Here are some simple quick tips when you are machining machining hard materials. 

• As material hardness goes up the SFM goes down.
• Use the strongest possible insert shape to maximize insert strength.
• Ceramic is a hard material therefore, the insert needs some edge preparation in order to withstand cutting forces and optimize performance.
• Utilize positive geometries for close tolerances or thin-walled parts.
• If multiple passes are required with one edge, vary the DOC to move the wear on the insert edge and improve tool life.
• If you encounter chatter, increase your feed rate. Heavy chatter is often a sign of the tooling being above centerline or there is too much toolholder overhang. The machine, part and tooling set-up must be rigid.

When you're considering inserts from NTK Cutting Tools for hard turning, take a look at the grades and styles.

1.  Light edge preps T styles ( T-land:  T0425  & T0525)
2.  Heavy edge preps:  Z and S style ( T-land and honed edge: Z0820, Z0825, S0820, S0825) or  J, P, and Q style (Double Chamfered and Honed edge: P4815,  P8015, Q8015)

We are very excited to announce that we are now able to offer on-site technical training to YOUR machinists at YOUR location!  This is offered at no charge  to customers who use any of the manufacturer's whom we represent in California and Nevada.  

However, just because you don't purchase things from us, don't feel left out! We also offer on-site topic specter training on any of the following topics for $150/hour.  

Each presentation lasts about 2 hours.  The presentations last approximately 45-60 minutes with the remaining time for Q&A and discussion about unique applications in your facility.

Ceramic tools have high resistance to heat and to wear and can be used to machine metals that are extremely hard, and they are chemically stable. These attributes allow them to be used to machine metals at high cutting speeds and in dry machining conditions because it is not necessary to reduce temperatures on the cutting edges of these tools.

​However, these favorable properties are exchanged in machining for lower toughness when these tools are compared with carbide tools. This deficiency can be offset by selecting an appropriate ceramic cutting grade and the type of tool.

Ceramic tools are based primarily on alumina (Al2O3) and silicon nitride (Si3N4) compounds and are available in a variety of grades that include ceramics mixed with other materials and reinforcing whisker materials that make them harder.

Reinforced or whiskered, ceramics use extremely fine-grained silicon-carbide crystals that are called “whiskers” because they resemble small hairs under a microscope to reinforce and toughen basic ceramic compounds.

In ceramic tool materials, single-crystal silicon carbide whiskers, on the order of one micron in diameter and 0.003937 in. (100 microns) in length, are intertwined within the alumina-matrix structure. These whiskers have a tensile strength of about 1 million psi and dramatically improve the fracture toughness of the tool material. They also effectively block and prevent propagation of cracks.

Cutting with ceramic inserts requires high surface speed and balanced feedrates. High speed is necessary to generate the high temperature in the shear zone and to ensure that the heat propagates into the chip-forming zone immediately ahead of the cutter. When cutting speeds are too slow, insufficient heat is generated to soften the material in this zone, and the cutting forces are raised and insert failure occurs.

A strategy for using ceramic inserts is to program fewer, but deeper cuts that bury the insert deep in the workpiece. This moves the notch formation further up the face of the insert to an area that has a larger, stronger cross section. Ramping cuts should be programmed to accommodate these tools and fixed depths of cut should be avoided to spread wear over a larger section of the insert.

When machining interrupted cuts with reinforced ceramics, it is important to keep the speed of the cutter high. A rule of thumb is to estimate the percentage of voids in the workpiece surface and increase cutting speed by that percentage. This increase in surface speed offsets the loss of heat generation created by the voids.

Whiskered ceramics work best on hard ferrous materials and difficult-to-machine nickel-base alloys, including Inconel, Waspoloy and Hastelloy. They do not work well on ferrous alloys below Rc 42 hardness because of the chemical reaction that occurs between iron and the carbon that is part of the silicon carbide reinforcing material.

There are five types os ceramic cutting tools.  Here are the basic differences:

ALUMINIUM OXIDE OR WHITE CERAMIC
NTK GRADES: HC1, CX3, HW2
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 
NTK GRADES: HC2, HC4, HC5, ZC4
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 has 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
NTK GRADES: SX1, SX2, SX8, SP2

• 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
NTK GRADES: WA1
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.

SIALONS
NTK GRADES: SX5
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.

The above text is from American Machinist's Cutting Tool Central.  For up to the minute information follow them on Twitter @AmericanMachnst