For those challenging components with long cycle times, the STC Series provides the customer with a whole host of practical options. The latest arrival, the STC1250 HD machining centre provides excellent static and dynamic properties as well as a tried and tested rotatable head, making it the new benchmark for heavy-duty machining in titanium and Inconel parts for the aerospace and power generation industries.
Lee Scott from Starrag said: “It’s a new addition to the STC family. This is a 5-axis machine with a B-axis table that holds the component and an A-axis on the head, you can actually have an A and C-axis head as well. This new HD is predominantly a machine for optimised roughing and high surface generation finishing of exotic materials like titanium and Inconel components.”
Discussing the differences between the new STC1250 HD and its predecessors, Lee adds: “What hasn’t changed from previous models is the head configuration. The head is very stiff and rigid and it has a compact design with a range of spindles, particularly geared spindles. We have an impressive drive system in the spindle, which is a gear-driven HSK100 unit and we also have a dampening brake, so we can lock the spindle and stop it from swivelling when undertaking very heavy rough machining.
"This also helps with dampening when machining in 5-axis mode. This provides very efficient heavy-duty machining capability that is perfect for aerospace structural components - it takes things to another level.”
Looking specifically at titanium machining, Lee continues: “In the UK alone, we have around 30 STC installations, it is a very successful range. What we have seen from customers is a desire to prove the roughing capability of the machine with no compromise on finishing quality and accuracy.
"That is exactly what we have achieved with the STC1250 HD. This has been achieved by changing the linear rails to a hydrostatic system - do not get that confused with a box-way system. We have a very advanced hydrostatic system, which is a box guideway with an continuous oil film between the two metallic parts that never drains away, so you have a zero-friction system with no ‘stick-slip’.”
The spacious STC1250 HD machining centre offers a 1.25m by 1.25m pallet with a remarkably large work envelope for accommodating workpiece loads up to 5,000kg on the pallet. This is complemented by an X, Y and Z-axis travel of 2.2 by 1.5 by 2.1m with a swing diameter of 2.2m. With such a large work envelope, the new features in the STC1250 HD can offer astounding benefits for manufacturers with large parts that may have considerable cycle times.
Discussing reports that the new features of the STC1250 HD can reduce cycle times in titanium machining by more than 30%, he adds: “At Starrag’s Aerospace and Turbine Competence Centre in Rorschach, we saw a 63mm deep cut with a porcupine cutter where buckets of swarf continually fall into the base of the machine. Traditionally, what would have been three or four passes with a tool can now be done with a single pass. The machine may draw more power in that single pass, but overall it has a significantly reduced cycle time when compared to the previous method of multiple passes.”
“On a hydrostatic system, movement is generally slower, but with the technology in the STC1250 HD, it isn’t. Whilst we can undertake heavy roughing, we still have a dynamic finishing capability of roughly 40m/min axis feed rates. Additionally, one of the biggest costs for titanium machining is tooling – and the ‘carbide burn per hour’.
"We have seen significant improvements in tool life and over the lifetime of the machine this makes a significant difference. Quality and surface finishes are also improved and throughput and productivity are also increased. Furthermore, as a zero friction system, the energy consumption is low. However, you do need to provide a lot of power to take heavy cuts, so naturally, it is an energy-consuming machine, but we have calculated that the machine has energy consumption 33% lower than a typical linear guideway machine.”
Highlighting how the hydrostatic system works, Lee adds: “There is a lot of oil in the system, but it is all contained in a recyclable system. On large guideways, there is a thin film of oil of 15 to 20µm. When a large structure moves around, it could theoretically displace the oil. To eliminate this, we have an innovative multi-pocket system that controls the functionality, pressure and volume of the oil to guarantee the accuracy of the entire machining system.
"Each axis is split into several pockets and by controlling each of the pockets, we can control the entire system within the machine. This is what ultimately enables this machine to take heavier cuts with better surface finishes whilst reducing the overall cycle time of components.
"Only launched in June 2023, after enjoying immediate sales for this product, Starrag has a lot of significant projects in the pipeline for the STC1250 HD and these will take some months to go through the process, but there is little doubt that the industry is already seeing the potential merits of the STC1250 HD.”
