Process and mechanism for threading the electrode wire of an EDM apparatus

• US 4,652,716 A
• Filed: 08/27/1985
• Issued: 03/24/1987
• Est. Priority Date: 03/24/1980
• Status: Expired due to Term

• Current Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Original Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Inventors: Schneider, Rudolf, Josserand, Joseph
• Primary Examiner(s): Paschall, M. H.
• Application Number:
  US06/769,730
• Time in Patent Office: 574 Days
• Field of Search: 219/69 M, 219/69 W, 219/69 E, 219/69 C, 219/69 R
• US Class Current: 219/69.17
• CPC Class Codes: B23H 7/102 Automatic wire threading

Abstract

A method and apparatus for threading the electrode wire of a travelling wire EDM apparatus through an aperture in a workpiece. Prior to automatically threading the wire through the aperture in the workpiece, the wire is continuously straightened by pulling longitudinally on the wire, and the wire is passed through a guide tube and through a nozzle to which fluid under pressure is supplied for forming a jet stream at the outlet of the nozzle. Prior to a threading or rethreading operation the wire is cut off proximate to the outlet of the nozzle. The nozzle outlet is brought in close proximity to the aperture in the workpiece and the jet stream is aimed at the aperture in the workpiece for guiding the wire through the aperture, while being maintained coaxially by the jet stream. The consecutive steps for feeding the end of the wire through an aperture in the workpiece are effected in sequence for initial threading of the wire through a pre-drilled stating hole in the workpiece, or for rethreading the wire through a cut in the workpiece after accidental rupture of the wire during a cutting operation.

Claims

1. An apparatus for threading and rethreading the electrode wire of a travelling wire EDM apparatus through an aperture in a workpiece, said apparatus comprising a spool supplying said electrode wire, a roller around which said wire is wound, a motor driven feed drum around which said wire is wound after passage around said roller, a pinch roller for applying said wire against said feed drum, brake means for applying a braking force on said roller whereby a first longitudinal pull is exerted on said wire between said roller and said motor driven feed drum, a guide tube for passage therein of said wire after leaving said motor driven feed drum, a nozzle having a passageway through which said wire is passed upon leaving said guide tube, means for supplying fluid to said nozzle for forming a jet stream of fluid maintaining said wire substantially coaxially in said passageway and in said jet stream of fluid, a wire cut-off mechanism disposed downstream of said nozzle and proximate said nozzle, a workpiece having an aperture for passing said wire upon leaving said nozzle, said nozzle and said wire cut-off mechanism being mounted on an end of a slide displaceable such as to place said nozzle in close proximity with said aperture in said workpiece, and a wire conveyor mechanism for engaging said wire after passage through said aperture for displacing said wire longitudinally while effecting a second pull on said wire between said motor driven feed drum and said wire conveyor mechanism, said second pull on said wire being effected at a force greater than that of said first pull.

2. The apparatus of claim 1 wherein said guide tube is telescopic, with an end portion thereof mounted on said slide.

3. The apparatus of claim 2 wherein said fluid supplied to said nozzle is at a pressure of at least 5 bars.

4. A method for threading and rethreading the electrode wire of a travelling wire EDM apparatus through an aperture in a workpiece, said method comprising feeding said wire from a supply spool to a braked roller, feeding said wire from said braked roller to a motor driven feed drum for effecting a first longitudinal pull on said wire by means of said feed drum while being tensioned between said braked roller and said feed drum, feeding said wire longitudinally through a telescopic guide tube, effecting a second longitudinal pull on said wire while in said telescopic guide tube for straightening said wire, passing said wire through a passageway in a nozzle, said nozzle being supplied with fluid for forming a jet stream of fluid maintaining said wire substantially coaxially in said nozzle passageway and in said jet stream of fluid, engaging said wire after passage through said nozzle passageway in a wire conveying mechanism whereby said wire conveying mechanism effects said second longitudinal pull on said wire between said feed drum and said wire conveying mechanism by over-running said feed drum by said wire conveying mechanism, cutting off said wire at a portion thereof downstream of said nozzle and proximate to said nozzle while simultaneously stopping said feed drum, aiming said jet stream of fluid to said aperture in the workpiece, restarting said feed drum for feeding the end of said wire through said aperture while being guided by said telescopic guide tube and said jet stream of fluid aimed at said aperture, simultaneously displacing a portion of said telescopic guide tube having an outlet proximate said nozzle and said nozzle toward the workpiece, and engaging the end of said wire after passage through said aperture with said wire conveying mechanism for re-establishing said second longitudinal pull on said wire.

5. The method of claim 4 wherein said fluid supplied to said nozzle is at a pressure of at least 5 bars.