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.

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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.

WHAT WORKPIECES REQUIRE DEEP HOLE DRILLING?

Molds for plastic, die casting, thermoforming, blow molding; aeronautical parts, hydraulic parts; mechanical transmissions; medical parts, and others&#;

Lightening, cooling, and optimizing the thermal and strain gradient in these workpieces are goals increasingly realized by drilling.

WHAT IS DEEP HOLE DRILLING?

A hole is defined as deep when the length of the hole exceeds at least 10 times the diameter of the tool, up to lengths of 150 times the diameter and more, depending on how the tool is guided through the machine.

This is such an extensive range that it includes different systems and tools:

For more deep drilling machineinformation, please contact us. We will provide professional answers.

• Helical drills
• Gun drills
• BTA tools

HELICAL DRILLS

Nowadays, not only the traditional twisted steel drills are available, but also micrograin carbide helical drills, HSS drills, etc. &#;, with different and complex cutting edge geometries, with or without the internal passage of lubricant-coolant.

These tools also have very different characteristics from each other, typically covering drilling ratios such as 12:1, 20:1 (length: diameter) but even higher, such as 30:1.

Their manufacturers will know how best to advise you.

GUN DRILLS

A characteristic shape, with a &#;V&#; groove along its entire length, distinguishes the gun drill, which has one or more central holes that carry the high-pressure lubricant-coolant to the cutting edge.

The geometry of the cusp has a non-symmetrical shape, working by rotating around its own axis: this is a single-cutting, non-self-centering tool, which absolutely needs a pilot hole or a drill bushing. After that, the tool guides itself by unloading the force on its own pads on its peripheral profile.

The lubricant-coolant is either full oil specific for deep hole drilling or emulsified water, also specific for deep hole drilling. The lubricant-coolant is driven away along with the machining chips along the &#;V&#; groove of the drill.

Regrinding the braze-welded cusp gun drill is a simple operation that can be performed independently every 40-80 m. Given the large number of possible regrinds, over its lifetime a gun drill is capable of drilling for more than m.

Gun drills with braze-welded single-cutting cusps (traditional) are available on the market, as well as gun drills with inserts: usually, on IMSA drilling machines these two types are used. Manufacturers also offer different types for special technical applications, on which they will know how best to advise you.

Gun drills should be properly supported every 40 times their own diameter. For example, we drill holes for a length of 120:1 relative to the diameter on one of our classic machines up to 1,000 mm equipped with 2 steady rests to support the gun drill.

BTA/STS TOOLS

Only usable on deep hole drilling machines, BTA/STS tools consist of a drill head screwed onto a pipe. Oil supply to the cutting edges is provided through an oil pressure head that feeds the circular crown created between the surface of the hole and the outer surface of the pipe on which the drill head is screwed. Chips and coolant are discharged by passing inside the pipe.

The large surface area available for oil passage promotes an excellent lubrication and cooling; in contrast, the passage clearance for re-entry is limited only to the inner surface of the pipe. This limits the use of this technology to drilling only materials with good machinability and with a sufficiently large diameter.

A drill bushing directs the BTA tool to the start of drilling. After that, the tool guides itself by unloading the force on its own pads on its peripheral profile.

The lubricant-coolant is either full oil specific for deep hole drilling or emulsified water, also specific for deep hole drilling. In this specific tool, the passage of the lubricant-coolant is characterized by high flow rates, with significantly lower pressures than in the gun drill method.

Since chips are discharged through the inside of the tool pipe, it is of paramount importance that the drill head performs an optimal chip-breaking action. Braze-welded, single-insert and multi-insert BTA heads are available on the market. Manufacturers also offer different types for special technical applications, on which they will know how best to advise you.

The drill pipe should be supported with appropriate vibration dampers, according to the tool manufacturers&#; instructions.

Deep hole drilling requires a good combination between machine and tool, particularly in terms of vibration dampening capability and lubrication-cooling system: all IMSA&#;s BTA-method drilling machines are developed from this concept.

WHY A SPECIFIC DEEP HOLE DRILLING MACHINE?

Using a gun drill on a non-dedicated machine tool, such as a lathe, a machining center or a milling machine, necessarily requires a pilot hole, which you will make with a short helical drill.
Next, you will use a first short gun drill.
Then, if the depth of the hole to be drilled is greater than the cantilever distance tolerated by the gun drill, you will have to proceed in several steps, using a gradually longer drill, which you will insert manually into the hole from time to time.
This is obviously a slow and non-automated process, recommended only in the case of occasional machining.

The best results in deep hole drilling are related to the guidance of the tool to prevent it from bending, and to the adequate influx of lubricant-coolant to dissipate heat and push chips out of the hole.

Technological parameters such as feed, speed, pressure and flow rate are crucial for chip control in this kind of machining.

Why is drilling with a specific deep hole drilling machine different? A drilling machine is conceptually made to include everything that ensures optimal use of the gun or BTA drills.

The machining unit of the drilling machine includes:

• a spindle with optimal power and speed for the application;
• movable steady rests, which on IMSA machines are self-spacing, for optimal support of the BTA drill or drill pipe;
• a fixed head (also called chip box) on the front of which there is a drill bushing that forms the &#;sight&#; for the drill, and through which coolant and chips coming out of the hole return, eventually falling onto the conveyor below.

The lubrication-cooling circuit of the drilling machine includes:

• pumps for the adduction of oil or emulsified water at the pressures and flow rates appropriate for the application;
• chip conveyor for collecting and separating chips and coolant leaving the holes;
• coolant collection tank;
• multi-level filtration system, for filtering 25 effective microns;
• refrigeration unit operating in parallel, in order to ensure the best operating temperature of clean oil.

On an IMSA drilling and milling center, you can still drill with maximum-length gun drills on the deep hole drilling unit and, moreover, place other shorter-length drills of various types (HSS with/without internal coolant passage, relatively short gun drills to be used overhanging, etc&#;) in the ISO40/ISO50 tool changer, which you will use on the auto-switching auxiliary spindle.

DRILLING MACHINES OPERATING WITH GUN DRILLS

As we have seen, the &#;gun drill&#; method employs gun drills with internal lubrication of oil or emulsified water specifically for deep hole drilling, brought to the cutting edge at high pressure.

Chips and coolant are evacuated along the outer groove of the tool. After filtering and cooling, the coolant is returned to high pressures and reused in machining.

The range of lengths and diameters covered by our block drilling machines goes, depending on the models:

• from drilling diameters 4-18 mm for depths up to 800 mm;
• to deep hole drilling centers for molds up to 45 t, drilling diameters from solid 5-50 mm for max. depth mm.

The range of our gun drilling machines for round workpieces goes, depending on the models:

• from drilling diameters 1.5-6 mm for depths up to 750 mm;
• to drilling diameters 8-43 mm for depth mm.

IMSA solutions in the use of the gun drill allow average feed rates of 80-120 mm/min (in case-hardening steel), explaining how drilling with deep hole drilling machines is extremely more effective and economical than drilling with non-dedicated machines.

IMSA employs both gun drills with braze-welded cusp (traditional) and next-generation drills with interchangeable chip breaker inserts on its machines. Superior power and stiffness are able to develop drilling feeds as much as 50-70% higher, compared with the braze-welded equivalent.

BTA/STS METHOD DRILLING MACHINES

This drilling method is referred to as BTA or STS by different tool manufacturers.

As we have seen, in this method the oil path and the chip path are opposite to the gun drill method. An oil pressure head brings coolant to the cutting edge by passing outside the drill pipe; through the inside of the pipe, chips and oil are discharged, driven by pressure. Chips and warm oil at the outlet are separated; after filtering and cooling, the oil is returned to pressure and reused in the machining.

The range of lengths and diameters covered by our cylindrical workpiece drilling machines with BTA tools goes:

• from drilling diameters 18-51 for depths up to mm
• to drilling machines for drilling diameters 50-200 mm for max. depths / mm.

If the machinability characteristics are good, the average feed rates measured on IMSA MFTB series machines are 250-350 mm/min in case-hardening steel. Their characteristics of reliability and speed make these deep hole drilling machines particularly suitable for the production environment.

The tools used can be either braze-welded (not regrindable) or with interchangeable inserts. The interval between regrinds is highly variable depending on the material and feed rates.

DEEP HOLE DRILLING SOLUTIONS FOR MOLDS

The range of IMSA gun drilling machines for molds (used for die-sets, tools, mold bases, mold inserts and drilled blocks in general) includes 3, 4 or 6 axis cnc gun drilling solutions which are ideal for small and medium-sized molds. Our range also includes cnc gun drilling and milling machines with 8-9 axes, perfect for medium and large-sized molds, used to create complex cooling channels with compound angle drilling and machining.

On the mold application, the IMSA team has always aimed to transform process needs into increasingly advanced deep hole drilling operational solutions.

A series of precautions borne out of experience, and the rigidity of our structures, enable an IMSA machine to drill traditional mold materials for 20 to 30 meters with a gun drill, before the drill needs to be grinded or replaced.

• The vertical Gantry column, supported at both the bottom and top, results in 16 times more stiffness than the traditional column structure supported only at the base;
• Machining units with two separate heads for deep hole drilling and milling perform switching between operations in fully automatic mode, therefore, even in unmanned shifts;
• The functions specific to the deep hole drilling process manage the electronic approach to the workpiece, read shear and thrust stresses to prevent drill breakage, and transform coordinates for inclined machining.
• The tables are conceptually made by providing for the handling and clamping required to handle the forces involved in deep hole drilling machining.

Look here at IMSA machines for molds and blocks

SOLUTIONS FOR MAKING ON-CENTER DEEP HOLES IN CYLINDRICAL WORKPIECES

Cylindrical steel alloy workpieces such as mechanical transmissions, grease nipples, automotive/aerospace rods, various barrels,&#; are often to be drilled with a blind or through-hole centered along their axis of rotation (on-center drilling). On the other hand, when holes parallel to the axis of rotation of the workpieces but not central to it are to be drilled, this is called off-center drilling.

For deep hole on-center drilling of cylindrical workpieces, IMSA offers a range of drilling machines using either the gun drill method or the BTA method, depending on the required diameters.

• The &#;U-shaped&#; structures of IMSA type MFT and MFTB drilling machines have zero drilling carriage height. The result of this solution is the cancellation of the bending moment that would normally be generated on the drill carriage, on the steady rests and on the oil pressure head, causing bending and vibration of the drill. The result is a considerable stiffness;
• Automatic workpiece loaders of various types are available;
• The functions specific to the deep hole drilling process read shear and thrust stresses to prevent drill breakage, and manage workpiece clamping pressures.

Look here at IMSA machines for on-center drilling of cylindrical workpieces

© I.M.S.A. S.r.l. &#; September 6, .

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