Development of an intelligent electrolytic in process dressing (ELID) grinding system 6

Conclusions Chapter Conclusions 6.1 Main contributions of the research ELID grinding is under research interest for last two decades and has evolved considerably since. This current research work in ELID grinding mainly composed of three major parts; development of a sensor integrated ELID grinding machine for both flat and curvilinear surface machining; optimizing the dressing power by monitoring the grinding condition; development of in-process truing system for the grinding wheel by applying controlled dressing. The main contributions of this study are reviewed as follows: 1. A sensor integrated intelligent machine tool has been developed and its performance has been evaluated. Two types of sensors, namely inductive sensor and laser sensor, were implemented to measure the metal bond profile and the wheel outer profile respectively. The machine is capable of grinding both flat and spherical surfaces. Surfaces with good optical properties (average surface roughness Ra < 20nm) were successfully achieved with this machine. 2. A new and essential methodology has been developed to compensate the tool wear in ELID grinding during spherical surface machining. Tool wear is one 115 Conclusions of the major concerns in ELID grinding because of its mechanism of wheel dressing which produces form error on the machined surface. That is why this proposed tool wear compensation method plays a vital role on the form accuracy of the machined surface. The system uses a touch probe and CMM (Co-ordinate measurement method) algorithm to measure machined surface radius, if the radius of the curved surface is deviated from the desired value then new cutting path is generated by considering the wheel wear. The process continues until the desired radius is achieved. The profile accuracy has been found to improve significantly when the tool wear compensation is used during grinding. 3. A new concept of controlled voltage dressing by monitoring the grinding condition has been implemented and its performance has also been evaluated. Conventional ELID grinding applies constant voltage across the dressing zone without monitoring the grinding wheel condition. This may lead to overdressing of the wheel which eventually will shorten the tool life. In this study grinding wheel condition has been assessed by continuously monitoring the grinding force ratio and the dressing voltage has been adjusted accordingly. The comparison result between the new concept and conventional grinding is found to be very much optimistic. The new methodology reduces the tool wear notably (almost 50%) in comparison to the conventional ELID dressing method. However similar surface characteristic (average surface roughness, peak to valley surface roughness) have been observed in both cases. Dressing 116 Conclusions current has also been found to be more stable and uniform in this new form of ELID grinding. 4. Truing of the grinding wheel is crucial in precision manufacturing, because non-uniform wheel may lead to unstable grinding and bad form accuracy on the machined surface. In ELID grinding the wheel is trued by applying electrical discharges (EDM method). This method has two bad effects; it creates thermal damages on the wheel surface and an extra attachment is required to carry out the EDM truing. In order to address these problems author has introduced a novel concept of wheel truing method in ELID grinding, where the pulse width of the ELID power supply is controlled inprocess by continuously monitoring the wheel profile. An inductive sensor has been used to measure the wheel profile. Proper signal conditioning has been carried out by considering the convolution effect between the wheel and electrode. A digital trunig controller has been designed, developed and assessed. The wheel profile has been found to improve appreciably as the controlled dressing is applied, moreover substantial improvement in wheelworkpiece contact is observed when in-process truing in ELID grinding is carried out. 6.2 Recommendations for the future work This thesis introduces a new design concept of ELID power supply. The proposed power supply has two objectives: one is to change the voltage amplitude according to the change in grinding condition and the other objective is to control pulse width by monitoring the grinding wheel profile. Currently these two objectives are not integrated on a single 117 Conclusions power supply; therefore the work can be extended to the design and development of a ELID power supply integrating the above mentioned two prime objectives. In ELID grinding the gap between the wheel and electrode varies as the wheel wears off. In this study author has implemented laser sensor to monitor the wheel outer circumferential profile. This sensor feedback can also be used as a feedback signal to adjust the gap (electrode/wheel) to its optimum position. Another extension of this work could be the development of a motorized gap control mechanism for ELID grinding. Injection electrode was used in this study, because experimentally it was observed to perform better over conventional electrodes [51]. An extensive analytical work can be carried out to compare the fluid flow performance between conventional electrode and injection type electrode. It is essential for the ELID grinding user to have proper assistance on selecting both ELID and grinding parameters such as in-feed/cycle, feed speed, voltage, pulse frequency, etc. All these parameters selection are strongly dependent on workpiece material, bond material etc. A further extensive experimental study can be carried out on developing an intelligent knowledge base for ELID grinding, which may assist the users to select the proper parameters during ELID grinding. 118 . in ELID grinding mainly composed of three major parts; development of a sensor integrated ELID grinding machine for both flat and curvilinear surface machining; optimizing the dressing power. dressing power by monitoring the grinding condition; development of in- process truing system for the grinding wheel by applying controlled dressing. The main contributions of this study are reviewed. during grinding. 3. A new concept of controlled voltage dressing by monitoring the grinding condition has been implemented and its performance has also been evaluated. Conventional ELID grinding