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 accom- modate additional changes in the vehicle’s design. Production began on the 13.39 x 8.27 x 4.33 in. (34.01 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 biggest challenge. “It’s such a long, narrow passage
way, in order to apply the ceramic coating and stucco sand, the articu- lations 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
The component helps cool electronics in the Abrams M1A1 tank, which is used by both the U.S. Marine Corps and U.S. Army.
special nozzle for the water jet blasting operation to ensure the thin-walled duct remained fully intact. Castings were pressure tested, and wall thick- ness was verifi ed via radiography. “Because of its placement within
Impeller Cast Using SLA-Printed Patterns N
eeding to replace two double suction impellers with 30-in. diameters,
SPX, Charlotte, North Carolina, decided to explore alternative casting processes to improve performance and
limit lead times. It contacted Tech Cast LLC, Myerstown, Pa., a producer of large, precision engineered invest- ment castings using stereolithography (SLA) rapid prototype technology, an additive manufacturing process that
produces objects from CAD models by printing successive layers of curable resin that are hardened via a beam of ultraviolet light. Because an older wood pattern
was the only model for the 500-lb. impeller, Tech Cast needed to generate a 3-D drawing for production of the mold. (T e 3-D printing was handled by a third party.) Despite having to generate a 3-D model from scratch, Tech Cast produced two impellers in corrosion-resistant martensitic stain- less steel at nearly equal cost in half the time as the traditional method. “It took us about two weeks to pro- duce an SLA prototype,” said Shawn McKinney, general manager, Tech Cast. “Actual manufacturing time, from receipt of the prototype to deliv- ery of the casting, was four weeks.” Cast nearly to net shape, the
The stainless steel impellers measure 30 in. in diameter and weigh 500 lbs.
components required signifi cantly less machining and avoided the time- consuming welding/grinding loops that typically were necessary with green sand casting. In all, the lead time dropped to six weeks from the previ- ous 12 weeks. Additionally, no defects
August 2015 MODERN CASTING | 43
the already crowded engine compart- ment, this is not an easy part to install and remove,” Barron said. “When we deliver it to [General Dynamics], we believe that they will never have to touch it again after installation.”
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