YUMA PROVING GROUND, Ariz. - As the busiest test center in the Army, YPG evaluates virtually every piece of equipment a Soldier is likely to put his or her hands on.
Since items under test are often inherently dangerous, the safety of evaluators is a key factor. Many of the fixtures and components to support this vigorous testing are not available on the commercial market, or need to be extensively modified for the proving ground's needs.
YPG boasts a developmental engineering team and skilled machinists who frequently conceive of and build elaborate test fixtures, but some projects are just too big for the proving ground's capabilities. It is then that YPG relies on its strong relationships with sister installations to meet the mission.
Recently, the item in question was an approximately 15,000-pound trunnion gun mount used to hold cannons of all sizes, from 25mm up to 155mm. YPG's current fleet of these steel fixtures are approximately 40 to 50 years old, half of which are worn beyond usability and repair.
"We use the fixtures for a significant portion of our ammunition testing," said Pierre Bourque, team lead. "It is a critical piece of test infrastructure and the hardware we've got predates the experience of almost everybody currently working at YPG."
Worse, some of the mounts came to the proving ground in the late 1980s from the now-defunct Jefferson Proving Ground, Indiana, and all schematics and plans for them were lost. Other mounts in the inventory had rudimentary plans from the 1970s or earlier that once got the job done, but are inadequate for modern manufacturing techniques.
The mounts aren't much to look at, except perhaps to those with a highly keen appreciation of abstract art. So what was so complex about replacing a large hunk of metal?
"It has extremely tight mechanical tolerances because it needs to be able to hold a cannon in position to within fractions of a millimeter," said Bourque. "A great deal of clever engineering went into converting the drawings and the actual manufacturing."
Since YPG doesn't have the capability to manufacture the mounts, test planners turned to sister installation Aberdeen Proving Ground (APG), which boasts a modern 70,000 square foot welding shop, a large offset mill, and institutional expertise in the artillery-testing mission in general and these exact gun mounts in particular.
"We refined the drawings, putting them in a computer-aided design format and adding additional details and comments," said James Borzatti, mechanical engineer in the engineering design and development branch at APG. "It turned into a grand methodology project on how to build the mount. There were a great many practices and procedures we had to review to find the most efficient way of building these."
The mounts themselves are brutal hunks of extremely high quality steel, but with delicate sub-assemblies that need to accommodate the extreme repeated concussion of cannon fire on virtually a daily basis, for decades, without fail. Precision became the watchword.
"Tolerances were tight and strict," said Bruce Rose, experimental fabrication division chief at APG. "Many of the larger components required that the various faces machined on them would take place in multiple steps. Some of these had 13 or 14 iterations before the final assembly was put on another sub-assembly."
The new mounts have a host of upgrades over their predecessors. Significant advances in metallurgy and welding techniques in past decades mean a more robust fixture, and an extensive analysis of the various elements in the mount provides an exact idea of which parts of the item are most prone to metal stress.
"One of the biggest threats to the longevity of the item is stress cracks that usually occur in the weld area," said Borzatti. "The model we have now has shown us where those high-stress areas are."
In the end, the first mount was trucked to YPG and recently saw action in the first of what will be many tests. Though the previous mounts provided decades of useful service, testers believe the new ones will do likewise with fewer costly maintenance inspections and repairs than in years past. As it stands now, the most conservative estimate of the cost savings achieved by producing these mounts within the command is on the order of $1 million.
"We know they last a long time because the last generation served the better part of 50 years," said Bourque. "The next generation should last that long, but now that we have engineering background on stresses and fatigue areas, we can tailor our sustainment methodologies to be much more efficient."
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