Railroad switches (points) maker sought very rigid, long table machine to mill Grade A rail steel, which, at 260BHN is tough and a German machining centre gave best tool life:metal removal ratio.
To the average railway traveller a stretch of rail and a set of points are just there to keep the train heading in the right direction. But, for today's suppliers to the rail industry, particularly with the involvement of high speed routes, the demands to meet a smooth ride with high orders of safety while performing a balancing act involving the economics of multi-million production operations, it means the latest manufacturing technology is an ever-growing factor of importance. Meeting these demands has certainly created a focus at Balfour Beatty Rail Track Systems of Sandiacre in Nottingham, leading the company to invest more than GBP 15 million over the last 10 years in new production methods to produce switches and crossing points.

Investment has resulted in the installation of Unigraphics CADCAM, instigation of new methods such as captive die forging of rails and the purchase of carefully selected multi-axis machine tools such as the recent Hedelius BC80-2500 from C Dugard of Hove in Sussex, and advanced sawing and fixturing systems in order to generate the important shape and form of the rail.

As a result, production times have also been reduced from some nine hours to under three for its switches and points.

Also high on the agenda at Balfour Beatty is the speeding up of response, reduction in lead times and the need for a constant eye on improving competitiveness against ever-tightening deliveries especially in the production of crossing points for Network Rail.

In addition, the company has to fight off a growing number of global competitors not only in the UK but also in export markets, such as the US, which adds to the importance of the capability of its machine tool selection process.

To ensure these criteria are met, the company has employed Steve Bond as production engineering manager.

Before taking up the task of justification and purchase of machine tools in 2000, Bond had extensive experience in the UK machine tool industry from design and development, through build, service and applications.

With this experience behind him, the company was in an ideal position to prepare initial plant purchase enquiries, in line with a host of proposed method changes, and investigate and select the most appropriate level of technology.

His role in heading up the department also involved the interface to co-ordinate the various stages of purchase with method improvements and supervise the trials, acceptance, installation and commissioning with his team of engineers.

The company's selection of the Hedelius was a prime example of the in-depth attention to detail being pursued - Steve Bond knew the concept he needed; where the forged switch back rail section could be scanned to check out the forging, then, utilising the multi-axis methods, move the spindle of the machine around the static component on the machine table to generate the required shape.

However, the prime factor in the whole process was going to be machine construction and this was put forward to selected suppliers.

Balfour Beatty needed a very rigid, long table machine to mill the Grade A rail steel, which, at up to 260 BHN can be tough.

Also, because of the lower feed rates that would be necessary to machine the forging and obtain the best tool life ratio to metal removal, Steve Bond was very conscious that harmonics in the machine structure could influence the tight 0.6 micron Ra finish required on the rail.

Another factor was the need to maintain the ideal cusp height in cut, which had to be within five to eight microns from each step-over.

According to Bond these requirements quickly limited the possible suppliers, especially when budget was brought into the equation.

Due to the projected target of processing some 350 to 400 tonnes of rail a month, Balfour Beatty was also having to purchase two machines.

On paper, the Hedelius quickly came to the fore because of the high rigidity box-welded bed design of the travelling column machine.

Balfour Beatty were very impressed by the development work that had been carried out by Hedelius, for instance, any influence of vibration and twisting forces could be absorbed by built-in hollow chambers in the bed, and in the attention to detail, such as in the welding and the way the bed was de-stressed.

To this concept was added the use of 12 guide elements to ensure the whole slideway system maintained its performance criteria even under high and varying loads.

Bond added: 'We particularly liked the ballscrew and driven nut arrangement that gave a very smooth feed making it ideal for the surface finish we were after.

Really,' he maintained, 'The machine looked right for the task and with the support of Dugard, justification was fairly straightforward.' Prior to the final decision to purchase, sample forgings were made and trials conducted at the Hedelius plant in Meppen, Germany.

'We really put the machine through its paces - we could not afford to have a key machining process in the plant that would compromise what we had to do,' he said.

And describes how as part of the trial the forgings were milled at the machine's maximum feed rate of 30m/min using Walter tooling and how it took the punishment.

'This was just for proving trials,' he said, 'In production we cannot afford to generate any heat in the rail during machining, it must be carried away in the swarf or it will change the structure of the material.

But we had to be sure of the machine and we also had to ensure the practicality of swarf control.' At Hedelius, the Balfour Beatty trials also involved quite a lot of experimentation by the German engineers and Steve Bond maintains the company was helpful by tuning the drives and ramp-up speeds to perfect the process.

Following the trial they were concerned that the BT40 standard head taper could possibly give problems and raised the specification of the machine to a larger BT50.

Now with the first machine installed, the Hedelius BD80/2500 machines the programmed shape into the switch rail sections which are set up on blocks and clamps on the long table.

In the machining process a welded joint in the rail has also to be milled.

The rail is first probed and data fed back to the Seimens 840 control.

Then for the first operation, up to 16mm of stock is removed from under the rail which includes any excess weld, in 3mm deep passes at 840 rev/min and 15m/min feed rate leaving 1mm for finishing.

A second cut is also used to take out any twist in the rail.

But, such is the rigidity of the set up that average insert life is 36h.

For the second operation the weld area of the rail is finished and blends in the rail profile produced over a length of 1.3m to provide a smooth transition on the track from the crossing point to the main line.

As Bond concluded: 'Everyone thinks a rail is just a rail, but the technology involved in crossings and points gets very complex with large numbers of individual components in a switch panel set.

This is one reason why it is critical that we are able to work very closely with a company such as Dugard as a chosen machine tool supplier.'