In recent years, many scholars have applied the diamond grinding method to systematically study the theory and process of plastic grinding of brittle materials of zirconia ceramics, brittle-plastic transition, material properties, cutting force and other parameters. Plastic way surface formation mechanism and geometric accuracy of zirconium ceramic parts, including research and development of related machine tool and grinding wheel technology.
1. Machining of zirconia ceramics:
The machining of zirconia ceramic materials is not only suitable for semi-sintered body ceramics, but also for fully sintered body zirconia ceramics.
The cutting process of semi-sintered zirconia ceramics is to reduce the machining allowance of fully sintered body ceramics as much as possible, thereby improving machining efficiency and reducing machining costs. The researchers conducted cutting experiments on zirconia ceramics and alumina ceramic semi-sintered bodies at different temperatures using various tools.
In the test, according to different machining requirements of zirconia ceramics, dry cutting and wet cutting methods were adopted, and valuable research results were obtained.
2. Grinding and polishing of zirconia ceramics:
The grinding and polishing of zirconia ceramics is a super-finishing method that uses free abrasives to finely remove the surface material to be processed to achieve the machining effect. In the ultra-finishing and finishing of ceramic materials, especially in the precision machining of ceramic balls for ceramic bearings, grinding and polishing have an irreplaceable position.
Optical materials such as optical glass and sapphire, semiconductor materials such as silicon wafers and GaAs substrates, and ceramic materials such as zirconia ceramics and alumina ceramics are mostly processed by grinding and polishing.
From the perspective of material removal mechanism, grinding is a machining method between brittle failure and elastic removal of zirconia ceramics, while polishing is basically carried out within the elastic removal range of materials.
Grinding and polishing are generally only used for the final process of zirconia ceramic ultra-finishing due to the small removal of zirconia ceramic materials and low machining efficiency.
The removal rate of zirconia ceramics processed by grinding and polishing has a great relationship with the toughness of the zirconia ceramic materials to be added. The higher the toughness of zirconia ceramics, the lower the machining efficiency of zirconia ceramics.
3. ELID grinding of zirconia ceramics:
The ELID grinding technology of zirconia ceramics is a new grinding process. DC pulse current is applied to make the metal bond of the grinding wheel as anode produce an anode dissolution effect and be gradually removed, so that the abrasive particles that are not affected by electrolysis protrude from the surface of the grinding wheel, so as to realize the dressing of the grinding wheel and keep the grinding wheel during the machining. sharpness.
The ELID grinding technology of zirconia ceramics has successfully solved the problem of dressing the metal-based superabrasive grinding wheel. At the same time, the micro dressing effect of on-line electrolysis enables the ultra-fine-grained grinding wheel to maintain the sharpness during the grinding process. Grinding creates favorable conditions.
Zirconia ceramics were ground on silicon wafers with #8000 (maximum abrasive grain diameter of about 2µm) cast iron-based diamond grinding wheels, and a high-precision surface with a maximum surface roughness of 0.1µm was obtained. Precision grinding of ceramic materials with bronze-based grinding wheels achieves the same results.
Using ELID grinding technology to achieve mirror grinding of brittle materials such as cemented carbide, ceramics, optical glass, zirconia ceramics, etc., the grinding surface quality is greatly improved compared with that of ordinary grinding wheel grinding under the same machine tool conditions. The surface roughness Ra value has reached nanometer level, and the grinding surface roughness of silicon glass-ceramics can reach Ra0.012µm.
This shows that the ELID grinding technology can realize the ultra-finishing of the surface of the brittle material of zirconia ceramics, but there is still an oxide film on the surface of the grinding wheel or the non-electrolyzed material on the surface of the grinding wheel is pressed into the surface of the workpiece, resulting in the glaze of the surface layer and The problems of changing the ratio of electrolytic grinding fluid need to be further studied and solved.
4. Plastic machining of zirconia ceramics:
The traditional zirconia ceramic material removal process can generally be divided into two types: brittle removal and plastic removal.
In the process of brittle removal of zirconia ceramics, material removal is accomplished by the expansion and intersection of cracks; while plastic removal is in the form of shearing chips to generate plastic flow of material.
For metal machining, the plastic cutting mechanism is easy to achieve, while for zirconia ceramic brittle materials such as engineering ceramics and optical glass, the use of traditional machining techniques and process parameters will only lead to brittleness removal without significant plastic flow. Under the action of extreme cutting force, brittle fracture occurs in the large and small particles of the material, which will undoubtedly affect the quality and integrity of the machined surface.
It can be seen from the machining practice that when machining brittle materials such as zirconia ceramics, a very small depth of cut can be used to achieve plastic removal, that is, the removal mechanism of zirconia ceramic materials can change from brittle failure to plastic deformation under small removal conditions.
The latest progress in the ultra-finishing technology of zirconia ceramics has made it possible to control the machining feed to a few nanometers, so that the main removal mechanism of brittle material machining may change from brittle failure to plastic flow.
The plastic chip deformation process can significantly reduce the subsurface (surface) damage. The new machining technology of zirconia ceramic hard and brittle materials is called plastic machining.
Ultrasonic machining method of zirconia ceramic material
Ultrasonic machining of zirconia ceramics is to apply ultrasonic vibration to the machining tool or the material to be processed, add liquid abrasive or paste abrasive between the tool and the workpiece, and press the tool against the workpiece with a small pressure.
During the machining of zirconia ceramics, due to the ultrasonic vibration between the tool and the workpiece, the abrasive particles suspended in the working fluid are forced to continuously impact and polish the surface to be machined at a large speed and acceleration. pressure effect, resulting in a material removal effect.
Ultrasonic machining of zirconia ceramics is combined with other machining methods to form various ultrasonic composite machining processes, such as ultrasonic turning, ultrasonic grinding, ultrasonic drilling, ultrasonic threading, ultrasonic vibration honing, ultrasonic grinding and polishing, etc.
The ultrasonic composite machining method is more suitable for the machining of zirconia ceramics, and its machining efficiency increases with the increase of the brittleness of zirconia ceramics.
The researchers studied the ultrasonic grinding of zirconia ceramic materials, which nearly doubled the machining efficiency of ceramic materials;
When machining alumina ceramics and zirconia ceramics, ultrasonic vibration is applied to the tool and the workpiece at the same time, so that the machining efficiency is increased by 2 to 3 times;
Ultrasonic vibration is applied to the drill bit for deep hole machining, which greatly improves the inner surface quality of the hole and the roundness of the hole.
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