4. Abrasive Machining
Abrasive machining is a material removal process that
involves the use of abrasive cutting tools.
There are three principle types of abrasive cutting
tools according to the degree to which abrasive
grains are constrained,
•Bonded abrasive tools
• Coated abrasive tools
• Free abrasives
6. Abrasive Machining
Why a smooth surface?
• Reduction in Friction
▫ Heat - Bearings
• Reduction in Wear
▫ Bushings/Bearings
• Appearance
▫ Car Body, Furniture
• Clearance
▫ Disk Head
• Sharpness
▫ Cutting Tools
7. Abrasive Machining
How do we get a smooth surface?
• Remove Material
▫ Abrasive Machining
• Flatten
▫ Burnishing – polish the metal by rubbing.
• Fill in Voids
▫ Add material
▫ Paint
▫ Finish
▫ Wax
8. Abrasives
• Small, hard nonmetallic particles with sharp edges
and irregular shapes
• Can remove small amounts of material, producing
tiny chips
• Abrasive processes can produce fine surface
finishes and accurate dimensional tolerances
9. Types of Abrasives
Conventional Abrasives
a. Aluminum oxide (Al2O3)
b. Silicon carbide (SiC)
Super abrasives
c. Cubic Boron Nitride (cBN)
d. Diamond
Natural abrasives (sand stone, emery, diamond)
Abrasives are harder than conventional tool materials
13. Grinding
• Grinding is the most common form of abrasive
machining.
• It is a material cutting process which engages an
abrasive tool whose cutting elements are grains of
abrasive material known as grit.
• These grits are characterized by sharp cutting
points, high hot hardness, chemical stability and
wear resistance.
• The grits are held together by a suitable bonding
material to give shape of an abrasive tool.
17. Major advantages of grinding
A grinding wheel requires two types of specification
• dimensional accuracy
• good surface finish
• good form and locational accuracy applicable to
both hardened and unhardened material
18. Major applications of grinding
Applications
• surface finishing
• slitting and parting
• descaling, deburring
• stock removal (abrasive milling) finishing of flat as
well as cylindrical surface
• grinding of tools and cutters and resharpening of
the same.
25. Surface Grinding
• Surface grinding is an abrasive machining process in
which the grinding wheel removes material from the
plain flat surfaces of the work piece.
37. Centerless Grinding
• Centerless grinding is a process for continuously
grinding cylindrical surfaces in which the work
piece is supported not by centers or chucks but by
a rest blade.
• The work piece is ground between two wheels.
• The larger grinding wheel does grinding, while the
smaller regulating wheel, which is tilted at an
angle i, regulates the velocity Vf of the axial
movement of the work piece.
41. Creep-Feed Grinding
• Grinding has traditionally been associated with small
rates of material removal and finishing operations.
• However, grinding can also be used for large-scale
metal removal operations similar to milling, shaping,
and planing.
• In creep-feed grinding, the depth of cut d is as much as
6mm, and the workpiece speed is low.
• The wheels are mostly softer grade resin bonded with
open structure to keep temperatures low.
• Creep-feed grinding can be economical for specific
applications, such as grinding cavities, grooves, etc.
45. Bonded Abrasives/ Grinding Wheels
Bonded Abrasives
• Most grinding wheels are made of abrasive grains
held together by a bonding material
Types of bonding material:
• Vitrified (glass)
• Resinoid (thermosetting resin)
• Rubber
• Metal (the wheel itself is metal; the grains are
bonded to its surface
49. Grinding Process
Grinding
- Grains have irregular shapes and random spacing
- Average rake angle is very negative (about -60° or
lower)
- Radial positions of grains vary
- Cutting speed is very high (ca. 600 ft/min)
55. Grinding Wheel - Wear
Types:
• Attritious Grain Wear
Grains develop a wear flat
• Grain Fracture
Necessary to produce sharp grain edges
• Bond Fracture
Allows dull grains to be dislodged from the
wheel
56. Grinding Wheel - Parameters
• The way the abrasive grains, bonding material, and
the air gaps are structured, determines the
parameters of the grinding wheel,
which are
• Abrasive material,
• Grain size,
• Bonding material,
• Wheel grade,
• Wheel structure.
58. Cutting Fluids
- Remove heat
- Remove chips, grain fragments and dislodged
grains
- Are usually water-based emulsions
- Are added by flood application
59. Grinding Ratio
G = Volume of material removed
Volume of wheel wear
Vary greatly (2-200 or higher) depending on the
type of wheel, grinding fluid, and process
parameters
Higher forces decrease the grinding ratio
60. Grinding
Design Considerations:
- Design parts so that they can be held securely
- Avoid interrupted surfaces if high dimensional
accuracy is required because they can cause
vibrations
- Ensure cylindrical parts are balanced and thick
enough to minimize deflections
- Short pieces may be difficult to grind accurately in
centerless grinding because of limited support by the
blade
- Parts requiring high accuracy form grinding should be
kept simple to prevent frequent wheel dressing
- Avoid small deep or blind holes or include a relief
61. Coated Abrasives
Coated Abrasives
Abrasive grains are deposited on flexible backing;
they are more pointed than those in grinding
wheels
Common examples: sandpaper, emery
63. Coated Abrasives
Belt Grinding
Uses coated abrasives in the form of a belt; cutting
speeds are about 2500-6000 ft/min
Microreplication
Abrasives with a pyramid shape are placed in a
predetermined regular pattern on the belt
66. Broaching
• Broaching is the process of removing metal with a
tool which has “teeth” arranged in a row. Each
tooth is successively higher than the previous
tooth and removes more material. In broaching,
one stroke or cycle of the machine produces a
finished part.
• Broaching is used to produce both internal and
external features. Production rates are high and
tolerances of +/- .0005” are possible.
69. Specification of broaching machine
• Max length of the stoke
• Max force developed by the slide in tonnes
• Types of drives
• Power rating of electrical motor in HP
• Speed and feed
• Weight of the machine
• Floor space required
70. Advantages & Disadvantages
▫ Advantages
Rough to finish in one pass
Production rates are high
Cutting time is quick
Rapid load and unload of parts
External and internal features
Any form that can be produced on a broaching tool can
be produced
Production tolerances are excellent
Surface finishes are equal to milling
Operator skill is low
71. Advantages & Disadvantages
▫ Disadvantages
Tooling cost can be high
In some cases--not suited for low production rates
Parts to be broached must be strong enough to
withstand the forces of the process
Surface to be broached must be accessible
72. TYPES OF BROACHING MACHINE
According to the nature and direction of primary cutting motion
▫ Horizontal broaching machine
▫ Vertical broaching machine
▫ Continuous broaching machine
According to the purpose
▫ Internal broaching machine
▫ External surface broaching machine
According to method operation
▫ Pull broaching machine
▫ Push broaching machine
According to the construction of the broach tool
▫ Solid broaching machine
▫ Inserted tooth broaching machine
▫ Progressive cut broaching machine
▫ Built-up broaching machine
73. • According to the function
▫ Keyway broaching machine
▫ Burnishing broaching machine
▫ Spline broaching machine
▫ Round hole broaching machine
▫ Surface broaching machine
• According to the number of main slides or stations
▫ Single broaching machine
▫ Double broaching machine
▫ Multiple slides broaching machine
• According to the motion of the broach tool relative to the
work
▫ Straight line motion broaching machine
▫ Stationary broach tool broaching machine
79. Types of broaching tool
According to the method of operation
▫ Push Broach
▫ Pull Broach
According to the kind of operation
▫ Internal Broach
▫ External Broach
According to their construction
▫ Solid Broach
▫ Built up of replaceable section
▫ Inserted tooth Broach
▫ Overlapping teeth Broach
▫ Progressive cut Broach
