Introduction

In the world of machining and manufacturing, precision is paramount.Whether you are crafting intricate components for an aerospace engine or shaping everyday objects, understanding the geometry of a single point cutting tool is essential for achieving accuracy and efficiency. In this blog, we will explore the critical aspects of single point cutting tool geometry and how it influences the machining process.

The Basics of Single Point Cutting Tools

A single point cutting tool is a fundamental element in many machining operations, including turning, milling, and drilling. It is called "single point" because it features a single cutting edge that removes material from a workpiece. The geometry of the cutting tool is designed to control the cutting process and ensure the desired shape and surface finish of the workpiece.

The different view of single point cutting tool is shown in Figure 1.According to ASA (American Standard Association) there are seven parameters of tool geometry as mentioned below as

`alpha_b`,`alpha_s`,`beta_e`,`beta_s`,`theta_e`,`theta_s`,R

Figure 1

where `alpha_b` is the back rake angle; `alpha_s` side rake angle; `beta_e`,end clearance angle;`beta_s`,side clearance angle;`theta_e`,end cutting edge angle;`theta_s` and side cutting edge angle;R,nose radius.

Key Elements of Single Point Cutting Tool Geometry

1.Cutting Edge and Nose Radius

The frontier is the part of the tool which dissects the workpiece and pulls out the material. It is commonly constructed from a durable member such carbide or high-speed steel to withstand the forces and wear associated with the machining process.
In the case of turning and boring operations, the radius of the nose is known as the rounded end of the cutting tool. It has an effect on the surface finish and also in a way protects against chipping and vibration.

2.Rake Angle

Angle of the rake is the included angle between the cutting edge and a reference plane parallel to the machined workpiece surface. It decides on how well it cuts material. A positive rake angle (r > 0°) have decreasing cutting forces and create less heat whereas a lower rake angle (with r < 0) improve the strength of the tool even though the heat produced in the process is comparatively high.

3.Relief Angle (Clearance Angle)

The relief angle (also known as a Clearance Angle) is the angle between the cutting edge and the normal plane to the work surface. It creates clearance at the cutting edge thereby ensuring that it does not interfere with the workpiece that reduces friction and its subsequent heat generation.

4.Back Rake and Side Rake angle

The back rake refers to the angle between the tool's top surface and a plane parallel to the machined surface, impacting chip flow and cutting forces.
Side rake is the angle between the side flank and a line parallel to the machined surface, influencing the shearing action in machining.

5.End Relief and Side Relief angle

End relief is the relief positioned behind the cutting edge in the tool's rotation direction, preventing rubbing and enhancing tool longevity.
Side relief is the relief found on the tool's sides, aiding in chip removal and reducing friction.

Now we will see about all the above key elements in details.

Back Rake Angle and Side Rake Angle:

Back rake angle is the angle between the face of the tool and a line parallel with base of the tool measured in a perpendicular plane through the side cutting edge. If the slope face is downward toward the nose, it is negative back rake angle and if it is upward toward nose, it is positive back rake angle. This angle helps in removing the chips away from the work piece. Generally, ceramic or brittle tool materials have negative back rake angle. It ranges from -`5^circ`to `15^circ`.

Figure 2

Side rake angle is the angle between the base of the tool shank and the face of the tool measured in a plane perpendicular to the plane through the side cutting edge and right angle to the base. If the tool face is sloping upward towards the side cutting edge, side rake angle is positive and it is negative when it is sloping downward towards the side cutting edge. Positive side rake angle results in lower cutting force and low power consumption,and thus better cutting action. Negative side rake angle is used for rough cut and heavy duty applications. It ranges from -`5^circ`to `15^circ`.

End Relief Angle and Side Relief Angle:

The angle between the planes of the end flank immediately below the end cutting edge and line perpendicular to the base and right angle to the axis is known as end relief angle and the angle between the planes of the side flank immediately below the side cutting edge and line perpendicular to base along the axis is known as side relief angle. Relief angles are provided to ensure that no rubbing occurs between the work surface and flank surfaces of the tool. For general turning operations, they range from `5^circ`to `15^circ`.

Figure 3

End Cutting Edge Angle and Side Cutting Edge Angle:

The angle between the plane along the end cutting edge and the plane perpendicular to the axis, both right angles to the base, is known as end cutting edge angle. End cutting edge angle provides a clearance to the trailing edge end of the cutting edge and machined surface to prevent the rubbing and drag action between them. Smaller value of end cutting edge angle generally uses less contact area with respect to the metal being cut. Larger end cutting edge angle results in vibration or chatter. It is limited to `5^circ`.

The angle between the plane along the side cutting edge and the plane perpendicular to the axis, both right angles to the base, is known as side cutting edge angle. It prevents the shock of the cut at the tip of the tool. It can vary from `0^circ`to `90^circ`.On increasing the angle, thickness of the chip decreases but its width increases.

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Figure 4

Nose Radius

The nose radius has a major influence on surface finish. A sharp point at the end of a tool leaves a groove on the path of cut. Increase in nose radius usually decreases tool wear and improves surface finish.Generally, for roughing largest nose radius is selected. A larger nose radius permits higher feed, but must be checked against any vibration tendencies.

Advantages of providing nose radius in cutting tool

Improved Tool Life: A small tip radius of the cutting edge better dissipates the cutting force between the different points of the cutting edge, reducing the stress concentration. This enhances tool life as, in this way, chipping or fracture are almost ruled out.
Surface Finish: the existence of a nose radius adds to the quality of the finish workpiece surface The curved edge reduces the possibility of leaving the flawing marks on the machined surface, mainly if you deal with materials that have poor machinability or tend to tear.
Reduced Cutting Forces: The use of a nose radius will result in a resulting in a smoother engagement of the tool and the workpiece hence the cutting forces will be significantly reduced. Lower cutting forces result in lesser wear on the tool, on the machine and in the improvement of machined part dimensional accuracy.
Improved Chip Control: The nose radius could affect chip formation by creating smaller, more controllable chips, which would imply the shorter edge radius. This can avoid the probability of chips bleeding, lower the chances of chip jamming, and thus increase machining efficiency.
Minimized Heat Generation:The curved surface of the r nose rim may reduce the friction and generated heat during the cutting process. This becomes useful when machining heat sensitive materials or during high cutting speeds because it helps in preventing the tool and the workpiece from thermal damage.
Enhanced Stability and Rigidity: A small nose radius allows the tool to have the stability and the rigidity for cutting. This is critical in machining under harsh conditions because it maintains tool integrity, and precision of the entire machining operation.
Versatility in Machining Operations: Nose radius tool with cross-functions can be more versatile across several machining operations. Whatever it is turning, milling or drilling of the tool the addition of the nose radius promotes the versatility of the tool in a wider variety of applications.

Disadvantages of providing nose radius in cutting tool

Reduced Sharpness: A more rounded nose radius will provide less sharp tip. In situations where precision and fine detail matters, larger nose radiuses might not be the best solution as they could decrease the sharpness of the tool.
Limited Access in Tight Spaces: In cases where the workpiece has close geometric constraints or features, a large nose radius may hinder the tool from reaching these regions. This is a limitation in machine tools that have complex machining operations where there is a need for exact tool movement.
Increased Cutting Forces in Some Cases:A smaller nose radius usually decreases cutting forces, but a too large one could cause the opposite effect. In some occasions, particularly with the softer materials, a bigger nose radius can lead to the increased cutting forces, which in turn can affect tool wear and the machine stability.
Tool Chatter and Vibration:Larger Nose radius can lead to tool chatter as well as vibration problems, especially when machining at high speeds and with less stiff setups. Chat can affect surface finish, tool life, as well as overall machining efficiency negatively.
Compromised Corner Accuracy: Concerning the machining of corners or sharp edges, having too big a nose radius may cause the deviation from the intended geometry. This is a challenge in applications where the most important thing is the highest possible corner accuracy.
Increased Cutting Temperatures: For a small nose radius, heat generation can be reduced, but a larger nose radius affects increased cutting temperatures, more obvious in heavy milling. Heat can cause thermal damage, which triggers both the tool and the workpiece.
Tool Wear in Certain Materials: In some materials, like, hard alloys or ceramics, a big nose radius can speed up wear of the tool. The wear caused by a larger radius becomes more significant because more area of the tool and the workpiece gets in contact.

Applications and Implications

Understanding the geometry of a single point cutting tool is crucial for various machining processes:

Turning: In the case of turning operations systems like lathe machining the entire end product shape and finish is determined by the geometry of the cutting tool. Rake angle and nose radius define the precision.
Milling: The cutting edges of milling cutters are shapped with specific geometries for milling slots, contours and even a portion of the surface on a workpiece. The geometry of the cutting tool determines the properties of the materials used, the quality of the surface.
Drilling: Geometry of the tip and flutes have direct bearing on the drilled hole size, accuracy, and chips that are ejected in drilling. Good relief and clearance angles are a must for productivity in drilling.
Surface Finish: The characteristics of the cutting tool geometries determine the quality of surface finish of the workpiece. Accurate angles and radii in the design can minimize roughness and increase aesthetics of the design.

Conclusion

The geometry of a single point cutting tool is a precise scientific discipline that governs the accuracy and quality of machining workpieces. By choosing appropriate tool geometry for a particular application, engineers and machinists are able to guarantee that the materials are shaped according to well defined precision and efficiency levels. Whatever be the case, be it making complex parts for an aircraft or making simple goods, the disciplined consideration and selection of tool geometry has always been a key element in the art of precision machining.

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