Tooling for Drilling Holes and Milling
Carbide Fundamentals
OBJECTIVES
Introduction
 Selecting of tools
 Tool size and shape
 Tool grade and materials
 Inserts
 Tool wear (Causes and consequences)
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INTRODUCTION
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Cutting tools are subjected to:
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Extremely severe friction.
Metal-to-metal contact between chip and work-piece.
Metal-to-metal contact resulting in high stress at high
temperatures.
During machining, cutting tools remove material
from the component to achieve the required
shape, dimension and surface roughness (finish).
• Wear occurs during the cutting action, ultimately
resulting in the failure of the cutting tool.
• When the tool wear reaches a certain extent,
the tool or active edge has to be replaced to
guarantee the desired cutting action.
Tools
1. Drills:
_ Drills, Center Drills
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Boring
Reaming
Tapping
Counter boring
Counter sink
2. End mill
3. Face Mill
4. Slit Mill
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Chip & Chip Thickness
• Type I: Discontinuous chip; segmented, fragmented, highly stressed
• Type II: Continuous chip deformation of material with low tensile properties.
• Type III: Continuous chip with built-up edge; high tensile material makes spring
shape chips.
Coolant:
• Oil Base
• Water Base
• Semi syntactic
• Full Syntactic
Tool Feed
RPM, IPM,IPR, IPT,ACT
Example:
• A 3 in. diameter end mill with 5
teeth is to machine a 1.125” width
of cut to a square shoulder.
• A chip load of .006 ipt. and a
spindle rpm of 400 are
recommended.
• Determine if corresponding feed
rate needs to be adjusted to
maintain chip thickness of .008”.
Feeding Direction For Milling Operation
1. Climb Milling
• Should be fed in the direction of cutter rotation.
• Causes the tool to make maximum thickness chip at the start of cut
and minimum thickness at the end of cut inside the material.
• Less clamping and horse power needed.
• Climb mill is recommended for thin parts.
• Cutting tool has longer life.
2. Conventional Mill
• Requires more fixture hold-down force.
• Recommended for casting and forging material and hot
rolled steel.
• Has high tool impact load and excessive tool wear on hard
materials.
Mill
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SELECTING AN INSERT:
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Insert shape
Geometric features
Lead angle
Type of operation
Maximum number of cutting edges
Strength needed to do the job
INSERT SHAPES
INSERT SHAPES (Continued)
Tool Holder Identification System
INSERT SIZE
The size of the insert is based on the inscribed circle*.
* (The largest circle that will fit inside the insert.)
Shape of Inserts
The shape of the insert will have a great effect on the strength
of the tool.
Lead or cutting edge angle:
- the angle at which the cutting tool enters the work
Cutting Edge
Rake angle:
• The angle at which the chips
flow away from the cutting
edge.
• Principle rake angles are:
– Positive rake
– Negative rake
– Natural rake
Provide more support for
cutting edge of inserts.
Neutral rake has twice as many
cutting edges as positive rake.
Positive rake should be used
when machining soft material
because chips are able to flow
away from the cutting edge.
TOOL NOSE RADIUS
 The nose radius of the tool directly affects tool strength
and surface finish as well as cutting speed and feeds.
 The larger the nose radius, the stronger the tool is.
 The greater the nose radius, the greater the degree of
roundness at the tip.
 Nose Radius affect :
- Tool strength
- Surface finish
- Cutting speed and feed
INSERTS
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In the(P/M) process, metal powders are
compacted into desired and often complex
shapes and heated without melting to form a
solid piece.
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The powder must be fed properly into the die
cavity, and proper pressures must be developed
throughout.
Compaction
• Blended powders are pressed into various
shapes in dies.
• The purposes of compaction are to obtain the
required shape, density, and particle-toparticle contact as well as to make the part
sufficiently strong for further processing.
Sintering
• The process that compact samples are heated in a controlledatmosphere furnace to a temperature below the melting point.
• The principle variables in sintering are temperature, time, and
the furnace atmosphere.
• Sintering temperatures are generally within 70 to 90% of the
melting point of metal or alloy.
•
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INFILTRATION
 Infiltration is accomplished by placing a lower
melting “slug” on or beneath the part prior to
entering the sintering furnace.
When this secondary part melts, it is absorbed
into the pores of the part by capillary action and is
diffused into the particles of the primary metal.
IMPREGNATATION
• The inherent porosity of P/M components can be utilized
by impregnating them with a fluid.
• Bearings and bushings that are lubricated internally with
up to 30% oil by volume are made by immersing the
sintered bearing in heated oil.
• The container is then placed in a vacuum chamber, and the
air is removed from the pores, being replaced by the
lubricant.
Examples of Powder-Metallurgy Techniques
(a) balls for ball-point pens
(b) automotive components such as piston rings,
connecting rods, brake pads, gears, cams, and
bushings
(c) inserts (tool steels, tungsten carbides)
(d) graphite brushes impregnated with copper for electric
motors
(e) surgical implants
CARBIDE TOOL GRADE
Carbide Tools come in a variety of grades.
The grade is based on carbide wear resistance
and toughness.
As insert becomes harder or more wear resistant,
it becomes brittle and less tough.
COATING OF CARBIDE INSERTS:
• Carbide is a very hard , durable cutting tool,
but it has wear. The wear resistance of carbide can
be increased by using coatings.
The most common type of coating includes:
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Titanium carbide(TiC)
Titanium nitride (TiN)
Aluminum oxide (AlO)
Ceramic
Diamond – coated Inserts (PCD)
Tool Wear
• The type of wear depends on the nature of the tool,
machined material, cutting conditions, and the type of
cutting (turning or milling).
• change of shape and size of tools from its original
shape.
• thermal phenomena in the high speed cutting process
cause physical–chemical phenomena which causes tool
wear.
• tool materials must have good hardness properties.
TOOL WEAR
Crater Wear
 Build up edge
 Chipping
 Cutting edge wear
 Flank Wear
 Thermal and Mechanical failure
 Edge Deformation
 Notch wear
 Ultimate Failure
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Crater Wear
• Diffusion, decomposition and abrasive wear.
• Hot chips decompose the cobalt and dissolve the coating.
• The soft cobalt wears out of the matrix, the carbide grains no longer
have any adhesion and therefore break off.
• Crater wear occurs when the binder is being replaced by the
material you are cutting
• Two criteria are currently used to evaluate the level of crater wear
of a tool
• The first is the depth of the crater KT
•
the second is the distance between the cutting edge and the crater
KM.
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the volume of the crater, the width of the crater and the roughness
of the crater.
Crater Wear
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Select a more wear resistant insert grade .
Change the chip breaker geometry.
Use coolant.
Reduce the cutting speed and feed
Built-Up Edge
• Material adhesion at a high pressure and low temperature,
• The work piece material sticks to the cutting edge.
• This built-up edge breaks off and takes pieces of the coating of insert with it.
• Possible solutions
• Increase the cutting speed.
• Use coolant
• Increase the feed
• insert with a sharper cutting edge geometry
Chipping
• Abrasive wear and local stress concentration.
• Hard micro inclusions in the work-piece material cause local stress concentration.
• Possible solutions
• Increase the cutting speed.
• Reduce the feed
• Reduce the risk of vibrations.
(The entrance or exit).
• Select a stronger cutting
edge geometry
• Select a tougher grade
Cutting edge wear
• Mechanical and thermal overloading.
• The heat softens the insert structure.
• As the cobalt softens and the insert becomes deformed.
• Possible solutions
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Reduce the cutting speed.
Reduce the feed.
Use coolant.
Select a more wear Resistant insert
Select an insert with larger nose radius
Flank Wear
• Abrasive wear.
• Hard micro inclusions in the work-piece cut into the insert.
• Small pieces of coating break off and also cut into the insert.
• The soft cobalt wears out of the matrix, the carbide grains no longer have any
adhesion and therefore break off
Thermal/Mechanical Failure
• Rapid change in the thermal load.
• Temperature differences between warm and cold zones cause
thermal stress.
• Fatigue leads to cracking.
• Possible solutions
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Use an abundant supply of coolant.
Reduce the cutting speed.
Reduce the feed.
Select a tougher hard insert grade.
Use a different machining method
(ratio between time in cut
and time out of cut).
Edge Deformation
• Mechanical and thermal overloading.
• The heat softens the insert structure.
• The cobalt softens and the insert becomes deformed.
Notching
• Oxidation (machining surface) and local stress concentration
because of Surface hardening (previous cut)
• Hard micro inclusions in the work-piece material cause a notch
where the work-piece comes into contact with the cutting edge
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Select a more wear resistant insert grade(oxidation).
Reduce the cutting speed (oxidation).
Reduce the feed(oxidation).
Select a tougher insert grade.
Select a smaller entering angle
Chip Hammering
• Abrasive wear and mechanical overload.
• The chips collide with
• the cutting edge and damage it.
• Possible solutions
• Change the feed.
• Change the cutting depth.
• Select a different
chip-breaker geometry.
• Select a tougher insert grade
Mechanical Fracture
• Mechanical overload. The combination of mechanical and
thermal load is so great that the insert breaks during the first
cuts (seconds).
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Possible solutions
Reduce the feed.
Reduce the cutting depth.
Select a tougher insert grade.
• Select an insert with a chip-breaker geometry for larger feeds.
• Select a thicker insert.
End of Presentation
• Drill
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• Mill
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