Hard-Fine Machining of Small to Medium-Sized Lots

Tool, machine and process innovations have steadily increased efficiency in the hard-fine machining of high volume production. For example, tool life has significantly increased and process cycle times have drastically reduced in grinding by using CBN high performance cutting materials. But the challenges involved in the hard-fine machining of small to medium-sized batches of components used in chucks are enormous. This requires machine tools that guarantee a maximum degree of flexibility, speed and precision to produce a wide range of sizes, weights and geometries of different components that must work perfectly and be produced quickly at low cost and according to individually specified requirements. This is the world of chucking device manufacturer SWS Spannwerkzeuge GmbH (Schlüchtern, Germany), which manufactures standard and custom chucks for a wide range of different branches and industries, from the automotive sector through medical technology, the optics industry to the machine tool industry.

This extremely diverse range of applications and customers involves delivering a wide range of different individual orders in small to medium-sized batches, each with highly specified requirements and machining challenges. The majority of shop time and work effort is spent on set-up and preparation: customized programming of machining processes for different workpieces of various sizes, weights and geometries; clamping; continual measuring and repeated feeding until the final dimensions are achieved. This is why SWS invested in a specially designed UGrind machine tool from DVS Universal Grinding GmbH (Dietzenbach, Germany) to reduce these efforts and ensure more efficient production.

Initially, SWS considered a hard-turning machine for precise and economic production of a large number of the required geometrical tolerances, but it was limited where extremely high manufacturing tolerance and surface requirements are necessary. They also looked at a grinding machine that made extremely demanding manufacturing qualities possible, but involved higher investment costs and longer machining times. They selected the UGrind for its innovative multi-function turret that integrates grinding and hard-turning, as well as milling and measuring, in a single machine and just one clamping – a first in the field of shop fabrication. In close cooperation with DVS, the UGrind machine was designed and specially constructed for the production of a large number of different chucking device components. This extremely compact machine tool has a footprint of only 7 sq m and provides the added bonus of intuitive operability using an in-house developed user interface that significantly reduces overall machining time but guarantees maximum manufacturing precision and workpiece variability.

The UCee user interface makes machining simple and safe via a multi-touch display that guarantees machine operators always have all the relevant information they need within their field of vision. For machining, the operator first defines the given workpiece geometry, the required machining surfaces and respective tool parameters. Then they select a suitable machining cycle before starting the manufacturing process with the push of a button. With UCee, standard machining cycles are no longer continually re-programmed. Instead, they are permanently saved through an integrated workpiece management feature and retrieved again specifically for application. The transfer of geometry data and tool allocation is prepared externally, at a PC for example, or via USB. These functionalities considerably reduced set-up and preparation effort and non-productive times at SWS.

When machining clamping device components, a precision of less than one micrometer is required for most of the various position and shape tolerances. To meet this standard, the UGrind has a vibration-damping machine bed made of granite that ensures maximum thermal and dynamic machine stability. The lever arm ratios of its multi-functional turret are optimized for a positive effect on the dimensional accuracy of the machine series. It has a radius of action of 270 deg and is equipped with six tools in line with the specific SWS requirements: one CBN grinding disc for machining outer diameters and flat surfaces, two inner grinding tools for the grinding of bore holes, two turning tools for external, internal and face turning, and one measuring probe that controls and monitors the entire machining process until the required target dimension is reached.

UGrind has a vibration-damping machine bed made of granite that ensures maximum thermal and dynamic machine stability. The lever arm ratios of its multi-functional turret are optimized for a positive effect on the dimensional accuracy of the machine series. It has a radius of action of 270 deg and is equipped with six tools in line with the specific SWS requirements: one CBN grinding disc for machining outer diameters and flat surfaces, two inner grinding tools for the grinding of bore holes, two turning tools for external, internal and face turning, and one measuring probe that controls and monitors the entire machining process until the required target dimension is reached.

This tool configuration machines high dimensions economically and reliably at SWS. Each clamping device component is hard-turned first at a high feed speed and cutting depth, then checked by the integrated measuring probe and ground in the same clamping – time-consuming manual re-measuring and repeated feeding are no longer necessary. The magnetic chuck and the optimum accessibility of the work chamber permits ergonomic loading and unloading, as well as precise and flexible clamping of tools with widely different characteristics. With the UGrind, SWS has increased their productivity in hard-fine machining small and medium-sized batches many times over – in speed, flexibility and precision – for a competitive advantage in their business.

SWS Spannwerkzeuge GmbH, Umgehungsstraße Nord 3, Schlüchtern, Germany 36381, +49-6661-96220, www.sws-spannwerkzeuge.de.

DVS Universal Grinding GmbH, Johannes-Gutenberg-Str. 1, Dietzenbach, Germany 63128, +49-6074-30406-81, Fax: +49-6074-30406-55, info@dvs-universal-grinding.de, www.dvs-universal-grinding.de.