BITS Faculty Publications
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Item An Investigation Of Surface Errors In Thin-Walled Machining(i-Manager, 2012) Bera, T.C.Prediction of surface errors in milling of thin-walled structures is not trivial due to cutting force induced deflections of workpiece. The situation becomes more complicated when the end mill adds cutter deflection errors to workpiece deflection. It is important to predict and analyze such variation of surface error from process planning and process control point of view. The study of surface error is also essential while overcoming the same by applying various compensation methods. This paper investigates cutter and workpiece deflection induced surface errors in peripheral milling of thin-walled straight and curved geometries. A flexible tool-workpiece system has been developed to estimate surface error in the presence of both tool and workpiece deflections. The effects of chip load and workpiece curvature on surface errors have also been investigated by using experimental and computational methodology. Based on the outcomes of the present study, it is concluded that the complex nature of tool and workpiece deflection induced surface error can be predicted both qualitatively and quantitatively in thin-walled machining. The results presented here provide useful insights into qualitative and quantitative nature of surface errors which will be helpful for product designers as well as process planners in improving machining productivity without sacrificing quality.Item Error compensation in flexible end milling of tubular geometries(Elsevier, 2011-01) Bera, T.C.There are many machining situations where slender tools are used to machine thin walled tubular workpieces. Such instances are more common in machining of aircraft structural parts. In these cases, cutting force induced tool as well as workpiece deflections are quite common which result into surface error on machined components. This paper presents a methodology to compensate such tool and workpiece induced surface errors in machining of thin walled geometries by modifying tool paths. The accuracy with which deflections can be predicted strongly depends on correctness of the cutting force model used. Traditionally employed mechanistic cutting force models overestimate tool and workpiece deflections in this case as the change of process geometry due to deflections is not accounted in modeling. Therefore, a cutting force model accounting for change in process geometry due to static deflections of tool and workpiece is adopted in this work. Such a force model is used in predicting tool and workpiece deflection induced surface errors on machined components and then compensating the same by modifying tool path. The paper also studies effectiveness of error compensation scheme for both synclastic and anti-clastic configurations of tubular geometriesItem Modelling of Energy Consumption for Milling of Circular Geometry(Elsevier, 2021) Sangwan, Kuldip Singh; Bera, T.C.Machine tools are dominant end users of electrical energy in manufacturing, and responsible for high carbon emissions. There is hardly any research work on the energy modelling for curved surface milling. The present study aims to develop energy consumption model for milling of circular geometries as a part of process planning for machining operations to reduce cost, improve energy efficiency and general productivity. The circular geometry may have concave or convex shape which leads to change in magnitude of curvature. Therefore, the magnitude and distribution of cutting forces and concerned cutting powers are quite different in both these machining situations. This necessitates the need to investigate this aspect comprehensively. A process geometry model is developed based on process geometry variables of feed per tooth along cutter contact path, entry and exit angles of tooth, engagement angle, undeformed chip thickness, etc. Next, the process geometry variables in conjunction with mechanistic cutting constants are used to develop a force model for estimating the feed force and normal force components. Lastly, a power consumption model is developed based on the instantaneous force component and velocity of milling cutter to estimate both the instantaneous and average power consumed during the milling process. Machining experiments are performed to conform the validity of the proposed model by comparing the measured power to their predicted counterpart. The developed model can be used for estimating the power consumption for milling of circular geometries reliably and efficiently without conducting the costly experiments. In addition to this, the proposed model extends the existing model by considering the effect of workpiece curvature and aims at providing a useful aid for prediction of power consumption in peripheral milling of circular surfaces. Therefore, an attempt has been made to provide a basic platform for in-depth comprehension and characterization of energy consumption. The proposed model has many applications particularly in die-mold manufacturing and aircraft industry and it can be extended to curved geometries having variable curvatures