Research On Evaluation Of Grain Retention Of Metal-Based Diamond Tools Based On Discrete Element Method

Sintered metal-based diamond tools are widely used in high-efficiency precision machining of hard and brittle materials due to its wear resistance and durability.During processing,the early abnormal shedding of diamond grains seriously affects the processing quality,tool life and consumption.It becomes a bottleneck problem for the promotion and application of these tools.A basic premise of how to improve the retention force of the abrasive grains is to find a method for evaluating the retention force of the abrasive grains effectively.For improving the quality of diamond tools,it is of great significance to study the evaluation method for evaluating the retention force of abrasive grains.In this paper,the discrete element method is proposed to carry out numerical analysis on the evaluation method for evaluating the retention force of abrasive grains.Firstly,the discrete element model of diamond segment is constructed,by focusing on solving the problem of the chosen of contact model and the calibration of all the parameters in the model.Then the model is used to analyze the limitation of the bending strength method which is the existing evaluation method for the retention ability.Then,a DEM 3D model of single grit shearing test is constructed to analyze the factors of the critical separation force of the abrasive/matrix interface,and reveals the root of excessive dispersion of the test results.On this basis,the discrete element model of the single-grit-scratching is established,and the factors of constant deep scratching and deepening scratching are studied.And then the rationality of evaluating the retention force of the abrasive grain by using the deepening scratching method was discussed,and the attention points were given.Focusing on the above research idea,the main work and conclusions of this paper are summarized as follows:(1)The combination of contact bond and parallel bond between particles is used to describe the quasi-brittle property of diamond segment in DEM model.A stepwise inversion method is proposed to calibrate the mesoscopic parameters of matel-matrix contained multi-components.It is proposed to construct a discrete element model of diamond segment by identifying two sub-models and the bond between diamonds and matrix.The model of diamond segment contained matrix of Co-Cu-Sn-WC-Ni was constructed,and its reliability was verified.(2)Simulation of the bending testing shows that if the bending strength is used to evaluate the bonding strength between diamonds and matrix in different diamond segment,somepremises must be guaranteed-the contact area between the abrasive grains and the matrix(related to abrasive concentration,particle size,crystal shape)and the position distribution of abrasive grains in different diamond segment is consistent or nearly consistent.(3)The discrete element model of single grit shearing test is constructed and verified.Then it finds that the critical force of the abrasive/matrix interface separation is greatly affected by the geometrical factors such as the protrusion height of the abrasive grains,the orientation(inclination angle and rotation angle),and the shape.The experiment results of the shearing test are quite dispersive.The reason is that the pushing force is loading at a point or a line on the diamond.(4)The discrete element model of single-grain constant-deep-scratching was constructed.And the simulations show that the scratching force of the abrasive grains increases with the increase of scratching depth and scratching speed,and it is less affected by the rotation angle of abrasive grains.The constant-deep scratching method is also not reliable in evaluating the retention froce because of the difficult estimate of the critical scratch depth(critical load),long scratch time and the fatigue effects induced by impacts.(5)The discrete element model of single grit deepening scratching is constructed,and the study shows that this method is insensitive to the geometric factors such as the shape and the rotation angle of the abrasive grains.It is more reasonable to evaluate the retention force of abrasive grain by using the single grit deepening-scratching method.In order to reduce the dispersion of results,it is recommended that the inclination of the abrasive grains should be as uniform as possible during the preparation of the sample,the low-speed scratching should be chosen,and the workpiece material should chosen a hard plastic material.