielding (TIG) eventually chosen for this fabrication. The base was a very important design feature, for which Fabwell welded 2 rings in a loose manner, one above and one below the base to allow the base some degree of movement during the long cycles and the high temperature it would be exposed to.


Fabwell did not want permanent distortion occurring as this could potentially leave the fixture unsteady and unsafe. The final design for the investment container consisted of having a split lid to hold the casting mould and thus prevent spillage. A small amount of CNC machining was required for creating the spigots on the lid. Photos of the investment container are shown below.

(Fig 1)


Fabwell embarked on a rigorous an internal testing and validation programme to prove out the principle of operation and ensure the investment container met the desired technical specification with regards to their size, weight, fit, form, durability and ease of assembly. The dimensions of all the components were verified on a CMM, following which quality checks were conducted. This was followed by high temperature testing of the container at the customer site (BEIS guidelines paragraphs 27c and 39).


As of December 2020, the project was completed with all technological uncertainties having been resolved.