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Ceramic machining

Ceramic cutting fluid is a non-metallic materials for cutting, grinding, grinding, drilling and other processing of a product. Dedicated to ceramic materials, zirconia, precious stones, jade glass and other non-metallic materials processing. MB-135 as a water-soluble fully synthetic cutting in non-metallic materials, processing excellence, at an affordable price, excellent performance.

How to choose cutting fluid

Select metal cutting fluid, first of all, according to the cutting process conditions and requirements, the initial judgments selected purely oily metal cutting fluid or water-soluble metal cutting fluid. Usually, we can choose according to the recommendation from the machine tool supplier. Secondly, we can choose according to the conventional experience. For example, when using HSS for low speed cutting, purely oily metal cutting fluid is usually used. When using carbide cutting tools for high speed cutting, Usually can be used water-soluble metal cutting fluid; difficult to access for the cutting fluid or cutting fluid is not easy to reach the cutting zone using purely oily metal cutting fluid (such as tapping, bore broaching, etc.), other cases can usually use water-soluble metal cutting fluid Wait. In short, according to the specific cutting conditions and requirements, according to the different characteristics of purely oily metal cutting fluid and water-soluble metal cutting fluid, taking into account the different actual situation of each factory, such as workshop ventilation, waste disposal capacity and before and after the procedure The use of cutting fluid, etc., to select the specific type of cutting fluid.

Wear and lubrication of ceramic cutting tools

1. Ceramic cutting tools with high hardness, wear resistance and high temperature mechanical properties, good chemical stability, easy to bond with the metal and so on, can be widely used in difficult-to-machine materials cutting, ultra-high-speed cutting, high-speed dry cutting and hard cutting Wait. The best cutting speed ceramic tool 3 to 10 times higher than carbide cutting tools, can greatly improve the productivity of machining. In the last three decades, various carbide, nitride, boride, oxide, whisker or minority metal additive technologies have been developed due to the effective control of the raw material purity and grain size in the ceramic tool manufacturing process, And the use of a variety of toughening and reinforcement mechanisms, so that the strength of ceramic knives, toughness, impact resistance and so have greatly increased. But ceramic cutting tools are not everything. Ceramic cutting tools in the cutting process to withstand high temperature, high pressure, will inevitably be subject to varying degrees of wear or damage. Existing research shows that each ceramic tool has its own specific processing range. Different ceramic tools (or ceramic tools of the same kind) have different wear patterns and tool life when processing different workpiece materials. Therefore, there exists The best match between ceramic tools and cutting objects. There are some reports about this research at home and abroad. However, due to the different experimental conditions and research methods, different researchers' experimental results and research conclusions are different.

In this paper, based on the existing research of the author, referring to the domestic and international related literature reports, this paper gives a comprehensive review of the wear and lubrication of ceramic cutting tools and the best match between the ceramic cutting tools and the processing objects, Of the development and development, the actual processing of ceramic cutting tool selection and wear control play a guiding and reference role.

2. Ceramic cutting tool wear mechanism

In the cutting process of ceramic cutting tools, there are always two friction pairs, namely the rake face and the friction between the vice and the flank and the friction between the workpiece. Among them, the former affect the tool rake face wear, the latter affect the tool flank wear and the machined surface quality, before and after the flank wear and tear are affecting the tool life. Ceramic cutting tools are mainly used in high-speed cutting applications. The cutting temperature can be up to 800 ~ 1000 ℃ (even higher), and the cutting pressure is also great. Therefore, the wear of ceramic tool is a combined result of mechanical wear and chemical wear. The wear mechanism mainly includes abrasive wear, bond wear, chemical reaction, diffusion wear, oxidation wear and the like. Existing research shows that the wear and tear of ceramic cutting tools are closely related to cutting conditions. Different ceramic tool materials Different workpiece materials under different cutting conditions, the dominant wear mechanism may be different. Such as low-speed cutting, due to the cutting temperature is low, the wear mechanism is often shown as abrasive wear; in high-speed cutting, then the high temperature caused by adhesive wear, chemical reaction, oxidation wear and diffusion wear mainly.

The author's research shows that: Al2O3-based ceramic tool in the continuous cutting steel, the wear mechanism is mainly associated with micro-chipping edge abrasive wear and bond wear, while cutting the main abrasive wear of iron. Wayne and Brandt et al. (1996) studied the processing of Inconel 718 with Al2O3 / SiCw ceramic tools and concluded that abrasive wear and bond wear are the main wear mechanisms of ceramic tools at low cutting speeds, whereas bonding at high cutting speeds Wear, chemical reactions and diffusion wear are the main wear mechanisms for ceramic tools. As Inconel 718 material high temperature strength, plastic deformation, severe processing hardening, cutting force and cutting temperature are high. When the cutting temperature is less than 900 ℃, the tool rake surface mainly to bond wear; when the temperature reaches 1200 ℃, Ni began to spread to the tool center. Due to the diffusion of Ni, on the one hand, the hardness of the tool material surface is reduced and the performance is reduced; on the other hand, the affinity between the tool and the workpiece is increased, and the bond wear is increased. Therefore, the cutting fluid (chlorinated paraffin cutting fluid better) must be used when machining Inconel 718 with Al2O3 / SiCw ceramic tools.

  Casto, who studied the use of Al2O3 / ZrO2 ceramic tool machining AISI 1040 material concluded: tool wear mechanism is mainly manifested as bonding wear and abrasive wear, and Si3N4 ceramic tool processing AISI 1040 steel, the tool surface is a serious chemical reaction. When AISI 4337 steel is machined with Al2O3 / ZrO2 and Al2O3 / TiCN ceramic inserts, the rake and flank wear mechanisms are different. Chemical reaction and plastic deformation are the main reasons for the rake surface wear. The flaw wear mechanism of the flank is that the ceramic particles break, resulting in the detachment of the ceramic particles. Brandt found that the plastic deformation of the surface of Al2O3-based ceramic tool cutting, and that this is because Al2O3 and FeO (steel surface oxidation products) or MgO (ceramic additives) formed a spinel structure, or Al2O3 and SiO2, CaO The role of the formation of a low melting point, low hardness compounds. The author's research shows that: Al2O3 / TiB2 ceramic cutting tool in the processing of high strength steel and hardened steel has good wear resistance, with the increase of TiB2 content, tool wear resistance increased.

For whisker toughening ceramic tools, the whisker toughening ceramic tool wear resistance due to the orientation of whiskers in the vertical hot pressing plane during hot pressing, resulting in different distribution of whiskers on different surfaces. Orientation, θ = 0 ° surface wear the worst performance, and θ = 90 ° surface wear the best performance. When the tool is mainly worn after the wear, the surface of θ = 90 ° should be selected as the flank of the tool. When the tool is mainly worn by the flank, the surface of θ = 90 ° should be selected as the rake surface of the tool. When the tool front and back flaws exist at the same time larger wear, you should select the θ = 45 ° surface as the tool before (after) the knife face, to improve the wear resistance of the tool.

Si3N4-based ceramics have been used as tool materials since the late 1970s and are now widely used in the machining of cast iron and nickel-based alloys. Si3N4-based ceramic cutting tools in the high-speed cutting abrasive wear occurs mainly in the high-speed cutting of carbon steel mainly chemical wear and tear. Chemical wear itself, the proportion of the total wear of ceramic tools is generally not large, but the chemical can greatly aggravate the degree of mechanical wear and tear, such as chemical dissolution and diffusion can cause the ceramic surface strength weakened, exacerbating the tool and the workpiece Bonding, resulting in severe bond wear and micro-fracture wear. When cutting AISI 1045 steel with Si3N4 ceramic tool, the wear rate is two orders of magnitude higher than that of gray cast iron. The interdiffusion of Fe, Si and other elements between workpiece and tool when cutting cast iron is much smaller than that of cutting steel. Cutting steel, Si3N4 ceramic tool wear mainly with the chemical effects between the tool and the workpiece, due to the chemical dissolution of Si3N4 particles and is constantly being removed from the glass phase, Si3N4 ceramic tool showed a high rate of wear. Si3N4 ceramic cutting tool when the high wear rate of steel is mainly due to the following two factors: ① Si3N4 oxidation in the tool surface layer of SiO2 is constantly being worn off; ② SiO2 and the workpiece surface FeO low melting point eutectic mixture. The chemical reaction between Sialon ceramic tool and iron-based alloy has been studied. The results show that the β'-Sialon particles react with the iron-based alloy at high temperature, and silicon and nitrogen dissolve and diffuse in the iron-based alloy. Alloying elements in steel have some influence on the reactivity between Sialon and steel. Elements such as nickel, silicon, carbon and phosphorus can reduce the reactivity, while elements such as chromium, molybdenum, titanium and vanadium increase the reactivity.

Although ceramic tool wear and cutting conditions are closely related, but the main factors that determine the wear characteristics of ceramic tool is still the ceramic material composition and microstructure. Ceramic tool wear is the basic phenomenon of material fracture and transfer, so the crack formation and expansion will have a significant impact on wear. Ceramic tool materials are mostly multiphase ceramics, there are glassy phase, stomata and impurities in the grain boundaries, and there are differences in thermal expansion mismatch and elastic modulus between the phases. The existence of the grain boundary pores will lead to stress concentration. The pores will induce the grain boundary cracks as the crack source. And the pores are mainly formed on the grain boundary. The crack propagates to the pores and connects with the pores, accelerating the crack growth. Rice et al.'s research shows that the increase of porosity leads to a great decrease of the wear resistance of ceramic tool. Excessive residual stress caused by mismatch between elastic modulus and thermal expansion can cause the material to crack without external load. As the polycrystalline ceramic additives added in the sintering process mainly in the form of glass phase exists in the grain boundary, high-speed cutting under high temperature conditions, the glass phase viscosity decreases and plastic flow, resulting in grain boundary slip, and in the crystal Boundary at the junction of stress concentration phenomenon. If the stress concentration makes the adjacent crystal completely plastic deformation, it will make the stress relaxation, if not with the adjacent grain boundary deformation adaptation, the stress concentration will cause grain boundaries crack. Crack nucleation, with the increasing degree of grain boundary slip will cause cracks. A large number of dislocations in the ceramic tool material crystals provide another way for nucleation of cracks. As the wear process progresses, the dislocations continue to multiply and more microcracks are formed at the grain boundaries due to dislocations , These cracks will be connected to form a continuous crack, resulting in reduced wear resistance of ceramic tools.

3. Ceramic cutting tool cutting lubrication

The ceramic cutting tool for the current need for lubrication is not uniform view. Some scholars believe that ceramic cutting tools with high hardness, high melting point, high temperature and other characteristics, and thermal shock resistance is poor, very sensitive to thermal stress, improper cooling effect will cause the tool to generate thermal cracks and damage, so the ceramic tool Cutting without cooling and lubrication to meet the requirements. However, there are also many researchers believe that the ceramic cutting tools in the processing of some difficult materials (such as the use of ceramic whiskers to toughen the nickel-based superalloy), you must make full use of cutting fluid (chlorinated paraffin cutting fluid better ). Proper cooling and lubrication can be useful for reducing wear on ceramic tools and extending their useful life. Tonshoff et al. Studied the effect of lubricants on the hardening of Al2O3 / TiC ceramic tool turning hardened steel, the cutting tests were carried out under dry cutting and lubrication with different lubricants respectively. The results show that the wear of tool, the quality of machined surface and the formation of chips are affected by the lubricant. Compared with dry cutting, the use of lubricants tool life extension, the workpiece surface quality has been significantly improved. This is mainly because the extreme pressure additives in the lubricant under the cutting conditions and the workpiece surface friction chemical reaction formed a chemical adsorption film. Through the component analysis of the workpiece surface under lubrication and cutting conditions, it was found that the extreme pressure lubrication film containing FeS and FePO4 and other components, it is this extreme pressure lubrication film to reduce cutting friction, inhibit the occurrence of bonding, and thus reduce Small tool wear.
Cheryl on the Si3N4 / TiC ceramic materials at 900 ℃ high temperature friction and wear tests showed that: Si3N4 and TiC oxidation occurs at high temperatures, the friction surface containing Si and Ti oxide protective film can significantly reduce the friction coefficient, and there Will help improve the wear resistance of materials. Cutting tests on nickel-base alloys with Si3N4-based and Al2O3-based ceramic tools found that the main cause of tool failure under dry-cutting conditions was severe rake wear and chip-to-tool bonding while the use of cutting lubricants improved tooling The cutting performance, improve the cutting efficiency and the surface quality of the workpiece. Some people have a variety of lubricants, additives on the ceramic - metal friction pair lubrication has been studied and found that the oil-based cutting fluid is more effective than water-based cutting fluid. When lubricated with ZDDP lubricants, the wear rate of Si3N4 ceramic tool when cutting 45 steel is reduced by two orders of magnitude compared with that of dry cutting. The wear rate of stainless steel is lower than that of dry cutting Can be reduced by an order of magnitude. Surface analysis found that the wear surface of Si3N4 and the workpiece ZnO, FeS, FePO4 friction chemical reaction products. The author of the Al2O3 / TiB2 ceramic cutter dry cutting hardened steel was studied, the results show that: The high-speed ceramic cutting tool with self-lubricating function. When the cutting speed is low, the cutting temperature is low, the wear mechanism of the tool is mainly abrasive wear and bond wear; when the cutting speed is high, the cutting surface of the average cutting temperature is higher, the actual instantaneous maximum temperature is greater than the average temperature, The XRD pattern of the tool wear zone after cutting shows the diffraction peak of TiO2, indicating that oxidation of TiB2 occurs under the effect of cutting high temperature. TiB2 oxide TiO2 can act as a solid lubricant between the chip and the rake face of the tool, thereby reducing the average friction coefficient μ of the cutting force and the rake face, as well as reducing the bond wear of the tool and increasing the cutting tool Wear resistance.

4 ceramic tool and processing object matching

Each ceramic tool has its own specific range of processing, different ceramic tool (or the same type of ceramic tool) in the processing of different workpiece materials, wear patterns and tool life are very different. Therefore, each ceramic tool has its best processing object, that there is the best match between the ceramic tool and the processing object.

Al2O3-based ceramic tool contains aluminum, Al2O3-based ceramic tool in the processing of aluminum and aluminum alloy greater affinity, the tool will have a greater bond wear and diffusion wear. Al2O3 / TiC and Al2O3 (/ W, Ti) C and other ceramic tools contain aluminum and titanium, with such ceramic tool processing of titanium and titanium alloys, aluminum and aluminum alloys also have greater affinity, so they are not suitable for processing Aluminum, titanium and their alloys. Pure iron and Al2O3 tool bonding tendency between steel and cast iron, pure Al