Abrasive flow machining (afm)
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Transcript of Abrasive flow machining (afm)
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Abrasive Flow Machining
Process Principle, Parameters and Capabilities
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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.
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• 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.
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Classification of AFM
• AFM is classified into three categories viz.
– One way AFM
– Two way AFM
– Orbital AFM
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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.
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• 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.
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• 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.
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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)
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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.
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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.