The overall objective of this project was to use clean and environmentally friendly waterjet milling and machining processes to rifle and hone cladded refractory lined medium caliber gun barrels with the technology possibly transferable to all caliber weapons.
Abrasive waterjet milling acts as a water-driven precision cutting and milling process. The cutting of the metal by the water jet is accomplished by adding abrasive particles (which are recycled) into the stream of water. Water jetting also provides a dynamic axial component at the nozzle in the form of high frequency pressure pulsations to increase the effectiveness of water jet technology not possible in traditional cutting tools. The major parameters that can be varied to change the dimensions and shape of the metal being cut are the water pressure, pass rate, garnet size, nozzle design, and nozzle angle.
Environmentally friendly waterjet technology was used to machine cladded liners of gun bores. The waterjet process demonstrated that internal dimensional tolerances were met using precision waterjet milling technology. Waterjet technology also demonstrated the ability to rough hone tubes cladded with refractory metals. Side-by-side firing tests were conducted under this ESTCP program at both Aberdeen Proving Grounds (APG) and the Picatinny Arsenal. The weapons dispersion stayed within specifications and barrels machined via waterjet technology performed consistently to barrels machined by conventional methods.
There were several environmental benefits demonstrated when using the explosive cladding/waterjet rifling processes on medium caliber weapons. Waterjet rifling allows for the successful implementation of refractory metal cladded liners into a production environment. This alternative coating and rifling process on medium caliber barrels helps avoid the electroplating of chromium and the associated exposure issues associated with hexavalent chromium. Environmental benefits and energy savings throughout the weapon lifecycle could be realized on medium caliber weapons with wide adoption of the explosive bonding/waterjet rifling processes. If implemented for medium caliber weapons, the processes could help reduce the use of hexavalent chromium plating and the resulting hazardous waste streams. Other benefits include the reduction in usage of costly tooling (broaches) and the reduction in the use of heavy metals and heat treatments necessary to make that tooling. Waterjet machining technology uses only water and garnet as the cutting abrasive and recycles both during the process thereby reducing both the waste water stream and the recycling treatment necessary when conventional cutting oils are used. This reduction in the waste stream and reduction in the need for oils and lubricants helps reduce the total life cycle costs compared to traditional manufacturing processes.