Machining & Machining

Tools
Unit-5A
Gear Manufacturing Methods
 Introduction
 Gears are used extensively for transmission of power. They find
application in automobiles, gear boxes, oil engines, machine tools,
industrial machinery, agricultural machinery, geared motors etc.
 To meet the strenuous service conditions the gears should have
robust construction, reliable performance, high efficiency, economy
and long life.
 Gears should be fatigue free and free from high stresses to avoid
their frequent failures.
 The gear drives should be free form noise and should ensure high
load carrying capacity at constant velocity ratio.
 To meet all the above conditions, the gear manufacture has
become a highly specialized field.
 Manufacturing of Gears
Manufacture of gears needs several processing operations in
sequential stages which are-
 Preforming the blank without or with teeth
 Annealing of the blank, if required, as in case of forged or cast
steels
 Preparation of the gear blank to the required dimensions by
machining
 Producing teeth or finishing the preformed teeth by machining
 Full or surface hardening of the machined gear (teeth), if required
 Finishing teeth, if required, by shaving, grinding etc.
 Inspection & testing of the finished gears.
 Gear Manufacturing
• 2 Categories: Forming and Machining.
• Forming means forming of shape by plastic
deformation in which volume remains constant
approximately before and after the process. It consists
of direct casting, rolling, powder metallurgy, injection
molding, drawing, extrusion, stamping, forging etc.
of tooth forms in molten, powdered, or heat softened
materials.
• Machining involves roughing and finishing operations
involving material removal. Cutting, Shaping, planing,
slotting, broaching, Milling, Grinding, Hobbing etc
Forming Methods for Gear
Manufacturing
 Casting
 Produce gear blanks or cast tooth
gears
 For casting of gears sand moulds or
permanent moulds are prepared, then
molten metal is poured into the mold
cavity to get the required gear.
 Cast iron gears rough, low strength,
and with some inaccuracies are
produced at low cost
 Recommended for manufacturing of large
sized gears where cost and power
transmission are important than operating
accuracy and noise level. Cast steel gear blank.
 Including sand casting, shell molding,
permanent mold casting, centrifugal
casting, investment casting, and die
casting.
 Sand Casting
Characteristics:
 Cheaper low quality gear in small numbers
 The tooling costs are reasonable
 Poor Surface finish and dimensional accuracy
 Due to low precision and high backlash, they are noisy.
 They are suited for non- critical applications
Applications: (without finishing operation)
 toys, small appliances, cement-mixer barrels, hoist gearbox of
dam gate lifting mechanism, hand operated crane etc.
Materials:
 C I, cast steel, bronzes, brass and ceramics.
 The process is confined to large gears that are machined later
to required accuracy
 Die Casting
forcing molten metal under high pressure into a mold cavity
created using two hardened tool steel dies having gear shape.
Characteristics:
• Better surface finish and accuracy (tooth spacing and
concentricity)
• High tooling costs
• Suited for large scale production
Applications: instruments, cameras, business machines, washing
machines, gear pumps, small speed reducers, and lawn movers.
Materials:
 zinc, aluminium and brass.
 The gears made from this process are not used for high speeds
and heavy tooth loading.
 Normally applied for small size gears.
 Investment Casting
 Investment means surrounded.
 a technique for making small, accurate castings in refractory
alloys using a mould formed around a pattern of wax or similar
material which is then removed by melting.
Characteristics:
• Reasonably accurate gears
• Applicable for a variety of materials
• Refractory mould material
• Allows high melt-temperature materials
• Accuracy depends on the original master pattern used for the mold.
Materials:
 Tool steel, nitriding steel, monel, beryllium, copper
 Production cost is high.
 Economical in complicated shape production
 Rolling
 The straight and helical teeth of disc or rod type external steel gears of small
to medium diameter and module are generated by cold rolling by either flat
dies (Flat Rolling) or circular dies (Round Rolling)
 Such rolling imparts high accuracy and surface integrity of the teeth which are
formed by material flow unlike cutting.
 Gear rolling is reasonably employed for high productivity and high quality
though initial machinery costs are relatively high. Larger size gears are formed
by hot rolling and then finished by machining
 Powder Metallurgy
 The metal powder is pressed in dies to convert into tooth shape,
after which the product is sintered. After sintering, the gear may
be coined to increase density & surface finish. This method is
usually used only for small gears.

Characteristics:
Accuracy similar to die-cast
gears
Material properties can be
Tailor made
Typically suited for small sized
gears
Economical for large lot size
only
Secondary machining is not
required

Applications : High quality gears, application in toys, instruments, small motor

drives etc.
 Injection Molding
 Producing parts by injecting molten material into a mold.
 Material for the part is fed into a heated barrel, mixed (Using a helical
shaped screw), and injected (Forced) into a mold cavity having
required gear shape, where it cools and hardens to the configuration
of the gear.
 These are low precision gears in small sizes
 Advantages of low cost and the ability to be run without lubricant at
light loads.
• Materials
 Nylon, cellulose acetate, polystyrene, polyimide, phenolics,
glasses, elastomers, confections, and most thermoplastic and
thermosetting polymers
• Applications
 Injection molded gears are used in cameras, projectors, wind shield
wipers, speedometer, lawn sprinklers, washing machine.
 Cold Drawing
 Cold drawing forms teeth on steel rods by drawing (pulling)
them through hardened dies.
 The cold working increases strength and reduces ductility.
 The rods are then cut into usable lengths and machined for
bores and keyways, etc.
• Any material that has good drawing properties, such as high-
carbon steels, brass, bronze, aluminum, and stainless steel, may
be used
Large variety of applications and have been
used on watches, electric clocks, spring wound
clocks, typewriters, carburetors, magnetos,
small motors, switch apparatus, taximeters,
cameras, slot machines, all types of
mechanical toys, and many other parts for
machinery of all kinds.
 Extrusion
• Bar is pushed through a die or series of several dies having
gear shape , the last having the final shape of the desired
tooth
• Material squeezed by die pressure into the shape of the die.
hence, the outside surface is work hardened and quite
smooth.
 After forming teeth on long rods, they are then cut into usable
lengths and machined for bores and keyways etc.
 Good surface finishes and pore free dense structure with
higher strength.
Materials: Aluminum, copper,
naval brass, non ferrous
metals,architectural bronze and
phosphor bronze
Applications: Splined hollow &
solid shafts, sector gears
 Stamping
 Similar to using a cookie cutter.
 A sheet of metal is placed between the top and bottom portions
of a die; the upper die is pressed into the lower section and
“removes” or cuts the gear from the sheet.
 This is a low-cost, very efficient method for producing lightweight
gears for no-load to medium-duty applications.
 Stamping is restricted by the thickness of the workpiece and is used
primarily for spur gears and other thin, flat forms
 Materials: all the low and medium carbon steels, brasses, and some
aluminum alloys. Nonmetallic materials can also be stamped.

Applications: toys, clock and timer

mechanisms, watches, small
appliances such as mixers, blenders,
toasters, and can openers, as well as
larger appliances such as washers
and dryers.
 Forging
 Forging is a process in which material is shaped by the application of
localized compressive forces exerted manually or with power hammers,
presses or special forging machines.
 The process may be carried out on materials in either hot or cold state.
 When forging is done cold, processes are given special names. Therefore, the
term forging usually implies hot forging carried out at temperatures which
are above the recrystallization temperature of the material.
 A cylindrical billet of the required material is heated and then forged into a die
cavity that has the shape of the finished gear.
 After being forged , the gear is allowed to cool in air
 High quality gears with an excellent surface finish and high fatigue strength (due
to advantageous texture, and grain flow pattern in the teeth) can be produced
 Applications: Gearboxes, agricultural equipment, material handling industries,
mining machines and marine transmissions
 Spur gears can be made but the die life is usually limited.
 Suitable for bevel and face gears
Machining Methods
for
Gear Manufacturing
 Machining Methods

 gears are manufactured in several routes ;

 The preformed blanks of are machined , finished and
then the teeth are produced by machining and
occasionally by rolling.
 Full gears with teeth are made by different processes and
then finished by further machining or grinding
 Accurate gears in finished form are directly produced by
near – net – shape process like rolling, plastic moulding,
powder metallurgy etc. requiring slight or no further finishing.
 The most commonly practiced method is preforming the
blank by casting, forging etc. followed by pre-machining to
prepare the gear blank to desired dimensions and then
production of the teeth by machining and further finishing by
grinding if necessary.
 Machining Methods: Forming & Generation
 2 Types by which gear tooth geometry is created by machining
methods
 Form Cutting or Forming – where the profile of the teeth are
obtained as the replica of the form of the cutting tool (edge);
e.g., milling, broaching , shear cutting and teeth cutting etc.
 the cutting edge of the cutting tool has a shape identical with the
shape of the space between the gear teeth
 Also called copying or profiling methods

 Generating – where the complicated tooth profile are provided by much simpler
form cutting tool (edges) through rolling type, tool – work motions, e.g., hobbing,
gear shaping etc.
 Characterised by Automatic indexing and the ability of single cutter to be used
to cut gears with any number of teeth for a given combination of module and
pressure angle
 The term generating refers to the fact that the shape of the gear tooth that
results is not the conjugate form of the cutting tool. Rather, the shape of the
tooth is generated by the combined motions of workpiece and cutting tool.
Gear Forming by
Machining
 Gear Milling
Forming is sub-divided into milling by disc cutters and milling by end mill cutter which
are having the shape of tooth space.
a Form milling by disc cutter: b Form milling by end mill cutter:
The disc cutter shape conforms to the The end mill cutter shape conforms to
gear tooth space. Each gear needs a tooth spacing. Each tooth is cut at a time
separate cutter. However, with 8 to 10 and then indexed for next tooth space for
standard cutters, gears from 12 to 120 cutting. A set of 10 cutters will do for 12 to
teeth can be cut with fair accuracy. Tooth 120 teeth gears. It is suited for a small
is cut one by one by plunging the rotating volume production of low precision gears.
cutter into the blank as shown in fig . The form milling by end mill cutter is
shown in fig .

To reduce costs, the same cutter is often used for the multiple-sized gears resulting in
profile errors for all but one number of teeth. Form milling method is the least accurate of
all the roughing methods.
 Gear Milling
Characteristics:
 use of HSS form milling cutters
 use of ordinary milling machines
 low production rate for
 need of indexing after machining each tooth gap
 slow speed and feed
 Gears having different modules and number of teeth
need separate milling cutters
 Less costly than hobs
 low accuracy and surface finish
 Inventory problem – due to need of a set of eight
cutters for each module – pressure angle
combination.
 Disc cutters are used for big spur gears of large
pitch
 End mill type cutters are used for teeth of large
gears and / or module.
 Indexing in form milling
 In form milling, indexing of the gear blank is required to cut all the teeth. Indexing is the
process of evenly dividing the circumference of a gear blank into equally spaced
divisions. The index head of the indexing fixture is used for this purpose.
 The index fixture consists of an index head (also dividing head, gear cutting
attachment) and footstock, which is similar to the tailstock of a lathe. The index head
and footstock attach to the worktable of the milling machine. An index plate containing
graduations is used to control the rotation of the index head spindle. Gear blanks are
held between centres by the index head spindle and footstock. Work pieces may also
be held in a chuck mounted to the index head
 spindle or may be fitted directly into the taper spindle recess of some indexing fixtures.

Note: To understand
indexing in detail refer
milling operations unit
slides
 Shaping, planing and slotting
 Shaper uses linear motion for cutting. Cutting edge
corresponds to the shape of the tooth space
 The tool reciprocates parallel to the centre axis of the blank
and cuts one tooth space at a time.
 Successive teeth are cut by rotating the gear blank through
an angle corresponding to the pitch of the teeth until all the
tooth have been cut.
 In Shaping both productivity and product quality are very Gear teeth cutting in
low used for repair and maintenance purpose. ordinary shaping
machine
 In Parallel Multiple Teeth Shaping all the tooth gaps are
made simultaneously, without requiring indexing, by a
set of radially infeeding single point form tools. Now
obsolete for very high initial and running costs.

 In principle planning and

slotting machines work on the
same principle. Planing
machine for large gears
whereas slotting, generally, for
internal gears.
 Broaching
 A broach is multi – toothed tool in which
each successive tooth takes a small cut but
when all the teeth have passed over the
gear blank to be machined the required
amount of material has been removed and
gear teeth are shaped with desired size and
accuracy.
 The form of the space of gear teeth
correspond to form of broach teeth.
 Teeth of small internal and external spur
gears; straight or single helical, of relatively
softer materials are produced in large
quantity. Internal gears, racks, splines and
sector gears
 External teeth are produced by a broaching
in one pass.
 Very high productivity and quality but cost
of machine and broach are very high.
Gear Generation by
Machining
 Gear Hobbing
 Gear hobbing is a machining process in which gear teeth are
progressively generated by a series of cuts with a helical cutting
tool (hob).
 Hob is a cylinder on the surface of which a continuous thread has
been cut having shape to match the tooth space and having the cross
section of involutes gear teeth. Length wise gashes or flutes are cut
across the spiral to form cutting edges
 All motions in hobbing are rotary, and the hob and gear blank rotate
continuously as in two gears meshing until all teeth are cut.
 Gear Hobbing
• It is a continues indexing process in which both the cutting tool & work piece
rotate in a constant relationship while the hob is being fed into work.
• The hob and the gear blank are connected by means of proper change gears.
• The ratio of hob & blank speed is such that during one revolution of the hob, the
blank turns through as many teeth.
• The teeth of hob cut into the work piece in Successive order & each in a slightly
different position.
• Each hob tooth cuts its own profile depending on the shape of cutter. One
rotation of the work completes the cutting up to certain depth.
• Hob teeth are shaped to match the tooth shape and space and are interrupted
with grooves to provide cutting surfaces.
• It is the most accurate machining process since no repositioning of tool or blank
is required and each tooth is cut by multiple hop teeth averaging out any tool
errors.
• Excellent surface finish is achieved by this method and it is widely used for
production of gears
Feed Directions in Gear Hobbing
• The direction of feed during hobbing operation
depends, upon the type of gear to be cut.
• Following directions are commonly used in gear
cutting.
1. Axial feeding
2. Radial Feeding
3. Tangential feeding
4. Combined radial and axial feeding
5. Diagonal Feeding
 Axial Hobbing
 This type of feeding method is mainly used for cutting spur or helical
gears. In this type, firstly the gear blank is brought towards the hob to
get the desired tooth depth.
 The table side is then clamped after that, the hob moves along the
face of the blank to complete the job.
 Axial hobbing which is used to cut spur & helical gears can be
obtained by ‘climb hobbing’ or ‘conventional hobbing!

Axis of Hobber and blank are parallel

 Radial Hobbing
 This method of hobbing is mainly used for cutting Bevel Gears. In this
method the hob & gear blank are set normal to each other.
 The gear blank continues to rotate at a set speed about its vertical
axes and the rotating hob is given a feed in a radial direction. As soon
as the required depth of tooth is cut, feed motion is stopped.

Axis of Hobber and blank are Perpendicular

 Tangential Hobbing
 This is another common method used for cutting worm wheel or gears
( non parallel and non intersecting). In this method, the worm wheel
blank is rotated in a vertical plane about a horizontal axis. The hob is
also held its axis or the blank.
 Before starting the cut, the hob is set at full depth of die tooth and then
it is rotated.
 The front portion of the hob is tapered up to a certain length & gives
the feed in tangential to the blank face & hence the name ‘Tangential
feeding or hobbing.

Axis of Hobber
and blank are
Tangential
 Gear Hobbing
Advantages
• high accuracy.
• Both internal & external gears can be cut
• Non – conventional types of gears can also be cut
 Gear Shaping
 Gear shaping is a generation process. All shaping processes involve
reciprocating motion of cutter
 Gear shaping cuts gear teeth with a gear shaped cutter mounted in a spindle with
its main axis parallel to the axis of the gear blank.
 The cutter reciprocates axially across the gear blank to cut the teeth, while the
blank rotates in mesh with the cutter at the required velocity ratio.
 The relative rpm of both (cutter and blank) can be fixed to any of the available
value with the help of a gear train.

the cutter is fed radically into the gear blank

equal to the depth of tooth required. The
cutter is then given reciprocating cutting
motion parallel to its axis. The teeth of the
gear are generated by axial stroke of the
cutter in successive cuts.
Cutting occurs on the downward stroke ,
while during upward stroke , the cutter and
work are moved apart to prevent then
rubbing against each other
 Gear Shaping-Generation process

As the cutter rotates with the gear, it forms the tooth space by incremental cuts
depending upon the used feed rate , since the teeth are formed by a series of
closely spaced individual cuts and the involute on the gear is , in fact a series of
finely spaced cuts. The depth of these cuts is, however exceedingly small , even
for relatively high feed rates and for all practical purposes, the involute can be
regarded as a smooth curve.
 Gear Shaping
Advantages
a) automatic indexing
b) For same value of gear tooth module a single type of cutter can be used irrespective of
number of teeth in the gear hence provides high productivity and economy.
c) The gear type cutter is made of HSS and possesses proper rake and clearance angles.
d) straight or helical teeth of both external and internal spur gears can be produced with high
accuracy and finish. Shorter product cycle time and suitable for making medium and large
sized gears in mass production.
e) Different types of gears can be made except worm and worm wheels.
f) Close tolerance in gear cutting can be maintained.
g) Accuracy and repeatability of gear tooth profile can be maintained comfortably.

Limitations
a) It cannot be used to make worm and work wheel which is a particular type of gear.
b) As one teeth of cutter completely cut one teeth of cutter only. Errors in one tooth of the
shaper cutter will be directly transferred to the gear
c) There is no cutting in the return stroke of the gear cutter, so there is a need to make return
stroke faster than the cutting stroke.
d) In case of cutting of helical gears, a specially designed guide containing a particular helix
and helix angle, corresponding to the teeth to be made, is always needed on urgent basis.
 Gear Shaping by Rack type Cutters
 Vertical spindle with pinion type cutter is already explained. This is
again vertical axis but with rack type cutter.
 Oldest method for manufacturing spur and helical gears by using a rack
type cutter
 The teeth are generated by a reciprocating planing action of the cutter
against rotating gear blank.
 2 Types- Sunderland Process & Magg Process
Magg Method
Blank axis is vertical. Rack cutter also reciprocates /slides vertically.
Cutter can be set any angle in vertical plane. And can also reciprocate
in any direction. Less accurate because of introduction of errors in
tooth geometry by periodical repositioning of rack and blank for
completion of entire circumference.
 Sunderland Method
 Gear blank is mounted with its axis in horizontal plane, while the cutter reciprocates
parallel to the axis of gear blank.
 The cutter is fed gradually into the gear blank to the required depth.
 The gear blank rotates slowly while the cutter rack is simultaneously displaced at the
same linear speed as the gear circumferential speed.
 This relative motion brings a new region of the blank and cutter rack into contact,
causing the cutter teeth to cut wheel teeth of the correct geometry in the gear blank.
 A full revolution of the gear blank will therefore require an impractically long cutter
rack.
 To keep the cutter rack to practical length, it is disengaged from the blank after the
blank has rotated one or two pitch distances.

 It is retracted to an appropriate
position and reengaged with the
blank and the process is restarted.
 This implies that a relatively short
cutter rack may be used with the
added benefit that all the teeth are
basically cut with the same cutter
teeth which benefits uniformity.
Gear Finishing
Processes
 Gear Finishing
 For effective and noiseless operation at high speed , it is important
that profile of teeth is accurate , smooth and without irregularities.
 In Milling , it may not have accurate profile because of use of limited
cutters.
 In Shaping and Hobbing, it composed to tiny flats. This difficulty
achieved by reducing feed rate but it increases cutting time.
 In many cases gears are hardened after cutting teeth to improve life
but it introduce slightly distortion or surface roughness.
 Finishing operation intended to perform following function :
1) Eliminate after effect of heat treatment.
2) Correct error of profile and pitch.
3) Ensure proper concentricity of Pitch circle and Centre hole.
 Gear Shaving
 Process of finishing of gear tooth by running it at
very high rpm in mesh with a gear shaving tool.
 A gear shaving tool is of a type of rack or pinion
having hardened teeth provided with serrations.
 These serrations serve as cutting edges which do a
scrapping operation on the mating faces of gear to
be finished. Both gears in mesh are pressed to
make proper mating contact.
 The gear shaving operation is composed by
the simultaneous rotation of
workpiece and cutter as a pair of gears with
crossed axes. The crossed
axes generate a reciprocal sliding action between
the flank, gear tooth and the cutter teeth.
• Soft materials like aluminium alloy, brass, bronze,
cast iron etc. and unhardened steels are mostly
finished by shaving process.
 Gear Shaving

 Different types of shaving cutters which while their finishing action work apparently
as a spur gear, rack or worm in mesh with the conjugate gears to be finished.
 All those gear, rack or worm type shaving cutters are of hard steel or hss and their
teeth are uniformly serrated) to generate sharp cutting edges
 Gear Shaving
 Most widely used method
 For the continuous production of large lots, it represents the best
cost/performance ratio.
 The main limit of the gear shaving process is the lack of the chance
to remove the distortion caused by heat treatment.
 In the automotive industry, the vast majority of gears used in
gearboxes are suitable for gear shaving.
 The productivity of a gear shaving machine is much higher compared to a gear
grinding machine.

Usually, when high noiselessness and strict

quality levels are strictly required, the grinding
operation is the best solution, although
obviously more expensive.
 Gear Rolling/Roll Finishing/Gear Burnishing
 This process involves use of two hardened rolling dies containing very accurate
tooth profile of the gear to be finished.
 The gear to be finished is set in between the two dies as and all three are
revolved about their axis.
 Pressure is exerted by both the rolling dies over the gear to be finished.
 The surface irregularity of gear teeth is squeezed by hard die through plastic
deformation of high spots and burrs on the profile of gear tooth resulting to
smooth surface
 The resulting cold Working of the tooth
surfaces improves the surface finish,
 also induces compressive residual
stresses thus improving their fatigue
life.
 Process improves only surface finish
of teeth and does not correct the tooth
profile or pitch of teeth.
 This process is suitable only for gears
which do not require high accuracy.

Gear
Abrasive grinding wheel of
Grinding
a particular shape and Form Grinding
geometry are used for • This is very similar to machining gear teeth by a
single disc type form milling cutter where the
finishing of gear teeth.
grinding wheel is dressed to the form that is
 The two basic methods for
exactly required on the gear.
gear grinding are form
grinding (non-generating)  Gear to be finished is mounted and reciprocated
and generation grinding. under the grinding wheel.
• The teeth are finished one by one and after one
tooth finished, the blank is indexed to the next
tooth space as in the form milling operation.
• Need of indexing makes the process slow and
less accurate.
• The wheel or dressing has to be changed with
change in module, pressure angle and even
number of teeth.
• Form grinding may be used for finishing straight
or single helical spur gears, straight toothed
bevel gears as well as worm and worm wheels.
 Gear Grinding
The simplest and most widely used method is very similar to spur gear teeth
generation by one or multi-toothed rack cutter. The single or multi-ribbed rotating
grinding wheel is reciprocated along the gear teeth as shown. Other tool – work
motions remain same as in gear teeth generation by rack type cutter. For finishing
large gear teeth a pair of thin dish type grinding wheels are used. Whatsoever, the
contacting surfaces of the wheels are made to behave as the two flanks of the virtual
rack tooth.

Gear teeth grinding on generation principle

 Gear Grinding
 Usually, gear grinding is performed after a gear has been cut and heat-treated to a
high hardness
 Grinding is necessary for parts above 350 HB (38 HRC), where cutting becomes very
difficult.
 Teeth made by grinding are usually those of fine pitch, where the amount of metal
removed is very small.
 In addition, grinding of gears becomes the procedure of choice in the case of fully
hardened steels, where it may be difficult to keep the heat-treat distortion of a gear
within acceptable limits.
 In a few cases, medium-hard gears that could be finished by cutting are ground in
order to save costs on expensive cutting tools such as hobs, shapers or shaving
cutters, or to get a desired surface finish or accuracy on a difficult-to-manufacture
gear.
• materials must be removed in small increments when grinding hence costly as
compared to cutting
• Ground gears attract more inspection than cut gears, and may involve both magnetic
particle inspection as well as macroetching with dilute nitric acid.
 Gear Honing
• Honing is suitable for finishing of heat treated gears.
• It is carried out with steel tools having abrasive or cemented carbide particles
embedded in their surface.I
• t is used for super finishing of the generated gear teeth. Honing machines are
generally used for this operation. The hones are rubbed against the profile
generated on the gear tooth.
 Gears that have been honed instead of ground offer excellent wear
characteristics and are extremely quiet.
 it is mostly used in automotive, aerospace, truck, and heavy equipment
industries.
 This method is suitable for any application where quiet, robust, and reliable
gearing is required.
• Benefits of gear honing gear honing:
• Corrects dimensional errors
• Corrects distortions caused by heat treatment
• Removes nicks caused by handling
• Improves surface finishing
 Gear Lapping
 Lapping is done on generally gears having hardness more than 45 RC to
remove burrs, abrasions from the surface and to remove small errors caused by
heat treatment.
 In this process the gear to be lapped is run under load in mesh with a gear
shaped lapping tool or another mating gear of cast iron.
 Abrasive paste is introduced between the teeth under pressure. It is mixed with
oil and made to flow through the teeth.

 Lapping typically improves the wear

properties of gear teeth, and corrects the
minute errors in involute profile, helix angle,
tooth spacing and concentricity created in
the forming, cutting or in the heat treatment
of the gears.
 Therefore, gear lapping is most often
applied to sets of hardened gears that must
run silently in service.
 Blast Finishing
 Blast finishing uses the high-velocity impact of particulate media to
clean and finish a surface.
 The most well known of these methods is sand blasting, which uses
grits of sand (SiO2) as the blasting media.
 Various other media are also used in blast finishing, including hard
abrasives such as aluminum oxide (Al2O3) and silicon carbide
(SiC), and soft media such as nylon beads and crushed nut shells.
 The media is propelled at the target surface by pressurized air or
centrifugal force.
 In some applications, the process is performed wet, in which fine
particles in a water slurry are directed under hydraulic pressure at
the surface.
 Blast Finishing
 for cleaning, smoothening and roughening of metal casts and forged
parts-Paint removal, Rust removal, Etching for shiny surface

 Cleaning operations using abrasive blasting can present risks

for worker’s health and safety.
 large amount of dust created through abrasive blasting is hazardous
Noise pollution & safety issues
 Shot Peening
 In shot peening, a high-velocity stream of small cast steel pellets
(called shot) is directed at a metallic surface with the effect of cold
working and inducing compressive stresses into the surface layers.
 Used primarily to improve fatigue strength of metal parts.
 Cleaning is accomplished as a by-product of the operation.
 Shots (round metallic, glass, or ceramic particles) produce force
sufficient to create plastic deformation
 it operates by the mechanism of plasticity rather than abrasion: each
particle functions as a ball-peen hammer. In practice, this means
that less material is removed by the process, and less dust created
 Shot Peening
 Peening a surface spreads it plastically, causing changes in the
mechanical properties of the surface.
 Its main application is to avoid the propagation of microcracks from a
surface. Such cracks do not propagate in a material that is under a
compressive stress
 Shot peening is often called for in aircraft repairs to relieve tensile
stresses built up in the grinding process and replace them with
beneficial compressive stresses.
 Depending on the part geometry, part material, shot material, shot
quality, shot intensity, and shot coverage, shot peening can increase
fatigue life up to 1000%.
 Plastic deformation induces a residual compressive stress in a peened
surface, along with tensile stress in the interior. Surface compressive
stresses confer resistance to metal fatigue and to some forms of
stress corrosion. The tensile stresses deep in the part are not as
problematic as tensile stresses on the surface because cracks are less
likely to start in the interior.
 Phosphate Coating
• Phosphate coatings are used on steel parts
for corrosion resistance, better adherence of lubrication, lubricity, or as a
foundation for subsequent coatings or painting.
• It serves as a conversion coating in which a dilute solution of phosphoric
acid and phosphate salts is applied via spraying or immersion and
chemically reacts with the surface of the part being coated to form a layer of
insoluble, crystalline phosphates.
• Phosphate conversion coatings can also be used on aluminum, zinc,
cadmium, silver and tin.
• The main types of phosphate coatings are manganese, iron and zinc.
Manganese phosphates are used both for corrosion resistance and lubricity
and are applied only by immersion.
• Iron phosphates are typically used as a base for further coatings or painting
and are applied by immersion or by spraying.
• Zinc phosphates are used for corrosion resistance (phosphate and oil), a
lubricant base layer, and as a paint/coating base and can also be applied by
immersion or spraying
Gear Testing
 Gear Testing-Parkinson Test
Principle & Construction
• A master gear is mounted on a fixed vertical spindle and the gear to be
tested on another similar spindle.
• These gears are maintained in mesh by spring pressure.
 Gear Testing-Parkinson Test
• The gears are mounted on the two spindles , so that they are free to rotate
without measurable clearance.
• The right spindle can be moved along the table and clamped in any desired
position and The right spindle slide is free to move.
• Working
• At first the dial gauge is set to zero and then both gears are mounted on
spindles
• The variation in dial gauge reading are any irregularities in gear under test.
• A recorder is fitted in the form of waved circular chart.
•
 Gear Testing-Parkinson Test
Limitation
• Friction in the floating
carriage reduces
sensitivity
• It is not suitable for <
300 mm gear diameter.
• Measurements are
directly depend upon
master gear.
• Error in pitch, helix and
tooth thickness are not
clearly identified.