Chris Boraston of AGS (pictured right) with Martin Kilmach of Carbon-DriveFor over three decades, the Swiss company Tschudin — represented in the UK by Coventry-based
Advanced Grinding Solutions — has been working consistently to reduce the heat generated by its centreless grinding machines and to improve their thermal stability, an endeavour that has seen machine beds made from natural granite to grinding spindles made of Invar, a nickel-iron alloy noted for its ‘uniquely low coefficient of thermal expansion’.
Urs Tschudin says the last piece of the puzzle has now been put in place with the new and highly advanced carbon-fibre spindles. “Our Tschudin Cube centreless grinding machine is the first grinding machine with little or no heat transfer; and with this spindle concept, we are underpinning our status as an innovator and offering our customers a new dimension of accuracy and stock removal rates. The machine’s carbon-fibre spindles — developed in collaboration with Carbon-Drive GmbH — have been tested and adapted for more than six months, with very successful results.”
Nikolas Ernst, Tschudin’s head of design, said: “How materials react to heat has a major influence on precision manufacturing; and because the temperature resistance of carbon fibre is particularly high, carbon spindles prevent thermal expansion in the machine. Moreover, they offer considerable dimensional stability and have a high bending stiffness, which means that compared with previous designs they can run at higher in-feeds, which in turn means a much higher cutting performance. In a series of tests, the carbon spindles have proven to be up to 20% more effective than steel spindles.”
Minimal thermal expansionAdding more detail to this development, Martin Klimach — the co-founder and managing director of Carbon-Drive, which was formed following a research project at the Technical University of Darmstadt — said: “Spindles made of carbon fibre have various advantages, first and foremost being minimal thermal expansion. Depending on the type of fibre and fibre orientation, we can produce carbon-fibre spindles with different properties and thus respond to the needs of Tschudin’s grinding process.”
Mr Tschudin and Mr Klimach met at an industry event in 2019. At the time, Carbon-Drive was working on milling spindles made from carbon fibre, but the idea of using carbon-fibre spindles in the grinding sector was one that both wanted to pursue further. The first grinding spindle was ready at the end of 2023 and has been tested and refined ever since.
Mr Tschudin continued: “The new carbon grinding spindles offer numerous advantages. By minimising the transfer of heat, production with a consistent high accuracy is guaranteed at all times; and the time-consuming warm-up of the machine, such as on a Monday morning after the weekend, is no longer necessary. Indeed, even if the machine stands still for a weekend, it can produce immediately within a maximum dimensional deviation of only 1µm.
“Furthermore, all parts can be produced to the exact dimensions, even with multi-track grinding, as the grinding wheel and regulating wheel remain parallel because thermal displacement is prevented. This allows the cube to work autonomously for long periods throughout unmanned shifts.
“Previously after machines had been stopped for a changeover or for a longer period of time it was necessary to cycle the machine without producing any parts until it was warm and the heat transfer had taken place, but this is no longer necessary with the new carbon-fibre grinding spindles. You can simply start the machine and begin production again straight away. For those making parts in small and medium batch sizes this is a real game changer. High grinding quality with full grinding gap coverage was already a feature of our machines, but with the carbon spindles we are further optimising this aspect and pushing it to the maximum.”
An ongoing developmentThe introduction of carbon spindles is another step in a decades-long development process. Tschudin has been using linear motors for more than 30 years and over 25 years ago, machine beds made of solid natural granite were introduced, which only heat up extremely slowly. In a further step, the grinding spindle slides were also made from granite blocks. On the Tschudin ecoLine 400, a spindle made of Invar was implemented 10 years ago and provided a 10% reduction in heat transfer; the carbon-fibre spindles, for which Tschudin has applied for a patent, have now reduced the heat transfer ‘to an absolute minimum’.
The Cube, Tschudin’s latest centreless grinding machine, is designed to produce parts up to 20mm in diameter and to plunge grind parts up to 150mm long. It is also equally adept at the through-feed grinding of parts and can be equipped with various automatic loading options and pre and/or post-process gauging for optimum efficiency within a small footprint.
The changeover time of the grinding and regulating wheels can be done in just 6min and the next series of workpieces produced seamlessly. This machine, which has a base of just 2.60 x 1.70m and been developed for machining small components, can be operated from both the left and the right side; and while the standard version of the Cube 350 will continue to be equipped with steel spindles, the carbon spindles are available as an option.
Summing up the benefits of the new grinding spindles, Chris Boraston — managing director of Advanced Grinding Solutions — said: “All grinding machines suffer from changes in temperature and machine designers have forever been fighting for better thermal stability to overcome that. While that stability might not be critical if you are working to tolerances of 10µm or more, as soon as you start to consider under 5um it becomes challenging; and while with Tschudin, depending upon the application, you can consider grinding to tolerances of 1µm — or even less — heat change becomes a major enemy.
“Most of the heat and vibration comes from the powerful grinding spindles, but the use of carbon fibre has been shown to drastically improve thermal stability to such an extent that it will no longer be an issue for most applications. For anyone looking to increase productivity, being able to do without lengthy warm-up cycles is a huge benefit.
“Further benefits will come by operators no longer having to fight to control the grinding process as machines heat up. Tschudin is already seeing cycle time reductions in the range of 10 to 20% as compared with traditional steel spindles, because you can start grinding straight away — and grind substantially faster when you do.”
Mr Kilmach concluded: “Advanced carbon composites have an unbeatable stiffness-to-weight ratio and offer up to 100-times better damping compared to steel. They can be designed to have no thermal expansion and are, of course, very light — characteristics that offers clear advantages over steel solutions, especially in the machine-tool sector.”