Abstract:
An improved cartridge case completely produced net shape on a progressive cold former that includes a trim to lengthy station with an internal shearing tool.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to cartridge cases and their manufacture. 
       PRIOR ART 
       [0002]    Brass cases for firearm cartridges are conventionally made in numerous steps and on successive machines, often with intermediate annealing steps. Traditionally, cases are formed from strip stock that is cupped and then drawn. Once drawn, the blanks are machined to length and to provide an ejector groove. The strip stock method produces a high scrap ratio, requires energy for annealing, is slow, and occupies considerably floor space. It is known to cold form a hollow thin wall intermediate blank for a cartridge case from solid wire. Whether made from strip stock or wire stock, when a heavily drawn preform is produced, it has an irregular edge on the open end which, traditionally, is machined for a precise end surface after discharge from the forming tooling. The preform, after discharge from the forming tooling, is also typically machined to create an ejector groove adjacent its head or rearward end. 
         [0003]    There are several additional drawbacks to these known methods of manufacturing cartridge cases. Transferring case preforms from one bank of forming machines, for example, to a bank of turning machines, introduces dimensional variations that can be difficult to manage because of the multiple potential combinations of machines used to make cases. Labor costs are typically involved in transferring blanks between successive machines and each of the machines must be monitored and maintained adding additional costs and variability to the manufacture of cases. The machining operations create scrap, in particle, chip shaving and/or dust form, giving rise to maintenance and scrap recycling issues. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides an improved cartridge case, as well as a method and apparatus for its manufacture. The case is fully cold formed from metal wire stock, typically brass, in a single forming machine. The disclosed case is of the rimless, solid head type with an ejector groove on the head end. The case is formed at high production speeds to finished shape with stock removal limited to cutting a short ring off the forward end of a deep drawn cylindrical wall to obtain a uniform edge and punching out a small slug to form the flash hole. The ejector groove is fully formed on the blank without corresponding material removal. The forming process improves the metallurgical properties of the blank, particularly at the critical area of the ejector groove. The inventive method renders the case less prone to failure through cracking or other mishap during assembly, usage and reloading. 
         [0005]    The inventive process starts with a blank cut from solid wire. The blank is upset and extruded to form early stages of a primer pocket, a tubular charge and bullet space, and the ejector groove. In later forming stages, areas of the blank associated with the primer pocket are upset and folded radially outwardly to form a rear wall or flange of the ejector groove. The tubular part that is the preform for the charge and bullet space is deep drawn axially into a thin wall tube, and then finish trimmed at its distal end with a novel orbital shear. After end trimming, the thin wall tube is forged into a slightly conical shape. The case is completed in the forming machine and requires no secondary machining or annealing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1A-1I  illustrate progressive forming steps, embodying aspects of the invention, used to make a cartridge case starting with a solid wire cutoff blank and finishing with a completed case; 
           [0007]      FIGS. 2A-2D  diagrammatically show forming equipment and instrumentalities, including tooling, used to perform the steps shown in  FIGS. 1A-1I ; 
           [0008]      FIG. 3  is a perspective cut-away view of a die station in which a preform ejector groove is formed on a blank; 
           [0009]      FIG. 3A  is an enlarged view of die sections used in the station illustrated in  FIG. 3 ; 
           [0010]      FIG. 4  is a cross-sectional view of a blank end trimming station; 
           [0011]      FIG. 4A  is an enlarged view of the cutting area of the blank end trimming station; and 
           [0012]      FIG. 5  is a fragmentary sectional view, on a greatly enlarged scale, of the mouth of the cartridge case of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    While the disclosed solid head cartridge case is sometimes referred to as “rimless”, it will be understood that this term applies to belted cases with their heads slightly larger than forward areas of their bodies. Despite the industry “rimless” terminology, the radially outer part of the cartridge case head at the back of the ejector groove can be considered a rim. 
         [0014]    Referring to  FIGS. 1A -1I , there is illustrated a preferred sequence of forming a finished cartridge case starting with solid wire stock in a progressive forming or forging machine. A blank  10 , shown in  FIG. 1A , is cut from coiled round wire stock with a shear operating synchronously with other operations of a forging machine described below in greater detail. A conventional transfer device, having an axial movement component, not shown, operates to shift a blank  10  from one station to the next, i.e. from right to left in  FIGS. 1A-1I . At a first forming station ( FIG. 1B ), the blank  10 , transferred from the cut-off station ( FIG. 1A ), is upset to square up its sheared end faces. At a second forming station ( FIG. 1C ), the blank  10  is formed with dimpled centers  11 ,  12  on its end faces to improve the forming concentricity in subsequent forming steps. In a third forming station ( FIG. 1D ), the blank  10  is triple extruded forming a cylindrical preform of a tubular wall  13  of a case cavity, an exterior surface of an eventual ejector groove  14  and a preform of a primer recess or pocket  16 . 
         [0015]    At a fourth station ( FIG. 1E ), the preform of the case cavity wall  13  is deep drawn to form another intermediate preform stage of this wall and a charge and bullet cavity  19 . An initial form of a head  18  of the blank is shaped to preform the ejector groove  14  at a fifth station ( FIG. 1F ). The end of the case cavity wall  13  is cut to finish length at a sixth station ( FIG. 1G ). In a seventh station ( FIG. 1H ) the ejector groove  14  is finish formed. At an eighth station ( FIG. 1I ), the outside diameter of the cylindrical preform wall is forged into a slightly tapered shape to form the finished cavity wall  13 . The center of a web  22 , representing a forward part of the head  18  is pierced to form a flash hole  24  thus producing a finished cartridge case  25  with the remaining part of the web effectively closing the inner end of the cavity  19 . 
         [0016]      FIGS. 2A-2D  schematically illustrate a multi-station forming machine  30  that includes tooling, i.e. dies, punches and other instrumentalities to perform the steps outlined above to manufacture finished cartridge cases  25  of the invention. The lower portion of these figures shows a die breast or bolster  31 ; a line at  32  designates a reference plane sometimes known as the face of dies (FOD) on the die breast. 
         [0017]    Blanks  10  are carried by a transfer mechanism from right to left in  FIGS. 2A-2D  stopping at each station to be progressively formed. The transfer mechanism can be of a style like that shown in U.S. Pat. No. 5,713,237 that can axially withdraw and insert a blank from and into a die of a workstation. A blank  10  is cut from round wire stock  36 , supplied from a coil, by a shear  37  and then transferred to a first station  46 . The blanks produced at the cut off shear preferably have a length to diameter ratio of at least 1.16 and more preferably a ratio of more than 1.5 and most preferably more than 1.7. The illustrated forming machine  30  has eight forming stations in addition to the cutoff station. The cutoff and successive stations are equally spaced along a horizontal line. Each station on the die breast  31  has a receiving or die bore  41  for a die case and on a reciprocating ram or slide  42  there is a coaxial tool bore  43  for receiving a tool or punch case. The cartridge case  25  described and illustrated is a 9 mm case; while brass is ordinarily used for manufacturing cases, other materials such as steel or aluminum may be used to practice the invention. At the first station, indicated at its centerline by a numeral  46  (as in subsequent stations), a sliding die ring  47  radially constrains the mid-section of the blank  10 . The ring  47  can slide axially relative to an associated die  39  so that it moves with the blank and does not significantly restrict the blank from being fully shaped in the corners of the die when upset by a punch  48 . In this first forming station  46  the blank  10  takes the shape of a pill with a length to diameter ratio of about 0.6. 
         [0018]    At a second workstation  51 , the blank is formed with the dimpled centers  11  and  12  on its end faces by a punch  52  and die  53  to improve the tool and blank alignment in the next stations. 
         [0019]    In a third station  55 , the blank  10  is subjected to a triple extrusion where the preform of the wall  13  of the cartridge case cavity  19 , the preform of the ejection groove  14 , and the preform of the primer pocket  16  are formed by a die assembly  56  and a punch assembly  57 . A reduced outside diameter of the preform of the head  18  is slightly smaller, e.g. about 0.35 mm smaller than the diameter of the eventual radial base of the ejector groove  14  (shown finished in  FIGS. 1H and 1I ). 
         [0020]    At a fourth station  60 , to the left in  FIG. 2B , the blank  10  is deeply drawn in a die assembly  61  over a punch  62  by progressively smaller wafers  63  to form the thin preform wall  13  of the case cavity  19 . A free end of the drawn tube or wall  13  is normally characterized by an irregular edge. 
         [0021]    At a fifth station  70 , to the right in  FIG. 2C , a preform of the ejector groove  14  is formed on the head end of the blank  10 . This is accomplished with a segmented die assembly  71  diagrammatically illustrated in  FIGS. 3 and 3A . Four segments  72  (only two segments are seen in the cross-section of these FIGS.) are cammed radially inwardly around the blank as they are driven into a conical bore  75  of a die case  73 . Upon further advance of the ram, the segments  72  are held closed by a high pressure lever  74  and gas spring  76  against forming pressures in the blank tending to open the segments  72 . The lever  74  operates on the segmented die assembly through rods  77 . As mentioned, the minor outside diameter of the preform of the case head  18  produced at the third station  55  ( FIGS. 1D and 2B ) is nominally the same, although preferably slightly smaller, than the diameter of the base or minimum diameter of the preform of the ejector groove  14  produced here. In this fifth station  70 , the distal or outer end of the blank head is folded or upset radially outwardly to initially make a preform rear flange wall or rim for the ejector groove. In their closed positions, as seen in  FIGS. 3 and 3A , the segments  72  collectively encircle an annular zone precisely complimentary to the rim and groove preforms so that the head area of the blank is fully constrained when a punch  78  reaches front dead center. 
         [0022]    At a sixth station  80 , the blank  10  is trimmed to remove the irregular free edge at the mouth of the drawn case cavity wall and to determine the finished length of the cartridge case. The blank material is removed preferably in one piece as a short scrap ring. The removal is accomplished in a shearing process that advantageously avoids creation of significant dust, particles and/or chips of the blank stock. Referring to  FIGS. 2C ,  4  and  4 A, the trimming apparatus, designated  81 , comprises a blank gripping device  82  on the die breast  31  and a shear tool or punch device  83  on the ram  42 . It will be seen that the gripping apparatus  82  is operated by motion of the ram  42 . The blank gripping apparatus  82  is housed in upper and lower die case sections  86 ,  87 . The upper die case section  87  supports a pair of opposed grippers  88 ,  89  at the face of die plane  32  when it is in a forward position in the die case bore  41 . Relative motion between the lower and upper die case sections  86 ,  87  results in closing and opening of the opposed grippers  88 ,  89 . This gripper motion is produced by cams (only one cam  91  is seen in the view of  FIG. 4 ) on the lower die case section  86  that operate levers (only one lever  92  is seen in  FIG. 4 ) on the upper die case section  87 . The illustrated cam  91  and lever  92  operate the lower gripper  89  while the unseen cam and lever operate the upper gripper  88 . The die case sections  86 ,  87  are biased toward the ram  42  by respective gas springs. A gas spring  93  biases the lower die case section  86  towards the ram; gas springs associated with the upper die case section  87  are not seen in the view of  FIG. 4 . A shear plate  94  on the lower die case section  86  is at a fixed axial distance in front of the section. The transfer delivers a blank  10  to this station  80  and sets its primer pocket preform on an alignment pin  96 . Initial movement of the lower die case section  86  relative to the upper die case section  87  resulting from contact of a leading plate  97  on the trimming apparatus  81  with the shear plate  94 , driven by advance of the ram  42  causes the grippers  88 ,  89  to engage and hold the blank  10  at opposite sides of the preform ejector groove. This gripping action is benefitted by the wedging afforded by the tapered sides of the preform ejector groove. 
         [0023]    Further advance of the ram  42  causes the lower case section  86  to drive the upper case section  87  against its spring bias. This displacement of the die case sections  86 ,  87 , as will be explained, allows the blank  10  to be trimmed over a relatively long part of the ram retraction stroke. 
         [0024]    The shearing device  83  mounted in the punch bore on the ram  42  at this sixth station  80  removes a short ring with the irregular edge formed at the free end or mouth of the cylindrical case body previously drawn at the fourth station  60 . The apparatus  81  includes an elongated cam  101  extending along the axis of the station  80 . At a distal end, the cam  101  holds a pin-like cylindrical cutting tool or shear  102  made of suitable hard tool steel sized to fit into the open end of the blank cavity  19 . The cam  101  is supported on two sets of four rollers  103 . One set of the rollers  103 , seen in  FIG. 4  are in horizontal planes with two above the cam  101  and two below the cam. The other set of rollers, not seen in  FIG. 4 , are in vertical planes with two on a side of the cam  101 , below the plane of the drawing, and two on the other side of the cam, above the plane of the drawing. The rollers  103  are journalled in a sleeve  104 . The sleeve  104  is adapted to slide axially in a tool holder  106  fixed on the ram  42 . External contours of the cam  101  are made to drive the cam from a “home” position concentric with the axis of the station  80  first laterally off center and then in a four lobed orbital path to effect full angular rotation about the station axis. The eccentric motion of the cam  101  is produced when the cam and sleeve  104  move axially relative to one another. 
         [0025]    The shear tool  102 , which has the shape of a plain cylinder and is initially centered on the station axis, enters the blank as the ram  42  approaches the die breast  31  and the grippers  88 ,  89  have locked in the ejector groove preform. The shear plate  94  carries an annular insert or collar  107  of suitably hard tool steel. The insert  107  has a central bore proportioned for a relatively tight slip fit over the thin wall case cavity. The various parts are dimensioned such that a cantilevered end of the tool  102 , having a radial end face with a sharp peripheral edge is at a plane at which the case blank is to be trimmed. Similarly, the peripheral edge of the bore of the insert  107  is sharp and lies essentially at the plane where the blank is to be sheared. Axial clearance between the end face of the tool  102  and edge of the bore of the insert  107  is as small as practical. The blank  10  is trimmed at this station  80  to determine its final length. 
         [0026]      FIGS. 4 and 4A  illustrate the position of the tool  102  and insert  107  when the ram is at front dead center, a condition where the ram  42  has no velocity. The die case sections  86 ,  87  are fully retracted into the associated die breast bore  41 . As the ram  42  retracts, the die case sections  86 ,  87 , and the insert  107  on the periphery of the blank, move in unison with the ram  42  and shear pin tool  102 , being driven towards the ram by their gas springs. A timed knockout pin mechanism, known in the art, holds the sleeve  104  stationary while the cam  101  is caused to move with the ram  42 . The leading plate  97  combined with retainer  108  positions the cam  101  allowing the cam to move laterally but not axially relative to the ram  42 . The outer peripheral edge of the tool  102  and the inner peripheral edge of the insert  107  cooperate in the shearing action to cut a scrap ring off of the main body of the cartridge case blank  10 . 
         [0027]    The gas springs associated with the die casing sections  86 ,  87  cause the sections to move out of the die bore following the heading slide or ram  42  until the upper section  87  reaches the limit of its motion in the die block. As the ram  42  continues to retract, the transfer grips the blank and the grippers  88 ,  89  are opened as the lower die case section  86  continues to follow the ram under the force of its gas spring. Limited continued movement of the lower die case section  86  pushes the shear plate  94  off the blank  10  thereby allowing the transfer to grip and move the blank to the next station. The severed short scrap ring is driven off the shear pin  102  with an air blast. The sleeve  104  is eventually returned to its starting position by the timed knockout mechanism and the cam  101  and shear pin  102  are likewise returned to their starting position. 
         [0028]      FIG. 5  illustrates the unique shape of the cartridge case mouth produced by the disclosed trimming apparatus  81 . An inner peripheral surface  105  at an edge  109  of the mouth of the finished case  25  is “rounded over” or bell mouthed by the internal cutting or shearing action of the shear pin tool  102 . This outwardly flared mouth geometry can facilitate assembly of a projectile into the cavity formed by the case wall  13 . 
         [0029]    The blank  10  is transferred to the seventh station  110  where, like the fifth station  70 , a segmented die assembly  111  is used. Conical segments  112  are assembled in a tapered bore  113  of a die case  114 . The segments  112  are held closed against forming pressures by a large gas spring and lever like that shown in  FIG. 3 . At this station  110 , the cartridge head including the ejector groove  14 , is precision finish formed. The finished head  18  includes a full shoulder or “rim” with a forwardly facing radial side surface  116  constituting the rear boundary of the ejector groove  14  . The ejector groove  14  is, additionally, defined by a cylindrical bottom  117  and a conical rearwardly facing side or surface  118 . The segments  112 , when closed, and die elements  121 ,  122  precisely define and tightly confine the head  18  including the peripheral boundary of the ejector groove  14  and primer pocket  116  when the ram  42  carrying a punch  114  reaches front dead center. Preferably, the segments of the sliding die assembly in both the fifth and seventh stations are four in number with the segments of the seventh station being displaced  45  degrees out of angular registration with the segments of the fifth station to reduce the possibility of flash on the blank which could occur between adjacent segments. Any head stamp to be applied to the cartridge case  10  is preferably done in the seventh station by the die elements  121 ,  122 . 
         [0030]    For purposes of this disclosure, the head of the cartridge case  10  is that part rearward of the front of the web  22 . From the foregoing, it will be seen that in each forming blow of the head material, the tooling completely constrains this material at front dead center of the ram stroke. 
         [0031]    The blank  10  is transferred to an eighth station  130  where the tubular thin cylindrical wall of the charge and bullet cavity  19  is forged into a slight taper in a punch assembly  131  and die assembly  132 . Additionally, the web  22  between the primer pocket  16  and the charge and bullet cavity  19  is pierced by a die pin  133  at the axis of the station  130  to create the primer flash hole  24 . The blank  10  is thus finished at this station  130  and is ejected as a finished part. 
         [0032]    The disclosed process of cold forming the material of the blank head  18  in the various forming steps creates a superior grain structure at the ejector groove  14  so that a harder, stronger and precision formed cartridge case head is produced which is less prone to jam or otherwise fail during ejection. 
         [0033]    The finished cartridge case wall  13  has exhibited a reduced tendency to crack, even though it is not annealed, when compared to conventionally cupped, drawn, annealed and machined cases. While the reasons for this improved performance are not fully understood, it is presently believed to be at least partially the result of extreme cold working of the blank and disruption of its grain structure when it is converted from a wire derived blank with a relatively high ratio of length to diameter of, for example, about 1.8 to a relatively flat pill-shaped blank with a relatively low length to diameter ratio of, for example, about 0.6. The relatively high length to diameter ratio is also beneficial in eliminating the effects of cut-off distortion in the end faces of the original form of the blank. 
         [0034]    Another factor in the crack resistance of the inventive case may be the avoidance of grain patterns aligned with the tubular wall. Apparently, the crack resistance of the inventive case is the reason it can be reloaded more times than conventionally made cases. 
         [0035]    The inventive cartridge case, being made on a single machine, is more readily held to precise dimensional standards. The disclosed process for making the cartridge case has the potential to greatly increase the production capacity of a facility of a given size over traditional methods while using less labor, floor space, energy and material. 
         [0036]    It should be evident that this disclosure is 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 disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.