CAM strategies and surfaces accuracy.

Peterka, Jozef ; Pokorny, Peter ; Vaclav, Stefan 等

1. INTRODUCTION

The basic sign of CAM is to minimize human intervention into the course of the production process by the exploitation of computer data processed in main elements of activities (Kuric et al., 2001).

The machining process is generally divided into roughing and finishing (Morovic, 2006).

Very important for CNC program generation is the choice of machining strategy. This strategy has influence on the final accuracy and final quality of machined part (Lipa & Moravcikova, 2007). Machining strategy is tool movement in machine space.

The machining strategy influences the surface accuracy and also herewith the technological properties of construction. It is very important for assembly (Senderska, 2006).

2. MODELLING AND PART MANUFACTURING

2.1 Part modelling

For research of influence of CAM strategies on surface accuracy was created the part (fig.1) in PowerShape system. The model has three identical cylindrical surfaces. Three different finishing strategies will be applied on these surfaces.

[FIGURE 1 OMITTED]

2.2 CNC data generation

Model was loaded to CAM system PowerMill. There were (after block, tool and milling strategy choosing) generated CNC data for roughing, rest machining, shape machining and finishing.

For finishing of individual cylindrical surfaces these strategies choosen were:

* Optimized Constant Z (fig.2).

* Spiral Finishing (fig.3).

* Offset Finishing (fig.4).

Tool and cutting conditions were identical for all three choosen strategies:

* End mill - D = 6 mm, z = 2.

* [v.sub.f] = 3000 mm. [min.sup.-1].

* n = 6000 [min.sup.-1].

* [a.sub.e] = 0,305 mm.

* [f.sub.z] = 0,25 mm.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Machining (roughing, rest machining, shape machining, and finishing) was realized by CNC milling centre EAGLE 1000 with control system Haidenhein i530.

3. MEASURING OF CYLINDRICAL SURFACES

Measuring of machined cylindrical surfaces was realized by optical 3D scanner GOM ATOS I--non contact measuring method (fig.5a) and after that the cylindrical surfaces was measured by Contura G2--contact measuring method (fig.5b).

[FIGURE 5 OMITTED]

Firstly, we scanned milled model by measuring with machine GOM ATOS I. So we got computer model of produced component. We also compared this model with computer model which was created according to technical documentation. This method is called CAD Comparison. (Buransky, 2008) There is coloured map of deviations produced surfaces and computer surfaces (fig.6).

[FIGURE 6 OMITTED]

By measuring with CMM machine Contura G2 were all three cylindrical surfaces measured gradualy. Each measuring was realized three times. After the measuring the arithmetical means of measured values were calculated. We got the values of deviation for applied milling strategies (fig.7).

[FIGURE 7 OMITTED]

4. CONCLUSION

The individual results of measuring are in (tab.1). Here are some used strategies of milling operation and appropriate deviations for non contact measuring and contact measuring.

It is liquet that for simple cylindrical surface the most suitable is the Optimized Constant Z milling strategy. The smallest deviations were recognized in both types of measuring.

According to the table it is possible to compare the differences between measuring of CMM machine and non contact machine. From CMM measuring we have expected the more correct results. And that was approved. The precision of res ults depends on the type of measuring.

In further research, we will mill more types of surfaces and also the free form surfaces. The various strategies of milling will be applied on these surfaces. The influence of milling strategies on precision of produced surfaces and the roughness of surface will be observed.

This article was written for grantproject VEGA 1/0130/08 Research of influence of CAM strategies on achieved dimension accuracy and roughness of machined surface in conditions of university Hi-tech laboratory.

5. REFERENCES

Buransky, I.; (2008) Utilizing Optical Methods of Measuring in Machines Production Technologies, In: International doctoral seminar:Proceedings, AlumniPress, pp. 48-53 ISBN 978-80-8096-058-2, Smolenice

Kuric, I.; Kosturiak, J.; Janac, A.; Peterka, J. & Marcincin, J. (2001). Computer Aided systems in the Engineering, Edis, ISBN 80-7100-984-2, Zilina

Lipa, Z.; Moravcikova, J.; (2007) The contribution of kinematic ratios in machining, In: Development of metal cutting DMC 2007, SjFTU pp. 225-22, ISBN 978-80-8073-858-7, Kosice

Morovic, L.; (2006). Utilization of Reverse Engineering in the Design and Manufacturing of Sport Shoes, In: International Doctoral Seminar, STU MTF, pp. 178, ISBN 80-227-2387-8, Smolenice

Senderska, K.; (2006). Approaches and Tools to Evaluation Support of Product Construction for Assembly, In: Inovations Transfer, SjF TU, pp. 214-215, ISBN 80-8073-701-0, Kosice

Tab 1. Results for milling strategies

STRATEGY MEASURED VALUES [mm]

 CMM GOM ATOS I
 Contura G2

Optimized
 Constant Z 0,0356 0,08
Spiral 0,0442 0,12
Offset 0,0491 0,09