What Is The Difference Between Positive And Negative Turning Inserts?

Introduction

In the world of cutting tools, turning inserts are an essential component. These inserts are used for various cutting operations, including turning, boring, and facing on various materials, including metals, plastics, and composites. Turning inserts come in different types, including positive and negative turning inserts. While they may seem similar, there are differences between the two that make them suitable for different cutting operations.

This article will provide an in-depth look at positive and negative turning inserts, highlighting the differences between the two types of inserts and their respective advantages and disadvantages.

Positive Turning Inserts

Positive turning inserts are also known as rectangular inserts, and they feature a positive top rake angle. These inserts are characterized by their cutting edge geometry, where the rake angle is greater than zero degrees and the main cutting edge is inclined relative to the tool''s axis. The positive rake angle provides enhanced cutting force, allowing for faster and more efficient cutting.

Advantages of Positive Turning Inserts

One of the main advantages of positive turning inserts is their ability to generate lower cutting forces. This feature is due to the increased rake angle, which results in the tool cutting with less friction and less heat generation. As a result, the tool doesn''t dull as quickly, reducing the need for frequent tool changes, and improving overall efficiency.

Furthermore, positive turning inserts are suitable for roughing operations on difficult-to-machine metal alloys, such as stainless steel and Inconel. These materials are known for their high work hardening and toughness, which can present challenges during machining. However, with their higher cutting force, positive turning inserts can easily machine these materials.

Disadvantages of Positive Turning Inserts

Despite their advantages, positive turning inserts also have some limitations. One disadvantage is their unsuitability for finish turning operations since they are more susceptible to insert chipping and premature breakage since they are quite thin. Additionally, the positive rake angle makes the tool more susceptible to vibration, which can cause poor workpiece finish or chatter during the cutting process.

Negative Turning Inserts

Negative turning inserts, also known as triangular inserts, feature a negative top rake angle, with a negative lead angle. The negative lead angle refers to the angle between the cutting edge''s axial position and the workpiece surface normal, which is a measure of the inclination of the insert towards the workpiece''s surface. Negative turning inserts effectively slice through workpieces, resulting in reduced cutting forces and longer tool life.

Advantages of Negative Turning Inserts

One of the primary advantages of negative turning inserts is their ability to generate less cutting force. The negative rake angle results in less contact between the workpiece and the cutting edge, reducing cutting forces and resulting in less heat generation. This feature reduces wear on the tool, resulting in more extended tool life.

Negative turning inserts'' design makes them suitable for finishing operations, especially when machining softer materials such as aluminum and brass. The inserts'' negative rake angle means that they are less likely to "grab" or dig into the material, resulting in a high-quality finish. Negative turning inserts can also be used on tough materials such as steel and titanium, as they are designed to handle high-speed cutting conditions.

Disadvantages of Negative Turning Inserts

The main disadvantage of negative turning inserts is their limited capability to machine on hard materials. The negative rake angle can cause increased cutting forces, making it challenging to produce good surface finishes when machining tough materials like stainless steel and Inconel. Also, since the tool''s geometry is not suitable for deep cutting, negative turning inserts are not ideal for roughing operations.

Conclusion

Positive and negative turning inserts have unique features and advantages that make them suitable for various types of cutting operations. Positive turning inserts are ideal for roughing operations on tough materials and generate less cutting force. Negative turning inserts, on the other hand, are perfect for finish cutting on softer materials, resulting in a superior finish.

In conclusion, choosing between positive and negative turning inserts depends on the cutting operation''s requirements and the material being machined. By understanding the differences between the two types of inserts, machinists can select the right tool for the job, resulting in increased efficiency and productivity.