High-effiency Grinding With Porous Composite-bonded CBN Wheels

Due to their high mechanical and thermal strength, excellent corrosion resistance and good fatigue resistance, nickel-based superalloys are widely used in aerospace, shipbuilding and chemical industries. However, the high strengths at elevated temperatures, high work hardening, and low thermal diffusivity are generally associated with the poor grindability of nickel-based superalloys, such as high grinding forces, high temperatures leading to possible thermal damage on the workpiece, and critical wheel wear during grinding with conventional abrasive wheels. At present, creep feed grinding with continous dressing using high porosity corundum wheel is still applied in areoengine industry to guarantee the machining quality of turbine blade roots. To meet the higher requirement of machining efficiency, high-efficiency deep grinding(HEDG) conbined with CBN superabrasive wheels has been developed in last decades and considered as the most promising grinding process to increase the manchining efficiency of nickel-based superalloys. However, the undeveloped manufacture technology of high performance CBN wheels and supporting grinding process have been greatly restricted the application of HEDG in manchining of nickel-based superalloys.For HEDG, a high porosity is expected for efficient chip and grinding fluid storage, and also a sufficient mechanical strength. As well known, the porosity increase is a disadvantage to the mechanical strength. As a promising pore forming agent, alumina bubbles have been firstly induced into the abrasive layer to fabricate a new type of porous composited-bonded CBN wheels in this paper.The main creative contents in this paper are as follows:(1) The raw materials were chosen and the sintering parameters were optimized. The fabricating process of porous composite-bonded CBN wheel working layer segments combined with induced brazing techonology was detailly introducd. Based on the microstructure of porous composited bond and the bonding interface forming between the active filler alloy and CBN grain, prahite particles and Al2O3 bubbles, the fabricating mechanism of porous CBN wheel segments has been discussed. Enough bonding strength of CBN grains has been achieved.(2) The influence of wheel texture such as pore size, porosity, graphite contents and CBN grains on bending strength of porous composited segments has been studied through experimental study and FEM analysis. A solution of the pore size matching for the grain size was put forward.(3) A porous CBN wheel with high porosity and high mechanical strength was fabricated. The grinding performance of porous CBN wheel grinding GH4169 nickel alloy was preliminary assessed by comparing with the vitrified CBN wheel and deeply evaluated in terms of grinding temperature, specific grinding force, specific grinding energy, wear characteristics and gound surface quality. Results imply the potential and promissing application of developed porous CBN wheel in HEDG.(4) To improve the homogeneity of wheel texture, a porous CBN wheel with multilayer defined grain distribution has been developed based on 3D-uniform distribution technology of CBN grains and bubbles. The specific grinding energy, grinding ratio, wheel dulling process and thermal demage with blunt wheel were investigated. A high material remove rate has been sucessfully achieved during high-efficiency deep groove grinding of GH4169 with lower specific energy and good surface integrity, which verify that the application of porous CBN wheel combined with HEDG could greatly improve the machining efficiency.