POWDERED METAL MULTI-LOBULAR TOOLING AND METHOD OF FABRICATION
Background
This invention generally relates to multi-lobular tooling for punching a multi-
lobular recess into, for example, the head of a fastener. The invention more
specifically relates to multi-lobular tooling and tooling blank which are formed of
powdered metal. The invention also relates to methods of forming a powdered metal
multi-lobular tool.
Multi-lobular tools, often referred to as "punch pins," are used to punch a
multi-lobular recess into, for example, the head of a fastener. Figure 1 illustrates a
multi-lobular punch pin 10. In use, the head 12 of the punch pin 10, i.e., having a
multi-lobular profile, is punched into a workpiece, such as the head of a fastener, to
form a multi-lobular recess.
Typically, punch pins are formed of standard tool steel such as M42 tool steel.
Tool steel, by nature, is very nonhomogeneous, and typically contains large, often
segregated carbides. Figure 2 provides an image of a punch pin formed of M42 tool
steel, where the image was taken with a microscope at 400x, along a transverse cross-
section (i.e., along line 2 in Figure 1). Figure 3 is similar, but is an image taken along
a longitudinal cross-section (i.e., along line 3 in Figure 1). As shown, carbides (the
lighter areas in the image), many of which are relatively large, can be found along
either cross-section. With regard to size, in a punch pin formed of conventional tool
steel, carbides as large as 10-50 microns or even larger often exist.
The presence of a carbide segregation tends to produce a hard, brittle or
weakened plane, wherein the material has a tendency to fracture or splinter. Generally
speaking, it is undesirable for a punch pin to contain large carbides and carbide
segregation, as carbides provide a point of weakness. This is especially true if a fairly
large carbide happens to exist along a lobe of a multi-lobular punch pin. In such case,
the carbide may cause the lobe to chip prematurely during use, as shown in Figure 4.
Figure 4 provides an image of a punch pin formed of M42 tool steel, where the image
was taken with a scanning electron microscope (SEM) at 35x, after the punch pin was
used in a number of cycles to punch multi-lobular recesses into workpieces. Not only
does it present a possible problem when a large carbide exists on a lobe of a punch
pin, but the problem is even more severe the larger the punch pin.
United States Patent No. 6,537,487 discloses a method of molding a powdered
metal part using a metal injection molding ("MIM") process. Such a process is
relatively complicated and uses a binder. The binder must be removed (i.e., de-
binding) during sintering, or prior to sintering. A finished part made with such a
process typically is only 95 to 98% dense, and has diminished column strength and
limited impact resistance.
Objects and Summary
An object of an embodiment of the present invention is provide a multi-lobular
tool and tool blank which are formed of powdered metal, thereby providing that the
tool is very homogenous and contains only carbides of an extremely small nature.
Yet another object of an embodiment of the present invention is provide a
relatively simple method of fabricating a multi-lobular powdered metal tool, where the
method does not require any de-binding steps, either prior to or during sintering.
Briefly, and in accordance with at least one of the foregoing objects, an
embodiment of the present invention provides a tool made of powdered metal, such as
a modified (in that molybdenum is added) T15 high speed steel (HSS) in powdered
form, and having a multi-lobular end profile for punching multi-lobular recesses into
workpieces, such as into the heads of fasteners.
Another embodiment of the present invention provides a method of fabricating
a tool made of powdered metal, where the tool has a multi-lobular end profile. The
method includes steps of: cutting a predetermined length from a rod formed of
powdered metal, such as a modified T15 HSS (modified in that molybdenum is
added); applying a 47 45° chamfer to both ends; grinding the outside diameter to a
predetermined size; applying oil and extruding a multi-lobular configuration on one
end of the cutoff in the extrusion die that is secured in a punch press; stress relieving
the part in a heat treat furnace; coining a trademark (if desired) onto the part; grinding
the outside diameter to a predetermined size; facing to predetermined length; shaving a
nose angle; heat treating to a predetermined hardness; grinding the nose angle to
achieve a desired finish and length; grinding the outside diameter step to a
predetermined size and length; and polishing the nose angle to desired finish.
Brief Description of the Drawings
The organization and manner of the structure and operation of the invention,
together with further objects and advantages thereof, may best be understood by
reference to the following description, taken in connection with the accompanying
drawings, wherein like reference numerals identify like elements in which:
Figure 1 is a perspective view of a multi-lobular punch pin;
Figure 2 provides an image of a punch pin formed of M42 tool steel, where the
image was taken with a microscope at 400x, along a transverse cross-section (i.e.,
along line 2 in Figure 1);
Figure 3 is similar to Figure 2 , but where the image has been taken along a
longitudinal cross-section (i.e., along line 3 in Figure 1);
Figure 4 provides an image of a punch pin formed of M42 tool steel, where the
image was taken with a scanning electron microscope (SEM) at 35x, after the punch
pin was used in a number of cycles to punch multi-lobular recesses into workpieces;
Figure 5 provides an image of a punch pin formed of a modified T15 HSS in
powdered form, in accordance with an embodiment of the present invention, where the
image was taken with a microscope at 400x, along a transverse cross-section (i.e.,
along line 2 in Figure 1);
Figure 6 is similar to Figure 5 , but where the image has been taken along a
longitudinal cross-section (i.e., along line 3 in Figure 1);
Figure 7 provides an image of a punch pin formed of a modified T15 HSS in
powdered form, where the image was taken with a SEM at 5 Ox, after the punch pin
was used in a number of cycles to punch multi-lobular recesses into workpieces; and
Figure 8 provides a flow chart of a method of fabricating a multi-lobular tool,
such as a punch pin, where the method is in accordance with an embodiment of the
present invention.
Description
While the present invention may be susceptible to embodiment in different
forms, there are shown in the drawings, and herein will be described in detail,
embodiments thereof with the understanding that the present description is to be
considered an exemplification of the principles of the invention and is not intended to
limit the invention to that as illustrated and described herein.
As discussed above, Figures 2-4 relate to a punch pin formed of M42 tool steel.
Figures 5-7 provide similar views, but relating to a multi-lobular tool, specifically a
punch pin, formed of a modified Tl 5 HSS in powdered form (modified in that
molybdenum is added), in accordance with an embodiment of the present invention.
As a result of being formed of powdered metal, the punch pin is much more
homogenous and contains only carbides (the lighter areas in the images shown in
Figures 5 and 6) which are relatively small, compared to carbides which are typically
contained in a punch pin formed of tool steel. As a result of being more homogenous
and containing only relatively small carbides, the punch pin is very robust and not
prone to chipping or otherwise failing during use (i.e., while being used to, for
example, punch recesses in the heads of fasteners).
Figure 5 provides an image of the punch pin, where the image was taken with a
microscope at 400x, along a transverse cross-section (i.e., along line 2 in Figure 1).
Figure 6 is similar to Figure 5, but where the image has been taken along a
longitudinal cross-section (i.e., along line 3 in Figure 1). As shown in Figures 5 and 6,
the carbides (the lighter areas in the images) are relatively small compared to those
present in the tool steel punch pin, as shown in Figures 2 and 3. Specifically, while
the carbides present in a punch pin made of tool steel can be 40 microns or more,
providing that the punch pin is formed of powdered metal, such a modified T15 HSS
in powdered form, provides that the carbides can be as small as 1-4 microns.
Figure 7 provides an image of the punch pin, where the image was taken with a
SEM at 50x, after the punch pin was used in a number of cycles to punch multi-lobular
recesses into workpieces. Comparing Figure 7 to Figure 4, the powdered metal punch
pin (Figure 7) exhibits merely acceptable wear with no chipping, while the tool steel
punch pin (Figure 4) exhibits some chipping at a lobe.
Because large carbides provide a point of weakness, and the lobes of a multi-
lobular tool, such as a punch pin, receive a lot of the stress during impact, it is
important to provide or insure that large carbides do not exist at a lobe of a multi-
lobular tool. Typically, multi-lobular tools, such as punch pins, are formed of tool
steel which is very non-homogenous. Providing that the multi-lobular tool is instead
made of powdered metal, such as a modified T15 HSS in powdered form, provides
that the grain structure of the part is much more homogenous. As such, there is less of
a likelihood or even no likelihood, that large carbides will exist in the area of, or on
one of the lobes. As a result, the punch pin is more robust and has improved column strength and impact resistance, and will have a longer useful service life.
Figure 8 illustrates a method of fabricating a powdered metal multi-lobular
tool, such as a punch pin as shown in Figures 5-7, where the method is in accordance
with an embodiment of the present invention. As shown, the method provides the
following steps: cutting a predetermined length from a rod from bar stock formed of
powdered metal, such as a modified T15 HSS (modified in that molybdenum is
added); applying a 47 45° chamfer to both ends; grinding the outside diameter to a
predetermined size; applying oil and extruding a multi-lobular configuration on one
end of the cutoff in the extrusion die that is secured in a punch press; stress relieving
the part in a heat treat furnace; coining a trademark (if desired) onto the part; grinding
the outside diameter to a predetermined size; facing to predetermined length; shaving a
nose angle; heat treating to a predetermined hardness; grinding the nose angle to
achieve a desired finish and length; grinding the outside diameter step to a
predetermined size and length; and polishing the nose angle to desired finish. The
process is relatively simple, and does not require any de-binding steps, as opposed to a
metal injection molding process, where a binder must be removed during sintering, or
prior to sintering. A finished part made with such an injection metal molding process
typically is only 95 to 98% dense. In contrast, a finished part fabricated with the
above-described method is theoretically 100% dense, and has improved column
strength, impact resistance, and tool life.
To provide the powdered steel bar, before perfoπning the fabricating steps
described above, the following process may be used:
1. Molten metal, of the proper composition, is atomized in an inert
atmosphere.
2. The resulting powered metal is sealed in a large steel "can" which
is a steel pipe 5 to 6 feet long and 10 to 12 inches in diameter.
3. The sealed can is placed in a hot isostatic press ( HIP ) which
exerts a pressure of 1000 atmospheres at a temperature 2100F.
4. After the HIP process, the steel can is machined off of the now
solid and 100% dense P.M. ingot.
5. The P.M. ingot is then processed like a conventionally poured ingot. While embodiments of the present invention are shown and described, it is
envisioned that those skilled in the art may devise various modifications of the present
invention without departing from the spirit and scope of the disclosure.