Additionally, compared to the conventional method, M1, the number of cavities machined has a great increase with the two trochoidal methods (M3, M4). However, there currently is also a limitation for trochoidal methods now - their machining efficiency is lower. Fig. 20b shows the comparison of machining time with all four methods. M3 and M4 require more time to machine the product mainly because of the need for having additional auxiliary trochoidal paths in the tool path. The machining time when using these methods is closely related to the size of cavity. The larger the cavity is, the less the proportion of the corner path in the overall tool path will be, and the narrower the time difference between the former and latter two paths will become.

In short, the trochoidal path methods present excellent load control capacity and greatly extend tool life. Further research studies on the optimization of trochoidal tool paths will be carried out in the future. The path geometry will be optimized to reduce the length of the trochoidal path, and the depth of cut, feed rate and other parameters will be increased within a controllable range of tool loads, thus to enhance machining efficiency.

6. Conclusion

(1) A method for the geometric modelling of the engagement angle in trochoidal machining is proposed. The corresponding relationship between the milling force curve and the engagement angle curve is analyzed through simulation. The changing trend of the engagement angle is very similar to the changing trend of the milling force. Therefore, in certain circumstances, the engagement angle can be used as a substitute for the milling force for analysis and calculation such as for large axial depths of cut and small radial depths of cut in cavity machining.

(2) In high-speed cavity milling, a cutting mode with a large axial depth of cut and small radial depth of cut are often used. This is taken as the background; then, we have implemented a serial of fundamental experiments of trochoidal machining. The result shows that milling force is the key issue in trochoidal machining, and it should be controlled. Based on the obtained effective conclusions, a proper control strategy for cavity trochoidal machining has been proposed.

(3) Based on the trochoidal control strategy, two realizations of cavity trochoidal machining have been proposed, and practical cavity machining experiments are compared. Experiments show that the feedrate adjustment method has weak control on

the milling force and tool vibrations, therefore, the tool wear is relatively big, and it is easy for the tool to be fatigued and damaged. However, trochoidal milling method is more effective at milling force control, reduction of tool vibrations, and tool wear. By increasing the axial depth of cut, the milling efficiency and tool wear of trochoidal milling method is better than the feedrate adjustment method.

In the future, the research of trochoidal machining should be focused on geometry optimization, milling with high axial depth of cut and high speed-rate, in order to improve the efficiency of trochoidal milling.

Acknowledgements

This work reported in this paper is conducted in conjunction with ‘NSFC-Guangdong Collaborative Fund Key Program U12012081’.

References

Altintas, Y., Spence, A., Tlusty, J., 1991. End  milling  force  algorithms  for  CAD systems. CIRP Annals-Manufacturing Technology, 40(1), 31-34.

Bae, S. H., Ko, K., Kim, B. H., Choi, B. K., 2003. Automatic feedrate adjustment for pocket machining. Computer-Aided Design, 35(5), 495-500.

Choy, H. S., Chan, K.  W.,  2003.  A  corner-looping  based  tool  path  for  pocket milling. Computer-Aided Design, 35(2), 155-166.