Research On Design,Additive Manufacturing And Grrinding Performance Of Structured Grinding Wheel

Additive Manufacturing(AM)can be applied to fabricating grinding wheels(GWs)with three-dimensional structures for an enhanced cooling efficiency,increased porosities to accommodate grinding debris,reduced grinding forces and temperature,improved surface quality of a ground workpiece,and increased life of the structures.This dissertation focuses on the design and fabrication of structured GWs by AM.The design is based on the grinding process with two principles of grinding force stability and cooling consistency,while the fabrication is mainly on the formation characteristics and quality optimization.The dissertation also investigates the influence of processing parameters in Selective Laser Melting(SLM)on the formation characteristics of diamond GWs,the relationship between the diamond spatters and the balling phenomenon,the formation mechanism of diamond spatters,and the influencing mechanism on the formation of GWs.A hybrid SLM/Sintering technique is proposed to fabricate structured GWs of a metal bond whose grinding performance is evaluated.A theoretical model of grinding force is established based on the influence of the GW structures on the uncut chip thickness in the grinding zone for the structured GWs.With the consideration of the GW structures on the heat partitioning coefficient in the grinding zone,a grinding temperature model is established.Calculations on the grinding forces show that the boundary length of the abrasive cell in the grinding zone directly affected the grinding force stability.The variation of the pore structure along the circumferential direction influences the consistency of the cooling effect that may be enhanced with an increased pore structure area on the abrasive cell.A design principle for structured GWs is proposed with the consideration of both grinding force stability and consistency of cooling effect.The dissertation further investigates the influence of the SLM processing parameters on the formation characteristics of diamond GWs,and establishes a relationship between the balling materials and the surface morphology,porosity,and flexural strength.The materials balling is a key factor affecting the GW’s formation characteristics.The GW porosity is decreased first and then increased slightly with laser linear energy density(LED).The flexural strength of the as-built GW is decreased with the increase of porosity with the maximum of 213.37 MPa.The effects of the coated diamond grains,remelting strategy,and composite bond material on the GW formation are studied.The balling size is decreased when using the coated diamond grains,leading to a decrease in porosity but an increase in flexural strength.The remelting strategy also reduces the balling size but brought a limited increase in flexural strength.It has been found that an addition of Ni Cr powders improved the bonding state of diamond grains and increased the hardness,enhancing the brittleness of the bond materials.This dissertation studies the spattering behaviors of diamond grains by analyzing the gas-solid interaction and the gas-solid-liquid interaction among the plume,diamond grains,and melt pool,revealing the formation mechanism of the diamond spatter.The results demonstrate that the ejected plume and the ambient gas flow are the main causes of the diamond spatters.The ambient gas flows toward the melt pool due to the ejected plume,entraining the diamond grains.The dynamic plume blows away the diamond grains around and inside the melt pool leading to diamond spattering as overcoming the surface tension.The influencing mechanisms of the diamond spatters on the GW formation are revealed through the study of surface morphology evolution.The diamond spattering causes the agglomerated bond material powders and diamond/powder,denudation zone,and impact zone on the powder layer,leading to an uneven powder layer,which may evolve into balling materials after material deposition layer-by-layer.The balling mechanisms of GWs caused by diamond spattering can also be applied to metal matrix composites(MMCs).Reducing the reinforcement size and volume percentage,and improving the wettability of the metal matrix can suppress the spattering effect.This dissertation proposes a hybrid SLM/Sintering technique to fabricate diamond GWs in SLM by studying the influence of sintering temperature on the GW properties,including porosity ratio,flexural strength,and wear resistance.The grinding ratio of the sintered GWs is greatly enhanced.The feasibility of the hybrid SLM/Sintering technique is researched by fabricating the abrasive segments with both orthogonal and rhombic structures for an enhanced flexural strength and elastic modulus.The structured GWs with the three-dimensional V-profile grooves and internal orthogonal structures are fabricated by the hybrid SLM/Sintering technique,and compared against a sintered diamond GW in terms of grinding performance on the Ti6Al4 V workpiece.The results indicate that the structured GW with V-profile grooves can effectively reduce the grinding forces,improving the workpiece surface integrity.The hybrid SLM/Sintering technique provides a new strategy for the fabrication of diamond GWs.