How Do I Choose A Turning Insert?

Introduction

When it comes to turning operations, choosing the right insert can have a major impact on the quality and efficiency of the process. With a wide variety of turning inserts available, it can be difficult to know which one to choose. In this article, we''ll cover the key things to consider when selecting a turning insert, including materials, coatings, geometries, and more.

Materials

One of the most important factors to consider when choosing a turning insert is the material of the workpiece being turned. Different materials require different cutting speeds, feeds, and cutting forces, which means that different inserts are needed to achieve optimal results.

For example, if you are turning a soft, non-ferrous material such as aluminum or brass, you may want to consider using a high-speed steel (HSS) insert or a carbide insert with a PVD coating. These materials are relatively soft and easy to cut, so a sharper cutting edge is more important than toughness or wear resistance.

On the other hand, if you are turning a harder material, such as hardened steel or cast iron, you will need an insert that is tough enough to withstand the high cutting forces and temperatures involved. In this case, you may want to consider a ceramic or CBN (cubic boron nitride) insert, which offers high toughness and wear resistance.

Coatings

In addition to the material of the insert itself, the coating on the insert can also have a major impact on its performance. Coatings are used to improve tool life, reduce friction and heat, and enhance chip control.

Some of the most common coatings used on turning inserts include TiN (titanium nitride), TiCN (titanium carbonitride), and TiAlN (titanium aluminum nitride). TiN is a general-purpose coating that provides good wear resistance and heat dissipation, while TiCN offers improved abrasion resistance. TiAlN is a newer coating that combines the benefits of both TiN and TiCN, providing excellent wear resistance and high-temperature stability.

There are also specialized coatings available for specific materials and applications. For example, a diamond-like carbon (DLC) coating can be used for turning aluminum and other non-ferrous metals, while a vapor-deposited diamond (CVD) coating is ideal for turning high-temperature alloys.

Geometries

The geometry of a turning insert refers to the shape of the cutting edge and the angles at which it is positioned. Different geometries are used for different cutting operations, such as roughing, finishing, and profiling.

Some of the most common geometries used on turning inserts include:

- Rake angle: The angle between the cutting edge and the surface of the workpiece. A positive rake angle (e.g. 10 degrees) means that the cutting edge is tilted upward, which results in a sharper cutting edge and lower cutting forces. A negative rake angle (e.g. -10 degrees) means that the cutting edge is tilted downward, which results in a stronger cutting edge and higher cutting forces.
- Relief angle: The angle between the top of the cutting edge and the flank of the insert. A larger relief angle (e.g. 15 degrees) provides more clearance for the cutting edge and reduces the risk of built-up edge. A smaller relief angle (e.g. 5 degrees) provides more support for the cutting edge and enhances rigidity.
- Nose radius: The radius at the tip of the cutting edge. A larger nose radius (e.g. 0.4 mm) provides a smoother surface finish and reduces the risk of chipping. A smaller nose radius (e.g. 0.1 mm) provides a sharper cutting edge and enhances precision.

Chip Control

Chip control refers to the ability of the insert to break and clear chips from the cutting zone. Poor chip control can lead to chip accumulation, which can result in poor surface finish, tool wear, and damage to the workpiece.

There are several features that can help improve chip control, such as:

- Chipbreaker: A chipbreaker is a re-entrant feature on the cutting edge that interrupts the chip flow and breaks the chips into smaller pieces. This helps prevent chip accumulation and improves chip evacuation.
- Wiper edge: A wiper edge is a flat surface on the cutting edge that follows the contour of the workpiece. This helps create a smoother surface finish and reduce the risk of chatter.
- Coolant holes: Coolant holes are used to deliver coolant directly to the cutting zone, which helps flush away chips and reduce heat buildup.

Conclusion

Choosing the right turning insert can be a complex process, but it is essential for achieving optimal cutting performance and efficiency. By considering factors such as material, coating, geometry, and chip control, you can select the insert that best suits your specific application.

It is also important to remember that no single insert is ideal for every cutting operation. Experimentation and testing may be necessary to find the right combination of cutting parameters and tooling for your specific needs.

Whether you are a seasoned machinist or a beginner, taking the time to carefully select and maintain your turning inserts can help you achieve optimal results and extend the life of your tools.