Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H7/00—Processes or apparatus applicable to both electrical discharge machining and electrochemical machining
  • B23H7/02—Wire-cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H7/00—Processes or apparatus applicable to both electrical discharge machining and electrochemical machining
  • B23H7/14—Electric circuits specially adapted therefor, e.g. power supply
  • B23H7/20—Electric circuits specially adapted therefor, e.g. power supply for programme-control, e.g. adaptive

Definitions

• the present invention relates to a device for fully automating cutting by electroerosion along a closed path or the ends of which reach the edges of the workpiece, eliminating the manual operations between the blanks and the finishes.
• EP 267,151 In order to avoid stopping the machining when the drop is no longer retained except by a narrow bridge of material in order to allow the operator to detach it manually, the applicant has developed a device described in EP 267,151.
• This device makes it possible to automatically perform a cut along a closed path, or the ends of which reach the edges of the workpiece by detaching at a predetermined time from the machining a scrap still retained by a narrow bridge of material.
• This auxiliary ejection device is mounted on the CNC machine 1 and is arranged to break a bridge of material maintaining a drop of any shape and to drop or eject this drop. According to some of the variants described in EP 267,151, it comprises a member which strikes or pushes the fall.
• the member enabling the fall to be expelled Before being actuated, the member enabling the fall to be expelled must generally be positioned facing the fall so as to act on it at a given point of impact.
• attachment point or “suspension point” the projection, on the impact surface, of the edge attaching the fall to the material bridge.
• the coefficient k depends on the speed of the ejector and the moment of the fall.
• this device remains effective for a wide range of use, that is to say for falls of very varied shape and size, without significant limitations due to the mass or the height of the fall, and without having to modify the force exerted by the ejector and the height of the material bridge, as well as the value of the coefficient k.
• the main factors of the latter seem to be the tensile strength of the material of the part and the distance from the point of attachment to the center of gravity of the fall.
• the device has a practically unlimited range of application and can, in most cases, be used without problem for any fall of less than a kilo and less than 120mm high. Much heavier and much higher pieces can also be ejected as long as they are not too complex in shape
• the device according to the present invention can have an infinite number of embodiments. Only some will be illustrated schematically and by way of examples by the appended drawing.
• Figure 1 is a schematic section of an EDM machine with a wire electrode comprising one of the possible variants of an ejection device according to the present invention.
• FIG. 2 illustrates an embodiment of a system making it possible to evacuate the ejected scraps.
• FIGS 3 to 4 show the results of tests carried out with this device.
• FIGS. 1 and 2 the fall is ejected by means of a pneumatically controlled piston which strikes it.
• a pneumatically controlled piston which strikes it.
• FIGS. 1 and 2 show a machine of known type for cutting by electroerosion using a wire electrode 8.
• the active part of the latter is stretched between two guides of known type (not shown) located inside the two heads.
• the table crossed movement 12 allows the wire electrode to be inclined relative to the lower machining head 9, located in the container 11. The movement is carried out in the plane perpendicular to the plane of FIG. 1, defined by the axes of Cartesian coordinates U and V.
• Each machining head also contains a nozzle for injecting the dielectric machining liquid and a contact bringing the wire 8 the electric current delivered by an electric pulse generator.
• a wire feed device (not shown) is mounted on the upper arm, movable vertically and already carrying the machining head 7, while a feed system of known type ensures continuous scrolling, and therefore renewal wire electrode 8.
• the upper machining head may also include a system for heating the wire, as well as an automatic wire cutting and re-threading device of the type described, for example in patents CH 641 709 and 646 356 or in the European application published under NO 206 041. Such a device makes it possible to automatically cut several successive contours on the same part.
• a second cross-motion table 10 supports the tray 11 and ensures the relative movements between the wire 8 and the workpiece 1. The movements are carried out in a plane perpendicular to the plane of FIG. 1 and defined by the axes of Cartesian coordinates X and Y.
• This part 1 is held on supports (not shown) located in the tray 11 and fixed to the latter.
• the electric generator also connected to the part 1 to be machined, causes erosive discharges between the wire electrode 8 and the part 1 which is cut by the advance progressive of the wire 8, along a preset path, controlled by the servomotors 15 and 16 of the cross-motion table 10, controlled by a digital control unit not shown.
• the latter is also connected (by connections not shown), on the one hand to the servomotors 13 and 14 which actuate the crossed movements of the table 12 and thus make it possible to obtain the desired inclination for the wire electrode 8 and, d 'other hand, to a motor 17 which controls the vertical movement of the upper machining head along the axis Z, along a rack.
• a member 21 is screwed onto the upper machining head 7 and carries a vertical piston 3 with pneumatic control.
• the lower head 9 is provided with a ram 4.
• Other organs are not shown, such as the system detecting whether the ejection of the fall has been successful or not.
• FIG. 1 illustrates the moment when the fall 2 has just been struck by the piston 3.
• the fall 2 still being retained on the part 1 by a triangular attachment 5, it controls the cutting of the wire 8, the movements according to - Y and - V, respectively of the tank 11 and the upper head 7 in order to offset the heads 7 and 9 and bring the piston opposite the ideal point M located between the attachment point 5 and the projection on the surface of the fall 2 of its center of gravity.
• Figure 2 illustrates when the fall detector that indicated that the ejection was successful, the numerical control commands the ascent of the piston 3 and a movement of the tank 11 along + Y, so that the ram 4 of the lower head 9 comes to push the fall 2 against the wall of the tank 11, the thus moving out of the work area. It will only remain to position the heads 7 and 9 facing each other by controlling the movement along + V of the head 7, to move the tray 11 so that the 2 heads . are opposite the pilot hole corresponding to the next path to be cut, to re-thread the wire, and to resume machining.
• a stop must be arranged so as to hold it during the ejection of the scrap.
• k 0.85
• the fastener is 5 mm high and has an angle of 1; tests carried out by the applicant have shown that these values are suitable for retaining most of the cut pieces by a triangular attachment.
• FIG. 3 represents the shape of the variation of the admissible mass for the fall 2 as a function of the distance a, for a given tensile strength and a roughing height.
• the curve of this figure 3 separates the favorable zone in which any ejection is successful, as confirmed by the checks carried out with the device after each ejection command, from a zone where the efficiency is no longer guaranteed (too heavy part or center of gravity too far from the point of attachment).
• the + zone represents the right conditions: all the forces can be absorbed in the triangle and the part is well held, the zone - the bad: the part is badly held and there is a risk of tipping. Automatic evacuation is however possible, provided that the position of the attachment point is reconsidered so as to bring it closer to the center of gravity.
• the height of the triangular attachment should be increased, from 5 to 6mm, for example.
• the height can also be increased.
• the resistance of the material being increased, the height can be reduced. In general, however, it is not less than 4mm for cylindrical parts and 4.5mm for conical parts.
• a suitable distance that is to say the smallest possible.
• the ejection can be carried out in a few tens of seconds, depending on the variant used.
• the device of the present invention is preferably used on an EDM machine whose digital control is programmed so as to automatically make the material bridge; it is generally constituted by a triangular attachment produced as described in application EP 267,151.
• the base of this fastener generally rests on the underside of the part which must then have a flat area at least 1mm wide at this point.
• the "height and angle of this fastener can preferably be modified, adjusted and checked at the start of machining. For most materials, a height of 5mm and an angle of one degree are suitable, in particular for parts whose the thickness is equal to or less than 25mm The thicker the part (and the drop), the wider the base of the fastener.
• the EDM machine of the present invention can have a control means which, after actuation of the ejector, indicates whether the ejection is successful or not. Otherwise, the program instructs the ejector to hit a second, then a third hit. If this is not successful, the machine can stop and display, for example an error message, or alternatively, go to the next ejection.
• the coordinates of the striking point are preferably modifiable by the operator.
• the automation and reliability of the device according to the present invention therefore considerably increase the autonomy and productivity of the machine on which it is mounted and makes it possible to avoid any marking of the part at the end of machining.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Mechanical Engineering (AREA)
• Automation & Control Theory (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=4215014

Family Applications (1)

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• 1991
  • 1991-05-10 EP EP19910908826 patent/EP0483316A1/de not_active Withdrawn
  • 1991-05-10 WO PCT/CH1991/000112 patent/WO1991017856A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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