Two chains with 20 pockets each hold all manner of tools for the high-end SmartLine Kombi millGrind grinding machine from Elb-Schliff (Soag GB, 02476 327619): not only grinding and dressing wheels, but also coolant nozzles, metalcutting tools (for milling, turning and boring), and even an additive manufacturing welding head.
The key technology is the automatic tool changer (ATC). Although not the company’s first machine to include an ATC, this unit is the fastest. Toolchange times of 10 seconds or less are promised, thanks partly to a preloading system that works in the background to ready the next tool required while the machine is grinding. A high speed shuttle collects tools from or deposits them to the ATC, interacting with a secondary tool loader. Given the size of the grinding wheels that need handling – up to 508 mm in diameter and weighing several kilos – Elb-Schliff has boosted the resistance of the mechanically-closed gripper so that it requires 6 bar of pneumatic pressure to be forced open. (This failsafe design prevents power or pressure cuts releasing cutting wheels).
Another important change is the tool-machine interface, which can be HSK 80 or HSK 100. Common for milling and turning machines, it has been adapted to accept grinding wheels.
The system can automatically change grinding and dressing wheels, as well as, for the first time, nozzles. Since they are adapted to deliver coolant to a particular diameter of grinding wheel, optimising coolant delivery for different wheels requires different nozzles. They are stored in small HSK fittings in the ATC.
HORIZONTAL MACHINING
Since milling, turning and boring tools also mount on the grinding spindle, travels are the same as those for grinding. Tools are held horizontally. The head assembly moves the horizontal spindle in Y and Z and the table moves the part in X (or possibly A, B and C, if an optional rotary table mounted on a rotating trunnion is installed instead).
Spindle power is either 36 or 48 kW, spindle speed is 8,000 rpm and feeds are 20 m/min in Y and Z, and 40 m/min in X.
For static turning, the tool spindle can be clamped in a locked position via a Hirth coupling, and the part turned on the rotary table, although turning is limited by the speed of the rotary table to 100 rpm.
Elb-Schliff CEO Markus Stanik cautions that this extra capability does not make the millGrind into an all-rounder, in spite of its name: “It is not a high class turning centre; it is a high class grinding machine with special extras.” Customers that have a small face to turn, or a slot to mill or holes to drill can handle these small operations instead of having to buy another machine.
Variety is the millGrind’s selling point. As the machine can hold standard tools, it can also hold the Ambit additive manufacturing head from Hybrid Manufacturing Technologies (www.hybridmanutech.com) that uses a laser to melt powder blown into a working area. The Ambit head can be held in the ATC, or permanently mounted vertically in a cabinet inside the machine’s working area.
With this unit, customers can repair expensive workpieces, explains Stanik. The repair process takes in multiple cycles of welding on material followed by cycles to grind the excess off. In between, the part’s shape is checked using a spindle-mounted touch-probe that can also be held in the ATC. This entire sequence can be completed in one set-up. Demand for this option comes from aerospace customers, says Stanik, although any industry with expensive workpieces might prefer to repair rather than replace them, he adds.
Since the SmartLine Kombi millGrind was first exhibited at the Paris air show in June 2015, Elb-Schliff has taken eight orders for the custom-made machine; three units will be delivered by June next year. Only one unit has been built incorporating the AM head, with the unit installed in the permanently-mounted in-cabinet configuration (left).
Most of the 150 grinding machines made annually by Elb-Schliff, based near Frankfurt, are standard units with limited options; speciality machines such as the millGrind make up the minority. All machines are assembled in-house, though some machining and production is subcontracted.
This article was originally published in the December issue of Machinery magazine.
