Development Of Vitrified Bonded Diamond Lapping Plate And Its Lapping Characteristics For Sapphire Substrate

As a kind of photoelectric crystal material with good optical,physical and chemical properties,sapphire（Al₂O₃）is widely used in military industry,aerospace industry,biomedical and many fields of people’s livelihood.However,in view of the high hardness,brittleness and chemical inertia of sapphire,the common free abrasive lapping methods have some disadvantages,such as low efficiency,high cost,unstable precision and quality,which restrict the further development and application of sapphire.Sapphire lapping with fixed abrasive has the advantages of high efficiency,high precision and low environmental pollution,which is very suitable for processing hard,brittle and difficult to process materials such as sapphire.In this paper,sapphire is processed by vitrified bond diamond lapping plate.The performance and processing effect of different physical and mechanical properties of sapphire lapping plate are explored,and the main processing parameters are optimized,in order to achieve efficient and stable flattening of sapphire substrate.First of all,in order to prepare the lapping plate which can be used for high-efficiency lapping of sapphire,two kinds of diamond pellets（1#and 2#）with different physical and mechanical properties were prepared by different pressing processes and formula design with low-temperature Al₂O₃-B₂O₃-SiO₂-Na₂O system vitrified bond,RVD type diamond abrasive and other auxiliary materials,Its hardness,bending strength and porosity are 81.83HRF,70.67 MPa,30.96%and 55.60 HRF,38.28 MPa,34.35%respectively,Then the ratio of the effective contact area between the diamond pellets and the sapphire substrate on the surface of the lapping plate and the area of the lapping plate processing area is taken as the evaluation index,the arrangement of diamond pellets on the surface of the lapping plate was optimized,and a vitrified bond diamond lapping plate based on Archimedes spiral structure was designed.Secondly,the lapping experiments of sapphire were carried out by using vitrified bond diamond lapping plate with different physical and mechanical properties.The effects of different lapping time,dressing cycle,lapping speed and lapping pressure on the processing effect（including material removal rate（MRR）,surface roughness Ra and morphology）and wear ratioηwere systematically studied.The surface morphology changes of the plate before and after lapping,and the lapping performance of the plate for sapphire substrate was analyzed.It was found that the higher the hardness of plate,the higher the hardness of the plate,the greater the material removal corresponding to the unit wear（wear ratio）,and the higher the material removal rate of the workpiece,but the surface integrity of the workpiece after processing was poor,and the surface roughness of the workpiece was larger;In different dressing cycles,the machining stability of 1#plate was better than that of 2#plate,but the self-dressing performance of the two kinds of lapping plates was poor;The wear forms of the two kinds of lapping plates were the same,and there would be abrasive wear,bond breakage and breakage,and abrasive breakage,but the specific degree of wear was not the same.Finally,aiming at the problems of low lapping efficiency,slow renewal rate of abrasive particles and insufficient self-dressing performance in the process of lapping sapphire with self-made plate,a method of lapping sapphire with free abrasive assisted lapping plate was proposed,and a systematic lapping experiments were carried out,and the main processing parameters were optimized by orthogonal experiments,The results show that the MRR of the workpiece is 3.81μm/min and the surface roughness Ra is 0.133μm when W20 particle size SiO₂abrasive was used to lap sapphire under the conditions of lapping speed 100 r/min,lapping pressure 0.345 kg/cm²,abrasive mass fraction 5%,lapping time 15 min and lapping fluid flow 25 ml/min,the MRR of the workpiece increases by 87.7%,the surface roughness Ra decreases by 20%,and the plateηincreases by 109%.