Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-01-18
2001-06-26
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C264S328100
Reexamination Certificate
active
06252192
ABSTRACT:
TECHNICAL FIELD
This invention relates to tool holders for EDM tooling.
BACKGROUND OF THE INVENTION
Several patents have issued since the commercial success of electric discharge machining (hereinafter “EDM”) relating to the devices which can hold EDM tooling so that it may be repeatably placed in operable position in the EDM machine and removed therefrom. Typically such devices, which are herein termed “tool holders”, may be repetitively positioned with great accuracy in and thereafter removed from the EDM machine many times during the course of a production run.
In the present state of the art, EDM tooling, also sometimes referred to as EDM electrodes, is formed from stock which is mounted in a tool holder, the tooling is then created, and thereafter remains with the holder throughout the useful life of the tooling. The tooling is created in the tool holder to avoid the problem of accurately positioning the tooling in the proper X, Y and Z orientations in the tool holder. The tool holder has certain locating devices that enables the holder (and in turn the tooling) to be repeatably positioned very accurately in the EDM machine. Thus, for each EDM tool, there is a tool holder. Tool holders of the prior art useable in EDM machines are shown in the following representative U.S. Pat. Nos. 4,621,821; 4,815,780; 4,855,558; 5,065,991; 5,415,382.
Presently, EDM tool holders are machined of metal. Such holders typically sell for $40.00 or more. As there must be one such holder for each EDM tool, users of such tooling tie up substantial monies just in the cost of the holders. Accordingly, inventory costs merely for tool holders become a significant item in a company's tooling inventory.
In addition to involving significant inventory costs, the prior art tool holders are made up of a collection of individual parts. For example, in the case of U.S. Pat. No. 4,815,780, there is a centering disk
13
which is held to the surface of a mounting plate
6
of the tool holder
2
by four screws
51
. The manufacture and assembly of these separate pieces not only is expensive but should this plate shift as a result of the tool holder being bumped, a $60,000 die being machined may be ruined because the tool holder was not positioned accurately in the EDM machine when it made its cut in the die. U.S. Pat. No. 5,065,991 discloses a generally similar centering disk and the same shortcomings are present in such arrangement.
In U.S. Pat. No. 4,855,558, tool holder
2
is made of metal and has four machined slots in the upper surface
30
and the flanks are cut to provide slightly bowed recesses such as at
37
b
as shown in
FIG. 4
so that when the rail
68
of the chuck
1
is drawn into the slot, the lip
38
d
deflects downwardly along the Z-axis. Forming the downwardly bowed recesses involves difficult machining, raising the cost of the tool holders.
SUMMARY OF THE INVENTION
We have developed a tool holder construction that reduces the cost of EDM tool holders to a fraction of today's cost and substantially reduces the likelihood that an accidental bumping of the tool holder will upset the accuracy of its positioning when inserted in the EDM machine.
Instead of fabricating the tool holders of metal involving the machining and assembly of several parts, we make the tool holder by injection molding an appropriate plastic having insert-molded therein electrical conductors or any other parts which are desirably formed of metal.
Accuracy in repeated positioning of the tool holder is accomplished by utilizing the inherent flexibility of the plastic material of which the holder is formed to design positioning devices which provide extreme accuracy in X, Y and Z directions. Thus, unlike the prior art tool holders which comprise an assembly of parts that may later shift if the tool holder is accidentally bumped, or which require intricate machining for each holder increasing production costs of the holder, our tool holder is essentially one piece and there is no significant risk that parts may accidentally shift, destroying accuracy of the holder.
We have found that our tool holder may be made more rigid and less liable to permit deflection of the EDM tool carried thereby, in several applications, if the holder is made using a MIM (metal injection molded) core or the like, insert molded in a plastic block. In lieu of a MIM core, a powdered metal core or a cast metal core or the like, may be used. Such cores will provide increased rigidity to reinforce or “back-up” the plastic material of the block. The plastic legs of our earlier design which locates the tool in the Z-axis are formed of the MIM core material, which also provides a conductive path between the EDM machine and the tool. A portion of the core is expanded for contact with the tool as in the other embodiments.
REFERENCES:
patent: 4395613 (1983-07-01), Barr et al.
patent: 4425060 (1984-01-01), Bilz et al.
patent: 4621821 (1986-11-01), Schneider
patent: 4815780 (1989-03-01), Obrist
patent: 4855558 (1989-08-01), Ramsbro
patent: 4922074 (1990-05-01), Sebzda, Sr.
patent: 5065991 (1991-11-01), Schneider
patent: 5415384 (1995-05-01), Obrist et al.
patent: 5788225 (1998-08-01), Iwata et al.
patent: 6015961 (2000-01-01), Lozon et al.
patent: 6160236 (2000-12-01), Nordquist
Lozon Robert J.
Olszewski Edward C.
Brooks & Kushman P.C.
Dunn Tom
Johnson Jonathan
Precision Die & Machine Company
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