Carbide inserts are the most used solution for many turning applications because they offer good performance at a reasonable price. However, ceramic inserts are worth considering as an alternative in some turning applications.
Ceramic is an advanced cutting material that is harder than carbide and enables machining at higher cutting speeds but is suitable for only specific applications and workpiece materials. The tools made of this material have high resistance to heat and to wear and can be used to machine metals that are extremely hard
This type of material is based on alumina (Al2O3) and silicon nitride (Si3N4) compounds and is available in a variety of grades which include ceramics mixed with other materials and reinforcing whisker materials that make the material harder.
The materials are molded at pressure more than 4,000 psi and they are sintered at approximately 3,000 degrees F. This process accounts in part for the high density and hardness of these tools. Oxide ceramics are used primarily for rough and finish turning, for grooving of gray and nodular cast iron and for continuous cutting at high cutting speeds without the use of coolant.
There are five types of ceramic cutting tools. Here are the basic differences:
ALUMINIUM OXIDE OR WHITE CERAMIC
Pure alumina strengthened by Zirconium.
- High hardness but relatively low strength, toughness and thermal conductivity making them prone to cracking if used with coolant.
- Offer excellent wear characteristic making this range ideal for finish turning, boring, and grooving of Cast Iron as well as
- Tube Scarfing.
MIXED OR BLACK CERAMICS
Alumina with metallic phase of Titanium Carbide and Titanium Nitride which improves thermal conductivity.
- Increased ability to cope with extreme cutting conditions.
- Used mainly for hard part machining (up to HRC62).
- Used extensively in Steel and bearing markets and for Cast Iron finishing operations.
- Recent improvements have seen greater wear resistance and toughness due to higher density and reduced porosity.
- The main advantage that mixed ceramic has over Cubic Boron Nitride (CBN) in hard part machining applications is the effect on part production costs. Whilst CBN has a better tool life, the cost per edge of a ceramic insert is a fraction of that of CBN (approx. one twentieth) whilst feed rates (chip thickness around 0.1mm) and cutting speeds (range between 50 - 200m/min) are not significantly higher.
SILICON NITRIDE BASED CERAMICS
- Low thermal expansion makes this range very resistant to thermal shock.
- High breaking strength sees their use in rough turning (even with heavily interrupted cuts), boring and milling of Cast Iron.
- Offers exceptional tool life.
- Cutting speeds up to 1000m/min, feeds of 1mm/rev.
- More stable in operations but tends to suffer from normal flank and crater wear rather than failures associated with white and black ceramics.
WHISKER REINFORCED CERAMICS
Pure alumina structurally strengthens from introduction of Silicon Carbide in the form of whiskers.
- Added tensile strength and fracture toughness even at elevated temperatures.
- Ideal for high-speed machining for Nickel based Aerospace alloys e.g. Inconel 718 correspondingly greater metal rates.
Alumina substrate strengthened by Silicon Nitride.
- A lower cost option than Whisker ceramic (but lower performance).
- Widely specified and used in the machining of Aerospace alloys.
Check Canela’s Ceramic inserts!