for the subject "machine tools and digital manufacturing"

1. Grinding and Grinding Machine

2. Grinding:
• Grinding is a process of removing material by abrasive
action of a revolving wheel on the surface of a work-piece in
order to bring it to required shape and size
• The wheel used for performing the grinding operation is
known as grinding wheel
• It consists of sharp crystal called abrasive held together by a
binding material or bond
• The wheel may be a single piece or solid type or may be
composed of several segments of abrasive blocks joined
together.

3. Types of grinding Machine
Grinding machines according to quality of surface finish, may be
classified as
1. Rough /Non-precision grinding
2. Precision grinding
Rough/Non-precision grinding
To remove more stock than other grinding
a)Floor stand and bench grinders
(b)Portable and flexible shaft grinders
(c)Swing frame grinders
(d)Abrasive belt grinders

4. Portable and flexible shaft grinders

5. Floor stand and bench grinders
• grinding of various materials and cutting tools in tool rooms,
foundries and general repair shops
• horizontal spindle having grinding wheels mounted on both
ends
• It can be suitably bolted on a bench at convenient height
• The floor or pedestal grinder is a bench grinder mounted on a
steel stand or pedestal of suitable height
• The horizontal spindle carrying the grinding wheel is normally
an extension on both side of the armature shaft of the motor
• These grinder are also used for polishing by replacing the
grinding wheel by polishing wheel

6. bench grinder
floor or pedestal grinder

7. SWING GRINDER
• Frame about 2-3 m length
• One end with grinding wheel
and motor
• Other end with balance weight

8. Abrasive belt grinders
• Endless belt of abrassive
cloth
• Drums driven by motor
• Support plate to prevent
giving up
• Work applied by hand
• Light grinding, polishing
works

9. Precision grinders
according to the type surface generated or work
done they may be classified as:
• (a)cylindrical grinding machine
• (b) surface grinding machine
• (c) Internal grinding machine
• (d) Tool and cutter grinding machine

10. Surface grinding machine
• Horizontal spindle and reciprocating table
• Vertical spindle and reciprocating table
• Horizontal spindle and rotary table
• Vertical spindle and rotary table

12. Cylindrical Grinders
Centre type
• The work piece held on centre by a chuck or in a suitable
holding fixture, rotating it about its axis
• Traversing of wheel or work is done either by hydraulic or
mechanical power or by hand
• Feed is given to the work or the wheel at the end of each
traversing movement

13. • Traverse grinding – workpiece reciprocates. Cylinders with
length longer than width of wheel can be grinded
• Plunger type grinding – work rotates on fixed position, wheel
feeds to produce cylinders of width equal to wheel
• For mounting small wheels, an auxiliary shaft is provided,
which runs at a relatively much higher speed than the motor
• Both external and internal cylindrical grinding can be done on
lathe by this equipment

14. • Centre less type
• work is supported by a combination of grinding wheel,
regulating wheel and a work rest blade
• It is used for both external as well as internal grinding
• Many hollow cylindrical and tapered workpiece, like bushes,
pistons, valves tube and balls etc either do not or cannot have
centre are best ground on centreless grinder

15. • a heavy base and two wheel heads, one carrying the grinding
wheel(large one) and the other regulating wheel(smaller)
• The workpiece rests on the blade between these two wheel
• grinding operation is performed by grinding wheel
• regulating wheel is to provide the required support to the work
piece while it is pushed by cutting pressure of grinding wheel
• The regulating the wheel essentially carries rubber bond and
helps in the rotation of work-piece due to friction
• Small, fragile or slender workpiece can be grinded
• No chatter or deflection

17. Internal grinders
Used for grinding internal surface of different holes, cylindrical,
tapered etc
Types:
1. Chucking internal grinders
2. Planetary internal grinders
3. Centreless internal grinders

18. Centreless internal grinders
• The work-piece is supported between
three rolls known as pressure roll,
supporting roll and a regulating
roll
• All rolls rotate in same direction
while the work-piece and grinding
rotate in opposite direction
• The grinding wheel remains contact
with the internal surface of the work-
piece
• The pressure roll is so mounted that it
can be swung to a slide to allow
loading and unloading of the work-
piece

19. Planetary internal grinders
• To grind holes in large, irregular shaped and heavy work-
piece
• The work-piece remains stationary, which is mounted on a
slide
• the axis of rotating grinding wheel travels along a circular path
around the axis of hole in the work piece
• The longitudinal traverse obtained by
– reciprocating movement of the grinding wheel spindle
– moving the slide forward and backward on which work-piece is
mounted

21. Chucking internal grinders
• Workpiece mounted on
chuck or magnetic plate
• Performed on lathe

22. Grinding mechanism
• engages an abrasive tool whose cutting elements are
grains of abrasive material known as grit
• grits are characterized by sharp cutting points, high hot
hardness, wear resistance and chemical stability.
• Fig illustrates the cutting action of abrasive grits of
disc type grinding wheel

23. Grinding wheels
• Multitooth cutter
• Made of hard particles called abrasives
• Wheel has 1 piece or segments of abrasive blocks
Wheel Materials
Abrasive:
• It is that material of grinding wheel which does the cutting
action
• Hard, tough and when fractured it forms cutting edges and
corners
• Attached to wheel by suitable bonding material
(a) Natural Abrasive
(b) Artificial abrasive

24. Natural Abrasive:
• By uncontrolled forces of nature
• sand stone, emery, corundum and diamond
• Sand stone or solid quartz
– for hand operated grindstones
– sharpening some wood-working tool
• Corundum
– 75-90% crystalline AL2O3+iron oxide
• diamond
– Truing and dressing other grinding wheel
– acts as an abrasive material for hard material
• Emery
– 50-60% crystalline AL2O3+iron oxide

25. Artificial abrasive:
• manufactured under controlled conditions in closed
electric furnaces to avoid the introduction of
impurities and to achieve the necessary temperature
for chemical reactions to take place
• Silicon carbide(SiC)
– silica sand + powdered coke + salt + saw dust
– heated in electronic furnace upto 4000ºC
– Resulted solid mass crushed, treated with alkalis
and made into grits
– To grind low tensile strength materials like cast
iron, bronze, Cu, Al, plastic etc

26. • Aluminum oxide(Al2O3)
– Most widely used
– Fusing bauxite and small amount of coke in electric
furnace
– Mass is crushed, washed, heated with alkalis, washed
again and graded
– High tensile materials like carbon steels, alloy steels,
wrought iron, HSS and tough bronze
• Artificial diamond
– The diamond produced through artificial means are
quite comparable to the natural diamond in their
grinding characteristics and give better result than the
latter.

27. Advantages and use of artificial Abrasive
The artificial abrasives have lately superseded the natural
abrasive for following reason
1. Uniformity in the product- controlled conditions in the
electric furnace
2. Quality of production and supply can be varied according to
the demands
3. They have largely abolished the dependence on natural means
to meet the growing demand of more abrasive material in the
modern manufacturing process

28. SPECIFICATION OF GRINDING WHEELS
• Standard wheel markings
• Diameter of the wheel
• Bore diameter of the wheel
• Thickness of the wheel
• Type of the wheel

29. • To maintain uniformity throughout the country in the
system of making grinding wheel, the Bureau of
Indian Standard has devised a standard system to be
followed by all manufacturer
• According to the system, the various elements and
characteristics of grinding wheels are represented on
all the wheels in a definite sequence as follows:
1. Abrasive 2. Grain size 3. Grade 4. Structure 5. Bond

30. Example:
A grinding wheel carrying the marking
125 x 25 x32 W A 46 L 4 V 17
125(mm)---wheel diameter
25(mm)--- Thickness of wheel
32 (mm)---Bore diameter
W---Manufacturer’s prefix to abrasive. It is optional.
A--- Abrasive(Al2O3)
46 ----Grain size(medium)
L ---grade (medium)
4 --- Dense structure
V --- Vitrified bond
17----it is the suffix denoting the bond type of the manufacturer

32. GRIT SIZE or GRAIN SIZE
• Small grit sizes produce better finishes
• Larger grit sizes permit larger material removal rates
• Harder work materials require smaller grain sizes to cut
effectively
• Softer materials require larger grit sizes
• Smaller grit sizes indicated by larger numbers and vice
versa Grain sizes in grinding wheels typically range
between 10 (very coarse) and 250 (very fine)

33. GRADE
• The grade of a bonded abrasive is a measure of its
bond strength
• The grade is also referred to as the hardness of a
bonded abrasive
• A hard wheel has a stronger bond and/or a larger
amount of bonding material between the grains than a
soft wheel

34. Selection Of Grinding Wheels
In selecting a grinding wheel, the following factors are considered:
Constant Factors
1. Properties of the material to be ground i.e., its hardness, toughness, strength etc.
2. The amount of stock to be removed.
3. Area of contact of the wheel with the workpiece.
4. Type of grinding machine and its condition.
Variable Factors
1. Wheel speed and work speed.
2. Dimensional accuracy required.
3. Quality of surface Finish required.
4. Speed and feed of the wheel.
5. Method of grinding i.e., wet or dry

35. • To hold abrasive grains together in the form of sharpening
stones or grinding wheels.
Several types of bonding materials used for making grinding
wheels,
• Vitrified bond
• Silicate bond
• Shellac bond
• Resinoid bond
• Rubber bond
• Oxychloride bond
These bonds may be used with either silicon carbide or aluminum
oxide.
BONDING AND TYPES OF BONDS

36. Vitrified bonding process:
• The clay and abrasive grains are thoroughly mixed with
sufficient water to make uniform mixture.
• The fluid mixture is then poured in to the mold and allowed to
dry.
• After cooling , the material trimmed to more perfect size and
shape.
• It is then heated in a furnace to a temperature 1260 deg .
• The clay vitrifies - it fumes and forms a porcelain or glass like
substance that surrounds and connects the abrasive grains.
• It gives good strength and porosity to allow high stock removal
• Denoted by “V”
• Tedious process
• Working speed below 2000m/min

37. Silicate bonding process:
• Silicate bonding wheels are made by mixing abrasive
grains with sodium silicate or water glass.
• The mixture is packed in to moulds and allowed to dry.
• The mould shapes are baked in a furnace at a temp of
260 deg for several days.
• The silicate bonded wheels are water proof.
• Denoted by “S”
• Rapid process than vitrified bonding
• Mechanical strength is less

38. Shellac bonding process:
• shellac bond wheels are also known as elastic bonded
wheels.
• abrasive and shellac are mixed in heated containers and
then rolled or pressed in heated molds.
• Later the shapes are baked at a temp 150 deg.
• The elasticity in this is grater than in other two types
and it has considerable strength
• It is not for heavy duty.
• Used for finishing chilled iron, cast iron and steel rolls
• Denoted by”E”

39. Resinoid bonding process:
• By mixing abrasive grains with synthetic resins and
other compounds.
• The mixture placed in molds and heated at about 200
deg.
• At this temp the resin sets to hold the abrasive grains
in wheel form.
• These wheels are used for purposes which require a
strong, high speed wheel.
• Denoted by “B”
• Destroyed by alkalis

40. Rubber bonding process:
• By mixing abrasive grains with pure rubber and sulphur.
• The mixture rolled in to sheets and wheels are punched
out of these sheets on a punch press.
• These are less heat resistant and reacts with water and
oil
• Hard, tough and more dense
• Denoted by “R”
• Suitable for parting operations

41. Oxychloride bonding process:
• this process consists of mixing abrasive grains with
oxide and chloride of magnesium.
• The mixing of bond and abrasive is performed in the
same way as for vitrified bond wheel.
• wheel segments for disc grinding operation.
• Denoted by “O”
• Weakest bond
• Affected by acidic solutions

42. Structure of a bonded abrasive is a measure of its porosity

43. DEFECTS IN GRINDING
• Glazing of the wheel is a
– condition in which the face or cutting edge acquires a glass
like appearance.
– the cutting points of the abrasives have become dull and
worn down to bond.
– makes the grinding face of the wheel smoother and that
stops the process of grinding.
• Sometimes grinding wheel is left loaded.
– cutting face is found being adhering with chips of metal.
– The openings and pores of the wheel face are found filled
with workpiece material particals, preventing the grinding
action.
– takes place while grinding workpiece of softer material.

44. Dressing
– The remedy for glazing and loading
– removes the loading and breaks away the
glazed surface so that sharp abrasive particles
can be formed again
– Different type of dressing operations are done
on a grinding wheel.
• dressing with the help of star dresser.
• number of hardened steel wheels with sharp points
on their periphery.
• The total is held against the face of revolving wheel
and moved across the face to dress the whole
surface.

45. Dressing Of Grinding Wheel

46. Truing
• Truing is the process of restoring the shape of
grinding wheel when it becomes worn and break
away at different points.
• Truing makes the wheel true and concentric with
the bore.

47. Truing Of Grinding Wheels
It is the process of changing the shape of the grinding wheels as it becomes
worn form an original shape owing to the breaking away of the bond.

48. LAPPING
• Loose abrasives function as cutting points finding
momentary support from the laps
• Material removal usually ranges from 0.003 to 0.03
mm but many reach 0.08 to 0.1mm in certain cases
• Mainly done on mating surfaces
• Super finishing operation
• Lapping compound = diamond+SiC+Al2O3+oil/water

49. HAND LAPPING
• lapping compound is spread on cast iron plate and
work piece is moved manually on it
• requires high personal skill because the lapping
pressure and speed have to be controlled manually
• the lap is made to rotate either in a lathe or honing
machine
• workpiece is reciprocated over it by hand
• Large size laps are made of cast iron, while those of
small size are made of steel or brass
• extensive use in finishing ring gauges

50. MACHINE LAPPING
• rotating table is used in place of the plate
• work piece to be lapped is given rotary motion by a
cage and rotated on the surface of the table
• Rotating lap is used above & below the work piece to
produce parallel surfaces

51. Machine lapping process is carried out for gauge
blocks, piston pin, ball bearings and engine valves

52. HONING
• Abrasive machining process that produces a precision
surface on a metal work piece by scrubbing an abrasive
stone against it along a controlled path.
• Typical applications are the finishing of cylinders for
internal combustion engines, air bearing spindles and
gears.
• Hole made by boring is obtained to required dimension
and finishing by honing
• The dimension to an accuracy of 0.005 mm can be
obtained
• One or more abrasive stones that are held under
pressure against the surface they are working on

53. • 6 to 8 honing sticks are held
together and metal is removed
by rotating or reciprocating
the holder
• wet cutting process
• Honing tool is rotated at a
speed of 0.5 - 2.5 m/s and
reciprocates at a speed of 0.2 –
0.5 m/s.
• Most honing is done on
internal cylindrical surface,
such as automobile cylindrical
walls

54. Broaching
• Machining process for removal of a layer of
material of desired width and depth
• enables remove the whole material in one
stroke by the cutter called broach
• Tool is a slender rod or bar type cutter having a
series of cutting edges with gradually
increased protrusion

55. Types
1. Internal broaching
• Work piece clamped on fixture
• To enlarge and finish various contours in through holes preformed
by casting, forging, rolling, drilling, punching
• Normally done in internal broaching machine
• Broaching splines
• Broaching keyways

56. 2. External broaching
• Competes with milling, shaping and planing
• Major applications
• grooves, slots, keyways etc
• external splines of different forms
• teeth of external spur gears or gear sectors

57. Semi Automatic Machine Tools
• Centre lathe is modified to improve production rate
• Capstan and turret lathes
• Distinguished feature – multiple tool holders
• Hexagonal turret/capstan head replaces tailstock
• Two tool posts on cross slide – in front and in rear
with 4 tools
• Turret indexed automatically
• Adjustable stops on turret saddle and cross slide
regulate cross feed and longitudinal movement

58. Turret and capstan lathe Engine lathe
1 There are two tool posts – fourway tool post
and rear tool post
There is only one tool post
2 Tailstock is replaced by an hexagonal tool
head called turret
Tailstock is located at the right side of the bed
3 A minimum of six tools can be held in the
turret
Only one cutting tool can be held in the
tailstock
4 Turret movement can be controlled
automatically
No provision to control the tool movement
(feed) automatically
5 More tools can be set on the turret and each
of them can be set at the work one by one
automatically
Only one tool can be put into machining at a
time. Tools have to be set everytime
according to the operation to be performed
6 Setting of cutting tool is easy Setting of tools will take more time
7 After the initial settings are made, a semi-
skilled operator can operate the machine
A skilled operator is necessary to work on the
machine
8 Tools can be indexed even when the
machine is on
The machine has to be stopped to change the
tool
9 Production cost is reduced as the rate of
production is more
The production cost is high
10 Motors with 15 HP are used Motors with 3 to 5 HP are used

59. Capstan lathe
Turret lathe

61. Automatic Lathes
• Machines the work piece automatically
– All movements, sequence of application, feeding
of raw material, parting off, unloading etc
• Depending on no of work spindles classified as
– Single spindle automatic lathe
– Multispindle automatic lathe

62. 1.Single spindle automatic lathes
• Used for large volume of production
• Jobs of rod, tubular or ring type and relatively small size
• Run continuously over a long time repeating same machine cycle
• Upto 5 radial tool slides, moved by cams mounted on cam shaft of
small size and power, but with high spindle speeds
Products are –
high quality
fasteners,
bolts, screws,
studs etc

63. 2. Multispindle automatic lathes
• Fastest type of production machines – 2,4,6,8 spindles
• All turret faces works on all spindles at same time
• No of components being machined = no of spindles in
machine
• Frame with headstock at right end
• Cross slides located at right and let sides of spindles and
carry cross feeding tools
• All auxiliary and working motion obtained from cam
mounted on cam shaft
• Machining accuracy is lower compared to single spindle
• Longer setup time and higher tooling cost

64. Multispindle automatic machines are of two types
Parallel action multi spindle
automatic machine
Progressive action multi spindle
automatic machine