Wire EDM dressing

from Wikipedia, the free encyclopedia

As drahterosives dressing the machine-integrated is dressing technology for metal bonded grinding wheels , respectively. Diamond or CBN grinding wheels with a sintered metal bond are dressed, profiled and sharpened in the grinding machine by means of wire EDM .

Procedure

The method belongs to the group of thermal, electrical-discharge method (Wire Electrical Discharge Dressing - WEDD). It is based on the basic principles of wire EDM. The dressing unit has a wire drive. This pulls the wire off the spool and conveys it past the grinding wheel via power supply lines and a thin wire guide disk with a circumferential groove. The grinding wheel rotates at full grinding wheel peripheral speed. The erosion site is rinsed with grinding oil using several nozzles. Finally, the wire used - the actual dressing tool - is fed to a wire cutter and shredded. The material is removed from the grinding wheel without contact using extremely short, quickly successive direct current pulses that generate a discharge in the dielectric in the gap between the electrode and the workpiece. During the discharge, tiny areas of the metal bond of the grinding wheel are melted and, at the end of the spark discharge, are washed out of the gap as small particles by the dielectric. A small crater forms. If discharge follows discharge, craters are created next to craters and thus a constant erosion of the bonding surface. The shape of the abrasive grains remains unaffected by the erosion process. There is always a discharge gap and therefore no mechanical contact between wire and grain or bond. When the grains are exposed from the bond, they fall out without the application of force.

Metal- bonded grinding wheels can be dressed in the grinding machine at full grinding wheel peripheral speed, i.e. H. profile and sharpen. This also gives the grinding wheel a high cutting ability with a high grain clearance.

Performance characteristics

  • Contactless dressing process
  • no wear on the dressing tool
  • all sintered metal bonds and electrically conductive hybrid bonds with diamond or CBN abrasive grain can be dressed
  • small geometries possible (depending on grain size and bond)
  • higher grinding performance achievable compared to mechanically dressed metal-bonded grinding wheels
  • a universal dressing tool can be used for a wide variety of wheel profiles
  • easy handling
  • Dressing possible at full wheel peripheral speed of up to 120 m / s
  • low dressing tool costs compared to mechanical dressing processes or dressing outside the grinding machine
  • high precision in the µm range reliably achievable even with complex profiles
  • System fully integrated in the grinding machine and control

Areas of application

For grinding ceramics, hard metal and hardened steel, grinding wheels with extremely hard abrasives made of diamond or CBN are used. In previous grinding processes, such grinding wheels often have a synthetic resin or ceramic bond. One possibility to increase the precision and economy of these grinding applications is to use grinding wheels with a sintered metal bond. However, their use has so far only made limited sense, as metal bonds can only be dressed to a very limited extent and only have an average cutting ability.

The process enables full use of the grinding properties of a metal-bonded diamond or CBN grinding wheel. Previous limits in grinding processes can be overcome. On the one hand, because it suddenly becomes possible to produce complex workpiece geometries at all or to bring their production into an economically sensible zone. On the other hand, because established grinding processes are becoming more economical, e.g. B. through shorter grinding times, shorter set-up times, longer dressing intervals or higher process stability.

Particularly suitable areas of application:

  • Grinding of hardened steel, hard metal, ceramics
  • External and internal grinding
  • Thread grinding
  • High speed grinding (HSG)

conditions

Only electrically conductive bond systems can be trained.

The grinding wheels used must be designed to generate the spark discharge between the abrasive grain bond and the wire electrode. The circuit is closed by means of a sliding contact on the grinding wheel. The grinding wheel must have a running surface for this contact, which in turn must be electrically connected to the grinding layer.

The method requires a dielectric fluid to build up the spark discharge and purge. A grinding oil must therefore be used. The function is guaranteed with every commercially available grinding oil (mineral oil, hydrocrack, PAO), as these always have dielectric properties. Added additives such as sulfur compounds can lead to odor formation during dressing.

literature

  • Eduardo Weingärtner: On-machine WEDD of metal bonded grinding wheels . Dissertation at the ETHZ 2013
  • Eduardo Weingärtner, Raoul Roth, Friedrich Kuster, Marco Boccadoro, Frank Fiebelkorn: Electrical discharge dressing and its influence on metal bonded diamond wheels. In: CIRP Annals Volume 61, Issue 1, 2012, pp. 183-186.
  • E. Weingärtner, S. Jaumann, F. Kuster, M. Boccadoro: Special wire guide for on-machine wire electrical discharge dressing of metal bonded grinding wheels. Annals of CIRP 59 (1): pp. 227–230 (2010)
  • E. Weingärtner, S. Jaumann, F. Kuster, K. Wegener: On-machine wire electrical discharge dressing (WEDD) of metal-bonded grinding wheels. International Journal of Advanced Manufacturing Technology 49 (9-12): pp. 1001-1007 (2010)
  • F. Fiebelkorn: Expansion of the performance of extremely hard grinding tools in series production. 5th European Conference on Grinding November 29-30, 2016, pp. 207-234, Aachen, Germany; Apprimus Verlag, Aachen, 2016. ISBN 978-3-86359-466-4