Patent Application
20120012024
Ammunition includes metallic cases or cartridges, commonly made of brass, which each package a bullet, gunpowder, and primer. The filled cartridge is formed to precisely fit a firing chamber of a firearm.
The manufacture of such brass cartridges is generally known to include annealing a cup of heavy-gauge brass and deep drawing the cup through a multi-stage press arrangement into a final shape of the cartridge. The process for brass further includes ironing cartridge sidewalls during drawing and re-drawing processes to taper the walls with respect to the base, with multiple intermediate anneals conducted between the deep drawing processes.
Brass, having a sufficiently low work hardening rate and low frictional forces, is usable with a multiple annealing and sidewall ironing process, and is suitable for such a deep drawing process including heavy sidewall ironing Steel, by contrast, has properties such as a high work hardening rate, high strength, and high frictional forces. These properties can lead to galling and scoring issues, which typically result in reduced die life and make heavy sidewall ironing during repeated re-drawing and annealing steps difficult and not generally feasible. Also, while carbon steel has been used to form cartridges, such cartridges included waxing, or application of a protective coating, to prevent rust.
While the specification concludes with claims which particularly point out and distinctly claim the invention, it is believed the present invention will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements and in which:
The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.
The following description of certain examples of the invention should not be used to limit the scope of the present invention. Other examples, features, aspects, embodiments, and advantages of the invention will become apparent to those skilled in the art from the following description. As will be realized, the invention is capable of other different and obvious aspects, all without departing from the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not restrictive.
The Blank
Blank (10) may be formed of a metal including but not limited to austenitic stainless steel. Austenitic stainless steel is known to those of ordinary skill in the art. It is an alloy including chromium and nickel, having austenite as a primary phase. This alloy exhibits high ductility, low yield stress, and high tensile strength when compared to other steels. An austenitic stainless steel composition may comprise, for example, weight percentages of approximately no more than 0.045% C, no more than 0.60% Si, from about 0.03% to 0.06% N2, from about 1.0% to about 1.4% Mn, from about 17.2% to about 17.8% Cr, from about 3.1% to about 3.4% Cu, from about 8.1% to about 8.4% Ni, no more than 0.035% P, no more than 0.002% S, and no more than 0.4% Mo. Alternatively, the austenitic stainless steel composition may comprise, for example, weight percentages of approximately 0.035% C, 0.45% Si, 0.045% N2, 1.2% Mn, 17.5% Cr, 3.25 Cu, 8.25% Ni, a low weight percentage of each of P and S, and 0.2% Mo. The above-described compositions are shown in TABLE 1 below, where M=maximum amount.
In a cold-rolled and annealed condition, such an austenitic stainless steel may have mechanical properties including 0.2% yield strength=31.5 ksi; ultimate tensile strength (UTS)=77.5 ksi; total elongation to fracture (based on an original gage length of 2″)=52.5%, and n-value (10% to Ult.)=0.404, and hardness of 68 HRBW. Such properties may be retrieved from a standard uni-axial tension test, conducted in accordance with ASTM E 8 and A 370. The n-value or strain hardening exponent is obtained at the same time but method of determination is covered under ASTM E646. Material tested in the examples described below, and the austenitic stainless steel described above, for example, may be melted, hot rolled between from about 2250° F. to about 2320° F., strip annealed between from about 1950° F. to about 2000° F., cold rolled, and finally annealed at about 1950° F.
The blanks may be prepared by any method known in the art.
The blank may be spin formed as shown in
Blank (10) includes a machine contacting surface (36) and an opposite underside surface (38). Surfaces (36, 38) are disposed generally parallel to one another. Blank (10) includes central axis (B) that is substantially perpendicular to head contacting surface (36). Blank (10) rotates about central axis (B) while one or more arms (22) of the rolling machine rotate about respective longitudinal axes (A) such that blank contacting surface (28) of head (26) of a rotating arm (22) works against machine contacting surface (36) of blank (10) to form button (14) and outer region (16), button (14) having a greater thickness than outer region (16). Alternatively, arms (22) may rotate while blank (10) remains stationary.
Alternatively, as shown in
The blanks may be compression formed by cold forming, warm forming, hot forming, or forging under straight compressive loading. As shown in
Further, the process may involve using a three-die compression tooling design. The first and second dies may appear similar to that shown in
Alternatively, an exemplary grinding operation as shown in
Alternatively, as shown in
Alternatively, as shown in
Alternatively, tooling (76) to form the blanks may be used. Such tooling includes inserts (78) and blocks (80) as shown in
An alternative exemplary tooling is made from Carpenter 883 (type H15) tool steel, made by CARPENTER TECHNOLOGY CORPORATION of 2 Meridian Blvd., Wyomissing, Pa., 19610-1339, which is a 5% chromium hot working tool steel usable for applications requiring extreme toughness. For example, the type H15 tool steel is known to have an ability to be used in hot forming and/or forging. With such steel tool, forming may be conducted at room temperature under static loading. An option is provided with the tooling to attempt to heat the die and the material. The type H15 tool, however, performs well with respect to cold forming as the tooling resists cracking and distortion to the loading surface (i.e., the surfaces remain flat and parallel).
Any shape for such tooling can be used as will be apparent to those of skill in the art in view of the teachings herein. For example, such tooling may include cylindrical blocks that are sized to create properly sized blanks. Alternative exemplary tooling may include S-7, which is an air hardening grade tool steel with 0.55% carbon, 3.25% chromium, and 1.4% molybdenum. Any tool steel can be used as will be apparent to those of skill in the art in view of the teachings herein based on factors such as cost and desired production life.
The above described tooling can be heat treated. A method of heat treating exemplary tooling, such as the above-referenced type H15 tooling, includes sealing the tool, or tooling, in stainless steel bags. The bags minimize surface oxidation of the tooling during the annealing process. Tooling should be protected from oxidation during the annealing either physically during annealing via a cover or protective holder such as the stainless steel bags or chemically via a controlled atmosphere. For example, in a controlled atmosphere, the bags would not be necessary.
The bags containing the tool steel are placed directly in a furnace at 1400° F. for 4 hours, heating from 1400° F. to 1850° F. at 50° F./hour increments, and holding at 1850° F. for 6 hours. The bags are then removed from the furnace and air cooled to 650° F. At 650° F., the bags are placed into the furnace and cooled at 50° F./hour increments to 200° F. and then air cooled once more to 120° F. Tempering occurs by placing the tooling in the furnace at 1000° F. for 6 hours and then air cooling to room temperature. Finally, the surfaces of the tooling are polished.
With respect to tooling including a center hole, the hardness of the blocks may be in the range of from about 54 HRC to 63 HRC, and without a center hole the hardness may be about 48-49. Generally, as hardness increases, so does strength; however, the material also becomes more brittle. An estimated yield strength based on hardness may be in the range of from about 200 ksi to 220 ksi.
While use of tooling with intermediate annealing steps are presented in the examples below, use of an annealed blank without any further annealing steps after beginning work operations on the blank are within the scope of this disclosure.
Exemplary Formation of Blanks into Cartridges
Blank (10) of
Additional required forming operations include the following: (1) an operation to form a reduced neck diameter, (2) an operation to form the cartridge rim, and (3) an operation to create a region in the rim that is configured to accept a primer cap, for example. The forming operations used may ones known to those of ordinary skills in the art that will be apparent in view of the teachings herein.
The blanks described in the examples below were pre-annealed. The initial blanks were formed from material going through a 50% to 60% cold reduction followed by a full anneal.
The forming process was tried on easier-to-form low carbon steel, having lower strength with lower work hardening than a higher carbon steel and having a range of about 0.05 to 0.15 C, for example. A 600 Kip Tinius Olsen universal testing machine and hardness blocks were used to conduct trials on the low carbon steel, for example, initially with a blank originally having a 2.06″ diameter and 0.04″ thickness. Starting at 100 Kip, the blank was loaded in 50 Kip increments such that a final blank was 2.22″ in diameter and 0.031″ thick at a center portion with a gradual taper to the edge, which had a 0.021″ thickness. A smaller blank with a diameter of 1.53″ was then tested to get higher compressive stress for the same amount of force. The final diameter for the smaller blank was 1.70″, the final center thickness was 0.0307″, and the final edge thickness was 0.016″.
An ASTM specification T301 stainless steel blank was formed. The T301 stainless steel blank had mechanical properties closer to the austenitic stainless steel composition described above, though the T301 stainless steel blank had a higher work hardening rate. The T301 stainless steel blank had an original diameter of 1.53″ and original thickness of 0.0472″. Going to 300 Kips in 100 Kip increments, a final diameter of 1.625″, final center thickness of 0.045″, and final quarter edge thickness of 0.039″ resulted. Hardness blocks were used as compression tools and, as such, were not shaped but were, for example, substantially flat. Hardness blocks were used as they were contemplated to be in the hardness range most suitable for this application. The hardness blocks used were 42 HRC and were slightly deformed after the forming was completed. These blocks were replaced with blocks of 62 HRC. The process was repeated, loading to 350 Kip, and unloading at 400 Kip. The final diameter was 1.64″ with a hardness of 85-100 HRB. When annealed at 1825° F., the hardness dropped to 53-58 HRB. After ultimately loading to 400 Kips, the final diameter was 1.76″, the final center thickness was 0.043″, the final edge thickness was 0.030″, and the final hardness was 90-93 HRB. The hardness blocks of 62 HRC eventually cracked, and it is expected that thicker blocks might prevent such cracking. Other tooling produced from S-7 tool steel and which generated forces up to 2.4 million lbs was later used and did not crack.
An ASTM specification T305 stainless steel blank was formed. The hardness blocks were replaced with compression plates, which included one flat plate and one with a 0.5″ diameter central hole. The plates were machined from available D-2 tool steel.
Tooling was next machined to include a central opening to make buttons (14) and was designed with replaceable compression inserts. The base was made from O-6 tool steel and inserts made from D-2 tool steel, and both base and inserts were in the high 50 HRC hardness range.
The T305 stainless steel blank was formed by loading to 250 Kips in 50 Kip increments, with a complete unloading between increments. Thickness was measured at three locations: the center (“T1”), ⅛″ from button (“T2”), and ⅛″ from the outer edge (“T3”). The final measurements followed: diameter=1.61″, T1=0.048″, T2=0.0414″, and T3=0.039″. The material was then loaded to 300 Kip, 350 Kip, and 400 Kip, resulting in the following final measurements: diameter=1.63″, T1=0.048″, T2=0.040″, and T3=0.039″. Hardness at position T2 was approximately 59.3 HRA (96.5 HRB), and hardness at position T3 was about 61.3 HRA (22 HRC). This test resulted in the tooling cracking and the central button dimpling up. The dimpling up was a result of the material being forced into an open region during compression. Thus a desired thickening occurred with an undesired buckling, resulting in realization of the need to have tougher tooling and to control the height of the opening. For example, a rod was inserted in an initial trial open hole in the tooling insert to form the button and to allow for proper clearance. Spacers were used to control the height of the tooling with respect to the blank in a vertical direction to prevent the material from buckling up. The height may be fixed or adjustable via spacers, for example.
A plate or insert with 0.5″ central opening was used on both the top and bottom ends of the tooling to address dimpling. An insert to control height was used on only one side. Another blank with a diameter of 1.5″ was loaded to 250 Kips in 50 Kip increments, resulting in the following final measurements: diameter=1.6″, T1=0.050″, T2=0.0424″, and T3=0.090″. The central button did not dimple as severely but did bulge such that the top surface did not remain completely flat. Additional shims were added to the top surface of a rod inserted in the central opening of the tooling to lower the height of the insert and adjust the clearance downwards.
A standard grade T305 stainless steel button blank was used. The buttons were cold reduced at room temperature four times with intermediate anneals at 1850° F. after each compression cycle. The blank was loaded to 400 Kips (approximately 205 ksi of stress over the surface area) on the first cycle, then to 300 Kips (approximately 151 ksi of stress over the surface area), then to 350 Kips (approximately 148 ksi of stress over the surface area), and then to 375 Kips (approximately 155 ksi of stress over the surface area). After the fourth cycle, average thinning was measured at 39.7%. The annealing temperature was 1825° F. for 30 minutes for each annealing process.
With respect to the first work operation, the original diameter was 1.5″, the original thickness for T1, T2, and T3 were each equal to 0.047″. The final measurements after the first work operation follow: diameter=1.63″, T1=0.048″, T2=0.414″, and T3=0.039″. A hardness at T2 was measured at 97 HRB pre-anneal, and after annealing at 1825° F. at 54 HRB.
With respect to the second work operation, the starting measurements were the same as the final measurements for the first work operation set forth above. The final measurements for the second work operation follow: diameter=1.7″, T1=0.0486″, T2=0.0367″, T3=0.0332″. A post-anneal hardness was measured at T2 at 62.5 HRB.
With respect to the third work operation, the starting measurements were the same as the final measurements for the second work operation set forth above. The final measurements for the third work operation follow: diameter=1.78″, T1=0.0494″, T2=0.033″, T3=0.0295″. A hardness at T2 was measured at 88 HRB pre-anneal, and after annealing at 1825° F. at 76 HRB.
With respect to the fourth work operation, the starting measurements were the same as the final measurements for the third work operation set forth above. The final measurements for the fourth work operation follow: diameter=1.86″, T1=0.049″, T2=0.0302″, T3=0.0265″.
Inserts of the tooling initially cracked under the formation process prior to the base fracturing. Forces used were up to 400,000 lbs. The button blank expanded from approximately about 1.5″ to about 1.9″ and achieved approximately 40% thinning with two intermediate anneals.
An austenitic stainless steel composition, as described above, of low work hardening characteristics, was formed into blanks. Austenitic stainless steel was reduced to 0.060″ thickness and annealed for another set of trials. Material was machined into 1.5″ diameter blanks that were reduced about 20% in thickness in a first compression cycle. Tooling heat-treated per the exemplary method described above was used, and button blanks received intermediate anneals and were reduced in thickness several more times, as described below.
The sequence used was as follows: loading 350 Kips of compressive force and then annealing the material at 1950° F., then loading to 425 Kips and annealing at 1950° F., followed by loading to 475 Kips and annealing at 1950° F., and finally to loading at 500 Kips and annealing at 1950° F. After each reduction, the initial hardness of 44.7 HRA was increased to an amount in the range of between 54.2 HRA to about 63.5 HRA, and after each anneal was decreased to an amount in the range of between 40.6 HRA to 44.1 HRA, as shown below in TABLE 2. Grain structure was inspected after the fourth anneal and found to be consistent with the grain structure of the original material.
TABLE 2 shows the measurements taken for hardness after each reduction and anneal. The codes represent four different button specimens tested, such that code 8 refers to a first button tested, code 16 refers to a second button tested, code 35 refers to a third button tested, and code 46 refers to a fourth button tested.
Referring back to the tested sequence, after a first reduction, the center thickness was measured at 0.0629″, the percentage thinning of the outer region was measured at 19.79%, and the diameter was measured at 1.64″. After the second reduction, the center thickness was measured at 0.0653″, the percentage thinning of the outer region was measured at 32%, and the diameter was measured at 1.75″. After the third reduction, the center thickness was measured at 0.0681″, the percentage thinning of the outer region was measured at 41.24%, and the diameter was measured at 1.87″. After the fourth reduction, the center thickness was measured at 0.0695″, the percentage thinning of the outer region was measured at 46.50%, and the diameter was measured at 1.95″.
In addition, some sequences were finally loaded to 600 Kips, such higher forces resulting into about an additional 5% of thinning, or just over 50% total thinning. For example, button blanks were cold reduced four times with an intermediate anneal after each forming stage and were compressed to a stress level of about 180 ksi in each stage. A total reduction level was achieved of just over 50% thinning with a final diameter of about 2.1″.
Having shown and described various embodiments of the present invention, further adaptations of the methods and systems described herein may be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. Several of such potential modifications have been mentioned, and others will be apparent to those skilled in the art. For instance, the examples, embodiments, geometrics, materials, dimensions, ratios, steps, and the like discussed above are illustrative. Accordingly, the scope of the present invention should be considered in terms of the following claims and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/364,263, filed Jul. 14, 2010, entitled “CONTOURED THICKNESS BLANK FOR AMMUNITION CARTRIDGES,” the disclosure of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61364236 | Jul 2010 | US |
