Industrial Placement & Individual Projects (2007/2008)

Industrial Placement

‘Optimising Superplastic Forming Die Shape and Platens for Next Generation Aero Engine Production’ 

Background

The design of hot forming dies was optimised in the 1980s for the engine types at the time, the knowledge bank has remained constant ever since. The current high by-pass ratio engines are larger and therefore require larger hot forming dies. The increase in size of dies and presses along with the increase in mass of material and thermal efficiency means the cooling time has increased significantly.  

The dies are regularly changed for routine maintenance, this includes die surface cleaning or re-cut. However, the current cooling rates are approximately 37°C per hour, this takes 3 to 4 days and consequently has an adverse impact on productivity. The actual die model has been simplified to fit into the scope of the project. The die is manufactured from cronite (HR4), a nickle based alloy. This project is of interest to Rolls-Royce, as the research done will be used by the company to conduct their own investigations on the hot forming process and improve the entire manufacturing process for fan blades.

 Aims and Objectives

The project has aim of the project is:

1.    To reduce the thermal cycling time during die change over/maintenance through optimised die and platen design.

These aims have been broken down into the following objectives

1.    Model current die and platen thermal stress during thermal cycling,

2.    Model current die and platen stress during forming,

3.    Consider ways of redesigning die to speeding up the cooling press,

4.    Define minimum working surface thickness before distortion occurs in normal surface,

5.    Develop designs to optimise die shape and to achieve maximum cooling rates 

Current Progress

The material used in the die is specially made for Rolls-Royce, as the material must perform at a temperature of 900°C and pressure in the region of 30bars this and the fact that Cronite has a high nickel content makes the material far too expensive therefore, it was beyond the scope of this project to conduct actual experiments on the material. Finite element analysis has been recognised as the best method of analysing the problem.

The finite element package Ansys was chosen to model the current die and platen stresses so far the progress has been reasonable. Several designs have been analysed and the best design will be taken to the next stage and studied in greater detail. The designs will be analysed structurally to determine the effect of the design change on the cooling time and to make sure the die can withstand the working conditions.