Abrasive flow machining (AFM), also known as extrude honing, is a method of smoothing and polishing internal surfaces and producing controlled radii. A one-way or two-way flow of an abrasive media is extruded through a workpiece, smoothing and finishing rough surfaces. One-way systems flow the media through the workpiece, then it exits from the part. In two-way flow, two vertically opposed cylinders flow the abrasive media back and forth. The process was first patented by the Extrude Hone Corporation in 1970.
The process is particularly useful for difficult to reach internal passages, bends, cavities, and edges. Particular advantages are the directional finishes produced, which optimize the flow coefficient of certain workpieces, and the perfectly-formed, tangentially-blended radii formed on edges, which improves high- and low-cycle fatigue strength of certain workpieces.