Using Lost Foam Casting for Highly Engineered Gearboxes
Gear Solutions Magazine describes how lost foam casting is used in our design and build process for helicopter test stands> RedViking has built powertrain test systems since the early 1990s. Early on, these were used for the automotive industry, and the integrated test stand gearboxes were relatively straightforward with parallel shafts and simple box shapes. Fabricated housings were efficient and cost-effective for gearboxes with simple geometries.Get more news about
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That all changed as RedViking began helicopter transmission testing. A helicopter transmission test stand must duplicate the real-world speeds and loads seen during flight and connect to the complex interfaces of the test piece. When compared to automotive testing, helicopter test stand gearboxes are much larger, have higher power, and must handle much higher loads. They also involve complex geometric orientations and require a higher degree of vibration isolation for test article verification and analysis. With helicopter test stand gearboxes, there are a lot of forces and dynamic properties in play. These are high-powered gearboxes, so it's critical to get castings with good consistent material and known properties so that the design can be validated. RedViking analyzes the test stand gearbox and the loading to ensure it will be appropriate for helicopter testing.
RedViking turned to Betz Industries, which uses the lost foam casting process. Betz has been in the casting business since 1933 and has been using the lost foam casting process since the early 1960s. Prior to that, it used wood patterns, but as product changes became more frequent, its customers required greater flexibility.
The Lost Foam Casting Process
David Moorhead, vice president of Betz Industries, describes the process of lost foam casting: “We receive the part data from our customer. Our CAD programmer takes that model, and slices it into multiple layers because our CNC machines cut in three axes only (X, Y, and Z). The foam block, which represents the thickness of any given layer, is placed on the CNC machine table, and the machine mills out all of the unwanted foam.”“Once those layers are all machined, they are taken to assembly, and they put that part back together. They follow an instruction booklet created by the CAD operator, and they rebuild that part by gluing the layers together, sanding the seams and any surface imperfections. The pattern is checked to the print or to the solid model to make sure that everything is right. Then, we ship the foam pattern to the foundry.”
“Once the pattern is received in the foundry, it goes into the coating process. The pattern is coated with our refractory wash, and the wash has two main purposes: It is the barrier between the iron and the molding sand during the pouring process, and it gives the foam pattern a more solid structure. Once the wash hardens, it becomes a very hard, ceramic-like material that keeps the pattern in its original shape.”
“Then the coated pattern is moved into the sand molding department. It’s placed on a steel bottom board with a steel flask around it. The sand is disbursed out of a mixer all around the pattern and hand-tucked to ensure proper compaction. A binder and catalyst are added to the sand to set a specific tensile strength before it’s disbursed from the mixer.”
Using Lost Foam Casting for Highly Engineered Gearboxes
