Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-02-09
2001-01-09
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C279S083000, C403S362000
Reexamination Certificate
active
06172319
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the art of tools for spark erosion or metal discharge machining, and more particularly to mounts for connecting electrode holders to die-sinking metal burning electrodes.
BACKGROUND OF THE INVENTION
There are a wide variety of applications that use spark erosion or electrical discharge machining (EDM) for high precision machining of a wide variety of conductive metals. The EDM process removes metal from a metal workpiece by using thermal energy produced from an accurately controlled electrical discharge spark to erode or vaporize metals. One type of electrical discharge machining is known as a die-sinking process in which the inverted image of a metal burning electrode is gradually impressed into the workpiece. The position of the electrode is typically driven and accurately controlled by a servo actuated ram. During an EDM process, the spark discharge is pulsed on and off at a high frequency cycle. Each spark discharge melts or vaporizes a small area of the workpiece surface. The melted metal particles are then cooled by the dielectric fluid in which the work piece is immersed in and then solidified into small erodable particles which are flushed away by the pressure and flow of the dielectric fluid. The impression of the electrode for each spark discharge is located in a very small area. The spark discharge typically travels the shortest distance across the narrowest gap through the dielectric fluid to the closest point on the workpiece thereby removing material at that location. The amount of material removed from the workpiece with each pulse is proportional to the energy contained in the pulse.
The advantages of EDM are well known, including the ability to remove material from workpieces that are very hard such as hardened steel or tungsten carbide with metal burning electrodes formed of soft conductive material such as copper with a tellurium pattern, or graphite. The EDM process is also highly precise and able to easily form complex patterns on a workpiece.
To interchangeably mount a variety of die-sinking electrodes on the ram, electrode holders and mounts are often used to releasably connect the electrodes to the ram. The electrode holder connects on the end of a ram. The mount is interposed between the electrode holder and the electrode. The mount typically includes a shank portion that is clamped into an opening of the electrode holder and a connector portion or tip portion which connects to the electrode.
As shown and described in a
General Catalogue
published by EROWA (1997), pages 78-100, a variety of mounts have been forged and/or machined from relatively hard conductive material including brass and steel material. A common way to connect a mount to the electrode is to machine threads on the tip portion of the mount which in turn screws into a tapped threaded hole formed in the electrode. It is also known to glue the mount directly on the electrode. For example, it is known to glue a closely machined smooth or slightly roughened cylindrical tip of the mount into a closely machined cylindrical hole in the electrode. It is a requirement that the mount be in good electrical contact with the electrode to facilitate communication of electricity therethrough for proper spark erosion of a work piece. The glue tends to act as an insulator and can cause problems in the EDM process when bad electrical contact exists. Therefore, close tolerances in the machining of the mounts has been necessary to ensure good electrical contact between the mount and the electrode. Even with closely machined tolerances, the glue can still occasionally cause poor electrical contact which is a significant disadvantage. Heretofore, prior mounts for interposition between an electrode holder and an electrode have suffered from being very expensive.
SUMMARY OF THE INVENTION
It is therefore the general objective of the present invention to provide a more economical mount for interposition between a metal burning electrode and an electrode holder.
In achieving this objective, it is a further object to maintain good electrical contact between a mount and a metal burning electrode.
Accordingly, the present invention is directed to a die cast mount for connecting a metal burning electrode to an electrode holder. The mount comprises a conductive body formed of cast material and includes a shank portion and a connector portion. The shank portion is sized to be received in an opening of the electrode holder for clamping therein and the connector portion is dimensioned for connecting to the metal burning electrode. Suitable cast material for the mount may be either aluminum material or zinc material. The fact that the mount is formed from an inexpensive cast material and does not require subsequent machining operations makes the mount of the present invention a very economical and inexpensive mount as compared with conventional brass or steel mounts.
It is an aspect of the present invention that the mount includes a gluing surface on the connector portion which is dimensioned to cooperate with a corresponding surface of the metal burning electrode. The mount may be connected to the metal burning electrode by gluing the gluing surface to the corresponding surface of the electrode.
It is another aspect of the present invention that the connector portion includes a plurality of deformable ears cast or formed thereon which project outwardly from the gluing surface. The deformable ears ensure electrical contact between the metal burning electrode and the mount. The deformable ears are dimensioned to deform in contact with the corresponding surface of the electrode when the mount and the electrode are connected. The relatively soft cast material of the ears allows the ears to easily deform and prevents the electrode from being damaged when a mount is tapped into the electrode.
It is a further aspect of the present invention that the gluing surface includes a plurality of grooves cast therein for receiving and retaining glue. When the mount is bonded to the metal burning electrode by glue, the glue that is received into the grooves improves both the axial strength and the radial strength of the glue bond between the mount and the electrode.
According to one embodiment, the connector portion of the mount is a cylindrical tip. The cylindrical tip includes a cylindrical gluing surface on the outer periphery thereof. The cylindrical surface is sized to be closely received in a cylindrical hole formed in the metal burning electrode. The cylindrical gluing surface includes at least one deformable ear projecting radially outward. The radius of the at least one deformable ear is sized slightly larger than the radius of the cylindrical hole so that it deforms in contact with the inner surface of the cylindrical hole when the mount and the electrode are connected to provide good electrical contact therebetween.
According to another embodiment, the connector portion includes a cylindrical tip having an internal cylindrical opening with the inner surface of the cylindrical opening providing a cylindrical gluing surface. Small electrodes such as pins or small rods may be inserted into the cylindrical opening and glued thereto. The cylindrical gluing surface includes at least one deformable ear projecting radially outward from the gluing surface which is radially inward toward the center of the cylindrical opening. The radius of the at least one deformable ear is sized smaller than the radius of the stem portion of the electrode so that when the electrode and mount are connected and bonded by glue, the deformable ear deforms in contact with the electrode to provide good electrical contact therebetween.
According to another embodiment of the present invention, the connector portion includes a tip having a longitudinally extending slot. The slot includes parallel side walls for receiving a blade portion of the metal burning electrode therebetween. The at least one deformable ear projects outwardly from the slot walls. The deformable ear provides a width betwee
Evans Geoffrey S.
Leydig , Voit & Mayer, Ltd.
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