Types Of Drill And Drilling Operations Engineering Essay

Drilling is the most common machining procedure whereby the operation involves doing unit of ammunition holes in metallic and nonmetallic stuffs. Approximately 75 % of all metal- film editing procedure is of the boring operation.

Drills normally have a high length to diameter ratio that is capable of bring forthing deep hole, nevertheless due to its flexibleness, necessary safeguard demand to be taken to keep truth and prevent drill from interrupting.

Drilled holes can be either through holes or blind holes ( see Figure 4.1 ) . A through holes

is made when a drill exits the opposite side of the work ; in blind hole the drill does non

issue the workpiece ( Groover, 1996 ) .

During the operation, french friess that are produced within the workpiece must go out through the flutes to the exterior of the tool. As the bit is formed and extracted towards the surface, it will bring forth clash. Friction later heat is besides generated when the drill spot touch the workpiece during the holemaking procedure. Therefore, bit disposal and film editing fluids are among the most of import elements need to be consider during this procedure.

Normally, holes produced by boring 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 coating and dimensional truth ( Kalpakjian & A ; Schmid, 2001 ) .

There are besides several setups needed during the boring operation as shown below:

A ) Drilling machine B ) Center punch C ) Hammer D ) Center drill

Tocopherol ) Turn drills F ) Coolant G ) Vernier calliper

H ) Two flute drill set:

I. Center drill

two. Countersink drill

three. Counter dullard drill

four. Drill assorted diameter

4.1.1 Types of Drills

A drill is a rotary-end film editing tool with one or more edged borders or lips and one or more consecutive or coiling channels or flutes for the transition of french friess and cutting fluids or coolants. The most common drills are as follows:

a ) Measure drills

to bring forth holes of two or more different diameters.

B ) Core drills

to enlarge bing holes

degree Celsius ) Counterboring & A ; Seting

to bring forth depression on the surface to suit caputs of prison guards & A ;

bolts.

vitamin D ) Center drill

a short & amp ; stubby drill to bring forth holes so that work piece can be mounted

between lathe centres.

vitamin E ) Topographic point drill

to get down a hole

degree Fahrenheit ) Spade drill

to take big and deep holes

g ) Crankshaft drill

good focus. Suitable for deep holes.

H ) Gun boring

deep hole devising, length-to-diameter ratios up to 300 or higher, self-

focus, lubrication & A ; coolant transition ~ truth of holes

I ) Trepaning

remotion of discoid piece.

J ) Turn Drills

to take the maximal volume of metals in a minimal period of clip. It does non bring forth a preciseness hole: nevertheless, this can be achieved by a reaming operation.

Amongst the type of drills listed supra, the turn drill is by far the most used film editing tools in the boring operation. The turn drill is provided with two coiling channels and two film editing borders. The french friess produced are guided up through these

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coiling channels. The channels besides serve every bit transition to the cutting fluid. In order that the cutting borders can cut off french friess, two motions are required at the same time ; rotational velocity and axial provender.

In turn drill, there are assorted angles to be considered ( see Figure 4.2 ) :

aˆ?Cutting angle ( ca ) or angle of

lip

: The two lips must be of same length and equal

angle. For ordinary work, the cutting angle is

59° and vary with metal to metal.

aˆ? If ca & gt ; = bore will non cut the metal easy and

will non keep its place centrally because of

being excessively level.

aˆ? If ca & lt ; = more power is needed to turn the drill

and bore will cut at slower rate due to the

longer cutting borders.

aˆ? If ca different=one cutting border will have on

rapidly and hole will be larger than drill. Will ensue in wobbling of spindle and bore wears out rapidly

aˆ?Lip clearance angle

: The cone shaped cutting terminal is the point from

the lips and varies from 12- 15° grades. In boring soft stuffs, the angle may be increased under heavy provenders. For difficult stuffs, the recommended angle is 9° grades. If reduced further the drill can non cut into the metal and may interrupt in the Centre along the web.

aˆ?Rake angle

: It is the angle between the flute and the

workpiece that is normally 70-75° grades. This helps to procure the lip over the right infinite to curve the french friess. If more there will be no border for cutting and if less the film editing border will be excessively thin and may interrupt under strain.

Figure 4.2: Standard geometry of a turn drill ( Groover, 1996 ) .

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4.2 Drilling Machine

Drilling can be done on a broad assortment of machines, runing from hand-held portable drills to multiple spindle caputs capable of managing 1000 of drills at the same clip. For ordinary workshop intents there are three chief types of boring machines in usage shown in Table 4.1 below.

The sensitive drill is used for light boring on little parts. The unsloped drill imperativeness is used for heavy responsibility boring and eventually the radial drill imperativeness is used for boring big, heavy workpiece that are hard to travel. There are besides other particular purpose boring machines runing from microscopic boring machine to deep-hole boring and turret caput drills ( Kibbleat. , 2002 ) .

The one which is being used in the Workshop, Kulliyyah of Engineering is the pillar- boring machine. The perpendicular provender is actuated by manus. The mechanic can feel the how fast the drill is cutting and can command it harmonizing to the status of the minute. These require some accomplishments in judging the appropriate provender rate.

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The types of boring machine can run from a simple bench type units used to bore little diameter holes, to big radial drills, which can suit big workpieces. The drill caput of a cosmopolitan boring machine can be swiveled to bore holes at an angle. For high production rate operations, a multiple spindles or besides known as pack boring can be used. This type of machine is capable of boring in one measure every bit many as 50 holes of changing sizes, deepness and locations.

Type of driller

Drill diam.

Millimeter

Spindle

velocity

Change

method

Rev./min

Bench

Up to 5

3

Belt

450-1800

Sensitive

Round

column

5 – 12

3

Belt

500-1500

Pillar

12 – 30

9

Gear box

50-1020

Radial arm

30 – 90

18

Gear box

15-850

Table 4.1: The regulations and rules of cutting velocities and RPM computations in boring

operations

Drilled holes are used to take up prison guards, bolts, shafts, electrical wiring, steam pipes, adjustment of furniture and equipment and farther more to go through through gases, fluids etc. It is clear that the production of holes is a major portion of Al technology industry. The drilled holes either have through or blind holes and the machine tool used to bring forth holes is normally the boring machine.

Drills are classified by stuff, length, form, figure, and type of spiral or flute, shank, point features, and size series. Drills are produced from high-velocity steel ( HSS ) , solid carbide, or with carbide brazed inserts. Most drills are made for right-hand rotary motion. Right-hand drills, as viewed from their point, with the shank confronting off from our position, are rotated in a counterclockwise way in order to cut. Left-hand drills cut when rotated clockwise in a similar mode.

Because of the great force applied by the machine in boring, it is indispensable to guarantee the rigidness of both cutting tools and workpiece. The drill must be right held and the workpiece clamped to the tabular array. There are three ways workpiece is normally held in boring machine, by utilizing: ( a ) vise, ( B ) fixtures and ( degree Celsius ) gigue. A vise is a general intent workholding device possessing two jaws that grasp the workpiece. A fixture is a workholding device that is normally custom designed for the peculiar workpiece. A gigue is a workholding device that is besides specially design to the workpiece. The difference between a gigue and a fixture is the gigue provides a agency of steering the tool during boring operation.

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4.3 BASIC FORMULA FOR DRILLING OPERATION

Cuting velocities and RPM computations are those operations that are purely boring operations, but the boring operation is besides used to execute other operations such as reaming, tapping, seting and counterboring. The following are the basic expression that are normally used in the boring operation.

aˆ? Cutting velocity is the peripheral velocity of the cutting border =Iˆ D N ; where

D is the drill diameter

and

N is the rotational velocity ( revolutions per minute )

The cutting velocity choice depends on both the workpiece and cutter stuffs ;

N = V x 1000rpm, where

IˆD

V is cutting velocity

and

N is rotational velocity ( revolutions per minute )

* Note that V is in m/min and D in millimeter

aˆ?Feed ( degree Fahrenheit ) is the distance the drill perforate per revolution ( mm/rev ) , the portion of each

cutting border is = f/2

aˆ? Depth of cut is taken as half the diameter for boring = D/2

aˆ? Drilling clip ( T ) can be given by the equation ;

T = L / degree Fahrenheit N ; where

degree Fahrenheit is the provender ( mm/rev )

N is the rotational velocity ( revolutions per minute )

L is the amount of hole deepness, attack and over travel distances

*The attack is normally considered as 0.4D while over travel scopes from 1 to 3mm.

aˆ?Material remotion rate ( MRR ) in boring is the volume of stuff removed by the

bore per unit clip.

MRR = ( Iˆ DA? / 4 ) . ( degree Fahrenheit ) . ( N )

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4.3.1 Sample Questions

1 ) 20 mm diameter drill is on a boring machine with cutting velocity 25. If the

provender is 0.25 mm/rev, what is the MRR? What is the MRR is the drill diameter

is tripled?

2 ) The hole of a diameter of 44.7 millimeter is to be drilled to a deepness of 60 millimeters and reamed to a diameter of 45 millimeter. The provender is 0.56 mm/rev for boring. The cutting velocity is 70.6 m/min. The reaming attack is 0.55 millimeter and over travel is 2 millimeter. Determine: –

a ) The provender and spindle velocity for reaming operation.

B ) The boring clip

degree Celsius ) The reaming clip

vitamin D ) The MRR for the boring operation.

4.4 Drilling Technique

In a standard boring operation, the undermentioned stairss are taken ( Gupta, 1996 ) :

a ) First, the workpiece is marked with a Centre clout at the Centre of the hole to

be drilled.

B ) It is so held steadfastly in a frailty or other suited clamping device and topographic point on the

tabular array of the boring machine.

degree Celsius ) The socket incorporating the drill is fitted in the machine spindle.

vitamin D ) The spindle is lowered by the manus lever and it is ensured that the point of the

drill is in exact alliance with the antecedently marked Centre of the hole.

vitamin E ) The motor is now started and the rotating drill is bit by bit pressed into the

workpiece to bring forth the coveted hole.

degree Fahrenheit ) The force per unit area should be often relived during the boring operations,

otherwise the film editing borders of the drill will be strained and the drill is damaged.

g ) In order to avoid botching the cutting border of the drill, coolant such as oil or soap

H2O should be used invariably during the boring operation

4.4.1 Cutting Fluids

A big figure of coolant and cutting oils are used in boring operations. A good film editing fluid will chill the workpiece and tool and will besides move as a lubricator between the bit and the tool to cut down clash and heat buildup. Table 4.2 lists some of the film editing fluids for different stuffs.

Type of cutting fluid

Materials

Dry

Soluble Oil Kerosene Sulfurised

Oil

Mineral

oil

Aluminum

ten

ten

Brass

ten

ten

Bronze

ten

ten

ten

Cast Fe

ten

Steels

Low C

ten

ten

Alloy

ten

ten

Stainless steel

ten

ten

Others

Emulsifying or soluble oils

assorted in H2O

:

For chief demand to utilize cheap chilling medium

Animal or mineral oils with

added S or Cl

:

For operations that tend to make more clash and for

reaming, counterboring, seting and tapping

operations

Table 4.2 List of cutting fluids for different stuffs

4.5 GUIDELINES IN DESIGN

The general design guidelines recommended by Kalpakjianat. ( 2001 ) for boring,

reaming and tapping operations are as follows:

a ) Design should let holes to be drilled on level surfaces and perpendicular to

the drill gesture. Exit surfaces for the drill should besides be level.

B ) Interrupted hole surfaces should be avoided or minimized for improved

dimensional truth.

degree Celsiuss ) Hole underside should if possible lucifer criterion bore point angles ( Section

4.1.1 ) . Flat undersides or uneven forms should be avoided

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vitamin D ) Through holes are preferred over blind holes. If holes with big diameters are

required, the parts should hold a preexistent hole.

vitamin E ) Part should be designed so that all boring can be done with a lower limit of

fixturing and without shifting the workpiece.

degree Fahrenheit ) It may be hard to ream blind or intersecting holes because of the

possibility of tool breakage. Extra hole deepness should be provided.

g ) Blind holes must be drilled deeper than subsequent reaming or tapping

operations that may be performed.

4.6 TROUBLESHOOTING

A general guideline to the likely causes of jobs in boring operations is listed

below Kalpakjian & A ; Schmid, 2001:

Problem

Possible Causes

Drill breakage

:

Dull drill ; prehending in hole because of french friess choke offing

flutes ; feed excessively high ; lip alleviation angle excessively little

Excessive drill wear

:

Cuting velocity excessively high ; uneffective film editing fluid ; rake angle excessively high ; bore burned and strength lost when sharpened

Tapered hole

:

Drill misaligned or bend ; lips non equal ; web non cardinal

Oversized hole

:

Same as above ; machine spindle free ; cheat border non

cardinal ; side force per unit area on workpiece

Poor hole surface coating

:

Dull drill ; uneffective film editing fluid ; welding of workpiece stuff on drill border ; improperly land drill ; improper alliance

Table 4.3: List of jobs and possible causes in boring operation

Figure 4.4: Causes of outsize boring: ( a ) drill

lips land to unequal lengths, ( B ) drill lips

land to unequal angles, and ( degree Celsius ) unequal

angles and lengths

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4.7 SAFETY RULES

Poor work wonts will take to hurts. Bit winging into unprotected eyes, dropping heavy tools, acquiring hair or vesture caught in a rotating drill are among many jeopardies that can be avoided through safe work wonts. The list below denotes a safety regulations that student/ machinist demand to be follow when making the boring operation:

a ) Workpieces should ever be secured with bolts and strap boodles, C-clamps or

fixtures. A drill imperativeness vise should be used when boring little parts. If a clinch

should come loose and a “ merry go unit of ammunition ” consequence, do non seek to halt it from

turning with your custodies. Bend of the machine rapidly.

B ) Ensure all parts are decently secured and safe to run before get downing the

machine.

degree Celsius ) Never clean the taper in the spindle when the drill is running, since this could

consequence in broken fingers or worse hurts.

vitamin D ) Always take the chow key instantly after utilizing it. A cardinal left in the

chow will be thrown out at high speed when the machine is turned on.

vitamin E ) Never stop the drill imperativeness spindle with your manus after you have turned off the

machine, crisp french friess frequently collect around the chow or spindle. Do non make

about, near or behind a revolving drill.

degree Fahrenheit ) Do non go forth the machine running unattended.

g ) Remove and clear all metal french friess in between machine parts before and after

use.

H ) Do non alter cogwheel when the machine is running.

I ) Use a coppice alternatively of your custodies to clean french friess off the machine. Never usage

an air jet for taking french friess as this will do the french friess to wing at a high

speed and may take to cuts and oculus hurts. Do non clean french friess or wipe oil

while the machine is running.

J ) When traveling the caput or tabular array on sensitive drill imperativenesss, make certain a safety clinch is set merely below the tabular array or caput on the column ; this will forestall the tabular array from all of a sudden dropping if the column clinch is prematurely released.

4.8 PROJECT Drilling

To be supplied by Sis Tuti

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