Process And Mechanism Of Extrusion Cutting For The Preparation Of Metal Fins

Metal scrap produced during the cutting process is one of the main pollution sources from the industry of metal processing,the recycle of these scraps is of great significance.However,the existing recycling methods were high cost and low efficiency,some of them may even cause secondary pollution,so there are strong demand for new ideas and developments of recycling processes.Forming extrusion cutting(FEC)could directly transform the waste material into useful metal fins instead of chips,avoid the cumbersome processes and high costs in other recycling technologies,and it was a process with wide developing prospect.As a novel metal forming process,the forming mechanism of workpiece material during FEC process is still unclear,leading to the lack of solution and method for many key technical problems.There are two main difficulties in the study.First is the distinct transverse flow of workpiece material from the press area to the fins area during the process of FEC,so the deformation process of material could not be concluded as plain deformation,and the research results based on plane strain state problem could not be used as reference.Second is the free surface on the top of metal fins make the forming results uncertain,which increase the analytic difficulty of mechanism.In this article,study began with the mechanism of metal cutting and on the basis of experiments,using theoretical analysis and finite element modelling simulation to make a systematic research on the forming mechanism of workpiece material during the preparation of metal fins by FEC.Several results were concluded as below.The control theory of metal fin's morphology after the process of FEC has been proposed.Based on the forming principle of extrusion cutting,working parameters which might affect the cross section morphology of metal fins were selected,and the evaluation standard was established,then systemic experiments has been applied with varying parameters.According to the hierarchy theory of forming power,the forming power affected by working parameters were classified into three classes: the raw power class,the secondary power class and the shaping motivation class.Which could clearly clarify the effect rules from the working parameters on the materials during FEC process,and provide theoretical guidance for the adjustment of chip's cross section morphology.To clarify the plastic flow mechanism of workpiece material during FEC process,coupled thermal-mechanical finite element model was built,and the simulation of working process was used to study the deformation state and the flow distribution of workpiece material.The control theory was improved through the contrastive analysis between the simulation results and experiment results.By analyzing the distribution of stress and strain on the workpicec material at different stage of the forming process,most of the working loads concentrates on the entrance location of forming channel,leading to its high failure risk,and will be a key difficult for the improve of FEC.How the transverse flow of workpiece materials effects the shear plane was studied,using velocity profile and point tracking to make clear the distribution of transverse flow.It did show the most distinctly transverse flow in the fins area,while most of it finished before the shear plane of the press area.Therefore,the shear plane of the press area kept complete during the process,and the deformation of materials in the press area after the shearing surface could be regarded as plane deformation.Critical assumption that "the flow speed of material in press area show equal proportional variation during FEC process" was made to build a geometric model of the process that could express the result of materials' transverse flow.According to this numerical model,the influencing mechanism was clearly showed as "restricted structuretransvers flow-cross section forming",and the variation trends of fins full height and the result of transvers flow while the restricted structure parameters changed were predicted.These predictions were validated by the finite element model simulation and processing experiments,which proved the accuracy and reliability of the model.To break the geometric limit and kinetic limit in FEC,former ploughing process was added to enlarge the specific surface area of fins prepared by FEC,and the new method named ploughing extrusion cutting(PEC).The analysis showing the essence of limit to be "the improvement of forming ability means the increase of load as well as the decrease of structural strength".During the processes of PEC,the pre-ploughing process completed most of the transverse flow in the processing area,which could reduce the work stress of the groove wall on the restricted tool during the extrusion cutting process,leading to the reduction of structural strength requirement on the groove wall,and enlarge the allowable geometric parameters of the groove wall.As a result,the deformation extent in the experiment of PEC increased greatly than that of FEC,chip strips could be successfully prepared with the aspect ratio of fins up to 3:1,the thickness ratio between the base and the whole chip down to 20% and the ratio of heat radiating area has a raise of 48.06%.Through the work described above,the working mechanism of FEC preparing metal fins was clarified,and the PEC improved from FEC show much better forming result,which provides a solid foundation for the application of FEC/PEC process to metal chips recycling.