iMechanica - design - Comments

Rolls-Royce project

Henry Tan — Thu, 13 Dec 2007 08:00:44 -0500

Waqas,

Can you put some of your results on this web, with pictures and physical explanations?

Henry.

Industrial Placement

Waqas Ahmad — Wed, 21 Nov 2007 19:17:42 -0500

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.

Laser Techniques been used

shengke zhi — Mon, 30 Jul 2007 08:44:58 -0400

I am sorry to say it is not laser photo pick-up.

It is Laser Speckle Pattern techniques, which means the reflected laser beam from the targeting area of the surface of a detecting shaft has less diffused scattering effect because of the coherent light, so that the reflected light is obtained by an 2D photo-array CMOS sensor placed in Fourier Plane. The light obtained generates plenty of light speckles whose size is bigger than the size of pixel in CMOS sensor. Assuming the position of the coherent light source is fixed, when the detecting shaft is rotating, the light speckle is moving along with the rotary shaft. In that case, the new speckle is generated when the previous speckle is moving out of the light beam.

The speckles has linear relationship witht the angle displacement of rotary shaft. Therefore, the IAS can extracted by measuring the angle displaced and the time elapsed.

Reduce Time

shengke zhi — Mon, 30 Jul 2007 08:30:20 -0400

The time reduction has two methods, including hardware technique based and software technique based.

For hardware based method, you can use an independent timer to trigger off the counter to measure the number of speed pulses in a suitable frequency, such as 1MHz. In that case, the time interval you obtained is so small that it apporaches to zero.

Another, for software based method, an internal timer is designed to trigger off the counter to measure the value of angle displaced. The interal timer can be programmed based on freuqnecy of a CPU within a computer which is used to acquire data, or be implemented based on the frequency of oscillater within the DAQ system.

Meanwhile, an internal timer is always employed to measure the time elapsed between two successive speed pulses. In that case, the software timer starts when the speed pulses is going up at the rising edge and stops when the speed pulses is falling down at the falling edge. Because the number of speed pulses per revolution is decided by the resolution of an encoder sensor in contact measurement of IAS, the degree presented by the speed pulses thus is reduced. Therefore, combing an accurate time interval is measured and an precise angle displaced, the exact IAS can be extracted.

photo picking-up technique

Henry Tan — Wed, 11 Jul 2007 12:25:25 -0400

How is laser used as a photo picking-up technique? Can you elaborate it?

reduce the measuring time to zero

Henry Tan — Wed, 11 Jul 2007 12:20:33 -0400

Shengke,
Thanks for the information.
How is it technically realized to reduce the measuring time to zero?
Henry.

Condition Monitoring focus on Instantaneous Angular Speed

shengke zhi — Wed, 11 Jul 2007 05:10:42 -0400

Hi Henry,

Thanks for letting me know the iMechanica. Since you start Condition Monitoring topic, I would like to give more details about Instantaneous Angular Speed technique in Condition Monitoring.

Instantaneous Angular Speed (IAS) is investigated for last 10 years in Condition Monitoring. The content of IAS is coming from angular speed. If the time taken is reduced apporaching to zero, we can measure the angle travelled to extract IAS, or if the angle travelled is reduced to zero, we can measure the time elapsed to extract IAS.

Conventional measurements of IAS are mainly contact measurement, such as using a shaft encoder. However, the installation problems are still not been solved. It is difficult to find a place to mount an encoder into machinery. Non-contact measurement of IAS becomes popular in recent year. magnetic pick up, photo pick-up techniques have already been employed.

To reduce the cost of the hardware, and improve operation capability, another optical non-contact measurement of IAS is investigated. This method majorly employ a normal laser optical mouse to measure the shaft speed of machinery to achieve condition monitoring.

For more details, it will come soon.