The Development And Research Of Key Applied Technologies In High Speed Deep Grinding Process

Advanced engineering ceramics have been extensively used as structural materials in modern manufacturing industries due to their excellent properties,such as high hardness at both ambient and elevated temperatures,low thermal expansion, and excellent wear resistance and chemical inertness.Nevertheless,the high hardness and brittleness also make the machining of the ceramics very difficult.As a result,the machining process is associated with a high cost.Grinding is a commonly used machining process for engineering ceramics.Therefore,the improvement of efficiency in ceramics grinding shall greatly reduce the total machining cost.In the past decades,a great attention has been paid to the development of high speed grinding technologies.In a high speed grinding process,the increase in grinding wheel velocity can significantly reduce the undeformed chip thickness per grit,and thus decrease the grinding force.This enables the improvement of ground surface quality and the elevation of material removal rate.High speed deep grinding (HSDG) is a process which integrated with high grinding velocity and large depth of cut in order to achieve high material removal rate while maintaining a high surface quality.The HSDG of ceramics is often accompanied with large grinding force and high grinding temperature.The deterioration of machining conditions thus accelerates the wear of the grinding wheel.Therefore,the active abrasives quickly lose their cutting abilities,and the machining quality is deteriorated.It is thus important to keep active abrasives in good cutting condition throughout the HSDG grinding process.Previous investigations have shown that electrolytic in-process dressing(ELID) is a good approach for continuously maintain the grit sharpness during grinding.However, this technique was mainly used for dressing the fine abrasive wheels.Several technical issues need to be resolved if the ELID technology is applied to a HSDG process for engineering ceramics.The key issue is how to maintain the ELID efficiency during a HSDG process.In a HSDG process,the increasing wheel velocity strengthens the air barrier around the grinding wheel,which affects the impinging of grinding fluid,thus results in low ELID efficiency and high grinding temperature.This project focused on the developments of key technologies for the HSDG of engineering ceramics,which tackled the key issues mentioned earlier.The technologies included the truing and ELID dressing for metal-bond diamond wheels, and the coolant supply technology.The significant results achieved are summarized below.1) It is challenging to true metal-bond diamond wheels with coarse abrasives directly using the electrical discharge truing(EDT).In this project,the electrical discharge/mechanical hybrid truing method was developed.In this new truing method,the bond material on the wheel surface was firstly removed by EDT, which also lowered the holding strength of the grits.The protruded abrasive grits was then abraded by mechanical removal.EDT and mechanical truing were carried out alternately until the wheel may meet the grinding requirements.Using this method,the coarser abrasive metal bonded wheels were efficiently trued,with a roundness error of smaller than 6μm.2) Mechanical pre-dressing was introduced into the ELID pre-dressing process. Using this approach,the oxide layer formed on the wheel surface was removed,and the electrical current during ELID pre-dressing was enhanced.This has significantly increased the pre-dressing efficiency.Additionally,a control model was also established,which effectively controlled the balance of metal bonded removal and wear of grinding wheel,and maintained the protrusion height of grits as a constant.3) A new electrolysis cathode was successfully developed and used as a core component in the HSDG-ELID system.The application of such a cathode has solved a long-standing problem,which is the low ELID efficiency at relatively high grinding speeds.The comparison between the closed and the conventional cathodes demonstrated that a much higher pre-dressing current,hence an improved ELID efficiency was obtained.In addition,a new electrolytic fluid specifically for dressing bronze-bond diamond wheels was developed,which enhanced the ELID efficiency as well.The comparison between the HSDG processes with and without ELID showed that ELID technology increased the number of effective cutting grits on the wheel surface and improved their cutting abilities,resulting in a decreased grinding force and improved surface roughness.4) A new coolant supply method was developed.This was accompanied with the design and fabrication of a closed Y-type nozzle.The HSDG experiments using the Y-type nozzle and the conventional L-type nozzle indicated that the closed Y-type nozzle improved the cooling conditions in the grinding zone,which enabled a higher materials removal rate.Additionally,the use of the new nozzle could better clean the wheel.This helped to maintain the wheel in a stable cutting condition and thus improve the quality of grinding.