Development of Aircraft Components

Prof.S.Rajendiran.et al. Int. Journal of Engineering Research and Application www.ijera.com
ISSN : 2248-9622, Vol. 6, Issue 7, ( Part -2) July 2016, pp.61-70
www.ijera.com 61|P a g e
Development of Aircraft Components
Prof.S.Rajendiran1
, Mrs.V.V.Krishna Vandana2
, Mr.S.K.Saidulu3
1
Prof and HOD, Mechanical Department, Ashoka Institute of Engineering and Technology, Malkapur
Hyderabad, Telangana 508252, Pin: 508252
2
Assistant Professor, Ashoka Institute of Engineering and Technology, Malkapur Hyderabad, Telangana
508252, Pin: 508252
3
Assistant Professor, Ashoka Institute of Engineering and Technology, Malkapur Hyderabad, Telangana
508252, Pin: 508252
ABSTRACT
When aircraft projects were taken up , new challenges were thrown open for the development of components. A
change in culture of making parts for land-based vehicles to high precision aircrafts components was essential.
Indigenous technologies were developed and implemented in realising the precision products. The experiences
are enumerated below:
I. LCA AIRCRAFT MOUNTED
ACCESSORY GEAR BOX (AMAGB)
Introduction
Developing Aircraft Mounted Accessory
Gear Box (AMAGB) for Light Combat Aircraft
(LCA). AMAGB will be housing Jet Fuel Starter
(JFS) unit, Integrated Drive Generator (IDG),
Hydraulic pumps etc.
The development of wooden patterns for
the cover casing and Main casing for AMAGB and
development of castings in Aluminium (LM-25)
were carried out at a vendor source. Further
development of the castings in Magnesium is being
carried out at HAL (Foundry and Forge).
When coordinating with the design group
right from the initial design and drawing stages. In
the due course suggestions were made to the
designers, whenever required, with a view to
produce the components as per drawing. At several
instances the designers have re-designed the
casings based on the manufacturer's suggestions for
produce ability of the casings.
Since it was the first time requirement at
Workshop to manufacture precision components
for Aircraft applications, an exposure to the
manufacturing environment of Aircraft components
was felt necessary. Hence various divisions of
HAL were visited to acquire and transfer the
technology of manufacture of Aircraft components.
Initially three pilot castings were made out
of Aluminium alloy / AZ 91C Magnesium alloy at
local vendor source. Further ten sets were supplied
by HAL (F&F). All the sets were successfully
machined at CNC machine complex of CVRDE.
The experiences gained during the machining of
the above casings were utilized to prepare this
report.
Machining features of Casings
Cover casing is a slender casting of 5 mm
section thickness. Not only the Aircraft quality but
also the machining of such a thin casting is the first
time requirement at work shop. Added to the above
are
(1) The flatness requirement is 0.010 mm over an
area of 400 x 750 sq.mm
(2) Tolerance on bore centre distance dimensions
is ±0.010 mm over a maximum length of 122
mm
(3) Tolerance on bore dimension should be within
–0.002 / - 0.005 over a maximum bore size of
Ø68. This tolerance level falls under IT3
grade.
(4) Concentricity of bores between Cover and
Main casings should be within 0.010 mm over
a depth of 200 mm
(5) Requirement to produce holes either by using
extra long series overhanging drills or at
angular position.
(6) Machining of tapped holes as per proprietary
standards and so on.
The drawings of the casings were
thoroughly analyzed and process planning was
carried out. Broadly the process flow is as follows
1. Semi finishing of Cover Casing.
2. Semi finishing of Main Casing.
3. Assembling Cover and Main Casings
4. Finish machining of Assembly Casing.
5. Finish machining of Cover Casing
6. Finish machining of Main Casing
The various aspects of machining of AMAGB
casings are discussed in the succeeding paragraphs.
RESEARCH ARTICLE OPEN ACCESS

Flatness
The designers have proposed to assemble
the Cover Casing and Main Casing without using
any gasket. Hence it is essential that the mating
surfaces of the casings need to be perfectly flat to
prevent any leakage through the interface of the
mating surfaces. During visits to HAL divisions, it
was learnt that there are two different approaches
for achieving the flatness.
(1) Machining the surface followed by scraping
and blue checking. This is being in practice at
HAL Koraput division.
(2) Machining the surfaces repeatedly to achieve
the required flatness. This method is followed
in HAL Engine Division, Bangalore.
It was decided to adopt the second
approach and hence the assistance of HAL
divisions was sought through AMAGB design
group and Aeronautical development agency
(ADA). Though some process sheets were
received, the process technology for achieving the
flatness through machining alone was not made
available. However it was decided to develop the
process technology in-house at CVRDE.
As the proposed approach involves
repeated reversal of the component and machining
of surfaces sufficient tooling pads have been
provided in the casting to create plane surfaces
parallel to the jointing surfaces of the castings. In
addition, tooling pads have been provided for
clamping the component, especially externally in
the cover casing to enable machining of jointing
surface in single setting and in the single pass of
the cutter.
For machining the jointing surface on a
CNC machine, necessary part program is to be
developed. While going through the designer's
drawing, one may find sufficient points for cutter
movement. Any programmer will naturally be
tempted to use those co-ordinate dimensions. But
practically, on the machine, when the program is
executed the system pauses the tool movement a
fraction of second at each changeover of the tool
direction. This instantaneous stop/start of the cutter
evidently leaves tool marks thereby resulting in
poor surface finish. Hence the problem was tackled
through a different approach.
The profile of the jointing surface consists
of circular arcs and line segments. As the design
drawing was created in AutoCAD, the points for
the tool path have been extracted from the
AutoCAD. Using the above points a part program
was generated and the machining was carried out.
Tooling
Initially a four fluted HSS end mill of Ø
20 mm was used for machining the surface. The
surface finish achieved was not satisfactory. The
cutter leaves tool marks due to back cut. The
problem was analyzed and it was concluded that as
the number of cutting edges are more, the axial
pressure on the component is more. Then an off-
hand ground single point fly tool was tried. The
result was most satisfactory. However controlling
the cutting geometry on the fly tool is difficult and
hence finally it was resorted to use a twin insert T-
MAX end mill, by removing one insert or to use a
single point end mill with throw away inserts.
Fixturing
Necessary fixtures were made and used.
However the job can be very well mounted directly
on the bed using block tooling’s to get better
flatness results. It was experienced that the
clamping torque should be even on all the clamping
bolts and should be minimal, otherwise the casing
deflects due to the tightening torque of the
clamping bolts.
Inspection on the machine bed
After machining the surface, the clamps
are released. A dial indicator (0.001 mm least
count) was mounted on the spindle head and the
readings on the machined surface in the clamp free
condition were checked. When the error obtained is
within permissible limits the component is taken up
for further machining. The components were also
inspected on CMM and then the mating
components (Cover casing and Main casing) were
blue checked and found that they match as per the
designer's requirements.
Linear Dimensions
The tolerance on liner dimensions is
controlled by selection of right machine tool,
cutting tools and correct part program.
Bore Dimension
The stringent tolerances on bores are to
IT3 Grade. (eg. the tolerance on Ø68 mm is -
0.002 /-0.015). However the requirement was met
by using imported SWISS precision CO boring
bars and boring cutters having accuracy of 0.005
mm on diameters.
Concentricity
Concentricity is achieved by finish
machining Cover and Main Casings in assembled
condition.
Extra Long Series Drills
Extra long series drills with more over
hang is unavoidable, to drill tapped holes for
mounting temperature and pressure sensors on
Cover Casing outer side. However it was suggested

to designer to relocate the pads to obviate
manufacturing problem.
Cross Hole Drilling and Cross Hole Boring
It is general practice to use jigs and / or
guide bushes to locate the tool for angular drilling.
But methods have been devised without using any
jig or guide bush to drill angular holes. Necessary
special tools are procured to drill Ø1 holes at
hydraulic pump stations in the Main Casing inner
side.
The primary requirement for drilling cross
holes is that either the component should be
aligned at the proper angle or the tool axis should
be moved along the required hole axis.
Machining of Tapped Holes as Per Proprietary
Standards
Assembly of Cover Casing and Main
Casing and also mounting of bearings are by using
special screws with locking arrangements. The
tapped hole is as per "ROSHAN" a proprietary
standard. The hole to be drilled is a stepped hole.
Hence necessary step drills (special) have been
procured and used. Alternatively two different
drills (specials) can also be used but resulting in
more operation time.
II. DEVELOPMENT OF FLEXIBLE
DIAPHRAGM FOR PTO SHAFT ASSY
Introduction
Power Take Off shaft assembly is an
important sub-assembly in the aircraft that connects
Aircraft Mounted Accessory Gear Box (AMAGB)
with Gas turbine engine through Engine Mounted
Accessory Gear Box (EMAGB). The primary
function of PTO shaft assembly is to transmit
power between EMAGB and AMAGB. AMAGB
functions in two modes, namely starter mode and
accessory mode. In starter mode it transmits power
from a gas turbine starter unit or Jet Fuel Starter
(JFS) unit mounted in the AMAGB to the Gas
Turbine. Once the engine attains its self sustaining
speed, the JFS drive is cut off by an Over Running
Clutch (ORC) assembly and the power flows from
gas turbine to the AMAGB through PTO shaft
assembly to drive the accessories such as Hydraulic
pumps and Integrated Drive Generator (IDG)
mounted in the AMAGB.
PTO shaft also has to absorb axial and
angular misalignments. Axial misalignments occur
to the extent of ± 5 mm due to thermal variations
and angular misalignments occur to the extent of
1.5° due to errors in EMAGB and AMAGB
mountings in the aircraft.
PTO shaft transmits 185 kW (250 HP) in
the aircraft whereas the total weight of PTO shaft
assembly is 1.6 kg. PTO shaft assembly is shown
in fig.1.
Flexible diaphragms are the important
elements in the PTO shaft assy. There are eight
diaphragms, four on either side of PTO shaft.
These four diaphragms are stacked together by
electron beam welding and then welded with the
central tube.
These diaphragms together absorb the
misalignments mentioned above.
Flexible Diaphragm
Flexible Diaphragm is a thin disc shaped
part. The thin section has a varying thickness of
2.2mm at the radius of 22mm to 0.4mm at the
radius of 52mm. The section profile approximates
to hyperbolic curve. The component is depicted in
fig.2. The profile data for the surfaces L & M are
identical and one surface is the mirror image of the
other about a mean line.

Design Requirements
From fig.2 it may be observed that the
diameters 36mm and 104mm are to be concentric
within 0.03mm and surfaces P and Q are to be flat
and parallel within 0.05mm. The surface finish of
surfaces L and M are to be finished by lapping to
Ra 0.1m. The required dimensional tolerances are
also indicated in the component drawing.
Manufacturing approach
The shape and size of the component
implies that this is highly difficult to produce by
resorting to the conventional machining methods. It
would be easier to produce the component by
unconventional methods such as ECM and so on.
Due to various reasons it had become essential to
produce the part by machining.
Considering the design requirements given
in section 2.1 and the raw material made available,
different process technologies have been developed
and established.
Initially the component was machined out
of Rolled plate or round bar. After several attempts,
finally an effective method producing from round
bar stock using hydraulic backup was established.
Machining from bar stock
The bar stock is of 120 mm in diameter.
The bar is sliced into discs of thickness 10mm.
The process sequence for producing the diaphragm
from the discs of 10 mm thick is given below.
Process sequence
1 Blank turning
2 Profile turning of surface L and boring
3 Step boring at surface Q
4 Profile turning of surface M using fixture with
hydraulic backup
5 OD turning using fixture
6 Bench work and
7 Inspection of cross section in 3D CMM.
Development of fixture with hydraulic backup
Initially, wax backup was used for turning
the second side of the profile from rolled plate. The
same wax back up was tried while machining the
part from round bar too. However wax is also
compressible though to a very less extent.
It is common practice to use hydraulic or
pneumatic clamping methods for machining thin
parts [3]. It is thought of to utilize the
incompressible nature of liquid in giving backup
while machining thin parts and thus an attempt is
made in that line.
The major considerations in developing
the hydraulic fixture are (i) the surfaces of the
diaphragm matching with the fixture should have
proper bearing to avoid leakage of liquid medium
(ii) proper clamping of the part is to be ensured (iii)
the fixture should be as simple as possible and (iv)
the fixture should also provide reference datum for
taking dimensions of the part.
In operation 2 the first side of the
profile(surface L) is machined, surfaces P & R are
turned and a distance of 1 ± 0.005 is maintained
between these two surfaces.

The turning fixture is depicted in fig.5 (a).
It consists of three datum surfaces C, D & E.
Surfaces C & D are precision turned parallely and a
distance of 1mm is maintained. Surface E is
parallel to surface C & D and perpendicular to Ø36
and Ø118.
The machining setup for turning second
side (surface M) is shown in fig. 5(b). The surfaces
P & R of the component are butt against the
surfaces C & D of the turning fixture, and the part
is clamped at the center as well as on the outer
edge. Straight cutting oil is filled between the
surfaces L & C through the tapped holes provided
at the back of the fixture plate and these holes are
suitably sealed using threaded plugs with ‘O’ rings.
Effects of hydraulic backup
1 In the wax back up method, the wax was
expendable; costlier compared to oil.
2 Straight cutting oil (servocut 945) available in
the machine is used. Oil is cheaper.
3 The wax is to be melted on a heater, poured in
the fixture and allowed to cool. Also it is to be
re-melted to remove wax after machining. This
consumes considerable preparatory time.
4 Filling of oil and draining is easier and
quicker.
5 Wax is slightly compressible but oil is
incompressible.
6 Even if the quantity of oil is just insufficient to
fill the space in fixture, it does not harm the
requirement as centrifugal action fills the rim
section of diaphragm leaving empty space only
at the hub portion where the section thickness
is more and also at that section the part is
rigidly clamped.
Experiments on tool geometry and cutting
parameters
In order to improve surface finish, trials
have been conducted with different tool
geometries, considering problems associated with
machining Titanium and its alloys [2]. It should
also be noted that, to turn the part, a standard tool
was modified as shown in fig.4, otherwise tool may
gouge with component. The cutting parameters
used during profile turning are as follows:
Cutting speed : 30m/min
Feed : 0.03mm/rev
Depth of cut : 0.05mm
The following table gives the surface finish values
as against tool nose radius.
Table 1 Effect of nose radius on surface finish
Nose
Radius(mm)
Surface finish
(Ra in µm)
0.8 0.7
1.0 0.4
1.2 0.6

Study on surface finish
The cutting parameters as used in the earlier
method were used and the surface characteristics
are analysed
1. In the product produced by the earlier method,
minute chatter marks were noticed. There is no
chatter mark in the product produced by using
fixture with hydraulic backup.
2. The surface finish was measured & better
surface roughness results were achieved
III. DEVELOPMENT OF SPUR GEARS
FOR AIRCRAFT GEARBOX
Introduction
In AMAGB there are twelve major gear
components driving two hydraulic pumps and one
integrated drive generator (IDG). The hydraulic
pump units activate the hydraulic lines in Aircraft
and IDG supplies electrical power to the Aircraft.
To appreciate the manufacturing criticalities
involved in these gear components let us consider a
typical gear as an example (Fig.1) say, Gear - PTO
Gear PTO – Description
Gear - PTO is an important item in the
AMAGB gear train (fig. 1.a) of 2 module with tip
relief to 0.010 μm. It is a gear integral with shaft.
This shaft itself acts as inner race of a bearing.

Effect of Tip Relief
Tip relief is provided tips of both the
pinion and the gear as shown in sketch A of Fig. 2
shows the effect of tip relief amplitude on the peak-
to-peak transmission error 2.
It is interesting to note
that overall compliance of the modified tooth
increased by about 20% and that the tooth contact
at the top and bottom of the tooth was eliminated.
The elimination of the contact reduces the stiffness
change, which occurs when a new tooth enters
contact.
Case Depth and Hardness on Gear Teeth
The gear teeth are to be carburised to a
depth of 0.6 to 0.9 mm and hardened to have soft
core (RC40) and hard case (RC 58 to 63).
Case hardened gears can withstand higher
loads than through hardened ones, but the through-
hardened gears are quieter in operation in normal
cases, have high endurance limit and cost less 3
.
However, since through-hardened gears are
vulnerable to distortion due to heat-treatment, they
are not recommended for high-speed drives.
Moreover, unless grinding of gear teeth is
practicable, through-hardened gears should not be
used in applications where accuracy is of utmost
importance. These gears have higher core strength
because of higher carbon content, but are less
ductile and less resistant to wear. Hardness
normally varies from HRC 30 to 55. These gears
are generally suitable for moderate strength and
impact resistance.
As a post-treatment, hardened gear steels
are sometimes tempered to permit machining of the
teeth. Hardness is somewhat sacrificed thereby,
but other properties are marginally altered.
Due to its comparative softness at the
core, the case-hardened gears possess interior
toughness. This in turn imparts shock or impact
resisting capability to these gears.
Case Depth and Hardness on Shaft Zone
On the shaft, the zone where bearing is
mounted needs to be carburised to a depth of 1.2 to
1.5mm and hardened to 58 to 63 RC. The shaft
itself acts as the inner race of the bearing, which is
considered as weight reducing effort in Aircraft
gearbox design.
Differential Case Carburising
We see, thus, that the gear tooth and shaft
area are carburised to different case depths and to
achieve this proper process planning is essential.
Hard Chrome Plating
On the shaft, the zone where dynamic
seals are assembled need to be hard chrome plated
to a depth of 0.07 to 0.13 mm, which has hardness
of 1200 VPN.
Hard Chromium (thick chromium) is
plated on steel, heat resistant, Copper base alloys,
Aluminium alloys, etc., to obtain a surface with:
- High hardness
- Low co-efficient of friction and hence as a
bearing surface
- Improved anti-seizure and anti-galling
properties to restore dimensions of worn out or
over machined surfaces (eg. Bearing surfaces)
Chromium is not normally suitable for
parts having hardness more than RC 45. Thickness
of hard-chromium plating is usually limited to 0.5
mm for aeronautical applications. As a practice,
hard chromium will be plated in excess and ground
or honed to the final dimension of the surface.
Where hard-chromium is meant for increase of
corrosion resistance, the coating may be composed
of a nickel undercoat and chromium top coat, with
minimum 15 μm chromium and a total thickness of
50 μm. Hard chromium plating causes a significant
reduction in fatigue strength of high strength steels,
which may be rectified to some extent by shot
peening the surface prior to hard-chromium plating
and by post heat-treatment. If resistance to fatigue
is an important consideration, hard-chromium
coating is not to be deposited in fillet areas. Hard-
chromium plating is usually limited to parts
operating below 4000
C.

Center Grinding
The component is to be finished to have
concentricity error of 0.01 mm over the cylindrical
diameters from one end to other. And also the
cylindricity errors are to be within 0.005mm. To
achieve these, the important operation to be carried
out after hardening treatment is center grinding.
Planetary conical wheel type center grinding
machine is used for grinding on both the ends.
Turning after Hardening
The component is thoroughly machined
after hardening and center grinding. This results in
bright surface free from quench cracks, if any, and
also it will be easy to dynamically balance the part
after complete processing. Web thinning to the
profile specified in detail ‘P’ of Fig.1 is carried out
using special turning tools. Thread cutting
operation is carried out on CNC lathe to have clean
threads without burrs.
Grinding of Cylindrical Surfaces
The diameters are toleranced to 4 μm and
also high surface finish (Ra.0.15) needs to be
achieved. Thus the part is ground with care using
dead center to minimize run out. Also the part is
super finished at the final stage.
Spline Cutting
Special spline cutters need to be used for
cutting internal splines and they were imported.
Gear grinding
The gear teeth are profile ground and to
achieve accuracies as per DIN class 5, the machine
used should be accurate and rigid and suitable
mandrels are to be developed. Reishauer gear
grinding machines were used for gear profile
grinding. The ground gears are subjected for nital
etching tests.
Serration cutting
Serrations as per Detail ‘R‘ of Fig.1 are
cut using specially developed press tools on a
hydraulic power press. These serrations are used
for assembling lock nuts, which are as per
proprietary standard.
Cross hole drilling
After case hardening, core hardness is RC
40. To drill cross-holes, high speed sensitive
drilling attachment was used.
Dynamic balancing
As the gears are running at 17,000 rpm
they are required to be dynamically balanced as per
ISO: 1940 – Grade G2.5. Permissible residual
unbalance is 1.04 g-mm.
Oxide phosphating
The parts are finally treated for oxide
phosphate to protect from environmental
deteriorations.
Inspection
Gears are checked thoroughly to assess
individual errors and composite errors. For this
Involute profile testers, Roll testers and other
standard measuring instruments and gauges are
used. Case depth and hardness are checked on test
pieces processed along with the component batch.
Depth of chrome plating is controlled by process.
However, test samples can also be used during
plating.
IV. MACHINING OF AIRCRAFT
BEARING RINGS
Introduction
Traditionally bearings have been
manufactured either from high carbon through
hardening steel or low carbon case hardening steel.
Both high-carbon and low-carbon materials have
survived because each offers a unique combination
of properties that best suits the intended service
conditions. But these materials are mostly used to
manufacture bearings, which are intended for
normal service applications. Whereas, in the case
of special applications like Aircraft and stationary
turbine engines where the bearings have to undergo
high speed and higher temperature environment,
high quality alloy steels are preferred most. Of the
alloy steels, high quality High speed Steel as per
AMS 6491B (M50) is one of the most widely used
materials for aircraft applications. The attempt to
machine such high quality steel for the specified
application was taken up for the first time and the
experiences, findings / problems encountered
during machining are reported in this paper.
Bearing rings
Ball Bearing mainly consists of two parts
viz. Outer race called Ring Outer and Inner race
called Ring Inner. These bearing rings are required
to be manufactured out of high quality high-
temperature bearing steel M50 HSS. It is high
carbon medium alloy steel consisting of important
carbide forming elements like Chromium,
Molybdenum and Vanadium. The composition of
the material is given in Table-1. The extent of
temperature ranges that are encountered during
service is from -54C to 150C.

Table-1: Chemical Composition of HSS M50
Problems faced and methodology followed
Generally, Inner and Outer rings of the ball
bearings are processed individually from separate bar
stocks. But in this venture, an economical way of
manufacture was followed considering the cost and
availability of raw material. The raw material for
the two rings was prepared by trepanning on the face
of the material followed by parting to separate
Fig.1: Trepanning Tool
Them into two pieces thereby saving
considerable raw material. Trepanning on the face
was attempted with thin and costly face grooving
inserts and tool holders. Since the ratio of groove
width to depth (aspect ratio) required to be trepanned
is quite high, frequent breakage of inserts was
encountered due to production of continuous chip
during grooving of annealed material and chip
clogging. Thus a novel method of trepanning the
groove using a simple grooving tool was attempted
which was found very successful. The grooving tool
developed in-house is shown in Fig. 1.
The trepanning operation is carried out by
initially face grooving to a certain depth and parting
off the required thickness of the rings. Then the
parted ring is reversed & held in lathe and face
grooving to the remaining depth is carried out thus
separating the inner and outer rings. This method of
trepanning is shown in Fig.2.
Fig. 2 Trepanning on a CNC lathe
Element Percentage
min max
Carbon 0.80 0.85
Chromium 4.00 4.25
Cobalt - 0.25
Copper - 0.1
Manganese 0.15 0.35
Molybdenum 4.00 4.50
Nickel - 0.15
Phosphorus - 0.015
Silicon - 0.25
Sulphur - 0.008
Tungsten - 0.25
Vanadium 0.90 1.10

After trepanning, the two rings were
processed individually on CNC Lathes by developing
suitable Mandrels. The raceway grooves are usually
formed using form tools in production environment.
But since the semi finishing operation was carried
out in annealed state, the grooving operation using
form tools was found to be unsuccessful. The surface
finish could not be maintained due to excessive
chattering due to higher contact area during forming.
Also the ductile nature of the spherodite structure of
the material leads to continuous chip production, burr
formation in the tool exit point and to some extent
formation of built-up edge on the tool face. Thus the
use of form tool for raceway grooving was
suspended and resorted to standard single point tools.
During raceway form turning, the burr
formation was noticed at tool exit point. Hence the
cutting parameters were modified suitably. Initially,
taking standard data from the standard metal cutting
Data Handbook, the cutting conditions were set. But
the data given in the books are particular to the ideal
conditions; hence considering wall thickness and
work piece clamping rigidity the cutting parameters
were optimized by conducting several trials. The
optimized cutting data is shown in Table-2. Tool
built-up normally arises due to higher friction and
contact pressure between the tool face and underside
of the flowing chip. Increasing the cutting speed,
reduction of temperature by administering sufficient
coolant and judicial selection of turning insert, which
is having low coefficient friction, can reduce this
problem. Hence Titanium Nitride coated P30 grade
cemented carbide copy turning insert, which is
having positive rake geometry, was selected and used
and thereby alleviated contact pressure and ensured
clean cutting during form turning.
Table-2: Optimized cutting parameters
Even with all these efforts the required
circularity could not be maintained owing to the slim
wall thickness and annealed condition (soft state) of
the work piece. To obviate this problem, it was
resorted to clamp the components using hydraulic
chuck in a CNC Lathe. As the contact pressure on the
jaw points is the primary candidate for problems like
ovality, it was decided to use collet type holding
arrangement wherein more area could be brought
into contact with chucking surface. Thus a collet type
special holding arrangement, which is in the softer
state, was devised and used to clamp the external
surface of the ring inner and to clamp the ring inner,
a close toleranced parallel type mandrel was used.
The soft state of the collet type chuck jaws acted like
soft jaw thus close tolerance could be achieved and
also speed of operation could be enhanced. The
hydraulic clamping helped to control the contact
pressure. The Special collet type arrangement and
mandrels are shown in Fig. 3&4.
Fig. 5: Collet type holding Device Fig. 6: Mandrel
The raceway profile was inspected using
contour checking instrument and the radii of the
grooves were inspected using custom-built ball type
Go and No-Go gauges. With these efforts the Inner
and Outer rings of the ball bearings were
successfully machined to the required dimensional
and geometrical parameters.
V. CONCLUSION
Machining technologies for Magnesium
alloy casings cast with mini core technology has
been developed, established and technology transfer
effected. High precision gears have been developed
and technology was made available to government
and private industries.
The maiden approach to develop thin
hyperbolic sectioned Flexible Titanium alloy
diaphragm was most successful.
The initial attempts for the indigenous
development of aircraft bearings using M50 alloy
bearing steel have shown promising results
beaconing the path for success.
Cutting conditions
Operation Speed (rpm) Feed mm/rev
Roughing 500 rpm 0.05
Finishing 700 rpm 0.03

Development of Aircraft Components

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