Most water jet cutting references apply to a primary process that begins the fabrication of a material, ushering it through its first stage of production rather then the middle or end section. This is partly because the waterjet cutting machinery is able to shape, form and cut materials with smooth edges that resembles the natural water corrosion process except done within minutes instead of months or years. Particularly when abrasive material, such as finely cut garnet or diamond pieces are mixed in with the water that is sprayed at high speeds at the material to cut it down to the precise dimensions dictated by the CNC program that usually runs it.
However, there is a secondary process that utilizes the same sort of hydraulic power as the abrasive waterjet cutting system except with less intensity. Abrasive flow machining is meant to smooth, polish and remove cracks and burrs from a surface that has hard to reach angles or cavities. Because of the fluid nature of water it is able to reach these spots and rid the material of blemishes, particularly when it washes over the surface at high jet speeds. Polymer resins known as media are mixed into the water just like abrasive waterjet cutting processes, to speed things up.
The same materials that benefit from water jet cutting systems also benefit from abrasive flow machining, such as metal alloys including stainless steel, aluminum, zinc, brass and titanium as well as plastics and other more traditional materials like glass and ceramics. This type of system is able to be integrated into a larger automation system because it is a secondary process and therefore is used after other manufacturing processes like drilling or laser cutting. Depending on the size and arrangement of jets, an abrasive flow machine is able to handle the cleaning of one or more objects at a time, or by way of a conveyor belt can go from one to another very quickly.
article from: http://blog.iqsdirectory.com/metal-cutting-services/abrasive-flow-machining-2/