Advances in materials have produced a ceramic end mill that performs well at lower cutting speeds and competes with cemented carbide in a wide range of applications. Your store may start using ceramic tools. #Titanium processing

Ceramic cutting tools provide a typical case for understanding the difference between hardness and toughness. These very hard tools have long been the solution for machining very hard metals such as aerospace alloys. However, due to their relative lack of toughness, turning has been their main application. These tools can withstand sustained high strength, such as stable cutting in uninterrupted turning-thank you, hardness-but they are susceptible to the banging impact of interrupted machining (such as milling), because long-lasting impact is all about toughness.

Like other ceramics, this tool can be dry cut and prefers high cutting speeds. The key difference: the new phase toughened solid tool performs well at the low cutting speed and relatively high feed rate of ceramics. The result is a solid ceramic circular tool that is very suitable for standard machining center functions. All photos are provided by Greenleaf.

Now, ceramic tool manufacturer Greenleaf says that innovations in ceramic toughness over the past five years have provided the potential to significantly expand the applicability of ceramic tools in milling. After two years of development, the company recently launched the "Xsytin 360" series of solid four-blade ceramic end mills. According to James Greenleaf, the company's third-generation owner, these tools are "the most extensively tested products we have launched." And the test continues, because ceramic tools with higher toughness are potentially promising tools in processing fields and applications. These applications are usually not related to ceramics and involve shops that have not turned to ceramic tools before.

Decades ago, it was this solution that achieved higher toughness and promoted Greenleaf's first major breakthrough in ceramic tools. The company launched a ceramic mold in 1973, which was manufactured using the proprietary hot pressing technology at the time. But in 1985, the company demonstrated and introduced a method of adding long and thin reinforcement crystals (called whisker reinforcement) to the microstructure of hard turning tools manufactured in this way and brought it to the market.

This innovation extended the life of these ceramic tools by 10 times and gave birth to the company's WG300 series of turning inserts.

(Memory channel: My first job in the industry was in the machining laboratory, where we evaluated the performance of aerospace alloy cutting tools. I spent a lot of time observing the cutting edges of WG300 blades under a microscope.)

The cutting diameter of four-edge ceramic end mills is 3/8 to 3/4 inch. Stability is a necessary condition for using good tools. Therefore, flute design to minimize vibration is an important part of the project.

The company also uses ceramic inserts for milling, albeit on larger diameter tools. But now, the latest major progress in ceramic toughness has prompted the company to introduce smaller diameter solid tools and insert ball-end tools. This latest toughness advancement is not due to the addition of different reinforcement mechanisms, but because the proprietary phase toughening process can better control the formation of ceramic materials, including the formation of whiskers. As the company explained, the phase toughening of the material provides a stronger material substrate and provides more predictive performance in other cutting tool ceramics prone to failure applications. The materials manufactured in this way are still biased towards hardness rather than toughness, but the current combination can not only meet the requirements of small diameter tools, but also closer to the needs of general machining and the performance of more mainstream machining centers.

Xsytin 360’s SiAlON (a ceramic that combines silicon, aluminum, oxygen, and nitrogen) is a material that James Greenleaf thinks he can confidently say: “This is the strongest ceramic material on the market. We finally feel that we have one The ceramics are good enough to provide a truly effective circular tool."

In the trial cutting, the performance and prospects of the new circular tools were not mainly reflected in the high speeds that these tools can achieve, but—please pay attention to this—significant improvements were found at the low speeds of these tools. The tool cuts well. Ceramic tools usually run at very high speeds (and run dry) because the thermal coefficient of ceramic makes the tools very heat-resistant. These tools even have a minimum cutting speed threshold for optimal performance. However, new, stronger ceramic tools do not require the typical strength of ceramics. The optimal speed range of the new solid ceramic end mill starts from 1,300 sfm, which is lower than other ceramic tools. For a 1/2 inch end mill, it is approximately 10,000 rpm. In short, all kinds of machine tools used in various workshops can reach the required speed.

Compared with cemented carbide end mills, ceramic tools can achieve higher cutting speeds and higher feed rates, thereby achieving a higher overall metal removal rate. Shown here are the parameters for processing Inconel 718. Please pay attention to the speed of the ceramic cutter. Although the speed is very high, it translates to only about 12,000 rpm.

However, even if the speed is lower than the typical speed of ceramic milling cutters, the company stated that its tests on materials such as the aerospace alloy Inconel 718 still show better metal removal rates and tool life than existing ceramic circular cutters. This is also because of tough freedom. The lower speed can match about 3.5 times the feed speed of existing ceramic end mills. The result is that the feed rate per tooth inch (chip load) is equivalent to the speed at which the shop may be accustomed to programming cemented carbide, but the spindle speed is much higher than that suitable for cemented carbide tools.

Hardness and toughness together mean that tool wear progresses slowly. Here the edge of a ceramic end mill with a diameter of 1/2 inch shows the wear after 72 minutes of milling 64 cubic inches of material on 4150 steel with a hardness of 52-55 HRC.

Compared with cemented carbide, the company reported that it has increased productivity by 10 times when milling hard steel, aerospace heat-resistant superalloys, vermicular graphite cast iron, and various cemented carbides. These alloys can now be used for augmentation by lasers, etc. Powder bed fusion of production parts manufactured by the material manufacturing process.

Productivity increases do require correct settings. Xsytin 360 milling cutters using phase toughened ceramics cannot replace cemented carbide; we have been talking about toughness, and cemented carbide is still a tougher material. Ceramic end mills that can reduce speed still require effective process control to protect the tool from impact-including control with rigid fixtures; short overhangs in tool settings; shrink fit, press fit, or hydraulic tools for low runout Frame; and by maintaining a consistent chip thickness to ensure a continuous cutting tool path. In fact, the groove design of the tool is part of this formula and another important part of the tool engineering design. This flute helps stability through improved geometry to minimize vibration. There is also a need for tool applications: a method of removing chips in the cutting path without coolant, because this ceramic, like the early ceramic tools, performs much better in dry running.

However, in many workshops that can achieve this level of stability and control, this tool is now a competitor to cemented carbide in an unprecedented way for ceramic circular tools. The level of toughness produced by phase toughening makes this change for us: Faced with the challenge of hard metals, many workshops now consider ceramic milling tools that have never used tools made of this material before.

4150 Steel processing is in action. The workpiece here is hardened to 54 HRC. The solid ceramic cutter has a diameter of 0.75 inches. The cutting speed is 1,500 sfm. For the 0.125 inch axial depth of cut and 0.0024 ipt, the feed rate for the full-diameter grooving pass is 0.001 ipt, the axial depth of cut is 0.125 inches, and the radial depth of cut is 0.060 inches.

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