On-line Monitoring Of Cutting Edge Wear Profile On Tool Bit Based On The Modified Model Of Machined Surface And Image Technology

Tool on-line monitoring opens more space for improving the production efficiency and production quality in metal machining.Tool on-line monitoring plays an important role in intelligent production.However,during cutting process,tool wear condition is always difficult to be observed and measured directly because the tool wear area is partially blocked by chip and workpiece.Therefore,it is more feasible to obtain the tool wear condition in real time and indirectly by monitoring the machined surface.Machined surface is generated by the cutting tool,and it is mainly affected by the tool profile,the machining parameters and the tool-workpiece material properties.It can be regarded as the mapping of the tool edge profile under the condition that the other main factors are already known.By monitoring the machined surface,it can not only control the machined surface quality directly,but also monitor the tool status indirectly.Tool edge condition(sharp / wear)can be obtained by indirect monitoring through studying and modifying the forming mechanism of machined surface.To realize the tool edge profile on–line monitoring,the following is required:(1)The formation mechanism of machined surface needs to be investigated,and its geometrical model considering the main factors needs to be modified;(2)The illumination model of machine vision image needs to be analyzed,and the correlation between image gray level and texture height needs to be investigated,then the 3D reconstruction of a single machined surface image needs to be carried out;(3)Combining the formation mechanism of machined surface and 3D reconstruction technique,the relationship between machined surface profile and tool edge profile needs to be analyzed,and then the effective contour of tool edge from the machined surface image needs to be extracted;(4)The on-line monitoring system needs to be applied and its feasibility in the laboratory and actual production(train wheel re-profiling)needs to be verified.The actual profiles of machined surface are affected by a number of factors such as tool geometry,machining parameters,physical properties of the workpiece material,and the rigidity of the machining system,where the tool geometry and machining parameters are the most commonly considered factors.In practice,the elastic-plastic deformation of the workpiece material,especially the plastic metal,is also an important factor affecting the formation of the machined surface,assuming that the rigidity of the machining system is sufficiently satisfactory.Based on the traditional model of machined surface formation(only considering the geometrical and machining parameters),the elastic-plastic deformation of the residual uncut layer is additionally considered,and a modified model to describe the machined surface formation is developed in this paper.The modified model is solved geometrically and mathematically to obtain the numerical solution of the modified model which includes the machined surface morphological parameters(such as roughness),and parameters to describe the elastic-plastic deformation of the residual uncut layer as well.This section is covered in Chapter 2 of the paper.The relationship between the gray image of the machined surface and the actual texture profile of the machined surface is mainly affected by the illumination model.In the existing researches,the calculation of the illumination model is very complicated and the application conditions are harsh.Based on the experience of the existing studies,a special illumination model suitable for the machined surface has been established in this paper.Through modeling and calculating,it is demonstrated that the gray level of machined surface image has a linear correlation with the height of machined surface profile,then,the 3D reconstruction of the machined surface morphology is achieved based on single image to obtain the 3D morphology from the machined surface image with machine vision,which lays a foundation for the back calculation of tool edge wear profile information from the machined surface image.This section is covered in Chapter 3.After obtaining the geometrical morphology of the machined surface,the effective contour of the tool edge corresponding to machined surface is restored to analyze the tool wear condition according to the mechanism of the modified geometry model of machined surface in Chapter 2.Other methods which obtain tool wear condition by the machined surface image,such as the fractal analysis,GLN and GLCM are calculated respectively and are compared with the proposed method in this paper.The results show that the proposed method with effective geometric contour restoration of the cutting edge is more intuitive,more robust,and applicable to general production and processing conditions.This part is covered in Chapter 4 of the paper.Chapter 2,3 and 4 are completed by theoretical analysis and corresponding experimental verification.In Chapter 5,the above contents are used to carry out the on-line monitoring of train wheel re-profiling,and the feasibility of the on-line monitoring system is verified.The above studies show that,the proposed modified model of machined surface deformation is more suitable for the actual machined surface condition than that of the traditional model.On the basis of modifying the machined surface model,the effective contour of the cutting edge is restored from the machined surface image combining with the 3D reconstruction technique of single machined surface image,which can recognize the tool edge profile visually and realize the tool wear condition on-line monitoring effectively.