Method for total form machining of metal

The method of abrasion forming friable material such as carbon blocks to form electrical discharge machining electrodes therefrom comprising the steps of moving a master model, having an abrasive surface which is a mirror image of a desired form to be abrasion machined in the friable material, which surface is related in size to the desired form to be machined by an additional movement to be imparted to the master model, toward the friable material with the abrasive surface of the master model and workpiece in engagement while imparting the additional relative motion between the master model and workpiece, which additional relative motion is in all directions in a plane perpendicular to the direction of movement of the master model and workpiece and flushing between the master model and workpiece to prevent build up of abraded particles of the workpiece on the master model.

The invention relates to electrical discharge machining and refers more 
specifically to structure for and a method of producing an electrode or 
the like. 
In the past, electrodes for electrical discharge machining of metals have 
generally been machined from blocks of electrode material, such as 
graphite or the like. The machining of each individual electrode 
separately or even with copy machines, whereby a number of the electrodes 
may be machined simultaneously, is a tedious process, wasteful of both man 
and machine time. In addition the individual production of electrodes by 
the usual methods produces slight variations from one electrode to another 
or in the mounting thereof, so that the electrodes are not exactly 
interchangeable. Thus, a considerable amount of set up time is required to 
exactly align an electrode which has been individually machined and 
mounted with a workpiece when changing of electrodes is required. 
In addition, with prior methods and tools for electrical discharge 
machining, it has often been necessary to machine a rough cavity with one 
or a series of electrodes after which a finish cut is made by a separate 
electrode. This is necessary due to wear of the electrode in the usual 
electrical discharge machine operation. Again changing of the electrode 
between a rough and finish or between two rough or two finish operations 
on a workpiece is wasteful of both man and machine time in set-up and 
changing and handling of the electrodes even if a quick-change system of 
tooling is used. 
It is therefore one of the objects of the present invention to provide 
improved structure for producing an electrical discharge machining 
electrode. 
Another object is to provide structure for producing an electrical 
discharge machining electrode or the like comprising an abrasive mirror 
image electrode form and means for machining a workpiece with the mirror 
image electrode form. 
Another object is to provide structure as set forth above wherein the means 
for machining a workpiece with the mirror image electrode form comprises a 
tool for moving the mirror image electrode form universally in one plane 
perpendicular to the usual direction of movement of the mirror image 
electrode form. 
Another object is to provide an improved method of producing an electrode 
for electrical discharge machining or the like comprising producing an 
abrasive mirror image electrode form and moving the mirror image electrode 
form toward a workpiece in a manner to abrade the desired electrode from 
electrode material. 
Another object is to provide a method of producing an electrical discharge 
machining electrode as set forth above wherein the manner of moving the 
electrode comprises moving the electrode toward the workpiece and at the 
same time moving the electrode universally in all directions perpendicular 
to the direction of movement of the electrode toward the workpiece. 
Another object is to provide a tool for use with an electrical discharge 
machine for supporting an electrode on the ram thereof including means for 
moving the electrode in all directions in a plane perpendicular to the 
movement of the ram. 
Another object is to provide structure as set forth above wherein the tool 
comprises a pair of slides movable perpendicularly to each other and 
eccentric means operable between the pair of slides for relatively moving 
the slides. 
Another object is to provide structure as set forth above wherein the 
eccentric means is adjustable as to eccentricity to determine the relative 
movement between the slides. 
Another object is to provide structure for and a method of producing an 
electrode for electrical discharge machining or the like which is simple, 
economical and efficient.

With particular reference to the Figures of the drawings, one embodiment of 
the present invention will now be disclosed in detail. 
In accordance with the invention, the electrical discharge machine tool 10 
is useful in conjunction with an electrical discharge machine 12 or 
similar structure for producing a finished workpiece with a single 
electrode. The finished workpiece may be in accordance with the invention 
an electrical discharge machining electrode produced by abrasion with a 
mirror image abrasive electrode form 14, as illustrated in FIGS. 7 through 
9 by the tool 10. 
More specifically, the electrical discharge machining apparatus 12 includes 
a mechanical section 14 having a head mechanism 16 including a ram 18 
movable vertically to which the electrical discharge machine tool 10 is 
secured by means of a quick-change dovetail arrangement 20 as disclosed in 
U.S. Pat. No. 3,222,494, and an electrical section 22 for providing an 
electrical signal between the electrode 24 and a workpiece 26 in the usual 
manner of electrical discharge machining. Servo control apparatus is 
provided operable between the electrical section 22 and the mechanical 
section 14 to control movement of the ram 18 in accordance with a gap 
maintained between the electrode 24 and the workpiece 26 in the usual 
manner of electrical discharge machines. 
Electrical discharge machining apparatus 12 are well known and, for 
example, are commercially available from Easco-Sparcatron, Inc. of 110 
Morgan Road, Ann Arbor, Michigan. They will not be considered in 
themselves further herein. 
The electrical discharge machining tool 10 is shown best in FIGS. 2 through 
5 in conjunction with a simple electrical discharge machining electrode 
24. The tool 10 includes the base 28, drive means 30, slide structure 32 
and slide structure 34. Tool 10 is completed by the electrode mounting 
member 36 to which the electrode 24 is secured. 
Base 28 is a generally rectangular metal member having a dovetail portion 
38 for quick, accurate securing of the tool 10 to the ram 18. An opening 
40 is provided through the base 28 to receive the bearings 42 and cylinder 
44 of the motor means 30. 
Slide structure 32 includes the guides 46 and 48 at the opposite sides 
thereof and the slide 50 positioned between the slide 50 is. The guides 46 
and 48 are rigidly secured to the base 28 by convenient means, such as 
bolts 52. The guides 46 and 48 are movable on the slide on bearing means 
54 and 56. An opening 58 is provided through the slide 50 to receive the 
cam cylinder 60 of the drive means 30. 
The slide structure 34 includes the guides 62 and 64 rigidly secured to the 
slide 50 by means of bolts 66 or the like. The slide 68 is movable between 
the guides 62 and 64 on the bearing means 70 and 72 at right angles to the 
slide 50. Opening 88 is provided in slide 68 to receive the cam cylinder 
86 of the drive means 30. 
The electrode supporting member 36 is as shown generally rectangular and is 
secured to the slide 68 by means of bolts 74 or the like. Electrode 24 in 
the shape of, for example, a recess which it is desired to machine 
electrically in a workpiece 26 is secured to the member 36 by convenient 
means, such as bolts 76. 
Drive means 30 includes the electric motor 78 which may be energized, such 
as by a servo mechanism similar to that used to drive the head 18 toward 
the workpiece in the usual electrical discharge machining apparatus to 
produce rotation of the output shaft 80 thereof. The drive means 30 
further includes the cylinder 44 secured to the shaft 80 for rotation 
therewith which cylinder is concentric with the shaft 80 and is mounted 
for rotation in the base 28 by the bearings 42. Cylinder 60 is secured to 
the shaft 80 and cylinder 44 by means of the pins 82 and 84, as 
illustrated best in FIG. 5. The drive means is completed by the cylinder 
86 secured in the opening 88 through the slide 68 and eccentrically 
secured to the cylinder 60 by the bolt 90. The eccentricity of the 
cylinder 86 with respect to the cylinder 60 may be adjusted by means of 
loosening the bolt 90 and rotating the cylinder 86 about the bolt 90 and 
retightening bolt 90. 
Thus in overall operation of the electrical discharge machining tool 10 the 
usual electrical discharge machine servo mechanism is used to drive the 
ram 18 toward a workpiece whereby the workpiece is formed by the electrode 
24 which in the case of a male electrode is formed slightly undersized. 
The drive means 30 is then caused to rotate whereby the slides 50 and 68 
provide universal movement of the electrode 24 in a plane perpendicular to 
the direction of movement of the ram 18 to finish a workpiece exactly. The 
finishing cut or movement lateral to the ram 18 desired may be adjusted by 
means of bolt 90 to provide any finishing cut desired. It will be readily 
understood that a considerably more sophisticated means for adjustment of 
the eccentricity between cylinders 60 and 86 may be provided as desired. 
Thus, it will be seen that a very accurately dimensioned workpiece may be 
produced by electrical discharge machining without the necessity of 
changing electrodes for a finishing cut through the use of the electrical 
discharge machine tool 10 provided in accordance with the invention. 
The electrical discharge machining tool 10 in addition has particular 
application in the production of electrical discharge machining electrodes 
from carbon or graphite blocks or the like, as shown in FIGS. 6 through 
10, by the method of the invention. 
As shown in FIG. 6, to produce a plurality of exactly interchangeable 
carbon electrodes for electrical discharge machining a master pattern 98 
for the electrodes is first machined in the usual manner. The master 
pattern 98 is then placed in a molding tray 100 in an inverted position, 
as shown in FIG. 6. A mixture of abrasive material, such as carborundum, 
emery or the like, and a plastic binder, such as an epoxy having minimum 
shrinkage properties, are then poured over the master pattern 98 which is 
slightly oversized in the case of a male master pattern. Members, such as 
small rods, are positioned in the matrix of abrasive material and plastic 
binder to provide flush openings 102 if desired in the oversize female 
electrode form mirror image 104 produced on setting of the plastic binder, 
as illustrated in FIG. 7. 
After the plastic binder has cured the female electrode form mirror image 
104 of the male master pattern 98 is removed from the pan 100 and the 
pattern 98 and secured to the generally rectangular member 106 by means of 
the bolts 108 in the manner disclosed in applicant's copending patent 
application, Ser. No. 454,585, filed of even date herewith. 
As shown best in FIG. 9, the member 106 is then secured to the electrode 
holding mounting member 36 of the electrical discharge machining tool 10 
and the tool 10 is advanced toward the carbon block 110 while the drive 
means 30 is actuated to abrade the surface of the carbon block 110. If 
desired the carbon block may be flushed through the flush holes 102 during 
abrading or vacuum apparatus or air pressure may be used to remove the 
abraded material from between the abrasive electrode form 104 and 
workpiece 110. Since the female abrasive electrode form 104 and the master 
pattern 98 are slightly oversize an electrode will be formed in the carbon 
block 110 of the exact desired size depending on the eccentricity of the 
cylinders 60 and 86 of the tool 10. 
In addition, since the carbon block 110 is secured to an electrode mounting 
member 112 having a dovetail locating portion 114 secured thereto and 
since the tool 110 is provided with similar dovetail locating structure 
38, the electrodes produced with the tool 110 in the manner indicated will 
be exactly interchangeable so that no time will be lost in setting up the 
electrode 116 produced as indicated above directly on the ram 18 of the 
electrical discharge machine 12 to perform a continuing electrical 
discharge machining operation as set forth above and as illustrated in 
FIG. 10. 
While one embodiment of the present invention and modifications thereof 
have been considered in detail, it will be understood that other 
embodiments and modifications are contemplated by the inventor. It is the 
intention to include all embodiments and modifications as are defined by 
the appended claims within the scope of the invention.