Volumetric Accuracy for Large Machine Tools (VALMT)

NCMS Project #: 140423

Problem: Large monolithic parts are integral within today’s weapons systems whether they be submarine pro­pellers, aircraft skins, airframe structures, or armored vehicle hulls.  The need for large machine tools to maintain close tolerances on shape and feature locations on these large parts presents unique manufacturing challenges.  Today’s best manufacturing processes, as good as they are, are not good enough.  Inefficient and costly assembly accommodations (such as make-to-fit, drill-at-assembly, shim-as-needed, and rework) are necessary because the best is not good enough.

Savings will be achieved when interchangeable parts can be made as was proven in the production of smaller firearm parts in 18th century armories.  The challenge today is to achieve the same levels of interchangeability in large parts manufacturing.  It is one thing to hold a 0.005” distance tolerance on a 6” part aligned with the axis of a small machine tool.  It is a different challenge to hold the same 0.005” tolerance on any diagonal measurement within the (20’ x 10’ x 5’ or larger) work envelope of a large five-axis machine tool.  It is a true challenge to simply measure these distances accurately and repeatability, let alone to achieve them consistently in production.

Benefit: High precision machines enable new manufacturing technologies such as eliminating mate drilling in assembly by producing full-size fastener holes during fabrication.  They can also eliminate the need to measure for and cut shims on parts with critical interfaces.  The costs for current assembly practices of measuring and fitting can be substantial – 0.5% to 1% of the cost of an aircraft.  The Boeing 737 or the F22 have costs of $200 to $300M per aircraft.  Savings of $1M per aircraft can realize a savings of $100M per year or more for a 737.  A new military jet like the JSF could save a similar amount.

The Navy will benefit from reduced rework and reduced total cycle time for manufacturing propellers.  Submarine propellers in particular demand very tight tolerances for surface contours in order to achieve “silent running”.  That precision is currently achieved by removing the huge forgings from the necessary very large machine tool to a large CMM for measurement, adding material where necessary, and then returning to the machine tool for another machining pass.  The technology of this project promises to minimize the number of passes.

Solution/Approach: WR-ALC will receive a test system for its airframe part making.  WR-ALC performs PDM on the F-15 and C-17 platforms.

The Naval Foundry and Propeller Center (NFPC) at Philadelphia will receive a system for propeller production.

Both test systems will be installed on project funds and supported for the life of the project.  Both test sites will make arrangements for commercial support after the project concludes.

Impact on Warfighter:

  • Cost – the system should reduce rework at both sites and reduce periodic maintenance costs for machine tool alignment.
  • Cycle Time – the system will also reduce total propeller production cycle time at NFPC.
  • Reliability – accurate machine tool error compensation will result in more reliable depot equipment.
  • Readiness – cycle time reductions at both test sites will result in greater total weapons system mission readiness.

DOD Participation:

  • U.S. Air Force (Warner Robins)
  • U.S. Navy (NFPC)
  • U.S. Army (Anniston) (observer)

Industry Participation:

  • Cincinnati Machine
  • Boeing
  • Siemens Energy & Automation
  • Automated Precision
  • NCMS

Final Report