On Abrasive Flow Finishing of Straight Bevel Gear
99
of the finishing medium. In these experiments, silicon carbide with 100 mesh selected
as abrasive particle according to the module of gear [7]. Moulding clay was used
for putty because of low cast, easy availability and its capability to hold the abrasive
particle against high extrusion pressure. AFF medium of selected abrasive particles, putty and blending oil (whose quantities are calculated according to required
composition of the AFF medium) were prepared by thorough hand mixing followed
by pressing in a deep drawing machine. Volumetric concentration of blending oil
was increased correspondingly reducing volumetric percentage of the putty in the
AFF medium to maintain of 1156 cm
3 volume (determined from the dimensions of
the AFF medium containing cylinder). Extrusion pressure, finishing time, concentration, type, hardness and size of abrasive particles, medium viscosity, geometry
and hardness of workpiece are significant AFF process parameters.
In Phase-1, four experiments were performed to identify optimum value of extrusion pressure by varying it at four levels (i.e. 2.5; 5; 7.5; and 10 MPa) and using
constant values of finishing time ‘t’ as 15 min, size of abrasive particles as 100 Mesh
(with corresponding diameter 150 µm), volumetric concentration of abrasive particle
as 30% and volumetric concentration of silicon oil as 10%. Seven experiments were
conducted using one factor at a time approach in Phase-2, by varying finishing time
‘t’ at seven levels (i.e. 10; 15; 20; 25; 30; 35; and 40 min) and using optimum value
of extrusion pressure ‘P’ obtained in Phase-1 experiment, size of abrasive particles
‘M a ’ as 100 Mesh (with corresponding diameter 150 µm), volumetric concentration
of abrasive particle ‘C av ’ as 30%, and volumetric concentration of silicon oil ‘O c ’
as 10%. Maximum surface roughness ‘R max ’ and average surface roughness ‘R a ’
were used as the responses in all these experiments. Additionally, surface roughness
profiles and surface morphology were studied for those straight bevel gears which
have shown maximum reduction in the considered parameters surface roughness.
They have been referred to as the best-finished gears.
Gears are subjected to fluctuating stresses, and therefore, surface roughness is
very important aspect because it affects their service life and operating performance.
Higher surface roughness causes less available contact area with its meshing gear
and frequent breakage of roughness peaks which result faster wear of flank surfaces
of a gear by pitting, micro-pitting, scuffing, abrasive wear and adhesive wear.
2.4 Measurement of the Responses
2.4.1 Measurement of Surface Roughness
Maximum surface roughness ‘R max ’ and average surface roughness ‘R a ’ of straight
bevel gears were measured before and after finishing by AFF using surface roughness tester (LD-130 MarSurf from Mahr Metrology, Germany) by probing in both
left and right flank surfaces at two different location. An average of all assessed
values of ‘R a ’ or ‘R max ’ were used to calculate the changes in maximum surface
roughness ‘R max ’ and average surface roughness ‘R a ’. Following relation was
99
of the finishing medium. In these experiments, silicon carbide with 100 mesh selected
as abrasive particle according to the module of gear [7]. Moulding clay was used
for putty because of low cast, easy availability and its capability to hold the abrasive
particle against high extrusion pressure. AFF medium of selected abrasive particles, putty and blending oil (whose quantities are calculated according to required
composition of the AFF medium) were prepared by thorough hand mixing followed
by pressing in a deep drawing machine. Volumetric concentration of blending oil
was increased correspondingly reducing volumetric percentage of the putty in the
AFF medium to maintain of 1156 cm
3 volume (determined from the dimensions of
the AFF medium containing cylinder). Extrusion pressure, finishing time, concentration, type, hardness and size of abrasive particles, medium viscosity, geometry
and hardness of workpiece are significant AFF process parameters.
In Phase-1, four experiments were performed to identify optimum value of extrusion pressure by varying it at four levels (i.e. 2.5; 5; 7.5; and 10 MPa) and using
constant values of finishing time ‘t’ as 15 min, size of abrasive particles as 100 Mesh
(with corresponding diameter 150 µm), volumetric concentration of abrasive particle
as 30% and volumetric concentration of silicon oil as 10%. Seven experiments were
conducted using one factor at a time approach in Phase-2, by varying finishing time
‘t’ at seven levels (i.e. 10; 15; 20; 25; 30; 35; and 40 min) and using optimum value
of extrusion pressure ‘P’ obtained in Phase-1 experiment, size of abrasive particles
‘M a ’ as 100 Mesh (with corresponding diameter 150 µm), volumetric concentration
of abrasive particle ‘C av ’ as 30%, and volumetric concentration of silicon oil ‘O c ’
as 10%. Maximum surface roughness ‘R max ’ and average surface roughness ‘R a ’
were used as the responses in all these experiments. Additionally, surface roughness
profiles and surface morphology were studied for those straight bevel gears which
have shown maximum reduction in the considered parameters surface roughness.
They have been referred to as the best-finished gears.
Gears are subjected to fluctuating stresses, and therefore, surface roughness is
very important aspect because it affects their service life and operating performance.
Higher surface roughness causes less available contact area with its meshing gear
and frequent breakage of roughness peaks which result faster wear of flank surfaces
of a gear by pitting, micro-pitting, scuffing, abrasive wear and adhesive wear.
2.4 Measurement of the Responses
2.4.1 Measurement of Surface Roughness
Maximum surface roughness ‘R max ’ and average surface roughness ‘R a ’ of straight
bevel gears were measured before and after finishing by AFF using surface roughness tester (LD-130 MarSurf from Mahr Metrology, Germany) by probing in both
left and right flank surfaces at two different location. An average of all assessed
values of ‘R a ’ or ‘R max ’ were used to calculate the changes in maximum surface
roughness ‘R max ’ and average surface roughness ‘R a ’. Following relation was