# Assessment of the Functional Properties of the Surfaces of Ductile Cast Iron Parts
## 5 Conclusions  
The following findings can be drawn on the basis of the experimental tests carried out and the measurements of the surface topography of the tested specimens:  
1. Ductile cast iron alloys are characterised by good machinability in terms of the periodic cutting speed as well as the qualitative effects of the resulting surface;
2. Good machinability translates into a stable machining process. Experimental work has shown that the machining process is stable over the entire range of machining parameters. Some difficulties (sensitivity of the process to the formation and development of self-excited vibrations) are noted under roughing conditions. The qualitative results of the surfaces obtained under these conditions in mechanical engineering are unsatisfactory. In such cases, it is noted that the values of the geometrical texture indices of the surface used as standard for defining the functionality of the part surface (e.g., \(Sa\) less than 3.2 \(\upmu\)m and \(Sz\) less than 25 \(\upmu\)m) are significantly exceeded;
3. It is fairly easy to meet the surface quality requirements when cutting EN-GS-600-3 ductile cast iron under finishing conditions. The material aspects associated with the disruption of the cutting process, which is caused by ferrite in ball form [53], do not contribute significantly to the reduction of the surface geometrical structure indices. The process is stable, and the surface condition is predictable;
4. Layered inhomogeneities and inclusions present in the cast iron alloy contribute significantly to the quality of the machinable surface. The rearrangement in the deeper layers beneath the product surface results in the detection during the shaping and finishing milling of cracks and pores that were previously not visible. Visible surface faults occur, especially in the softer graphite phases contributing to surface burrs and collapse. An increase in surface roughness height is thus observed as the feed and depth of cut are changed in combination with a constant cutting speed;
5. As a result of an inadequate material structure, the cutting process can become uncontrollable, but this does not necessarily imply a deterioration in machinability as assessed by the criterion of a high periodic cutting speed;
6. The surface of machined cast iron is characterised by a relatively small number of high peaks, which contribute to a reduction in its load-bearing capacity. Machine and equipment parts manufactured from this material must initially be lapped, or lapping (and/or honing) treatments must be designed into the process to reduce these peaks;
7. The milled surfaces of cast iron parts are characterised by satisfactory fluid retention values, and the large volume spaces created during the cutting of softball graphite phases (in the core and valley bottoms) become pockets in which lubricant can accumulate (thus improving the self-lubricating properties of the mating product surfaces).  
Conceptualisation, D.G., K.F., and M.J.; methodology, D.G. and B.P.; software, A.P.; validation, A.P. and B.P.; formal analysis, B.P.; investigation, D.G., K.F., and M.J.; resources, D.G.; data curation, A.P. and M.J.; writing--original draft preparation, D.G. and R.G.; writing--review and editing, M.J. and A.P.; visualisation, D.G. and B.P.; supervision, B.P. and P.Z.; project administration, R.G.; funding acquisition, P.Z. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding authors.  
Author [PERSON] was employed by the Dynpap Sp. z o. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.