The aerospace industry considers simultaneous 5-axis machining state of the art. It is common practice in the machining of turbine buckets, impellors, bladed disks and ends. Increasingly, there are applications for this process also to be found in the automotive industry. However, conventional single-spindle machining centers are here often not considered an economical proposition, owing to the large batch sizes involved. With its twin-spindle machining center, SW now offers suitable solutions also for this sector of the industry. The BA S03 vertical and the BA W04 and BA W06 horizontal machining centers cover most of its mass production requirements with the application of simultaneous 5-axis machining operations.
EMO Press release: The BA S03: 5-axis machining at SW
16/08/2007 - Oliver Hagenlocher
Over the last few years simultaneous 5-axis machining has gained widespread acceptance in the automotive industry and amongst its sub-contractors. 5-axis milling makes great demands on the dynamics and precision of a machine – demands which the machining centers from SW are predestined to fulfil.
The BA S03 – predestined for 5-axis machining
The design of the BA S03 Vertical Machining Center – a monobloc enclosed on three sides and topped by a gantry – combines a minimal footprint, extreme rigidity and the greatest possible protection of guideways and drive components against the ingress of chip particles and coolant. The degree of rigidity is further increased by the box-in-box design of the three-axis unit. The BA S03 features ball screw drives in the linear and direct drives in the rotary axes. The torque drives guarantee backlash-free operation. A gantry drive in the Y-axis ensures an absolutely parallel movement of the slide, even where cutting forces exert off-centre pressure. The direct drives for the swivel axes, in conjunction with direct measuring systems, offer a positioning accuracy of +/- 5 angular seconds. This ensures that the positioning accuracy Tp achieved in the whole of the machining area of the BA S03 is 0.01 mm to VDI DGQ 3441. The acceleration of up to 10 m/s2, linear axis speeds of max 75 m/min and rotary axis speeds of up to 50 rpm ensure that idle times are kept to a minimum.
Doubling production – with two spindles
SW has been offering manufacturing solutions that utilise twin-spindle 5-axis machining processes since the middle of 2004. Turbochargers, in particular, are being manufactured in ever increasing numbers, owing to the hefty demand for diesel engines. “Our twin-spindle solution gives us a great advantage over the single-spindle process, especially when it comes to the manufacture of impellors, which calls for relatively few tools. All it usually involves is between 3 and 5 tool changes. With the SW chuck the workpieces are quickly loaded and unloaded. It all results in very short idle times. In fact, the twin-spindle design of the BA S03 allows us to double production,” is how Erik Pfeiffer – Manager of Technological Developments at Schwäbische Werkzeugma-schinen GmbH – explains the advantages of twin-spindle 5-axis machining. The twin-spindle design has no adverse effects on programming, as both Z-axes are controlled by identical departure commands, so that only one spindle has to be programmed – just as on a single-spindle machining center. “Although it allows us to almost double production, the setup effort is about 50% of that for two single-spindle machining centers”, states Erik Pfeiffer.
Twin-spindle machines – also for small batch production
There are viable applications for the small batch production too. Where parts are milled from solid stock, the raw material (e.g. aluminium or titanium) is usually held in two concentrically clamping universal chucks. This makes resetting easier and quicker, as all component variants can be clamped in the same chuck. Idle times can be ignored, as the machining process itself takes pretty long. “The cycle times of complex components, especially in titanium, can be in the tens of minutes or even hours. A much more pertinent question is how to increase the output per machine. This can be done with a twin-spindle machining center. With a batch size of 10 components and a cycle time of 1 hour per component, it makes a great deal of a difference whether the machine will yield one component per hour or two,” is how Erik Pfeiffer puts it.
Process integrity through simulation
To be able to arrive at a cycle time that is as accurate as possible and to generate and optimise the NC program in the early stages of a project, SW employs the 3-D machine simulation system eM RealNC also for their 5-axis machining operations. All NC axes are parameterised (speed, acceleration, jerk rate, V-constant, etc.) for the purpose. In the same way, all movements of the chain-type tool magazine are simulated, to be able to assess the time taken for tool changes as accurately as possible. Canned cycles and subroutines are also displayed. The user finds a sense of security in being able to look at possible collision factors and can also reduce idle times. The result of simulation will be realistic cycle times, providing a basis for optimal capacity planning before a single chip has fallen, thus reducing run-in periods.