Abrasive flow machining is a finishing process that uses a semi-solid abrasive putty to remove small amounts of material from workpieces. The putty is forced through or across the workpiece using hydraulic pressure to deburr, radius, polish and perform other surface finishing operations. It is well suited for finishing metals, ceramics and plastics in a uniform and economical manner, though it is not used for heavy material removal due to its low material removal rate. The process involves selecting abrasive media based on the material and desired finish, and using tooling and pressure to direct the flow of media through restrictions in the workpiece.

1. Abrasive Flow Machining
Process Principle, Parameters and
Capabilities

2. 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.

3. • 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.

4. Classification of AFM
• AFM is classified into three categories viz.
– One way AFM
– Two way AFM
– Orbital AFM

8. 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.

9. • 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.

10. • 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.

11. 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)

12. 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.

13. 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.