The heart of machining

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aerospace

The heart of machining - Starrag offers in-house spindle technology at its best

In-house development and production of motor and geardriven spindles – which machine manufacturer can offer this? Starrag has built up unrivalled expertise in this field over several decades. Customers benefit from an application- specific spindle design, leading technology and the highest quality, as well as from very quick service in the event of any – although rare – malfunctions.

“The spindle is the heart of a milling machine. It makes a decisive contribution to ensuring that the machining results correspond to what the user expects,” emphasises Rainer Hungerbühler, Sales Director Aerospace and Turbines. “I am glad that we have our own spindle production here in Rorschacherberg and a corresponding competence centre. This allows us to design the spindle precisely for the machine and the respective application, which is very important for us as a solution-oriented supplier of turnkey production systems.”

A win-win for customers. You get products in which the kinematics of the machine, the drives and the spindle perfectly fit together. This accompanies the fact of machining difficult-to-machine materials such as titanium and Inconel, structural components made of aluminium or to other applications. Rainer Hungerbühler explains: “To do this, we design the spindle characteristic curve in such way that the required cutting parameters are available for optimum machining of the respective components.”

Rainer Hungerbühler, Sales Director Aerospace and Turbines

“Our gear-driven spindle is almost indestructible. This means it ensures high process and work safety and causes virtually no machine downtime.”

The sales manager points out another advantage: “In-house production means we are independent of external spindle manufacturers. During the coronavirus pandemic, we saw how very good suppliers had problems meeting their delivery commitments. Because of our in-house production, we and our customers were not affected by this."

Rainer Hungerbühler, Sales Director Aerospace and Turbines | Silvan Huber, Master of Science FHO in Engineering

Long-term success with gear-driven spindles

Starrag began manufacturing gear-driven spindles back in 1920 and has acquired a great deal of expertise over many years. Today, this feature is on all machines of the STC series produced in Rorschacherberg. The five- and six-axis machining centres enable to extremely economical machining of demanding structural components as well as multi-blades and casings with long cycle times. “Our STC machines benefit from Starrag’s own gear-driven spindle in many ways,” explains Rainer Hungerbühler. “Because their design has a very small interference contour, we can get very close to the workpiece with the head. This means the user can use short tools, which support a stable milling process and results in long tool life.” He highlights another strength: “Our gear-driven spindle is almost indestructible. This means it ensures high process and work safety and causes virtually no machine downtime.”

To meet the different machine sizes and applications, Starrag offers the gear-driven spindles with two different motors and in different gear ratios. The 37 kW version with a maximum speed of 8,000 rpm and 940 Nm torque at continuous load (S1 operation) is used most frequently. However, a variant with 1,600 Nm and a speed of 4,500 rpm is also available. “Our gear-driven spindle (620 Nm torque) rotating at up to 12,000 rpm with the HSK-A100 interface common to the STC machines is quite something. I don’t know of any other supplier who has a spindle like this in their product range,” explains Rainer Hungerbühler.

Motor spindles on the road to success

The Spindle Competence Centre deals primarily with motor spindles – in addition to the long-established gear-driven spindles. Starrag has also been developing and building these for around 25 years. But recently they have been experiencing a push. Silvan Huber, Master of Science FHO in Engineering, is responsible for motor spindles and direct drives as a development engineer since 2014. “So far, we have installed almost 2,500 motor spindles in our machines. We installed 160 last year alone, twice as many as the year before.” He is convinced that the output will double again in the next two years.

Starrag boasts an extremely wide range of motor spindles. The range begins with a 2.5 kW spindle with 2 Nm torque. The upper limit is marked by spindles with a torque of up to 350 Nm.

He thinks the reason for this is in the quality and leading technology of Starrag motor spindles – which is largely due to “our team of experts working with state-of-the-art development, assembly, overhaul and testing facilities to ensure the best products for customers.” This has also convinced those responsible at the plants in Chemnitz and Vuadens, to use Starrag motor spindles in the Heckert H series and the new Bumotec centres s181 and 191neo.

“All five-axis turbine blade machining centres of the LX series and the NB 151 blisk machining centre are equipped with our own motor spindles. On the STC milling centres, if no gear-driven spindle is installed, our 18,000 HSK-T100 is used,” Silvan Huber explains.

New developments at the highest level

Starrag boasts an extremely wide range of motor spindles. The range begins with a 2.5 kW spindle with 2 Nm torque. The upper limit is marked by spindles with a torque of up to 350 Nm. In terms of speeds, the range extends from 12,000 rpm to 40,000 rpm.

Silvan Huber highlights the recently introduced 80 kW motor spindle (250 Nm and 18,000 rpm; S1 rated operation), which promises unprecedented productivity and is therefore offered for the entire STC series. It is equipped with an HSK-T100 tool interface, provides a tool clamping force of > 45 kN, a shaft clamping force of 1,400 Nm and is suitable for internal coolant supply up to 140 bar. According to Silvan Huber, the spindle is attractive not only because of its performance data, but also because of its high quality, which is based on in-house production and components such as bearings and motors that are purchased exclusively from renowned manufacturers. This has an impact on stability, running times and service life. It is also equipped with various sensors that ensure high precision.

The plant in Chemnitz, which equips its Heckert machining centres with this spindle, recently provided measurement results for axial shaft displacement – less than 10 μm over the entire speed range. “Considering that a speed of 18,000 rpm and the resulting thermal expansion result in a displacement of around 200 μm, we have succeeded very well in compensating for this deviation by means of sensor technology,” the technical developer is pleased to report.

Technology leader

Starrag is already working on further optimisations. Silvan Huber explains: “At the moment, we are focusing in particular on increasing the spindle speed and thus the cutting performance. This paves the way for innovative and process-optimised milling strategies.” The latest new developments also apply to details. On some spindle types, this includes coolant spray nozzles in the spindle nose, the spray angle of which can now be programmed and thus automatically adjusted to the tool length. Another innovation are spindles for the Bumotec machining centres s181 and 191neo, which support cryogenic machining. Silvan Huber comments: “We have developed a motor spindle with a special rotary feed-through so that the cryogenic CO2 cooling can reach the tool cutting edge. This is a special solution that is suitable for machining 3D-printed prostheses, but can also be significant beneficial for PEEK (high-performance plastic) machining or drilling titanium parts.”

In any case, he is certain that: “With the motor spindle developments over the last few years, we have risen to the technological forefront. And we will continue to improve until we reach the top of the world.”

The Spindle Competence Centre deals primarily with motor spindles – in addition to the long-established gear-driven spindles.

“With the motor spindle developments over the last few years, we have risen to the technological forefront.”

Rainer Hungerbühler, Sales Director Aerospace and Turbines

As good as new again after overhaul

A third factor that the developers are focusing on – the service life of the motor spindles. Starrag usually provides a warranty for one year. Sales Director Rainer Hungerbühler comments on this offer: “The service life of a motor spindle depends not only on its quality, but also on the load to which it is subjected. Therefore, we cannot make any general statements about the service life. We can, of course, provide all our customers with assistance immediately if they need an overhaul of their spindle or experience downtime.”

Starrag has a great level of experience and expertise in overhauling motor spindles, a task which is carried out by highly qualified personnel in Rorschacherberg. There, original spare parts are stocked and the spindle can be restored to almost new condition. Moreover, a renewed manufacturer’s warranty on the components replaced. Starrag also maintains spare parts warehouses worldwide which can ship spindles within 24 hours.