Drilling holes with high length-to-diameter ratios

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In the field of manufacturing technology, deep hole drilling refers to the drilling of bore holes with high length-to-diameter ratios.

Definition of deep hole drilling

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According to the VDI Standard , deep hole drilling processes are manufacturing processes for the machining of bore holes with diameters between D = 0.2... mm and whose drilling depth is usually greater than three times the diameter.[1] For small diameters, length-to-diameter ratios of up to l/D &#; 100 can be achieved, in special cases even up to l/D = 900.[2][3][4] With large diameters, the l/D ratio is usually limited by the travel or the bed length of the deep hole drilling machine.[4][5]

Deep hole drilling

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Soldered single-edged BTA solid drilling tool (left); symmetrical twist drill (right)

Deep hole drilling also differs from normal drilling in that, depending on the drilling process and the drilling diameter, cooling lubricant must be pumped to the cutting edges in large quantities and under high pressure. This ensures good cooling and at the same time good lubrication of the contact areas between the workpiece and the cutting edge of the tool on the one hand and the workpiece and guide pads of the tool on the other. In addition, the cooling lubricant continuously removes chips from the cutting zone, which makes surface-damaging and time-consuming chip removal strokes unnecessary and therefore improves the quality of the borehole and the productivity of the processes.[1] For the production of deep holes, two different tool types are distinguished. On the one hand, there are tools with an asymmetrical single cutting-edge design. These deep hole drilling tools include single-lip deep hole drills, the single-tube system (BTA deep-hole drilling) and the double-tube system (ejector deep-hole drilling), which are referred to as the "classic" deep hole drilling processes. On the other hand, there are tools with symmetrically arranged cutting edges. These include spiral deep hole drilling tools and double-lip deep hole drilling tools, which can also be assigned to the deep drilling processes due to the drilling depths to be achieved with them. Deep Hole drilling was made originally in china.

The mentioned tool types differ with regard to the realizable diameter range, the achievable l/D ratios, the surface quality and their productivity. Symmetrical tools can only be used in the small diameter range of D = 0.2 ... 32  mm to produce holes with an l/D ratio up to a maximum of l/D = 85, the standard is an l/D ratio of l/D = 30. With asymmetrical tools, holes in the diameter range of D = 0.5...  mm can be produced and the upper limit of the l/D ratio is usually limited by the machine dimensions. The figure shows selected deep hole drilling methods with their usual application diameters, whereby it becomes clear that deep hole drilling methods do not compete with each other in all diameter ranges. The advantage of the symmetrically designed tools compared to the "classical" deep hole drilling tools in the small diameter range is the feasibility of significantly higher feeds f, which can be 6 times higher compared to the usual values for single-lip deep hole drilling.[1][6][7][8]

Tiefbohrverfahren mit ihren üblichen Anwendungsdurchmessern

In addition to the high l/D ratio, the "classic" deep hole drilling methods are characterized by high productivity and high surface quality compared to the conventional drilling methods with twist drills. The high drilling quality is characterized by low surface roughness, small diameter deviations and a high geometrical accuracy. Important for the good surface quality is the asymmetrical design of the deep hole drilling tools. The "classical" tools for single-lip deep hole drilling, BTA deep hole drilling and ejector deep hole drilling are, with a few exceptions, designed asymmetrically and have a secondary cutting edge (circular grinding chamfer) and guide pads. Due to this design features, a certain amount of the cutting forces during the process is transferred via the guide pads to the bore hole wall. These force components at the tool head are supported at the produced borehole wall and thus guide the tool in the bore hole itself. The distribution of the process forces during deep hole drilling is therefore different from conventional drilling, where the forces are largely absorbed by the tool shank and thus by the machine spindle. Due to the process force distribution to bore hole wall in deep hole drilling, the drill guides itself and thus the process benefits from a comparatively low straightness deviation. The "support" of the guide pads on the borehole wall also results in a forming process that (ideally) smooths the bore hole wall. Due to this forming process the surface roughness caused by the engagement of the cutting edges during drilling can be decreases by about 70%.[9] Thus very high surface qualities with bore hole tolerances of IT 9 to IT 7 can be achieved by deep hole drilling processes. Subsequent steps to improve the surface quality of the bore hole can often be reduced or eliminated completely. A further advantage is the low burr formation for trough holes and for over-drilling cross holes.[1] Due to the high surface quality combined with a high productivity, the use of deep hole drilling methods can be economical even at low drilling depths.[5][10]

Deep hole drilling methods

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Single-lip deep hole drilling

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Single-lip deep hole drilling is usually used to produce holes in the diameter range of D = 0.5...40 mm. This range of application is currently limited at the lower end by the manufacturing technology to realize the coolant channels inside the tool and the increasing challenges in grinding technology with decreasing tool diameters. The upper limit results from the more economical use of alternative deep hole drilling methods.[1][12] Characteristic for single-lip deep hole drilling is the internal coolant supply through one kidney-shaped or two circular cooling channels. The chip/coolant mixture is discharged in a v-shaped longitudinal groove on the tool, the so-called gullet. The coolant mass flow is the only transport mechanism for removing the chips. For this reason, a diameter-dependent high-pressure coolant supply is necessary. The general structure of single-lip tools is divided into three parts: the drill head, the shank and the clamping sleeve. Usually the drill head is joined to the shank by brazing. The clamping sleeve is the clamping element of the tool and forms the interface to the tool holder and thus to the machine tool. Solid carbide tools are often used for smaller tool diameters and tools with a high-performance design. With these more powerful tools, the drill head and the shank are made of a single carbide rod. The drill head is usually made of carbides of the ISO cutting application group K 10 to K 20 and is coated if required. In special applications, PCD, cermets, ceramics or high-speed steels are also used.[1] The choice of the drill head geometry is made depending on the existing machining situation. In this respect, a distinction is made between different cutting edge angles and the circumferential shape of the guide pads. With the usual standard grinding for single-lip drills, the main cutting edge is divided into an outer and an inner cutting edge, which differ in different cutting edge angles depending on the bore hole diameter. The choice of the circumferential shape, i.e. the number and arrangement of the guide pads on the circumference of the single-lip drill, is also important. Compared to conventional drilling with twist drills, single-lip drilling is characterized by its suitability and high process reliability with large length-to-diameter ratios. In addition, single-lip drilling achieves comparatively high bore hole qualities, which can reduce the need for post-processing.[1]

Tools

Single-lip deep hole drill with replaceable cutting edges and guiding elements Single-lip deep hole drill made of solid carbide

As can be seen in the pictures, a single-lip deep hole drill consists of a tool holder, a shank and the drill head (usually carbide). As far as the design is concerned, it can be generally said that the shank is a few 1/10th of a millimeter to 1 millimeter smaller than the drill head. It can also be seen that approximately 1/4 of the shank consists of a grove, in which the coolant flow flushes the chips out of the bore hole. The cutting head itself carries guide surfaces which are in contact with the bore hole wall and guide the drill. Conventional twist drill on the other hand are usually guided by the axis of the machine tool.

The actual cutting edge is asymmetrically arranged and runs from the cutting edge corner via the tip to the centre of the drill. The tool thus works with a single cutting edge. The cutting forces, which are not cancelled out because of the asymmetrical design, are supported on the bore hole wall. The chips produced at the cutting edge are surrounded by coolant from the outside and then flushed away from the cutting zone through the grove in the shank. Up to a diameter of approx. 10 mm the tools have one cooling channel, for larger diameters two or more channels are used.

BTA deep hole drilling

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Principle of the BTA deep hole drilling method

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The disadvantages of single-lip deep hole drilling, such as the contact of the chips with the generated bore hole surface or the low torsional moment, were the motivation to develop a modified deep hole drilling method that avoids these problems and retains the good properties. As a result of the above, a new deep hole drilling method was developed around , which was given the name BTA deep hole drilling in the early s. BTA stands for "Boring and Trepanning Association" which was dominated by the now liquidated company Gebrüder Heller in Bremen Germany. Under their leadership, the new process was created during the Second World War by combining their own developments with those of Burgsmüller and Beisner. Burgsmüller replaced the grooved drill shaft used until then by a tube with a closed cross-section, which was more torsionally rigid, and for the first time conveyed the chips through the inside of the tube. Burgsmüller used a double-edged tool and an air-oil mixture, which is nowadays used in production with minimum quantity lubrication. Beisner improved the tool design and introduced oil as cooling lubricant. Heller, which was the first company to introduce carbide-tipped single-lip deep hole drilling tools, had the patent for the cutting edge/guide pad constellation which was then also used for the BTA tools.

During the machining process, the coolant is fed to the cutting zone, as shown in the figure, through the ring gap between the hole produced and the drill tube with the aid of the drilling oil supply unit (BOZA). The BOZA also seals between the workpiece and the drill tube. For this purpose, it has a conical rotating workpiece holder which is directed towards the workpiece and is pressed against the workpiece with high pressure. This centres the workpiece and creates a sealing contact surface. In most cases, the rear side of the BOZA is sealed by a stuffing box, which also guides the drill tube. In the BOZA, the tapping bush is usually integrated, which means that working with a pilot bore hole in the BTA process is rarely necessary.

Tools

BTA deep hole drilling tool for drilling with one cutting edge from botek BTA deep hole drilling tool for solid drilling with split cutting edges from BTA-TiefbohrsystemeBTA deep hole drilling tool for drilling with split cutting edge from botek

The chips are removed through the openings integrated in the drilling head with the aid of the cutting oil flow. Therefore, the openings are called "chip mouth". In this way, the chips can be removed without contact to the bore hole wall. Due to the circular cross section of the tool and the drill tube, the process has a higher torsional resistance moment compared to single-lip deep hole drilling, which allows a significantly higher cutting performance to be achieved. The BTA process is used for bore hole diameters of D = 6... mm. For industrial processes it is used in a range from approx. D = 16 mm. It is possible to manufacture BTA drill heads with a diameter of D &#; 6 mm, but there is no known application case until today.[13][10][11]

Ejector deep hole drilling

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Process principle for ejector deep hole drilling

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Ejector drilling head with soldered-on cutting edges and guide elements from SandvikEjector drilling head with replaceable cutting edges and guide elements from Sandvik

The ejector deep hole drilling is used in a diameter range of approx. D = 18 ... 250 mm. It is a variant of the BTA process in which the drill heads used are structurally comparable to the BTA tool system. The only difference are additional coolant outlets on the circumference of the tool. The coolant is supplied through the ring space between the drill tube and the inner tube, which also gives the process the name two-tube process. The coolant emerges laterally from the already mentioned coolant outlets, flows around the drill head and flows back into the inner tube transporting the produced chips. Part of the coolant is fed directly into the inner tube via a ring nozzle. This creates a negative pressure (ejector effect) at the chip mouth, which facilitates the backflow in the inner tube. The system can be operated via an external high-pressure pump or the internal coolant supply of the machine. Since, in contrast to the BTA process, no sealing against escaping coolant is required, the ejector process can also be used on conventional lathes and machining centres. As the pipe cross-section through which the chips are to be removed is reduced by the double tube system, the cutting capacity is lower than with the BTA process. For this reason, lower cutting speeds are usually selected for ejector deep hole drilling. In addition, the lower rigidity is accompanied by poorer concentricity properties (IT9 to IT11).[1][14][13][7]

A prerequisite for the implementation of the process is the use of a connecting piece which is inserted into the turret holder of the lathe or the spindle of the machining centre. Through this connection piece, the coolant is fed from the connected pump unit into the ring gap between the inner and outer tube. To enable this function, two different versions are available. A rotating connection piece is required for machining centres, and a non-rotating connection piece for lathes. The required installation space must be taken into account when selecting the machine tool.

Tools

The design of the tools for ejector deep hole drilling is almost identical to that of the BTA deep hole drilling tools. The additional coolant discharge outlets are shown in the illustrations.

Methods associated with deep hole drilling

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In addition to the classical deep hole drilling methods, there are a number of other methods for the final processing of deep holes. The hole can be post-processed with regard to their surface finish or can serve as a basis for machining complex and non-cylindrical contours.

Internal profiling

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For various reasons, there are components with deep holes whose inner contours are rotationally symmetrical but not uniformly cylindrical. Such components can have contours without undercuts, e.g. for centrifugal casting moulds or conical bores in extruder cylinders, and with undercuts, e.g. for propeller shafts or landing gears. To produce such chamber pockets, high quality pre-drilling is required. If the radially extendable cutting tool holder is controlled via an NC axis and connected to the NC bore slide of the deep hole drilling machine, it is almost possible to produce any bore hole wall contour in one cut over the entire contour length. The position of the cutting edge can be modified by an axial displacement, e.g. by using an internal thrust tube. In addition, the guide pads can also be adjusted hydraulically. Since the guide bore has already been machined after the first cutting step for the so-called long chamber method, the guide pads must also be radially adjustable to support the tool for larger chambers. As an alternative to this method, the so-called short-chamber method does not require extendable guide pads, as the tool is only seated in the pre-drilled guide hole.[15][16][17][18]

Skiving and smooth rolling

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Skiving improves the roundness and the dimensional accuracy of the bore hole diameter. The process creates an open surface profile, which is particularly suitable for subsequent machining processes such as smooth rolling or honing. In the field of machining hydraulic cylinders and cylinder liners, skiving and smooth rolling is considered a manufacturing process related to deep hole drilling, although it has a cutting and also a forming component. The reason for this is the wide use of combined skiving and smooth rolling tools.[19][20][21][22][23][24][25][26]

Single edge reaming

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Another machining process to increase the surface quality and dimensional accuracy of a bore hole is the use of single-bladed reamers. Reaming is the countersinking of a pre-drilled hole, where the tool is supported by the guide pads themselves. Therefore, the tool geometry of these reamers is very similar to single-lip drills. The difference to single-lip deep hole drilling with low cutting depth is the usually missing circumferential chamfer, a long side cutting edge parallel to the milling axis and the low coolant volumes and pressures.[27][28]

Deep hole drilling machines

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Designs of deep hole drilling machines (examples with indication of feed and cutting movement)

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Machine tools on which deep hole drilling is performed (examples partly with indication of feed and cutting movement)

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For machining with deep hole drilling processes or processes associated with deep hole drilling, deep hole drilling machines are mainly used as standard (multi-purpose) or special machines. Gun drills are an archetypal example. Often single-lip deep hole drills are used on machining centres for the production of holes with smaller drilling depths (up to approx. 40 × D). Ejector drilling is mainly used on conventional machine tools. Since deep hole drilling has a high productivity, only comparatively powerful machines are used. Basically, a coolant system is required that provides coolant with (compared to other drilling methods) above-average volume flow at higher pressures. A deep hole drilling system consists of the deep drilling machine and the coolant tank with further peripheral equipment for coolant preparation and chip handling. The ejector drilling process was developed as deep hole drilling technology which can be used on conventional machine tools. The use of single-lip deep hole drilling is particularly common on machining centres in series production. On the right you can see schematic drawings of conventional deep hole drilling machines.[1]

Literature

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VDI &#; The Association of German Engineers guidelines

• VDI : Tiefbohren mit Einlippenbohrern
• VDI : Tiefbohren mit äußerer Zuführung des Kühlschmierstoffs (BTA- und ähnliche Verfahren)
• VDI : Blatt 2 Tiefbohren; Richtwerte für das Schälen und Glattwalzen von Bohrungen
• VDI : Blatt 1 Tiefbohrverfahren
• VDI : Tiefbohren auf Bearbeitungszentren
• VDI : Abnahmebedingungen für einspindelige und mehrspindelige Tiefbohrmaschinen

Individual references

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1. a b c d e f g h i j k

   VDI-Richtlinie , Richtwerte für das Tiefbohren mit Einlippenbohrern, Berlin: Beuth-Verlag

2. ^

   U. Heisel, R. Eisseler (), "Hybride Bearbeitung beim Einlippentiefbohren. Beeinflussung der Spanlänge durch Schwingungseinkopplung", Präzisions- und Tiefbohren aktuell, VDI Berichte Nr. (in German), Düsseldorf: VDI

3. ^

   J. Steppan, C. Wangenheim (), "Mittenverlaufsreduzierung von Bohrungen mit einem L/D &#; Verhältnis größer 500 durch ein alternatives Fertigungsverfahren", Präzisions- und Tiefbohren aktuell, VDI Berichte Nr. (in German), Düsseldorf

4. a bBiermann, D.; Bleicher, F.; Heisel, U.; Klocke, F.; Möhring, H.-C.; Shih, A. (). "Deep hole drilling". CIRP Annals. 67 (2): 673&#;694. doi:10./j.cirp..05.007

5. a b

   D. Thamke (), "Möglichkeiten und Grenzen der Trockenbearbeitung", Fachgespräch zwischen Industrie und Hochschule "Bohren und Fräsen im modernen Produktionsprozess", Dortmund (in German)

6. ^

   P. Müller (), "Hochleistungswendelbohrer für das Tiefbohren", Präzisions- und Tiefbohren aktuell, VDI Berichte Nr. (in German), Düsseldorf: VDI

7. a b

   T. Upmeier (), "Innovative Prozessgestaltung für das Tiefbohren", Präzisions- und Tiefbohren aktuell, VDI Berichte Nr. (in German), Düsseldorf

   Want more information on Deep Drilling Machine? Feel free to contact us.

8. ^

   VDI-Richtlinie (), Tiefbohren mit äußerer Zuführung des Kühlschmierstoffes (BTA- und ähnliche Verfahren), Berlin: Beuth-Verlag

9. ^

   U. Weber (), Beitrag zur messtechnischen Erfassung des Tiefbohrprozesses, Altendorf: Druck Gräbner

10. a b

    O. Weber (), Untersuchungen zur bohrtiefenabhängigen Prozessdynamik beim BTA-Tiefbohren, Essen: Vulkan Verlag

11. a b c dH. Fuß (), www.Tiefbohren.info

12. ^W. König, F. Klocke (), Fertigungsverfahren 2 &#; Schleifen, Honen, Läppen, Heidelberg: Springer Verlag, ISBN 3-540--9

13. a b

    W. König, F. Klocke (), Fertigungsverfahren 1 &#; Drehen, Fräsen, Bohren, Heidelberg: Springer Verlag, pp. 163&#;176

14. ^

    T. Bruchhaus (), Tribologische Untersuchungen zur Optimierung von BTA-Tiefbohrwerkzeugen, Essen: Vulkan Verlag

15. ^botek Präzisionsbohrtechnik GmbH, www.botek.de, Riederich

16. ^

    M. Eckhardt (), "Die praktische Bestimmung der Lage, des Verlaufs und der Koaxiliatät tät von Bohrungen", Technica 10: 678&#;682

17. ^

    Dinglinger, E. (). "Neue Erfahrungen mit Tieflochbohrwerkzeugen". Werkstatttechnik und Maschinenbau. 45 (8): 361&#;367.

18. ^

    B. Stürenburg (), Optimitierung der Spanbildung und Minimierung des Späneeintrages in das Werkstück für das Bohren von Al-Legierungen, Technische Universität Kaiserslautern

19. ^

    H. O. Stürenberg (), "Zum Mittenverlauf beim Tiefbohren. Teil 1", TZ für Metallbearbeitung, 77 (6): 34&#;37

20. ^

    F. Bleicher, A. Steininger (), "Aktive Beeinflussung von Tiefbohrprozessen zur Reduktion des Bohrungsmittenverlaufes", VDI-Tagung Präzisions- und Tiefbohren

21. ^Deng, C.-S.; Chin, J.-H. (). "Hole roundness in deep-hole drilling as analysed by Taguchi methods". International Journal of Advanced Manufacturing Technology. 25 (5&#;6): 420&#;426. doi:10./s-003--5. S2CID .

22. ^

    K. D. Enderle (), "Reduzierung des Mittenverlaufs beim Einlippen-Tiefbohren durch Kühlmittelpulsation", Berichte aus dem Institut für Werkzeugmaschinen der Universität Stuttgart, 6

23. ^

    U. Heisel, T. Stehle, R. Eisseler, P. Jakob (), "Produktiver in die Tiefe &#; Höhere Prozessstabilität dank Dämpfung sowie längere Standzeiten in hochharten Stählen", Werkstatt und Betrieb, 12: 68&#;71

24. ^Ishida, T.; Kogure, S.; Miyake, Y.; Takeuchi, Y. (). "Creation of long curved hole by means of electrical discharge machining using an in-pipe movable mechanism". Journal of Materials Processing Technology. 149 (1&#;3): 157&#;164. doi:10./j.jmatprotec..11.043.

25. ^

    L. C. Ketter (), The Gundrilling Handbook (4 ed.), North Haven: Campbell Viking Press

26. ^

    B. Greuner (), "Die Herstellung von Hydraulikzylindern nach dem BTA-Verfahren", Maschinenwelt, 4

27. ^Jung, J.; Ni, J. (). "Prediction of Coolant Pressure and Volume Flow Rate in the Gundrilling Process". Journal of Manufacturing Science and Engineering. 125 (4): 696&#;702. doi:10./1..

28. ^

    F. Pfleghar (), Verbesserung der Bohrungsqualität beim Arbeiten mit Einlippen-Tiefbohrwerkzeugen, Universität Stuttgart

The development of a &#;deep hole&#; in which the diameter is 10 times greater than the depth is required in a variety of industrial applications. In order to drill holes in a straight line, specialized deep hole drills with a particular tool for drilling deep holes is necessary.

What is Deep Hole Drilling?

A hole is regarded to be deep if it has a depth-to-diameter ratio (D:d) that is larger than 10, and in general, holes with this ratio are considered to be deep. Deep hole drilling into metal has a variety of applications across a number of different industries. Its roots can be traced back to the requirement for gun barrels that were straighter and more accurate, and it expanded as other industries began integrating deep hole drilling processes to improve their own applications.

Deep hole drilling comprises of BTA drilling and gun drilling, in addition to other procedures tailored for specific tolerance requirements and often carried out on BTA-style deep hole drilling equipment. BTA drilling is the most common type of deep hole drilling. Deep hole drilling is capable of attaining tight diameter control, straightness, and excellent surface quality in workpieces, and it is employed in a variety of materials ranging from aluminum to super-alloys.

Deep hole drilling procedures make use of specialized tools and setups in order to supply high pressure coolant, remove chips in a clean manner, and achieve depth-to-diameter hole ratios in metal that are greater than what a standard CNC machine is capable of doing. Because of this, producers are able to consistently, accurately, and efficiently meet the production needs as well as the tolerances of their manufacturing processes.

The process of deep hole drilling is often carried out using specialized equipment designed specifically for the task. These machines are built and put together in a way that optimizes the procedures for straightness and efficiency. Deep hole drills are now capable of gundrilling up to a certain depth-to-diameter ratio because technological advancements have made it possible for them to be outfitted with high pressure, through-spindle coolant. UNISIG manufactures extremely competent BTA and gundrilling machines, some of which have applications with D:d ratios greater than 400:1.

Deep Hole Carbide Drills

 

These spiral-flute deep hole carbide drills have an innovative flute geometry that was created for optimal chip evacuation from deep holes in a variety of materials. This geometry was developed for use by spiral-flute drills. The tools have a maximum coolant duct profile so that they can provide the cutting edge with the most effective possible amount of coolant. It guarantees both an effective supply of coolant to the cutting edge as well as optimum chip removal from the cutting area. Chips may be removed without any issues even from very deep holes thanks to the design features of this drill, which, when combined with the optimum cutting settings, result in clean cuts. Chip packing and the ensuing jamming of the tool are successfully avoided thanks to this feature.

Process of Deep Hole Drilling

Rotating Tool

• Components that are not symmetrical, or spherical sections with holes that are not centered, are typical applications for this technique
• The speed of the tool spindle is what determines the cutting speed
• When compared to rotating the workpiece or using a counter-rotating method, drill drift can often be rather substantial

Workpiece Rotating

• Utilized most frequently for spherical components that have a hole that is deep and centered
• The speed of cutting is governed by the component and is balanced to allow for high rotation speeds
• When compared to using merely a revolving tool, drill drift is significantly minimized

Workpiece with Counter-Rotating Tool

• Ideal procedure for spherical objects that have a hole that is both deep and on center
• The rate of cutting is dependent on both the tool and the workpiece rotating at the same speed
• Offers the highest possible degree of hole straightness and concentricity

Applications of the Deep Hole Drills

There are a variety of applications for deep hole drills, and practically every industry uses them. Each of these applications has its own set of stringent criteria and one-of-a-kind problems, such as tight tolerances, difficult materials, and aggressive production targets.

The following are some samples of common applications, processes, and tolerances. These examples are not actual part, but they are representative of what is feasible when employing deep hole drills with the appropriate machine setup, tooling, and process understanding.

• Fuel Injector Bodies

For high-precision, high-volume items, it is possible to make the many holes at the exacting tolerances necessary by using a 3-spindle gundrilling center that is automated with robotics and conveyors.

• Fuel Rails for Diesel Engines

Gasoline rails ought to have very small holes that are completely straight and won&#;t break when subjected to the pressure of the gasoline. The utilization of gundrilling makes it feasible to bore holes that are in accordance with these very stringent requirements, which are quite exact.

• Sheet for Heat Exchangers in Tube

It is feasible to correctly drill thousands of holes in a short period of time using a multi-spindle tube sheet drilling machine, maximizing productivity in the process. This is accomplished by drilling the holes one at a time.

• Equipment Used for Landing an Aircraft

Drill and shape the landing gear actuating cylinders using high-strength alloys while preserving an exceedingly tight straightness tolerance.

• Fluid Assembly Ends

In order to construct the apparatus needed for hydraulic fracturing, a block of steel is given a number of holes that need to be drilled into it. There is a need for machines and equipment that can meet the challenge posed by a substantial workpiece that also has accurate tolerances.

• Hydraulic Cylinder Inside Bore

To produce superior hydraulic cylinders, an existing bore should be finished to the point that it satisfies the requirements for a surface polish that is as reflective as a mirror.

• Oilfield Exploration Equipment

It is possible to drill holes in long workpieces with extraordinary depth-to-diameter ratios without making compromises the accuracy of the roundness or wall thickness of the holes. This is accomplished by using a drill bit with a larger diameter than its depth.

• Exploration of the Oil Field Downholes

Trepan holes may be drilled in long workpieces with extraordinary depth-to-diameter ratios without affecting the accuracy of the hole&#;s roundness or wall thickness. Trepan holes are named for the trepan tool, which was developed in the 19th century.

Difficulties of Using Deep Hole Drills

The following are the four most important obstacles to overcome:

• Chip evacuation;
• Walking
• Tool runout
• Coolant evacuation

The behavior of the drill bit having a tendency to twist about the axis of rotation while it is working is referred to as the phenomenon known as runout. When the length of the drill is increased, there will be more runout, which will result in the hole having a wider diameter. It is simple for the axis of the hole to become off because of the excessive length of the drill pipe, its lack of rigidity, and its sensitivity to vibration. This has a detrimental effect, not only on the accuracy of the machining but also on the effectiveness of the manufacturing.

An activity referred to as &#;walking&#; takes place when the drill tip first makes contact with the workpiece in the process of drilling. If the surface being drilled isn&#;t exactly perpendicular to the axis of rotation of the drill, then the drill will be driven in that direction by a force that acts laterally (and a long, thin drill can bend slightly.) As a consequence of this, the hole will most likely be drilled at an obtuse angle and at the incorrect place. It is also possible that the drill will be harmed by this. Regardless of whether the surface is as-cast or has been rough milled, the possibility of the same event happening still exists.

It is necessary to remove the material that was cut away at the bottom of the hole in order to make room for the drill to progress further. When drilling deep holes, these chips have a propensity to wind their way around the flutes of the drill and accumulate to the point where they scrape against the sidewalls of the hole. As a direct consequence of this, the temperature will build, which will ultimately result in the drill either failing or being jammed. Chip removal and bit wear can only be assessed by listening to the sound, observing the chips, monitoring the machine load, checking the oil pressure, and paying attention to a variety of other indicators. It is difficult to get a good look at the cutting condition itself.

The use of cutting fluid to maintain a cold cutting contact is an integral part of the vast majority of the processes that are involved in precision machining. It is not easy to get liquid all the way to the bottom of a hole that is quite deep. There is a lot of work that needs to be done. As a consequence of this, the temperature at the drill tip increases to the point where it has the potential to cause damage to the workpiece or even weld to it. It might be challenging to remove chips from the surface. If the chip chamber becomes clogged, the drill bit will experience damage as a result.

Deep Hole Drill Advantages

1) The deep hole drilling machine is constructed of high-quality cast iron after secondary treatment, so the stability of the casting and accessories is extremely excellent, relatively strong stiffness, and it is thus much appreciated by users. Furthermore, the popularity of the deep hole drill is naturally connected to the technical innovation and maturity.

2) Three axes of deep hole drills are now utilizing imported good stiffness and heavy load and high speed and accuracy of the ball in a straight line guide rail, so as to assure that continues on the deep hole processing, processing of high accuracy and the service life of guide rail, now using the process of deep hole drill can offer greater torque, so that more practically applicable.

3) As a result of the maturation of the technology, the spindle of the modern deep hole drill is entirely comprised of an imported motor. This not only guarantees that there is adequate power, but it also enables the motor to be switched freely and correctly during high and low speed processing. In order to guarantee the dependability of the machine&#;s operation, an automated oil-cooling system has been included. This system ensures that the machine can maintain a temperature that is consistent throughout the processing.

4) Since the deep hole drill is computer controlled, system compatibility is also getting better and better. This allows software such as CAD and CAM software to be compatible, which tends to make the machine in better operability, processing can be customized according to the particular job demand function, as well as deep hole drilling machines have become the favorite of the industry.

What has just been discussed is the reason why the deep hole drill is being utilized in the deep hole processing on an increasingly regular and widespread basis. Because of all of the benefits that it offers, the deep hole machine tool has quickly become the most popular piece of machinery in its field. In addition, as a result of advances in technological know-how, today&#;s machine tools are able to have their functions modified in accordance with the particular specifications of a given project, which is also a very useful feature.

Precautions For Using Deep Hole Drills

1) The coaxiality of the centre lines of the spindle and tool guide sleeve, toolbar support sleeve, workpiece support sleeve, etc. should fulfil the criteria in order for deep hole cutting and machining to be successful.

2) The depth of the hole that has to be cut should be at least as much as the diameter of the workpiece. The system for the cutting fluid should be clear and functioning normally; On the machined end face of the workpiece, there should not be a central hole, and drilling should be avoided on the inclined plane; It is important to maintain the usual shape of the chip in order to prevent the production of strip chips that are straight; When processing the through-the-hole, make sure you use a higher speed. To minimize damage to the drill, limit the speed of the machine when it is close to breaking through the material, or stop the machine entirely.

3) Cutting fluid for deep hole machining: because the process of deep hole machining generates a significant amount of cutting heat that is difficult to dissipate, it is essential to provide an adequate amount of cutting fluid to lubricate and cool the tool. This is because the cutting heat is not easily dissipated. In most cases, the 1:100 emulsion or the severe pressure emulsion is the one that is chosen; Extreme pressure emulsion or high concentration extreme pressure emulsion is selected for use in situations in which high machining precision and surface quality as well as machining toughness materials are required. The kinematic viscosity of cutting oil is typically between 10 and 20 cm2/s at a temperature of 40 degrees Celsius, and the flow velocity of cutting fluid is between 15 and 18 metres per second; When the diameter of the machining is relatively small, you should use a cutting oil with a low viscosity; The ratio of cutting oil might be 40% EP vulcanised oil, 40% kerosene, and 20% chlorinated paraffin when doing deep hole machining that requires a high level of precision.

Useful Tips For Deep Hole Drills

• In order to guarantee the dependability of the end face seal, the end face of the workpiece is oriented such that it is perpendicular to the axis of the workpiece.
• A preliminary shallow hole is drilled on the hole site of the workpiece before the formal machining is performed. This hole can play a guiding and centering role throughout the drilling process.
• Automatic tool feeding is highly recommended whenever possible since it helps extend the useful life of the tool.
• If the guidance components in the liquid feeder and the moveable center support get worn over time, they need to be changed as soon as possible to prevent the precision of the drilling from being compromised.
• Continue feeding the drill into the pilot hole at a maximum of 50 revolutions per minute and 12 inches per minute (300 millimeters per minute) until you are approximately 1/16 inch from the bottom of the pilot hole (1.5mm)
• At this stage, the pilot hole will provide adequate support for the conclusion of the drill.
• After that, you may activate the coolant, and you can gradually increase the speed of the engine up to 75% of the recommended federate and 50% of the required rpm.
• Once you have reached a distance of about 1xD below the bottom of the pilot hole, you are in a position where it is safe to increase the rpm and feed rate to 100% of the required speed and feed rate.
• When playing through holes, slow down by half and federate up to seventy-five percent immediately before the escape.
• Before pulling the drill out of the hole, ensure that the coolant has been turned off and that the speed has been lowered to 50 revolutions per minute.

Best Practices for Precision Deep Hole Drilling

The machine tool is the first step in the production of precise and deep holes. On a CNC machine equipped with a spindle of superior quality, one may anticipate the best possible outcomes. Runout is reduced, and a high level of control is provided over the drilling cycle as a result of this. (It is important to bear in mind that when working with spherical components, it is often preferable to spin the workpiece while keeping the drill stationary, or even to have both components counter-rotating.)

The toolholder and the actual drill follow next in the sequence. The holder is responsible for maintaining the drill&#;s position on the axis, and the drill itself needs to be perfectly straight and symmetrical about the axis.

It is necessary to prepare the surface in order to prevent the drill from wandering. Milling a flat pad may be part of this process in addition to fixturing the workpiece to place the surface in a perpendicular position. Although beginning with a centre or pilot drill guarantees that the hole will be in the appropriate location, doing so requires yet another tool change.

The actual drill that is used has to have the capacity to bore deep holes. The most important need is a central hole, which will be used to transport cutting fluid to the cutting tip. The cutting temperatures will drop as a result, and the chips will be expelled. Instead of having two cutting edges, a deep hole drill bit designed specifically for larger holes will only have one of those edges. This again helps remove chips from the surface.

&#;Peck&#; drilling is an option that can be used in situations when it is not viable to transfer fluids through the hole. This requires removing the drill from the hole, which will also remove chips from the hole, and then replacing the drill. Some machine shops like to employ a set of drills that gradually expand in length since doing so will increase the amount of time spent on each cycle.

Conclusion

All of HUANA&#;s deep hole drills benefit from our use of cutting-edge technology, which enables us to achieve extremely tight tolerances and outstanding precision. Our services are both immediate and cost-effective, and we will provide you with an expert solution in the shortest amount of time possible thanks to the availability of a broad variety of deep hole drills. Please get in contact with HUANA as soon as possible for further details.

 

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