Short Answer:

Clearance angle is the angle formed between the flank surface of a cutting tool and the surface of the workpiece being machined. It prevents the back portion of the tool from rubbing against the work surface and reduces friction between the tool and the material. This helps in smooth cutting, reduces tool wear, and improves surface finish.

The clearance angle is very important in tool geometry because it affects tool life, heat generation, and the quality of machining. Proper clearance angle ensures easy chip removal and allows the cutting edge to cut freely without interference from the tool body.

Detailed Explanation :

Clearance Angle

The clearance angle is one of the most essential angles in the design of a cutting tool. It is defined as the angle between the flank of the tool and the surface of the workpiece being cut. The main purpose of providing a clearance angle is to prevent the tool flank from rubbing against the finished surface of the workpiece. Without this angle, excessive friction, heat, and tool wear would occur, resulting in poor surface quality and inefficient cutting performance.

When a cutting tool removes material from a workpiece, the cutting edge must penetrate and shear off the material. The clearance angle ensures that only the cutting edge contacts the material, while the rest of the tool body remains clear of the surface. This promotes smoother operation, better chip flow, and longer tool life.

Purpose of Clearance Angle

The clearance angle serves several important purposes in machining:

It prevents rubbing or friction between the tool flank and the workpiece surface.
It reduces heat generation and tool wear.
It allows the cutting edge to penetrate the workpiece material easily.
It improves the surface finish of the machined part.
It increases the efficiency and accuracy of the cutting process.

Providing a proper clearance angle is essential because too small an angle can cause rubbing and tool failure, while too large an angle may weaken the tool edge and cause breakage.

Types of Clearance Angle

The clearance angle is generally divided into two main types depending on its orientation on the tool:

Side Clearance Angle:
- It is the angle between the side flank of the tool and the machined surface.
- It helps the side cutting edge to move freely along the work surface without rubbing.
- This angle affects the side cutting action and chip flow direction.
End Clearance Angle:
- It is the angle between the end flank of the tool and the machined surface.
- It allows the end cutting edge to enter and exit the material smoothly.
- It mainly affects the vertical cutting force and surface finish.

Both angles together ensure that the tool maintains proper clearance in all directions during cutting operations.

Importance of Clearance Angle in Tool Geometry

The clearance angle is a very important part of tool geometry because it directly influences tool performance, wear, and the quality of machining.

Reduction of Friction: The clearance angle minimizes contact between the tool and the workpiece, reducing frictional forces.
Heat Control: By reducing friction, it helps in lowering the temperature at the cutting zone.
Surface Quality: A correct clearance angle produces a smoother surface finish as there is no rubbing action.
Tool Life: Proper clearance increases the life of the cutting tool by preventing excessive wear.
Ease of Cutting: It helps the cutting edge penetrate the material with less resistance, improving efficiency.

Effect of Clearance Angle on Machining Performance

The clearance angle has a direct effect on several aspects of the machining process:

If Clearance Angle is Too Small:
- The tool rubs against the workpiece surface.
- This generates excessive heat and friction.
- The surface finish becomes poor, and the tool may lose its cutting edge quickly.
If Clearance Angle is Too Large:
- The cutting edge becomes weak and brittle.
- The tool may break or chip under cutting forces.
- It reduces tool life and causes uneven cutting.

Therefore, an optimum clearance angle must be maintained for efficient cutting and longer tool life.

Typical Values of Clearance Angle

The value of the clearance angle depends on factors like the tool material, workpiece material, and type of machining operation.

For High-Speed Steel (HSS) tools, the clearance angle usually ranges between 6° to 12°.
For Carbide tools, it is smaller, around 4° to 8°, due to their higher hardness and brittleness.
For softer materials, larger clearance angles are preferred to reduce rubbing.

These values are selected carefully to balance cutting performance and tool strength.

Factors Affecting Selection of Clearance Angle

Workpiece Material: Softer materials require a larger clearance angle, while harder materials need smaller angles.
Tool Material: Tools made from stronger materials (like carbide) can work with smaller angles.
Type of Cutting Operation: Finishing operations use slightly larger clearance angles for smoother surfaces, while roughing uses smaller angles for tool strength.
Cutting Speed: At higher cutting speeds, smaller clearance angles are used to maintain edge stability.

Proper selection of clearance angle based on these factors ensures maximum efficiency and minimum tool wear.

Role in Chip Formation and Heat Generation

During cutting, the chip slides over the tool face and the flank comes close to the newly machined surface. If the clearance angle is insufficient, the tool rubs against the surface, increasing heat and friction. This not only affects chip flow but also damages the surface finish. With the right clearance angle, chips flow freely, heat is reduced, and the operation remains stable.

Thus, the clearance angle indirectly contributes to efficient chip formation and lower temperature at the cutting zone.

Conclusion:

Clearance angle is a critical element in the geometry of a cutting tool that prevents friction and rubbing between the tool and the workpiece. It ensures smooth cutting, better chip flow, reduced heat generation, and longer tool life. The correct selection of clearance angle depends on the material, speed, and type of operation. A properly maintained clearance angle enhances machining efficiency and ensures high-quality surface finish.