Metal deforming – With cutting – By shearing tool-couple
Reexamination Certificate
1999-06-09
2002-04-16
Peterson, Kenneth E. (Department: 3724)
Metal deforming
With cutting
By shearing tool-couple
C072S329000, C029S893330, C083S620000, C083S687000
Reexamination Certificate
active
06370931
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of smooth-edged metal parts, and, more particularly, to the production of smooth-edged metal parts having complex perimeter configurations, such as gears and sprockets.
BACKGROUND OF THE INVENTION
Numerous methods exist today for producing metal parts. One such method is stamping, by which stock material, typically a metal sheet, is fed into a punch press. The punch press, typically via some sort of die and punch arrangement (stamping die), stamps out parts, which can be in the form of “blanks.” A blank, an example of which is shown in
FIG. 2
, is typically a right cylinder solid having a desired perimeter outline and the same thickness as the original metal stock. For example, conventional round washers, which have a simple circular perimeter, are usually manufactured via a stamping process in conjunction with an integral piercing process for providing a center hole. Blanks may be used as parts in and of themselves, or may be used as intermediate articles of manufacture for producing parts from the blanks.
The production of blanks, or more complex parts such as stamped gears or sprockets, is typically carried out either by a conventional stamping process or by a “fine blanking” process.
In the conventional stamping process, the cooperating punch and die produce an initial shearing action after which the blank is severed from the surrounding stock material by fracturing. This results in the stamped gears or blanks having a disadvantageous feature known in the art as “die break.” A ridge, known as “shear,” extends around the edge of the stamped blank and divides the portion of the blank that has sheared from the portion that has fractured. The fractured portion is the “die break,” and is rough and granular in nature. As the thickness of the stock from which the blank is produced increases, so does the problem of die break.
In order to obtain a smooth-edged piece (that is, a blank or gear having a vertical side edge without shear), a secondary operation called “shaving” is, in traditional prior art, required. Besides being an additional manufacturing step, shaving is disadvantageous in that the amount of material being removed is very small, e.g. approximately 0.010 inch, and is typically in the form of metal slivers. These small pieces may be difficult to remove from the manufacturing machine. Another problem with shaving is that if the metal has a yield strength exceeding 60,000 PSI, small tears may form in the side of the blank. In a gear, these tears (which develop in the gear teeth) may make the gear unacceptable for use.
Another disadvantage in producing gears using conventional stamping methods is that the gear teeth may be deformed on the die-side of the gear blank. This deformation is called “die roll” or “pull down”, and can exceed 60% of the material thickness.
The problem of die break is largely averted by using the fine blanking process. One such fine blanking machine is disclosed in U.S. Pat. No. 3,570,343 to Wolnosky et al.
Fine blanking is an extrusion process carried out by clamping the blank and stock material in such a manner as to prevent die break when the extrusion punch and die perform the blanking operation. Although fine blanking eliminates the die break portion of the blank, it suffers from substantial drawbacks.
Two of the most serious problems with fine blanking are the need to provide a special press and the slow operational speed of such a press. Typically, the special press is a triple action punch press which operates to provide three required forces: shear pressure, “vee ring” pressure, and counter pressure. The required special press is particularly expensive and must be extremely robust to provide sufficient support to absorb reaction, sudden pressures, and vibration.
Additionally, fine blanking presses must securely clamp both the blank and the stock material from which the blank is stamped. To this end, it has been necessary to provide a special component feature to encircle the area to be blanked out. That special component conventionally comprises an upstanding pointed ridge which serves to engage and bite into the stock material around the area to be blanked out. The ridge is termed a “stinger” and may be embodied in a tooling component known as a blanking die, or may be embodied in a tooling component known as a “stripper,” which is utilized to remove the surplus stock material after the stamping or blank has been removed. In either event, the precise location of the stinger and the need to securely clamp the surplus blank material necessarily results in a press which is intricate, expensive, and cumbersome. Also, the use of a stinger requires sufficient surplus stock material to permit the desired clamping, thereby causing waste.
Furthermore, when it comes to producing tooth forms, for gears or sprockets for example, the fine blanking process is limited. As a general rule, for fine blanking, the tooth thickness at the pitch radius should be equal to 60% of the stock thickness. This may be unacceptable. Also, to prevent die break, the roots and crests of the gear teeth must be radiused, and in cases where tooth width approaches a minimum limitation (typically around 40% of stock thickness), die roll at the tips of the teeth will be considerable.
These limitations regarding gear and sprocket production also apply to the conventional stamping methods, and to the GRIP FLOW® brand metal stamping apparatus disclosed in U.S. Pat. Nos. 4,267,753 and 4,951,537 issued to the present inventor. As such, it has been necessary to employ secondary, additional operations to produce acceptable gear teeth, e.g. gear hobbing, gear cutting, gear broaching, gear grinding, etc. These methods require expensive machines, skilled labor, high maintenance costs, and operate at limited production speeds.
SUMMARY OF THE INVENTION
Wherefore, it is an object of the present invention to overcome the aforementioned problems and drawbacks associated with the prior art designs.
Another object of the invention is to provide a stamping die that produces metal parts that are extremely true to measurement and that have cut surfaces equal in quality to those which can be machined.
Yet another object of the present invention is to provide a stamping die capable of manufacturing metal parts having complex perimeter edge configurations, such as gears, sprockets, and gear racks.
Another object of the invention is to provide a stamping die for producing gears, sprockets, and the like, having straight sided, uniform gear teeth.
Still another object of the present invention is to provide a stamping die that eliminates the need for metal shaving, and that can be configured to reduce mess and stamping die contamination, both of which limit production speed.
To attain these and other objects, the present invention provides a stamping die that produces gears or other parts having quality tooth forms with smooth and straight edges. The parts are preferably made from pre-stamped, smooth edged metal blanks having substantially the same diameter as the parts to be manufactured.
A bottom portion of the stamping die includes a non-moving trim punch whose perimeter shape corresponds to the shape of the desired part. The trim punch extends through a complementary shaped opening provided in a biasable stripper plate, which surrounds the trim punch and is vertically moveable with respect thereto. The stripper plate further includes a recess surrounding the trim punch for aligning the blanks.
An upper portion of the stamping die is precisely aligned and vertically moveable with respect to the lower portion. The upper portion is mounted to the punch press ram. Connected to the underside of the upper portion is a trim die. The trim die has a concentric bore disposed therethrough whose perimeter is also in the shape of the desired part. The trim die bore is aligned with the trim punch, and there is only a minimal radial clearance between the two (i.e. the trim die bore is dimensioned to allow the trim die bore to enter therein with a mi
Choi Stephen
Davis & Bujold P.L.L.C.
Peterson Kenneth E.
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