008618266359149
A little push – and the 12-metric-ton column accelerates on the machine bed without any further action. The STC 1250 HD 5-axis machining center, with its horizontal linear axes having hydrostatic bearings for frictionless gliding, gives rise to significantly higher stock removal rates, improved dynamics, and longer tool life.
Starrag machines have been setting standards in the economical machining of structural components, multiblades, and casings, as required in the aerospace industry. The STC series is designed for simultaneous 5-axis heavy machining of titanium and Inconel parts due to its excellent static and dynamic properties. The machines are equipped with Starrag’s robust gear spindle and a compact swivel milling head, enabling use of shorter, more stable tools for more efficient machining.
To further increase efficiency in titanium machining, heavy machining specialists have performed a range of studies. Bernhard Güntert, head of the test field at Starrag AG, explains: “The main sticking points are the machine’s rigidity and damping properties. These factors have far-reaching effects on the possible cutting depth and tool wear, and therefore on the economic efficiency.”
Hydrostatics increase performance
When it comes to vibration damping, hydrostatic guides can’t be topped. “More than 15 years ago we already had hydrostatically guided machining centers. However, the dynamics of these machines left a lot to be desired, which is why we equipped the subsequent STC series with roller guides. Given customer demands and the lessons we’ve learned, we wanted to change it back,” explains Rainer Hungerbühler, sales director for aerospace and turbines. So, Starrag developers re-addressed the topic of hydrostatics. “Our new STC 1250 HD is fantastic. The first tests have already shown it sets a completely new benchmark in terms of stock removal rates during roughing. It even has considerable advantages to offer in terms of dynamics,” Hungerbühler says.
A look behind the scenes
Rolando Senn, lead designer in hydrostatics, explains the strengths of this technique: “The essential feature of hydrostatic guides is the permanent oil film between the slide and the bed or the standing structural part. This means there’s no contact between the guide rails and the carriage travels completely without friction.”
Without friction, there’s no wear, and the oil dampens the vibrations occurring during machining. The large contact surfaces also ensure tremendous rigidity. “We’ve increased this even further by choosing one with pre-tensioned handle guides instead of a statically open system,” Senn explains.
To classify these strengths, it’s necessary to look at the essential characteristics of other guide systems. Hydrodynamic guides have similar properties to hydrostatic guides, but one major disadvantage: the guide elements come into contact when stationary. The separating oil film only forms when they are moving, so static friction must be overcome when starting up, which causes the undesirable stick-slip effect. Pure sliding guides also exhibit a stick-slip effect and are additionally subject to high friction and corresponding wear. Roller guides aren’t as prone to friction and wear, but they’re also less rigid and damping. In addition, micro-vibrations occur during the rolling process, which can impair surface quality during finishing operations.
Triple chip volume during roughing
The user derives the greatest advantages from using hydrostatic guides in roughing operations. Due to the significantly higher rigidity and damping compared to roller guides, cutting depths can be increased 3x with roughing times reduced accordingly.
The damping effect makes the chipping barely noticeable. During a test machining operation, even experienced machinists were surprised, Hungerbühler reports: “We were standing right next to the machine and hardly noticed any noise or vibrations. Only a glance through the window showed us the cutting process had already started; the milling cutter was in full engagement and really thick titanium chips were flying.”
The STC 1250 HD also benefits from the hydrostatic bearing during finishing. The increased rigidity reduces pitching of the column, which limits jerking and acceleration. “Instead of using a 2.5" (63mm) diameter ball screw as before, we now use one with a 3.1" (80mm) diameter on the HD. That means a 61% larger cross-sectional area, which is incorporated 1:1 into the rigidity in the axial direction,” Senn says.
The higher dynamics are noticeable in higher starting speeds, accelerations, and faster 5-axis movements, ultimately reducing finishing times.
Greatly reduced tool wear
One of the biggest cost factors in titanium machining are the tools, which are subject to heavy wear. The excellent damping provides improvements in this respect, i.e. significantly longer service lives, even when the speeds are increased.
The frictionless movement of the two linear axes and absence of micro-vibrations also benefit accuracy and surface quality, particularly in 5-axis simultaneous machining with its frequent changes of direction. Starrag ensures further process optimization by equipping the hydrostatic guides with pressure and temperature sensors. Users can thus track the loads on the guides during the process and use the recorded data for further adjustments.
True values show themselves
Using the example of a typical structural component, a framed door with dimensions of 3.1" x 11.8" x 48" (80mm x 300mm x 1,220mm), Starrag made a comparison with the previous STC 1250. The 81.8 lb (37.1kg) forged part made of Ti6Al4V had a 0.5" (13mm) allowance on each side and had to be machined to 12.1 lb (5.5kg). The specification: a perfect surface with thin walls and floors. With the hydrostatic STC 1250 HD, it was possible to halve the roughing time and reduce the total machining time by 30%.
These values can be used to calculate another, initially unexpected advantage: the reduced energy consumption during roughing. This is because the halved roughing time saves the user – despite the 1/3 higher power consumption – half of the drive power previously required plus that of the basic load, which consists of the power consumption of the cooling lubricant system, hydraulics, pneumatics, cooling, etc. Overall, it consumes 33% less energy.
(https://www.aerospacemanufacturinganddesign.com)
More About KYOCM:
Located in industrial area of the Zhaozhuang Industry Park in Linqing, Shandong, Kaiyou Bearings Co., Ltd. is a professional bearing manufacturer and exporter with nearly 20-year experience. The products have reached the international advanced level with advanced production technology and modernized measuring management. Products are widely used in electrical and mechanical trades, the farm machinery industry, the automobile industry and all kinds of transmission facility manufacturing extensively. The products have a good sale in domestic and international dozens of country or region. Companies with the “integrity-based, quality firs” as the operational concept.
2023 New Week Hot Products Recommended:
KYOCM cylindrical roller bearings can meet the challenges of applications faced with heavy radial loads and high speeds. Accommodating axial displacement (except for bearings with flanges on both the inner and outer rings), they offer high stiffness, low friction and long service life. KYOCM cylindrical roller bearings include single row cylindrical roller bearings, double row cylindrical roller bearings and four row cylindrical roller bearings.
Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life. Split bearings are intended primarily for bearing arrangements which are difficult to access, such as crank shafts, where they simplify maintenance and replacements.
For dimensions and specifications, contact us now:
Add: No.57 Youzhuang Commerial Street Zhaozhuang industry Garden Linqing City Shandong China
Tel: 0086-635-2632030
Fax: 0086-635-2632918
Email: yobearing@hotmail.com
Web: www.kyocm.com
2023-12-21