Diverse grinding wheel handling applications in confined spaces

A great deal of potential in confined spaces: Haas is expanding the range of possibilities of its Multigrind® CA and CB grinding machines with a fully automated compact storage rack for up to 70 grinding wheels and up to 20 coolant protectors. A pre-finished linear axis system from SCHUNK is the key to flexible grinding wheel handling in minimum space. In unmanned operation, the compact storage rack promises optimized set-up times and highly flexible production.

Be it aviation, medical technology or tool production: falling batch sizes, shortened product life cycles, high cost pressure, and the need to be able to implement workpiece modifications as quickly as possible are increasingly determining machine designs for grinding. The times when the same product would run for seven or eight years unmodified are a thing of the past. If in engine construction or in the orthopedics industry entire part families are to be produced or complex workpieces machined, even the most modern grinding machines have until now always reached their limits, as the number of workpieces is not sufficient for high variance. Haas Schleifmaschinen has taken up the market's requirement and developed a modular tool rack to rectify precisely this bottleneck. For Chief Executive Officer Thomas Bader, the concept is flourishing: "The first users are enthusiastic. Since introducing the system, setup times were reduced from several weeks to a few days a year."

Custom-made pre-finished axis system

Until it was ready, one challenge in particular had to be mastered: the storage rack should have as small a base area (2,000 x 2,400 mm) as possible. At the same time, it had to provide enough space for a large number of grinding wheels with diameters between 20 mm and up to 300 mm, and for the corresponding coolant protectors, combined with the grinding wheels of the corresponding size. The trick was to use an individually designed, pre-finished axis system from SCHUNK, the competence leader for gripping systems and clamping technology, which flexibly combines and provides grinding wheels and coolant protectors.

The minimum change-over time for an individual combination of wheel and protector within the storage rack, i.e. in during processing time, is merely 28 s. The actual change onto the machine is carried out with a tool change time of merely 10 s. Furthermore, milling cutters can also be handled using the system. These are used with increasing frequency particularly in the field of medical technology in order to machine small contours or radii that cannot be reached with grinding wheels. As an interface to the machine that is separated from the storage rack to protect it from oil mist with the safety doors, a shuttle table is used instead of the conventional machine tool changer.

The interfering contour-optimized axis system was designed by SCHUNK with the specific application in mind and includes valve terminals, cable tracks, and the connection to the central lubrication, which were supplied fully assembled. Two multi-tooth guided SCHUNK universal grippers PGN-plus take on the varied handling of the grinding wheels and coolant protectors. Therefore, the grippers are fitted with specially designed top jaws, whose complex contours are adapted to one another in a way that the various protector variants or the HSK-80- and HSK-50 grinding wheel mountings are reliably gripped. The gripping force maintenance ensures that the tools are safely held in the event of a sudden power failure. Visual sensors monitor the workpiece presence. Special blow-off nozzles clean before handling the respective interfaces from potential impurities. With the aid of a SCHUNK swivel unit SRU-plus, the bottom gripper can be used both in combination with grinding wheel and coolant protector and for removing and filling the individual grinding wheels and milling cutters.

Compact space miracles

The linear system is trimmed through and through for compactness and process reliability. Three SCHUNK Beta 120 toothed belt drives from the SCHUNK catalog range take on the linear motion in the X-direction. The two axes at the head of the axis system are synchronously driven by a servomotor whilst the third axis is electrically synchronized at the base, and is also fitted with a servomotor. The latter ensures a high level of rigidity of the entire system, and prevents the system from vibrating during highly dynamic movements with accelerations of up to 5ms-2 and speeds of up to 60 m/min. This allows that very fast axis movements are achieved. What is more, there is no waiting time when changing tools, and the wear of the entire system is minimised.

In the Z-direction, a powerful SCHUNK Delta 240C spindle axis is used, which is fitted with a rod lock and extendable spindle and shaft encoder. This permanently monitors the position, and in case of breakage or collision it effects the emergency stop of the axis system. In the Y-direction, SCHUNK is exploiting every inch of technical feasibility: Its own linear module developed for confined spaces will unite compact dimensions with a particularly large stroke of 490 mm. Without the room being required for storage, the slide moves completely to the end of the module. This was the only way it was possible for the gripper to reach both the storage rack with the coolant protectors and the right rack with the grinding wheels and milling machines. It was a special challenge for the team at SCHUNK to make the system on the one hand compact enough so that the prescribed space is sufficient - and on the other big enough so that the strokes are sufficient in order to be able to efficiently operate the left and right shelf system.

Broad standard range

Besides designing and constructing the axis system, SCHUNK has also taken on designing the drives and calculating the cycle time. Here, attention was paid particularly to a high level of process reliability, but also a high level of efficiency. What is most worthwhile is that the SCHUNK standard range comprises all conceivable drive variants from the spindle drive right up to the highly dynamic linear direct drive with a fine gradation of the various sizes. On the other hand, the linear technology specialists at SCHUNK have an extensive pool of experience from various projects for automated tool and workpiece loading of milling, lathes, and grinding machines. Ideal requirements for reliably getting a handle on even the most fiddly of requirements such as the extreme compactness of the Haas grinding machine storage rack.

Since 1989, Haas has been paving the way towards automated grinding processes. Here, besides process reliability when grinding, reduced set-up times and unmanned production are primary focal areas. Haas provides integrated grinding wheel changers for its machines from an early stage. Added to this, over the years was the automated dressing of the grinding wheels and the automated workpiece loading using robots or gantry systems. Multigrind CU grinding machines can be connected with one another, and operated fully automatically in series. The programming of the handling systems always takes place precisely like the programming of the grinding processes directly at Haas via its own Horizon software.

Short distances minimise change-over times

"Due to new grinding wheels and materials, grinding processes are in a permanent state of change", Chief Executive Officer Thomas Bader explains. Primarily the improved possibilities with corundum wheels, which can be dressed very precisely, would have significantly influenced the processes over the past few years. "Due to the fact that at Haas, the machine, automation, clamping equipment, and software all originate from a single source, users are able to implement highly efficient processes and achieve results accurate to the nearest micron. This is exactly what our customers appreciate," Bader stresses. With respect to the storage rack this means: Specifically attuned to the respective range of parts, the tools, and coolant protectors are stored in such a way so that the shortest possible distances are required in order to make a change. The warehousing concept was developed solely by Haas and combines tools and protectors stored in fixed positions with those that are stored randomly. The integration of the axis system ready to be fitted into the machine is quickly and easily completed. All pneumatic and electrical connections and the connection to the central lubrication of the grinding machine are provided by SCHUNK, and merely have to be connected to the machine. In order to ensure maximum process reliability, the current input of all axes is continually monitored.

For the future, Thomas Bader is anticipating a growing significance of systems as flexible as these. The harder and more demanding the material, the greater the trend towards grinding becomes, as milling would entail immense costs for the tools, the grinding expert determines. If you have large part ranges, short reaction times and a high grinding medium consumption, meaning you have to keep a lot of sister tools in stock, the large grinding wheel tool rack quickly pays for itself.