3D tool wear simulation for turning process.

Patrascu, Gabriela ; Carutasu, Nicoleta Luminita ; Dragomirescu, Cristian George 等

1. INTRODUCTION

Turning operation is characterized by continuous cutting process; the entrance and exit of cutting tool takes place infrequently and takes only a short time. In continuous cutting process, if the effects of tool are neglected, cutting thickness, chip shape, and various cutting process variables will have no great change and steady state can be assumed. Tool wear calculation can be simplified by assuming that tool wear is created completely by the steady state cutting process and neglecting the effect of entrance and exit phase (Carutasu, 2007).

Prediction of tool wear is complex because of the complexity of machining system. Tool wear in cutting process is produced by the contact and relative sliding between the cutting tool and the workpiece and between the cutting tool and the chip under the extreme conditions of cutting area. Any element changing contact conditions in cutting area affects tool wear. These elements (Xie, 2004) come from the whole machining system comprising workpiece, tool, interface and machine tool.

Under high temperature, high pressure, high sliding velocity and mechanical or thermal shock in cutting area, cutting tool (Huang & Liang, 2003) has normally complex wear appearance, which consists of some basic wear types such as crater wear, flank wear, thermal crack, brittle crack, fatigue crack, insert breakage, plastic deformation and build-up edge. The dominating basic wear types vary with the change of cutting conditions.

Tool wear estimation with the help of finite element method can predict not only tool life, but also wear profile of both crater wear and flank wear, and relate tool wear with some wear mechanisms. This tool wear estimation method will relate the geometry appearance to physical basic of tool wear and bridge the gap between macro and micro studies of tool wear (Kalhori, 2001). This is very meaningful for the scientific research and education.

For tool designer, it is very helpful to optimize tool geometry and structure knowing wear profile and wear mechanism; for material engineer, it is useful to improve tool material according to the determined main wear mechanism. In this tool wear estimation method, tool wear is related to wear mechanism, once tool wear mathematical model for a combination of tool-workpiece material is determined, it is possible to estimate tool wear by program without doing any experiment.

2. CASE STUDY

This paper presents the current modelling capabilities available in modified DEFORM 3D[TM] system to simulate metal cutting environment in turning process. The insert and a part of workpiece were meshed in order to have a practical number of elements for calculations. Work piece was made of Romanian OLC45 steel. The TNMG 332 insert with PF chipbreaker geometry (fig. 1) were made available in STL form, generated from CATIA V5R8 system (Patrascu, 2007). The cutting process parameters were: 1) cutting depth: 0.254 mm and 0.635 mm; 2) feed: 0.254 mm/rot; 3) Cutting speed: 100 ... 400 m/min. For the proposed orthogonal machining model, cutting conditions and the material properties of the workpiece are the inputs. The computer simulation predicted the values of chip thickness, cutting forces, shear angle, tool stress distributions, tool wear (fig. 2 and 3), temperature distributions, contact length etc. with increased accuracy as the cutting surface speed increased as shown by the decrease in the difference between the values of the same cutting surface speed. From these predictions we can make a few observations listed below:

* Tool wear and chipping of the cutting edge affect the performance of the cutting tool in various ways. The cutting forces are normally increased by wear of the tool. Crater wear may reduce forces by effectively increasing the rake angle of the tool.

* Tool wear influences the tool geometry this may affect the dimensions of the component produced in a machine with set cutting tool position or it may influence the shape of the components produced in an operation utilizing a form tool (Carutasu, 2007).

* As increased temperatures at the tip of the cutting tool leads to the reduction of the hardness value, that is the thermal softening, and thus to the flank wear of the cutting tool. The results reveal that by increasing process variables in machining the wear and temperature increases causing thermal softening of tool causing it to wear (Patrascu, 2007).

* The results obtained have been verified with the available results from literature for the variation of wear with the temperature and thermal softening of carbide tool. The results prescribed demonstrate the significance of cutting parameters (speed, feed and depth of cut) in thermal analysis for study of the cutting tool wear.

[FIGURE 1 OMITTED]

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3. CONCLUSION

The conclusions that are made from the results are listed below:

* Tools wear decreases with increases of cutting speed. The flank wear increases with increase in modified cutting tool temperature (due to increase in the strain rate), but there is a nonlinear trend so we can find an optimum value of cutting parameters so as to give minimum strain rate, because heat generated increases with increase in the strain rate.

* The flank wears increases significantly with the increase in the cutting velocity.

* The tool wear is directly proportional to the resultant cutting force and approximately follows a linear trend.

* The comparison analysis provides positive results to continue future research in the computer simulation program to validate the use of this model for tool wear prediction.

* At present, numerical implementation of tool wear estimation is only developed for the cutting process with steady state. Therefore the estimation of tool wear should be studied by developing new simulation procedure.

* The tool wear data showed different trends, the crater depth increased as the cutting surface speed increased.

* Further studies are necessary for improving the model to study the effects of chip-groove parameters on the natural contact length, the tool temperature and contact stress distribution, etc.

[FIGURE 3 OMITTED]

4. ACKNOWLEDGEMENTS:

The authors would like to thank Prof. Jawahir I.S. from University of Kentucky for his support and Mr. Erwin Reiss of Scientific Forming Technologies Corporation (SFTC) for the use of three month free evaluation license of DEFORM 2D and 3D software and for his helpful suggestions and discussions.

5. REFERENCES

Carutasu, N.L. (2007). Contribution Regarding Designing Machines-Tools Structure Elements for High Speed Machining, Ph.D. Thesis, University POLITEHNICA of Bucharest, Bucharest, Romania

Huang, Y., & Liang, S.Y. (2003). Modelling of the Cutting Temperature Distribution Under the Tool Flank Wear Effect, Proc. Inst. Mech. Eng., Part C: J. Mech. Eng. Sci., 217, pp. 1195-1208, ISSN 0954-4062

Kalhori, V. (2001). Modelling and Simulation of Mechanical Cutting, Ph.D. Thesis, Luled University of Technology, ISSN 1402-1544, Sweeden

Patrascu, G. (2007). Research Concerning the Optimization Through Simulation of the Cutting Process, Ph.D. Thesis, University POLITEHNICA of Bucharest, Bucharest, Romania

Xie, L.I. (2004). Estimation of Two-dimension Tool Wear Based on Finite Element Method, Ph.D. Thesis, Universitat Karlsruhe (TH), 2004