EP4663318A1

EP4663318A1 - Long cartridge case - method of forming a closed end metal tube

Info

Publication number: EP4663318A1
Application number: EP25181528.8A
Authority: EP
Inventors: Christopher W. Snavely; David L. Frank
Original assignee: National Machinery LLC
Current assignee: National Machinery LLC
Priority date: 2024-06-11
Filing date: 2025-06-07
Publication date: 2025-12-17
Also published as: CA3273840A1; MX2025006541A; CN121104552A; IL321016A; US20250375805A1

Abstract

A method of forming a closed end metal tube comprising cutting a blank 10 from a solid round metal wire, backward extruding an axial hole 11 in the blank 10 to produce a hollow sidewall 12 with a thickness, and reducing the sidewall thickness by using one or more Modified Hooker extrusions.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method of forming a closed end metal tube according to claim 1.

PRIOR ART

The traditional process used to manufacture Rifle Cases, or any munitions cartridge case, is to use a process referred to as "Cup and Draw". This process starts with strip stock material to form the part. The first step is to stamp out small discs and form cups. Then these cups are annealed before being introduced to several Draw operations. This process requires numerous wash and annealing steps between drawing operations using multiple pieces of equipment to end up with a fully drawn component. This process has been used for 150 years and is still used for many applications to this day.
Brass cases for firearm cartridges are conventionally made in numerous steps and on successive machines. Traditionally, cases are formed from brass strip stock that is cupped and then drawn in multiple stages. Annealing steps between the drawing stages are ordinarily required, especially where relatively long cases, such as rifle cases, are being manufactured. The strip stock method produces a high scrap ratio, requires energy for annealing, is slow and prone to dimensional variability, and occupies considerable floor space.
U.S. Patent Nos. 10,495,430 and 11,333,473 disclose a method of making long cartridge cases that involves multiple backward extrusions of an initially solid cylindrical blank.
Thus, a long cartridge case blank is achieved that can be finish drawn to a tube wall thickness that heretofore required annealing between conventional drawing processes. The high forces involved, at times, can cause poor tool life, leaving a need for a tube forming process that places less stress on the tooling.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the disadvantages of the prior art. It is further an object of the present invention to create an enhanced method of forming a closed end metal tube. In particular, less stress is placed on the tooling of the forming machine using the enhanced method.
At least one of these objects has been solved by the features of the independent patent claim. Other preferred embodiments are indicated in the dependent claims.
According to a first aspect of the present disclosure, the object is achieved by a method of forming a closed end metal tube comprising cutting a blank from a solid round metal wire, backward extruding an axial hole in the blank to produce a hollow sidewall with a thickness, and reducing the sidewall thickness by using a Modified Hooker extrusion.
The invention requires only one backward extrusion which is less severe than in the prior art process to form a hollow part suitable for use in making a long cartridge case or in other words to form elongated hollow parts made from solid metal wire. Additional backward extrusions are avoided by using one or more modified successive Hooker extrusions to obtain a desired wall thickness in the workpiece which can be a preform for a long cartridge having a length greater than 2-1/2 times its diameter.
Said disclosed improved forming method requires rethinking the formation of the extruded holes prior to drawing the part over the draw mandrel. This method involves backward extruding the smallest diameter axial hole first and then following up with one or more "Hooker Extrusions". Conventionally, a "Hooker Extrusion" is defined as: The forward extrusion of the outside diameter of a hollow part with a mandrel used to maintain the inside diameter of the extruded part.
The "Modified Hooker extrusions" are varied from conventional Hooker extrusion practice. With a conventional Hooker Extrusion, the internal diameter of the part is maintained. Here, the Modified Hooker extrusions maintain the external diameter of the part.
By reducing the total forming load and energy, tool life is improved and a smaller and faster cold forming machine can be used. In other words, the outer diameter of the sidewall may stay confined during the Modified Hooker extrusion. Thus, the tooling life is further improved in said forming method.
During said Modified Hooker Extrusion, the elongated hollow part is machined by a tool, e.g. a punch, wherein the tool is inserted into the axial hole of the elongated hollow part and is designed to produce a wall thickness that is less than the wall thickness of the hollow part after backward extrusion. The tool is only inserted into the axial hole by a first moving distance so that the area below the tool in the hollow part comprises the thicker wall thickness on the sidewall.
In another embodiment a succession of Modified Hooker extrusions are performed on the sidewall. Thus, the workpiece is formed smoothly, while the external diameter of the part is maintained. During a second Modified Hooker extrusion, the tool is inserted into the axial hole of the elongated hollow part and is designed to produce a wall thickness that is less than the wall thickness of the hollow part after the first Modified Hooker extrusion. The tool is only inserted into the axial hole by a second moving distance so that the area below the tool in the hollow part comprises the thicker wall thickness on the sidewall. The second moving distance is less than the first moving distance of the first Modified Hooker extrusion.
In another embodiment the forming part is finish drawn to the final sidewall thickness of the desired part. The part can be finish drawn to the final sidewall thickness of the desired part on a smaller forming machine compared to the known method.
In another embodiment the method is performed on a single forming machine. The estimated total forming load is reduced by 50% and the energy consumption is reduced by 40% compared to previously multiple backward extrusion processes.
By means of the following figures, the invention is explained in more detail by means of examples of embodiments. The list of references is part of the disclosure.
Positional indications, such as "above", "below", "right" or "left" are in each case related to the corresponding embodiments and are not to be understood as restrictive. Indications, such as "first", "second", or "further" are in each case related to the corresponding device and are not to be understood as restrictive or enumeration.
In order to facilitate better understanding of the present invention, reference is made below to the drawings. These show only exemplary embodiments of the subject matter of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.
In the figures and the associated description, identical or functionally analogous parts are provided with the same reference numerals.
The invention also encompasses individual features shown in the figures, even if they are shown there in connection with other features and/or are not mentioned above. Further, the term "comprising" and derivatives thereof do not exclude other elements or steps. Likewise, the indefinite article "a" or "one" and derivatives thereof do not exclude a plurality. The functions of multiple features recited in the claims may be performed by a single unit. The terms "substantially", "approximately", "about" and the like in connection with a characteristic or a value define, in particular, also exactly the characteristic or exactly the value. All reference signs in the claims are not to be understood as limiting the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates forming steps used in practice of the invention;
FIG. 2 shows the start of the Modified Hooker extrusion; and
FIG. 3 shows the completion of the Modified Hooker extrusion.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Traditionally, a cartridge case has a tapered inside diameter associated with a tube wall thickness that reduces away from a cartridge head towards the open end. The forming steps illustrated in FIG. 1 are typically done on a multi-station cold forming machine. A blank 10 is cut off from a solid round metal wire fed to the forming machine 20 (step 0). At a first station 21 of the forming machine 20 the blank 10 is squared up by a first tool (step 1), and at a second station 25 of the forming machine 20 the blank 10 is backward extruded by a second tool with an inside diameter (iD) reduced from what was previously done, thereby reducing tool loads (step 2). The required forming load to produce a backward extruded hole 11 decreases as the reduction in area decreases. The backward extruded hole 11 comprises a minimum hole diameter and therefore the sidewall thickness D0 at its maximum. Here the backward extrusion results in a hole 11 that is minimal while the earlier process requires a hole that is maximal to form a mouth of the blank.
The backward extruded blank 10 as shown in FIG. 1, is subjected to a first Modified Hooker extrusion at the next station (step 3) and a second Modified Hooker extrusion at the following station (step 4). Said first Modified Hooker extrusion leads to an initial decrease in the wall thickness of the sidewall 12 compared to the wall thickness after said backward extruding process. The outer diameter aD of the sidewall 12 stays confined during the Modified Hooker extrusion. A second Modified Hooker extrusion leads to a further decrease in the wall thickness of the sidewall 12 compared to the wall thickness after said first Modified Hooker extrusion process. The outer diameter aD of the sidewall 12 stays confined during the Modified Hooker extrusion. Thus, a cartridge case with a tapered inside diameter is formed, associated with a tube wall thickness that reduces away from a cartridge head towards the open end. FIG. 2 illustrates the start of a Modified Hooker extrusion 30, and FIG. 3 illustrates the completion of a Modified Hooker extrusion. After backward extrusion semi-finished cartridge is placed in a container 31 of said modified Hook extrusion 30. A punch 32 exerts a force on the semi-finished cartridge and forms the semi-finished cartridge into shape along a first moving distance 13 in the axial hole 11 with an initial decrease in the wall thickness of the sidewall 12 from a sidewall thickness D0 to a decreased sidewall thickness D1. It is seen from FIGS. 2 and 3 that only the sidewall 12 of the blank 10 is extruded so that the reduction in area is relatively small. The estimated total forming load is reduced by 50% and the energy consumption is reduced by 40% compared to previously multiple backward extrusion processes. A further Modified Hooker extrusion will further reduce the sidewall thickness to the sidewall thickness D2 along a second moving distance 14 (see FIG. 1, step 4). The part can be finish drawn to the final sidewall thickness of the desired part on the same forming machine as the previous forming steps are performed - see FIG 1, step 5.
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.

References:

9 closed end metal tube, 10 blank, 11 axial hole, 12 sidewall, 13 first distance, 14 second distance, 20 forming machine, 21 first station of 20, 25 second station of 20, 30 Modified Hooker extrusion, 31 container of 30, 32 punch of 30, iD inside diameter, aD outer sidewall thickness, D0 initial sidewall thickness, D1 first decreased sidewall thickness, D2 second decreased sidewall thickness

Claims

A method of forming a closed end metal tube (9) comprising cutting a blank (10) from a solid round metal wire, backward extruding an axial hole (11) in the blank (10) to produce a hollow sidewall (12) with a thickness, and reducing the sidewall thickness by using a Modified Hooker extrusion.
A method as set forth in claim 1, wherein during the Modified Hooker extrusion, the outer diameter (aD) of the sidewall (12) is confined.
A method as set forth in claim 1, wherein a succession of Modified Hooker extrusions are performed on the sidewall (12).
A method as set forth in claim 1, wherein the forming part (9) is finish drawn to the final sidewall thickness of the desired part.
A method as set forth in claim 4, wherein the method is performed on a single forming machine (20).