What is the reason for the high-speed machining of ceramic tools?

10 June 2022
When we hear ceramic cutting tools is the first impression that they are fragile, like teacups/bowls, they will shatter once dropped from a height? So what is a ceramic cutting tool, is it the same as pottery like a teacup/bowl? The following describes the differences between the two.
1. Different raw materials
The main raw material of pottery such as cups/bowls is clay, while the ceramics used in cutting tools are based on high hardness and chemically stable raw materials, such as alumina Al2O3 and zirconium dioxide ZrO2. They are made from a much harder material than clay.
2. Different molding methods
Pottery such as teacups/bowls are mostly made by hand or hand-made utensils. The ceramic tool for cutting is to put the raw material into a special mold, and then use special equipment to stamp and form with a pressure of about 1-2 tons per square centimeter, thereby eliminating the gap between the particles and forming a high-strength ceramic tool material.
3. Different sintering temperature
Pottery such as teacups/bowls is sintered at a relatively "low temperature" of around 900-1,300°C, while ceramic tools used in cutting are sintered at a "high temperature" above 1,500°C. In addition, the sintering temperature and sintering time are strictly controlled to ensure the production of high-quality, high-performance ceramic tools.
The same is ceramics. Due to the above-mentioned differences in raw materials and production processes, ceramic cutting tools have two excellent characteristics. Let's take a look at how ceramic tools can take advantage of these properties in high-speed machining.
High hardness even in high temperature environments

In high temperature environment, can also maintain high hardness


The same goes for cutting tools. The higher the ambient temperature, the greater the reduction in material hardness. The hardness of cemented carbide and cermet will drop to about 35% of the normal temperature state at 1000 °C.
And ceramics (white porcelain HC1, black porcelain HC2, silicon nitride ceramics SX6) have a much smaller decrease in hardness under the same conditions. In particular, the silicon nitride ceramic SX6 material, even when the temperature reaches 1000 ℃, its hardness can still be maintained at about 73% of the average temperature state.
High flexural strength is maintained even in high-temperature environments
High flexural strength can be maintained even in high temperature environments
The graph above shows the relationship between ambient temperature and material flexural strength.
Cemented carbide has the characteristics of high flexural strength and is not easy to crack at room temperature. Even so, the intensity drops sharply as the ambient temperature rises. When the temperature reaches 1200°, the strength drops to about 35% compared to the average temperature.
And the strength drop is much smaller in the same conditions for ceramics (white porcelain HC1, black porcelain HC2, silicon nitride ceramics SX6) under the same conditions. In particular, in silicon nitride SX6 material, even at a temperature of 1200 °, its strength can still be maintained at about 82% of the average temperature.
We know that during the cutting process, the friction between the tool and the material to be processed will generate a large amount of cutting heat. The faster the cutting speed, the higher the temperature of the tooltip rises, and the harder it is to maintain the hardness and flexural strength of the tool, which limits the cutting speed that can be used in normal machining. Ceramic cutting tools utilize their material properties of high hardness and good flexural strength in the high-temperature field to achieve high-speed machining far exceeding that of cemented carbide, thereby greatly improving production efficiency. Let's see what it actually does:
pcd and pcbn cutting tools


The example of cast iron and heat-resistant alloy processing is shown in the figure: cast iron processing achieves a 3-fold increase in efficiency; heat-resistant alloy processing achieves a 15-fold increase in efficiency.


---EDITOR: Cynthia Lee

---POST: Cynthia Lee
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