Unstable tool wear rate in die sinking EDM with copper electrode

[hamdi husssein]

hi all;
actually i have done an experiment using die sinking EDM using one copper electrode and three different work piece material copper aluminum and stainless steel to perform a comparative study in term of MRR, TWR and surface roughness. i used ( pulse current 8, 12, 16, 20 and 24 Am... the pulse off is 7 micro second), so that i expected to have the same result in published papers i have read but i came up with confusing result for example i got unstable tool wear rate and my question is there any justification for this issue. i have attached these figures to have a look and please not that ,2,3 and 4 representing the 13,25,50 and 100 micro second .
Thanks
Hamdi

 

[Baluncore]

I would question the measurement accuracy of the tool wear observed.
You show only 4 points but then fit a high amplitude sine curve, assuming exact data.
You could repeat part of your experiment to determine variation, then plot the error bars.
You should check on why your measured results for Al might be sporadic. It could be that the Al has a hard oxide layer that is damaging the die or upsetting the measurement.

 

[Baluncore]

Thanks for replying Sir;
i would like to mention that i used four points like many other published papers i have read.
i am wondering if you do not mind to send you the other graphs for example the relation between the pulse current and the tool wear ratio. sorry for disturbing you as it is the first experiment i did so that i used the same values of pulse duration and pulse current and pulse off time that are used in published paper where the copper is used as electrode and stainless steel was used in that paper as a wrokpeice.
Thanks

I think you should run the same Aluminium test at the same four currents, but repeat all tests three or more times.
That way you will discover how much variation is due to your experimental technique.