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What is Abrasive Flow Machining?

Larry Ray Palmer
Larry Ray Palmer

Abrasive flow machining (AFM), also known an extrude honing, is an industrial process used in metalworking. This process is used to finish the interior surfaces of cast metals and produce controlled radii in the finished product. The process of abrasive flow machining produces a smooth, polished finish using a pressurized media.

The medium used in abrasive flow machining is made from a specialized polymer. Abrasives are added to the polymer, giving it the ability to smooth and polish metal while retaining its liquid properties. The liquid properties of the polymer allow it to flow around and through the metal object, conforming to the size and shape of the passages and the details of the cast metal.


Abrasive flow machining equipment is made in single and dual flow systems. In a single flow system, the abrasive media is forced through the project at an entry point and then exits on the other side, leaving a polished interior to mark its passage. For more aggressive polishing, the dual flow abrasive flow machining system might be employed.

In dual flow systems, the abrasive media flow is controlled by two hydraulic cylinders. These cylinders alternate motions, pushing and pulling the media through the project. This delivers a smoother, highly polished end result in much less time than a single-flow system.

The process of abrasive flow machining is used in the finishing of parts that require smoothed interior finishes and controlled radii. Examples of these parts include automotive engine blocks and other precision finished parts. The process also is used in the metal fabrication and casting industry to deburr the dies and remove recast layers from molds used during production.

Abrasive flow machining makes it possible to polish and smooth areas that otherwise would be unreachable, because the ability of the media to flow through the part is the only limiting factor. In addition, the process of abrasive flow machining can be almost completely automated, freeing human workers to perform other tasks and providing a cost-effective solution for part finishing. The equipment used in this process can handle several thousand parts per day and can still provide consistent results. These abilities have made abrasive flow machining a common factor in the part-finishing operations of many industries.

Hydro-erosive grinding (HEG) is a specialized form of abrasive flow machining. It is used to force abrasive media through the orifices and the intersection of holes in metal parts to achieve a uniform radius. This technique allows for calibration of static flow rates in equipment.

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