The tool wear modify the shape of the cutting edge. For this reason, the roughness is affected negatively.

When people increase the DOC above a minimum value, the stability of the process (vibration) decrease, and for this reason, the roughness increase.

Please, see the figure attached.

In relation with the MMR you need to analyze in separate way the feed and the cutting speed. Lower feed gives better roughness and higher cutting speed gives better roughness.

You are welcome.

Thanks a lot sir it will be helpful.

Sorry. I think that I made a mistake. I misunderstood the question.

DOC almost does not affect tool wear (See Taylor law).

At the same part, if you use higher DOC, the MMR increase, because the total machining time is reduced significantly (you need less operations to modify the original part to the final part).

When we increase the depth of cut, many variables will cause tool wear and thus the process will be hindered, since temperature will increase and the smoothness of the cut will be affected. From my experiemcee the type of tool also plays a role, for example HSS steel will have shorter tool life if you increase the DOC, and you will not have good cutting edge.