Experimental Study On Dressing Of Ductile Iron Based CBN Grinding Wheels By Lost Foam Casting Process

Austenite-bainite ductile iron based c BN grinding wheels fabricated by Lost Foam Casting(LFC)had high strength and good grain retention properties.However,this kind of c BN grinding wheels was difficult to dress because they have big gringding allowance due to their low dimensional accury.Big size of c BN grains were used in this kind of grinding wheels.Also,the austenite-bainite ductile iron has high strength and hardness.In this paper,the performance of electrolytic dressing on ductile iron based c BN grinding wheels with big size of c BN grains were mainly studyed,on account of the good electrical conductivity of cast iron bond.Mechanical dressing and mechanical-electrolytic dressing were studyed as well.The grinding performance of c BN grinding wheels dressed by different dressing methods was studyed.The experimental results revealed that the optimum process parameters for electrolytic dressing method were as follow: the gap S=1mm,the concentration W=30%,the current I=1.5A,the duty cycle Y=20%,the period T=1000?s.The electrolytic dressing process was hard to continue after the dressing process conducted for 30 mins due to the inactivating.Therefore the desired machining accuracy of c BN grinding wheels cannot be achieved by electrolytic dressing method.By using Si C roller to dress the wheel,the highest dressing efficiency was obtained when the speed ratio q=+0.3.The dressing efficiency decreased with the increase of the dressing time.The desired accuracy of the wheel was obtained after being mechanical dressed for 120 mins.However,by using mechanical-electrolytic dressing method or electrolytic-mechanical-electrolytic dressing method the dressing time needed was only 75 mins.And more importantly,the number and the height of protrusion of the c BN grains were much bigger in the grinding wheels dressed by electrolytic-mechanical-electrolytic dressing than the ones by electrolytic-mechanical-electrolytic dressing or mechanical dressing.Accordingly,the number of the grains being damaged or abraded or pulled out was much smaller.Under the same grinding parameters,the order of the grinding force,force ratio,and the specific energy of the grinding wheels from high to low was the mechanical dressinggrinding wheel,mechanical-electrolytic dressing grinding wheel and the electrolytic-mechanical-electrolytic dressing wheel.Also the differences between the grinding force,force ratio,and the specific energy increased with the increase of the cutting depth.After grinding 45 mins,the grinding force and force ratio of grinding wheels being dressed by mechanical method or mechanical-electrolytic method began to increase sharply.However,the grinding force of grinding wheel being dressed by electrolytic-mechanical-electrolytic method increased slowly.Its grinding force was still small after the grinding performance had been conducted for 90 mins.The grinding force and force ratio of dull grinding wheels can be reduced by further electrolytic dressing or mechanical dressing with Si C oil stone.The decrement of the force by electrolytic dressing was twice more than by the mechanical dressing.The time when the ground surface of the workpiece began to appeare vibration pattern was delayed in the order of grinding wheel dressed by mechanical dressing method,mechanical-electrolytic dressing method,and electrolytic-mechanical-electrolytic method.It was observed that after grinding performance was conducted for 45 mins obvious metal adhesion and abrasion platform appeared in the c BN of the grinding wheels dressed by mechanical method or mechanical-electrolytic method.On the contrary,most of the c BN grits in the grinding wheels which were dressed by electrolytic-mechanical-electrolytic method were in perfect condition after grinding performance was conducted for 90 mins.