Lean Process Shellcase Induction Annealing

The mission of Case X Case is to design a more reliable, faster, and cheaper annealing process that will simplify shell casing production flow while maintaining similar/better quality of current neck annealing operations.

Opportunity

During the manufacturing process, brass shell casings are work hardened into a brittle state that must be reversed to ensure a quality product. This is done by applying heat to the brass shell cases, thus reversing the effects of work hardening by annealing (softening) the cases. Vista currently uses a large batch oven process to achieve the required annealing. This current process requires batch sizes of 15,000 to 20,000 shells to be prepped and stored and utilizes a combination of gas and electric ovens to achieve annealing temperatures for a sustained period of 15 minutes. The failure of a proper anneal can mean losing the entire batch.

Solution

Induction annealing offers the ability to anneal each case individually as they pass though Vista’s manufacturing process. It achieves this by sending a high-frequency alternating current through a coil conductor (such as a copper coil) and generates a magnetic field. When a conductive material (such as a brass casing) is placed within this magnetic field, eddy currents are generated within the casing material, thus causing molecular friction and heating the conductive material.

The proposed induction process can achieve annealing temperatures within ½ second intervals with all required case sizes, matching current case production rates. This process is capable of a steady, single piece flow output. This process can be integrated into the current production line, eliminating the need for a large batch oven process that requires sitting inventory and added cost. This streamlined system is more efficient and cost effective, saving Vista money. By using induction technology, the case neck can be directly targeted while avoiding the case head. This process also allows for more fine tuning by adjusting the current used. These features allow for more controlled annealing and more efficient heating per case.

Background
Vista Outdoor is a global designer, manufacturer and marketer of consumer products in the outdoor sports and recreation markets. Ammunition comprises about 60% of thier business as the world’s leading producer of centerfire, rimfire, and shotshell cartridges. They are a wholly and vertically integrated manufacturer, taking in raw materials and controlling the fabrication process thru to the retail shelf space as well as direct to consumer sales. This project will work directly with the Lewiston facility where they manufacture some of the most iconic brands in the industry, servicing civilian recreationalists and more than 80% of law enforcement nationwide.

Cartridge shellcases are formed from brass wire through backward extrusion draws and subsequent forming and cutting operations. This intensive work hardening shortens grains and increases latent energy, reducing the ductility needed in the finished part. Targeted ductility is required to allow for case mouth expansion during loading and firing while still retaining adequate head hardness characteristics.

Current anneal processes use natural gas‐powered, belt‐fed, batch ovens. This method forces a tradeoff between thruput and part‐to‐part consistency; As parts are ‘stacked’ on a conveyance belt, the depth of the stack determines the time needed ‘in soak’ at temperature to sufficiently reach the middle‐most parts. Defects introduced by this process can propagate through an entire batch or, if not, at least prove inseparable from good parts. Batching is currently done in 10,000 to 20,000‐piece bins, increasing in‐process inventory and material handling costs.

Case mouth anneal is of critical importance to shellcase function and safe firearm operation. Cases that are too hard can split at the mouth upon firing. This is not detrimental assuming the split stays in the mouth and doesn’t propagate down the case body and vent propellant gas into the unsupported portions of the chamber. In some cases, however, a hard case mouth can split during seating of the projectile which can prevent the round from chambering properly in the firearm. Conversely, cases that are too soft will not have enough hoop strength to retain the projectile during the combustion event. If the projectile is dislodged from the case mouth before sufficient pressure is generated, this can lead to an increased combustion volume and inability to reach the intended peak pressure. This can result in a “bullet‐in‐bore” defect where the projectile becomes lodged before exiting the muzzle end of the bore. This is the most critical of defects as a second round fired into the now‐obstructed bore can cause catastrophic failure of the firearm. Even notwithstanding a second firing, the firearm is now inoperable; a life or death mishap in a lethal force encounter.

Deliverables
This project’s success will hinge on the ability to properly anneal the case mouth. Equipment developed is not expected to run at the two part per second rate typically needed to match upstream operations but must demonstrate the ability to consistently anneal with a high rate of confidence. Quality of anneal will be verified in a number of ways including: microscopy to look for appropriate grain growth, micro‐hardness evaluations, and function testing of sufficient quantity to establish statistical probability of defect rate. A one‐in‐a‐million defect rate is unacceptable as we load 18 million rounds each and every week of centerfire handgun alone!

This projects end goal is to produce the following...


 * One‐part flow case mouth annealing device applicable to 9mm, .40, and .45


 * A near zero defect rate


 * Analysis and flow diagrams documenting current and ideal state process


 * Cost saving analysis from reduction in human labor and inventory


 * A process that does not pose a hazard to employees

=Design Considerations=

Our system would be added onto an already single piece flow system within the current manufacturing process. This process must take place after any work hardening and be easily modified to fit our system. There are several tapering machines which meet this criteria. Below are two ways our system could be integrated into the tapering machines.

Design proposition 1:

Annealer could be inserted as the shells come from the hopper, leading into the tapering machine. This is our primary design focus.

Design proposition 2:

Annealer could be inserted as the shells exit the tapering machine. This is an alternative approach consideration.

=Test Bed Prototype Design=

This prototype was used to demonstrate the functionality of using induction to heat shell casings and to validate the math models for power use in the final design.



=Final Prototype Design= This Final Prototype Design was selected based on previous testing. It was purchased from U.S. SOLID. This unit has a digital readout of current and can be adjusted with built in controls. It can be set to run continuously or manually based on user needs. It also contains safety features such as an on-board cooling system that insures instrument safety during use.



=Testing=

Test 1: Validation
Test 1 was used to validate our math models for determining the power required to anneal shells at sub-second speed. Results showed a quadratic relationship and this equation was used to find the required power for sub-second annealing was ~1.335kW.



Test 2: pass/fail press testing​
Test 2 was used to determine ball-park amp ratings where annealing occurred in each shell type. To find these ranges shells were annealed for one second at staggered amperage settings and their results were recorded and compared against a control sample set of traditionally annealed shells. It was discovered that when shells were over-annealed they consistently buckled when pressed. When shells were not annealed they would split or butterfly. It was then the goal to find the power setting where around 70% of the shells would buckle. Below are the resulting ballpark figures as well as the press used and various failure modes encountered.



Test 3: Drop Test
This test was used to discover the effects of free-fall annealing. Shells were dropped 3 inches above the coil and their approximate shell temperature was measured by Thermal Camera. It was quickly discovered that dropped shells were unable to achieve annealing temperature. In conclusion further design iteration was needed.



Design Modification
This modified design was created to allow for continued testing. These modifications would create a controlled time delay in the rate at which shells were dropped, and in how long they were held in the induction coil. This allowed for shells to achieve the needed temperatures necessary for testing.



=Value Streams=

Current State Value Stream Map:



Projected State Value Stream Map:



=Final Design Validation=

=Team Members=

=Additional Documentation=

Project Schedule

Meeting Minutes Archive

Presentations

Client Interview