To understand the swing motion, I must first explain what you are trying to achieve at impact. For the ball to be lofted high into the air the clubface must hit down and under the ball. To have a chance of pulling off this move you must understand the correct delivery position.
The swing motion has to be much more vertical than any other shot. When you are hitting a long iron or fairway wood you need to sweep the ball off the top of the grass. To loft the ball into the air with your sand wedge you need to strike down crisply on the ball with a very vertical angle of attack.