Case study 2.
Yoke End.

What does it do?

The part under scrutiny is known as a “Yoke End” and secures the GRP bar across the track, between the rails, attached on both sides to the rail fastenings.

Benefit 1. The new investment casting can be fitted to any combination of rail fastening or sleeper type without drilling, which weakens the concrete sleeper, and is therefore fast and easy to use. The GRP bar secures vital components between the rails which provide communications such as signal status, speed of train, status of braking system etc and these types of installations are becoming more and more important.

The railway is a harsh environment where vibration – caused by the train – can have very serious implications and keeping any infrastructure secure between the rails, so that it cannot break free and become dangerous as trains pass over at up to 350kph, is of paramount importance. The potential for disaster, should anything fail and break free, is the reason to constantly improve the components.

Benefit 2. Our approach to supply the Yoke Ends as an investment casting, rather than the current fabrications, offered the continued improvement in strength and weight reduction which the customer is always striving to achieve.

Evaluation of problems

The problems were mostly that the existing part was not permanently weather proof, was heavier than necessary due to production method and had passed not surpassed the testing required at the time. To further strengthen the existing fabrication to new standards would have proved very expensive and involved possible weight increase, heavier welds (welds weaken the metal at the site of the weld and are more susceptible to fatigue failure) and might require a long development time to make the necessary improvements through many iterations and testing.

Then, after this redesign and testing cycle, the likelihood of further developments trackside requiring further changes, only highlighted the limitations of the existing part and the ongoing problem that would continue to exist with the fabrication.

Options

We now begin the process to change, where necessary, the current design through consultation with the customer, working together to determine that which is vital and that which is cosmetic.

At DGI we have the tools to build and test a product in a “virtual” world including the simulation of the chosen manufacturing process. This means that you can bring your current fabrication to us and we can remodel in our SolidWorks package before testing the strength with Comsos stress analysis and then simulating a casting technique to identify whether the project is viable during manufacture.

This remodelling process would be a consultation between your design team, identifying the requirements and our team advising the process.

This process has been tried and tested over many projects and identifies an alternative part capable of meeting and exceeding the current requirements, but not having the boundaries due to available materials i.e. bar width, plate width, welding limitations etc.

After completing the process described, it was decided on a completely new shape, lighter and stronger, using stainless steel to combat the harsh environment.

Of the choices available, it was decided that the new part should be made using our Premium Grade Investment Casting process. This process fully enabled the production of the new, improved stainless steel design and using our Cosmos stress analysis program we were able to prove the mechanical properties required before further stringent testing by the customer.

Added benefits

Although it was not a large issue with this part (a small amount of laser cutting), the Investment Casting process can reduce machining because our part is created without draft angles, has a smooth and accurate surface finish and can be cast within a tolerance of +/- 0.125mm/ 25mm.

During the design stage we usually ask for the completed assembly to help understand the requirements of the finished part, but also that we might identify any ancillary parts which are fitted to the casting during assembly. It may be possible to incorporate these parts into the new casting saving money, inventory as well as assembly time. The finished casting is then stronger than the jointed parts in most cases.

The cosmetic appearance, although less important, is a useful “billboard” for your company if you choose to include the company logo. The weight saving offers benefits for the unit cost due to less material, freight costs to move the same number of parts for a reduced cost and trackside when engineers have to install these parts.

The stainless steel finish removed the paint/powder coat stage and potential for this to degrade during trackside life.

    
Logistics

Having chosen a suitable material, our customer was able to provide a CAD model which was redrawn by DGI to accommodate the investment casting process. Our bespoke casting simulation software is then used to confirm sound cast integrity. This works by simulating the mould, material and temperature at casting to “flush” out any traps or pitfalls. By identifying these potential issues before casting saves significant time and money. Then the existing part was benchmarked using Cosmos stress analysis, to enable us to identify the weak sections of the fabrication and to enable us to compare our cast alternative. 

DGI's design was submitted to customer in both 2 and 3D formats complete with stress analysis comparison for approval (at this point a prototype part is an option but was not deemed necessary in this case).
The tooling orders are placed and sample parts produced for formal approval and fit and function testing before production begins.

The outcome

The new sample parts were received with great enthusiasm by the customer and were assembled onto the GRP bar before being shipped for testing. The parts completed all tests and a small modification was identified to further improve performance of the GRP bar rather than our casting. Our investment casting distorted at extreme load without breaking, as per the design specification.

The customer is very happy and after testing, intends to ship these all over Europe in the coming months knowing that even as train speeds increase over existing levels, these parts will continue to maintain the safe environment when installing essential communication and safety equipment between the rails.
Commercially, these parts are also maintenance free being Stainless Steel and have a very high level of repeatable strength while being lighter than the original part.

Summary

The customer now has a stronger, lighter component which incorporates additional features which were not commercially viable as a fabrication. The use of stainless steel improves the life expectancy of the part and removes the need for an extra painting process and the finished investment casting actually costs less than the original fabrication. The classic “win, win” situation.

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