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1. In sheetmetal design process, is it necessary to remove marked portion in the drawing (refer image) ?
2.If it does ,how to remove ?
You certainly should not shear every corner in a design. The idea is that you have bend relief notches. There are some options in Creo to do this. I normally just extend the bend beyond that edge. In general, I am not overly happy with the interface and performance of how bend relief's are managed in the Sheetmetal package but it works for many. I try to detail it to what is -actually- done by the shop.
You can also "extrude" cut the small remainder if you prefer. Just make sure that you can still "unbend" or "flat pattern" a part once you perform a non-sheetmetal operation. Some operation that happened near a bend line feature could make the unbend/unfold operations fail.
That obnoxious little tab is usually left behind as a result of using "rip" for the end relief. Try using an Obound for the end relief of your Flat or Flange and choose a diameter large enough to cut that little tab away. You may also find using "No Relief" is the way to go in some cases.
My first post as a new user - took me a long time to discover the solution to that particular problem.
Welcome to the forum, JRH!