On Abrasive Flow Finishing of Straight Bevel Gear
97
In context of gear finishing, AFF find more suitable because of use of flexible
finishing medium which can go easily inside the intricated root flank surfaces of
bevel gear and form a complementary shape of tooth gap. The complementary shape
of finishing medium acts as flexible grinding stone and a continuous movement of
it causes abrasion and impart finishing to it. Referring to previous research work, it
found that a very limited work performed on finishing of gear by AFF, and it mainly
emphasized on reduction of average surface roughness. No work reported on reduction of maximum surface roughness and on improvement of surface morphology of
straight bevel gear using AFF. Therefore, this work aim to improve maximum and
average surface roughness of straight bevel gear using AFF and to study their surface
morphology and bearing area of straight bevel gear which shows higher reductions
in surface roughness.
2 Materials and Methods
2.1 Gear Material and Specifications
Alloy steel 20MnCr5 which is widely used for commercial applications of straight
bevel gears was selected having 91.3 Rockwell hardness at B scale (HRB). The
chemical composition of gear material is 1.10% Cr; 1.19% Mn; 0.18% C; 0.019% P;
and 0.017% S; and balance Fe (by wt%). The specifications of gear are involute gear
teeth having 4.8 mm module, 10 number of teeth, 32° pitch cone angle, 20° pressure
angle, 15 mm face width, 48.9 mm pitch circle diameter, 59 mm outside diameter
and 20 mm bore diameter.
2.2 Experimental Setup and Fixture for AFF of the Gears
A two-way vertically configured experimental setup of AFF was developed a photograph of same is shown in Fig. 1a. It contains two hydraulic cylinders placed vertically
opposite to each other and two medium containing cylinders. A hydraulic power unit
is connected to hydraulic cylinders to reciprocate their piston and further to the
piston of medium containing cylinders. A special fixture was developed for holding,
and supporting work gear as shown in Fig. 1b and to enable their finishing by AFF
process. It has two cylindrical discs made of Metalon having an axial cylindrical boss
to hold and support the work gear. It has 10 circumferential holes of 8 mm diameter
in upper disc and 5 mm diameter holes in bottom disc according to pitch circle diameters of the work gear. A central hole in both part of fixture provided along with four
locating pins at upper part of disc corresponding to drilled holes in lower part of disc
to avoid any dislocation of both part of fixture while extruding finishing medium.
The work gear was placed on boss in its fixture such a way that drilled holes located
97
In context of gear finishing, AFF find more suitable because of use of flexible
finishing medium which can go easily inside the intricated root flank surfaces of
bevel gear and form a complementary shape of tooth gap. The complementary shape
of finishing medium acts as flexible grinding stone and a continuous movement of
it causes abrasion and impart finishing to it. Referring to previous research work, it
found that a very limited work performed on finishing of gear by AFF, and it mainly
emphasized on reduction of average surface roughness. No work reported on reduction of maximum surface roughness and on improvement of surface morphology of
straight bevel gear using AFF. Therefore, this work aim to improve maximum and
average surface roughness of straight bevel gear using AFF and to study their surface
morphology and bearing area of straight bevel gear which shows higher reductions
in surface roughness.
2 Materials and Methods
2.1 Gear Material and Specifications
Alloy steel 20MnCr5 which is widely used for commercial applications of straight
bevel gears was selected having 91.3 Rockwell hardness at B scale (HRB). The
chemical composition of gear material is 1.10% Cr; 1.19% Mn; 0.18% C; 0.019% P;
and 0.017% S; and balance Fe (by wt%). The specifications of gear are involute gear
teeth having 4.8 mm module, 10 number of teeth, 32° pitch cone angle, 20° pressure
angle, 15 mm face width, 48.9 mm pitch circle diameter, 59 mm outside diameter
and 20 mm bore diameter.
2.2 Experimental Setup and Fixture for AFF of the Gears
A two-way vertically configured experimental setup of AFF was developed a photograph of same is shown in Fig. 1a. It contains two hydraulic cylinders placed vertically
opposite to each other and two medium containing cylinders. A hydraulic power unit
is connected to hydraulic cylinders to reciprocate their piston and further to the
piston of medium containing cylinders. A special fixture was developed for holding,
and supporting work gear as shown in Fig. 1b and to enable their finishing by AFF
process. It has two cylindrical discs made of Metalon having an axial cylindrical boss
to hold and support the work gear. It has 10 circumferential holes of 8 mm diameter
in upper disc and 5 mm diameter holes in bottom disc according to pitch circle diameters of the work gear. A central hole in both part of fixture provided along with four
locating pins at upper part of disc corresponding to drilled holes in lower part of disc
to avoid any dislocation of both part of fixture while extruding finishing medium.
The work gear was placed on boss in its fixture such a way that drilled holes located