You could have given little more information as to why are you have raised this query? Are you student or professional? If latter then are you doing this activity on your own or you have been told to do so?
What kind of industry you work in and what is your finished product? Have you spoke with the production personnel of your company? What they say on this?
I recommend you mapping entire the production process. Possibly you would find the answer to your query yourself., If not then upload the process here and then we will help you. But before that please provide the information asked in the above questions.
In my personal opinion I do not recommend categorising activities like core or non-core. Take for instance garment manufacturing company. Obviously stitching is their core activity but then what about about buttonholes or buttons? What about ironing? Should we categories these as non-core? Above all what about folding the garment? Since the folding is non-core activity, should the workers fold the garment in crumpled manner?
I recommend you doing job analysis instead. Certain jobs require the higher level of skills. These are obviously "core" activities.
Dinesh V Divekar
27th April 2014 From India, Bangalore