Rifling By Flow Forming

Editors Note: The following article by BARIŞ GÜN and ILHAN GÜVEL of Istanbul, Turkey describes the patent pending manufacturing process to produce rifled barrels by means of Flow Forming. The methods described in this article appear to have merit and are provided to inform the firearm manufacturing and forensic science communities. The authors are seeking comments and investors in bringing this manufacturing method to the industry. Anyone wishing to comment on the method can post messages on the firearmsID.com community forum located here. Contact the authors via the links at the bottom of this page.

APPROVED PATENT APPLICATION : TPE 2007-G-173863
INTERNATIONAL PATENT CLASS (IPC) : F41A 21/18 , F41A 21/00

BARIŞ GÜN	ILHAN GÜVEL
MECHANICAL ENG. BSc.	NAVAL ARCHITECTURE
DESIGN AND MANUFACTURING ENG. MSc.	AND MARINE ENG. BSc.

Flow forming is a chipless cold forming method which is used to manufacture dimensionally precise, round seamless hollow components.

In flow forming; a hollow axis symmetric preform is fitted to a mandrel. After both are made to rotate, compression forces are applied to the outside diameter of the preform by hydraulically-driven or ballscrew-driven CNC-controlled rollers. For most applications three rollers are used.

By a pre-calculated amount of wall thickness reduction, in one or more passes, the material is compressed above its yield strength, plastically deformed and made to flow. The desired geometry of the workpiece is achieved when the outer diameter and the wall of the preform are decreased and the available material volume is forced to flow longitudinally over the mandrel.

Cross-sectional wall reductions for most materials are in excess of 90% of the starting wall thickness. Typically, the preform can be flow formed up to six times its starting length before a need for reannealing of the metal is required.

The inside surface quality of the finished workpiece is almost same with the outside surface quality of the mandrel.

Flow forming process has two typical types which have been appeared due to fixing necessities of preform shapes.


Figure-1 Forward Flow Forming	Figure-2 Backward Flow Forming

First type is forward flow forming (Figure-1) and it is used to form preforms which have a shape with one side is partially closed or fully closed. In forward flow forming, a tailstock is used to fix the preform to the mandrel. The elongation of the workpiece during forward flow forming is at the same direction with the relative axial movement of the rollers.

Second type of flow forming is backward flow forming (Figure-2) and it is used to form preforms with a continuous hole inside. In backward flow forming, a toothed ring is used to fix the preform to the mandrel and it is also used for reloading of the finished workpiece. The elongation of the workpiece during backward flow forming is at the opposite direction to the relative axial movement of the rollers.

For precision long flow forming operations, typically three rollers placed with 120° design is used. These rollers have precalculated radial and axial offsets between each other to achieve necessary forming conditions.

Figure-3 Typical 3-Roller Design

Figure-4 Offsets of 3-rollers

As a result of the cold work (strain hardening) that occurs during the process cycle, a flow formed component will have considerably higher mechanical properties than the ones of the starting material. Typically, the preform material is plastically deformed with wall reductions in excess of 90% of the starting wall thickness, causing a substantial refinement of the grain structure and a total realignment of the grain’s microstructure in a very uniform, axial direction. The greater the wall reduction, the finer the grain’s microstructure of the finished component. If necessary, the grain structure can be recrystallized by a post forming annealing cycle.

Flow forming offers the unique possibility of forming to size a pre-hardened workpiece, thus eliminating the difficulties and high costs associated with final machining, grinding and honing of a hardened and distorted hollow component. Flow forming method also allows to achieve high dimensional accuracies and at the same time guarantee conformance to required mechanical properties.

Figure-5 shows an illustration of the grain’s microstructure of a preform to flow formed zone and Figue-6 shows the improvement of mechanical properties for an AISI 316 workpiece.

Figure-5 Grain’s Microstructure

Figure-6

Flow forming of a barrel can be described as a special application of forward flow forming which is used to form grooves and lands inside the barrel while also forming outside of the barrel.

In rifling by flow forming, a barrel preform over a special mandrel containing reverse image of desired grooves and lands are flow formed by rollers. During the process, the barrel material flows in axial and radial directions. Axial flow elongates the barrel and radial flow forms the rifling.


BEGINNING OF THE OPERATION	DURING THE OPERATION	END OF THE OPERATION

Figure-7 Rifling Process

Figure-8 Material Flow

Figure 9- Elongation and Rifling

It is also possible to form different outside diameters during flow forming without any stop of the rifling inside unless each point of outer surface of rifled zone must be less than the preform’s beginning outer diameter.

Rifling by flow forming method will be the mostly using method for manufacturing tomorrow’s barrels. This method has many advantages compared with the conventional methods; cutting (broach rifling), button rifling, forging and electrochemical rifling.

The photographs below show the Aluminum parts flow formed and rifled for trials of the method in less than 30 seconds with x3 times elongation in length. Grooves and lands have been formed approximately x8 times thicker than real applications.

MACDOR Machine Industry And Trade Co. Ltd.
Altiyol Gaziosmanpasa Sok. No:10/13 Kadikoy/Istanbul, TURKEY
Tel: +90216365376 Fax: +902163365381 E-Mail: info@macdor.com
Barış Gün (GSM +905434324720)
lhan Güveli (GSM +905423765241)

FirearmsID.com Feature Article, October 2007