HK1207839B - A method of making a cartridge case on a single progressive forming machine - Google Patents

Description

Method for manufacturing cartridge cases on a single progressive forming machine

Technical Field

The present invention relates to cartridge casings and their manufacture.

Background

Brass cases for firearm ammunition are usually manufactured in a number of steps on continuous machines, usually with an intermediate annealing step. Traditionally, the shell is manufactured from a strip of material which is formed into a cup shape and then drawn. Once drawn, the blank is machined to length and an emitter slot is provided. The strand method produces a high scrap rate, requires energy for annealing, is slow, and occupies considerable floor space. It is known to cold form hollow thin-walled intermediate blanks for cartridges from solid wire. Whether manufactured from strip or wire material, when producing a redraw preform, it has irregular edges on the open end which, typically, is machined to a precise end surface after ejection from the forming tool. After exiting the forming tool, the preform is also typically machined to create an emitter pocket near its head or trailing end.

These known methods of manufacturing cartridge cases have a number of additional drawbacks. Transferring the shell preform from, for example, one working face of the forming machine to a working face of the rotating machine will cause dimensional variations that can be difficult to manage due to the various possible combinations of machines used to make the shell. Transferring blanks between successive machines typically involves labor costs, and each machine must be monitored and maintained, adding additional cost and variability to the manufacture of the shells. Machining operations generate waste, particularly in the form of chips and/or dust, creating maintenance and waste recovery problems.

Disclosure of Invention

The present invention provides an improved cartridge case and method and apparatus for its manufacture. The shell is formed entirely of metal wire (typically brass) cold in a single forming machine. The shell of the present invention is of the solid head type without edges, with an emitter slot at the head end. The shell is formed into the final shape at high production speeds and material removal is limited to cutting a short ring from the front end of the deep drawn cylindrical wall to obtain a uniform edge and punching out smaller pieces to form the fire-through holes. The emitter slot is formed entirely on the blank without corresponding material removal. The forming method improves the metallurgical properties of the blank, particularly at critical areas of the emitter slot. The method of the present invention makes the shell less susceptible to failure through cracks or other damage that may occur during assembly, use, and reloading.

The method of the present invention begins with a blank cut from a solid wire. The blank is upset and squeezed to form the initial stages of the primer pocket, the tubular charge and bullet space and the launcher groove. In a later forming stage, the blank area associated with the primer pocket is upset and folded radially outward to form the rear wall or flange of the launcher slot. The tubular part, which is a preform for the charge and bullet space, is deep drawn axially into a thin walled tube and then trimmed at its distal end by shearing with a novel rail. After finishing the trimming, the thin walled tube is forged to a slightly conical shape. The shell is completed in the forming machine and no additional machining or annealing is required.

Drawings

FIGS. 1A-1I illustrate progressive forming steps for making a cartridge case, beginning with a solid wire severing the blank and ending with a finished case, embodying aspects of the present invention;

FIGS. 2A-2D schematically illustrate a forming apparatus and instrument, including tools, for performing the steps shown in FIGS. 1A-1I;

FIG. 3 is a perspective cut-away view of a mold station wherein a preform emitter slot is formed in the blank;

FIG. 3A is an enlarged view of a mold portion used in the station shown in FIG. 3;

FIG. 4 is a cross-sectional view of a blank end trimming station;

FIG. 4A is an enlarged view of the cutting area of the blank end trimming station; and

figure 5 is a partial cross-sectional view, on a larger scale, of the mouth of the cartridge casing of the present invention.

Detailed Description

Although the solid head cartridge cases of the present invention are sometimes referred to as "rimless", it should be understood that this term is used for belt cases (belted cases) in which their heads are slightly larger than the front area of their bodies. Although the industry is entitled "rimless," the radially outer portion of the cartridge case head, rearward of the launcher slot, can be considered a rim.

Referring to fig. 1A-1I, a preferred sequence for forming the final cartridge shell in a progressive forming or forging machine is shown, starting with a solid wire material. The blank 10 shown in fig. 1A is cut from coiled round wire material by a shearing operation that is synchronized with other operations of the forging machine, described in more detail below. A conventional transfer device (having axially moving components, not shown) operates to move the blank 10 from one station to the next, i.e., from right to left in fig. 1A-1I. In the first forming station (fig. 1B), the blank 10 delivered from the cutting station (fig. 1A) is upset to flatten its sheared end faces. At the second forming station (fig. 1C), the blank 10 is formed with dimple centers 11, 12 on its end faces to improve the concentricity of formation in the subsequent forming step. In the third forming station (fig. 1D), the blank 10 is triple extruded to form a cylindrical preform of the tubular wall 13 of the shell cavity, the outer surface of the final emitter slot 14 and a preform of the priming recess or pocket 16.

At the fourth station (fig. 1E) the preform of the shell cavity wall 13 is deep drawn to form the wall and another intermediate preform stage of the charge and bullet cavity 19. At the fifth station (fig. 1F), the initial shape of the head 18 of the blank is formed into the pre-fabricated emitter slot 14. At the sixth station (fig. 1G), the end of the shell cavity wall 13 is cut to final length. At the seventh station (fig. 1H), the transmitter slot 14 is finally formed. At the eighth station (fig. 1I), the outer diameter of the cylindrical preform wall is forged to a slightly conical shape to form the final cavity wall 13. The centre of the web 22 (representing the front part of the head 18) is pierced to form a fire-through hole 24, thus creating a final cartridge casing 25 in which the remainder of the web effectively closes the inner end of the cavity 19.

Fig. 2A-2D schematically illustrate a multi-station forming machine 30, which machine 30 includes tools, i.e., dies, punches and other instruments, to perform the steps described above to produce the final cartridge case 25 of the present invention. The lower portion of these figures shows the mold work surface or table 31; the line at 32 refers to a reference plane, sometimes referred to as the die Face (FOD) on the die face.

In fig. 2A-2D, the blank 10 is conveyed from right to left by the transfer mechanism and stopped at various stations for incremental formation. The transfer mechanism can be of a type similar to that shown in us patent 5713237 which enables the blank to be axially withdrawn from and inserted into the die of the workstation. The blank 10 is cut from the circular wire material 36 supplied by the coil by a cutter 37 and then passed to a first station 46. The billet produced in the shear cut preferably has a length to diameter ratio of at least 1.16, more preferably a ratio in excess of 1.5, and most preferably in excess of 1.7. In addition to the cutting station, the illustrated forming machine 30 has eight forming stations. The severing stations and successive stations are equally spaced along the horizontal. Each station on the die face 31 has a receiving or die hole 41 for a die casing and the reciprocating ram or slide 42 has a coaxial tool hole 43 for receiving a tool or punch shell. The cartridge case 25 described and shown is a 9mm case; although brass is commonly used to make the housing, other materials, such as steel or aluminum, may also be used in the practice of the present invention. At the first station, indicated by 46 at its centre line (and also in the subsequent stations), a sliding die ring 47 radially constrains a central portion of the blank 10. When upset by the punch 48, the ring 47 is able to slide axially relative to the associated die 39 so that it moves with the blank and does not significantly restrict the blank from adequately forming in the corners of the die. In the first forming station 46, the blank 10 takes the shape of pellets, having a length to diameter ratio of about 0.6.

At the second station 51, the blank is formed with dimple centers 11 and 12 on its end surfaces by a punch 52 and die 53 to improve tool and blank alignment in the next station.

In the third station 55, the blank 10 is triple extruded, wherein a preform of the walls 13 of the cartridge case cavity 19, a preform of the firing slot 14 and a preform of the priming charge pocket 16 are formed by the die assembly 56 and the punch assembly 57. The reduced outer diameter of the preform of the head 18 is slightly smaller, for example, about 0.35mm smaller than the diameter of the final radial bottom of the emitter pocket 14 (the final product shown in FIGS. 1H and 1I).

At a fourth station 60, on the left side of fig. 2B, the blank 10 is deep drawn over a punch 62 in a die assembly 61 through a progressively smaller disc 63 to form the thin preform wall 13 of the shell cavity 19. The free end of the drawn tube or wall 13 is normally characterized by an irregular edge.

At a fifth station 70, on the right side of fig. 2C, a preform of the emitter slot 14 is formed on the head end of the blank 10. This is accomplished by a segmented mold assembly 71, shown schematically in fig. 3 and 3A. Four segments 72 (only two of which are visible in these cross-sectional views) project radially inwardly around the billet as they are driven into tapered holes 75 of a die shell 73. By further advancement of the ram, the segment 72 is held closed by the high pressure lever 74 and gas spring 76 against the pressure created in the blank that will open the segment 72. The lever 74 operates on the segmented mold assembly through a rod 77. As described above, the minimum outer diameter of the preform of shell head 18 produced at third station 55 (FIGS. 1D and 2B) is generally the same as the bottom or minimum diameter of the preform of emitter slot 14 produced therein, although preferably slightly smaller. In the fifth station 70, the distal or outer end of the head of the blank is folded or upset radially outwardly to first create a preform rear flange wall or rim for the emitter slot. In their closed position, as shown in fig. 3 and 3A, the segments 72 collectively enclose an annular region that is precisely complementary to the edge and flute preforms, and therefore will fully define the head region of the blank when the punch 78 reaches the front dead center.

At the sixth station 80, the blank 10 is trimmed to remove the irregular free edge at the mouth of the draw shell cavity wall and to determine the final length of the cartridge shell. The blank material is preferably removed in one piece as a short scrap ring. The removal will be done in a shearing process which advantageously avoids the production of significant dust, particles and/or swarf of the stock material. Referring to fig. 2C, 4 and 4A, the trimming device (shown as 81) includes a blank holder 82 on the die surface 31 and a shear tool or punch device 83 on the ram 42. It will be appreciated that the clamping device 82 is operated by movement of the ram 42. The blank holder 82 fits into the upper and lower mold shell portions 86, 87. The upper mold shell portion 87 supports a pair of opposed grippers 88, 89 at the face of the mold plane 32 (when it is in its forward position in the mold shell bore 41). Relative movement between the lower and upper mold shell portions 86, 87 causes closing and opening of the opposed grippers 88, 89. Such gripper movement is generated by cams on the lower mold shell portion 86 (only one cam 91 is visible in the view of fig. 4) which operate levers on the upper mold shell portion 87 (only one lever 92 is visible in fig. 4). The cam 91 and lever 92 shown operate the lower gripper 89 while the cam and lever, not visible, operates the upper gripper 88. The mold shell portions 86, 87 are biased toward the ram 42 by respective gas springs. A gas spring 93 biases the lower mold shell portion 86 toward the ram; the gas spring associated with the upper mold shell portion 87 is not visible in the view of fig. 4. The shear plate 94 on the lower mold shell portion 86 is at a fixed axial distance in front of that portion. The transfer device conveys the blank 10 to the station 80 and places its priming charge preform on the alignment pin 96. Initial movement of the lower mold shell portion 86 relative to the upper mold shell portion 87 due to the leading edge plate 97 on the trimming device 81 contacting the shear plate 94 (driven by advancement of the ram 42) causes the grippers 88, 89 to engage and hold the blank 10 on opposite sides of the preform launcher slot. This clamping action benefits from the wedge created by the tapered sides of the preform emitter slot.

Further advancement of ram 42 causes lower housing portion 86 to drive upper housing portion 87 (against its spring bias). This displacement of the die shell portions 86, 87 (as explained later) enables the blank 10 to be trimmed over a relatively long portion of the ram retraction stroke.

The shearing device 83 mounted in the punch hole on the ram 42 at the sixth station 80 removes the shorter ring having the irregular edge formed at the free end or mouth of the cylindrical shell body (previously drawn at the fourth station 60). The device 81 comprises an elongated cam 101 extending along the axis of the station 80. At the distal end, the cam 101 holds a pin-shaped cylindrical cutting tool or cutter 102, which cutting tool or cutter 102 is made of a suitable hard tool steel, sized to fit into the open end of the billet cavity 19. The cam 101 is supported on two sets of four rollers 103. A set of rollers 103 (visible in fig. 4) is in a horizontal plane and two are above the cam 101 and two are below the cam. The other set of rollers (not visible in fig. 4) is in the vertical plane and two on one side of the cam 101 (below the plane of the figure) and two on the other side of the cam (above the plane of the figure). The roller 103 is journalled in a sleeve 104. The sleeve 104 is adapted to slide axially within a tool holder 106 secured to the ram 42. The outer profile of the cam 101 is made so that the drive cam is first laterally off-center from a "home" position concentric with the axis of the station 80 and then driven in a four-lobe orbital path so as to perform a full angular rotation about the station axis. The eccentric movement of the cam 101 is generated when the cam and the sleeve 104 are moved axially relative to each other.

When the ram 42 is close to the die face 31 and the grippers 88, 89 have locked into the emitter slot pre-form, the shear tool 102 enters the blank, the shear tool 102 having the general cylindrical shape and being centered first on the station axis. Shear plate 94 carries an annular insert or collar 107 of a suitable hard tool steel. The insert 107 has a central bore for relatively close sliding fit over the thin walled shell cavity. The various components are sized so that the cantilevered end of the tool 102 (having a radial end face with a sharp peripheral edge) is at the plane where the shell blank is to be trimmed. Similarly, the peripheral edge of the aperture of the insert 107 is sharp and lies substantially at the plane at which the blank is to be sheared. The axial clearance between the end face of the tool 102 and the edge of the bore of the insert 107 is as small as possible. The blank 10 is trimmed in this station 80 to determine its final length.

Fig. 4 and 4A show the positions of the tool 102 and the insert 107 when the ram is at the front dead center (the state where the ram 42 has no speed). The mold shell portions 86, 87 are fully retracted into the associated mold face holes 41. As the ram 42 retracts, the die housing portions 86, 87 and inserts 107 on the periphery of the billet move in unison with the ram 42 and shear pin tool 102, driven toward the ram by their gas springs. A synchronized ejector lever mechanism known in the art causes the sleeve 104 to remain stationary while causing the cam 101 to move with the ram 42. Leading edge plate 97 in combination with retainer 108 positions cam 101 to allow lateral movement of the cam, but not axial movement relative to ram 42. The outer peripheral edge of the tool 102 and the inner peripheral edge of the insert 107 cooperate in a shearing action to cut a scrap ring from the body of the casing blank 10.

The gas springs associated with the mold shell sections 86, 87 force the sections out of the mold bore as the head slides or rams 42 until the upper section 87 reaches its limit of movement in the mold body. As the ram 42 continues to retract, the transfer device grips the blank and the grippers 88, 89 open as the lower mold shell portion 86 continues to follow the ram under the force of its gas spring. Limited continued movement of the lower mold shell portion 86 will push the shear plate 94 away from the blank 10, thereby enabling the transfer device to grip and move the blank to the next station. The severed short ring of scrap is driven off the shear pin 102 by the air jet. The sleeve 104 is finally returned to its starting position by the synchronized ejector rod mechanism and the cam 101 and the shear pin 102 are likewise returned to their starting positions.

Figure 5 shows the unique shape of the cartridge mouth produced by the trimming device 81 of the present invention. The inner peripheral surface 105 is "radiused" or bellied at the edge 109 of the mouth of the final shell 25 by the internal cutting or shearing action of the shear pin tool 102. This outwardly flaring mouth geometry can facilitate the assembly of the projectile into the cavity formed by the shell wall 13.

The blank 10 is transferred to a seventh station 110. similar to the fifth station 70, a segmented mold assembly 111 is used in this seventh station 110. The tapered section 112 fits into a tapered bore 113 of a mold shell 114. The segment 112 is held closed against the build pressure by a large gas spring and lever (similar to that shown in figure 3). At this station 110, the case head including the launcher slot 14 is precisely finalized. The resulting head 18 includes an integral shoulder or "edge" having a forward facing radial side surface 116 that bounds the rear of the emitter slot 14. In addition, the emitter slot 14 is defined by a cylindrical bottom 117 and a tapered, rearward facing side or surface 118. When the ram 42 carrying the punch 114 reaches the front dead center, the segment 112 (when closed) and the die elements 121, 122 precisely determine and closely define the head 18, which head 18 includes the perimeter boundaries of the launcher slot 14 and the primer pocket 116. Preferably, the number of segments of the sliding die assembly in the fifth and seventh stations is 4, and the segments of the seventh station are offset from the segments of the fifth station by an angle of 45 degrees in order to reduce the possibility of flash on the blank (flash may occur between adjacent segments). Any head punch to be applied to the cartridge case 10 is preferably performed in the seventh station by the die elements 121, 122.

For the purposes of this disclosure, the head of the cartridge case 10 is the rearward portion of the front of the web 22. As previously mentioned, it is noted that in each forming stroke of the head material, the tool completely restrains the material at the front dead center of the ram stroke.

The blank 10 is passed to an eighth station 130 in which eighth station 130 the tubular thin cylindrical wall of the charge and bullet cavity 19 is forged to a slight taper in a punch assembly 131 and a die assembly 132. In addition, the web 22 between the primer pocket 16 and the charge and cartridge cavity 19 is pierced by the die core rod 133 at the axis of the station 130 to create the primer pierce hole 24. In this way, the blank 10 is completed in this station 130 and discharged as a final part.

The inventive method of cold forming the blank head 18 material in multiple forming steps creates a super grain structure at the launcher slot 14, resulting in a harder, stronger and accurately formed shell head that is less likely to jam or otherwise fail during the launch process.

The final casing wall 13 has a reduced tendency to fracture when compared to conventional cupped, drawn, annealed and machined casings, although it is not annealed. The reasons for such improved performance are not fully understood, and are presently believed to be due, at least in part, to the extreme cold work of the billet and the disintegration of its grain structure as it transitions from a wire billet having a relatively high length to diameter ratio (e.g., about 1.8) to a relatively flat shot-shaped billet having a relatively low length to diameter ratio (e.g., about 0.6). The relatively high length to diameter ratio also helps to eliminate the effect of cut distortion in the end face of the original shape of the blank.

Another factor in the resistance of the shell of the present invention to cracking may be the avoidance of particle patterns aligned with the tubular wall. It is clear that the resistance of the shell of the invention to rupture is the reason why it can be recharged more times (compared to a conventionally manufactured shell).

The cartridge case of the present invention, manufactured on a single machine, is easier to maintain accurate dimensional standards. The method of the present invention for making cartridge cases has the potential to greatly increase the throughput of a given size of equipment compared to conventional methods while using less labor, floor space, energy and materials.

It is understood that the present invention has been disclosed by way of example, and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this invention. Therefore, it is intended that the invention not be limited to the particular details disclosed, except as required by the following claims.

Claims (5)

1. A method of manufacturing a cartridge casing on a single progressive forming machine, comprising: cold forming by a tool an elongated circular wire blank which increases its diameter and forms holes on each end thereof and an intermediate web between the holes; drawing a portion of the blank having one of the plurality of holes into a thin wall to form a cavity for ultimately receiving the charge and the bullet; trimming the free end of the drawn thin wall while the blank is supported in the machine, so as to obtain a uniform edge; and upsetting the blank at the other hole in a segmented die that defines the blank into a final shape of the case head including the launcher slot.

2. The method of claim 1, wherein: the thin wall is forged to be slightly tapered.

3. The method of claim 1, wherein: the web is pierced to form fire-through holes.

4. The method of claim 1, wherein: the thin wall is trimmed by a shearing operation from the inside of the thin wall.

5. The method of claim 1, wherein: the blank is cut from a coiled wire material.