GB2466641A

GB2466641A - A hydraulic forming process for polygonal rifled tube

Info

Publication number: GB2466641A
Application number: GB0823641A
Authority: GB
Inventors: Simon Trendall
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-12-31
Filing date: 2008-12-31
Publication date: 2010-07-07
Anticipated expiration: 2028-12-31
Also published as: GB0823641D0; GB2466641B

Abstract

The formation of polygonal rifled tube from a tubular blank (3) in a container (1) having a polygonal rifled bore (2) of the desired form by means of load applied to and causing displacement of fluid (4) filling tubular blank (3). The load applied being of sufficient magnitude to cause plastic deformation of the tubular blank (3) against the polygonal rifled bore (2) of container (1). The walls of container (1) being of sufficient bulk to withstand, without taking permanent set, the load required to cause plastic deformation and attendant autofrettage. Thus tubular blank (3) permanently takes the form of polygonal rifled bore (2). Release of the applied load permits elastic contraction and removal of the newly formed polygonal rifled tube ready for finishing as a barrel, barrel liner or projectile casing.

Description

A HYDRAULIC FORMING PROCESS FOR POLYGONAL RIFLED TUBE

The present invention relates to a process for hydraulically forming polygonal rifled tube for barrels of firearms of all classes and mechanically fitted projectile casings for use in polygonal rifled barrels.

A typical barrel has the grooves or rifling formed by one of the following methods cutting with a single point tool, broaching, swaging or forging over a mandrel. The single point cutter is slow and requires highly skilled operators, broaching requires expensive machines and cutters swaging requires large diameter blanks to resist the forming forces and stresses occasioned by this method may cause machining problems, forging requires expensive machines and mandrels and with each process tool wear is rapid. Mechanically fitted projectiles are well known in the art such as the Whitworth hexagonal shell. The complex form was difficult to machine and required thick walls limiting the payload of the shell.

The objective of the invention is solved by the features of claim one.

By replacing the form tool or cutter with fluid wear is effectively eliminated from the form tool and die.

Another advantage is that the tube is subject to autofrettage. With a tube not subject to autofrettage the load on the tube wall is not uniform across the thicknesss of the wall, the load in the wall decreases from the inner surface of the tube toward the outer surface such that the outer portion of the wall is doing no useful work in resisting internal load. An autofrettage tube has the wall plastically deformed and this causes a uniform distribution of load across the wall from an internal load. Thus an autofrettage tube can be lighter and use less material for the same strength A further advantage is that thin walled projectile casings may be made by the process without expensive machining and with improved capacity for payload.

The present invention will now be described by way of example with reference to the accompanying drawings in which;-Figure 1: Is a schematic cross section of the forming die and unformed tube along the line A A. Figure 2: Is a schematic cross section of the forming die and the formed polygonal rifled tube along the line D D Figure 3: Is a schematic cross section of the forming equipment along the line B B. Figure 4: Is a schematic cross section of the forming equipment along the line C C. Figure 1 shows a container (1) defining a polygonal rifled bore (2) with a tubular blank (3) located in said bore. The tubular blank (3) contains a body of fluid (4). Figure 2 shows the effect of a load applied to and displacement of the body of fluid (4) when the magnitude of the load is sufficient to cause plastic deformation of the tubular blank, causing the tubular blank (3) to be formed into polygonal rifled tube (9) by contact with the polygonal rifled bore (2).

Figure 3 shows the forming equipment required to achieve the plastic deformation of a tubular blank (3) into a polygonal rifled tube. The polygonal riled bore (2) of the container (1) is provided with vents (5) to preclude the trapping of fluid between the tubular blank (3) and the polygonal rifled bore (2) as any fluid trapped would prejudice the formation of the tubular blank (3) into a true copy of the polygonal rifled bore (2) . The body of fluid (4) fills a reservoir defined by the tubular blank (3) and two end caps (6 and 7). A piston (8) passes through an end cap (7) via a sealing means (10) to act upon the body of fluid (4) . Figure 4 shows the effect of a load of sufficient magnitude to cause plastic deformation of the tubular blank (3) into polygonal rifled tube (9) being applied to the piston (8) in the direction of arrow (11) . To form a polygonal rifled tube (9) by this method would require the body of fluid (4) to be subject to a pressure in the region of 6500 bar. The walls of the container (1) must be of sufficient bulk to withstand, without taking permanent set, the forming pressure. For the load applied in the direction of arrow (11) ,via the piston (8) to act on the body of fluid (4) causing the desired plastic deformation of the tubular blank (3) either the body of fluid (4) must be sealed and or the velocity and travel of the piston (8) must be sufficient to compensate for any leakage. If the end caps (6 and 7) are provided with recesses to accommodate the ends of the tubular blank (3) an the tubular blank (3) is a push fit in the recesses, as long as the wall of the end caps (6 and 7) is of sufficient bulk to withstand without plastic deformation and or can derive adequate support from the container (1) to resist the internal forming pressure. Internal pressure will expand the tubular blank (3) to seal against the end caps (6 and7), being a push fit will limit any expansion to within the elastic limit so removal after forming presents no problem. The piston (8) must be free to enter the body of fluid (4) under load applied in the direction of the arrow (11) . Reducing the radial clearance between the piston(8) and end cap (7) to a minimum, typically less than 0.01mm, means a seal (10) can be used,also the maximum flow rate along the radial clearance can be coped with,in the event of seal failure, by appropriate piston (8) travel and velocity.The ends of the polygonal rifled tube (9) that enter the end caps (6 and 7) will retain their original form and there will be a transformation region between the two forms,this must be allowed for in calculating the length of the tubular blank(3) as must the reduction in length due to radial expansion on forming. Provision needs to be made for the end caps to move to accommodate this or stretching of the tubular blank (3) in the transformation region accepted.

Thus with a tubular blank (3) filled with fluid and sealed by end caps (6and7) in a container (1) with a polygonal rifled bore (2) pressure applied to the body of fluid (4) by the piston (8) causes displacement of fluid. As the pressure increases elastic then plastic deformation of the tubular blank (3) takes place until the tubular blank takes the form of the polygonal rifled bore (2) thus a polygonal rifled tube (9) is formed. Release of the forming load will allow elastic contraction of the polygonal rifled tube (9) facilitating removal from the container (1) and end caps (6 and 7) At each of the vertices of the polygonal rifled tube will form internal and external radii dependant on the wall thickness, material strength and forming pressure. The pressure required to form a polygonal rifled tube is dependant on wall thickness and material, the thinner the tube the lower the forming pressure required. Thus use of a thin polygonal rifled tube (9) as a liner for a built up barrel, either wire or fibre wrapped or built up with one or more concentric tubes could offer useful savings. For small arms projectiles will readily deform to the polygonal form but with heavier weapons a mechanically fitted projectile is required, this is readily made by forming the projectile casing in the same manner as the polygonal rifled tube and internal grooving of the casing may be carried out on the tubular blank (3) prior to forming.

Claims

CLAIMS1. A method of forming polygonal rifled tube comprising the steps of: -providing a forming die comprising a container with a bore, said bore conforming to a substantially polygonal cross section and the length of said bore being equal to or greater than that of said polygonal rifled tube, the wall thickness of said forming die being sufficient to prevent plastic deformation due to the loads applied during the process of forming and autofrettage; -providing a tube the major outside diameter of which is less than the minor diameter of the substantially polygonal bore of said forming die; -inserting said tube into said forming die; -apply a hydraulic load to the interior of said tube of a magnitude sufficient not only to cause said tube to deform plastically adopting substantially the form of the substantially polygonal bore in said forming die but also to cause autofrettage to occur; -releasing said hydraulic load; -liberating said tube from said forming die.
2. A method according to claim 1 further comprising the step of heat treatment.
3. A method according to any previous claims further comprising the step of machining.
4. A method according to any previous claims, characterised in that said hydraulic load is applied by filling said tube with fluid and applying load there to.
5. A method according to any previous claims wherein the walls and vertices of the substantially polygonal bore of said forming die are aligned helically about the major axis.
6. Rifled tube formed according to the method of any of claims 1-5.