Study on Modeling of Chip Formation

ByWolelaw E.

BDU BIoTSchool of Mechanical and Industrial EngineeringManufacturing Engineering Program

For the Partial Fulfillment of the Course of Metal Cutting Theory and Applications

Instructor: Getye M.

Bahir DarNovemeber 2011

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Presentation Outlines

• Introduction• Objective• Methodology• Statement of the problem• Literature review• Analytical modeling of chip formation • Numerical modeling of chip formation• Conclusion and Recommendations• References

BIoT PG in Manufacturing Eng.

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Introduction

• Primary concern in metal cutting is production of chips

• Chips may constitute fewer to 50% of the initial work piece

• Removal may differ from product to product

• From rough to precision work of 0.25μ or even less

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… Continued

• Chip formation is the heart of metal cutting which needs to be understood

• It influences power requirement, tool life, work quality and efficiency

• Attempts were made in the past to

understand the process by modeling

• This paper tries to review past experience in modeling chip formation based on bibliographic study

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Objective

• To review theoretical backgrounds and models of chip formation

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Methodology• Literature review on the subject• General overview is only treated

Statement of problem

• Chip shape and size varied widely in machining operations.

• Poor surface finish, work piece accuracy• Short tool life• Low productivity

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Literature review

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•The single shear plane model was analyzed by Merchant in 1945

•Palmer and Oxley (1959) developed a thick-zone chip formation model•They studied metal cutting at low speed and derived slip line field using modified Hencky relationship

•Oxley (1961) developed another thin shear model which assumes none uniform stress at the rake face of tool

…Continued

• Okushima and Hitomi (1961) made the other analysis of thick zone model chip formation

• This analysis is complex with requiring more assumptions

• Klamecki (1973) developed finite element modeling based on single shear plane

• Later different investigators modified and powerful soft wares are commercially available in the market.

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Evolves from observation• “Quick – Stop” •Micro level pictures (Photomicrographs)

Analytical Modeling of Chip Formation

Fig.1 Early observations on chip formation

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Orthogonal cutting

•Straight tool edgeNormal to direction of cutting and feed

Fig. 2 Chip formation model

…Continued

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Fig. 3 Force circle diagram

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…Continued

Fig. 4 Velocity diagram

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…Continued

V- Velocity of work pieceVS- Shear velocityVC- Chip velocity

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…Continued

Fig. 4 Shear strain

Numerical Modeling of Chip Formation

• Analytical modeling methods have limited applications

• Numerical methods came up to address this problem

• FEM is now gaining acceptance in modeling chip formation

• Material property, tool property, temperature, cutting fluid, tool material interface … could be imposed

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•

• It is based on dividing a continuum system- describe element properties as matrices- assemble them- this gives the behavior of the system

• While FEM is very powerful, the result will be only as good as the properties fed in

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…Continued

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2D Machining2D Machining

Work piece

Cutting tool Cutting speed

…Continued

Fig. 5 Chip formation modeling in two dimensional machining

…Continued

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•Kinematic and thermal constraints are induced in this analysis

•Other chip formation factors are also imposed

Fig. 6 Study areas in 2D FEM modeling of chip formation Mechanical and thermal boundary conditions (Source: P.J. Arrazola et.al 2oo5)

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Conclusion and Recommendation

• Current modeling methods are not capable of predicting chip formation

• This is mainly because the modeling methods are based on the oversimplified orthogonal cutting method

• Chip formation is a complicated process taken place within a short period requiring determination of several parameters

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• A diversity of physical phenomenon exists at the process zone due to different systems

• Result of system interaction• Interaction effects are even complex

• Studying past experience, understanding the system and its interaction and looking for new options is important

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…Continued

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[1] CENK KILIÇASLAN. MODELLING AND SIMULATION OF METAL CUTTING BY FINITE ELEMENT METHOD. A Thesis Submitted to the Graduate School of Engineering and Sciences of İzmir Institute of Technology in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in Mechanical Engineering. 2009.

[2] DeGarmo, E. Paul. Materials and Processes in Manufacturing 2nd edition. Macmillan Publishing Co. Inc. 1974.

[3] Edward M. Trent and Paul K. Wright. Metal Cutting 4th edition. Butterworth–Heinemann.2000.

[4] P.J. Arrazola et al. Finite element modeling of chip formation process with ABAQUS/EXPLICITTM 6.3. VIII International Conference on Computational Plasticity. COMPLAS VIII E. Oñate and D. J. Owen (Eds) © CIMNE, Barcelona, 2005.

[5] Shaw, Milton C. Metal Cutting Principles. Oxford Series on Advanced Manufacturing, 1996. [6] Vahid Kalhori. Modeling and Simulation of Mechanical Cutting. Ph. D Thesis, Luleă University of Technology, Sweden, 2001.[7] Viktor P. Astakhov. On the inadequacy of the single-shear plane model of chip formation. International Journal of Mechanical Sciences 47 (2005) 1649–1672. [8] Viktor P. Astakhov and S.V. Shvets. A system concept in metal cutting. Journal of Materials Processing Technology 79 (1998) 189–199. [9] V.P. Astakhov , M.O.M. Osman, M.T. Hayajneh. Re-evaluation of the basic mechanics of orthogonal metal cutting: velocity diagram, virtual work equation and upper bound theorem International Journal of Machine Tools & Manufacture 41 (2001) 393–418.

References

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Thank you