Traveling wire EDM apparatus with automatic wire rethreading mechanism

• US 4,350,864 A
• Filed: 06/12/1980
• Issued: 09/21/1982
• Est. Priority Date: 06/21/1979
• Status: Expired due to Term

• Current Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Original Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Inventors: Girardin, Roger, Janicke, Johann
• Primary Examiner(s): Reynolds, B. A.
• Assistant Examiner(s): PASCHALL, MARK H
• Application Number:
  US06/158,914
• Time in Patent Office: 831 Days
• Field of Search: 219/69 M, 219/69 W, 219/69 S, 219/69 C, 83/926 B, 83/884
• US Class Current: 219/69.12
• CPC Class Codes: B23H 7/10 Supporting, winding or electrical connection of wire-electrode

Abstract

An automatic wire rethreading mechanism for traveling wire EDM apparatus wherein the workpiece is cut by electrical discharges by an electrode in the form of a wire, comprising a mechanism for automatically threading the electrode wire through a pre-drilled hole in the workpiece, the automatic wire threading mechanism being adapted to thread the wire at the beginning of a cutting operation and any time the electrode wire is ruptured in the course of a cutting operation. The position of the pre-drilled hole is memorized, as well as the relative position of the wire and workpiece at the instant of wire rupture. The workpiece and the electrode wire holders are returned to their start position along a predetermined path and, after threading the wire again through the pre-drilled hole, the electrode wire and the workpiece are displaced relative to each other, without applying electrical discharges between the electrodes, along the already cut path until the wire electrode and the workpiece are positioned relative to each other in the same position as occupied when the electrode wire ruptured.

Claims

1. An EDM apparatus for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of an axially traveling wire, said apparatus comprising means for threading an end of said wire through a hole pre-drilled through the workpiece, wire feeding means grasping the end of said wire and drawing said wire axially through a machining zone between said wire and said workpiece, at least two servo motors for displacing said wire and said workpiece transversely relative to each other according to a programmed cutting path, memory means for storing data representing the relative position of said wire and said workpiece corresponding to the threading of said wire through said pre-drilled hole and for storing data representing the relative position of said wire and said workpiece at any instant said wire ruptures in the course of a cutting operation, means for detecting rupture of said wire, means for determining a return path for said wire and said workpiece to said threading relative position permitting rethreading said wire through said pre-drilled hole whereby said return path passes through an intermediate point wherein said wire is positioned exteriorly to the surface of said workpiece, means for returning said wire and said workpiece through said return path through said intermediate point to said threading relative position permitting rethreading said wire through said pre-drilled hole, means cutting off said wire proximate its end at said intermediate point of said return path wherein said cut-off wire portion is discarded exteriorly to the surface of said workpiece, means for rapidly returning said wire and said workpiece through said cutting path to their relative position at the instant said wire rupture was detected, and means for cutting off electrical discharges between said wire and said workpiece from the instant of said wire rupture until said wire and said workpiece are returned to said wire rupture relative position.

2. The apparatus of claim 1 wherein said wire is grasped at its end by said wire feeding means at said intermediate point of the return path, and further comprising means for operating said means cutting off said wire at said predetermined point.

3. The apparatus of claim 1 further comprising a disposal receptacle at said intermediate point for recovering the cut-off end of said wire, and means for operating said means cutting off said wire at said intermediate point.

4. An EDM process for cutting a workpiece by a traveling wire electrode comprising threading said wire electrode through a hole pre-drilled in said workpiece prior to effecting a cutting pass in said workpiece, grasping the end of said wire passed through said hole in conveyor means for feeding said wire longitudinally, applying electrical machining pulses across a machining zone between said wire and said workpiece, transversely displacing said wire and said workpiece relative to each other for effecting a cut in said workpiece along a pre-programmed path, detecting rupture of said wire when occurring at any point of said cutting path, cutting off said machining pulses upon detection of said wire rupture, returning said wire and said workpiece from the position of wire rupture to their initial relative position corresponding to the location of said pre-drilled hole in said workpiece by passing through an intermediate position wherein the end of said wire is suspended outside the area of said workpiece, cutting off the end of said wire at said intermediate position, rethreading the end of said wire at said initial relative position through said pre-drilled hole, grasping the end of said wire and entraining said wire by means of a feeding mechanism for longitudinal feed through the machining zone between said wire and said workpiece, returning said wire and said workpiece through the previously cut path to the point of wire rupture, and starting said cutting operation from said point of rupture by re-establishing electrical discharges across said machining zone and by displacing said wire and said workpiece relative to each other according to said pre-programmed cutting pass from said point of rupture on.

5. The process of claim 4 further comprising recovering the cut-off end of said wire in a disposal receptacle at said intermediate position.

6. The process of claim 4 further comprising automatically grasping the end of said wire and introducing it into said conveyor means at said intermediate position prior to cutting off said wire.