The main processing method of zirconia ceramics is diamond grinding wheel grinding. With the good self sharpening structure and suitable for high speed grinding, With low density, high strength, high hardness, low expansion,Vitrified Bond Diamond Wheel for Grinding Zirconia Ceramics is the first choice .
coefficient, wear resistance, corrosion resistance, heat insulation, good chemical stability, zironia ceramic materials have wide application prospects in energy, aerospace, computer, machining and other fields.
Zirconia ceramics have many excellent mechanical properties. With reversible transitions between rhombic, tetragonal and cubic phases, it is the basis for the development and application of zirconia as a new material.
Tetragonal zirconia has toughening and excellent mechanical properties, making it best for structural ceramics. It is mainly used in components of engines and internal combustion engines, pumps, bearings, sealing rings, electronic tubes, fiber optic connectors, bioceramic hip joints, dental ceramics, engine parts, textile screw guides, blades, scissors, cutting tools, and bulletproof armor in the military.
In adiabatic internal combustion engines, ductile zirconia can also be used for cylinder liners, piston crowns, valve guides, intake and exhaust valve seats, bearings, cams and piston rings.
The thermal efficiency of ceramic insulated internal combustion engines has reached 48%( that is 30% for ordinary internal combustion engines). The internal combustion engine eliminates 360 parts such as radiators, water pumps and cooling pumps, resulting in a mass reduction of 191KG
Some countries such as Japan, USA and Germany not only use ductile zirconia to make engine, but also use it to manufacture computational drive components, seals and cooling blades for aircraft engines.
Zirconia ceramic materials feature high birittleness, low fracture toughness, and it is difficult to grind effectively for the current processing method. The development of diamond grinding wheels with high efficiency and low cost has become a hot topic of ceramic grinding in recent years.
1.Method of processing zirconia ceramics
Zirconia ceramics have the common features of engineering ceramics and functional ceramics, with high shear stress resistance, extremely low tensile strength and large elastic modulus, which is one of the factors that make it difficult to machine ceramic materials.
After years of research and exploration, the processing technology continues to change, and the ceramic processing methods gradually improve, and the processing efficiency is also constantly improving.
Grinding is the main means of ceramic processing. With the continuous deepening and development of many scholars in the 1980s, a series of theoretical guidance are gradually formed. Grinding methods are also constantly changing and updating.
1.1Ductile mode grinding technology
Shen JY proposed the ductile mode grinding technology and established a critical cutting thickness model for brittle material grinding by the fracture propagation criterion and microhardness indentation method, effectively controlling surface cracks and other defects in ceramic grinding.
This technology mainly uses high stiffness and high resolution grinding machines by controlling the grinding depth, making the brittle materials removed in the ductile mode.
This means that the grinding mechanism of brittle materials changes from brittle fracture to plastic flow, and choose the grinding parameters and characteristic parameters of the grinding wheel to achieve the better machining surface. It is a nano-grinding technology.
This means that the grinding mechanism of brittle materials changes from brittle fracture to plastic flow, and appropriate grinding parameters and characteristic parameters of the grinding wheel are selected to achieve better machining surfaces. It is a nanoscale grinding technology.
For example, in an experimental case, the grinding experiment of zirconia ceramics by diamond grinding wheel with W0.5 micro powder showed that the ultra smooth mirror surface of surface roughness Ra=3μm can be obtained at a grinding wheel linear speed Vs=11.8m/s and an economic speed V＝40mm/min.
When using traditional grinding for zirconia cermic workpieces with thinner thickness, cracks may occur due to small vibrations. The ductile mode grinding is a method of processing ceramic materials. The combination of ultrasonic ductile mode grinding will be a trend in future ceramic material processing.
1.2 Laser preheating assisted grinding
Earlier, scholars from Purdue University proposed laser preheating assisted grinding.
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This method is to focus a laser beam with enough energy and irradiate it to the appropriate part of the ceramic material to be processed, preheat it in a relatively short time.
so that the surface of the ceramic material will be vaporized or melted to promote the change of metallographic structure and generate considerable thermal stress, improving the fracture toughness of the ceramic material, and make it change from brittle failure to plastic deformation, thus removing the surface material of the workpiece.
Some scholars have pointed out that it does not need for mold fixation in the process of ceramic material processing, and non-contact grinding is used.
The processing of three-dimensional complex shaped material can be done by controlling the focusing position of the laser beam on the surface of the ceramic material.
During laser preheating, zirconia ceramic material will change from brittleness to plasticity. During grinding, the microcrack expansion caused by brittleness will be reduced, improving the roughness of hard and brittle materials.
1.3 ELID Mirror Grinding Technology
ELID new technology that successfully developed in Japan in the early 1990s is a kind of processing method of precision ceramic.
It is mainly uses diamond grinding wheel with micro abrasive cast iron fiber bonded by utilizing weak electrolysis to make the metal bonding agent on the surface of the grinding wheel continuously ionize and dissolve, generating a passivation film that can prevent the grinding debris from adhering to the grinding wheel, increasing the self sharpening of the grinding tool.
Choosing appropriate bonding agents can effectively achieve mirror grinding. Later, scholars improved their technology by using several micrometers or even submicron sized diamond particles for ELID grinding of ceramic materials and obtaining the mirror surface with high precision and low surface roughness that can replace grinding and polishing within a certain range.
ELID grinding technology is used for form grinding of brittle materials such as tungsten carbide, ceramic materials and optical glass, achieving mirror grinding, greatly improving the quality of the surface which roughness can reach the nanometer level.
In the high speed grinding process, it can avoid the errors caused by secondary clamping, and the processing efficiency can be significantly improved, especially when processing the hard materials with taper, which can effectively eliminate taper errors.
4 Ultrasonic grinding
Ultrasonic grinding mainly impacts and polishes the workpiece to be processed with the ultrasonic and vibrated tools to drive the abrasive suspension between the workpiece and the tool, making the local materials to be eroded into powder, achieving the purpose of perforation, cutting, grinding and polishing.
This technology has gone through several decades of development and has formed a series of theoretical foundations and practical values through discussions by domestic and foreign experts and scholars.
Ultrasonic grinding technology does not reply on the conductivity of ceramic materials, nor have corresponding thermal physical effects. Moreover, there is no organizational change on the surface of ceramic workpieces, and residual stress and burns occur after processing.
The macroscopic force during the machining process is relatively small, suitable for precision machining of hard and brittle materials with various shapes, sizes, and complex requirements that are not conductive.
The ordinary and ultrasonic assisted grinding on zirconia ceramics were done by different grinding parameters. Experimental comparison shows that grinding force of zirconia ceramics decreases significantly with the increase of grinding speed during the ordinary grinding,while ultrasonic grinding does no show significant changes. Ultrasonic grinding depth can reach 25 μ m. which is higher than ordinary grinding.
Dr. Cai have studied the zirconia ceramic processing from the perspectives of grinding tool particle size, grinding tool speed and grinding thickness.
The research showed that this method features high removal rate, high processing accuracy and high economic benefits. Grit 240#, grinding tool speed 1000mm/min, feed speed 3mm/s, grinding thickness 0.1mm, these parameters are the best, and the surface roughness of ceramic is Ra=3.2 μ m.
Compared with electric discharge, electrolysis and laser technologies, ultrasonic grinding does not rely on material conductivity and does not have thermal physical effects, making it particularly suitable for micro processing of hard and brittle materials such zirconia.
2 Diamond wheels for processing zirconia ceramics
Zirconia ceramic materials is difficult to machine, with high hardness and brittle. Diamond grinding wheels are used for grinding zirconia. There are resin bond, vitrified bond, metal bond and electroplaed bond. Different bond are used for different ceramic materials and processing requirements.
Electroplated diamond grinding wheels are usually used for grinding for special purpose, and are mostly used for the production of small and irregular shaped grinding tools.
The coating is particularly thin and the life is relatively short. In addition, electroplated diamond grinding tools have a wide range of roughness and relatively low processing accuracy.
Dr. Meng adopted a ring-shaped electroplated diamond grinding wheels with a length of 2.25mm, diameter of 0.5mm and grit of 0.64 μm which was used for grinding LT55 ceramic under certain process conditions.
And then the surface morphology is relatively complete and the surface roughness can reach 0.172μm. Dr. Tong conducted an experimental comparison: When new electroplated diamond grinding wheel grinding, the surface roughness of the ceramic workpiece is relatively high, but after 160h, the surface roughness can reach Ra=1.6μm.
After another 200h, the surface roughness can reach 0.4μm. Therefore, the grinding whee can be used for rough grinding between the new wheel and 300h after grinding, and can be used for precision grinding later.
Vitrified bond diamond grinding wheels have good heat resistance and wear resistance, easily to be controlled machining accuracy and to be dressed. They are suitable for grinding materials to be difficult machined.
With the improvement of matching technology and emergence of high speed and high rigidity grinding machines and specialized grinding fluids, the applications of vitrified bond diamond grinding wheels are wide.
However, vitrified bond diamond diamond grinding wheels with high brittleness and poor impact resistance can damage the workpiece due to the improper control. In terms of processing, some scholars use the vitrified bond diamond grinding discs with both sides with the average particle size of diamond is 9μm, concentration 100% to process the alumina ceramic materials.
The results indicate that the roughness reaches Ra=0.164μm. In another experiment, diamond grinding wheel with 120# and speed of 170m/s are used, the proportion of surface cracking of the workpiece decreased from 48% at 25m/s to 12%.
Another experiment, vitrified bond diamond grinding wheels are used for grinding engineering ceramics at a speed of 160m/s, achieving a high grinding ratio of 5100 times.
Professor Tong’s research shows that under constant pressure grinding conditions, the removal rate of alumina is the highest and the that of zironia is the lowest due to the sharp edge of the grinding wheel in the early stages of grinding.
With the small fracture toughness of alumina ceramics, cracked and broken chips will occur , forming grain boundary damage when grinding. Therefore, the removal rate of grinding is higher. But zirconia has a large fracture toughness, strong ability to resist cracking tension, resulting in a mixture a plastic flow and cracked and broken damage, so the grinding removal rate is low.
Research has shown that the diamond grinding wheel with the average grain size less than 25μmis used for grinding in the plastic mode, thereby eliminating surface crack defects.
There is a large amount of grinding heat when zirconia ceramics grinding. For the resin bond diamond grinding wheel, it will be resin carbonized black edges. Moreover, the grinding wheel has short life , thus increasing the costs.
Metal bond diamond grinding wheels can easily cause tool blockage, and the abrasive grains cannot fall off in a timely manner after blunt grinding, resulting in poor self sharpening. In the other engineering ceramics grinding, research has shown that diamond grinding wheels with a speed of 160m/s is used for silicon nitride ceramics, the grinding efficiency is doubled compared to that of 80m/s. and the grinding wheel life is 5 times that of 80m/s and 7 times of that 30m/s, and obtaining the good surface quality.
The grinding speed of metal and resin bond is relatively low, usually between 12-50m/s, grit in the 80-W40. The diamond concentration is 50-100% for resin bond wheels, and that is 75-150% for metal bond wheels.
Conclusion of Vitrified Bond Diamond Wheel for Grinding Zirconia Ceramics
In recent years, engineering ceramics and functional ceramics have become one of the focuses, especially zirconia ceramic materials which have been a hot research topic for scholars. There is a significant process after numerous studies and explorations for zirconia ceramic grinding.
However, zirconia ceramic is a hard and brittle material, the processing efficiency will be further improved during grinding due to its features. Vitrified bond diamond grinding wheels features high strength, high hardness and high machining accuracy, and are suitable for high speed and high precision grinding machines.
It will be the first choice for zirconia ceramics grinding in the future. In addition, vitrified bond diamond grinding wheels with ultra high speed are used for integrating and automation precision grinding zirconia ceramic material on high precision grinding machines, which will improve the precision of the ceramic surface, reduce the microcracks, greatly improve the processing efficiency of zirconia ceramics.