ADVANCED ARENA: Why Ceramic Cutting Tools?
February 1, 2012
Ceramic materials have been used in the cutting industry for over 100 years. In fact, it did not take long for manufacturers in the metalworking industries to understand the benefits of using ceramics to increase productivity and efficiency in many applications. Ceramic cutting tools are constructed mainly from alumina (Al2O3) and silicon nitride (SiN). Recent advances have also introduced the use of silicon carbide (SiC) and ceramic matrix composites (CMCs) in order to enhance the performance of the cutting tool.
Each of these ceramic materials has its own particular characteristics, but, in general, they all exhibit excellent hardness, toughness and thermal conductivity. In fact, the advantages of using ceramic materials in manufacturing revolve around ceramic’s greater ability to withstand much higher temperatures than tools made from carbide or high-speed steel. Generally speaking, ceramic tools’ heat resistance exceeds 4000°F vs. about 1600°F for tools made from carbide powder.
In addition, ceramic’s ability to operate at higher temperatures can result in a softening of the workpiece material, which allows for deeper and cleaner cuts. Thus, ideal machining temperatures (e.g., 2200°F for nickel alloys) can be accommodated by ceramic. However, these high temperatures are unattainable for carbide tools because they exceed the melting point of the cobalt binder.
The manufacturing of ceramic tools also offers advantages over typical manufacturing of carbide tools in that they are typically prepared using powder metallurgy techniques and can be manufactured closer to near-net finish, thus saving the tool manufacturer hard machining costs. The main drawback of ceramic tools is that they are brittle and do not withstand thermal shock very well, which means that they are better applied to continuous, long-run applications.
World Market for Ceramic ToolsIn 2011, the global market for ceramic cutting tools was over $1 billion and equaled 8.5% of the total market for metal- cutting tools (see Figure 1). From 2011 to 2016, the market will show above average growth of 6.8% annually (with year-to-year fluctuations). After a sharp decline in 2009 of over 30%, the global market for ceramic tools started a rebound in 2010 (see Figure 2). It is expected to reach pre-2009 levels in the second half of this year.
Relative growth rates will be stronger than that of carbide, high-speed steel (HSS) and cermet tools, but lower than the growth rates for super-hard tools such as polycrystalline cubic boron nitride (PcBN) and diamond (PCD and single crystal). By 2016, the global market for ceramic cutting tools is expected to reach $1.5 billion.
Key TrendsMany general factors affect the demand for ceramic tools, including:
- end-use market environment
- competitive pressures from other tool types
- customer preference and current workflow
As mentioned previously, ceramic tools exhibit higher heat and wear resistance over carbide or HSS. This has led to greater use of ceramic tools in jobs that require longer run times and where the workflow would benefit from the softening of the material due to higher temperatures. For example, ceramic tools are having a strong impact in the manufacture of aerospace parts made from hardened materials such as Inconel®, Waspalloy®, and Hastelloy®, as well as within the medical devices market where materials such as stainless steel, titanium, and biocompatible metals are used in implants and prosthetics.
The limiting factors of the market for ceramic metal-cutting tools include strong competition from super-hard materials tools such as PcBN and PCD. The prices of these tools are continually dropping, and they are not only becoming more affordable, but they have higher wear resistance and can be used at higher speeds as well. However, it should be kept in mind that diamond tools (minus any specialized coating) can only be used on non-ferrous materials, and ceramic tools are still a better choice when short runs do not justify the higher tool price.
Ceramic Tool TypesCeramic grade tools are typically classified into three general categories: oxide, nitride and matrix ceramics. Oxide ceramics are alumina-based and are generally used in roughing and finishing applications of cast and gray irons. Increasingly, oxide ceramics are being used in dry machining applications at high speeds. This is due to the advancements within materials science, including the incorporation of whisker-based materials. Nitride ceramics exhibit extremely high fracture toughness and are used for roughing and semi-roughing of cast irons under harsh conditions, such as when there is considerable starting and stopping that would typically increase fracturing.
CMCs contain ceramics mixed with other hard materials like cemented and titanium carbides. They can also contain reinforcing whiskers and other materials to increase wear resistance and toughness under hot machining conditions. These are commonly referred to as SiC-whisker reinforced. Alumina reinforced with SiC whiskers is the toughest and most resistant to thermal shock of the oxide-based ceramics due to the extremely high tensile strength of the SiC whiskers. It offers the additional benefit of being able to be run without coolant, thus making dry machining a common application while also being able to offer an increase in machining rates up to 800%.
These benefits lead to increases in efficiency. For example, many machinists would slow cutting speed if temperatures were to approach maximum carbide limits. It is the opposite for ceramic tools, which excel in higher temperature conditions.
Solid vs. Indexable ToolsCeramic tools are offered in both solid and indexable types. Solid tools dominate in drilling applications where inserts are used in milling and turning applications. Solid ceramic tools are being more widely employed in high-speed machining, particularly drilling. The benefits of this tool type include high output, dry machining, decreased production and cycle times, high production per machine tool, and greater flexibility when using single-spindle machine tools.
Indexable tools make up over 75% of the demand for ceramic tools. Indexable tools offer cost savings due to their ability to change out only the insert and not the entire tool. They offer comparable tool life to solid tools, along with savings on individual tool cost. Ceramic inserts are used mainly in finishing, turning of hardened material and super-alloys, and in the finishing of stainless steels.
In 2011, milling made up the majority of the demand for ceramic inserts, comprising 60.8% of the total market. Turning made up the second largest market at 36.7%, while drilling was only 2.2% of the total. In solid tooling, however, the mix was level among milling, turning and drilling demand.
When looking particularly at ceramic inserts, the main drivers include greater application in the finishing of hard-to-machine materials after roughing has been completed with carbide tools. In addition, advanced grades are being developed for hard turning applications; however, difficulties continue in achieving the cutting edges necessary for many hard turning applications.
In 2011, silicon nitride- and alumina-coated inserts made up a combined percentage of demand for ceramic inserts at 39.5%. SiC whisker and SiN follow next, comprising 17.3% and 15.4%, respectively.
Trends in Ceramic ToolingOver a forecast period of five years, ceramic tools will continue to find their place in the application matrix, especially as greater emphasis is placed on specificity in machining. Advances in materials development, along with the preparation of ceramic tools, will increase the efficacy and the wear resistance of ceramic tools. Some key advances include:
- New material compositions will be developed based on high-purity ceramic powders (particularly Al2O3), as well as continued enhancement using SiC carbide whiskers and matrix composites. These improvements continue to increase the versatility of ceramic tools and broaden the scope of applications in which they can be competitively and effectively employed.
- Optimized powder processing will lead to finer grain size (<100 nm), which will lead to finer cutting edges and greater tool wear resistance. The development of the finer grain size has led to some issues in tool construction, but some of these have been offset by the use of composites that increase the strength of the tool. The benefit of the finer edge size and wear resistance leads to close to near-net finishing in the workpiece material, which reduces cycle times and the need for finishing through traditional and time-consuming grinding.
- The improvement of coated ceramic tools will be essential in more general applications where longer run times will justify the added expense of ceramic tools.