Support for Thin Sections for Machining
Aircraft companies solve the demanding problem of supporting components for finish-machining by using Cerrobend. The rotors have thin blades that are bent over a mandrel to an airfoil shape. Final machining involves several difficult contouring cuts and requires positive support of these thin sections.
Pictured above are four stages of manufacturing of rotor blades. Left to right are: the milled rotor with blades bent to shape; same rotor fully encased in solid Cerrobend; the machined rotor prior to removal of supporting Cerrobend; and the finished part after machining and melting out of the Cerrobend.
Cerrobend has a melting temperature of 158º F. It slightly expands during solification and is ideal for workholding devices. A holding tank of hot water (approximately 175º F. - 200ºF) is all that is required to keep the alloy molten. Cerrobend pours easily at safe temperatures and solidifies withn a few minutes.
The molten Cerrobend is dipped from the holding tank (rear) and poured into the jig around the rotor being invested for machining. Note the ease and safe handling of the Cerrobend. A laddle could also be used
The workpiece shown fully invested in Cerrobend. Although quenching with cold water reduces the grain structure within the Cerrobend, allowing it to air cool will give the workpiece better dampening properties. Cerrobend expands slightly on cooling to provide a tight fit.
Contour machining proceeds the same as with a solid workpiece. You can see the machined rotor blade tips which are held in perfect allignment and dynamic balance throughout the machining operation.
Cerrobend can be removed easily by using steam or a hot water bath. Individual parts can be hand cleaned with slight scouring with a brush in the case of anodized aluminum rotors. Metal chips will float on top of the molten Cerrobend.
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