Robot helps to make robots
When industrial robot manufacturer, Kuka, decided to boost productivity by automating the manufacture of large components at its Augsburg factory in southern Germany, it understandably chose one of its own 6-axis robots to handle the components. To machine them, the firm opted for a Burkhardt+Weber (B+W) MCX 900 horizontal machining centre.
Sole agent for B+W in the UK and Ireland, Kingsbury, describes how its principal’s twin-pallet machine has allowed Kuka to increase output of two different robot components by 10 per cent and machine 300 extra per year.
Instead of undertaking the lengthy procedure of loading the two types of part directly into fixtures on the pallets, the operator places them considerably more quickly in two racks served by the robot. One rack holds eight main arms and the other stores eight rotating column elements, each destined for two robot models within Kuka’s KR Quantec series.
The racks are configured as rotary carousels, the motions of which are controlled by the robot’s CNC system as 7th and 8th axes. When full with raw castings, the two material handling stations enable eight hours of unattended machining.
To start a cycle, the handling robot unloads a machined component, which can be up to 1.5 metres in length, from a pallet on the MCX 900 and loads the next raw casting for a similar component into the same fixture. Production of the other type of component is already in progress on the second pallet in the machining area. Meanwhile, the robot automatically exchanges its handling gripper for a live tool and brushes, deburrs and cleans the part it has just picked up.
One of the pallets is equipped with a hydraulic fixture for clamping the KR Quantec arm and the second pallet has a similar fixture for the column component. Each fixture is actuated automatically when the respective parts are loaded and unloaded by the robot. A hydraulic proportional control unit with sensor feedback from the fixtures adjusts the clamping pressure during the cycle according to whether roughing or finishing is in progress.
While one part is machined, the other pallet is waiting to be presented to the spindle, so there is very little idle time. The cell works around the clock, the night shift normally being unmanned. Overall, operator attendance at the machine is now just 30 per cent whereas before, a person was employed full-time to run the process.
The MCX 900 is one of the most dynamic machining centres in its class, with rapid traverse rates up to 60 m/min in all axes, further reducing non-cutting times. Large (size 65) roller bearing guideways ensure long-term machining accuracy.
The rotary table supports a load of three tonnes including workpiece, fixture and pallet. Low centre of gravity and a large axial roller bearing ensure rigidity for withstanding high torques of up to 40,000 Nm during machining.
Swing diameter is 1,850 mm throughout the 1,600 mm X-axis travel. Y and Z travels are 1,600 and 2,200 mm respectively. The two-step, gear-driven spindle, rated at 7,000 rpm / 37 kW / 1,220 Nm, achieves optimum machining performance. Control is provided by a Sinumerik 840D sl with 19” touch-screen monitor and a B+W-specific operator panel.
An extended, 330-position magazine provides more than double the number of stations needed for cutters and sister tools to machine the two component types. The cell is therefore future-proofed for changes to production requirements. Maximum tool weight is 60 kg and diameters of 350 mm can be accommodated, allowing the use of heavy-duty, highly productive milling cutters and boring bars.
A special feature is an automatically exchangeable tool extension with a diameter of 150 mm and a length of 350 mm, with integral clamping. It minimises the number of long tools needed and provides greater rigidity than typical modular tool holders.