Evolutionary step

Starrag also offers MT-hybrid versions of STC machining centres

Companies in the aviation and energy industry want to be able to machine casings, impellers and other complex components in one clamping operation. Starrag therefore offers the successful STC 5-axis machining centres in another MT variant which, in addition to drilling and milling functions, will also take on turning tasks.

The STC series has developed into the standard for economical machining of demanding structural components, multi-blades and casings. Their advanta- geous static and dynamic properties as well as the tried-and-tested swivel head set the benchmark for simulta- neous 5-axis heavy-duty cutting of titanium and Inconel parts in the aviation industry and in energy production. Numerous equipment options make them readily usable for HSC machining of aluminium components.

The philosophy for machining such components has changed a bit in recent years, according to Project Manager Marcel Leuch. He explains: “Today our customers want to carry out as many operations as possible in one clamping operation and ideally then collect the finished component from the machine. This will provide clear accuracy benefits and allow you to profit from shorter downtimes.” This trend is supported by advances in the programming of such hybrid machining centres.

In practice – for example with casings – it is a question of being able to carry out the necessary turning operations in addition to the predominant milling, drilling and threading operations. To give another example, machine operators want to be able to use the same machine to mill impellers and then carry out fine machining on them, by turning the outer contour.

For processing the interior of casings and similar components, the STC series can be equipped with angle heads, loaded completely and fully-auto-matically from the magazine to the spindle.

Starrag has already been meeting requirements such as these for a few years, for example with the STC 800, the smallest version of the 5-axis machining centre range. It is offered as an MT version with a rotary table to meet all of the demands for high-performance turning. Since – as Marcel Leuch says – the demand for larger machines with this technology has increased, decision-makers at Starrag opted to develop a matching MT variant for every STC machine.

Securely-mounted rotary table sets standards

The central new component of the Starrag STC MT variants is the fast- turning rotary table, which replaces the conventional machining table while maintaining the same axis arrangement. This means that for models STC 1000 to STC 1600, the linear X-axis and the rotary B-axis are located in the workpiece. The Y- and Z-axes and swivel axis A are located in the tool. Being of a good size, the workpiece interference diameter is ideal for machining large, cubic parts such as casings. The rotary table used in models STC 1000 MT to STC 1600 MT is designed and built at the Mönchengladbach site. They have also been used for a long time in turning lathes from Berthiez, also a part of the Starrag Group. “Our STC MT machines, or their users, are now also benefiting from this experience,” says Marcel Leuch happily. Our rotary tables are built so well that they are able to main- tain a comparatively high speed even under significant load. The STC 1000 MT can be loaded with up to 3 tons and rotate the component at up to 500 rpm. Even the STC 1600 MT with its load capacity of 8 tons can turn at 320 rpm.

STC series

The Starrag STC 1250 MT also demonstrates high turning performance. A test cut was able to achieve cutting depths of 8 mm with 7/10 mm pitch.

The crucial advantage of the selfconstructed rotary tables is in the rigid bearing. While alternative rotary tables use an internal bearing and external motors for cost reasons, the Starrag Group uses a large external bearing that provides significantly higher resistance to tilt and radial rigidity. The rotary tables can run at high speeds even when heavily loaded, and are not short of torque: an STC 1250 MT, for example, provides 6,000 Nm.

Turning as if on a dedicated machine

Even when it comes to control, there is nothing left to be desired: Multi-task tools with several blades can be used, and eccentric turning is no problem either. “We have already produced several eccentric and conical polygons,” confirms Marcel Leuch. To guarantee high machining quality, it’s not just the tool that is clamped to the spindle while turning. On models STC 1000 MT to STC 1600 MT it is also possible to clamp the rotary table guide. This reduces the effect of an imbalance in the workpiece, which would create small oscillations in the X-axis.

Marcel Leuch supports the theory with results of a test: “We put a sample casing blank with a diameter of 1,800 mm on an STC 1250 MT. In a test cut, we were able to achieve cutting depths of 8 mm with 7/10 mm pitch.” This shows that top-quality turning is possible. The user can confidently dispense with clamping the component for further machining on a separate turning lathe.


Starrag STC 1250 MT demonstrates high turning performance

Starrag STC machining centres are now also available as MT hybrid versions. All milling and turning work on demanding structural components, multi-blades and casings can thus be done in one clamping operation.

The deployment of a Starrag STC MT machine therefore offers the user a number of benefits. Since all milling and turning operations can be done in a single clamping operation, the re-tooling overheads disappear, reducing the setup time. Even in terms of pure machining time, the user is at least as fast as before. However, component accuracy increases since re-clamping errors are avoided. In addition, fewer fixtures are required, perhaps even saving the cost of the investment in a turning lathe. Component logistics are certainly simplified.

Milling quality as high as ever

When it comes to drilling and milling, the user fears no losses compared to the proven machining centres of the STC range. As before, several work spindles are available to choose from, the majority of which were developed and produced by Starrag themselves in Rorschacherberg. The spectrum ranges from the 37 kW gear spindle with a torque of 1,300 Nm and up to 5,600 rpm for heavy titanium machining, to the 120 kW motor spindle which turns at up to 30,000 rpm for HSC and high-performance milling.

The customer can choose from various Starrag tool magazines and changers as required.

The Swiss machining specialists have developed a special solution for machining the interior of casings and similar components. The STC series can be equipped with angle heads, which can be loaded completely and fully-automatically from the magazine to the spindle. But not only that: Starrag offers the option of equipping the same angle head with a multitude of different tools using the tool changer. This opens up tremendous flexibility in terms of the complete machining the customer desires.

Starrag STC machining centres