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Drawn Shell Casing Simulation

A DEFORM-2D simulation modeled the multi-station drawing and cold heading of a copper case (shell) used in an ammunition cartridge. Product: DEFORM Premier; DEFORM-2D; Forming Express (2D) Courtesy: American Ballistics Summary: SFTC worked with American Ballistics to develop an optimized cold drawing progression for a copper cartridge shell casing. The DEFORM-2D Multiple Operation environment was coupled with the DOE/Optimization Module to perform an in-depth series of process studies. The product was successfully launched, with DEFORM simulations instrumental in improving the efficiency of the development process compared to slow, costly shop trials. Case Study: Ammunition comes in many shapes and sizes, serving purposes including defense, hunting and sport. Finished forms are typically standardized to fit specific weapons and produced in high volume. Ammunition can be constructed of multiple components including a case (shell), bullet (projectile), propellant (explosive) and primer (fuse). The “case” or “casing” frequently comprises most of the product’s body. Casings are manufactured in a broad range of metal forming processes. Those for firearm rounds are usually created in sequences (progressions) of cold drawing operations. Small-arms cartridge cases are primarily made from a grade of brass called “cartridge brass”. Slugs of material are blanked from sheets of the metal. The slugs are then formed to a desired shape by passing them through a series of drawing dies. The drawing process stretches the material to length while forming the cavities for bullets, propellants and primers. American Ballistics has operated fully-integrated case and bullet production for decades. The company annually manufactures millions of rounds of specialized ammunition for domestic and foreign military and law enforcement customers. The company was assisted by Scientific Forming Technologies (SFTC) in developing a multiple-stage progression for the production of a cold drawn, brass shell casing. Two-dimensional (2D) axisymmetric finite-element analyses were carried out in the entry-level Forming Express (2D) system or the advanced DEFORM-2D system. The multiple-operation (MO) environment of DEFORM facilitated an easy to set up and reusable simulation project. It addressed cupping, annealing, drawing, heading and pocketing operations. Design iterations evaluated blank, die and punch parameters across the progression. Critical outputs under review in each iteration included effective strain (work hardening), drawn cup length and shell wall thickness. Parts were expected to be defect-free and require forming loads compatible with existing press specs. Initial designs were evaluated one-by-one, per station, based on experience and best practices. Design iterations were simulated, evaluated and modified if necessary. Some established station designs had to be reworked due to their impact on downstream stations. The team then applied the DEFORM DOE/Optimization Module to their DEFORM-2D project to facilitate a more comprehensive study. The module integrates design of experiments (DOE) methodology, simulation sampling automation and statistical postprocessing into the DEFORM MO environment. DOE studies evaluated the impact of select punch, die and blank geometry variations using a full-factorial sampling matrix. The risk of fracture was predicted by the Cockroft-Latham damage model. Parts deemed “defect-free” were those that did not exceed a “critical” damage value. The part height and diameter were the output responses of specific interest. The final progression design was established after two only DOE studies. The first study revealed the sensitivity of the output variables to the input variables. This allowed the team to focus efforts on the decisions that would drive maximum impact. A refined set of input variables was evaluated in the second DOE study. This facilitated the identification of an optimized design of acceptable length and low fracture risk (low damage). With the drawing progression established, the final step was an analysis of the combined heading and “pocketing” operation. Pocketing is the forming of a primer pocket into the end of the shell casing. The design of this particular station was optimized to avoid various defects common in such an operation. Meanwhile, the predicted forming load was confirmed to be compatible with American Ballistics’ heading press. The new ammunition product was successfully launched by American Ballistics as a result of this development project, aided by DEFORM. Similar two-dimensional DEFORM simulations of round ammunition products are extremely accurate, fast and mature. Simulation run times are typically measured in minutes. High-detail models and extensive DOE or optimization studies are thus quite practical for designers and engineers to run.