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6/10/2017
Drilling
Drilling Machine…
Drilling Machine
•
•
•
It is the simplest and accurate machine used in
production shop
...
Clamped in position
and the drill rotates to make a hole
...
5 to
15mm
• Operator
senses the
cutting action
so sensitive
drilling
machine
• Drilling is the operation of producing circular hole in workpiece using a rotating cutter called DRILL
...
• The drilling operation can also be accomplished in lathe, in
which the drill is held in tailstock and the work is held by the
chuck
...
• The most common drill used is the twist drill
...
• The upright drill press is used for heavy duty
drilling and finally the radial drill press is used
for drilling large, heavy work piece that are
difficult to move
...
Radial drill Press
• This is the largest drill
press designed to drill
up to 100-mm diameter
holes in large
workparts
...
Drilling machines - Drill press
• Sensitive or Bench drill
press
• Upright drill press
Other drilling machines
Geometry of twist drill
• The gang drill is a drill press consisting of a series
of drill presses connected together in an in-line
arrangement so that a series of drilling
operations can be done in sequence
...
• Numerical control drill presses (CNC)are available
to control the positioning of the holes in the
workparts
...
Figure : Standard geometry of a twist drill
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• The twist drill is the most used cutting tools in the
drilling operation
...
• The chips produced are guided up through these
spiral grooves
...
• In order that the cutting edges can cut off chips,
two movements are required simultaneously;
rotational speed and axial feed
...
• Some standard drill types are,
straight shank: this type has a cylindrical shank and is
held in a chuck;
taper shank: his type is held directly in the drilling
machine spindle
...
Cutting Drill angles
• In twist drill, there are various angles to be considered:
Cutting angle (ca) or angle of lip:
The two lips must be of same length and equal angle
...
Lip clearance angle:
The cone shaped cutting end is the point from the lips
and varies from 12- 15º degrees
...
For hard materials, the recommended angle is
9º degrees
...
Cutting conditions in drilling
• The twist drill is a
cutting tool with two
symmetrical opposite
cutting edges, each
removing part of the
material in the form of
chip
...
: Basics of a drilling
operation
...
This helps to secure the lip over the
correct space to curl the chips
...
Motions of Drill and Cutting Velocity
• In drilling, the primary motion is the rotation
of the cutting tool held in the spindle
...
• Cutting velocity V in drilling is not a constant
along the major cutting edge as opposed to
the other machining operations
...
The maximum cutting speed is given by:
3
6/10/2017
Feed in Drilling
V = πDN
where D is the drill diameter, and N is the
rotational speed of the drill
...
• Feed (f) is the distance that the drill penetrates
per revolution (mm/rev), the share of each
cutting edge is = f/2
• Two types of feed in drilling can be identified:
feed per tooth fz: has the same meaning as in the
other multi-tooth cutting tools
...
• feed per minute fm: feed per minute is calculated
taking into account the rotational speed N,
fm = 2fzN
Drilling time
• Feed per minute is used to adjust the feed change
gears
...
• In core drilling, a drilling operation used to enlarge an
existing hole of diameter D(hole), depth of cut is given
by
d = 1⁄2 (D(drill) – D(hole))
where D(drill) is the drill diameter, and D(hole) is the
diameter of the hole being enlarged
...
*The approach is usually considered as 0
...
Apparatus needed during drilling
operation
Drill materials
• Drills are normally made of high-speed steel
(HSS) but carbide-tipped drills, and drills with
mechanically attached carbide inserts are
commonly used in many operations, especially on
CNC drilling machines
HSS drill- Low cost and Carbide- tipped drills- high
production and in CNC machines
Other types are:Solid Carbide drill, TiN coated drills,
carbide coated masonry drills, parabolic drills,
split point drill
•
•
Normally, holes produced by drilling are bigger than the drill diameter and
depending on its applications; the drilled holes will subjected to other
operations such as reaming or honing to better surface finish and
dimensional accuracy
There are also several apparatus needed during the drilling operation as
shown below:
Drilling machine
Center punch
Hammer
Center drill
Twist drills
Coolant
Vernier caliper
Two flute drill set: i
...
Countersink drill; iii
...
Drill various diameter
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6/10/2017
Drilling And Drills
Drill fixed to the spindle
Types of drills
– Twist drill: most
common drill
– Step drill:
produces holes
of two or more
different
diameters
– Core drill: used
to make an
existing hole
bigger
Drilling operations
Drilling Centre Hole
Drilling Deep Holes
Drilling Thin
Material
Drilling Pilot Hole
Tool Nomenclature
Twist drill
lip clearance angle
10-12°
margin
flute
land
flute
dead centre
cutting lip
28
Tool Holding devices
Work Holding Devices
• The different methods used for holding drill in
a drill spindle are
• By directly fitting in the spindle hole
...
If the hole is larger than
~30 mm, its a good idea to drill a smaller pilot
hole before core drilling the final one
...
• Step drilling is used to drill a stepped (multidiameter) hole in a solid material
...
The hole is used to seat internal hexagonal
bolt heads
...
• Reaming provides a better tolerance and surface
finish to an initially drilled hole
...
The tool is called
reamer;
6
6/10/2017
Types of cutters
• Center drilling is used to drill a starting hole to
precisely define the location for subsequent drilling
...
A center drill has a thick
shaft and very short flutes
...
• Gun drilling is a specific operation to drill holes with
very large length-to-diameter ratio up to L/D ~300
...
Accuracy
of 0
...
• The difference in geometry between a reamer and a twist drill are:
The reamer contains four to eight straight or helical flutes,
respectively cutting edges
...
Boring tool is held in the boring bar which has the shank
...
005mm can be achieved
...
Cone angles of 60°, 82°, 90°, 100°, 110°, 120°
Counter Bore Tool:Special cutters uses a pilot to guide the cutting
action
...
Counter bore and spot facing
Types of cutters
Combined Countersinks and central drill :Special drilling tool to start the hole accurately
...
Gun drill :Machining of lengthy holes with less feed rates
...
Machine Table Vice
Tapping:For cutting internal thread
Multi cutting edge tool
...
Minor dia of the thread is
drilled and then tapping is
done
...
• Machines should be cleaned after use
• Chips should be removed using brush
...
• Machines should be lightly oiled to prevent
from rusting
8
6/10/2017
Drilling
Safety Precautions
• Do not support the work piece by hand – use work
holding device
...
• Never place tools on the drilling table
• Avoid loose clothing and protect the eyes
...
• Creates a round hole in a
workpart
• Contrasts with boring
which can only enlarge an
existing hole
• Cutting tool is called a drill
or drill bit
• Customarily performed on
a drill press, but can be
done on a vertical mill
and on a lathe
Figure 21
...
Blind Holes
Used to slightly
enlarge a hole,
provide better
tolerance on
diameter, and
improve surface
finish
Figure 22
...
13 - Two hole types: (a) through-hole, and (b) blind hole
IENG 475: Computer-Controlled
Manufacturing Systems
51
6/10/2017
Tapping
52
Provides a stepped
hole, in which a
larger diameter
follows a smaller
diameter partially
into the hole
The tool is called
a tap
Figure 22
...
14 (b) tapping
IENG 475: Computer-Controlled
Manufacturing Systems
IENG 475: Computer-Controlled
Manufacturing Systems
Counterboring
Used to provide
internal screw
threads on an
existing hole
6/10/2017
50
Reaming
Through-holes - drill exits the opposite side of work
Blind-holes – drill does not exit work on opposite side
6/10/2017
IENG 475: Computer-Controlled
Manufacturing Systems
53
6/10/2017
IENG 475: Computer-Controlled
Manufacturing Systems
54
9
6/10/2017
Accurate Hole-making
•
Boring Machine
Sequence of Operations:
• In machining, boring is the process of
enlarging a hole that has already been drilled
(or cast), by means of a single-point cutting
tool (or of a boring head containing several
such tools), for example as in boring a cannon
barrel
...
1
...
Drilling
3
...
Reaming
IENG 475: Computer-Controlled
Manufacturing Systems
6/10/2017
55
TYPES OF BORING
Boring machine
• There are various types of boring
...
Lineboring (line boring, line-boring) implies
the former
...
HORIZONTAL BORING MACHINE
• The two types of the boring
machine, each of which has several
varieties, are the horizontal boring
and drilling machine, and the vertical
boring and turning mill