Everything You Should Know About Deep Hole Drilling

What Is Deep Hole Drilling?

What Is Deep Hole Drilling?

Deep hole drilling is a process of machining a hole ten times deeper than the hole diameter. A deep hole is characterized by at least a depth-to-diameter ratio of up to 10:1. It is suitable for creating holes of desired depth in different CNC machining materials ranging from aluminum to the strongest super-alloys.

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Deep hole drilling is a widely used technique in many industry applications. However, it originated from the need to drill straight gun barrels with high accuracy in which the required depth-to-diameter ratio can reach 20:1.

Later on, the technology advanced and extended to other applications, including making automotive parts like cam-shafts, crank-shafts, fuel rail, and fuel injector bodies, creating lo holes in injection molding, aerospace parts like landing gear, different parts in the oil and gas sector, general engineering components like hydraulic cylinders, etc.

Importance of Deep Hole Drilling in Modern Industries

Medical Device Deep Hole Drilling

Modern industries like aerospace benefit a great deal from deep-hole drilling. Here are the typical roles this operation plays in respective applications:

Aerospace and Defense

Deep hole drilling techniques offer the tight tolerances and high accuracy required in machining aerospace components such as landing gear and turbine blades. Deep drilling processes produce holes exactly to tolerances to ensure optimal performance and low weight of these components.

Meanwhile, the defense industry is another primary field where deep-hole drilling is widely embraced. Manufacturers in this field use this drilling strategy to make accurate holes in the gun barrel with the preferred surface finish.

Automotive Applications

Engineers and product designers in the automotive field rely on deep-hole drilling to achieve preferred tolerances in machining automotive parts and components. For instance, the fuel injectors in vehicle engines require small and highly accurate holes to inject fuel into the combustion chamber efficiently. Also, the crankshafts and cylinder blocks require precise deep holes to function effectively.

Also, deep-hole drilling is pivotal in machining hydraulic cylinders for engineering vehicles and other industrial applications. These hydraulic cylinders are crucial for bulldozers, forklifts, excavators, etc. Deep hole drilling is ideal for making holes with the desired precision to ensure seamless motion.

Oil & Gas Exploration

Custom Deep Hole Drilled Petroleum Logging Instruments

The oil and gas industry benefits from deep-hole drilling because it helps make boreholes for oil and gas extraction. The process offers extreme depth-to-diameter ratios in long workpieces without compromising wall thickness or accuracy in roundness. Deep hole drilling is perfect for making holes with a depth-to-diameter ratio of up to 20:1.

Key Benefits of Deep Hole Drilling

Deep Hole Drilling Machine

Below are some of the common benefits of deep hole operations:

Precision and Accuracy

Since deep hole drilling operations are automated, they allow precise and accurate depth-to-diameter ratios in drilled holes. Hence, deep drilling is ideal for attaining holes with dimensions that are exact to requirements in industries such as aerospace and defense.

Improved Surface Finish

Deep hole drilling processes offer a better surface finish than conventional methods done with twist drills. Deep drilling involves the use of specialized tools and setups for high-pressure coolant flow and effective chip evacuation, ensuring the superior surface quality of the hole. Consequently, this excellent surface finish mitigates friction and wear, ensuring the durability and proper performance of moving parts.

Enhanced Tool Life

The tools used in deep-hole drilling are usually durable since they are made of super-strong materials and have unique geometries. As such, these tools can withstand wear and prevent consistent tool changes. Hence, the extended tool life of deep-hole drilling machines helps to save costs while ensuring peak productivity.

Common Techniques in Deep Hole Drilling

Deep Hole Drill Principle

Product manufacturers and designers rely on different deep-hole drilling processes to achieve superior-quality final products while controlling costs. This section discusses the standard techniques used in deep hole drilling:

Gun Drilling process

Gun Drilling & BTA Drilling

This deep-hole drilling method uses a machine with a thin cutting tool to achieve highly accurate and straighter holes in a workpiece. The introduction of gun drills transformed the drilling game because they offer higher accuracy than conventional-style drills.

The gun drill comprises a straight flute cutting edge and a single internal coolant hole. As such, you can supply pressurized coolant through the inner holes while you remove chips through the single-flute gun drills within the shank. Hence, material removal occurs at the same time as the drilling.

However, you might be able to perform the deep hole operations with a standard CNC gun drilling machine, depending on the hole&#;s depth-to-diameter ratio. However, you can use special tools to achieve higher precision. A specialized deep-hole drilling system can achieve larger diameters of about 400:1.

BTA Drilling

The Boring and Trepanning Association introduced the BTA drilling in the s. This process involves inserting a special hollow tooling in the hole pushing pressurized coolant into the hole on the outside of the drilling tool during the operation. Then, it removes the chips through the hole within the drill.

Besides, the BTA tooling or single tube system comprises a hollow drill tube fastened to a threaded indexable cutter head, depending on the diameter and depth of the hole that requires drilling. The diameter range of the BTA tools ranges from 0.80 &#; 8.00 inches (20 &#; 200mm) and can attain depths of about 16.00 inches (400mm).

Ejector Drilling

Ejector drilling or a double-tube system is often used on machining centers and conventional machine tools. It provides drilling depths of about 100 x D. Despite being a BTA drilling system variant; it has no sealing to prevent the metal-working fluid at the workpiece from exiting. Therefore, this drilling technique is suitable for oblique boring or discontinuous parts since covering up the metal-working fluid circuit is impossible.

Moreover, you must feed the metal-working fluid through an annular space between the inner and drill tubes. Then, the fluid comes out from the side of the drilling head, flowing over the drill head to cool and lubricate it. The fluid pushes the chip through the internal cavity of the inner drill rod for efficient removal. Introducing some of the fluid into the thinner tube ring nozzle would be best.

Considerations for Tools and Equipment for Deep Hole Drilling

Deep Hole Drilled Petroleum Logging Instruments Parts

Deep hole drilling can be quite complex, irrespective of the sophistication of the machinery. Also, there are higher chances of errors when drilling a deep hole. However, here are some helpful considerations for effective hole drilling:

Choosing the Right Drill Bit

Using the appropriate drill bit to drill straight holes is essential to avoid drill deviation or inaccuracies. Drilling deep holes with incompatible drill bits can result in expensive mishaps. As such, manufacturing experts often prioritize the drill bit&#;s compatibility and durability.

However, full-face crown drill bits exhibit improved lifespan even though it is subjected to the hardness and rigidity of the material&#;s surface. Therefore, it is advisable to use the right drill bits to drill precise and accurate holes easily.

Importance of Coolants

Coolants are crucial in deep hole drilling because they ensure proper cooling and lubrication of the hole drilling operation. These coolants help to maintain moderate temperatures, ensuring longer tool life.

These high-pressure coolants are also responsible for efficient chip evacuation from the cutting zone, preventing surface damage and chip removal strokes that may take time. Coolants allow the drilling process&#;s productivity and improve the hole quality.

Modern Innovative Equipment

Manufacturers often use specialized equipment designed explicitly for deep-hole drilling procedures. These innovative equipment are set up to optimize the hole drilling operation for straightness and efficiency.

The technological advancement of drilling equipment allows you to attain a certain depth-to-diameter ratio since a computer controls the process. Similarly, there are different deep-hole drilling techniques with varying modes of operation. Hence, choosing the one that fits your project demands best is essential.

Challenges and Solutions in Deep Hole Drilling

Deep Hole Drilling Cutter

Here are some of the challenges you may encounter during deep hole drilling operations and helpful ways to overcome them:

Avoiding Common Mistakes

Machinists often encounter common mistakes like misalignment or drill bit incompatibility, resulting in scrapped parts, poor surface finish, and excessive machine tool wear. Consequently, you may have to incur additional machining costs and experience delayed production.

Solution: Partner with a service provider with vast knowledge of the techniques and tools used in deep-hole drilling. Similarly, it is advisable to implement process documentation and quality control measures to mitigate human errors and detect mistakes early.

Ensuring Workpiece Stability

Deep hole drilling is a complex metalworking process that involves making long, straight holes in components. As such, workpiece deflection can occur when the workpiece is not properly held in position, resulting in inaccuracies. Therefore, it would be best to ensure workpiece stability when making holes.

Solution: Use special fixturing mechanisms to steady the workpiece, mitigate deflection, and ensure drilling accuracy. Also, it is advisable to plan the drill entry point carefully to reduce impact and mitigate chances of deflection.

Overcoming Material Challenges

Although deep hole drilling has extensive material compatibility, each material poses challenges. Certain materials, such as plastics, may experience deformation, while rigid materials like titanium may cause consistent machine tool wear during deep hole drilling.

Solution: Using drill bits with the correct geometry, material, and coating on the workpiece material would be best to avert this challenge. You can use drill bits with solid carbide or diamond coatings for better wear resistance. However, optimize feed rates, speed, and coolant selection to mitigate heat and ensure proper cutting frequency.

Why Choose AT-Machining for Your Deep Hole Drilling Needs?

Your One-Stop CNC Machining Services From China

AT-Machining is the right machining partner for your CNC and deep-hole drilling needs. We leverage our range of hole-drilling machines with our machinists and product engineer expertise to achieve preferred tolerances and outstanding accuracy in your final products and prototype machining. We have years of experience offering reliable deep-hole drilling services across all fields.

As your trusted manufacturing partner, we are committed to serving you superior quality products with high precision at cost-effective prices. Our quality control experts ensure your products meet strict quality standards. We promise expert machining solutions within the shortest possible time.

Experience our cost-effective and reliable machining services as we handle your next project! Our clients have enjoyed long-term partnerships as we consistently offer expert solutions. We are a top custom parts manufacturer, deep hole drilling services, and surface finishes provider across different sectors.

Conclusion

Deep hole drilling is a versatile process that benefits various applications with stringent requirements and unique challenges in machining rigid materials with tight tolerances. This operation offers the preferred depth-to-diameter ratio for your hole-drilling projects. However, it would help to understand everything about the process to effectively exploit its benefits in achieving high-quality products.

FAQs about Deep Hole Drilling

How Does Deep Hole Drilling Differ from Drilling?

Deep-hole drilling differs from regular drilling since cooling lubricant must be passed to the cutting edges in high volume and under high pressure, depending on the intended drilling technique and diameters.

What Is the Best Drill Bit for Drilling Deep Holes in Wood?

The typical drill bits for making deep holes in wood are Auger bits. These drill bits have a helical or spiral shape and comprise a sharp point on their tip, allowing drilling efficiency. This tip efficiently pulls the bit through the drilled wood to achieve the preferred depth.

What Is the Standard Ratio for Deep Hole Drilling?

Generally, a normal drilling process has a length-to-diameter ratio usually smaller than 5. Hence, deep-hole drilling is characterized by a length-to-diameter ratio greater than 5.

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:

• 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.

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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

 

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