Recovery Of Cutting Capability And Clean Regeneration Of Worn Cemented Carbide Inserts

With the greater demand of cemented carbide tools,the value of the worn cemented carbide tools had attracted a lot of attentions.In this dissertation,it aimed to explore recovery of cutting capability and clean regeneration of worn cemented carbide inserts.Firstly,according to the quality of the worn cemented carbide inserts,they could be divided into three categories:modified,repairing and regeneration utilization.Afterwards,the residual life of worn inserts of modified utilization was evaluated by BP neural network.The results showed that the prediction error of BP neural network was about 10%,which realized the prediction of the residual life.With reasonable processing modes and parameters,the residual life of worn inserts of modified utilization was 1000-1500 m,which indicated that modified utilization was efficiency and reasonable for worn inserts.Next,the cutting performances of worn inserts repaired by welding homogeneous PCBN tool bit were researched.The assessment of the repairing mode was based on the feasibility of technicality,economy and greenness,which was verified by the continuous tuning of hardened steels and intermittent turning of ductile iron.The evaluation indicated that the cutting performances of the welded homogeneous PCBN inserts were better than that of coated cemented carbide tools,meanwhile this utilization mode had better economic and environmental benefits.According to the failure mechanisms of homogeneous PCBN for the machining of hardened steels and ductile iron,the wear resistance and toughness needed to be improved.In order to balance the wear resistance and fracture toughness,the functionally gradient design was introduced to the PCBN composites.Material system was determined through the physical-chemical compatibility analysis between the workpiece and tool material:the matrix was CBN,and the binders were Co,Al and TiC.The graded structure was optimized according to the residual stress distribution under varied thickness ratio and component gradient.The results indicated that a smaller thickness ratio with an appropriate component gradient could improve the mechanical properties.The mechanical impact resistance and cutting performance of graded PCBN were also analyzed,demonstrating that the functionally gradient material performed better.The graded PCBN tool materials starting with CBN-TiC-Al-Co mixtures and having a three-layer symmetrical graded structure were obtained by high temperature high pressure method.The analysis of mechanical properties had been conducted through the optimization of thickness ratio,component gradient and sintering process.In addition,the toughening and strengthening mechanisms were also investigated based on the crack prolongation mode.The graded PCBN composites with a three-layer structure of C1/C4/Cl and a thickness ratio of 0.3 sintered at 1500? for 10 min under a pressure of 5.8 GPa acquired the optimum mechanical properties of flexural strength of 710 MPa and hardness of 36.5 GPa,which were higher than that of the homogeneous PCBN material about 13%and 14%,respectively.Through the XRD analysis,no diffraction peaks of Al and Co were detected,meanwhile,there was no trace of Ti compounds except TiC,illustrating that the reaction could only take place among Al,Co and CBN under this condition.When the sintering temperature was 1350?,the reaction products were AlN and Co2B.The content of AlN was found to increase with the temperature rising to 1450? but the content of Co2B remained stable.The major phase of Al compounds gradually converted to AlB2 when the temperature reached to a high level.At the temperature of 1550?,the diffraction peak of AlN disappeared,but the appearance of AlB2 was harmful to the mechanical strength and hardness.The toughening mechanism of the graded PCBN material could be well characterized by the crack prolongation modes.When the crack propagated in the graded PCBN material from surface to the interior,the path became tortuous,while in the homogeneous PCBN material it was almost flat to the end.In the surface of the graded PCBN material,when the crack extended from binder phases to matrix phase,it would bend and deflect along the grain boundary,enlarging the newly ruptured surface areas and resulting in the intergranular fracture.When the cracks met the CBN grains with smaller size,it would penetrate the grains and then deflect duo to the "pin effect",which strengthened the grain boundary and increased the energy required for rupture as well as promoting the transgranular fracture.Comparing the cutting performance in the continuous turning and intermittent turning between the welded graded and homogeneous PCBN inserts,the tool life of the welded graded PCBN inserts were always longer.When the worn cemented carbide tools could not recover the cutting capability,they would be regenerated.As most of the worn cemented carbide inserts were modified with coatings,so stripping of coatings was mandatory before regeneration to avoid impurities.Due to the low efficiency and long procedure of the current means,the hybrid laser-waterjet technology was adopted for the coating removal to call for the demand of lower energy consumption and less environment pollution.The multi-objective optimization model for energy conservation and high efficiency to achieve the optimum parameters was presented.Compared the single-objective with multi-objective optimization,it was found that the multi-objective optimization could achieve the minimum energy consumption as well as ensuring the efficiency.According to the quality of the substrate after coating removal by hybrid laser-waterjet,it could be seen that the hybrid laser-waterjet technology was more suitable for the coating removal of complex shape tools with the requirement for re-cutting.However,after high temperature oxidation+ball milling,the worn cemented carbide tools could only be used for regeneration of W and Co because of the great damage to the substrate.