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. Oxide ceramics
Whiskered ceramicsReinforced 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. Silicon nitrides
When used with powerful machine tools, silicon nitrides enable high cutting speeds (more than 800 in./min.) and feeds (0.2 to 0.3 in./min.) for rough boring cast iron. Silicone nitride tools offer fracture resistance, but their relatively low resistance to chemical wear limits their use in machining nodular cast irons. However, wear-resistant, chemical vapor deposit (CVD) alumina coatings have expanded the range of applications for silicon nitride-based tools to include these difficult-to-machine irons. Gray cast iron and nodular graphite cast iron can be milled at cutting speeds of 500 to 800 in./min or sometimes faster than 1,000 in./min. Five Types of Ceramic Cutting Tools.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.
MIXED OR BLACK CERAMICS NTK GRADES: HC2, HC4, HC5, ZC4 Alumina with metallic phase of Titanium Carbide and Titanium Nitride which improves thermal conductivity.
SILICON NITRIDE BASED CERAMICS NTK GRADES: SX1, SX2, SX8, SP2
WHISKER REINFORCED CERAMICS NTK GRADES: WA1 Pure alumina structurally strengthens from introduction of Silicon Carbide in the form of whiskers.
SIALONS NTK GRADES: SX5 Alumina substrate strengthened by Silicon Nitride.
The above text is from American Machinist's Cutting Tool Central. For up to the minute information follow them on Twitter @AmericanMachnst
11 Comments
syed irshad ahmad qadri
7/27/2015 15:42:50
dear sir,
Reply
Deept Murti Madhav
1/28/2022 23:15:30
Dear sir,
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4/2/2019 19:56:35
Thanks for helping me understand that there are silicon-carbide crystals which resemble hair which is why they are called whiskers. I just got curious about stuff like this since I heard my best friend that he needs to buy some. It appears that it is for the holes that he needs to drill from a piece of metal equipment he has to make it work again.
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1/16/2020 02:22:10
We are one of the finest manufacturer and exporter of Industrial tools in India. The company deals in cutting tools, measuring tools, welding tools, carpentry tools, jewelry making tools, etc. since 1975.
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8/26/2020 19:21:04
I liked that you pointed out that you will want to consider how well the tool you are looking into getting will work. It is good to know that you will want to consider what extreme conditions the tool will be able to help you with. Personally, I would want to talk to an expert about what type so f tools I should look into getting.
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1/12/2021 01:27:46
You have described it so well. Thank you such a great knowledge. keep sharing!!
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Ibrahim
2/14/2021 08:16:05
Kindly explain the factors considered in application of the three ceramic grade cutting tools
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8/16/2021 23:52:49
Impressive post with great content.
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10/1/2021 13:27:20
According to Value Market Research, the latest technology trends and global market opportunity analysis in the High Purity Silica Powder Market industry growing with a high CAGR in the upcoming year. Our report has categorized the market based on technology, service, development, vertical and region. https://www.valuemarketresearch.com/report/high-purity-silica-powder-market
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10/12/2021 01:50:16
Impressive Blog Post.
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4/19/2022 12:31:15
It's great that you talked about ceramic cutting tools and how they come with heat-resistant features. A few days ago, my cousin said he needs to find a special tool for a project that he's working on. My cousin's on a deadline, and he needs to find that tool now, so I think your tips could help him. Thank you for the advice on choosing a ceramic cutting tool based on its speed and performance.
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