entendiendo el barrenado

1. 1
Drilling Basics

2. 2
Primitive Drill
Native American

3. 3
Primitive Drill
Native American and Egyptian

4. 4
What is a Drill?
“Drills are defined as rotary end-
cutting tools having one or
more cutting lips and one or
more helical or straight flutes
for the passage of chips and
the admission of cutting
fluids.”

5. 5
Twist Drills

6. 6
Nomenclature

7. 7
a
a
a
a
a
a
Types of Twist Drills
Taper Shank
Straight Shank
High Helix
Low Helix
Spot Drill
Multi-Diameter

8. 8
Other Hole Operations

9. 9
Chip Formation
Photomicrograph of section
normal to chisel edge, .037”
radius, 3/4” Diameter Drill.
Photomicrograph of section
normal to chisel edge, at exact
center of hole, 3/4” Diameter
drill.

10. 10
Chip Formation
Photo of chip formed by the
chisel edge, at bottom of
drilled hole.

11. 11
Chip Formation Physics

12. 12
Max. chip
temperature
= 1300 F
Ave. shear
temperature
 536 F
1300°
1200°
1100°
930°
850°
675°
400°
290°
180°
70°
Chip Thermograph
 Heat starts at the shear zone.
 Reaches maximum temperature on the rake face of
the cutting tool.

13. 13
Forces in Drilling
Thrust
Torque
Force in the Z
axis expressed
in lbs. of Thrust.
Rotational force
expressed as
Torque in in-lbs
or foot-lbs.

14. 14
 Speed refers to the spindle rotational speed.
» Speed it expressed as Surface Feet per Minute (SFM)
» SFM is a linear distance a point on the tool O.D. would travel in
one minute.
» SFM must be converted to RPM for the machine controller.
» Note diminished SFM at the centerline.
Speed
RPM)
x
(Diameter
.262
SFM
RPM)
x
(Diameter
12
π
SFM
Speed
Surface
Calculate
To


Diameter
SFM)
x
(3.82
RPM
Diameter
x
π
SFM
x
12
RPM
RPM
Spindle
Calculate
To



15. 15
Drilling Feed
 Feed refers to the rate of advancement.
» Feed is typically expressed as Feed per Revolution (FPR)
– the distance the drill travels in one revolution.
» For most machines feed must be converted to Inches per
Minute (IPM)
– the distance the drill travels in one minute.
FPR
x
RPM
IPM 

16. 16
Horsepower
 MRR (Material Removal Rate) =.785xD2xRPMxIPR
» D=Diameter
» RPM=Revolutions Per Minute
» IPR=Inch Per Revolution
 “K” Factor = Cubic Inches Of Material That 1 Hp Will Remove
 HP=MRR/K

17. 17
Thrust
 T=0.7x(Dia./2)xIPRxMF=Pound
s
» T=Thrust (Pounds)
» IPR= Inch Per Revolution
(Feed Rate)
» MF= Material Factor (lbs/in2)

18. 18
Material and K Factors
Material Material Factor
Lb/in2
“K” Factor
In3
/min/HP
Aluminum 110,000 3.60
Cast Iron 230,000 1.72
Low Carbon Steel 240,000 1.65
High Carbon and Alloy Steel 320,000 1.24
300 Series Stainless Steel 370,000 1.07
400 Series Stainless Steel 380,000 1.04
Nickel Based Alloys 550,000 .72
Titanium 370,000 1.07

19. 19
Drill Points
 The drill point is made of a combination of surfaces that
create a series of compound angles.
» Point geometry varies for different materials.
– 90° included angle for Aluminum
– 118° included angle for General Purpose
– 135° to 150° for hardened materials

20. 20
Helix
 The Helix is the angle the flute is tilted relative to the drill
axis.
» High helix drill are freer cutting, but tend to be weak.
– Recommended for soft materials.
» Low helix drills are stronger and require more force.
– Recommended for hard materials and applications where drill
tends to “grab”.

21. 21
Lip Clearance
 Lip clearance is the
clearance behind the
cutting edge. (Same as
flank clearance)
» Softer materials require
more clearance than hard
materials.
– 6° to 9° for steel and hard
materials
– 12° to 15° for Aluminum
and other soft materials.

22. 22
Web Thickness
 The web is the area between the flutes.
» Web thickness determines the strength of the drill.
» The larger the web the greater the drill rigidity
» Web sizes determines how much room is available for chip
formation.

23. 23
Web Thickness
 Web thickness is the smallest cross-section thickness
between the flutes.
» Typically the web thickness is tapered through the body of the
drill, narrow at the point and wider toward the shank.
» The wider the web the more thrust is required.
» The web needs to thinned at the drill is reconditioned to
maintain the proper web thickness.

24. 24
Chisel Edge
 The chisel edge is the edge
formed at the center of the
drill point as the result of the
point angle and the Lip relief
angle.
» The chisel edge takes the
greatest forces in drilling due
to the combination of thrust
forces and zero surface
speed.
» As the drill point and Lip relief
angle changes the chisel
angle will change.

25. 25
Land
 The land is the area of the drill body between the flutes.
» The land is recessed from the margin to provide side clearance
to reduce rubbing.
» The body clearance diameter is measured across the lands.

26. 26
Margins
 The margin is portion the land the extends beyond the
body diameter to the full diameter of the drill.
» The margins provide a bearing surface for the drill to ride in
while in the hole.
» Typically most two flutes drills have a single margin on each
flute.
» Multiple margins drills can have two or more margins per flute.

27. 27
Indexable Drills
 Indexable drills incorporate many the same features as
solid drills.
» Flute, Body, Shank, etc.
– Typically indexable drills do not have a margin.
» Inserts provide the rake surface, clearance angles, and chip
breakers.
» Inserts can have multiple edges and a variety lead angles.
» All Indexable drills are one effective regardless of the number
of inserts.

28. 28
Chip Control
 Chip control is imperative with indexable drills.
 Uncontrolled chips will:
» prevent coolant from getting to the drill tip causing the drill to overheat.
» Cause chips to wrap around the tool creating a safety hazard and poor hole
finish.
 The chip breaker on the drill insert has to be matched to ductility of the
material and the feed per revolution of the drill.
 Chip control can come from grooves, “Rills”, or Dimples on the insert.

29. 29
Chip Control
General Purpose
Machining
“T” - Land
Rake Face

30. 30
Replaceable Point Drills

31. 31
Coolant
 Coolant is required on all
Indexable Drills and Strongly
recommended for replaceable
tipped Drills
 Necessary to flush chips away
from the cutting edges of the drill
» Chip removal from the hole
» Reduces the cutting tool
temperature
» Provide lubrication to prevent
BUE
 Recommend Minimum of 150
PSI
 Reduce the feed 10% when
using external flood coolant.

32. 32
Coolant
 Through coolant holes can be through the web or the land
of the drill
 Through the land is preferable because it leaves a greater
cross-section through the web which increases the
strength of the drill.

33. 33
Coolant
Old Method
Central Coolant Hole
New Method
Twin Coolant Holes

34. 34
External Coolant
Directed at the Point
Acceptable up to
Depth=2X Dia.
Not Directed at the Point
Unacceptable

35. 35
Internal Coolant
Through the tool Coolant
Most Recommended
In Stationary applications
both internal and
external coolant is
recommended

36. 36
Replaceable Point Drills
Coolant
6% to 8% concentration—10% + SS
Through the Tool for Optimum Performance

37. 37
Offsets
Moving the drill off Center
 Allows the drill to produce a
larger diameter than its
effective diameter
 Can improve chip
evacuation
 May improve surface finish
 Only on indexable drills with
1:1, 2:1, 2.5:1 & 3:1 L/D
 See Catalog for
recommended offsets for
each size drill

38. 38
History
• Originally, the most effective manner of manufacturing gun
barrels was to hand forge a long strip of steel around a rod in
a spiral fashion .
• An interim process consisted of drilling the barrel with a set
twist drills. but the method was slow and you needed to
retract the drill frequently to evacuate the chips.
• The gundrill was born when a
coolant flow were injected
through the straight drill.
• The last steps were to braze
a carbide head and develop
high pressure pumps.

39. 39
Gundrill => One Lipped Drill
Due to the one lipped geometry,
the gundrill is self guided : The
cutting forces flatten the pads
against the bore wall.
Advantages:
• Very deep hole making
• Tight tolerances & good surface
quality (no reaming needed)
• No peck drilling needed
• Good tool life due to internal coolant
• 10 to 15 possible regrinds
Disadvantages:
• Low feed rate due to 1 lip
• High coolant pressure needed

40. 40
Driver
Shank
Tube
Crimp or Solid
Carbide
Tip
Brazed Joint
Gun Drills

41. 41
Pad Forms
Ø D (mm) 3<Ø≤3,5 3,5<Ø≤5 5<Ø≤10 10<Ø≤12 12<Ø≤13 13<Ø≤15 15<Ø≤17 17<Ø≤19 19<Ø≤21 21<Ø≤23 23<Ø≤25 25<Ø≤30 30<Ø≤35 Ø >35
P (mm) 0,11 0,13 0,14 0,15 0,16 0,18 0,2 0,25 0,3
La (mm) 0,2 to 0,3 0,3 to 0,4 0,3 to 0,5 0,5 to 0,8 0,6 to 1 0,8 to 1,2 1 to 1,4 1,2 to 1,6 1,4 to 1,8 1,6 to 2 1,8 to 2,2 2 to 2,4
α 22 °
0,01 x D 0,12
0,4 to 0,6
Not measurable
Measurable

42. 42
Back Taper
Standard backtaper (.7%) :
- Average straightness control
- Low risk of tip jamming in hole
Backtaper from .7% to 2.0 %
- Low risk of tip jamming in hole
- Bad straightness control
- Better tool life (in shrinking materials)
Backtaper from 0% to .7%
- High risk of tip jamming in hole
- Very high straightness control
- Good surface finish
- Poor tool life

43. 43
Special Designs
 Gun drills can be designed with a variety of different
heads for different applications
Countersink drill for blind hole
drilling
Countersink drill for through-
hole drilling
Step drill for Countersink and
full drilling

44. 44
Coolant Holes
 The drilling heads are provided with holes which
coolant is fed to the cutting lips. The coolant holes
can have various designs
 Small diameter drills have a kidney-shaped coolant holes in
the drill head, whereas larger diameter drills are provided with
two coolant holes. In special cases, drills with solid carbide
shanks, are provided with a single round coolant hole.
Drill Head Cross Sections

45. 45
Typical Horizontal GunDrill Machine
Tool Driver
Steady rest
bushing
Sealing
housing
Drill
Bushing carrier
Drill
Bushing Support
Workpiece
Standard
Accessories for
Typical Gun Drill
Machine Assembly
Sealing
disk Guide bush

46. 46
Centering Guiding Hole
for Gun Drill Operation
in Machining Center
Bushing Guide Barrel
for Gun Drill Stabilizing
in Machining Center
Gun Drills in Machining Centers
Center Machine Application
•Drill pilot hole .0004”-0010” larger than the drill diameter,
to a depth of 1.5 times the diameter of the drill.

47. 47
Special Considerations
Most Common Conditions
Reduce feed
50% on >5°
Reduce Feed
60% on start
Reduce Speed
on start
Reduce feed
when crossing

48. 48
Special Considerations
Drilling on a slope, irregular surface, or a partial hole
is Not Recommended

49. 49
Spot Drills

50. 50
Lathe Alignment
When using an indexable drill on a
lathe, align the drill with the inserts
parallel to the machine ways.
Indexable drills on lathe must be
properly aligned before taking the
first cut.
Note in line with the inserts the drill can be +/- .005” offset from
centerline, but cannot be offset perpendicular to the insert.

51. 51
When to Replace
The Tip
 Limit cutting edge wear to
.008” to .012”
 Power consumption
exceeds 125%
 Drill begins to vibrate or
chatter

52. 52
When to Replace
The Tip
 Change in hole Diameter
 Deterioration of the surface
finish

53. 53
Failure Modes
FAILURE MODES AND
APPLICATION REVIEW
ABRASIVE WEAR
CHEMICAL WEAR
NOTCHING
THERMAL CRACKING
CHIPPING/FRACTURE
BUILT UP EDGE
DEFORMATION

54. 54
Failure Modes
 30-70-100 RULE:
» LOOK AT INSERT AT 30%, 70%, AND 100% OF TOOL LIFE
AND ANALYZE PROGRESSION OF WEAR
» ALLOWS FOR BETTER VIEW OF FAILURE MODE
(DEVELOPMENT OF FAILURE)
 MOST FAILURE MODES WILL EVENTUALLY RESULT
IN FRACTURE.
 THE IDEA IS TO EXTEND TOOL LIFE BY COMBATTING
THE FIRST FAILURE MODE THAT APPEARS.

55. 55
Substrate Properties
Balancing performance characteristics of substrates has
many factors which require attention
Wear
Resistance
Toughness
Decrease Grain Size
Decrease Cobalt
Increase Alloys
Decrease Cobalt
Shock
Thermal
Deform.
Increase Cobalt
Decrease Alloys
Increase Grain Size
Increase Alloys
Decrease Cobalt
Flank
Wear
Cratering

56. 56
Coating Properties
Balancing performance characteristics of coatings has many
factors which require attention
Wear
Resistance
Toughness
TiC, TiCN, Al2O3
Higher Coat
Thickness
Al2O3
PVD Coated
Mech.
Shock
Thermal
Shock
TiCN, TiN
PVD Coated
Al2O3
PVD Coated
Flank
Wear
Chemical
wear

57. 57
Abrasive Wear
DESCRIPTION:
ATTRITION OF THE
PRIMARY CLEARANCE
SURFACE OF AN INSERT
CAUSED BY THE
RUBBING ACTION
BETWEEN THE TOOL
AND THE MATERIAL
BEING MACHINED

58. 58
Abrasive Wear

59. 59
Abrasive Wear
 SELECT A HIGHER WEAR RESISTANT GRADE
 SELECT A COATED GRADE
» HIGHER SURFACE HARDNESS EVEN AT ELEVATED
CUTTING SPEEDS
 THIS IS THE PREFERRED FAILURE MECHANISM
DUE TO ITS PREDICTABILITY AND AN ABILITY TO
SEE THE EFFECT OF WEAR ON THE
WORKPIECE BEFORE ANYTHING
CATASTROPHIC OCCURS

60. 60
Cratering, Chemical Wear
DESCRIPTION:
DISSOLVING OF THE
CARBIDE MATERIAL
INTO THE CHIP AS IT
FLOWS ACROSS THE
RAKE FACE
CAUSED BY A CHEMICAL
INTERACTION BETWEEN
THE HOT CHIP AND THE
INSERT

61. 61
Cratering, Chemical Wear

62. 62
Cratering, Chemical Wear
 REDUCE SPEED
» CUTTING EDGE TEMP.
 REDUCE FEED
» LESS STRESS ON INSERT
 SELECT A COATED GRADE
» HIGHER TEMP. STABILITY AND INERTNESS
 CHANGE GEOMETRY
» REDUCE FORCES ON INSERT RAKE FACE

63. 63
Notching
DESCRIPTION:
LOCALIZED HIGHER
WEAR ON BOTH THE
RAKE AND FLANK
SURFACES
PREFERENTIALLY AT
THE DEPTH OF CUT
CAUSED BY HIGHER
SURFACE HARDNESS
AND CHEMICAL
INSTABILITY OF THE
TOOL MATERIAL WHERE
EXPOSED TO AIR

64. 64
Notching

65. 65
Notching
 SELECT A GRADE WITH HIGHER MECHANICAL
SHOCK RESISTANCE
» INCREASED TOUGHNESS
 INCREASE LEAD ANGLE
» THINNER CHIP & GREATER SHEARING ACTION
 VARY DEPTH OF CUT
» MULTIPLE PASS APPLICATION
 INCREASE HONE SIZE OR CHANGE GEOMETRY
» TO INCREASE EDGE STRENGTH

66. 66
Thermal Cracking
DESCRIPTION:
CRACKS FORMING
PREFERENTIALLY ON
INSERT RAKE FACE
PERPENDICULAR TO
THE CUTTING EDGE
CAUSED BY THERMAL
EXPANSION AND
CONTRACTION
EXPERIENCED IN
INTERRUPTED CUTTING
(MILLING)

67. 67
Thermal Cracking

68. 68
Thermal Cracking
 REDUCE SPEED
» CUTTING EDGE TEMPERATURE
 TURN COOLANT OFF
» LESS GROSS TEMPERATURE CHANGE
 SELECT A COATED GRADE
» PVD FOR SURFACE COMPRESSION OR OXIDE FOR
THERMAL INSULATION
 SELECT A GRADE WITH HIGHER THERMAL
SHOCK RESISTANCE
» REDUCE THERMAL CRACK INITIATION AND
PROPAGATION

69. 69
Chipping/Fracturing
DESCRIPTION:
BREAKING OFF OR
FRACTURING OF
SEGMENTS OF THE
CUTTING EDGE
CAUSED BY INSUFFICIENT
MECHANICAL STRENGTH
OR MECHANICAL SHOCK
RESISTANCE OF THE
TOOL MATERIAL

70. 70
Chipping/Fracture

71. 71
Chipping/Fracture
 SELECT A GRADE WITH HIGHER MECHANICAL
SHOCK RESISTANCE
» INCREASED TOUGHNESS
 INCREASE LEAD ANGLE
» THINNER CHIP & GREATER SHEARING ACTION
 IMPROVE SYSTEM RIGIDITY
» MORE STABLE SET-UP
 INCREASE HONE SIZE OR ADD T-LAND
» INCREASED EDGE STRENGTH

72. 72
Built Up Edge
DESCRIPTION:
WORKPIECE MATERIAL
ADHERING TO THE
INSERT RAKE FACE
CAUSED BY HEAT AND
PRESSURE OF THE
CUTTING PROCESS AND
CHEMICAL AFFINITY OF
WORKPIECE MATERIAL
TO THE TOOL

73. 73
Built Up Edge

74. 74
Built Up Edge
 SELECT A COATED GRADE
» INERTNESS BETWEEN CHIP AND INSERT; DECREASED
FRICTIONAL EFFECTS
 INCREASE SPEED AND/OR FEED
» PUT HEAT INTO THE CHIP
 APPLY COOLANTS AT LOW SPEED AND WORK
HARDENING CONDITIONS
» INCREASE LUBRICITY
 USE POSITIVE RAKE TOOL GEOMETRY
» LOW FORCES

75. 75
Deformation
DESCRIPTION:
INSERT SOFTENS DUE
TO HEAT AND DISTORTS
DUE CUTTING
PRESSURE.
CAUSED BY HEAT AND
PRESSURE OF THE
CUTTING PROCESS.

76. 76
Deformation

77. 77
Deformation
 REDUCE SURFACE SPEED
» TO REDUCE HEAT
 REDUCE FEED
» TO REDUCE TOOL PRESSURE
 USE A GRADE WITH HIGHER THERMAL OR WEAR
RESISTANCE
 USE TITANIUM ALUMINUM NITRIDE (PVD) OR
ALUMINUM OXIDE (CVD)
» FOR BETTER THERMAL RESISTANCE

78. 78

79. 79
Safety
 Always Wear Satety Glasses with side shields
 Use proper machine guards
 Do not wear loose clothing, Rings, Scarves,
Bandanas, Neck Ties or anything that can be
caught in a rotating spindle.
 Make sure the drill does not bind in the hole and
chips can evacuate freely
 Do allow chips to wrap around or bind the tool
 Beware of hot chips