Smooth hiding of parts in motion study

Hello everyone,

I am trying to make an animation of an assembly where a part will be hidden for some time and then it will reappear. But I can not get a smooth transition from visible to hidden state for that part. I am creating the key points from where the part will start hiding and where it will be finally hidden.

The problem is that the part is not getting any smooth transition in between the key-points and getting hidden suddenly. How can I fix the problem.

Thanks in advance. 

SolidworksSimulation