Chip breaker geometry selection using FEM simulation.

Croitoru, Sorin Mihai ; Patrascu, Gabriela ; Dragomirescu, Cristian George 等

Abstract: This paper presents a methodology for selection of removable inserts with chip breaker in roughing turning operations based on FEM simulation. The optimization objective includes the contributing effects of cutting forces and effective stress maximum values. Case studies are presented to demonstrate its application in the selection of cutting tool inserts chip breaker geometry.

Key words: FEM simulation, cutting process, cutting forces, tool wear.

1. INTRODUCTION

In practice, when selecting inserts for turning operations, chip-breaking diagrams are helpful and they are commonly used (Kalhori, 2001). Such diagrams are published by tool manufacturers and show the application range under standardized and simplified conditions such as turning operation, side cutting edge angle, large work diameter, etc., for the variation of feed and depth of cut only. Because of the complicated rake face geometries of these inserts, analytical prediction of cutting forces, tool life, etc., is extremely difficult (Miner, 2005), (Patrascu & Croitoru, 2005). Thus, modelling the three-dimensional chip breaking process was initially restricted to these conditions. Predicting stress and temperature distributions using finite element (FEM) based on numerical simulation of chip formation has the ultimate potential for identifying optimum tool geometry and the cutting conditions. By using this knowledge, tool life and surface finish can be improved in high speed machining and better inserts can be selected and designed (Mohora et al., 2001).

2. CASE STUDY

This paper presents a methodology for selection of removable inserts with chip breaker in roughing turning operations based on FEM simulation. The optimization objective includes the contributing effects of cutting forces and effective stress maximum values. The simulation software DEFORM3D[TM], specifically developed for large strain deformations, automatically separates the chip from the workpiece around the tool tip based on metal flow, material properties and tool geometry. Different insert geometries were used. No lubricant is used at the tool-workpiece interface.

The model of the simulation is plane-strain and nonisothermal. In the simulations the workpiece is assumed to be rigid-plastic and to have a rectangular shape.

For simulation of turning process it was used a plane strain deformation model. The insert and a part of workpiece were meshed in order to have a practical number of elements for calculations (Patrascu, 2004). Workpiece (fig. 1) was made of Romanian OLC45 steel. Depth of cut was 1 mm, cutting speed 300m/min, and feed 1 mm/rev. The round inserts ([phi] = 25 mm) without and with chip breaker geometry were made available in STL form, generated from CATIA V5R16 system (fig. 2) (Patrascu & Croitoru, 2005).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Relief angle was 7[degrees]. The design of round insert with spherical radial cells chip breaker (fig. 2, c) used the idea that only an additional deformation would lead to the chip break, which is a wanted phenomenon in case of cutting steel. In this case, the steel tend to deliver long curly chips, which tangle between themselves - on one hand - or with the cutting tool--on the other hand. This implies additional efforts to take the chips out of the active cutting zone.

3. RESULTS

In figures 3, 4 and 5 the graphics of the cutting force components for the 4 studied cases are presented. It can be observed (table 1) that cutting force is lower in case of bi-truncated cones chip breaker, feed force is lower for inserts without chip breaker and radial force is lower for bi-truncated cones chip breaker. After the analysis of the cutting force components' values (fig. 3...5) and maximum effective stress values the following table can be stated.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. CONCLUSIONS

Cutting simulations are developed to become an instrument for design of cutting tools. These computational will increase the understanding of the cutting process. Simulations can reduce the number of experiments required during the design process. It is also possible to perform parametric studies in a way that is difficult to achieve by experiments. It is now simple to choose from the studied cases the type of chip breaker. Obviously, the first criterion is the minimum values of the cutting force components. There is another criterion to be used when choose the chip breaker: the fact that the chip breaks. This breakage will appear when the equivalent stresses are greater than the specific break stress limit of the work piece material. In conclusion, for practical cases, we will use inserts with bi-truncated cones chip breaker.

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.

4. REFERENCES

Kalhori, V. (2001). Modelling and Simulation of Mechanical Cutting, PhD Thesis, Lulea University of Technology, Department of Mechanical Engineering, Sweden, pp. 5-27.

Miner, W.D. (2005). A Tool Wear Comparative Study in Turning Versus Computer Simulation in 1018 Steel, MS Thesis, Brigham Young University, pp. 5-20.

Mohora, C., Cotet, C.E. & Patrascu, G. (2001). Simularea sistemelor de productie. Simularea proceselor, fluxurilor materiale si informationale, Editura Academiei Romane and Editura Agir, ISBN 973-27-0868-9 and ISBN 973-8130-69-7, Bucharest.

Patrascu, G. (2004). 3D Simulation of Turning Process using FEM Software, Proceedings of the International Conference on Manufacturing Systems ICMaS 2004, Constantin, I., Ghionea, A., Constantin, G. (Ed.), pp. 297-300, ISBN 973-27-1102-7, Bucharest, 2004 October, Editura Academiei Romane, Bucharest.

Patrascu G., Croitoru S.M. (2005). Prediction of Cutting Forces using FEM Simulation and Modelling for Optimal Selection of Chip Breaker Inserts Geometry, Proceedings of the 8th Conference on Management of Innovative Technologies (MIT'2005), Mihael Junkar, Paul R. Levy, (Ed.), pp. 187-191, TAVO & LAT, ISBN 961-6238-96-5, Fiesa, Slovenia.

Table 1. Cutting forces simulated values.

 Max.
 eff.
 Fx, [N] Fy, [N] Fz, [N] stress

without chip breaker 173,69 6840,13 890,79 1512,49
bi-truncated cones chip 334,64 5209,5 319,39 1533,43
 breaker
spherical radial cells chip 397,34 5251,19 415,54 1515,32
 breaker
radial canals chip breaker 390,18 6532,24 1945,57 1495,8