The use of ceramic cutting tools is on the rise, that news is less dramatic than it seems, because solid ceramic end mills and inserts are usually easier to use than carbide tools. Changing to using ceramic cutting tools doesn’t need really any special process changes. Contrary to what people might think about ceramic tooling.
All the tools really needs is speed, the run out of the tool doesn’t have to be any different from a solid carbide end mill and because the tools perform effectively when used without coolant, considerations related to coolant become irrelevant.
What the tools need to function is HEAT- the heat comes from fast, dry cutting, the same heat that might be destructive to other tools like carbide. Cutting speeds with ceramic end mills can be much higher than those of solid carbide. The benefits of ceramic over carbide are the greater heat resistance of ceramic which allows cutting speeds up to 20 times higher than solid carbide cutters and inserts, with surface speeds up to 1,000m/min possible.
The use of hard materials accounts for part of the reason why the use of ceramic tooling is increasing. Nickel-based high temperature alloys as Inconel especially in the aerospace industry is increasing, as is the use of these alloys in other industries. Many applications in the past and still are today low cutting speeds, high torque machine tools. The increasing availability of machines with high spindle speeds is an advantage when using ceramic cutting tools.
In the picture above the material is Inconel 725. The “sparks” seen are a result of the tool using heat as part of its cutting action. What look like sparks are actually the material being converted to powder.
We mustn’t forget that carbide tools are still needed. While ceramic tools wear much more slowly than carbide in hard materials, it still does wear out. Ceramic tools wears gradually, doing so all the time it is cutting, this means that the cutting edge is slowly and constantly changing. The end of the ceramic tools life is when the cutting edge has eroded away.
So normally, ceramic tools are used for roughing applications. Ultimately, carbide cutting edges still must perform the final finishing cuts.
Recommendations using ceramic cutting tools.
Continuous cutting is highly recommended. Interrupted cutting can damage the cutting edge or increase chipping of the cutting edge.
When for example inside milling operations it is recommended to increase the radial width of cut gradually. Increasing the width of cut (Ae) gradually will maintain tool life.
Down milling/climb milling is recommended. Up cutting can be unstable.
Like milling with solid carbide we prefer to use down milling, starting with a thick chip and ending with a thin chip.
The primary causes of wear when machining nickel-based alloys such as Inconel with ceramic tools are chemical wear caused by the temperature and built-up edges (BUE). Do not remove any built up edge manually as this may cause chipping of the cutting edge. The built up edge will be removed by the heat generated during the next cutting cycle.
While ceramic tools present excellent machining opportunities, it is nevertheless worth considering whether the high machining temperatures that ceramic milling cutters reach could result in damage to the work piece material. Machining with ceramics at high temperatures can affect the outermost layer of the machined work piece. As ceramic tools are only used for roughing operations, the only thing that needs to be ensured is that the depth of the damage to the material is less than the offset for finishing. A rule of thumb is to allow a stock of more than 0.30mm for the finishing operation.