Milling Process

BTA drilling process and it's key technical considerations

In the intricate realm of metalworking, the milling process stands as a cornerstone, with roots extending back to ancient civilizations. From its humble beginnings as a manual craft to the sophisticated computer numerical control (CNC) systems of today, milling has undergone a transformative journey, revolutionizing the landscape of metal cutting - towards the nuanced facets of efficient milling.

At its core, metal cutting theory is the compass guiding milling operations towards precision and excellence. It's not merely about removing material but an intricate play between tool and workpiece, where the mastery lies in optimizing the balance between material removal and dimensional accuracy. As we navigate the complexities of milling, our compass points us to a triad of critical considerations: the holy grail of 'Quality-Cost-Delivery.'

Quality of machining, the first pillar, transcends mere aesthetics; it's about achieving the desired specifications with meticulous precision. Next, the Cost per piece becomes a focal point, intertwining intricately with productivity. A judicious selection of tools emerges as a pivotal decision, as the right tools pave the way for efficiency, cost-effectiveness, and, ultimately - a superior end product.

Chip formation becomes a silent yet telling storyteller in this process, offering insights into the health of milling operations. Forces at play during milling operations, when optimized, not only enhance machining precision but also play a pivotal role in cost reduction. Troubleshooting in milling is akin to detective work, unraveling the mysteries behind imperfections and inefficiencies.

Let's get into it!

What is Millng?

At the heart of milling lies the utilization of a rotating, multi-edge cutting tool, executing precisely programmed feed movements against a workpiece in virtually any conceivable direction.

Initially recognized for its prowess in generating flat faces, milling has evolved dynamically with the advent of advanced machines and software.
This evolution is reflective of an expanding scope, driven by the rising demand to craft diverse forms and surfaces beyond the conventional flat profiles.

As technology advances, so does the versatility of milling, pushing the boundaries of its traditional applications and paving the way for innovative solutions in the realm of metal cutting.

Cutting Parameters

In milling operations, cutting parameters are fundamental variables that dictate the efficiency and precision of the metal removal process. These parameters involve the dynamic interplay between the cutting tool and the workpiece, influencing factors such as tool life, material removal rate, and surface finish.

Cutting Speed | V or Vc meters per minute - m/min)
Definition: The linear speed at which the cutting point moves across the workpiece.
Significance: Higher cutting speeds are often associated with increased material removal rates but must be optimized to minimize tool wear.

Feed | fz millimeters per tooth - mm/tooth)
Definition: The distance the cutting tool advances into the workpiece per revolution.
Significance: Balancing feed rate is crucial, affecting both material removal and tool life.

Depth of Cut (a, in millimeters - mm):

Symbol: a
Definition: The radial depth by which the cutting tool penetrates into the workpiece.
Significance: Controls the amount of material removed in each pass, influencing both cutting forces and tool wear.
4. Spindle Speed (N, in revolutions per minute - RPM):

Symbol: N
Definition: The rotational speed of the milling spindle holding the cutting tool.
Significance: Correlates with cutting speed, affecting tool performance and heat generation.
5. Axial Depth of Cut (ap, in millimeters - mm):

Symbol: ap
Definition: The depth by which the cutting tool penetrates axially into the workpiece.
Significance: Together with radial depth, it influences the overall material removal strategy.
Understanding and optimizing these cutting parameters are essential for achieving the delicate balance between material removal efficiency, tool life, and surface finish in milling operations. Proper selection and adjustment of these variables contribute to enhanced productivity and the production of high-quality machined components.

BTA drilling Tool & basic geometry

The tool geometry in BTA drilling is carefully designed to meet the specific requirements of deep hole drilling operations. The BTA tool typically consists of multiple components, including the drill body, inserts, guide pads, and a backstop. The drill body is designed to provide stability and support to the cutting inserts. The inserts feature a special geometry with cutting edges optimized for chip formation and evacuation. They are usually made from carbide or high-speed steel, chosen based on the work-piece material and drilling conditions. The cutting inserts come in various geometries (round, square, triangular) based on application requirements.
The guide pads help maintain the alignment and stability of the drill during the drilling process. The backstop, positioned behind the inserts, prevents excessive tool deflection and assists in accurate hole positioning. The overall tool geometry is carefully engineered to achieve efficient chip evacuation, minimize cutting forces, and ensure dimensional accuracy and surface finish. The selection of appropriate tool geometry is crucial for successful and productive BTA drilling operations.

Rake Angles and Clearance Angles:
The recommended rake angle for BTA drilling is typically around 6° to 10°. As for the clearance angle, a value between 6° and 10° is generally suitable. These angles help optimize chip formation and evacuation, reduce cutting forces, and improve tool life.

Tool Spindle & Feed Axis

Most BTA drilling machines employ tool spindles with angular contact ball bearings for precision and stability. Angular contact ball bearings offer high rigidity, load capacity, and accuracy, ensuring smooth operation during drilling.

Tool spindle drives in BTA drilling machines may vary depending on the specific machine design. Some common types include direct drive, belt drive, and gear drive. The choice depends on factors such as torque requirements, speed control, and machine architecture.

Feed Axial drives in BTA drilling machines are responsible for managing axial forces and ensuring stability during drilling. One common type of axial drive is the ball-screw drive with a servomotor. The servomotor provides precise control over the axial feed, allowing for accurate drilling depths and chip evacuation.

Applications insights on BTA drilling

Materials:
BTA drilling is applicable to a wide range of work-piece materials, including steels, stainless steels, superalloys, non-ferrous metals, and composites. The diameter range typically starts from 20mm and can extend up to 1000mm, while the maximum achievable length may reach up to a staggering 20 meters.

Dimensional and Geometric Tolerances:
BTA drilling is renowned for its ability to achieve high dimensional and geometric tolerances. Achievable dimensional tolerances can be as tight as ±0.02 mm per diameter. Geometric tolerances, such as straightness, concentricity, and cylindricity, can be held within microns.

Surface Roughness:
With appropriate cutting parameters and tool geometry, BTA drilling can achieve surface roughness values (Ra) ranging from 1 to 6 micrometers. Additional post-processing techniques, such as honing or burnishing, can be employed to further improve the surface finish if required.

BTA drilling Process Ranges

BTA drilling is the ideal process for a wide range of deep hole diameters & hole depths. BTA drilling is capable of drilling quite extreme L/D ratios with quite tight tolerances.

Diameter Range (in mm):
⌀8 to ⌀65. : Brazed type perishable tool
⌀10 to ⌀114 : Spade drill type
⌀16 to ⌀28. : Indexable type single Insert
⌀ 25 mm + : Indexable type with multiple Inserts

BTA tool heads come in various configurations such as brazed tip consumable type - for low production volumes, indexable insert type for high production volumes, and so forth, each one serving a purpose of its own.

General types of BTA Tool Heads

Architecture of BTA drilling machines

Configurations:
1) Vertical BTA Machines: Vertical BTA machines are designed for drilling operations where the work-piece is held vertically. They are suitable for various applications, including automotive, aerospace, and oil and gas industries.
2) Horizontal BTA Machines: Horizontal BTA machines are used when the work-piece is held horizontally, and drilling is performed along the horizontal axis. These machines are commonly used in industries such as energy, heavy machinery, and defense.

Spindle matrices:
1) Single-Spindle BTA Machines: These machines feature a single spindle and are suitable for drilling applications with lower production volumes or smaller work-pieces.
2) Multi-Spindle BTA Machines: Multi-spindle BTA machines have multiple spindles, allowing simultaneous drilling of multiple holes. These machines are ideal for high-volume production and larger work-pieces.

Key Features of BTA Drilling Machines

▸ Rigid Machine Structure: BTA machines are designed with a robust and rigid structure to minimize vibrations and ensure accurate drilling.
▸ Programmable Spindle Speed and Feed Rate: BTA machines offer the flexibility to adjust spindle speed and feed rate according to work-piece material and drilling requirements.
▸ Chip Evacuation System: Effective chip evacuation is critical in BTA drilling. BTA machines are equipped with efficient chip evacuation systems to remove chips from the drilling zone, preventing chip clogging and ensuring uninterrupted drilling.
▸ Coolant System: BTA machines feature high-pressure coolant systems that deliver cutting fluid to the cutting zone, providing efficient cooling, lubrication, and chip evacuation.

Mechanical Aspects of BTA Machines:
▸ Spindle Power and Torque: BTA machines employ powerful spindles capable of providing high torque to handle the demanding drilling requirements of deep hole applications.
▸ Axial Thrust Control: BTA machines incorporate axial thrust control mechanisms to manage and minimize the axial forces generated during drilling. This ensures stability, accuracy, and reduced tool wear.
▸ Precision Guideways: BTA machines utilize precision guideways to maintain accurate alignment and enable smooth movement during the drilling process, enhancing overall drilling performance.

Key Components of BTA Drilling Machines

Typical BTA drilling machines consist of several key components that contribute to the accuracy, efficiency, and reliability of the drilling process.

Drill Guide Bushing:
The precision drill guide bushing is an essential component in BTA drilling. It serves to guide the BTA tool during the initial drilling phase, ensuring accurate hole positioning and diameter. The drill guide bushing also acts as a seal against the workpiece, effectively containing the coolant during the drilling process.

Pressure Head:
The pressure head surrounds the BTA tool and drill guide bushing, playing a vital role in coolant delivery and chip evacuation. It introduces coolant around the outside of the tool to provide effective cooling and lubrication during drilling. Additionally, it aids in the efficient removal of chips throughout the drilling operation.

Vibration Dampeners:
Vibration dampeners are employed to stabilize long drills and mitigate vibrations caused by high rotational speeds. Equipped with rotating bearings and inserts, these devices come into contact with the tool, providing damping effects. Longer BTA machines may feature multiple traveling vibration dampeners to ensure optimal stability, while shorter machines may not require any.

Drilling Spindle:
The drilling spindle is responsible for transmitting power, torque, and rotation from the motor to the BTA tool. It is designed to deliver high power and torque precision while minimizing vibrations. Additionally, the spindle incorporates a central hole through which chips and coolant are evacuated during drilling operations.

Coolant System:
The coolant system is a critical aspect of BTA deep hole drilling, significantly impacting its reliability and performance. It typically consists of a carefully designed reservoir that holds coolant, and a high-volume pump responsible for delivering the cutting fluid to the BTA tool. As the coolant progresses through the metal cutting operation, it enters a filtration system designed to remove chips and small particles. The incorporation of low-micron coolant filtration and filter condition feedback helps prevent chip accumulation, resulting in reduced downtime, extended tool life, and improved surface finish.

Coolant Temperature Control:
Controlling coolant temperature is crucial in BTA drilling machines as the drilling headstock and coolant pumping system generate heat during operation. Elevated temperatures can negatively affect tool life, accuracy, and the overall machine environment. To manage heat, BTA machines employ either a heat exchanger or a chiller. These devices are responsible for maintaining the cutting fluid at an optimal temperature, ensuring efficient drilling performance and minimizing thermal effects on the drilling process.

These components work together to ensure precise drilling, efficient chip evacuation, and effective cooling and lubrication, contributing to the success of BTA drilling operations.

Milling Process

BTA drilling process and it's key technical considerations

Contents

What is Millng?

Cutting Parameters

BTA drilling Tool & basic geometry

Tool Spindle & Feed Axis

Applications insights on BTA drilling

BTA drilling Process Ranges

Architecture of BTA drilling machines

Key Features of BTA Drilling Machines

Key Components of BTA Drilling Machines

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