Short Answer:

Rake angle is the angle formed between the face of a cutting tool and a plane perpendicular to the work surface. It plays a very important role in metal cutting because it helps control chip flow, cutting force, and heat generation during machining. The rake angle decides how easily the tool can cut into the workpiece and remove material in the form of chips.

Rake angles are mainly of two types: positive rake angle and negative rake angle. A positive rake angle makes cutting easier with less force but reduces tool strength, while a negative rake angle increases tool strength but requires more power for cutting.

Detailed Explanation :

Rake Angle

Rake angle is one of the most important geometry parameters of a cutting tool. It is defined as the angle between the face of the tool and a line perpendicular to the surface being cut. The face of the tool is the surface over which the chip flows during the cutting operation. The rake angle directly affects the performance, efficiency, and quality of the machining process.

In simple terms, the rake angle determines how the material will shear off and flow as a chip during cutting. A properly selected rake angle ensures smooth chip removal, reduces cutting forces, minimizes tool wear, and improves surface finish.

Purpose of Rake Angle

The main purpose of providing a rake angle on a cutting tool is to make cutting easier and efficient. It allows the cutting edge to enter the workpiece material smoothly and reduces friction between the tool and the chip. The rake angle helps in:

1. Controlling the direction of chip flow.
2. Reducing the amount of cutting force required.
3. Improving surface finish.
4. Reducing heat generation during cutting.
5. Increasing tool life and efficiency.

Without a proper rake angle, cutting would require more power, generate more heat, and cause rapid tool wear.

Types of Rake Angle

There are mainly two types of rake angles used in cutting tools:

1. Positive Rake Angle:
   • In a positive rake angle, the face of the tool slopes away from the cutting edge.
   • It reduces cutting resistance and allows easy chip flow.
   • It is suitable for cutting soft or ductile materials such as aluminum, copper, and mild steel.
   • Advantages include lower cutting force, less heat generation, and smoother surface finish.
   • However, the tool becomes weaker due to a thinner cutting edge.
2. Negative Rake Angle:
   • In a negative rake angle, the face of the tool slopes toward the cutting edge.
   • It increases the strength of the cutting edge and is suitable for hard materials or heavy cutting conditions.
   • It can withstand shocks and vibrations during cutting.
   • Disadvantages include higher cutting forces and more heat generation.

Factors Affecting Rake Angle

Several factors influence the selection of an appropriate rake angle:

1. Type of Work Material:
   Softer materials require a higher positive rake angle, while harder materials need a smaller or negative rake angle.
2. Type of Cutting Tool Material:
   Tools made from hard materials like carbide can use smaller rake angles, while high-speed steel tools often use larger rake angles.
3. Type of Machining Operation:
   Roughing operations use smaller rake angles to handle heavy loads, while finishing operations use larger rake angles for better surface finish.
4. Cutting Speed and Feed Rate:
   Higher speeds generally require smaller rake angles to avoid tool breakage, whereas lower speeds can allow larger rake angles.
5. Chip Type and Cutting Conditions:
   The nature of chips produced also affects rake angle choice. Continuous chips need a smaller rake angle, while discontinuous chips work better with larger rake angles.

Effect of Rake Angle on Cutting Process

The rake angle has a significant effect on the performance and results of machining operations:

1. Effect on Cutting Forces:
   A positive rake angle reduces cutting forces, making the process smoother and requiring less power.
2. Effect on Chip Formation:
   Proper rake angle helps in controlling chip thickness and direction, preventing chip clogging or entanglement.
3. Effect on Tool Life:
   An incorrect rake angle may cause excessive tool wear or breakage. A balanced rake angle improves tool life by reducing stress on the cutting edge.
4. Effect on Surface Finish:
   A positive rake angle provides a better surface finish, while an incorrect angle may result in rough or uneven surfaces.
5. Effect on Heat Generation:
   The rake angle influences the heat generated during cutting. A positive rake angle reduces friction, leading to lower temperature at the cutting zone.

Measurement of Rake Angle

Rake angle is generally measured with reference to two planes:

1. Orthogonal Rake Angle: Measured in a plane perpendicular to the cutting edge.
2. Back Rake Angle: Measured in a plane parallel to the tool’s axis or shank.

The accurate measurement of rake angle is important to ensure consistent tool performance and desired machining results.

Selection of Rake Angle in Practice

The selection of rake angle is based on the combination of work material, tool material, and cutting conditions. Some general guidelines include:

• For soft materials: Use a larger positive rake angle (10° to 20°).
• For medium-hard materials: Use a moderate rake angle (5° to 10°).
• For hard materials: Use a smaller or negative rake angle (0° to -10°).

Correct selection improves productivity and ensures longer tool life.

Conclusion:

Rake angle is a critical element in the geometry of cutting tools that controls chip flow, cutting force, and tool life. It plays a major role in determining how effectively a material can be cut and how much power is required. Choosing the right rake angle ensures smooth operation, longer tool life, and a better surface finish. Therefore, understanding and maintaining the correct rake angle is essential for efficient and economical machining operations.