![Percage sineholing mitis](https://upload.wikimedia.org/wikipedia/commons/2/23/Percage_sineholing_mitis.jpg)
Drilling is a
cutting
Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force.
Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the scal ...
process where a
drill bit
Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order ...
is spun to cut a hole of circular
cross-section in solid materials. The drill bit is usually a rotary
cutting tool
In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...
, often multi-point. The bit is
pressed against the work-piece and rotated at rates from hundreds to thousands of
revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
. This forces the cutting edge against the work-piece, cutting off
chips (swarf) from the hole as it is drilled.
In
rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
drilling, the hole is usually not made through a circular cutting motion, though the bit is usually rotated. Instead, the hole is usually made by hammering a drill bit into the hole with quickly repeated short movements. The hammering action can be performed from outside the hole (
top-hammer drill) or within the hole (
down-the-hole drill
A down-the-hole drill, usually called DTH by most professionals, is basically a jackhammer screwed on the bottom of a drill string. The fast hammer action breaks hard rock into small cuttings and dust that are evacuated by a fluid (air, water or ...
, DTH). Drills used for horizontal drilling are called
drifter drill
A drifter drill, sometimes called a rock drill, is a tool used in mining and civil engineering to drill into rock. Rock drills are used for making holes for placing dynamite or other explosives in rock blasting, and holes for plug and feather qua ...
s.
In rare cases, specially-shaped bits are used to cut holes of non-circular cross-section; a
square
In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90- degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length a ...
cross-section is possible.
Process
Drilled holes are characterized by their sharp edge on the entrance side and the presence of
burrs on the exit side (unless they have been removed). Also, the inside of the hole usually has helical feed marks.
Drilling may affect the mechanical properties of the workpiece by creating low
residual stress
In materials science and solid mechanics, residual stresses are Stress (physics), stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable. For example, l ...
es around the hole opening and a very thin layer of highly
stressed and disturbed material on the newly formed surface. This causes the workpiece to become more susceptible to
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
and
crack propagation
Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics t ...
at the stressed surface.
A finish operation may be done to avoid these detrimental conditions.
For
fluted
Fluting may refer to:
*Fluting (architecture)
* Fluting (firearms)
* Fluting (geology)
* Fluting (glacial)
*Fluting (paper)
Arts, entertainment, and media
*Fluting on the Hump
''Fluting on the Hump'' is the first album by avant-garde band Kin ...
drill bits, any chips are removed via the flutes. Chips may form long spirals or small flakes, depending on the material, and process parameters.
The type of chips formed can be an indicator of the
machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...
of the material, with long chips suggesting good material machinability.
When possible drilled holes should be located perpendicular to the workpiece surface. This minimizes the drill bit's tendency to "walk", that is, to be
deflected from the intended center-line of the bore, causing the hole to be misplaced. The higher the length-to-diameter ratio of the drill bit, the greater the tendency to walk. The tendency to walk is also preempted in various other ways, which include:
* Establishing a centering mark or feature before drilling, such as by:
**
Casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
,
molding, or
forging a mark into the workpiece
**
Center punching
**
Spot drill
Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order ...
ing (i.e., center drilling)
**
Spot facing
A spotface or spot face is a machined feature in which a certain region of the workpiece (a spot) is faced, providing a smooth, flat, accurately located surface. This is especially relevant on workpieces cast or forged, where the spotface's smoo ...
, which is machining a certain area on a casting or forging to establish an accurately located face on an otherwise rough surface.
* Constraining the position of the drill bit using a
drill jig
A jig is a type of custom-made tool used to control the location and/or motion of parts or other tools.
Description
A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in the manufacturing of products..
An ex ...
with
drill bushing
A drill bushing, also known as a jig bushing, is a tool used in metalworking jigs to guide cutting tools, most commonly drill bits. Other tools that are commonly used in a drill bushing include counterbores, countersinks, and reamers. They are des ...
s
Surface finish produced by drilling may range from 32 to 500 microinches. Finish cuts will generate surfaces near 32 microinches, and roughing will be near 500 microinches.
Cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...
is commonly used to cool the drill bit, increase tool life, increase
speeds and feeds, increase the surface finish, and aid in ejecting chips. Application of these fluids is usually done by flooding the workpiece with coolant and lubricant or by applying a spray mist.
In deciding which drill(s) to use it is important to consider the task at hand and evaluate which drill would best accomplish the task. There are a variety of drill styles that each serve a different purpose. The subland drill is capable of drilling more than one diameter. The spade drill is used to drill larger hole sizes. The indexable drill is useful in managing chips.
Spot drilling
The purpose of spot drilling is to drill a hole that will act as a guide for drilling the final hole. The hole is only drilled part way into the workpiece because it is only used to guide the beginning of the next drilling process.
Centre drilling
Centre drill is a two-fluted tool consisting of a twist drill with a 60° countersink; used to drill countersink center holes in a workpiece to be mounted between centers for turning or grinding.
Deep hole drilling
![Rixö granitbrott 23](https://upload.wikimedia.org/wikipedia/commons/6/63/Rix%C3%B6_granitbrott_23.jpg)
Deep hole drilling is defined as drilling a hole of depth greater than ten times the diameter of the hole. These types of holes require special equipment to maintain the straightness and tolerances. Other considerations are roundness and surface finish.
Deep hole drilling is generally achievable with a few tooling methods, usually
gun drilling or BTA drilling. These are differentiated due to the coolant entry method (internal or external) and chip removal method (internal or external). Using methods such as a rotating tool and counter-rotating workpiece are common techniques to achieve required straightness tolerances. Secondary tooling methods include trepanning, skiving and burnishing, pull boring, or bottle boring. Finally, a new kind of drilling technology is available to face this issue: vibration drilling. This technology breaks up the chips by a small controlled axial vibration of the drill. The small chips are easily removed by the flutes of the drill.
A high tech monitoring system is used to control
force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
,
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
,
vibration
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, su ...
s, and acoustic emission. Vibration is considered a major defect in deep hole drilling which can often cause the drill to break. A special coolant is usually used to aid in this type of drilling.
Gun drilling
Gun drilling was originally developed to drill out gun barrels and is used commonly for drilling smaller diameter deep holes. The depth-to-diameter ratio can be even greater than 300:1. The key feature of gun drilling is that the bits are self-centering; this is what allows for such deep accurate holes. The bits use a rotary motion similar to a twist drill; however, the bits are designed with bearing pads that slide along the surface of the hole keeping the drill bit on center. Gun drilling is usually done at high speeds and low feed rates.
Trepanning
![Trepanned hole in steel plate](https://upload.wikimedia.org/wikipedia/commons/c/cf/Trepanned_hole_in_steel_plate.jpg)
Trepanning is commonly used for creating larger diameter holes (up to ) where a standard drill bit is not feasible or economical. Trepanning removes the desired diameter by cutting out a solid disk similar to the workings of a
drafting compass. Trepanning is performed on flat products such as sheet metal, granite (
curling stone
Curling is a sport in which players slide stones on a sheet of ice toward a target area which is segmented into four concentric circles. It is related to bowls, boules, and shuffleboard. Two teams, each with four players, take turns sliding h ...
), plates, or structural members like
I-beam
An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish language, Polish, Bulgarian language, Bulgarian, Spanish language, Spanish ...
s. Trepanning can also be useful to make
grooves for inserting
seals
Seals may refer to:
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impress an emblem, used as a means of a ...
, such as
O-ring
An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more par ...
s.
Microdrilling
Microdrilling refers to the drilling of holes less than . Drilling of holes at this small diameter presents greater problems since coolant fed drills cannot be used and high spindle speeds are required. High spindle speeds that exceed 10,000 RPM also require the use of balanced tool holders.
Vibration drilling
![Percage vibratoire multi-matériaux MITIS](https://upload.wikimedia.org/wikipedia/commons/6/6a/Percage_vibratoire_multi-mat%C3%A9riaux_MITIS.png)
The first studies into vibration drilling began in the 1950s (Pr. V.N. Poduraev, Moscow Bauman University). The main principle consists in generating axial vibrations or oscillations in addition to the feed movement of the drill so that the chips break up and are then easily removed from the cutting zone.
There are two main technologies of vibration drilling: self-maintained vibration systems and forced vibration systems. Most vibration drilling technologies are still at a research stage. In the case of self-maintained vibration drilling, the
eigenfrequency
In linear algebra, an eigenvector () or characteristic vector of a linear transformation is a nonzero vector that changes at most by a scalar factor when that linear transformation is applied to it. The corresponding eigenvalue, often denoted ...
of the tool is used in order to make it naturally vibrate while cutting; vibrations are self-maintained by a mass-spring system included in the tool holder. Other works use a piezoelectric system to generate and control the vibrations. These systems allow high vibration frequencies (up to 2 kHz) for small magnitude (about a few micrometers); they are particularly suitable for drilling small holes. Finally, vibrations can be generated by mechanical systems: the frequency is given by the combination of the rotation speed and the number of oscillation per rotation (a few oscillations per rotation), with magnitude about 0.1 mm.
This last technology is a fully industrial one (example: SineHoling® technology of MITIS). Vibration drilling is a preferred solution in situations like deep hole drilling, multi-material stack drilling (aeronautics) and dry drilling (without lubrication). Generally, it provides improved reliability and greater control of the drilling operation.
Circle interpolating
![Orbital-drilling](https://upload.wikimedia.org/wikipedia/commons/f/f3/Orbital-drilling.gif)
''Circle interpolating'', also known as ''orbital drilling'', is a process for creating holes using machine cutters.
Orbital drilling is based on rotating a
cutting tool
In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...
around its own axis and simultaneously about a centre axis which is off-set from the axis of the cutting tool. The cutting tool can then be moved simultaneously in an axial direction to drill or machine a hole – and/or combined with an arbitrary sidewards motion to machine an opening or cavity.
By adjusting the offset, a cutting tool of a specific diameter can be used to drill holes of different diameters as illustrated. This implies that the cutting tool inventory can be substantially reduced.
The term orbital drilling comes from that the cutting tool “orbits” around the hole center. The mechanically forced, dynamic offset in orbital drilling has several advantages compared to conventional drilling that drastically increases the hole precision. The lower thrust force results in a
burr-less hole when drilling in metals. When drilling in
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
s the problem with
delamination
Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling a ...
is eliminated.
Material
Drilling in metal
![HSS Twist Drill into Aluminium with Lubricant](https://upload.wikimedia.org/wikipedia/commons/a/a8/HSS_Twist_Drill_into_Aluminium_with_Lubricant.jpg)
Under normal usage, swarf is carried up and away from the tip of the drill bit by the fluting of the drill bit. The cutting edges produce more chips which continue the movement of the chips outwards from the hole. This is successful until the chips pack too tightly, either because of deeper than normal holes or insufficient ''backing off'' (removing the drill slightly or totally from the hole while drilling).
Cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...
is sometimes used to ease this problem and to prolong the tool's life by cooling and lubricating the tip and chip flow. Coolant may be introduced via holes through the drill shank, which is common when using a gun drill. When cutting
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
in particular, cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the process of drilling the hole. When cutting brass, and other soft metals that can grab the drill bit and causes "chatter", a face of approx. 1-2 millimeters can be ground on the cutting edge to create an obtuse angle of 91 to 93 degrees. This prevents "chatter" during which the drill tears rather than cuts the metal. However, with that shape of bit cutting edge, the drill is pushing the metal away, rather than grabbing the metal. This creates high friction and very hot swarf.
![Magnetic Drilling Machine from BDS](https://upload.wikimedia.org/wikipedia/commons/0/00/Magnetic_Drilling_Machine_from_BDS.jpg)
For heavy feeds and comparatively deep holes
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
-hole drills are used in the drill bit, with a lubricant pumped to the drill head through a small hole in the bit and flowing out along the fluting. A conventional
drill press
A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to i ...
arrangement can be used in oil-hole drilling, but it is more commonly seen in automatic drilling machinery in which it is the workpiece that rotates rather than the drill bit.
In
computer numerical control (CNC)
machine tool
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. All ...
s a process called ', or ''interrupted cut drilling'', is used to keep swarf from detrimentally building up when drilling deep holes (approximately when the depth of the hole is three times greater than the drill diameter). Peck drilling involves plunging the drill part way through the workpiece, no more than five times the diameter of the drill, and then retracting it to the surface. This is repeated until the hole is finished. A modified form of this process, called ''high speed peck drilling'' or ''chip breaking'', only retracts the drill slightly. This process is faster, but is only used in moderately long holes, otherwise it will overheat the drill bit. It is also used when drilling stringy material to break the chips.
When it is not possible to bring the material to the СNС machine, a Magnetic Base Drilling Machine may be used. The base allows drilling in a horizontal position and even on a ceiling. Usually, for these machines, it is better to use cutters because they can drill much faster with less speed. Cutter sizes vary from 12mm to 200mm DIA and from 30mm to 200mm DOC(depth of cut). These machines are widely used in construction, fabrication, marine, and oil & gas industries. In the
oil and gas industry, pneumatic magnetic drilling machines are used to avoid sparks, as well as special tube magnetic drilling machines that can be fixed on pipes of different sizes, even inside. Heavy-dut
plate drilling machinesprovide high-quality solutions in the manufacturing of steel construction, bridge construction, shipyards, and various fields of the construction sector.
Drilling in wood
Wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
being softer than most metals, drilling in wood is considerably easier and faster than drilling in metal. Cutting fluids are not used or needed. The main issue in drilling wood is ensuring clean entry and exit holes and preventing burning. Avoiding burning is a question of using sharp bits and the appropriate
cutting speed
The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often considered as a pair because of their combined effect on the cutting process. Each, however, ...
. Drill bits can tear out chips of wood around the top and bottom of the hole and this is undesirable in fine
woodworking
Woodworking is the skill of making items from wood, and includes cabinet making (cabinetry and furniture), wood carving, woodworking joints, joinery, carpentry, and woodturning.
History
Along with Rock (geology), stone, clay and animal parts, ...
applications.
The ubiquitous twist drill bits used in metalworking also work well in wood, but they tend to chip wood out at the entry and exit of the hole. In some cases, as in holes for rough carpentry, the quality of the hole does not matter, and a number of bits for fast cutting in wood exist, including spade bits and self-feeding
auger
Auger may refer to:
Engineering
* Wood auger, a drill for making holes in wood (or in the ground)
** Auger bit, a drill bit
* Auger conveyor, a device for moving material by means of a rotating helical flighting
* Auger (platform), the world's f ...
bits. Many types of specialised drill bits for boring clean holes in wood have been developed, including brad-point bits,
Forstner bits and
hole saw
A hole saw (also styled holesaw), also known as a hole cutter, is a saw blade of annular (ring) shape, whose annular kerf creates a hole in the workpiece without having to cut up the core material. It is used in a drill. Hole saws typically ...
s. Chipping on exit can be minimized by using a piece of wood as backing behind the work piece, and the same technique is sometimes used to keep the hole entry neat.
Holes are easier to start in wood as the drill bit can be accurately positioned by pushing it into the wood and creating a dimple. The bit will thus have little tendency to wander.
Others
Some materials like
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
s as well as other non-metals and some metals have a tendency to heat up enough to expand making the hole smaller than desired.
Related processes
The following are some related processes that often accompany drilling:
;
Counterboring : This process creates a stepped hole in which a larger diameter follows a smaller diameter partially into a hole.
;
Countersinking
A countersink (symbol: ⌵) is a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common use is to allow the head of a countersunk bolt, screw or rivet, when placed in the hole, to sit flush with or below the ...
: This process is similar to counterboring but the step in the hole is cone-shaped.
;
Boring : Boring precisely enlarges an already existing hole using a single point cutter.
;
Friction drilling
Friction drilling is a method of making holes in metal in which the material is pushed out of the way with the aid of heat from friction. The process is also called thermal drilling, flow drilling, form drilling, or friction stir drilling.
Fricti ...
: drilling holes using plastic deformation of the subject (under heat and pressure) instead of cutting it.
;
Reaming
A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precisio ...
: Reaming is designed to enlarge the size of a hole to leave smooth sides.
;
Spot facing
A spotface or spot face is a machined feature in which a certain region of the workpiece (a spot) is faced, providing a smooth, flat, accurately located surface. This is especially relevant on workpieces cast or forged, where the spotface's smoo ...
:This is similar to milling, it is used to provide a flat machine surface on the workpiece in a localized area
See also
*
Laser drilling
Laser drilling is the process of creating thru-holes, referred to as “popped” holes or “percussion drilled” holes, by repeatedly pulsing focused laser energy on a material. The diameter of these holes can be as small as 0.002” (~50 μm). ...
*
Drilling rig
A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill wat ...
References
External links
{{Authority control
Hole making
Machining
Woodworking