An internal cooling grinding wheel:From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy’s final service performance.The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy.Still,managing cooling,lubrication,and chip removal are difficult.This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy.The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel.The structure of the grinding wheel was optimized using computational fluid dynamics(CFD).The flow field in the grinding area achieved the highest overall flow rate,distribution homogeneity,and effective exit flow when the internal flow channel had four throughholes.The exit for the inner runner is located at the abrasive edge and diamond staggered pattern.Single-layer brazing was used to create cubic boron nitride(CBN)abrasive rings with various abrasive patterns.The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model.A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169.The results show that,under the same conditions,a diamond-shaped staggered pattern obtains lower grinding temperature,lower surface roughness,better surface morphology,and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern.The average effective flow rate calculated by CFD is increased by 42.3%when compared to the disordered pattern.In the experiment,compared to the disordered arrangement,with the increase of grinding wheel’s rotating speed and coolant pressure,the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2%and 51.7%respectively,and its surface hardening degree decreases by 11.1%and 11.7%respectively.

Experimental investigation on heat transfer enhancement of mist/air impingement jet

The heat transfer performance of a mist/air jet impingement on a constant-heat flux surface was experimentally investigated.Two objectives were outlined in the current study.The first objective is to assess the effects of mist/air volumetric flow rate ratio,impinging mode and heat flux on the heat transfer characteristics of free mist/air jet impingement.The second objective is to assess the effect of swirl flow induced by the spinning grinding wheel on the mist/air jet impingement,simulating the heat transfer process on a grinding work-piece surface subjected to the mist/air jet impingement.The results show that the addition of dilute water droplets to air flow results in significant heat transfer enhancement.Once the mist/air ratio is increased to a certain value,the increase of heat transfer with the mist/air ratio becomes slow.For a given mist/air ratio,as the increase of heat flux,the contribution of droplet evaporation to the overall heat transfer is weakened relatively,resulting in a decrease of heat transfer enhancement in comparison to the lower heat flux case.The heat transfer coefficient in the stagnation region for the oblique jet is much lower than the normal mist/air jet impingement,while in the region away from the stagnation,the local heat transfer coefficient for the oblique jet is higher than the normal jet.As regards as the mist/air jet impingement in the vicinity of grinding zone is concerned,when the jet impinging direction is consistent with the rotating direction of rotating disk,the swirl flow induced by the rotating disk could entrain more droplets to enter the jet impinging stagnation zone,which is beneficial to convective heat transfer enhancement.Furthermore,as the rotational speed of disk increases,the temperature deceases in impinging jet stagnation zone.