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.

Comparison of roller-spreading and blade-spreading processes in powder-bed additive manufacturing by DEM simulations

The roller-spreading and blade-spreading are main powder spreading methods in powder-bed additive manufacturing.The discrete element method was introduced to simulate nylon powder spreading by both roller and blade spreaders.The two spreading processes were compared from several aspects including particle flow behavior,particle contact forces,forces exerted on spreaders,particle segregation and powder layer density.It is found that powder spreading methods mainly affect the movement trajectory of particles,particle contact forces and forces exerted on spreaders.Complicated dispersion and circulation movement of particles occur inside the powder pile by roller-spreading,while particles have relatively weak dispersion by the blade-spreading.The normal force applied to the roller introduces a compacting effect on the powder pile and creates strong force chains that distribute uniformly in the powder pile.Therefore,the powder bed with higher density can be obtained by roller-spreading in thicker powder layer due to the compacting effect.The blade spreader sustains tangential force mainly,so the blade-spreading process limits its application to thicker powder layer.As the powder layer thickness increases,the roller-spreading is more sensitive to segregation index than that of the blade-spreading.The comprehensive comparison of two spreading processes provides criteria for selecting spreading methods.

Dynamic Study of Nonlinear Optical Properties in Tetrasodium Salt of Copper Tetrasulfophthalocyanine/Water Solution

The nonlinear refraction of tetrasodium salt of copper tetrasulfophthalocyanine in water was investigated by using Z-scan technique at 532 nm with different input energy and different pulse width. We reported the competition between the excited-state refraction and excited-state-thermal-induced refraction. The sign change of nonlinear refraction induced by thermal effect was observed and analyzed. In addition, we found that the excited-state refraction cannot counteract with excited-state-thermal-induced refraction due to different physical mechanism.