Research On Wear Characteristic Of Fixed Abrasive Pad

Fixed abrasive machining technology has been the concern of scholars,with its unique advantages.It has not only universality in the field of application,but also particularity and pertinence because of material differences.The development and performance evaluation of fixed abrasive pad(FAP)have been a hot research topic.And the moderate benignant wear of FAP is the key to the formation of self-conditioning during micro/nano machining process.In this paper,based on the difference of material characteristic,FAP wear characteristic was studied quantificationally by both the experiment and theoretical analysis.The main research work and results are as follows:(1)Mechanical behaviors of calcium fluoride(CaF2)was researched by indentation and scratch experiments.The process of brittle-ductile transition of CaF2 crystal was investigated.The hardness of CaF2 crystal is 1.58 GPa,the fracture toughness is 0.527 MPa·m0.5,the theoretical critical depth is 0.806 ?m,and the actual critical depth from plastic domain to microcrack domain is 1.623 ?m.The indentation size effect indicates the chemical softened layer has a catalytic role on the cutting behavior to a certain extent.(2)The multi index optimization of FAP characteristic and process parameters on soft-brittle materials processing was studied by orthogonal exper iment.The effects of FAP hardness,lapping pressure,pad speed and slurry pH on material removal rate(MRR),FAP wear rate(PWR),wear ratio,surface quality,retention rate of material removal and FAP wear unevenness were investigated in fixed abrasive lapping of CaF2 crystal.In addition,the material processing properties,FAP wear characteristic and self-conditioning were analyzed.The optimal parameters are FAP hardness ?,pressure 3 psi,pad speed 60 rpm and slurry pH 9,which MRR is 6.23 ?m/min,retention rate of MRR is 90.3% in thirty minutes,wear ratio is 38.2,and achieves high efficiency and low damage lapping effect.Meanwhile,FAP wear is stable with a better s elf-conditioning.PWR is smaller,and the service life of FAP is longer.(3)Based on different hardness,elastic modulus and material removal mechanism between hard-brittle materials and soft-brittle materials,material removal and FAP wear mechanism were studied in fixed abrasive lapping of hard-brittle materials.The dynamic influences of K9 glass lapping and FAP wear were explored.The results show that FAP with copper powder has a better self-conditioning and wear resistance,a higher MRR and wear ratio.The optimal parameters are slurry pH 9,lapping pressure 3 psi,pad speed 60 rpm,which wear ratio w as maximum and the stability is good,FAP has an excellent utilization and self-conditioning ability.There are two cycles in fixed abrasive lapping: 1)“formation-removal” cycle of the metamorphic layer,2)“swelling-wear” cycle of FAP matrix.The former affects material removal rate and surface quality.The latter affects processing performance,self-conditioning and service life of FAP.(4)Based on "swelling-wear" cycle of FAP matrix,the formation model and wear model of the swollen layer were established,and wear mechanism was also analyzed.The relationship between FAP wear and FAP properties,material properties,and process parameters was explored.A “swelling-wear” equilibrium model was established,and the causality affecting the balance was analyzed.The results show that the copper content,the additive concentration and the diffusion coefficient of the additive affect the swelling rate of the matrix.The pressure,relative velocity and the properties of FAP and workpiece affect FAP wear rate.FAP wear resistance increases and FAP wear rate decreases,with the increase of the matrix hardness.FAP wear rate increases,with the increase of the workpiece hardness,which is consistent with the previous experimental results.(5)Wear nonuniformity of pad surface was investigated.The model of pad wear was established,and the effect of lapping parameters on pad wear nonuniformity was studied.As the results indicated,the greater the rotate speed ratio between the workpiece and pad is,the more seriously the central region on pad wear.When the form of straight-line swing is sine,the rotate speed ratio is 1.11,the swing scope coefficient is 2,and the swing frequency coefficient is 0.1~0.2,wear tracks get increasingly complex,and the uniformity of pad wear is better.In addition,an optimization method of pad shape was proposed in order to achieve relatively better well-distributed wear.A better hold of surface contour is obtained,and the online processing time after conditioning is prolonged.