Drilling From Wikipedia, the free encyclopedia For other uses, see Drilling (disambiguation). This article needs additional citations for verification. Please help improve th is article by adding citations to reliable sources. Unsourced material may be ch allenged and removed. (June 2008) titanium drilling Drilling is a cutting process that uses a drill bit to cut or circular cross-section in solid materials. The drill bit is a l, often multipoint. The bit is pressed against the workpiece es from hundreds to thousands of revolutions per minute. This edge against the workpiece, cutting off chips from what will ing drilled.
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Exceptionally, specially-shaped bits can cut holes of non-circular cross-section ; a square cross-section is possible. Contents [hide] 1 Process 1.1 Spot drilling 1.2 Center drilling 1.3 Deep hole drilling 1.3.1 Gun drilling 1.3.2 Trepanning 1.4 Microdrilling 1.5 Vibration Drilling 2 Material 2.1 Drilling in metal 2.2 Drilling in wood 2.3 Others 3 Related processes 4 See also 5 References 6 External links 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 i nside of the hole usually has helical feed marks. Drilling may affect the mechanical properties of the workpiece by creating low r esidual stresses around the hole opening and a very thin layer of highly stresse d and disturbed material on the newly formed surface. This causes the workpiece to become more susceptible to corrosion at the stressed surface.A finish operati on may be done to avoid the corrosion.Zinc plating or any other standard finish opertion of 14 to 20 microns can be done which helps to avoid any sort of corros ion. For fluted drill bits, any chips are removed via the flutes. Chips may be long s pirals or small flakes, depending on the material, and process parameters. Th e type of chips formed can be an indicator of the machinability of the material, with long gummy chips reducing machinability. When possible drilled holes should be located perpendicular to the workpiece sur face. This minimizes the drill bit's tendency to "walk", that is, to be deflecte d, which causes the hole to be misplaced. The higher the length-to-diameter rati
o of the drill bit, the higher the tendency to walk. The tendency to walk is als o preempted in various other ways, which include: Establishing a centering mark or feature before drilling, such as by: Casting, molding, or forging a mark into the workpiece Center punching Spot drilling (i.e., center drilling) Spot facing, which is facing a certain area on a rough casting or forging to est ablish, essentially, an island of precisely known surface in a sea of imprecisel y known surface Constraining the position of the drill bit using a drill jig with drill bushings Surface finish in drilling may range from 32 to 500 microinches. Finish cuts wil l generate surfaces near 32 microinches, and roughing will be near 500 microinch es. Cutting fluid is commonly used to cool the drill bit, increase tool life, increa se speeds and feeds, increase the surface finish, and aid in ejecting chips. App lication of these fluids is usually done by flooding the workpiece or by applyin g a spray mist. In deciding which drill(s) to use it is important to consider the task at hand a nd evaluate which drill would best accomplish the task. There are a variety of d rill 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 s izes. The indexable drill is useful in managing chips. Spot drilling See also: Drill bit#Center drill and spotting drill The purpose of spot drilling is to drill a hole that will act as a guide for dri lling the final hole. The hole is only drilled part way into the workpiece becau se it is only used to guide the beginning of the next drilling process. Center drilling See also: Drill bit#Center drill and spotting drill The purpose of center drilling is to drill a hole that will act as a center of r otation for possible following operations. Center drilling is typically performe d using a drill with a special shape, known as a center drill. Deep hole drilling Deep hole drilling is defined as a hole depth greater than five times the diamet er of the hole. These types of holes require special equipment to maintain th e straightness and tolerances. Other considerations are roundness and surface fi nish. Deep hole drilling is generally achievable with a few tooling methods, usually g un drilling or BTA drilling. These are differentiated due to the coolant entry m ethod (internal or external) and chip removal method (internal or external). Usi ng methods such as a rotating tool and counter-rotating workpiece are common tec hniques to achieve required straightness tolerances. Secondary tooling method s include trepanning, skiving and burnishing, pull boring, or bottle boring. Fin ally a new kind of drilling technology is available to face this issue: the vibr ation drilling. This technology consists in fractionating chips by a small contr olled axial vibration of the drill. Therefore the small chips are easily removed by the flutes of the drill. A high tech monitoring system is used to control force, torque, vibrations, and acoustic emission. The vibration is considered a major defect in deep hole drill ing which can often cause the drill to break. Special coolant is usually used to aid in this type of drilling.
Gun drilling Main article: Gun drill Another type of drilling operation is called gun drilling. This method was origi nally developed to drill out gun barrels and is used commonly for drilling small er diameter deep holes. This depth-to-diameter ratio can be even more than 300:1 . The key feature of gun drilling is that the bits are self-centering; this is w hat 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 alon g the surface of the hole keeping the drill bit on center. Gun drilling is usual ly done at high speeds and low feed rates. Trepanning Trepanning is commonly used for creating larger diameter holes (up to 915 mm (36 .0 in)) where a standard drill bit is not feasible or economical. Trepanning rem oves 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 meta l, granite (curling stone), plates, or structural members like I-beams. Trepanni ng can also be useful to make grooves for inserting seals, such as O-rings. Microdrilling Microdrilling refers to the drilling of holes less than 0.5 mm (0.020 in). Drill ing 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.[citation n eeded] Vibration Drilling Titanium chips - conventional drilling vs vibration drilling Vibration drilling of an aluminum-CFRP multi-material stack with MITIS technolog y The first works on vibration drilling began in the 1950s (Pr. V.N. Poduraev, Mos cow Bauman University). The main principle consists in generating axial vibratio ns or oscillations in addition to the feed movement of the drill so that chips c ould be fractionated and easily removed from the cutting zone. One can find two main technologies of vibration drilling: self-maintained vibrat ions systems and forced vibrations systems. Most vibration drilling technologies are still at a research stage. It is the case of the self-maintained vibrations drilling: the eigen frequency of the tool is used in order to make it naturally vibrate while cutting; vibrations are self-maintained by a mass-spring system i ncluded in the tool holder. Other works use a piezoelectric system to generat e and control the vibrations. These systems allow high vibration frequencies (up to 2 kHz) for small magnitude (about a few microns); they particularly fit dril ling of small holes. Finally vibrations can be generated by mechanical systems:[ 7] the frequency is given by the combination of the rotation speed and the numbe r of oscillation per rotation (a few oscillations per rotation), the magnitude i s about 0.1 mm. This last technology is a fully industrial one (example: SineHoling® technology of MITIS). Vibration drilling is a favoured solution in order to face issues like deep hole drilling, multi-material stacks drilling (aeronautics) or dry drilling (without lubrication). Generally it allows increasing the reliability and the c ontrol of the drilling operation. Material
Drilling in metal High speed steel twist bit drilling into aluminium with methylated spirits lubri cant Under normal usage, swarf is carried up and away from the tip of the drill bit b y the fluting of the drill bit. The cutting edges produce more chips which conti nue the movement of the chips outwards from the hole. This is successful until t he chips pack too tightly, either because of deeper than normal holes or insuffi cient backing off (removing the drill slightly or totally from the hole while dr illing). Cutting fluid 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 in troduced via holes through the drill shank, which is common when using a gun dri ll. When cutting aluminum in particular, cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the pro cess of drilling the hole. For heavy feeds and comparatively deep holes oil-hole drills can be used, 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 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 tools a process called peck drilling , 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 dril l part way through the workpiece, no more than five times the diameter of the dr ill, and then retracting it to the surface. This is repeated until the hole is f inished. A modified form of this process, called high speed peck drilling or chi p breaking, only retracts the drill slightly. This process is faster, but is onl y used in moderately long holes otherwise it will overheat the drill bit. It is also used when drilling stringy material to break the chips. Drilling in wood Wood 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 i ssue in drilling wood is assuring clean entry and exit holes and preventing burn ing. Avoiding burning is a question of using sharp bits and the appropriate cutt ing speed. Drill bits can tear out chips of wood around the top and bottom of th e hole and this is undesirable in fine woodworking 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 rough holes for carpentry, the quality of the hole does not matter, and a nu mber of bits for fast cutting in wood exist, including spade bits and self-feedi ng auger bits. Many types of specialised drill bits for boring clean holes in wo od have been developed, including brad-point bits, Forstner bits and hole saws. 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 nea t. 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 plastics 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 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 drilling holes using plastic deformation of the subject (under heat and pressure ) instead of cutting it. See also Laser drilling References ^ Wolfram (mathematical software) website: Drilling a square hole ^ Practical demonstration of square-hole bit, YouTube video ^ a b c d Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Pro cesses Reference Guide, Industrial Press Inc., pp. 43 48, ISBN 0-8311-3049-0. ^ Bralla, James G. (1999). Design for manufacturability handbook. New York: McGr aw-Hill. p. 4-56. ISBN 978-0-07-007139-1. ^ "What Is Deep Hole Drilling? An Overview". ^ Paris, Henri (2005). Modelling the Vibratory Drilling Process to Foresee Cutti ng Parameters. CIRP Annals - Manufacturing Technologies. pp. 367 370. ISSN 10.1016 /S0007-8506(07)60124-3 0007-8506, 10.1016/S0007-8506(07)60124-3. ^ Peigné, Grégoire (2009). Axial machining device. ^ Smid, Peter (2003), CNC programming handbook (2nd ed.), Industrial Press, p. 1 99, ISBN 978-0-8311-3158-6. ^ Hurst, Bryan (2006), The Journeyman's Guide to CNC Machines, Lulu.com, p. 82, ISBN 978-1-4116-9921-2. ^ Mattson, Mike (2009), CNC Programming: Principles and Applications (2nd ed.), Cengage Learning, p. 233, ISBN 978-1-4180-6099-2. External links Look up drilling in Wiktionary, the free dictionary. Feeds for high speed drills [show] v t e Metalworking [show] v t e Woodworking Categories: MachiningWoodworking Navigation menu Create accountLog inArticleTalkReadEditView history Main page Contents Featured content Current events Random article Donate to Wikipedia Interaction Help About Wikipedia Community portal Recent changes