Tool Life and Negative Top Rake – Application and Performance Compared to Positive Top Rake
In the ITI Turner trade, cutting tool geometry plays a crucial role in machining performance and tool life. One of the most important aspects of tool geometry is the top rake angle. The choice between negative top rake and positive top rake significantly affects cutting forces, surface finish, and tool durability. This chapter explains tool life, negative top rake, and its performance in comparison with positive top rake.
Tool Life
Definition
Tool life is the duration for which a cutting tool performs effectively before it needs replacement or re-sharpening.
Factors Affecting Tool Life
- Cutting speed
- Feed rate
- Depth of cut
- Tool material
- Cooling and lubrication
Importance
- Reduces machining cost
- Improves productivity
- Ensures consistent quality
Top Rake Angle
Definition
The top rake angle is the angle formed between the face of the cutting tool and a plane perpendicular to the workpiece axis.
Positive Top Rake
Characteristics
- Tool face slopes downward
- Reduces cutting force
- Produces smooth cutting action
Advantages
- Lower power consumption
- Better surface finish
- Suitable for soft materials
Limitations
- Weaker cutting edge
- Shorter tool life
Negative Top Rake
Definition
In negative top rake, the tool face slopes upward, making the cutting edge stronger.
Characteristics
- Stronger cutting edge
- Higher cutting forces
- Less sharp cutting action
Applications of Negative Top Rake
- Machining hard materials
- Heavy cutting operations
- Use with carbide tools
- High-speed machining
Performance Comparison
| Parameter | Positive Rake | Negative Rake |
|---|---|---|
| Cutting Force | Low | High |
| Tool Strength | Low | High |
| Tool Life | Short | Long |
| Surface Finish | Better | Moderate |
Effect on Tool Life
Negative rake increases tool life by providing a stronger cutting edge and reducing wear. Positive rake, while easier to cut, leads to faster tool wear.
Advantages of Negative Top Rake
- Longer tool life
- Suitable for hard materials
- Better heat resistance
Limitations
- Higher cutting force
- More power required
Selection Criteria
- Use positive rake for soft materials
- Use negative rake for hard materials
- Consider machine power and tool material
Application in Turner Workshop
In the Turner trade, tool rake selection is based on the material being machined. Negative rake is used for heavy-duty operations, while positive rake is used for finishing operations.
Proper selection improves efficiency and tool life.
Importance
- Improves machining performance
- Reduces tool wear
- Enhances productivity
Conclusion
Tool life and rake angle are important factors in machining. Negative top rake provides stronger cutting edges and longer tool life, while positive rake offers smoother cutting and better finish.
Understanding their differences helps in selecting the right tool geometry.
In conclusion, proper selection of rake angle ensures efficient and high-quality machining in the ITI Turner trade.