Abrasive Flow Machining

Process Principle, Parameters and Capabilities

Process Principle

• AFM is a finishing process that removes a small quantity of material.

• It uses semi-solid, abrasive laden putty through or across a work piece.

• It extruded across edges or surfaces to deburr, radius, polish, remove recast, perform mirror surface machining.

• A hydraulic ram forces the abrasive medium through the work piece.

• As abrasive medium flows through the part, its velocity will change with the different cross – sectional areas.

• Due to its low MRR, it is not suited for mass material removal.

• It is used for finishing in metals, ceramics, and many plastics in uniform and economical manner.

Classification of AFM

• AFM is classified into three categories viz.

– One way AFM

– Two way AFM

– Orbital AFM

Equipments

• Machine

– It is constructed with two opposing medium chambers that are hydraulically or manually clamped together.

– The pressure for extruding medium ranges from 0.69 to 22 MPa (100 to 3200 psi)

– Lower pressure preferred for fragile parts or loose fixtures.

– Little heat is generated due to friction hence medium coolants are recommended.

• Tooling

– Uses only to hold the part or parts in position.

– To contain and direct the flow of abrasives.

– Any number of parallel restrictions can be processed with uniform results.

– Replaceable inserts made of nylon, Teflon or hardened steel are used. Can last for up to thousands of parts.

• Media

– AFM media is pliable material that is resilient enough to act as a self forming grinding stone when forced through restrictions.

• Media contains base and typically two or three abrasive grit sizes.

• Base contains an organic polymer, specially hydrocarbon gels; it determines the degree of stiffness.

• Four types of abrasive are commonly used viz.

Aluminum oxide, silicon carbide, boron carbide and diamond.

• Abrasives are available in grit sizes ranging from 8 to 700 meshes.

Process Parameters

• Flow Rate – 11.3 to 378 L/min. (3 – 100 GPM)

• Cycles – 3 to several hundred

• Pressure – 0.69 – 22 MPa (100 – 3200 psi)

Process Capabilities

• AFM is able to increase surface smoothness up to 10 times.

• The limit for best surface finish is 0.05 microns.

• Large surface irregularities like deep scratches or large bumps cant be removed.

• Out of roundness and taper cant be corrected.

• Holes must be of dia. at least 0.2 mm for effective processing.

Process Summary

• Advantages – Debur, polish, and radius in one operation

– More repeatable than manual method

– Finish inaccessible area

– Batch production

– Faster than manual

• Disadvantages – Fixtures can be expensive

– High capital investment

– Cant process blind holes.