Guest Lecture
On
Advanced Manufacturing Processes
Prepared By
Prof. Shinde Vishal Vasant
Assistant Professor
Dept. of Mechanical Engg.
NDMVP’S Karmaveer Baburao Thakare
College of Engg. Nashik
Contact No- 8928461713
E mail:- [email protected]
Website:- www.vishalshindeblog.wordpress.com
PROF.V.V.SHINDE NDMVP'S KBTCOE NASHIK 03/10/2016 1
Grinding Process
• Grinding is a material removal and surface generation
process used to shape and finish components made of
metals and other materials.
• The precision and surface finish obtained through grinding
can be up to ten times better than with either turning or
milling.
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Grinding
• Grinding is a surface finishing operation where very thin
layer of material is removed in the form of dust particles.
• Thickness of material removed is in range of 0.25 to 0.50
mm.
• Tool used is a abrasive wheel.
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Types Of Grinding Machine
• There are many forms of grinding, but the four major industrial grinding
• Surface grinding
• Cylindrical grinding
• Centerless grinding
• Internal grinding
• Electrochemical grinding
• Belt grinder
• Bench grinder
• Tool and cutter grinder
• Gear grinder
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Major Advantages And Applications Of Grinding
Advantages
• Dimensional accuracy
• Good surface finish
• Good form and locational accuracy applicable to both hardened and
unhardened material
Applications
• Surface finishing
• Slitting and parting
• De-scaling , De-burring
• Stock removal (abrasive milling) finishing of flat as well as cylindrical
surface
• Grinding of tools and cutters and re-sharpening of the same.
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Grinding Wheel Materials
• Most abrasives used in industry are synthetic. Aluminum oxide is used in three quarters of all grinding operations, and is primarily used to grind ferrous metals.
• Next is silicon carbide, which is used for grinding softer, non-ferrous metals and high density materials, such as cemented carbide or ceramics.
• Superabrasives, namely cubic boron nitride or "CBN" and diamond, are used in about five percent of grinding. Hard ferrous materials are ground with "CBN", while non-ferrous materials and non-metals are best ground with diamond.
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Standard Shapes Of Grinding Wheels
• Straight wheel
• Cylinder
• Tapered
• Recessed one side
• Straight cup
• Recessed both sides
• Flaring cup
• Dish
• Saucer
• Mounted wheels
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Selection Of Grinding Wheel
For grinding a job the right grinding wheel is to be selected. The selection of a grinding wheel will depend on the following factors.
• Material to be ground
• Amount of stock to be removed
• Finish required
• Area of contact
• Wheel speed
• Work speed
• Personal factor
• Method of cooling
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Standard Marking System for Aluminum-Oxide
and Silicon-Carbide Bonded Abrasives
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Standard Marking System for Cubic-Boron-
Nitride and Diamond Bonded Abrasives
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Grinding Fluid The Grinding fluid serves three main functions :
• Reduces Wheel wear.
• Cools the w/p.
• Flushes away the chips.
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Grinding Process
Grinding is an abrasive machining process that uses
a grinding wheel as the cutting tool.
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Surface Grinding
Surface grinding uses a rotating abrasive wheel to remove
material, creating a flat surface.
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Surface Grinding
• It is machine basically used to grind flat surface.
• Job is mounted to a table which moves
longitudinally as well as in transverse direction.
• Manual feed or power feed.
• Work piece is clamped to the table by operating
magnetic chuck.
• Required grade of grinding tool is fixed to spindle.
• Grinding operation is carried out be operating both
table traverse wheel and vertical feed hand wheel.
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Types Of Surface Grinding Machine
Basically there are four different types of surface grinding
machines characterised by the movement of their tables and
the orientation of grinding wheel spindles as follows:
• Horizontal spindle and reciprocating table • Vertical spindle and reciprocating table • Horizontal spindle and rotary table • Vertical spindle and rotary table
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Surface grinding
• In surface grinding, the spindle position is either horizontal or
vertical, and the relative motion of the work piece is achieved either
by reciprocating the work piece past the wheel or by rotating it. The
possible combinations of spindle orientations and work piece motions
yield four types of surface grinding processes illustrated in the figure
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Horizontal And Vertical Grinding Machines
• This machine may be similar to a milling machine used mainly to grind flat surface.
However, some types of surface grinders are also capable of producing contour
surface with formed grinding wheel.
A: rotation of grinding wheel B: reciprocation of worktable C: transverse feed D: down feed 03/10/2016 PROF.V.V.SHINDE NDMVP'S KBTCOE NASHIK 19
Cylindrical Grinding
• It is a process of grinding curved surfaces.
• Surface may be straight or tapered.
• Work piece is mounted on two centers, one is tailstock
centre and the other is headstock centre.
• Head stock center may or may not revolve.
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Cylindrical Grinding
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Cylindrical Grinding
• In this operation, the external or internal cylindrical surface of a work piece
are ground. In external cylindrical grinding (also center-type grinding) the
work piece rotates and reciprocates along its axis, although for large and
long work parts the grinding wheel reciprocates.
• In internal cylindrical grinding, a small wheel grinds the inside diameter of
the part. The work piece is held in a rotating chuck in the headstock and the
wheel rotates at very high rotational speed. In this operation, the work piece
rotates and the grinding wheel reciprocates.
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External Cylindrical Grinding
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Internal Cylindrical Grinding
Internal grinding is used to grind the internal diameter of the workpiece.
Tapered holes can be ground with the use of internal grinders that can
swivel on the horizontal.
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Plunge Cut Grinding
Infeed (Plunge) Grinding is used
to grind work pieces which have
projections or shoulders,
multiple diameters or other
irregular shapes which preclude
the use of through feed grinding.
For example :- Grinding of crank
shaft.
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Centerless Grinding Machine
• It is used to grind curved surface work piece which are long and slender.
• Work piece rests on a work-rest blade and is backed by a second wheel called as regulating wheel.
• Grinding wheel pushes the work piece down the work-rest blade against the regulating wheel.
• Center less grinding differs from centered grinding operations in that no spindle or fixture is used to locate and secure the work piece.
• The work piece is secured between two rotary grinding wheels, and the speed of their rotation relative to each other determines the rate at which material is removed from the work piece.
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Center less Grinding
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Thread Grinding
Figure - Thread grinding by (a) traverse and (b) plunge grinding.
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Electrochemical Grinding
• The wheels and work piece are electrically conductive.
• Wheels used last for many grindings - typically 90% of the
metal is removed by electrolysis and 10% from the abrasive
grinding wheel.
• Capable of producing smooth edges without the burrs caused
by mechanical grinding.
• Does not produce appreciable heat that would distort work
piece.
• Decomposes the work piece and deposits them into the
electrolyte solution. The most common electrolytes are sodium
chloride and sodium nitrate.
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Applications
• Grinding turbine blades
• Grinding honeycomb metals for aerospace
application
• Sharpening hypodermic needles
• Machining carbide cutting-tool inserts
• ECG is used to remove surface defects from parts
where excessive material removal and residual
stresses are undesired, such as re-profiling
locomotive gears
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Electrochemical Grinding
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Specification Of Grinding Wheel
i. Abrasives
ii. Bond
iii. Grit/grain size
iv. Grade
v. Structure of wheels
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Specification of Grinding wheel
• Specification of a grinding wheel ordinarily means compositional
specification. Conventional abrasive grinding wheels are specified
encompassing the following parameters.
– The type of grit material
– The grit size
– The bond strength of the wheel, commonly known as wheel
hardness
– The structure of the wheel denoting the porosity i.e. the amount
of inter grit spacing
– The type of bond material
– other than these parameters, the wheel manufacturer may add
their own identification code prefixing or suffixing (or both) the
standard code.
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Dressing Of Grinding Wheel
• When the sharpness of grinding wheel becomes dull
because of glazing and loading, dulled grains and chips are
removed (crushed or fallen) with a proper dressing tool to
make sharp cutting edges and simultaneously, make
recesses for chips by properly extruding to grain cutting
edges. Thus, these operations are for the dressing.
• Dressing is the process of breaking away the glazed
surface so that sharp particles are again presented to the
work.
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Grinding-Wheel Dressing
Figure (a) Forms of grinding-wheel dressing. (b) Shaping the grinding face of a
wheel by dressing it with computer control. Note that the diamond dressing tool is
normal to the surface at point of contact with the wheel. 03/10/2016 PROF.V.V.SHINDE NDMVP'S KBTCOE NASHIK 37
Truing And Dressing Of Grinding Wheel
• Truing is the act of regenerating the required geometry on the grinding
wheel, whether the geometry is a special form or flat profile. Therefore,
truing produces the macro-geometry of the grinding wheel.
• Truing and dressing are commonly combined into one operation for
conventional abrasive grinding wheels, but are usually two distinctly
separate operation for super abrasive wheel.
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Difference Between Truing And Dressing
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Balancing Of Grinding Wheel
• Due to high rpms, unbalanced grinding wheels may have
negative effects both on quality and productivity.
• It is essential to control the vibrations induced in the
machine as an effect of the imbalance of mechanical
parts and the rotating grinding wheel.
• To enable the full potential of modern tool grinding
machines and to produce efficiently according to today`s
standards, it is absolutely essential to use balanced tools.
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Safety Precautions
• Wear goggles for all grinding machine operations.
• Check grinding wheels for cracks before mounting.
• Never operate grinding wheels at speeds in excess of the recommended speed.
• Never adjust the work piece or work mounting devices when the machine is operating.
• Do not exceed recommended depth of cut for the grinding wheel or machine.
• Remove work piece from grinding wheel before turning machine off.
• Use proper wheel guards on all grinding machines.
• On bench grinders, adjust tool rest 1/16 to 1/8 inch from the wheel.
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Types Of Super Finishing Processes
Honing.
Burnishing.
Polishing Buffing.
Lapping.
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Honing
• Honing is a finishing process, in which a tool called hone carries
out a combined rotary and reciprocating motion while the work
piece does not perform any working motion. Most honing is done
on internal cylindrical surface, such as automobile cylindrical
walls.
• Honing is an abrasive machining process that produces
a precision surface on a metal work piece by scrubbing
an abrasive stone against it along a controlled path.
• Honing uses a special tool, called a honing stone or a hone, to
achieve a precision surface. The hone is composed of abrasive
grains that are bound together with an adhesive. Generally,
honing grains are irregularly shaped and about 10 to 50
micrometers in diameter (300 to 1,500 mesh grit). Smaller grain
sizes produce a smoother surface on the workpiece.
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Setup Work piece
(Pipe)
Coolant
Honning
Tool or
Hone
Machine
Bed
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Honning Tool
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Advantages And Disadvantages
ADVANTAGES
• Low cost simple fixturing
• Accuracy in thin walled parts
• Accuracy in long bores
• Honing maintains the original bore
centreline
• Bores are corrected with least
possible amount of material
removal
• Material removal in all materials
regardless of hardness.
• Any degree of surface finish in a
part.
• High stock removal rates ( up to 12
times faster than internal grinding)
DISADVANTAGES
• Honing is a slow process.
• Horizontal honing may
create oval holes unless the
work is rotated or supported.
• If the workpiece is thin,
even hand pressure may
cause a slightly oval hole.
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Applications
• finishing of cylinders for internal combustion engines
• air bearing spindles
• Gears
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Super finishing /Micro honing
• Super finishing is a micro finishing process that produces a controlled
surface condition on parts which is not obtainable by any other method. The
operation which is also called ‘micro stoning’ consist of scrubbing a stone
against a surface to produce a fine quality metal finish.
• The process consists of removing chatter marks and fragmented or smear
metal from the surface of dimensionally finished parts.
• As much as 0.03 to 0.05 mm of stock can be efficiently removed with some
production applications, the process becomes most economical if the metal
removal is limited to 0.005 mm
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Super finishing
Figure:- Schematic illustrations of the super finishing process for a cylindrical part. (a) Cylindrical mircohoning, (b) Centerless microhoning.
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Lapping
• In lapping, instead of a bonded abrasive tool, oil-based fluid suspension
of very small free abrasive grains (aluminum oxide and silicon carbide,
with typical grit sizes between 300 and 600) called a lapping compound
is applied between the work piece and the lapping tool.
• The lapping tool is called a lap, which is made of soft materials like
copper, lead or wood. The lap has the reverse of the desired shape of the
work part. To accomplish the process, the lap is pressed against the work
and moved back and forth over the surface.
• Lapping is sometimes performed by hand, but lapping machines
accomplish the process with greater consistency and efficiency.
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Lapping
Figure (a) Schematic illustration of the lapping process. (b) Production lapping on
flat surfaces.(c) Production lapping on cylindrical surfaces.
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Advantages:-
1.Increase wear life of part. 2.Improve accuracy and surface finish. 3.Improve surface flatness. 4.Provide better seals and eliminate need for gaskets.
Applications:- Lapping is used to produce optical lenses, metallic
bearing surfaces, gauges, and other parts requiring very good finishes and extreme accuracy.
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Lapped Objects
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Burnishing
• Burnishing is the plastic deformation of a surface
due to sliding contact with another object. Visually,
burnishing smears the texture of a rough surface and
makes it shinier. Burnishing may occur on any sliding
surface if the contact stress locally exceeds the yield
strength of the material.
• Burnishing is a Super-finishing process.
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SETUP
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Advantages
• Mirror Finish in One Pass, Accurate Sizing, Close
Tolerances, Eliminates Lapping & Honing
• Improved Metallurgical Properties - Work Hardened
Surface, Increase in fatigue strength,
• No Additional Machine Investment - attachable to
any Standard Machine Tool Already Present in the
Shop
• Long Tool Life No Operator Skill Required Low
Torque & Power Requirements Maximum Parts
Interchangeability
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Applications
• Bright burnishing tools are being used in
sectors like Automobile, Aircraft, Defense,
Spacecraft, Railways, Textile, Machine Tool,
Motors and Pump Industry, Hydraulic and
Pneumatic Farm Equipment, Home
Appliances etc., and areas where close
tolerance and superior surface finish is
required.
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Polishing
• Polishing is a finishing operation to improve the surface
finish by means of a polishing wheel made of fabrics or
leather and rotating at high speed. The abrasive grains are
glued to the outside periphery of the polishing wheel.
• Polishing operations are often accomplished manually.
• Polishing is the process of creating a smooth and shiny
surface by rubbing it or using a chemical action, leaving a
surface with a significant specular reflection
• Polishing may be used to enhance and restore the looks of
certain metal parts or object on cars and other
vehicles, handrails, cookware, kitchenware, and
architectural metal.
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Setup
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Advantages & Disadvantages
ADVANTAGES
• Gives a natural appearance with a
high gloss and sheen.
• Produces a relatively durable finish.
• Never requires stripping.
• Can be applied with a standard low
speed weighted floor machine.
• If oxalic acid or oxalate is included
in the powder, it will remove fine to
medium scratches.
• Only done periodically, not daily or
weekly.
• Compounds composed of aluminum
oxide will not etch floor.
DISADVANTAGES
• A messy process, requiring
additional work to clean up.
• If oxalic acid is included in the
powder, it can cause etching or
blistering of marble and
limestone depending on the skill
of the person using it.
• Requires equipment (i.e., a floor
machine, wet vac, mop, mop
bucket, etc.).
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Buffing
• Buffing is a finishing operation similar to polishing, in which
abrasive grains are not glued to the wheel but are contained in a
buffing compound that is pressed into the outside surface of the
buffing wheel while it rotates. As in polishing, the abrasive
particles must be periodically replenished.
• As in polishing, buffing is usually done manually, although
machines have been designed to perform the process
automatically.
• Buffing wheels are made of discs of linen, cotton, broad cloth
and canvas
• Buffing is also used to manufacture light reflectors.
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Buffing
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Summery of Abrasive machining processes
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