Patent Application
20140298979
The present invention relates to a novel method for producing a gun cartridge casing.
Typically gun cartridge cases are drawn from sheet metal discs in three ‘stages’. First a cup is formed from the sheet metal disc. Thereafter the cup is drawn to the desired length by a number of forming operations through punches of decreasing diameters until a suitable length of the part is attained. The drawn part is then provided with a neck, if necessary. Finally, the bottom of the drawn and necked part is provided with a groove to form the final cartridge case.
After each drawing stage the parts are annealed, pickled, rinsed and subjected to further quality improvement measures.
For the annealing process the part should be clean, which requires a washing before the annealing. After the annealing the part is pickled, bondered and/or lubricated, which is required for the following drawing operations.
Depending on the calibre, the drawing process is typically carried out in a transfer press, where the product is deep drawn in a number of sets comprising pairs of punches and dies (stations) to receive workpieces leaving a deep drawn tool. If the drawing is carried out in a transfer press, the transport is accomplished by using mechanical grippers.
Normally a transfer press comprises 5 to 12 stations. Due to the heavy reduction in strength of the sheet, usually from an initial strength of about 3 to 4 mm to final strength of about 0.3 mm, the material is hardened. Further, the forming capability is reduced with every step. Therefore, the processes according to the state of the art require at least one further intermediate annealing process (incl. washing and pickling), sometimes depending on the calibre even more.
After the ironing process in the transfer press there is necking process for most of the rifle cartridges. The necking is done after an annealing process to reduce the material stress before this critical forming process. Typically the necking is done in 2 stations.
The groove and trim are formed using special equipment, which is separate from transfer press. For this to be achieved, the case is fixed in a collet chuck and turned while a shaped turning tool cuts the groove and a second one trims the length.
It will readily be realised that such processes are laborious, costly, and require costly investments.
It is therefore an object of the present invention to provide a method for producing a gun cartridge casing which can be performed on a single transfer press.
There is provided a method for manufacturing a gun cartridge casing comprising the steps of:
In an embodiment of the invention, the steps (b) of producing a blank from a metal sheet, and (c) of producing a cup are carried out in one cutting and forming station.
If the cartridge case is to be provided with a groove, it is advantageously produced in a method for manufacturing a gun cartridge casing having a groove in a single multiple station deep drawing transfer press comprising the steps of:
Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:
Some cartridge cases, particularly those used in rifles, require the presence of a neck. Also the neck is advantageously produced within the same multiple station deep drawing transfer press after step in a method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of:
Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:
If a cartridge case having a groove and a neck is to be produced, then it may be produced in a method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of:
Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:
If the cartridge case is to be equipped with a neck, such as in many rifle cartridge cases, it is desirable to produce it in the same multiple station deep drawing transfer press as all previous steps. In said machine, the neck is preferably produced at the very end of the process. Pistol cartridge cases are normally not provided with a neck.
A forming station in the multiple station deep drawing transfer press usually comprises a pair of a punch and a die where the metal sheet is formed, first into a metal cup, and subsequently into a cartridge case with elongated form in relation to the metal cup, a stripper, an ejecter and a gripper which transports the cup of cartridge case from one forming station to the next one. In case a neck is formed, the forming station does not comprise a punch. There is just a die which forms a neck on the open side of the cartridge case and an inner pilot to maintain the wall thickness.
According to the present invention there is also provided a multiple station deep drawing transfer press for manufacturing a gun cartridge casings in a single machine, which comprises a cutting device for cutting discs out of a metal sheet and a number of forming stations for drawing and forming said metal discs, wherein in at least one forming station comprising a punch and a die, the die exhibits a splitted punch to form a groove.
According to the present invention, the metal sheet, which is preferably a brass sheet, is fed directly into a deep drawing transfer press. Preferably a zig-zag feeder for providing a multiple cut is used to feed the material to the cutting tool which cuts discs out of sheet metal. A zig-zag feeder will utilize the material in a most efficient manner without needless waste of material.
Thereafter, a cup is formed in the transfer press, and the cup is transferred to subsequent stations of the transfer press, preferably without any intermediate washing, pickling and/or bondering. During various forming steps, the wall thickness of the case is reduced to a final wall thickness.
To allow the further deep drawing and ironing operations without any annealing process to the final wall thickness, a reduction of the true strain of per operation is required. Preferably, according to the process of the present invention, the number of forming stations (pairs of punches and dies) is higher than in known processes. Preferably, the multiple station deep drawing transfer press used in the method according to the present invention comprises 12 to 25, preferably 15 to 25 forming stations in total. For Example, to include a neck, without any intermediate annealing step, the number of forming stations used for step (e3) is preferably from three to seven, most preferably from four to five.
In step (c) the cup is preferably formed in one forming station, where the thickness of the metal is preferably reduced by 40% to 70% while a cup is formed.
Preferably, the number of forming stations for carrying out drawing and forming steps (d) of the cup to form a cartridge case is from three to nine, more preferably from four to eight, such as from five to seven. In these forming stations, the wall thickness of the cup or of the intermediately drawn cases is preferably reduced by a higher percentage during the earlier stages of the drawing process of step (d) than in later stages of the step (d). For Example, according to a preferred embodiment the wall thickness of the cup is reduced by 30% to 50%, more preferably about 40% in a first forming station of step (d). While normally the reduction is about 60% to 70%.
According to a further preferred embodiment, the wall thickness of the drawn case is reduced in a second forming station of step (d) by a lower percentage than in a first forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 20% to 30% in a second forming station of step (d).
According to a still further preferred embodiment, the wall thickness of the drawn case is reduced in a third forming station of step (d) by a lower percentage than in a second forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 10% to 25%, preferably 10% to 20% in a third forming station of step (d). While normally the reduction is about 25% to 35%.
According to a still further preferred embodiment, the wall thickness of the drawn case is reduced in a fourth and any further forming station of step (d) by an equal or a lower percentage than in a third forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 10% to 20% in a fourth or any further forming station of step (d).
With the increasing number of forming stations and therefore with increasing bed size, the forming and coining force increases which may result in a winkling of the punch. The press force, depending on the caliber of the gun cartridge case, is preferably chosen between 75 to 250 tons, and a bed length is preferably from of 1000 to 3000 mm. Preferably, a ridged mechanical press or ideally a servo spindle press is used, which can actively correct the punch winkling.
Preferably, one or two flash holes are pierced in the drawn case within the deep drawing transfer press.
As described above, according to the state of the art, the grooving process is typically carried out in an external operation, in a turning method, wherein material is removed from the blank. The method according to the present invention, however, for the first time integrates the grooving steps in a transfer press, and does not remove material while the groove is formed.
The groove is formed in two steps. For forming the groove, the first operation is a drawing operation where the bottom of the case is reduced in diameter to the required groove diameter. In a further station in the deep drawing transfer press, the bottom of the case is held with a splitted punch, then, the bottom and primer pocked are coined into the case. The material flows radially and, thus, the groove is formed. To release the case of the splitted punch, the punch is opened into its segments.
This is further demonstrated by appending
| Number | Date | Country | Kind |
|---|---|---|---|
| 13162784.6 | Apr 2013 | EP | regional |
