Hello,
In UiPath community we used to get questions like, how to merge different excels into a single Excel and to add the output to different sheets in the same output file.
The below video helps you to learn the concept with a practical demo. It used a counter variable and used that counter value as the sheet name.
The automation is developed with the default excel activities.
Those who need the Workflow can message me. 
Please give your valuable comments 
ashokkarale
MD_Farhan1
Ajay_Mishra
postwick
Dheerendra_vishwakarma
Anil_G
chandreshsinh.jadeja
Gautham_Pattabiraman
vrdabberu
aravindbalineni123