Reverse Engineering a 30-Year-Old HVAC Duct
needed to update the heating, ventila- tion and air conditioning (HVAC) system on the Abrams M1A1 tank, it faced a few obstacles. General Dy- namics approached Barron Industries, Oxford, Mich., with potential project, but the investment casting fi rm decided to no-quote. T e particular part’s complexity and relatively small order—only a few dozen would be needed annually—led Barron to assume it couldn’t be competitive price-wise. But General Dynamics, which has worked with Barron since the 1980s, encouraged the engineers to take a second look, and they were awarded the bid. T e next problem: General Dy-
W
namics had an example of the part and its blueprint from 1983, but no model. Previously an aluminum fabrication, the duct helps cool electronics on the Abrams tank. T anks to ongoing rede- signs of surrounding components, the duct faced restrictive spatial require- ments and multiple attachment points, which made investment casting the logical choice for production. “We had to reverse engineer it,” said
Bruce Barron, president and CEO. “T e information we received was minimal, so we generated our own 3-D model data
hen General Dynamics Land Systems, Sterling Heights, Mich.,
The duct’s thin walls in the tapered section of the 1.25-lb. casting presented a number of challenges.
imported from our coordinate-mea- suring machine. Really, once we could generate a 3-D fi le, we had something that could be utilized by the toolmaker, process engineer, machinist and fi nal inspection personnel. T at put everybody on the same page.” After generating a model from
the nearly 30-year-old blueprints and part, Barron engineers received minor changes from the customer, including the relocation of an outlet to accommodate additional changes
in the vehicle’s design. Production began on the 13.39 x 8.27 x 4.33 in. (34 x 21 x 11 cm) duct, with special attention focused on the tapered “necked down” section of the 1.25- lb. casting, which presented the big- gest challenge. “It’s such a long, narrow passage
way, in order to apply the ceramic coating and stucco sand, the ar- ticulations within the robot program required some modifi cations,” Barron said. “It required some part-specifi c process engineering.” T e ceramic removal also proved
challenging. Engineers developed a special nozzle for the water jet blasting operation to ensure the thin-walled duct remained fully intact. Castings were pressure tested, and wall thickness was verifi ed via radiography. “Because
of its place- ment within the
already crowded engine compart- ment, this is not an
easy part to install and remove,” Barron said. “When we
36 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2015 The component helps cool electronics in the Abrams M1A1 tank, which is used by both the
U.S. Marine Corps and U.S. Army.
deliver it to [General Dynamics], we believe that they will never have to touch it again after installation.”
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